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Home My WebLink About02790 - Technical Information Report King County, Washington DDES FILE NO. L98P0007 Technical Informat�'on Report RevisedMarch 1, 1999 Revised May 19, 1999 Revised June 11, 1999 �k � �o F��,ti�y a� �' �' .� Z 3� ' � � _ � s ,� Z8� 2� �► R�f� Pre ar-ed b : � ��IVAL'�� P .Y James A. Morin, P.E. EXPIRES � - �o! Brett K. Pudists Reviewed by: William J. Goggin, P.E. �� -- �� —� — .� TRIAD ASSOCIATES December 14 1998 TRIAD JOB # 95 - 243 2 � �� J TABLE OF CONTENTS SECTION I: PROJECT OVERVIEW....................................................................................................1 SECTION II: FINAL CONDITIONS SUMMARY...............................................................................3 SECTION IIA: DRAINAGE VARIANCE SUMMARY....................................................................12 SECTION III: OFF-SITE ANALYSIS.................................................................................................13 Or�sr[�Fi.ow Arr,�.Ysts.......................................................................................................................... 15 North Basin—Pre-Developed Conditions........................................................................................... I S North Basin—Post-Developed Conditior�s......................................................................................... 16 South Basin—Pre-Developed Conditions........................................................................................... 16 South Basin—Post-Developed Conditiats.......................................................................................... 16 OffsiteFlow Summary......................................................................................................................... 18 SECTION IV: DETENTION ANALYSIS AND DESIGN..................................................................19 SECTION V: CONVEYANCE SYSTEMS ANALYSIS AND DESIGN............................................25 DEV ELOPED RUNOFF(RATIONAL METHOD) .............................................................................................26 OnsiteConveyance Sizing...................................................................................................................26 Summa o Flows Used in Pi e Sizin ............................................................................27 ►�' P g•••••.............. Offsite Conveyance Capacity Check...................................................................................................30 OffsiteCapacity Analysis....................................................................................................................31 Time of Concentration Detailed Calculatio�t......................................................................................32 SECTION VI : SPECIAL REPORTS AND STUDIES.......................................................................33 SECTION VII: BASIN AND CO1�INIUNITY PLANNING AREAS..................................................34 SECTION VIII: OTHER PERMITS....................................................................................................35 i SECTION IX: EROSION/SEDIMENTATION CONTROL DESIGN..............................................36 SECTION X: BOND QUANTITIES WORKSHEET..........................................................................39 SECTION XI: MAINTENANCE AND OPERATIONS MANUAL...................................................40 TECHNICAL INFORI�IATION REPORT FOR WINDV►'OOD - Page i I :�l'1`L' .`Ul� Existing Conditions Map Developed Conditions Map Hearing Examiners "Conditions of Approval"—Copy Backwater Analysis Data TECHNICAL INFORMATION REPORT FOR WINDVVOOD - Page il King County Department of Development and.Environmental Services TECHNICAL INFORMATION REPORT (TIR) WORKSHEET Part 1 PROJECT OWNER AND Part 2 PROJECT LOCATION AND PROJECT ENGINEER DESCRIPTION Project Owner Project Name Ribera - Balko Enterprises Windwood Address Location 13740 SE 246th St. Kent WA Township > > Phone 98042 Range 2 3 Project Engineer •••••••••••••Section 05 William J. Goqqin Company Triad Associates Address/Phone Kirkland WA 98034 5- 21 - 48 Part 3 TYPE OF PERMfT Part 4 OTHER REVIEWS AND PERMITS APPLICATION XX Subdivison DFW HPA Shoreline Management Short Subdivision COE 404 Rockery Grading DOE Dam Safety Structural Vaults Commercial FEMA Floodplain Other Other COE Wetlands � Part 5 S(TE COMMUNITY AND DRAINAGE BASIN Community Newcastle Community Planning Area Drainage Basin Lower Cedar River Sub-basin Part 6 S(TE CHARACTERISTICS River Floodplain Wetlands Stream Seeps/Springs Critical Stream Reach High Groundwater Table Depressions/Swales Groundwater Recharge Lake XX Other �at to moderate slope upland Steep Slopes Part 7 SOILS Soil Type Slopes Erosion Potential Erosive Velcoties Till Soils(AgC) 6-15$ M[xjPratP Additional Sheets Attached Part 8 DEVELOPMENT LIMITATIONS REFERENCE LIMITATIONJSITE CONSTRAINT Ch. 4-Downstream Analvsis Level 1 Downstream Analysis Included in T.I.R. Additional Sheets Attached Part:9 'ESC.REQUIREMENTS MINIMUM ESC REQUIREMENTS MINIMUM ESC REQUIREMENTS DURING CONSTRUCTION AFfER CONSTRUCTION XX Sedimentation Facilities X�Stabilize Exposed Surface XX Stabilized Construction Entrance XX Remove and Restore Temporary ESC Facilities XX Perimeter Runoff Control XX Clean and Remove All Silt and Debris Clearing and Graing Restrictions XX Ensure Operation of Permanent Facilities XX Cover Practices Flag Limits of SAO and open space XX Construction Sequence preservation areas Other Other Part 10 SURFAGE WATER SYSTEM Grass Lined Tank Infiltration Method of Analysis Channel KCRTS Vault Depression XX Pipe System Compensation/Mitigati Energy Dissapator Flow Dispersal on of Eliminated Site Open Channel Wetland Waiver Storage Dry Pond � Stream Regional XXWet Pond Detention Brief Description of System Operation Combinec� Detention/Wet Pond which drains to King County Biofiltration Swale. Facility Related Site Limitations Reference Facility Limitation � Part�11� STRUCIIJRALANALYSfS =Part:�2;.:EASEMENTS/TRACTS Cast in Place Vault Drainage Easement Retaining Wall Access Easement Rockery>4' High Native Growth Protection Easement : Structural on Steep Slope gg Tract Other Other P.art y 3 S(GNATURE OF PROFFSSIONAL ENGINEER � I or a civil engineer u supervision my supervision have visited the site. Actual site conditions as erved wer incorporated into this worksheet and the attachments. To the best of my knowl ge the inform on r ' ' accurate. � _ � 2r7-rjc�'- Si ned/Date Section I: PROJECT OVERVIEW The proposed project is the construction of Windwood, a 109 lot single-family plat on approximately 28 acres. The project is located on the north side of SE 128`h Street, east of 148`h Avenue SE. More generally, the site is located in Section 11, Township 23 North, Range 5 East W.M. in King County Washington (refer to the Vicinity Map on the following page). In general, the site is located in the Lower Cedar River Sub-basin of the Cedar River Basin as defined in the King County Basin Reconnaissance Program Summary (Volume II� (refer to Basin Map and the Basin Reconnaissance Map, both of which are located in the appendix of this report). More specifically, runoff from the site drains to the Maplewood and Orting Hill Sub-basin. Refer to the Renton Qicadrangle Map as well as the Sub-basin Map, both located in the appendix, for basin delineation. A site visit was made on February 4, 1998, a cold and cloudy day. Onsite vegetation consists of second growth forest with light to moderate understory. In general, the site slopes southwesterly at approximately 8°Io. The site can be divided into three drainage sub-basins, all of which combine to one basin just over one-quarter mile downstream of the site. Refer to the "Downstream Drainage Analysis" section of this report for additional downstream information. TECHNICAL INFORMATION REPORT FOR WINDWOOD - Page 1 s� �9 ,� �'9� �c`�} '' � TO �r�Y Y� �'o NN PARK p �2 T�ti �S S,90U SE 116th ST �O W W � h � � � e e Q SE I20th t � N � ST COALfE7L0 � e r r � PARK t ♦ � � b 124th � �' 3 •�� 3i TO !—405 ��` � � PARK �— d� R/DE NE 4th ST SE 128th .tST � a sE i.re�e s sf r.u�d � ddAPLE � � P � � v h Vicinity Map NTS TECHNICAL INFORMATION REPORT FOR WINDWOOD -Page 2 Section II: FINAL CONDITIONS SUMMARY The following is an item by item copy of the King County Hearing Examiners Recommendations with Triads' response to each item in bold. A complete copy of the Hearing Examiners findings is included in the appendix. Some of the Hearing Examiner's recommendations have been modified to comply with the City of Renton's requirements. FINDINGS, CONCLUSIONS&DECISION: Having reviewed the record in this matter, the Examiner now makes and enters the following: CONCLUSIONS: 1 Based upon the whole record, and according substantial weight to the determination of environmental signifzcance made by the Land Use Services Division, it is concluded that approval of this subdivision as recommended below would not constitute a major action significantly affecting the qualiry of the environment. All evidence of environmental impact relating to the proposed action and reasonable alternatives to the proposed action have been included in the review and consideration of this action. 2 If approved subject to the conditions recommended below, the proposed subdivision will comply with the goals and objectives of the Comprehensive Plan, Newcastle Communiry Plan, Subdivision and Zo�aing Codes, and other official land use controls and policies of King County. 3. If approved subject to the conditions recommended below, this proposed sicbdivision will make appropriate provision for the public health, safety and general welfare and for drainage ways, streets, other public ways, water supply, and sanitary wastes; and it will serve the public use and interest. . 4. The conditions recommended in the Land Use Services Division's Preliminary Report as I amended below are in the public interest and are reasonable requirements. DECISION: GRANT preliminary approval to the proposed plat of WIND WOOD, as described by the Applicants preliminary plat drawing (Exhibit No. 7J, as amended by the relocation of the 1 Sl st Avenue SE cul-de-sac (Exhibit No. 19); SUBJECT to the following conditions of final plat approval: 1. Compliance with all platting provisions of Title 19 of the King Counry Code. • Since the subject site is now witlun the City of Renton,all platting provisions of the City of Renton will be complied with. 2. All persons having an ownership interest in the subject property shall sign on the face of the final plat a dedication that includes the language set forth in King Count_y Council Motion No. 5952. • All signatures required by the City of Renton will be on the final plat. TECHNICAL INFORMATION REPORT FOR WINDWOOD - Page 3 3. The plat shall meet the base density(and miriimc�nz density)of the R4 zone classiftcation. All lots shall meet the minimum dimensional reguirements of the R4 zone classi�cation or shall be as shown on the face of the approved preliminary plat, whichever is larger. Minor revisioizs to the plat that do not result in substantial changes may be approved at the discretion of the Department of Development and Environmental Services. • The preliminary plat approval from King County was for lll lots,which met King County requirements. In order to be annexed into the City of Renton,the project was modified to meet the City of Renton density requirements. These requirements allow a maximum of 1091ots to be created on this site. Therefore,the engineering plans and Final Plat will show a 1091ot layout. 4. The applicant must obtain flnal approval from the King County Health Department. Prior to final recording of the plat, the applicant must secure public sewage disposal service for the plat from the City of Renton or King Cocc�aty Water District#90. Annexation of the site or approval by the BRE will be necessary, and the required sewer system improvements(including a sewer trunk line extension a�ui an on-site collection s_ystem)will regasire a sewer comprehensive pan amendment. • The City of Renton will supply municipal sewer service to the project and all approvals will be obtained through the City of Renton Department of Public Works. A trunk sewer will be constructed in SE 128'h Street to serve the project in accordance with the City of Renton Comprehensive Sewer Plan. 5. All construction and upgrading of public and private roads shall be done in accordance with the King County Road Standards established and adopted by Ordinance No. 11187, as amended. • All construction and upgrading within the City annexation area will compty with the City of Renton requirements. Offsite roadway improvements outside of the City of Renton will comply with KCRS Ordinance No. 11187. 6. The applicant must obtain the approval of the King Cou�aty Fire Protection Engineer for tlte adequacy of the fare hydrant, lvater mairz, arul fire flotiv standards of Chapter 17.08 of tlae King County Code. • Since this project wi116e within the City of Renton,the City Fire Marshall will review the plans for compliance with the City's fire protection requirements. 7. Final plat approval shall require full compliance with drainage provisior2s set forth in King County Code 9.04 and the storm drainage requirements and guidelines as established by the Surface Water Management Division. Compliance may result in reducing the number and/or location of lots as shown on the preliminary approved plat. The follotiving conditions represe�tt portions of the Code and requirements and shall apply to all plats. a. Drainage plans and analysis shall comply with the 1990 King Counry Surface Water Design Manual and updates which were adopted by Public Rule effective January 1, TECHNICAL INFORMATION REPORT FOR WINDWOOD - Page 4 1995. DDES approval of the drai�tage an�l roadway pla�is is reqt�ired prior to aray cortstrtsction. • The drainage system has been designed to the King County 1998 Standard for detention and water quality per the requirement of drainage variance no. L98V0039.The pipe conve}�ance system has been designed to the King County 1990 Standard. b. Current standard plan notes and ESC notes, as established bv DDES Engiraeering Review, shall be shotiti�n on the engiizeering plans. • The current notes are on the plans. c. The following note shall be shown on the final recorded plat: All building downspouts,footing drains, and drains froin all irnperviot�s surfaces suclr as patios and driveways shall be connected to the permanent storm drai�: outlet a,r shown on the approved construction drawings# on file with DDES and/or the Department of Public Works. This plan shall be submitted with the application of a�zy building permit. All connections of the drains must be constr«ctecl and approved prior to the ftnal building inspection approval. For tlzose lots that arc� designated for individual lot infltration systems, the systems shall bc� cor�stru�red at the time of the building permit and shall comply with plans on file. " • This note«�ill be addcd to the final recorded plat, if required bv the City of Rcntc�n. %. T1�ie drainage desig�i shall be iri accordance with the Cedar River Basin Plan. The retentic� detention standard shall be Level 2 per SW 19 and the water guality treatment desien sh��I�� Basic Treatment per BW 12(see Maplewood and Oning Hill Subbasins Mtii"; • The drainage design complies with the Cedar River Basin Plan.The detentia�. ..-,.:,:. �:.� ; :;� , designed to meet the KCRTS Level II Standard and the water quality facility complies with t Basic Treatment menu. 9. An existing drainage course exists along the west site boundary adjoining proposed lots 91 through 98(in 150th Avenue SE riglzt-of-way). This drainage course shall be analyzed at engineering plan submittal for capacity per the 1990 King County Surface Water Design Manual, to ensure no drainage impacts following development of the Windwood site. Onsite or offsite improvements may be required to achieve adequate drainage conveyance. • The Windwood detention/water quality facilities have been designed to include most of the watershed to this offsite drainage course.The drainage course will therefore receive substantially less runoff tha�the current condition. 10. The following road improvements are reguired with this subdivision to be constructed according to 1993 King County Road Standards(KCRS): (Metro wants bus improvements.) a. 154th Avenue SE(between the entrance and SE 127th Street)and SE 124th Street shall be improved to the full-width urban neighborhood collector standard. TECHNICAL INFORMATION REPORT FOR WINDWOOD -Page 5 • 154"'Ave.SE between the entrance and SE 127`h Street has been designed to the Neighborhood Collector standard with the exception of the design speed. A Neighborhood Collector is normally designed for 35MPH,However,in this short segment of road between intersections it is not reasonable to expect vehicles to be travelling at 35MPH. Therefore,a 25MPH design I speed has been used for this segment of roadway. A metro bus stop has been provided near 154th Ave SE at SE 128`h Street. ' b. OFFSITE: On the south side, SE 124th Street from the west site boundary to 148th I Avenue SE shall be improved to the urban neighborhood collector standard_north side shall also be improved per DDES approval, but not to the full urban neighborhood collector standard. Plans for this improvement shall be submitted at , engineering plan submittal. • A'/z street improvement to Neighborhood Collector standards has been provided for 124t1' Street between 148`h Ave.SE and the western site boundary. The north side of this street is to remain in its present condition to 149`�Avenue SE and will taper to match the full Neighborhood Collector design on-site between 149`h Street and the site boundary. c. SE 127th Street shall be improved to the urban subcollector sta�ulard. SE 127th Street shall extend east to the east property boundary. • SE 127`h Street has been designed to the urban subcollector standard.and the improvements extend to the property boundary. d. 1 SI st Avenue SE, 152nd Avenue SE(between SE 124th Street to SE 126th Street), SE 126th Street, and 153rd Avenue SE(from SE 124th to SE 127th Street)shall be improved to the urban minor access standard. • These referenced streets have been designed to the urban minor access standard. e. 152nd Avenue SE(from SE 124th Street, nonh to cul-de-sac)shall be improved to the urban minor access standard. � 152"d Street has been designed to the urban minor access standard. f. Access Tract H shall be improved to the private access road standard per Section 2.09 KCRS • Access Tract H has been designed ta the private access road standard. g. Access Tract L shall be improved to the joint use drivewa_y standard per Section 3.01 KCRS. � Access Tract L has been designed to the joint use driveway standard. l2. Modifications to the above road conditions may be considered according to the provisions of Section 1.08 KCRS A safe waiting area and shelter footing will be provided for school bus and METRO bus pickup at the project entrance(154th Avenue SE and SE 128th). If reguested by the Issaquah School District, a bus pullout will also be provided at or near the Windwood entrance. Also, a safe waiting area for school bus pickup will be provided at 148TH Avenue SE and SE 124th Street. TECHNICAL INFORMATION REPORT FOR WINDWOOD - Page 6 • A Metro bus shelter has been induded in the design for SE 128`h Street.A school bus pickup was requested by the Issaquah School District at the project entrance and has been designed to the Districts requirements. A second safe waiting area has been provided on 148`�Ave SE at ' SE 124"'Street � i. The Windwood properry froritage along the riorth side of SE 128th Street shall be �� improved to the urban principal arterial standard, with provision for a bike lane. � The frontage improvements along SE 128`�'St have been designed to accommodate an eastbound left turn lane with sufficient roadway width to allow a 5 foot wide bike lane to be installed when the south side of the roadway is improved. I1. Preliminary plat review has identified tlze following specific sensitive area requirements which apply to this project. All other applicable requirements from KCC 21A.24 shall also be addressed by the applicant: �i. T1te Class II wetlands shall have a buffer width of SO feet, rneasured from the wetland edge. Buffer averaging is acceptable so long as the provisions of KCC 21A.24.320B are satisfied. • This buffer has been included in the design,including some buffer averaging in accordance with KCC 21A24.320B. b. 77ie Class 111 wetlands(except i-tnregi�lated 1ti�etlands)shall hai�e a bicffer�i�idth of 2 S feet, rneasured from the wetland edge. • This buffer has been included in the design. c. One Class 111 wetland, Wetland F, is proposed to be fzlled. This is acceptable per KCC 21A.24.330.K, with appropriate mitigation as specified in subsection g. below. • This wetland is shown to be filled on the plans. Mitigation will be provided and will be presented on a separate plan set being prepared by B-12 Associates,Inc. d. The wetlands and their respective bc�ffers slzall be placed in Sensitive Area Tracts (SAT). • Sensitive area tracts are shown on the plans. e. A minimum building setback line of 15 feet shall be required from the edge of the SAT. • The 15 foot BSBL is shown on the plans. f. The wetland and sensitive area tract(s)shall be delineated and signed in accordance with KCC 21A.24.160. The sign details shall be shown on the engineering plans. • The proposed subdivision complies with the sensitive areas requirements as outlined in KCC 2IA.24.160. A sign detail is included in the engineering plan set. g. A�nal enhancement/mitigation plan must be submitted for review and approval by DDES along with the engineering plans for this proposal. The plan must include proposed fznal grades, hydrology, construction and monitoring notes and a detailed planting plan, showing species, site location. TECHNICAL INFORMATION REPORT FOR WINDWOOD -Page 7 • A final enhancement/mitigation plan for the site will be submitted under separate cover by B- 12 Associates. h. Mitigation required purstcant to this project must be completed prior to final plat approval. If this is not possible, due to seasonal requirements or other circumstances beyond the applicant's control, the applicant may post a performance borul that guarantees tlaat all required mitigation measures will be completed within one-year of plat construction. • Final plat compliance item. i. Once mitigation work is completed to DDES's satisfaction, the performance bond may be replaced by a maintenance bond in a form and amount sufficient to guarantee satisfactory workmanship, materials and performance of the approved plan for a period of five years. • Final plat compliance item. j. Upon satisfactory completiora of the final monitoring inspection, DDES staff shall release the maintena►tce bond. If the project has not rnet the established performance standards at the end of the monitoring period, the applicant shall be responsible for the preparation and implementation of a contingency plan to remedy the situation. � Final plat compliance item. 12. The proposed subdivision shall comply with the Sensitive Areas Ordinance as outlined in KCC 21A.24. Permanent survey marking, and signs as specified i�z KCC 21A.24.160 shall also be addressed prior to final plat approval. Temporary marking of sensitive areas and their buffers (e.g., with bright orange construction fencing)shall be placed on the site and shall remain in place until all construction activities are completed. • The proposed subdivision complies with the sensitive areas requirements as outlined in KCC 21A.24. Fencing requirements are shown on the engineering plans. 13. Tlie follou�ing ��ote shall be shotivfi o�i the frnal e�tgi�aeeri�ig plan and recorded plat: RESTRICTIONS FOR SENSITIVE AREA TRACTS AND SENSITIVE AREAS AND BUFFERS Dedication of a sensitive area tract/sensitive area and buffer conveys to tlie pccblic a be�ieficial interest in the land within the tract/sensitive area and bufJ`'er. This interest includes the preservation of native vegetation for all purposes that benefit the public health, safety mzd welfare, including control of surface water and erosion, maintenance of slope stability, and protection of plant and animal habitat. The sensitive area tracdsensitive area and buffer imposes upon all present and future owners and occupiers of the land subject to the tact/sensitive area and buffer the obligation, enforceable on behalf of the public by King County, to leave undisturbed all trees and other vegetation within the tract/sensitive area and buffer. The vegetation within the tract/sensitive area and buffer may not be cut pruned, covered by fzll, removed or damaged without approval in writing from the King County Department of Development and Environmental Services or its successor agency, unless otherwise provided by law. TECHNICAL INFORMATION REPORT FOR WINDWOOD - Page 8 The common boundary between the tracdsensitive area and buffer and the area of development activity must be marked or otherwise flagged to the satisfaction of King County prior to any clearing, grading, building construction or other development activity on a lot subject to the sensitive area tracdsensitive area and buffer. The required marking or flagging shall remairz m place until all development proposal activities in the viciniry of the sensitive area are completed. No building foicndations are allowed beyond the required 1 S foot building setback line, unless otherwise provided by law. • The required note is shown on the final engineering plans and will be shown on the recorded plat. 14. All utilities within proposed rights-of-way must be included within a franchise approved by the King County Council prior to final plat recording. � Noted. IS. The applicant or subsequent owner shall comply with King Counry Code 14.75, Mitigation Payment System(MPS), by paying the required MPS fee and administration fee as determined by the applicable fee ordinance. The applicant has the option to either: (I)pay the MPS fee at final plat recording, or(2)pay the MPS fee at the time of building permit issuance. If the first option is chosen, the fee paid shall be the fee in effect at the time of plat application and a note shall be placed on the face of the plat that reads, "All fees required by King Counry Code 14.75, I Mitigation Payment System(MPS), have been paid."If the second option is chosen, the fee paid , shall be the amount in effect as of the date of building permit application. � Final plat compliance item. 16. Suitable recreation space shall be provided consistent with the requirements of KCC 21A.14.180 and KCC 21A.14.190. The applicant will provide at least 43,290 square feet of recreation space within Tracts D, F, J, and K A concepta�al recreation facilities plan shall be submitted prior to engineering plan approval. The applicant shall obtain DOES and King County Parks Depanment approval of the detailed recreational facilities plan before final plat approval will be gra►ited. • Final plat compliance item. 17. A homeowners'association shall be established to the satisfaction of DOES in order to maintain the recreation facilities mid associated lmulscaping, and sensitive areas. • Final plat compliance item. 18. Street trees shall be provided on-site as follows: TECHNICAL INFORMATION REPORT FOR WINDWOOD - Page 9 a. At a minimum, trees shall be planted at a rate of one tree for every 40 feet of frontage along SE 128th Street, SE 124th Street, and 154th Avenue SE. Spacing may be modified to acconimodate sight distance requirements for drive�vays and intersections. b. Trees shall be located within the street right-of-way and planted ira accordance with Drawing No. 5-009 of the 1993 King County Road Standards, c�nless King County Public Works determirzes that trees should not be located in the street right-of-way�. c. If Public Works determines that the required street trees should not be located within the right-of-way, they shall be located no more than 20 feet from the street right-of- way line. d. The trees shall be owned and maintained by the abutting lot owners or the homeowners association or other workable organization unless the County has adopted a maintenance program. This shall be noted on the face of the final recorded plat e. The species of trees shall be approved by ODES if located within the right-of-way, and shall not include poplar, cottonwood, soft maples, gum, any fruit-bearing trees, or any other tree or shrub wltose roots are likely to obstrccct sa�titary or storm sewers, or that is not compatible with overhead utility lines. f. The applicant shall submit a street free plan and bond quantity sheet for review and approval by DDES prior to engineerrng plan approval. • (a. — f.) A street tree plan is included with the Construction Plans that meets these requirements. g. The applicant shall contact Metro Service Planriirzg at (206) 684-1622 to determine if SE 128th Street is on a bus route. If SE 128t1i Street is a bus roacte, tlae street tree plan shall also be reviewed by Metro. • SE 128"'Street is a Metro bus route and a copy of the Construction Plans has been submitted to Metro for their review. h. The street trees mt�st be irzstalled and inspected, or a performance bo�zd posted prior to recording of the plat. If a performance bond is posted, the street trees must be installed and inspected within one year of recording of the plat. At the time of inspection, if the trees are found to bc installed per the approved plan, a maintenance bond must be submitted or the performance bond replaced with a maintenance bond, and held for orae year. After orie year, the maintenance bond may be released after DDES has completed a second inspection and determined that the trees have been kept healthy and thriving. • Final plat compliance item. A $538 landscape inspection fee shall also be submitted prior to plat recording. The i�tspectio�z fee is subject to change based on the cicrrent County fees. � Final plat compliance item. ORDERED this ISth day of October, 1998. TECHNICAL INFORMATION REPORT FOR WINDWOOD - Page 10 Section IIa: DRAINAGE VARIANCE SUMMARY The following is a summary of the Drainage Variance Request items in response to the King County DDES letter dated November 18, 1998. A copy of the DDES letter is included at the end of this section. Excerpt from the letter: 3. A flow control device that splits the discharge to the flow paths on the north and south sides of Southeast 128`h Street may be used. The splitter must be located within the drainage tract of Windwood. The release rates in each path must approximate the eYisting release rates. As an alternative, a single discharge to the Southeast 128`h Street frontage from the detention facility must equal the release from the existing middle and southern subbasins(identified in finding 4.b.and c.above). Tlze detention pond provides sufficient control of the flow during all design storm conditions to limit the total flow in the ditches along both sides of SE 128`h Street to pre-construction levels. Refer to the flow comparisora table in Sectiort 3 of this report for comparison data. (NOTE: The 10 year storm flow is slightly exceeded but the difference is considered to be negligible). Therefore, a flow splitter is not required for this project. TECHNICAL INFORMATION REPORT FOR WINDWOOD - Page 12 Section III: OFF-SITE ANALYSIS Resources Used for the Analysis Adopted Basin Plan The site is located in the Cedar River Basin, Lower Cedar River Sub-basin. According to the Draft Proposed Lower Cedar River Basin and Nonpoint Pollution Action Plan, the site drains to the Orting Hills Sub-basin. The site is also located in the Newcastle Community Planning Area. ' Critical Drainage Area Maps The site is not located in any of the critical drainage areas discussed in the reference section of the 1990 Kina Countv Surface Water DesiQn Manual. Flood Plain/Floodway Map The site is not located in or near any floodplains as shown on the Flood Insurance Rate Map (see the attached FIRM map). Sensitive Areas Folio The Kin� County Sensitive Areas Folio and Wetlands Inventorv did not reveal the site to be in a critical area with regards to landslide, seismic, erosion, coal mine or wetland areas. Please refer to the appropriate maps attached to this section of the report. King County Soil Survey According to the King County S.C.S. Soils Survey, the site is underlain with Alderwood soil belonging to the SCS type `C' hydrologic group. Please refer to the attached Soils Map. King County Complaint History None available TECHNICAL INFOK:4tATION REPORT FOR VVIND��'OOD - Page 13 Dual Basin Characteristics This project has two distinct basins, the south and the north basins. The flows to the west from the northerly portion of the project flow along SE 124`h ST and then south along 148`h Ave SE. The south basin flows westerly along SE 128`h St. Both basins meet at the northeast corner of the SE 128`h St/ 148`h Ave SE intersection. At this point the northerly basin is 37.0 acres and the southerly basin is 30.2 acres. The proposed project will subtract 6.9 Acres form the north and add it to the south basin. A flow splitter will be added to the south basin R/D facility so that the relative percentage of flow is maintained from the predeveloped to the developed stages at this point. In the predeveloped state 54% of the flow comes from the north basin and 46% from the south. The proposed development will adjust the flows from the R/D facility so that 45°Io will flow to the south basin system and 55°Io will flow to the north basin to rebalance the relative flows. See the calculations at the end of this section for the detailed analysis. Wetland Recharge The proposed project will be built around an existing wetland. To maintain the runoff that , flows to this wetland, roof and footing drains from proposed lots 31 thru 40 will be tight � lined to the wetland to recharge the volume of water that flows to the wetland in the ' predeveloped state. These lots will account for run off volumes in the 2, 5, 10 and 25 year I events. See the wetland recharge calculations at the end of this section for the detailed , calculations. TECHNICAL INFORMATION REPORT FOR WINDWOOD - Page 14 OFFSITE FLOW ANALYSIS In general, the proposed project site is located within two distinct drainage basins as ; delineated on the Offsite Ezisting Conditions Map located at the end of this section. In the predeveloped state, approximately 7.60 acres of the site drain to the North Basin while the remainder of the site, with the exclusion of the onsite wetland area, drains to the South Basin. Refer to the Level One Downstream Draina e� Analysis for the Windwood ', project for a detailed description of the downstream drainage routes. ' Due to the nature of the proposed conveyance and detention system for this project, runoff from area that was previously tributary to the North Basin (7.60 acres} will be redirected and conveyed to a detention facility, located near the southwest corner of the site, prior to discharging to the South Basin. Pre and post developed flows for each basin were compared, at the intersection of 148`h Avenue SE and SE 128`�' street, to verify that the post-developed flows were similar to the pre-developed flows for each basin. The flows were generated using the King County Runoff Time Series (KCRTS) hydrologic modeling program using a 15-minute time series. A summary of the flow calculations has been provided on the pages that follow. Refer to the Offsite L'xisting Conditions Map as well as the Offsite Developed Conditions Map, located at the end of this section, to aid in the flow calculation summary. KCRTS Corastarzts for Both Basiris Regional Scale Factor= 1.0 (Sea-Tac) Soil Type —Till (Till Vs Outwash) 15 minute Time Series (15-minute Vs 1-hour per King County Standards) Data Type—Reduced (Reduced Vs Historic) North Basin —Pre-Developed Conditions Total Area= 37.00 Ac Impervious Area = 4.65 Ac Till Forest = 20.00 Ac Till Grass = 1?.35 Ac TECI�NICAL INFORI�IATI01�` REPORT FOR �'�'IND�i'OOD - Pa�e 1� North Basin-Post-Devel -;s� E f + Total Area= 30.10 � *Impervious Ar�.� - Till Forest = 20.00 :' Till Grass = 5.20 Ac *Impervious area increased due to Irc�n�a��e i��prc��e�nen�s alon�� S[� 1��3`�� S�rcct as well as along 148`h Avenue SE. South Basin-Pre-Developed Conditions Total Area= 3020 Ac Impervious Area = 4.55 Ac Till Forest = 19.70 Ac Till Grass = 5.95 Ac South Basin-Post-Developed Conditions In the post-developed conditions, a large portion of the South Basin's runoff will be conveyed to the proposed detention facility associated with this project while the remainder of the basin's runoff pattern is unchanged. Thus, the South Basin can be divided into two basins, namely the Detained South Basin and the Un-Detained South Basin. Calculations for flows leaving the proposed detention pond (Detained South Basin) are outlined in Section IV (Retention/Detention Analysis and Desigrt) of this report. The total flow from the South Basin was determined by arithmetically summing the peak rates of discharge from the Detained South Basin with the peak rates of discharge from the Un-Detained South Basin. TECHN[CAL INFORh�IATION REPORT FOR �i'IND�VOOD - Page 16 Detai�zed South Basin (flotivs leavi�i,� tlie�roposed detefitiori acilit��l Total Area= 29.10 Ac *Impervious Area = 12.40 Ac Till Grass = 16.70 Ac *Impervious area includes portions of SE 128`h Street which are tributary to the proposed detention pond. Un-Detained South Basin (flows not conveyed to the proposed detention facilit� Total Area= 8.0 Ac *Impervious Area = 3.30 Ac Till Grass = 4.70 Ac �Impervious area includes frontage improvements on the north side of SE 128�n Street. Flow Comparison Table North Basin South Basin Return Period Pre-Develo ed Post-Develo ed Pre-Develo ed *Post-Develo ed 2 yr 3.34 2.96 2.82 2.12 10 yr 5.80 3.66 3.75 4.00 25 yr 7.68 6.33 6.17 5.45 50 yr 11.37 8.71 8.62 7.26 100 yr 13.27 9.99 9.85 8.18 *Note: See Flow Calculations Exhibit at the end of this section for a summary of the Un-Detained and Detained flows for the South Basin. TECHNICAL INFORMAT[ON REPORT FOR��'IND«'OOD - Page 17 Offsite Flow Summary Though there is an increase in impervious area as a direct result of this project, the overall peak rate of runoff at a point located downstream of the site did not increase for the storm events analyzed, with the exception of the 10 year storm event, due to the restrictive nature of the proposed detention facility. The peak rate of runoff from the 10 year event did result in a slight increase of approximately 6.7% to the peak rate of runoff tributary to the South Basin. Based on the above flow comparison, it appears that the post-developed flow levels will be held at or below the pre-developed flow rates for most storm events. The addition of a flow splitter to the downstream conveyance system, that would be installed to proportion flows from the South Basin to the North Basin, does not appear to be beneficial to this drainage basin. It appears that the proposed conveyance and detention system discharges post-developed flows that are reasonably similar to pre-developed flows tributary to each basin. T�:(:HNICAL INFOR;�IATION REPORT FOR�VIND�VOOD - Yage 1� SECTION 3.2 RUNOFF COMPUTA'I70N AND ANALYSIS MEI'HODS FIGURE 3.2.2.A RAINFALL REGIONS AND REGIONAL SCALE FACTORS ST 1.0/ ST 1.1 ST 1.0 �p 0.8 LA 0.9 � 1.0 LA 1.2 q�(y iMOMOY1fN COYMT♦ �<Yl j ,l� ' � „ RIMO COYMtY �C . .' R I ^'Q,, _� 4 � /",-. _,'� 1 I^� ( _� .. . .1� � IJ�{ � �� . . 4� �- �� -- �; �, r ,, ^ , ,,� i ,;. , �, ,__ . :,� �; , : :> • r �`� ��` ��• �ie�o , �,/ ,.., ��i_ ,- .—'�� ,�r %-. � L b . ;� ,J! � � .s ��,ae oNo�.:. - € � r �'�'/ �`� � � � ; . �frJ, , � � +� � . �K �� //'/! ' '/ ^� ,�� - s j��. 1 B " ' `f '--�' J�i�• i ��Y�� {�s�'O : '� si � -i�� y iaai f , f�L_, \ . � :t- t�c..; ��} � " ``;. 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' •m � p O z � �] y w � o o� .oz � � � w � ct� z � � � � a � � � o z O � � x �"� ' ' z r � � � ° � z � � �d 3.2.2 KCRTS/RUNOFF FILES METHOD—GENERATING TIME SERIES TABLE 3.228:EQUNALENCE BETVVEEN SCS SOIL TYPES AND KCRTS SOIL TYPES SCS Soil Type SCS KCRTS Soi( Notes Hydrologic Group Soil Group —� Alderwood (Ag6,AgC,AgD) C Till � A�ents, Aldervvood Material (Am6, AmC) C Till Arents, Everett Material (An) B Outwash 1 Beausite (BeC, BeD, Be� C Tili 2 Bellingham (Bh) D Till 3 Briscot (Br) D Till 3 Buckley(Bu) D Till 4 Earlmont(Ea) D Till 3 Edgewick(Ed) C Till 3 Everett(EvB, EvC, EvD, EwC) A/B Outwash 1 Indianola (InC, InA, InD) A Outwash 1 Kitsap (KpB, KpC, KpD) C Till Klaus (KsC) C Outwash 1 Neilton (NeC) A Outwash 1 Newberg (Ng) B Till 3 Nooksack (Nk) C Till 3 Norma (No) D Till 3 � Orcas (Or) D Wetland �, Oridia (Os) D Till ' 3 ' Ovall (OvC, OvD, OvF) C Till 2 Pilchuck(Pc) C Till 3 � Puget (Pu) D Till 3 Puyallup(Py) B Till 3 Ragnar(RaC, RaD, RaC, RaE) B Outwash 1 Renton (Re) D Till 3 Salal (Sa) C Till 3 Sammamish (Sh) D Till 3 Seattle (Sk) D Wetland Shalcar(Sm) D Till 3 Si (Sn) C Till 3 Snohomish (So, Sr) D Till 3 Sultan (Su) C Till 3 Tukwila (Tu) D Till 3 Woodinville (Wo) D Till 3 Notes: 1. Where outwash soils are saturated or underlain at shallow depth (<5 feet) by glacial till, they should be treated as till soils. 2. These are bedrock soils, but calibration of HSPF by King County DNR shows bedrock soils to have similar hydrologic response to till soils. 3. These are alluvial soils,some of which are underlain by glacial till or have a seasonally high water table. In the absence of detailed study,these soils should be treated as till soils. . 4. Buckley soils are foRned on the low-permeability Osceola mudflow. Hydrologic response is assumed to be similar to that of till soils. I 1998 Surface Water Design Manual 911/98 3-25 WINDWOOD-FLOW ANALYSIS NORTH BASIN EXISTING Flow Frequency Analysis Time Series File:northpre.tsf Project Location:Sea-Tac ---Annual Peak Flow Rates--- ----Flow Frequency Analysis------- Flow Rate Rank Time of Peak --Peaks-- Rank Return Prob (CFS) (CFS) Period 4.00 4 2/09/O1 12:45 13.21 1 100.00 0.990 2.41 7 1/06/02 1:00 7.68 2 25.00 0.960 7.68 2 12/08/0217:15 5.80 3 10.00 0.900 1.91 8 8/26/04 0:45 4.00 4 5.00 0.800 5.80 3 11/17/04 5:00 3.51 5 3.00 0.667 334 6 1/18/0615:00 3.34 6 2.00 0.500 3.51 5 11/24/06 1:00 2.41 7 130 0.231 13.21 1 1/09/08 6:30 1.91 8 1.10 0.091 Computed Peaks 11.37 50.00 0.980 NORTH BASIN DEVELOPED Flow Frequency Analysis Time Series File:northdev.tsf Project Location:Sea-Tac ---Annual Peak Flow Rates-- ----Flow Frequency Analysis------- Flow Rate Rank Time of Peak --Peaks-- Rank Return Proh (CFS) (CFS) Period 3.30 5 2/09/01 12:30 9.90 1 100.00 0.9� 2.12 7 1/OS/0215:00 633 2 25.00 096� 633 2 12/08/0217:15 3.66 3 10.00 09(' 1.88 8 8/23/0414:30 335 4 5.00 0.80( 3.66 3 11/17/04 5:00 330 5 3.00 0.66" 2.96 6 10/27/0510:45 2.96 6 2.00 O.SOi 335 4 10/25/06 22:45 2.12 7 1.30 0.2�I 9.90 1 1/09/08 6:30 1.88 8 1.10 0.091 . �, � � - , � . , _ , ,. Flo�r Frequency Analysis Time Series File:southpre.ts, Project Location:Sea-Tac ---Annual Peak Flow Rates--- -----Flow Frequency Analysi� - -- Flow Rate Rank Time of Peak --Peaks-- Rank Return ]�r,�!� (CFS) (CFS) Period 3.26 4 2/09/O 1 1230 9.85 1 100.00 0.99�� 2.04 7 1/OS/0215:00 6.17 2 25.00 0.960 6.17 2 12/08/02 17:15 3.75 3 ]0.00 0.90�� 1.76 8 8/26/04 0:45 3.26 4 5.00 0.800 3.75 3 11/17/04 5:00 3.15 5 3.00 0.667 2.82 6 10/27/0510:45 2.82 6 2.00 0.500 3.15 5 ]0/25/06 22:45 2.04 7 130 0.231 9.85 1 1/09/08 6:30 1.76 8 1.10 0.091 Computed Peaks 8.62 50.00 0.980 FILE: KCRTS PEAKS KCRTS PEAK FLON'OUTPUT 2`10!99- BKP WINDWOOD-FLOVV ANALYSIS UNDETAINED SOUTH BASIN Flow Frequency Analysis Time Series File:southund.tsf Project Location:Sea-Tac --Annual Peak Flow Rates--- ---Flow Frequency Analysis------- Flow Rate Rank Time of Peak --Peaks-- Rank Return Prob (CFS) (CFS) Period 1.57 6 8/27/O1 18:00 4.63 1 100.00 0.990 1.13 8 1/OS/0215:00 332 2 25.00 0.960 3.32 2 12/08/0217:15 2.17 3 10.00 0.900 1.26 7 8/23/0414:30 1.82 4 5.00 0.800 1.72 5 10/28/0416:00 1.72 5 3.00 0.667 1.82 4 10/27/0510:45 1.57 6 2.00 0.500 2.17 3 10/25/06 22:45 1.26 7 130 0.231 4.63 1 1/09/08 6:30 1.13 8 1.10 0.091 Computed Peaks 4.19 50.00 0.980 DETAINED SOUTH BASIN(Pond Discharge) Time Series File:rdout.tsf Project Location:Sea-Tac ---Annual Peak Flow Rates-- --Flow Frequency Analysis------- Flow Rate Rank Time of Peak --Peaks-- Rank Return Prob (CFS) (CFS) (ft) Period 2.13 2 2/09/0120:00 3.55 10.37 1 100.00 0.990 0.484 7 12/29/O1 10:00 2.13 9.01 2 25.00 0.960 1.62 4 2/28/03 7:00 1.83 8.20 3 10.00 0.900 0.385 8 8/26/04 7:00 1.62 7.69 4 5.00 0.800 0.545 6 1/06/0515:00 1.55 7.55 5 3.00 0.667 1.55 5 1/18/06 23:00 0.545 6.46 6 2.00 0.500 1.83 3 11/24/06 7:00 0.484 5.07 7 1.30 0.231 3.55 1 1/09/0810:00 0385 3.22 8 1.10 0.091 Computed Peaks 3.07 10.31 50.00 Q.980 TOTAL FLOW TO SOUTH BASIN=UNDETAINED SOUTH BASIN+DETAINED SOUTH BASIN 2 Year Flow = 1.57+0.55=2.12 cfs l0 Year Flow = 2.17+ 1.83 =4.00 cfs 25 Year Flow = 332+2.13 =5.45 cfs✓ 50 Year Flow = 4.19+3.07=7.26 cfs 100 Year Flow = 4.63 +3.55=8.18 cfs FILE: KCRTS PEAKS KCRTS PEAK FLOW OUTPUT 2/10/99-BKP 1 � � ' i ��, iX]� i " ........../�, 1 .`..,..,�.... w...,.,.,y lG�,:.2 1 '_\ /� 7 ��. � �� ` ' .. ._ }4 J xuzxi \ � `'r �I � ,\ I � wyai.�r �1 � 11 r �51.6! �: � � IJ I � ` �� % I 1 �� -..�i_I` • Wy� :. �.......� c l \ 1• __� �-. \ t i6i.6i / � \ � i6iSC I��Y�� ." � • �- � 1 �, , : : �� 6,�, �••,. � ' .......__ .._ 1 \ 1.2N. ..... ... .. 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E �, ,, aJ�Z�a7 -- __ I Wetland Recharge Calculations 12/02/98 HYDROGRAPH SUMMARY Hydrograph Description HYD PEAK TIME VOLUME AREA NUM [CFS) [Min] [CF] [Ac] Predevelo ed,2 1 0.164 480 3991* 2.12 Predevelo ed,5 r 2 0.370 480 6925* 2.12 Predevelo ed, 10 r 3 0.507 480 8820* 2.12 Predevelo ed,25 r 4 0.717 480 11700* 2.12 Develo ed,2 r 5 0.069 480 1804 0.91 Develo ed,5 r 6 0.152 480 3095 0.91 Develo ed, 10 r 7 0.207 480 3925 0.91 Develo ed,25 r 8 0292 480 5182 0.91 Extra Area,2 r 9 0.185 480 3375 0.80 Extra Area,5 r 10 0275 480 4866 0.80 Extra Area, lOvr 11 0.330 480 5767 0.80 Extra Area,25 r 12 0.410 480 7084 0.80 Total Flow to Wetland,2 r** 13 0.254 480 5180** 1.71 Total Flow to Wetland,5 r** 14 0.427 480 7961** 1.71 Total Flow to Wetland, 10 r** 15 0.537 480 9692** 1.71 Total Flow to Wetland,25 r** 16 0.702 480 12266** 1.71 **Total flow to wetland at or greater then the predeveloped *condition. Wetland Recharge Area Page 1 of 10 � �� Hyd No, 1_ N!d Mo, 13...... � w u c � r � 0 Q r, ,'�� I ;' � _ �- __ , 3 6 9 12 15 18 Z1 24 Z7 i iNe in Ilours H�d No. : 1 Rate : � . 1� cfs Time: 8 . 00 hr Vol : 0 .09 Ac-ft Int : 10 . 00 min H�d No. : 13 Ra�e : 0 .25 e€s Time : 8 . 00 �� Vol : e . l� �ic-ft �nt : 10 . 00 min Wetland Recharge Area Page 2 of 10 0 a �� ,a �o, a� Hyd No. 14 M w U E M � � 4 S I�; �`''�, ; '�� ;� 3 6 9 12 15 18 21 24 27 T ine in Hours Hyd No . : 2 Rate : 0 . 37 cfs Time : 8 . 00 hr Vol : 0 . 16 Ac-ft Int : 10 . 00 min Hyd No. : 14 Rate: 6 .4� cfs Time : � . 66 hr Vol ; 0 .18 Ac-ft Int : 10 . 00 min Wetland Recharge Area Page 3 of 10 0 � I.E(� Nyd No, 3_ Hyd tb. 15...... A w U E MO � � �� Q 1 f. i• ! % 3 6 9 12 15 18 21 24 2� Tine in Hours Hyd No . : 3 Rate : 0 .51 cfs Time : 8 . 00 hr Vol : 0 .20 Ae-€� I�� : 10 . 00 min H�d No. : 15 Rate : 0 .54 cfs Time: 8 . 00 hr Vol : 0 .22 Ac-ft Int : 10 . 00 min � Wetland Recharge Area Page 4 of 10 ro �� Hyd No. 4_ Hyd Ho. 16 M w u E *o �8 �� 1 S , � , ;' , Jr�;. - -- \ 3 6 9 12 15 18 21 24 27 Tine in Hours H�d NO. : 4 Ra�e : 0 . 72 e€s Time : 8 . 00 �� itol : 6 .29 i�c-ft �nt : 16 .�6 min �Iyd No. : 16 Rate : 0 .70 cfs Time: 8 .00 hr Vol : 0 .28 Ae-�� I�� : 10 .00 min Wetland Recharge Area Page 5 of 10 Wedand Recharge Calculations 12/02/98 BASIN SUMMARY BASIN ID: DV 10 NAME: DEVELOPED lOYR SBUH IviETHODOLOGY TOTAL AREA..: 0.91 Acres BASEFI.OWS : 0.00 cfs RAINFALL TYPE..: USER1 PERVIOUS AREA PRECIPITATION..: 2.95 inches AREA..: 091 Acres TIME INTERVAL..: 10.00 min CN..: 79.60 TIME OF CONC..: 15.00 min IMPERVIOUS AREA ABSTRACTION COEFF : 0.20 AREA..: 0.00 Acres CN..: 98.00 PEAK RATE: 0.21 cfs VOL: 0.09 Ac-ft TIME: 480 min BASIN ID: DV2 NAME:DEVELOPED 2YR SBUH METHODOLOGY TOTAL AREA..: 0.91 Acres BASEFLOWS : 0.00 cfs RAINFALL TYPE..: USER1 PERVIOUS AREA PRECIPITATION..: 2.00 inches AREA..: 0.91 Acres TIME INTERVAL..: 10.00 min CN..: 79.60 TIME OF CONC..: 15.00 min IMPERVIOUS AREA ABSTRACTION COEFF : 0.20 AREA..: 0.00 Acres CN..: 98.00 PEAK RATE: 0.07 cfs VOL: 0.04 Ac-ft TIME: 480 min BASIN ID: DV25 NAME: DEVELOPED 25YR SBUH METHODOLOGY TOTAL AREA..: 0.91 Acres BASEFLOWS : 0.00 cfs RAINFALL TYPE..: USER1 PERVIOUS AREA PREC�ITATION..: 3.45 inches AREA..: 0.91 Acres TIME INTERVAL..: 10.00 min CN..: 79.60 TIME OF CONC..: 15.00 min IMPERVIOUS AREA ABSTRACTION COEFF : 0.20 AREA..: 0.00 Acres CN..: 98.00 PEAK RATE: 0.29 cfs VOL: 0.12 Ac-ft TIME: 480 min Wetland Recharge Area Page 6 of 10 Wetland Recharge Calculations 12/02/98 BASIN SUMMARY BASIN ID: DVS NAIvIE:DEVELOPED SYR SBUH METHODOLOGY TOTAL AREA..: 0.91 Acres BASEFI.OWS : 0.00 cfs RAINFALL TYPE..: USER1 PERVIOUS AREA PRECIPITATION..: 2.60 inches AREA..: 0.91 Acres TIME INTERVAL..: 10.00 min CN..: 79.60 TIME OF CONC..: 15.00 min IMPERVIOUS AREA ABSTRACTION COEFF : 020 AREA..: 0.00 Acres CN..: 98.00 PEAK RATE: 0.15 cfs VOL: 0.07 Ac-ft TIME: 480 min BASIN ID: EX10 NAME: EXISTING lOYR SBUH METHODOLOGY TOTAL AREA..: 2.12 Acres BASEFLOWS : 0.00 cfs RAINFALL TYPE..: USER1 PERVIOUS AREA PRECIPITATION..: 2.95 inches AREA..: 2.12 Acres TIME INTERVAL..: 10.00 min CN..: 78.90 TIME OF CONC..: 10.00 min IMPERVIOUS AREA ABSTRACTION COEFF : 0.20 AREA..: 0.00 Acres CN..: 98.Q0 � PEAK RATE: 0.51 cfs VOL: 0.20 Ac-ft TIME: 480 min BASIN ID: EX2 NAME:EXISTING 2YR SBUH METHODOLOGY TOTAL AREA..: 2.12 Acres BASEFI.OWS : 0.00 cfs RAINFALL TYPE..: USER1 PERVIOUS AREA PRECIPTTATION..: 2.00 inches AREA..: 2.12 Acres TIME INTERVAL..: 10.00 min CN..: 78.90 TIME OF CONC..: 10.00 min IMPERVIOUS AREA ABSTRACTION COEFF : 0.20 AREA..: 0.00 Acres CN..: 98.00 PEAK RATE: 0.16 cfs VOL: 0.09 Ac-ft TIh'IE: 480 min Wetland Recharge Area Page 7 of 10 Wetland Recharge Calculations 12/02/98 BASIN SUMMARY BASIN ID:EX25 NAME:EXISTING 25YR SBUH METHODOLOGY TOTAL AREA..: 2.12 Acres BASEFLOWS : 0.00 cfs RAINFALL TYPE..: USER1 PERVIOUS AREA PRECIPTTATION..: 3.45 inches AREA..: 2.12 Acres TIME INTERVAL..: 10.00 min CN..: 78.90 TIME OF CONC..: 10.00 min IMPERVIOUS AREA ABSTRACTION COEFF : 0.20 AREA..: 0.00 Acres CN..: 98.00 PEAK RATE: 0.72 cfs VOL: 0.27 Ac-ft TIME: 480 min BASIN ID: EX� N�ME: EXISTING�YR SBUH METHODOLOGY TOTAL AREA..: 2.12 Acres BASEFLOWS : 0.00 cfs RAINFALL TYPE..: USER1 PERVIOUS AREA PRECIPITATION..: 2.60 inches AREA..: 2.12 Acres TIME INTERVAL..: 10.00 min CN..: 78.90 TIME OF CONC..: 10.00 min IMPERVIOUS ARI :� ABSTRACTION COEFF : 0.20 AREA..: u.uu :��<< CN..: 98.00 PEAK RATE: 0.37 cfs VOL: 0.16 Ac-ft TIME: 480 min SBUH h1E'I'HODOLOGY TOTAL AREA..: 0.80 Acres BASEFLOWS : u.�n� . RAINFALL TYPE..: USER1 PERVIOUS AR1. . PRECIPITATION..: 2.95 inches AREA..: 0.50 Ar� TIME INTERVAL..: 10.00 min CN..: 85.00 TIME OF CONC..: Z0.00 min IMPERVIOUS ARl ',. ABSTRACTION COEFF u �� }�}_� �� oc n�� Pt�::�h fZ�T}�.: ll.�� cf. �OI.: u.13 -�r-ft 1 Ul}:: -l`i11 niin ��'etlanc� Rechar�'e Ar�a Ya��e S of 1� Wetland Recharge Calculations 12/02/98 BASIN SUMMARY BASIN ID: X2 NAME: EXTRA 2YR SBUH METHODOLOGY TOTAL AREA..: 0.80 Acres BASEFLOWS : 0.00 cfs RAINFALL TYPE..: USER1 PERVIOUS AREA PRECIPITATION..: 2.00 inches AREA..: 0.50 Acres TIME INTERVAL..: 10.00 min CN..: 85.00 TIME OF CONC..: 20.00 min IMPERVIOUS AREA ABSTRACTION COEFF : 020 AREA..: 0.30 Acres CN..: 98.00 PEAK RATE: 0.18 cfs VOL: 0.08 Ac-ft TIME: 480 min BASIN ID: X?5 '�lA��tE: E.l'TR:A?>�"R SBUH METHODOLOGY TOTAL AREA..: 0.80 Acres BASEFLOWS : 0.00 cfs RAINFALL TYPE..: USER1 PERVIOUS AREA PRECIPTTATION..: 3.45 inches AREA..: 0.50 Acres TIME INTERVAL..: 10.00 min CN..: 85.00 TIME OF CONC..: 20.00 min IMPERVIOUS AREA ABSTRACTION COEFF : 0.20 AREA..: 0.30 Acres CN..: 98.00 PEAK RATE: 0.41 cfs VOL: 0.16 Ac-ft TIME: 480 min BASIN ID:XS NAME:EXTRA SYR SBUH METHODOLOGY TOTAL AREA..: 0.80 Acres BASEF7..OWS : 0.00 cfs RAINFALL TYPE..: USER1 PERVIOUS AREA PRECIPITATION..: 2.60 inches AREA..: 0.50 Acres TIME INTERVAL..: 10.00 min CN..: 85.00 TIME OF CONC..: 20.00 min IMPERVIOUS AREA ABSTRACTION'COEFF : 0.20 AREA..: 0.30 Acres CN..: 98.00 PEAK RATE: 0.27 cfs VOL: 0.11 Ac-ft TIN1E: 480 min Wetland Recharge Area Page 9 of 10 'f l�f _ � --- -- --� •— --- —• --- - . � r. 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I� � ,,��t� � fE� . . / � �� ,, �, �E ' `�, '�,� i� �1','.�`�� t' ,�� ' �� .•--, - � F� �� ,i ..� �1�/ . �,Mr� � '�1!_�._�`,�i.r�� . , , �! , , � � � ��Af r -�� /� �� , � *��- � ��1�1�, E ��;� E� � � � i --->i a�i�w�� j�l�� --� � ' �l'. . � �,� �� / �,1�,t� �1/,�� ►,� ��'- �� fo Jq�ru'c�� . .. _ _ ��,,,, / � /,�i �, � � � .� , � �.� ,.� �'1�. _ , �� ,�� .. �.. �. .� �� , ��ir �►��- �, � �� ., . , . �� : �� . , •' � •�� . �� .�� . . . . � , ��" , . , . . , ��, , ' ��/,f��► � . . � � � � • . � � '��►I��lMt:�i;�:� _ �� *�►��' , .. , �� . • '� _______ , , � , , . , .. ... , King County, Washington Level One Downst�eam D�ainage Analysis R�visedJuly 8, 1998 ��By.� B�t�.� Noole E.Pa�ling Re�viewed By: ��r�1;�m T �� 'i��` ��f. -�_::��... - �a.. C `�� TRIAD ASSOCIATES Februar 12 1998 Triad Job No . 95 - 243 King County, Washington Level One Downst�ean� D�ainage Analysis RevisedJu�.�y 8, 1998 _ -- ,�� . �`P �, c w py.e�.P.C�B�,. �,�. F , poc,�y BI1�K.PLl+�1SCS � � Ncole E.Pa�ling � � �� ¢� C � 1'1J�vl�� EXPIRES /-2Z^qq • William J. C�gin PE _ � __ c � ! � II TRIAD ASSOCIATES II�� ebruar 12 1998 Triad Job No . 95 - ? 4 � �I Projax No.95-243 TABLE OF CONTENTS Paee TABLEOF CONTENTS......................................................................................................................................I INTRODUC'I'ION....................................................................................................................................»..........1 VICINITYMAP...................................................................................................................................................2 RESOURCES USED FOR ANALYSIS..»...........................................................................................................3 AdoptedBasin Plan..............................................................................•-•-•-•-�--._........................................---3 CriticalDrainage Area Maps.......................................................................................................................3 FloodPlain/Floodway Map........................................................................................................................3 SerrsitiveAreas Folio....................................................................................................................................3 KingCounty Sorl Srovey...............................................................................................................................3 UPSTREAM DRAINAGE ANALYSIS...............................................................................................................4 DOWNS'I'REA1Vi DRAINAGE ANAI.YSIS........................................................................................................4 B,4sQ1 A.............................................................................................................................................................5 Ba5ir1B.............................................................................................................................................................5 BAsnvC.............................................................................................................................................................6 SUMMARY..............................................................................................:...........................................................6 APPENDIX Drainage Basins $�jn j�pnnaiccan�� Renton Quadrangle Map Sub-basin Map Community Planning Areas Map F.I.RM. Map Seismic Hazard Areas Landslide Hazard Areas Erosion Hazard Areas Coal Mine Hazard Areas Streams and 100-Year Floodplains Wetlands SCS Soils Map USGS Map Upstream Map Downstream Map Offsite Analysis Table In Pocket Onsite Basin Map LEVEL ONE DOWNSTREAM DRAINAGE ANALYSIS FOR WINWOOD—Page i Projoct No.95-243 INTRODUCTION The proposed project is the construction of Winwood, a 112 single-family plat on approximately 28 acres. The project is located on the north side of SE 128`� Street, east of 148`� Avenue SE. More generally, the site is located in Section 11, Township 23 North, Range 5 East W.M. in King County Washington(refer to the Vicinity Map on the following page). In general, the site is located in the Lower Cedar River Sub-basin of the Cedar River Basin as defined in the Kin�ty Basin Reconnaissance Proeram Summ,arY_(Volume II� (refer to Basin Map and the Basin Reconnaissance Map, both of which are located in the appendix of this report). More specifically, runoff from the site drains to the Maplewood and Orting Hill Sub- basin. Refer to the Renton Quadrangle Map as well as the Sub-basin Map, both located in the appendix, for basin delineation. A site visit was made on February 4, 1998, a cold and cloudy day. Onsite vegetation consists of second growth forest with light to moderate understory. In general, the site slopes southwesterly at approximately 8%. The site can be divided into three drainage sub-basins, all of which combine to one basin just over one-quarter mile downstream of the site. Refer to the "Downstream Drainage Analysis" section of this report for additional downstream information, LEVEL ONE DOWNSTREAM ANALYSIS FOR WINWOOD—Page 1 Triad Associates Projax No.95-243 124 '� � — i �— � � � II i t� bS � � < < `� � � �' y � l� � � � � � i�`: � � II Q � NE 47H ST < < � S� I281N ST g � :r�. �� o�� a� + I 6 �ETANtR?OYO ` "S w 1 vS � I T I �' �y�5i � � e _ � � ` �t h _ SE 1S2N0 ST � 2� I � ��p AIO(NJT 6 1 � w QU4ET J I - C£A!£TARY p�,� L l�U� 7 Vicinity Map NTS LEVEL ONE DOWNSTREAM ANALYSIS FOR WIlVWOOD-Page 2 Triad Associates Projoci No.95-243 RESOURCES USED FOR ANALYSIS Adopted Basin Plan The site is located in the Cedar River Basin, Lower Cedaz River Sub-basin. According to the Draft Proposed Lower Cedar River Basin and Nonpoint Pollution Action Plan, the site drains to the Orting Hills Sub-basin. T'he site is also located in the Newcastle Community Planning Area. Please refer to the appendix for appropriate maps. Critical Drainage Area Maps The site is not located in any of the critical drainage azeas discussed in the reference section of the 1990 King County Surface Water Desi�ManuaL Flood Plain/Floodway Map The site is not located 'm or near any floodplains as shown on the Flood Insurance Rate Map (see the FIRM map located in the appendix). Sensitive Areas Folio The Kin� County Sensitive Areas Folio and Wetlands Inventorv did not reveal the site to be in a critical area with regards to landslide, seismic, erosion, coal mine or wetland areas. Please refer to the appropriate maps in the appendix of this report. ging County Soil Survey According to the King County S.C.S. Soils Survey, the site is underlain with Alderwood soil belonging to the SCS type `C' hydrologic group. Please refer to the Soils Map located in the Appendix. LEVEL ONE DOWNSTREAM ANALYSIS FOR VJINWOOD-Page 3 Triad Associates Projax No.95-243 UPSTREAM DRAINAGE ANALYSIS The site is situated near the top of a ridge therefore there is little upstream area that is tributary to the site (refer to the IISGS Map and the Lower Cedar River Basin Map in the appendix). The upstream limit shown on the Upstream Map exhibit (see appendix) was taken from the Lower Cedar River Basin Map. Based on field observations, the actual upstream tnbutary azea boundary was found to extend offsite to the northeast. However, the Cedar River basin mapping boundary line was used for this Level 1 analysis to maintain continuity with the existing watershed data for this azea. The total azea tn�butary to a point located one-quarter mile downstream of the sfte is approximately 250 acres. Of the 250 acres of upstream basin, the site constitutes approximately 12%. DOWNSTREAM DRAINAGE ANALYSIS I _ Refer to the Downstream Map and Offsite Analysis Tables located in the appendix to aid in the following discussion. Based on existing topography, the site can be divided into three drainage sub-basins. As depicted on the Onsite Basin Map, located in the appendix, basin A and B sheet $ow to the west properiy line and continue downstream across neighboring properties. Runoff from basin C drains directly to the existing ditch located along the south property line. A detailed description of the draivage path for each basin is located on the pa.ges that follow. LEVEL ONE DOWNSTREAM ANALYSIS FOR WIIdWOOD-Page 4 Trrad Associates Projed No.95-243 Basin A Currently, runoff sheet flows southwesterly across Basin A where it is collected in an existing ditch located along the eastem edge of 150`� Ave SE. The ditch drains to a culvert (point A on the Downstream Map) where it then turns west. Runoff from the ditch continues westward until it reaches 148`� Ave SE, where ft then turns south (point B). From this point, runoff flows south to the intersection of 148`� Ave SE and SE 128�' Street (point C) where it is then conveyed west, underneath 148`� Ave SE, via an existing 24-inch diazneter culvert. Runoff then flows west, in a roadside ditch located on the north side of 128`� Ave SE, where it then enters a 24-inch diameter ; inlet to an existing detention pond (point D). The pond's outflow control structure (point E) directs pond outflow under SE 128`� Street via a 42" CMP which merges with runoff from Basins B and C at a catch basin on the south side of SE 128�' Street (point �. The combined runoff from all three onsite basins outfalls into an open channel (point G) and continues to flow south until it enters tnbutary 0307 (see Renton Quadrangle Map and Sub-basin Map located in the ' appendix). The exact path of the drainage course from Point G of the Downstream Map to Tnbutary 0307 of the Quadrangle map is not documented in any of the available reference material. However, field observations by Triad Associates and topographic maps of the area both advocate that drainage from the Windwood site is flowing into Tnbutary 0307. Basin B , C�rrently, runoff sheet flows southwesterly across Basin B and is collected by a series of onsite swales and small wetland areas. Based on field observation, the wetland azeas appear to drain to a seasonal swale that conveys runoff westward (refer to the Onsite Basin Map exhibit). It is apparent that runoff continues in a southwestern direction across neighboring properties where it is ultimately collected in the existing roadside ditch located along the north side of SE 128'� Street. This roadside ditch conveys runoff from onsite basins B and C. The ditch flows west, through a series of driveway culverts, before entering a 36-inch CMI' culvert at the intersection of LEVEL ONE DOWNSTREAM ANALYSIS FOR WW WOOD-Page 5 Triad Associates Projax No.95-243 148�'Ave SE and SE 128`� Street (point �. This culvert conveys runoff south, under SE 128`� Street, where it drains to a roadside ditch(point I). The ditch continues west, through a series of driveway culverts, and merges with drainage from onsite basin A at an existing catch basin (point F�. The combined runoff from all three onsite basins then continues south as mentioned in the previous downstream description for onsite basin A(see above). Basin C Runoff from Basin C sheet flows directly to the existing roadside ditch located on the north side of SE 128`� Street and leaves the site at point M. From here, runoff flows through a series of driveway culverts and combines with runofffrom onsite basin B. The combined runofffrom onsite basins B and C continue downstream as mentioned in the previous downstream description for onsite basin B (see above). SUMMARY The site contains three existing drainage subbasins, and a small upstream tributary area, all of which generate runoff that merges at a single point approximately 1700 feet downstream of the property's southwest comer. Adverse downstream capacity and erosion concerns were not evident at the time of this report. LEVEL ONE DOWNSTREAM ANALYSIS FOR WII�IWOOD-Page 6 Triad Associates Projed No.95-243 APPENDIX - .�. , t t. r�- i �' _� J .��I ,�► �/► - - . - _ - - ; •+' `1 �` hI _ _._ t _ .- - � - _ _-` ` _ .::... ... . { . /� � i a � � _ , \ � l OM�1 GM I \ k _ ,1 .�s.. � _�\.. - � / ' ' ��`� �� / J 1 . _.. . . •\� � � ' ' 1 � � _ 1 _ �'�� ! `` �, 0�'r �__ _ ' _ "rl� ` .� " - y- f� I � 11 '!� � � � � � ,J ^` �,��,�, _ `� � �7•� �H � \ •' (� � � // � ,' � w... \ , �f � �f �" . __ . - _ � _ o:� �` _ +'� - .i--- . 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'- ` � Reconnaissance � � E c �Zo ��: I o �6 z o `° - . � 2� � O iZ � . � � � � L � ,'^p 0 �.25�� c :I �� 163.80 16�.80 �3 � L N � � � � N N a� � l76I��c. 291.60 -------�i.s - � � Q'+ .n � � � � O . .n p� �5� . _-____-___-------- �63 i638a � • :' � - /4 MILE �� . . 1 � � , 1 �n � � N �n o.is _ s e.i� i, � c o ` .j -v ry�° .� a •� a �� D ,� � l �° POINT � °' ��=:I ° � � � D � �, ti - L 5o L �- izo � X. Hayes ' o o � o o � a " ii 9 • U N ;.b l e+ L o a� � ` � (I) Ov' 0.35AG. N :I: O S �C� ^' ❑�- N a - � � � o•zi�c. * � � � ' r � a O + ', I � � � � BAS11�1 C , I o ,� ,,, o r. ,} 0.41 A(.. � �� ❑ 0 0 w � Q O ' � U � :I: ( �--� ) 1j �C /8 Y 20 O i p �, ! � -:�v. EsMr. 35 0 . � ns � � I • - � ��J. ' �{ ♦ • • • ♦� _.� _ _ + • �- ��- _ � i�Q�-�! =J jo x - 2 '�-- � i°°s t -i s 3.ia_ , -�--- '. �-- ��-. _ _ _ - _- - - T:�- - _ -- - - �,_� ,� -- - - -- - = - - - =-- --- - __- �= -�x�--- T - --_---_ - - - - - T - - - - ----I 2 8 H� - - - - - - - - - - - - - - - - - � -S. - - _ - - - E. _ :i - _ _ E• 28T . H T. .....:.......::.. .. . . . . ....,.� .... ..•.....•..---• . ._ �..... ..: .::::... (F. MANIFOLD R�D.) � • l�l S O 1VI ��. � r�. ^�5 11'; 'i ;77.',7 145.07 150 248.14 BS .,. 300.29 O 1--1 • d- -e • �-- .3--- .�, � ; Sp , �� 40�.,. -- �, RENTON MlCL � r. First � T �� _ � �' � = K ° J o � a � N Sav.�aan v r � � �� . �O�� .I /�� J � �� a �1 � � ' �n „ �c �n ,n �9 Assn. � `" � 't' � � �^ 82.1 68,n °' I I � �: �' AG.Ralph S.Miller Q ��.. '`^ m O i�150.145 �^ � I r � y �,63/aC- '� " "' ^ ,�, � W � v� � , �� , Nels & Gladys Swanson � � ��y d l � ' - . I • , Q Q, ' , � :, 4� Q � i- . . 3 � a� . � � � � � � I A C � �, j Q �, Q :, 90 go � J�;,.G1 150 I5o �o � 3oo.oi ...� rp �n v � �� ,,., o �j Q ..... (601.15) (600.01) . � � � � ,r s �' S P 1075c 6oI.15 (600. I) v � �Zy ,� �--� �� r � , c � iD � �r - ,., � s $ I � '�"' �v �) : lol � gp � ,�A d, I. � � • E , o 90 8o i4 � , � I e� O u� � � 0 �TH•::•:•:•'•:•ST.•�•- •-'�'�' � ` � 3 � ,_s ^ Z aoo.ss N r N �T = . �z �z; iZo � �' �r °� � � iv ' a ,y C'd t I � i1 31 � W . U o Q � N 2 � o Q O . .,' ,�, � ' � �0 � � �� o I � 20 �8 - -- -- 72 72 72 �� I _ ,o � � v _ �284? - -- .. �s� 3a2 60i�5 °N' � C 'D (599.43) I � � I N `�' o �. � - -� " SCALE 1" = 200' � o ,� � i ,� _ � � � '^ o �, _o �; • - 240 _ a; o o g � � - I,�., I 2 � �+ o o�2� o � �,, cD � �' 6 - 5 d DO��VNSTREAM MAP - � io2 t� - �, �, c, � -� 300.7 a+ r' - F + � 2 SO .'�' � � � I ^ , � �� . n.. � -��1 OFF-SITE ANALYSIS DRAINAGE SYSTEM TABLE Surface Water Design Manual, Core Requirement#2 Basin: Cedar River Basin Subbasin Name: Lower Cedar River Subbasin Number: A Symbol Drainage Drainage Component Slope Distance Existing Patential Observations of field inspector Component Type Description from site Problems Problems resource reviewer� nr residertt Name, Size discharge Type:sheet,swale, consrtictiorts,undef capacity,pondirtg see map stream,channel,plpe, dra(nage basln,vegetatlon, % 1/4 mf=1320 ft overtopping,flooding,habltat or organlsm trlbutary area,likellhood of probfem, pond;Sfze:dfameter, cover,depth,type of senslflve destructlon,scouring,bank sloughing, avertlow pathways,poter�t�al lmpacts. surface at�a < area,volume sedlmentatlon,Inclslon,other eroslon A 12" CMP culvert depth of 1-2 feet 1 Site none none No problems observed B roadside ditch ditch w/2' of depth 2 620 none none No problems observed C 24" conc. culvert 24" conc. Culvert 1 1450 none none No problems observed Triad Associates OFF-SITE ANALYSIS DRAINAGE SYSTEM TABLE I e � Surface Water Design Manual, Core R quirement#2 Basin: Cedar River Basin Subbasin Name: Lower Cedar River Subbasin Number: B/C Symbol Drainage Drainage'Compnnent Slope D�stance Existing Potential Obs�rvations of field inspector Component Type Description from site Problems Problems resource reviewer, or resident Name, Size discharge Type:sheet,swafe, ` consrtictiorts,under capacity,ponding see map sNeam,chanrtel,plpe, dralnaga basin,vegetatlon, 96 1!4 mf=1320 ft overtopping;flooding,habltat or organlsm tdbutary area;likellhood oTproblem, 'I pond;Sfze'diameter, cover,depth,type of senslNve destroctlon,scouring,bank sloughfng, overilow pathways,potentiaf fmpacts. surface area area,voluma sedimentation,(nclsion,other eroslon M Sheet flow into grass-lined ditch, depth 6 Site none none No problems observed roadside ditch varies 1-2 feet N 18"concrete tightline drainage under 6 100 none none No problems observed culvert drivewa O 18" concrete tightline drainage under 6 425 none none No problems observed culvert drivewa H 36" concrete tightline drainage under 1 700 none none No problems observed culvert 128th St. SE to south I outfall into road- very shallow ditch, grass 1 800 none ponding No problems observed, potential side ditch lined ondin due to to o ra h J 18"CMP culvert depth of ditch increases 1 855 none none No problems observed atthis oint K 24" concrete tightline drainage to 1 1155 none none No problems observed culvert ditch downstream L roadside grass-lined 1 1320 none none No problems observed 1/4 mile ditch � T�iad Assoclates Section IV: DETENTION ANALYSIS AND DESIGN DESIGN CONSTRAINTS Storm runoff, for the site, is conveyed to a detention pond at the southeast corner of the property adjacent to the NE 128`h ST right of way. The pond is sized to KCRTS Level II standard matching storm frequency and durations for the following events: KCRTS Level II Standard Storm Event Matching Predeveloped Developed lh 2yr 2yr Syr Syr l0yr l0yr 25yr 25yr SOyr SOyr VOLUMETRIC SAFETY FACTORS After sizing the pond and control structure to match the frequency and durations for the KCRTS Level II standard, a ten percent safety factor has been added to the pond size without increasing the pond depth . An ADDTTIONAL Triad safety factor of ten percent has been added to account for errors in construction /grading of the pond. Therefore the total Volumetric Factor of Safetv is t«�enty percent. TECIINICAL INFORIIIATION REPORT FOR WINDVVOOD-PAGE 19 EXISTING CONDITIONS � � � Soil Type and Land Use Cover � Based on King County Soils Maps the site soil type is Alderwood which is classified as Till Soils for the KCRTS calculation. The northern area (2.24 Acres), which drains to the offsite wetland, will not be improved under this site plan, does not flow to the proposed pond and therefore will not be included in these calculations. The site has a mix of Forest, Grass and Impervious cover groups. These groups were identified using the site topography maps (in AutoCAD form), outlined with polylines and measured with CADD. See the "Existing Conditions Map" later in this section. The identified and measured areas are: Total Area= 31.1 Ac, "Till Soils", Sea-Tac Scale Factor= 1.0 Land Cover Type Forested = 23.2 Acres Grass = 7.1 Acres Impervious Area = 0.8 Acres (bldgs., pavement and driveways) Using the latest "King County Runoff Time Series Program" (version 4.25) and the areas listed above a predeveloped (PREDEV) time series was computed. The flow frequencies for this time series are: Predeveloped Flow Frequency Return Period Peak Flow (cfs) 100 yr 3.54 50 yr 3.08 25 yr 2.16 10 yr 2.02 5 yr 1.88 ' 3 yr 1.70 2 yr 1.12 'h-2yr 0.55 TECHNICAL INFORA�IATION REPORT FOR VI'IND�i`OOD-PAGE 20 The KCRTS Level II Standard requires the predeveloped '/z 2yr to the SOyr must be matched for frequency and duration with no more then a ten percent allowable excursion. DEVELOPED CONDITIONS Soil Type and Land Use Cover The plat proposes 109 lots on 24.6 Acres. This is 4.4 d«�elling units per gross acre (109/24.6). King County Runoff Curve Numbers (Table 3.5.2B, K.C.S.W.D. manual) translate this density into 46% Impervious. This percentage was used to compute impervious and pervious (54°Io) area for the plat, plus 1.1 Acres of additional impervious area from street improvements. See the "Developed Conditions Map" later in this section. The identified and measured areas are: Total Area = 29.1 Ac, "Till Soils", Sea-Tac Scale Factor = 1.0 Land Cover Type Forested = 0.0 Acres Grass = 16.7 Acres Impervious Area = 12.4 Acres (bldgs., pavement and driveways) I� Using the latest "King County Runoff Time Series Program" (version 4.25) and the areas , listed above a predeveloped (DEV)time series was computed. The flow frequencies for this time series are: Developed Flow Frequency Return Period Peak Flow (cfs) 100 yr 9.39 50 yr 8.08 25 yr 5.46 10 yr 4.93 5 yr 4.74 3 yr 4.50 2yr 4.16 TECHNICAL INFORMATION REPORT FOR VVINDWOOD-PAGE 21 The Developed Flows leaving the design detention pond are: Developed Flow Frequency Return Period Peak Flow (cfs) 50 yr 3.07 25 yr 2.13 10 yr 1.83 5 yr 1.62 3 yr 1.56 ' 2 yr 0.55 See the KCRTS calculations at the end of this section for the detailed frequency and duration analysis. TECHNICAL INFORMATION REPORT FOR �'�'IND��'OOD-PAGF,22 Biofiltration Swale Calculations: A biofiltration swale was sized according to Chapter 6.3 in the September 1998 Edition of the King County Surface Water Design Manual. Because the swale will be located downstream of the combination detention\wetpond which is providing Level 2 flow ' control and is located in till soils, the swale must be designed as a wet biofiltration swale. The wet biofiltration swale was sized for the full 2-year release rate (Identified in the September 1998 Edition as QWq) from the detention facility using the steps and equations below (Draft KCSWDM, Section 6.3.1.1): Step 1: Calculate Design Flow (See KCRTS output at the end of this section) QN,q = 0.55 cfs Step 2: Calculate swale bottom width b = w. nW /1.49 1 67S 5 s=0.01, 0.33, nW —0.20 �Q 9 9 y �, y= y— b =4.33' Step 3: Determine design flow velocity VWq = QWy/Awq; where AWy =by+Zy2; Z=3(3:1 side slopes) V Wy= 0.313 ftls < 1 fps OK Step 4: Calculate swale length L= 540Vwq L= 170 feet Step 5: Adjust swale layout to fit oia site. A�oP = (b� �- bslope� I-i where b; = bottom width, bsioPe= side slope width to design w.s., I.; = initial length A�op= (2+ 4.33) 170 = 1,076 L.f= Adjusted Swale length = 140' 140= 1,076/(X + 2); X = 5.68 = b��om recalculate VWq� lfps; L= 540V,vq Vwq = 140/540 =0.259 fps < 1 fps OK TECHNICAL INFORMATION REPORT FOR WINDWOOD—PAGE 23 Step 6: Pro��ide cu�ti�e��a�zcc cu��ucit��for flo�i�s 1�igher tlicrn Q,,.�j V�oo = Q�odA►oo< 5.0 fps; Aloo= bt�o«om*y�oo + Zside slopes�Y��>��, Ai�= 9.861 sf, Q��= 3.55 cfs V��= 0.36 fps < 5 fps The required dimensions for the biofiltration swale is 170 feet long by 4.33 feet wide (bottom width). The proposed design of the biofiltration swale is 5-feet 8-inches wide by 140 feet long and sloping longitudinally at 1%. Emer�ency Spillway Desi�n Use September 1998 KCSWDM Standards Qioo = 9.39 cfs (See KCRTS output at the end of this section) L= �Qioo/ (3.21 H'�`)] —?.4H Use H = 0.4 feet L = 109 feet, say 11 ft Windwood 95-243 Jim Morin,Revised:l2/OS/98 Page I of 7 Flow Frequency Analysis Predeveloped Time Series File:predev.tsf Project Location:Sea-Tac ---Annual Peak Flow Rates--- -----Flow Frequency Analysis----- Flow Rate Rank Time of Peak - - Peaks - - Rank Return Prob (CFS) (CFS) Period 2.16 2 2/09/Ol 15:00 3 .54 1 100.00 0.990 0.873 7 1/05/02 16:00 2.16 2 25.00 0 .960 2.02 3 2/28/03 3:00 2.02 3 10. 00 0 .900 0.333 8 8/26/04 2:00 1.88 4 5. 00 0.800 1.12 6 1/05/05 8:00 1.70 5 3 . 00 0.667 1. 88 4 1/18/06 16:00 1.12** 6 2 .00 0.500 1.70 5 11/24/06 4:00 0.873 7 1_30 0.231 3 . 54 1 1/09/08 6:00 0.333 8 1.10 0.091 Computed Peaks 3 .08 50.00 0.980 ** 1/z Q2 = 0. 50 * 1 .12 = 0. 55 CFS Developed Time Series File:dev.tsf Project Location:Sea-Tac ---Annual Peak Flow Rates--- -----Flow Frequency Analysis------- Flow Rate Rank Time of Peak - - Peaks - - Rank Return Prob (CFS) (CFS) Period 4.50 5 2/09/O1 2:00 9.39 1 100.00 0.990 3 .41 7 1/05/02 16:00 5.46 2 25. 00 0.960 5.46 2 2/27/03 7:00 4.93 3 10.00 0.900 3 .40 8 8/26/04 2:00 4.74 4 5.00 0.800 4.16 6 10/28/04 16:00 4.50 5 3 .00 0.667 4.74 4 1/18/06 16:00 4 .16 6 2 .00 0.500 4. 93 3 10/26/06 0:00 3.41 7 1.30 0.231 9.39 1 1/09/08 6:00 3.4Q 8 1.10 0 .091 Computed Peaks 8.08 50.00 0.980 Pond Outfall Time Series File:rdout.tsf Project Location:Sea-Tac ---Annual Peak Flow Rates--- -----Flow Frequency Analysis------- Flow Rate Rank Time of Peak - - Peaks - - Rank Return Prob {CFS) (CFS) (ft} Period 2.13 2 2/09/O1 20:00 3 .55 10.37 1 100.00 0.990 0.484 7 12/29/Ol 10:00 2.13 9.01 2 25.00 0.960 1.62 4 2/28/03 7:00 1.83 8.20 3 10.00 0.900 0 .385 8 8/26/04 7:00 1.62 7.69 4 5.00 0.800 0 . 545 6 1/06/05 15:00 1.55 7.55 5 3 .00 0.667 1. 55 5 1/18/06 23:00 0.545 6.46 6 2 .00 0.500 1.83 3 11/24/06 7:00 0.484 5.07 7 1.30 0.231 3 .55 1 1/09/08 10:00 0.385 3 .22 8 1.10 0. 091 Computed Peaks 3 .07 10. 31 50. 00 0 .980 Windwood 95-243 Jim Morin,Revised:l2/OS/98 Page 2 of 7 Retention/Detention Facility Type of Facility: Detention Pond Side Slope: 2 .00 H: 1V Pond Bottom Length: 242 .36 ft Pond Bottom Width: 70.36 ft Pond Bottom Area: 17053. sq. ft Top Area at 1 ft. FB: 33070. sq. ft 0.759 acres Effective Storage Depth: 10.20 ft Stage 0 Elevation: 489.50 ft Storage Volume: 243257 . cu. ft 5 .584 ac-ft Riser Head: 10.20 ft Riser Diameter: 18.00 inches Number of orifices: 2 Full Head Pipe Orifice # Height Diameter Discharge Diameter (ft) (in) (CFS) (in) 1 0 .00 2.81 0.685 2 6.50 5.88 1.800 8.0 Windwood 95-243 Jim Morin,Revised:12/05/98 Page 3 of 7 Stage Elevation Storage Discharge Percolation Surf Area (ft) {ft) (cu. ft> (ac-ft) (cfs) (cfs) (sq. ft) 0.00 489.50 0. 0.000 0.000 0.00 17053 . 0.03 489 .53 512. 0.012 0.037 0.00 17091. 0. 06 489 .56 1025. 0_024 0.052 0 .00 17128. 0.09 489.59 1540. 0.035 0.064 0.00 17166. 0.12 489.62 2055. 0.047 0.073 0.00 17203 . 0.15 489.65 2572. 0.059 0.082 0.00 17241. 0.18 489.68 3090. 0.071 0.090 0.00 17279. 0.21 489.71 3609. 0.083 0.097 0.00 17316. 0 .23 489.73 3955. 0.091 0.104 0.00 17342 . 0.41 489.91 7097. 0.163 0.137 0.00 17569 . 0.58 490.08 10102. 0.232 0.163 0.00 17784 . 0.75 490.25 13143. 0.302 0.186 0.00 18000. 0.93 490.43 16403. 0.377 0.207 0.00 18230. 1.10 490.60 19520. 0.448 0.225 0.00 18448. 1.27 490.77 22674. 0.521 0.242 0.00 18667 . 1.44 490 .94 25865. 0.594 0.258 0.00 18887 . 1.62 491 .12 29284. 0.672 0.273 0.00 19121_ 1.79 491.29 32552. 0.747 0.287 0.00 19343 . 1.96 491.46 35857. 0.823 0.301 0.00 19566. i 2.14 491.64 39397. 0.904 0.314 0.00 19803 . 2.31 491.81 42779. 0.982 0.326 0.00 20028. 2.48 491.98 46199. 1.061 0.338 0.00 20254. 2 .65 492 .15 49657. 1.140 0.350 0.00 20480. 2.83 492 .33 53360. 1.225 0.361 0.00 20721. 3 .00 492.50 56896. 1.306 0.372 0.00 20950. 3.17 492.67 60470. 1.388 0.382 0.00 21179. 3.35 492.85 64297. 1.476 0.393 0.00 21423 . 3 .52 493.02 67951. 1.560 0.403 0.00 21654 . 3 .69 493.19 71643. 1.645 0.412 0.00 21887 . 3 .86 493 .36 75373. 1.730 0.422 0.00 22120. 4.04 493 .54 79366_ 1.822 0.431 0.00 22368. 4.21 493 .71 83177. 1.909 0 .440 0.00 22603 . 4.38 493 .88 87027. 1.998 0.449 0.00 22839. 4.56 494.06 91146. 2 .092 0.458 0.00 23090. 4.73 494.23 95077. 2.183 0.467 0.00 23328. 4.90 494.40 99047. 2 .274 0.475 0.00 23567. 5.08 494.58 103294. 2 .371 0.484 0.00 23820. 5.25 494.75 107346. 2 .464 0.492 0.00 24061. 5.42 _ 494.92 111437. 2.558 0.500 0.00 24303 . 5 .59 495.09 115569. 2 .653 0.508 0.00 24545. 5 .77 495.27 119987. 2.755 0.515 0.00 24803 . 5 .94 495.44 124201. 2.851 0.523 0.00 25048. , 6.11 495.61 128455. 2 .949 0.531 0.00 25293 . 6.29 495.79 133004. 3 .053 0.538 0.00 25554. 6.46 495.96 137341. 3 .153 0.545 0.00 25801. 6.50 496.00 138368. 3 .176 0.547 0.00 25860. 6.56 496.06 139912. 3 .212 0.560 0.00 25947. 6.62 496.12 141461. 3 .247 0.593 0.00 26035. 6.68 496.18 143015. 3 .283 0.644 0.00 26123. 6.74 496.24 144574. 3.319 0.713 0.00 26211. 6.81 496.31 146400. 3 _361 0.796 0.00 26314. 6.87 496.37 147970. 3 .397 1. 130 0.00 26402 . 6. 93 496 .43 149545. 3 .433 1. 180 0.00 26490. 6. 99 496.49 151126. 3 .469 1.220 0.00 26578. 7.05 496 .55 152711. 3 .506 1.260 0.00 26667 . Windwood 95-243 Jim Morin,Revised:l2/OS/98 Page 4 of 7 7.22 496.72 157231. 3.610 1.370 0.00 26918 . 7.40 496.90 162062. 3 .720 1 .470 0.00 27186 . 7.57 497.07 166667. 3.826 1 .560 0.00 27439 . 7 .74 497.24 171314. 3 .933 1.640 0.00 27693 . 7.92 497.42 176279. 4.047 1.720 0.00 27964. 8.09 497.59 181011. 4.155 1.790 0.00 28220. 8.26 497 .76 185785. 4.265 1 .860 0.00 28477. 8.43 497.93 190600. 4.376 1.930 0.00 28735. 8.61 498.11 195745. 4.494 1.990 0.00 29009. 8.78 498.28 200647. 4.606 2.050 0.00 29269. 8.95 498.45 205592. 4.720 2.110 0.00 29530. • 9.13 498.63 210873. 4.841 2 .170 0.00 29807. 9.30 498.80 215905. 4.956 2 .220 0.00 30070. 9.47 498.97 220979. 5.073 2 .270 0.00 30334. 9.64 499.14 226096. 5.190 2 .330 0.00 30598. 9.82 499.32 231561. 5.316 2 .380 0.00 30880. 9.99 499.49 236767. 5.435 2 .430 0.00 31146. 10.16 499.66 242015. 5.556 2 .480 0.00 31414. 10.20 499.70 243257. 5.584 2.490 0.00 31477. 10.30 499.80 246370. 5.656 2 .980 0.00 31635 . 10.40 499.90 249499. 5.728 3.850 0.00 31793 . 10.50 500.00 252642. 5.800 4.970 0.00 31951. 10.60 500.10 255801. 5.872 6.290 0.00 32110. 10.70 500.20 258974. 5.945 7.790 0.00 32269. 10.80 500.30 262163. 6.018 9.240' 0.00 32429. 10.90 500.40 265367. 6.092 9.790 0.00 32589. 11.00 500.50 268586. 6.166 10.310 0.00 32749. , 11.10 500.60 271820. 6.240 10.800 0.00 32909. 11.20 500.70 275069. 6.315 11.260 0 .00 33070. 11.30 500 .80 278333. 6.390 11.700 0.00 33231. 11.40 500.90 281613. 6.465 12.120 0.00 33392 . 11.50 501.00 284908. 6.541 12.520 0.00 33554. 11.60 501 .10 288218. 6.617 12.910 0.00 33716. 11.70 501.20 291543. 6.693 13.290 0.00 33879. 11.80 501.30 294884. 6.770 13 .660 0.00 34041. 11.90 501.40 298240. 6.847 14.010 0.00 34204. 12 .00 501.50 301612. 6.924 14.360 0.00 34368. 12 .10 501 .60 304999. 7.002 14.690 0.00 34531. Windwood 95-243 Jim Morin,Revised:l2/OS/98 Page 5 of 7 Hyd Inflow Outflow Peak Storage Target Calc Stage Elev (Cu-Ft) (Ac-Ft) 1 9.39 ******* 3 .55 10.37 499.87 248406. 5.703 2 4.50 2 .16 2 .13 9.01 498.51 207490. 4.763 3 4 .45 ******* 1.83 8.20 497.70 184046. 4.225 4 5.46 ******* 1.62 7.69 497.19 169929. 3 .901 5 4.74 ******* 1.55 7.55 497.05 166169. 3 .815 6 2 .76 ******* 0.54 6.46 495.96 137243 . 3 .151 7 3 .41 ******* 0.48 5.07 494 .57 103176. 2 .369 8 3.40 ******* 0.39 3.23 492 .73 61644. 1 .415 ---------------------------------- Route Time Series through Facility Inflow Time Series File:dev.tsf Outflow Time Series File:rdout Inflow/Outflow Analysis Peak Inflow Discharge: 9.39 CFS at 6:00 on Jan 9 in Year 8 Peak Outflow Discharge: 3 .55 CFS at 10:00 on Jan 9 in Year 8 Peak Reservoir Stage: 10.37 Ft Peak Reservoir Elev: 499.87 Ft Peak Reservoir Storage: 248406. Cu-Ft . 5.703 Ac-Ft Flow Frequency Analysis Time Series File:rdout.tsf Project Location:Sea-Tac ---Annual Peak Flow Rates--- -----Flow Frequency �nalysis- Flow Rate Rank Time of Peak - - Peaks - - Rank Return Prob (CFS) (CFS) (ft) Period 2_13 2 2/09/01 20:00 3 .55 10.37 1 100.00 0.990 �---D�r��W M•Ml•5• 0.484 7 12/29/O1 10:00 2 .13 9.01 2 25.00 0.960 1.62 4 2/28/03 7:00 1.83 8 .20 3 10. 00 0.900 0.385 8 8/26/04 7:00 1.62 7 .69 4 5_00 0.800 0.545 6 1/06/05 15:00 1.55 7.55 5 3.00 0.667 1.55 5 1/18/06 23:00 0.545 6.46 6 2.00 0.500 1.83 3 11/24/06 7:00 0.484 5. 07 7 1.30 0.231 3 .55 1 1/09/08 10:00 0.385 3 .22 8 1.10 0.091 Computed Peaks 3 .07 10 .31 50. 00 0 .980��S11.N �1'1.W•S �8�.50 + ►b•31z 4�1q -8l (�9G-swu� d c�`1.5�t 10 •31 � ��°�•$'1 �UKr�lo�.i, ZS�r I�wS= q��i.�+`�°�" �lqg'`�'� ' Windwood 95-243 Jim Morin,Revised:l2/OS/98 Page 6 of 7 Flow Duration from Time Series File:rdout.tsf Cutoff Count Frequency CDF Exceedence_Probability CFS $ $ $ 0.030 39449 64.333 64.333 35.667 0.357E+00 0.090 5218 8 .509 72.842 27.158 0.272E+00 0.150 4505 7.347 80.189 19.811 0.198E+00 0.210 3795 6.189 86.378 13 .622 0 .136E+00 0.269 2992 4.879 91.257 8.743 0.874E-01 0.329 2015 3 .286 94.543 5.457 0.546E-01 0.389 1252 2 .042 96.585 3.415 0.341E-01 0.448 873 1.424 98.009 1.991 0.199E-01 0.508 539 0.879 98.888 1.112 0.111E-01 0.568 456 0.744 99.631 0.369 0.369E-02 0.628 39 0.064 99.695 0.305 0.305E-02 0.687 18 0.029 99.724 0.276 0.276E-02 0.747 28 0.046 99.770 0.230 0.230E-02 0.807 12 0.020 99.790 0.210 0.210E-02 0.867 6 0.010 99.799 0.201 0.201E-02 0.926 1 0.002 99 .801 0.199 0. 199E-02 0.986 0 0.000 99.801 0.199 0_199E-02 1.05 3 0.005 99.806 0.194 0 .194E-02 1.11 2 0.003 99.809 0.191 0 .191E-02 1.17 4 0.007 99.816 0.184 0 .184E-02 1.23 6 0 .010 99.826 0.174 0.174E-02 1.28 9 0.015 99.840 0.160 0.160E-02 1.34 11 0.018 99.858 0.142 0.142E-02 1.40 13 0.021 99.879 0.121 0.121E-02 1.46 11 0.018 99.897 0.103 0.103E-02 ' 1.52 11 0.018 99.915 0.085 0.848E-03 1.58 12 0.020 99.935 0.065 0.652E-03 1.64 9 0.015 99.949 0.051 0.506E-03 1.70 4 0.007 99.956 0.044 0.440E-03 1.76 4 0.007 99.962 0. 038 0.375E-03 1.82 6 0.010 99.972 0.028 0.277E-03 1.88 4 0.007 99.979 0.021 0.212E-03 1.94 2 0.003 99.982 0.018 0.179E-03 2.00 2 0.003 99.985 0.015 0.147E-03 2.06 4 0.007 99.992 0.008 0.815E-04 2.12 4 0.007 99.998 0.002 0.163E-04 ---------------------------------- Route Time Series through Facility Inflow Time Series File:dev.tsf Outflow Time Series File:rdout Inflow/Outflow Analysis Peak Inflow Discharge: 9.39 CFS at 6:00 on Jan 9 in Year 8 Peak Outflow Discharge: 3.55 CFS at 10:00 on Jan 9 in Year 8 Peak Reservoir Stage: 10.37 Ft Peak Reservoir Elev: 499.87 Ft Peak Reservoir Storage: 248406. Cu-Ft . 5.703 Ac-Ft Flow Frequency Analysis Time Series File:rdout.tsf Project Location:Sea-Tac Windwood 95-243 Jim Morin,Revised:l2/OS/98 Page 7 of 7 Duration Comparison Anaylsis Base File: predev.tsf New File: rdout.tsf Cutoff Units: Discharge in CFS -----Fraction of Time----- ---------Check of Tolerance------- Cutoff Base New $Change Probability Base New $Change 0.549 � 0.77E-02 0.40E-02 -47.6 � 0.77E-02 0.549 0.530 -3 .6 0.616 � 0.64E-02 0.32E-02 -50.9 � 0.64E-02 0.616 0.536 -13 .1 0.683 � 0.56E-02 0.28E-02 -50.6 � 0.56E-02 0.683 0.538 -21.2 '�, 0.750 � 0.48E-02 0.23E-02 -52.7 � 0.48E-02 0.750 0.541 -28.0 0.818 � 0.42E-02 0.21E-02 -50 .8 � 0.42E-02 0.818 0.545 -33 .4 0.885 � 0.37E-02 0.20E-02 -46 .5 � 0.37E-02 0.885 0.564 -36.3 0.952 � 0.30E-02 0.20E-02 -33 .7 � 0.30E-02 0.952 0.643 -32 .5 1.02 � 0.26E-02 0.20E-02 -24.5 � 0.26E-02 1.02 0.711 -30.2 1.09 � 0.23E-02 0.19E-02 -15.1 � 0.23E-02 1.09 0.753 -30.7 ' 1 .15 � 0.19E-02 0.19E-02 0.9 � 0.19E-02 1 .15 1.16 0 .5 1 .22 � 0.15E-02 0.18E-02 16.1 � 0.15E-02 1.22 1.32 8.2 1 .29 � 0.13E-02 0.16E-02 27 .3 � 0.13E-02 1.29 1.39 7.8 1 .35 � 0.11E-02 0.14E-02 30.8 � 0 .11E-02 1.35 1.46 7_7 1 .42 � 0.91E-03 0.12E-02 26.8 � 0.91E-03 1.42 1.50 5.5 1 .49 � 0.72E-03 0.95E-03 31.8 � 0.72E-03 1.49 1.55 4.4 1. 56 � 0.59E-03 0.68E-03 16.7 � 0.59E-03 1.56 1.60 2.6 1. 62 � 0.52E-03 0.52E-03 0.0 � 0.52E-03 1.62 1.64 0.8 1. 69 � 0.42E-03 0.46E-03 7.7 � 0.42E-03 1.69 1.72 2.0 1.76 � 0.26E-03 0.38E-03 43 .8 � 0.26E-03 1.76 1.83 4.3 1.82 � 0.18E-03 0.28E-03 54.5 � 0.18E-03 1.82 1.95 6.7 1.89 � 0.15E-03 0.20E-03 33.3 � 0.15E-03 1.89 2.01 6.4 1.96 � 0.13E-03 0.16E-03 25 .0 � 0.13E-03 1.96 2.01 2.9 2 .03 � 0.65E-04 0.11E-03 75.0 � 0.65E-04 2.03 2.08 2 .7 2 .09 � 0.49E-04 0.49E-04 0.0 � 0.49E-04 2.09 2.11 0.8 2 .16 � 0.33E-04 O.00E+00 -100.0 � 0.33E-04 2 .16 2.12 -1.9 Maximum positive excursion = 0.117 cfs ( 9.3°0) occuring at 1.26 cfs on the Base Data:predev.tsf and at 1.38 cfs on the New Data:rdout.tsf Maximum negative excursion = 0.320 cfs (-36.3$) occuring at 0.880 cfs on the Base Data:predev.tsf and at 0. 560 cfs on the New Data:rdout.tsf r��;,�ut.dur + -�-_� � � -- o � r.j =}; ••� --�,i- � :•� �; + � � r � t + � � � � + F,� �T t � �: � � + Q' �t. �� oo �`---� � -� U O -'t-�_ � '�'- � '_�- +� +_ �J --.# � Frobabilit� Exc�edence �`+ G �. 10-3 14�� 1 ��-a 10-z 1 �-' 1 — Return P�riod � z � io zo �a 1oa � � "' + r�-:�:_��._a t.F`:.�-�:_�; i r� ~,��:_;—T:7 r. � _ � ¢ � � � � � + + � 0 � II m � R I �.L tp ,� �ry } O Q I, + I dJ � I Q� �- � � � M� � � � � � I� 1 � � I F� 20 �.i 44 �rG 64 ?� 80 �Q �5 �� 9� Cumuloti�re Frabobilit}r ST 1.0/ ST 1.1 - -- ST 1.0 LA 0.8 LA 0.9 LA 1.0 LA 1.2 u MiaH couMrr �' • 1 �I 11EfT� OTM� J` OKINO COUNTY : .. � '�•' •' ^� . .- . �f r �jh ,... � : �N � �;� -- `_ �,-J �-- . f '� _ �. � v 1 ;� .� s t . 4` - � � �-Y I _ .+:� � l�,'L d^.- `�' , � �(W I.'� � ��Vel �S f i < f !� • r��-.��`� �� e r�- ` x ! 1 � � ' F �1 4 �� i, �EOY D , , S ,` _, . :,F r � q J -�� 1 � ;�� . �� AE OND fl, _ � '' - /,=7 �� —� f l� � �J�� 1 � - + ;�� _ '7 �3. - j I rr Q �; 'i �� ;--� ,� _ .�, N _ . :a',�f ti t�r� � ,r ; ��` " =� � _ . , . �---r.. . .f .�wtt � 6 g� \�"'� AT7t � coikc-� ._ .:_,� ♦ � � � �� - �E�LE �E �� _8a7 t�: 1" � . 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Regional Scale Factors �A o.9 — LA 1.0 LA 1.2 .._=i Incorporated Area � River/Lake Major Road q�2-4 c�/��v �D �Z ��_ �2 (,c,,�v�� 2c,�4�� /�� `'C �' (.oc.J FCow l. � I gg<gg �� . � �� e � HI�(' �� Otl �1 �vW�y,> �� W:.� �'�,53,ca �R8�8�' I 1��t��►v �2.�v�- Q =�G)��s �� J-� �� • � �:...:f � : F� q�o° a�e�c�-1 c� = 2, �-3 S I I-E ,�'� � 0 2 �� = 2�-38 ) �� L C � C � ; D,vo4� c r-s Of�� Z. � �r 0�U vi �//�� o F wC-�2 i t-�-t.G-� Ftow ��_� c cx,�vc�w�r 1-, 2"•H.�yc. hc.�ow�c� }.� F�va s r-�uc/}- c� _ �i.3 3 �L. — o�2�) �}- �'s Q af� L-_ = o,Z F-} -� (3.3�) N �.s � / Z �- - - - - --- �� c�� rrC� Q,� Gch,�t'c�✓D /N�C.ow F�'kr� �2ooF F �;o�-✓) �4,4.i� ��-�1� �,� _ �.D c� �ih,��x,) ��Q�� ««« �yH�ao ¢�`�� L = 0� Z �L -� < <o-D v woo � J /,s �Www;> �� }��L� �N�� i ��a�a�< �R�� ":...:� � � �.,45� c�J 2'� /i-L�owi4-�}K: (-� � _ �_� /� , ( ,v-� L = d, Z (� z�) `f— ► �� C 3.r 3�(� z_) _ � Z �5 0 ' @ r '' �c.c.o w.4-�.c-c �-� U S L I 2�S � LI.�vG�� i i BioSwale Input Output Q (cfs) 0.00 0.55 n 0.200 0.200 B (ft) 4.33 4.33 Trap. LSSlope 3.00 3.00 RSSlope 3.00 3.00 y (ft) 0.33 0.33 S (ft/ft) 0.010 0.010 L (ft) 200.000 200.000 t(min) 0.000 10.645 A(sfl 1.757 Pw(ft) 6.421 V (ftls) 0.313 R (ft) 0.274 Job: Windwood Description: Design By: Geoff Tamble Date: 12/16/98 I I I,. .. ,\ � -. , Page 1 BioSwale Input Output Q(cfs) 0.00 0.55 � n 0.200 0.200 B (ft) 5.68 5.68 Trap. , � LSSlope 3.00 3.00 '� RSSlope 3.00 3.00 y(ft) 0.29 0.29 S (ft/ft) 0.010 0.010 L(ft) 140.000 140.000 t(min) 0.000 7.925 A(s fl 1.868 Pw (ft) 7.487 V (ftls) 0.294 R(ft) 0.249 Job: Windwood Description: Design Velociry Check By: Geoff Tamble Date: 12/16/98 Page 1 , BioSwale � Input Output Q (cfs) 0.00 3.55 ! n 0.350 0.350 B (ft) 5.68 5.68 Trap. LSSlope 3.00 3.00 RSSlope 3.00 3.00 y(ft) 1.10 1.10 S (ft/ft) 0.010 0.010 � j L(ft) 140.000 140.000 � t(min) 0.000 6.481 A(sf) 9.861 Pw(ft) 12.628 V(ftJs) 0.360 R (ft) 0.781 Job: Windwood Description: 100-yr capacity By: Geoff Tamble Date: 12l16/98 Page 1 � x1et.61 � � %t61.2d \ - 1.., c \ \ � j / l � 161.]] � . / � � i37.39 :...� / _ \ \ � x \/� t " I � x - � V t � � ,-`-.-� E ---- t : � �� ---'--�� :..j : � � � � � t E ,e,.�o � tAAD ApppAT6e 1 , i.....,..1 � / � // � ■ " " X�s�.3s\ r�.t� � 6, PLA T � � � �� ix« J \ rr r 1r.r� _x......__ L ` �e � ' r�r�ra�. --�-----�"___-` -......_ \ \ % x'El.'7 i,♦ ---`,_ ".�....:�:.r;.,�....; � � � � BaGL�DARY _� t�LL f��a t �L�N M YJ1� t�Y� 1 ` ```t"-----' �os 1 \ � 7.3 A C ieves � / f�r AM �war�.� ` � 1 \ f x,6,�� x / \ x 3.32 �� \\ \ xi61.27 �� __� � x1511�` � ` �\ I1 �\ � / - � � x160.51 L...: x � � � isen � � � x �� t � .`....___..._.....�_......_�......._. ....... ....._. � �..._ ......„_.. � F��' � 3 ' ' �� \ I I \� ``--- � -- 1 / � ,�., ,�.5, � " I \ ✓ 1 x I S].S! 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' •159.@� \ ISfl13 � � / '"""' / _"' _' ".. � �: i __ 1 `� i • • 1 ; � : \ \ ' x � � -�:. _....1...._., %. \; � �� . � • x l --- - . . ._.... ; �_ '= �' , � �-�u;�, \ ( 1 _ : . : . 1 � \ : f �`� � � � ` � : ; ..w� � - ) ;; � �E� � � l:l t ' 1 .( .; �� }¢4,� � � _ . ;.._ . � • f... . . • . / :� �� x. \ � � ;� . � � , � � ,, .....:� � � „ t �� X,�., __ �'� .. .... � \ \ � \-�=_. °t_-, � :\ � ° , � � � \ s..� -�'��_`. � � ��-=..._: ( `t__.-.-° � 39.18 \ F i i\ 1 \ \ � � r ` � \ \ x 159.a, 'S9.)9 � ..: I :_. \ � � � \ , .� 4 € . , , ,3z� � .� x,�.3 � _:� � : ::l l...:- t I . _� ,:;- �� \ �:. '�� -j� �� : '-� i x, �.� � �� I �� _-__� _____- .... --��' � � .'' �... , , . � � : , , . 5 ..... � i � ;.' ' (' � � PROpQS�j/\/''� \ � x x \ ^ ' ----�.. ` x � � � � �\j,�-.�_. / � \ \1 "r':( - /�I \( \ \\ `�'�\1 \ `t \ r �R( . \�/YLJ\ \ 7'9}5 155.69 J I .... I� / �� j'_'" 1 . �,..... ' � ' , ` ' '____ _ -..16).1� . i ` � • �i � __ \ i , ' �'� . �. i i \ �I _ �+�– I I '�� \ \ l \ � � 'S955 _"__'�� ..... �._ ( _ � � \ ;� � �1 \ ,�� , � � 1� � � � _ �� . �.. - : : : _ x _ 7 �- - _�—�— — — _ — a � -- -- � .'U I � I � `��j `_'..;' i i ,-�- � �!'=' — �. � ` _ ��/ � � av w m . : ;......_...�.. ...; ` - . SE 128 TH S T � I """� ��2� 4 43,500 SF: �� ' ' �� Section V: CONVEYANCE SYSTEMS ANALYSIS AND DESIGN The on-site storm drainage system was designed, in accordance with the 1990 King County Surface Water Design Manual (KCSWDM), to provide at least 0.5 ft of freeboard at each catch basin in the system for the 25-year storm event. The system was then checked with the 100-year storm event, and no overtopping occurred. The King County Backwater Analysis Program (version 4.22) was used to design the conveyance system for the project site. Please reference the Appendix for the actual program output. The rational method was used to determine the peak flows from the area tributary to the pipe system, please refer to the Pipe Sizing Map located in this Section. The King County Precipitation values for this area are as follows: PR= 3.40 in 25yr event PR= 3.90 in 100yr event For analysis purposes the pipe system was divided into three different models. The main system, called WW1, starts at the detention pond (outfall 69A) and includes CB's 69, 65, and 66 up to CB 8, 38, 39 to CB 49. WW2 starts at CB 65 and goes to CB 64, 62, 60 up to CB 34. WW3 starts at CB 8 and goes to CB 8A, 9, 10 up to CB 24. '� The WW1 model was run using tailwater elevations, in the detention pond, for the 25 and 100 year events (see KCRTS, Flow Frequency Analysis at the end of Section IV, page 5 of 7). The resultant water surface elevations for the design storms in CB 65 and CB 8 where used as tailwater elevations for the WW2 and WW3 models respectively. TI�:('lll�[(',�L I\FOR!��1;�"flOv K[?POR'1' F(lK 11'I�[)11`OOI) - Y;�GI? 2: DEVELOPED RUNOFF (RATIONAL METHOD) Onsite Conveyance Sizing Wei�hted "C" Total area to be conveyed by the pipe system = 20.87 Acres. In the developed condition 46°Io (9.60 Ac) will be impervious (C =0.90) and 54% (11.27 Ac) will be grass (C = 0.25). The resultant, combined, weighted "C" is found to be: [9.60(0.90) + 11.27 (0.25) ] / 20.87 =0.60 Developed Runoff Q = CIRA IR= PR 1R l bR 1R = aR \ TC� aR = 2.66, bR =0.65 (25yr event) aR = 2.61, bR = 0.63 (100yr event) W W 1 Model: Tc = 20.9 min. A = 20.9 Acres C = 0.60 IR = 3.4 ( 2.66 (20.9)-0 6') = 1.254 QZS = 0.60(1.254)20.9 = 15.7 cfs IR = 39 (�.63 (20.9)-0.63) = 1.511 Q,�� = 0.60 (1.511)20.9 = 18.8 cfs WW2 Model: Tc = 12.9 min. A = 5.1 Acres C = 0.60 IR = 3.4 ( 2.66 (12.9)�obs) = 1.716 Q�5 = 0.60(1.716)5.1 = 5.2 cfs IR = 3.9 (2.63 (12.9)-o.6s) = 2.048 Q,��, = 0.60 (2.048)5.1 = 6.2 cfs TECHNIC:�L INFORI�IATION REPORT FOR �VIND�VOOD-PAGE 26 WW3 Model: Tc = 15.8 min. A = 7.4 Acres C = 0.60 IR = 3.4 ( 2.66 (15.8)-0.65) = 1.504 Q25 = 0.60(1.504)7.4 = 6.6 cfs IR = 3.9 (2.63 (15.8)-0.63) = 1.802 Qioo = 0.60 (1.802)7.4 = 7.9 cfs Summary of Flows Used in Pipe Sizing model 25 year Event (cfs) 100 year event (cfs) WW1 15.7 18.8 WW2 5.2 6.2 WW3 6.6 7.9 WW4 - 9.9 ratios The Q ratio was calculated at each pipe junction based solely on areas. The CI (Q=CIA) , for each catchment was assumed to be constant. The Q ratio becomes the ratio of new ' area contributing flow divided by the total up stream area at the catch basin. The I� following three pages summarizes the Q ratio calculations at each catch basin. Final Pipe Sizing The final pipe sizes selected for each pipe run was determined by 1) maintaining 0.5' of free water surface freeboard at each catch basin for the 25 year event and 2) keeping the catch basin grates below the free water surface (as much as practical)for the 100 year storm. With the exception of CB 37 which overtops by 0.05' far the 100 year event, all catch basins are confirmed to work with the pipe sizes / slopes shown on the plan. TECHNICAL IVFORh1ATI01\' REPORT FOR �i'IND�i�00D-PAGE 27 Pipe Run (Model): WW1 Junction Drainage Area Cumlative Area Added (�-Ratio Comments CB# to CB only Area Above CB at Junction (ac) (ac) (ac) 49 0.99 0.00 0.99 0.00 47 0.92 0.99 0.92 0.93 31 0.12 1.91 0.12 0.06 45 028 1.91 0.28 0.15 43 1.10 2.19 1.10 0.50 41 1.10 3.29 1.10 0.33 39 0.52 4.39 0.52 0.12 38 021 4.91 0.21 0.04 37 0.30 5.12 0.30 0.06 8 7.36 5.42 7.36 1.36 WW3 joins WW1 7 0.20 12.78 0.20 0.02 6 0.37 12.98 0.37 0.03 5 0.60 13.35 0.60 0.04 3 0.40 13.95 0.40 0.03 68 0.30 14.35 0.30 0.02 66 0.60 14.65 0.60 0.04 65 5.10 1525 5.10 0.33 WW2 joins WW1 69 0.30 20.35 0.30 0.01 20.77 Pipe Run (Model): WW2 Junction Drainage Area Cumlative Area Added Gl-Ratio Comments CB# to CB only Area Above CB at Junction (ac) (ac) (ac) 34 0.95 0.00 0.95 0.00 59 0.25 0.95 0.25 0.26 58 0.10 1.20 0.10 0.08 56 1.10 1.91 1.10 0.58 54 1.20 2.19 1.20 0.55 53 0.35 3.29 0.35 0.11 60 0.45 4.39 0.45 0.10 62 0.40 4.91 0.40 0.08 64 0.30 5.12 0.30 0.06 Joins VWV1 5.10 Pipe Run (Model): WW3 Junction Drainage Area Cumlative Area Added Q-Ratio Comments CB# to CB only Area Above CB at Junction (ac) (ac) (ac) 24 0.44 0.00 0.44 0.00 23 0.10 0.44 0.10 0.23 22 0.30 0.54 0.30 0.56 21 0.50 0.84 0.50 0.60 20 0.33 1.34 0.33 0.25 18 0.90 1.67 0.90 0.54 16 0.80 2.57 0.80 0.31 15 1.01 3.37 1.01 0.30 13 0.33 4.38 0.33 0.08 11 1.10 4.71 1.10 0.23 9 0.80 5.81 0.80 0.14 8a 0.75 6.61 0.75 0.11 Joins WW1 I� 7.36 I The overtopping of CB 37 by 0.05' is considered acceptable since the next CB downstream ( CB 7 ) has an additional 0.75 ` of freeboard. The sheet flow across the intersection from CB 37 will have acceptable depth and will no interfere with traffic flow. FREEBOARD TABLE 25-yr and 100-yr Catch Basin Rim Elev. HGL Elev. Freeboard HGL Elev. Freeboard (ft) 25-yr(ft) 25-yr(ft) 100-yr(ft) 100-yr(ft) 3 504.30 501.47 2.83 503.55 0.75 5 504.86 501.83 3.03 503.95 0.91 6 505.86 502.44 3.42 504.63 1.23 7 505.86 502.79 3.07 505.11 0.75 8 506.57 502.99 3.58 504.40 2.17 8A 507.26 50438 2.88 505.96 1.30 9 508.86 505.87 2.99 506.75 2.11 11 510.79 507.47 3.32 509.08 1.71 13 S 15.51 511.57 3.94 513.01 2.50 15 517.78 512.85 4.93 �14.84 2.94 16 517.50 513.50 4.00 515.65 1.85 18 521.24 518.43 2.81 518.56 2.68 20 526.10 523.04 3.06 523.12 2.98 21 526.10 523.27 2.83 523.35 2.75 22 528.64 525.40 3.24 525.46 3.18 23 528.78 525.64 3.14 525.68 3.10 24 529.83 525.88 3.95 525.88 3.95 31 524.92 520.71 4.21 520.79 4.13 34 528.01 525.11 2.90 525.18 2.83 37 506.12 503.66 2.46 506.17 +0.05 38 513.53 510.39 3.14 510.85 2.68 39 512.60 511.22 1.38 512.07 0.53 41 515.50 512.99 2.51 514.00 1.50 43 520.24 517.49 2.75 517.64 2.60 45 52323 52022 3.01 520.30 2.93 47 524.10 521.31 1.79 521.40 2.70 TECHNICAL INFORM:�T[ON REPORT FOR �VIND�i'OOD- PAGE 28 49 526.39 523.37 3.02 523.43 2.96 53 519.81 517.71 2.10 518.50 1.31 Catch Rim Elev. HGL Elev. Freeboard HGL Elev. Freeboard Basin (ft) 25-yr(ft) 25-yr(ft) 100-yr(ft) 100-yr(ft) 54 521.91 519.60 2.31 521.15 0.76 56 524.31 521.54 2.77 522.51 1.80 58 526.31 523.25 3.06 523.38 2.93 59 526.31 523.55 2.76 523.65 2.66 60 516.60 S 14.43 2.17 514.82 1.78 62 513.97 510.93 3.04 511.18 2.79 64 512.64 509.40 3.24 509.60 3.04 65 512.64 500.25 12.39 501.84 11.80 66 507.80 �00.76 7.04 502.60 SZO 68 505.19 501.10 4.09 503.09 2.10 69 512.00 499.19 12.81 500.40 11.60 TECHNICAL INFORMATION REPORT FOR WINDWOOD-PAGE 29 Offsite Conveyance Capacity Check The offsite conveyance system (Proposed Bioswale to the existing ditch along the north side of SE 128`h ST) must have the capacity to convey the 100 year release rate from the detention pond ( 9.39.cfs ) with a minimum of 6" of freeboard. The pipe system was modeled (WW4) with the pipe sizes and inverts from the plans and assuming the ditch outfall along 128`h st has a maximum water surface of 478.00 feet. This represents the ditch flowing 2 feet deep and is assumed to be conservative. The conveyance system, as designed, is adequate to convey this flow. The freeboard at the bioswale will be 0.75 ft. FREEBOARD TABLE 100-yr Catch Basin Rim Elev. HGL Ele�. Freeboard (ft) 100-yr(ft) 100-yr(ft) 77 485.09 483.76 1.33 76 491.50 489.55 1.95 76a 492.00 490.48 1.52 Bioswale 492.00 491.25 0.75 TECHNICAL INFORMATION REPORT FOR«'IND�VOOD—PAGE 30 Offsite Capacity Analysis BACKWATER COMPUTER PROGRAM FOR PIPES Pipe data from file:d:\ww4.bwp Surcharge condition at intermediate junctions Tailwater Elevation:478. feet Discharge Range:9.39 to 9 .39 Step of 0.1 [cfs] Overflow Elevation:492. feet ' Weir:NONE Upstream Velocity:0. feet/sec CB 77 . 131 LF - 18"CP @ 4.27� OLTPLET: 476.50 INLET: 482 .09 INTYP: 5 JUNC NO. 1: OVERFLOW-EL: 485.09 BEND: 1 DEG DIA/WIDTH: 2 .0 Q-RATIO: 0.00 Q(CFS) HW(FT) HVJ ELEV. * N-FAC DC DN TW DO DE HWO HWI *****************************************,r***********************+r*******,r***** 9 .39 1.67 483 .76 * 0.012 1.19 0.66 1.50 1.50 1. 19 ***** 1.67 CB 76 . 133 LF - 18"CP @ 4.35$ OUTLET: 482.09 INLET: 487.88 INTYP: 5 JLTNC N0. 2: OVERFLOW-EL: 491.50 BEND: 1 DEG DIA/WIDTH: 2 .0 Q-RATIO: 0.00 Q(CFS} HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI ******************************************************************************* 9.39 1.67 489.55 * 0.012 1.19 0.66 1.67 1.67 1. 19 ***** 1.67 CB 76A . 20 LF - 18"CP @ 0.60� OUTLET: 487 .88 INLET: 488.00 INTYP: 5 JUNC NO. 3: OVERFLOW-EL: 492.00 BEND: 90 DEG DIA/WIDTH: 4.0 Q-RATIO: 0.00 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI ******************************************************************************* 9.39 2 .48 490.48 * 0.012 1.19 1.35 1.67 1.67 1.68 2 .48 2 .26 Bioswale . 16 LF - 18"CP @ 0.63� OUTLET: 488.00 INLET: 488.10 INTYP: 5 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HVJI ********************,r********************************************************** 9.39 3 .15 491.25 * 0.012 1.19 1.30 2.48 2.48 2 .49 3 .15 2.12 ' Mws = 491.25, top of swale =492.00, freeboard = 0.75 ft, OK TECHNICAL INFORMATION REPORT FOR WINDWOOD-PAGE 31 Time of Concentration Detailed Calculation DEVELOPED TIME OF CONCENTRATION --------------------------------------------------------------------- --------------------------------------------------------------------- BASIN SUMMARY BASIN ID: WW1 NAME: DEV. TOC SBUH METHODOLOGY TIME OF CONC. . . . . : 20.9 min ' TcReach - Sheet L: 215.00 ns:0.0500 p2yr: 2.00 s:0.0200 TcReach - Channel L: 515.00 kc:42.30 s:0.0080 TcReach - Channel L: 625.00 kc:42.30 s:0.0220 TcReach - Channel L: 790.00 kc:42.30 s:0.0050 BASIN ID: WW2 NAME: temp to determine tc SBUH METHODOLOGY I TIME OF CONC_ . . . . : 12.9 min TcReach - Sheet L: 200.00 ns:0.0500 p2yr: 2.00 s:0.0200 TcReach - Channel L: 670.00 kc:42.30 s:0.0120 TcReach - Channel L: 430.00 kc:42.30 s:0.0120 BASIN ID: WW3 NAME: temp to determine tc SBUH METHODOLOGY TIME OF CONC. . . . . : 15.8 min TcReach - Sheet L: 170.00 ns:0.0500 p2yr: 2.00 s:0.0100 TcReach - Channel L: 270.00 kc:42.30 s:0.0050 TcReach - Channel L: 500.00 kc:42.30 s:0.0220 TcReach - Chanael L: 650.00 kc:42.30 s:0.0100 TECHNICAL INFORMATION REPORT FOR WINDWOOD-PAGE 32 WW1 BACKWATER COMPUTER PROGRAM FOR PIPES, 25 Year event Pipe data from file:d:\wwl.bwp Surcharge condition at intermediate junctions Tailwater Elevation:498.51 feet Discharge Range:15.7 to 15.7 Step of 0 . 1 [cfs] Overflow Elevation:536.39 feet Weir:NONE Upstream Velocity:0. feet/sec CB 69 . 36 LF - 24"CP @ 0. 64$ OUTLET: 497 . 00 INLET: 497 .23 INTYP: 5 JUNC N0. 1: OVERFLOW-EL: 512.00 BEND: 1 DEG DIA/WIDTH: 4.5 Q-RATIO: 0.01 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI **************************,r**********,r**********************************,r****** 15.70 1.96 499.19 * 0 .012 1 .43 1.36 1. 51 1 .51 1 .43 ***** 1 . 96 CB 65 . 91 LF - 24"CP @ 0.64� OUTLET: 497 .23 INLET: 49; .81 INTYP: 5 JUNC NO. 2 : OVERFLOW-EL: 512.54 BEND: 80 DEG DIA/WIDTH: 4.0 Q-RATIO: 0 .33 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI ***********,r****************************************************,r************** 15.54 2 .44 500.25 * 0.012 1 .43 1.35 1.96 1 . 96 1. 61 2 .44 2 .38 CB 66 . 170 LF - 24"CP @ 0. 50$ OUTLET: 497 .81 INLET: 498 .66 INTYP: 5 JUNC NO. 3: OVERFLOW-EL: 507 .80 BEND: 5 DEG DIA/WIDTH: 4.0 Q-RATIO: 0.04 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HY10 HWI *******************************************************************+*********** 11 . 69 2 . 10 500.76 * 0.012 1 .23 1 .21 2 .44 2 .44 1 . 96 2 .10 1 . 69 CB 68 . 104 LF - 24"CP @ 0 .50� OUTLET: 498 .66 INLET: 499 .18 INTYP: 5 JUNC NO. 4: OVERFLOW-EL: 505.19 BEND: 5 DEG DIA/WIDTH: 4.0 Q-RATIO: 0 . 02 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO H6^1I ****************************************************************************��* 11 .24 1. 92 501 . 10 * 0 .012 1 .21 1 . 18 2 . 10 2 .10 1 .76 1_92 1 . 65 CB 3 . 99 LF - 24"CP @ 0 .490 OUTLET: 499 .18 INLET: 499. 67 INTYP: 5 JUNC NO. 5: OVERFLOW-EL: 504.30 BEND: 5 DEG DIA/WIDTH: 4.0 Q-RATIO: 0.03 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI *******************************************************************�*********�� 11.02 1.80 501.47 * 0.012 1 .20 1.17 1.92 1 . 92 1. 56 1.80 1 . 63 VVV�'1_2�E3.DOC P��ge 1 ��f 3 WW1 CB 5 . 82 LF - 24"CP @ 0.50� OUTLET: 499.67 INLET: 500.08 INTYP: 5 JUNC N0. 6: OVERFLOW-EL: 504.86 BEND: 5 DEG DIA/WIDTH: 2 .0 Q-RATIO: 0.04 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI ***********************************************************�******************* 10.70 1.75 501.83 * 0.012 1. 18 1. 14 1.80 1 .80 1.47 1.75 1.61 CB 6 . 94 LF - 24"CP @ 0.50$ OUTLET: 500.08 INLET: 500.55 INTYP: 5 JUNC NO. 7: OVERFLOW-EL: 505.83 BEND: 90 DEG DIA/WIDTH: 2.0 Q-RATIO: 0.03 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI ****,r******************************************************�******************* 10.29 1.89 502 .44 * 0.012 1.15 1. 11 1.75 1.75 1.36 1.89 1.77 CB 7 . 28 LF - 24"CP @ 0.50$ OUTLET: 500.55 INLET: 500.69 INTYP: 5 JUNC N0. 8: OVERFLOW-EL: 505.83 BEND: 90 DEG DIA/WIDTH: 2 .0 Q-RATIO: 0_02 Q(CFS} HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI ******************************************************************************* 9.99 2 .10 502.79 * 0.012 1.14 1.09 1.89 1.89 1.78 2 .10 1.74 CB 8 . 68 LF - 24"CP @ 0.50$ OUTLET: 500.69 INLET: 501.03 INTYP: 5 JUNC N0. 9 : OVERFLOW-EL: 506.57 BEND: 0 DEG DIA/WIDTH: 2.0 Q-RATIO: 1.36 Q(CFS) HVJ(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI ******************************************************************************* 9.79 1.96 502.99 * 0.012 1.12 1.08 2 .10 2 .10 1 .85 1.96 1.53 CB 37 . 21 LF - 12"CP @ 1.00� OUTLET: 502_03 INLET: 502 .24 INTYP: 5 JLTNC N0.10: OVERFLOW-EL: 506.12 BEND: 1 DEG DIA/WIDTH: 2.0 Q-RATIO: 0 .06 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HVJO HWI *********************,r**********�********************************************** 4.15 1.42 503 .66 * 0.012 0.87 0.93 0. 96 0.96 0.93 1.26 1.42 CB 38 . 197 LF - 12"CP @ 3 .23$ OUTLET: 502 .24 INLET: 508.60 INTYP: 5 JUNC N0.11: OVERFLOW-EL: 513 .53 BEND: 90 DEG DIA/WIDTH: 2.0 Q-RATIO: 0 .04 ' Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI II *************************************,r***************************************** 3 . 91 1. 77 510.37 * 0.012 0 .84 0. 54 1.42 1 .42 0. 84 ***** 1 .77 \��'��1 -;B.DO(� P.i:�� ' ��1� ; WW1 CB 39 . 21 LF - 12"CP @ 0.76� OUTLET: 508.60 INLET: 508.76 INTYP: 5 JUNC N0.12 : OVERFLOW-EL: 512. 60 BEND: 90 DEG DIA/WIDTH: 2 .0 Q-RATIO: 0. 12 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI *,r*****************************************************,r*********************** 3 .76 2 .46 511.22 * 0.012 0.83 1.00 1.77 1.77 1.81 2 .46 1.70 CB 41 . 136 LF - 12"CP @ 2 .18� OUTLET: 508.76 INLET: 511.72 INTYP: 5 JUNC N0.13 : OVERFLOW-EL: 515.50 BEND: 1 DEG DIA/WIDTH: 2 .0 Q-RATIO: 0 .33 Q(CFS) HW{FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI ******************************************************************************* 3.36 1.27 512 .99 * 0.012 0.79 0.56 2.46 2 .46 0.79 ***** 1 .27 CB 43 _ 200 LF - 12"CP @ 2 .37$ OUTLET: 511.72 INLET: 516.46 INTYP: 5 JUNC N0.14: OVERFLOW-EL: 520.24 BEND: 1 DEG DIA/WIDTH: 2 .0 Q-RATI�: 0_SO Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI ******************************************************************************* 2.53 1.03 517.49 * 0.012 0.69 0.46 1.27 1.27 0.69 ***** 1.03 CB 45 . 200 LF - 12"CP @ 1.49$ OUTLET: 516.46 INLET: 519.45 INTYP: 5 i JUNC N0.15: OVERFLOW-EL: 523.23 BEND: 1 DEG DIA/WIDTH: 2.0 Q-R.ATIO: 0.15 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI i ******************************************************************************* ii 1.68 0.77 520.22 * 0.012 0.56 0.42 1. 03 1.03 0.56 ***** 0.77 I� CB 31 . 84 LF - 12"CP @ 0. 67� OUTLET: 519 .45 INLET: 520. 01 INTYP: 5 I JUNC N0.16: OVERFLOW-EL: 524.92 BEND: 1 DEG DIA/WIDTH: 2.0 Q-RATIO: 0.06 I� Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI I ************************************,r******************:r*********************** 1.46 0.70 520.71 * 0.012 0. 52 0 .48 0.77 0.77 0. 52 ***** 0 .70 CB 47 . 52 LF - 12"CP @ 1. 13� OUTLET: 520 .01 INLET: 520.60 INTYP: 5 JLTNC N0.17 : OVERFLOW-EL: 524.10 BEND: 1 DEG DIA/WIDTH: 2 .0 Q-RATIO: 0 . 93 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI ****************************************************,r************************** 1.38 0.71 521.31 * 0.012 0.50 0.40 0.70 0.70 0. 50 ***** 0 .71 CB 49 . 164 LF - 12"CP @ 1.40� OUTLET: 520.60 INLET: 522 .89 INTYP: 5 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI ****��*��******************�***********************�*************************** 0.72 0.48 523 .37 * 0.012 0.36 0.27 0 .71 0 .71 0.36 ***** �.48 WWI_25B.DOC Page 3 of 3 WWl BACK4IATER COMPUTER PROGRAM FOR PIPES, 100 year event Pipe data from file:d: \wwl.bwp Surcharge condition at intermediate junctions Tailwater Elevation:499.87 feet Discharge Range:18.8 to 18.8 Step of 0 .1 [cfs] Overflow Elevation:536.39 feet Weir:NONE Upstream Velocity:0. feet/sec CB 69 . 36 LF - 24"CP @ 0.64$ OUTLET: 497 .00 INLET: 497 .23 INTYP: 5 JUNC NO. 1: OVERFLOW-EL: 512.00 BEND: 1 DEG DIA/WIDTH: 4.5 Q-RATIO: 0.01 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HVJO HWI ******************************************************************************* 18.80 3 .17 500.40 * 0.012 1.57 1.58 2 .87 2.87 2 .86 3 .17 2 .23 CB 65 . 91 LF - 24"CP @ 0.64$ OUTLET: 497.23 INLET: 497 .81 INTYP: 5 JUNC NO. 2: OVERFLOW-EL: 512.54 BEND: 80 DEG DIA/WIDTH: 4.0 Q-RATIO: 0.33 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI *******************************************�*********************************** 18.61 4.03 501.84 * 0.012 1.56 1.56 3.17 3.17 3 .12 4.03 2 .83 CB 66 . 170 LF - 24"CP @ 0.50$ OUTLET: 497 .81 INLET: 498 .66 INTYP: 5 JUNC N0. 3 : OVERFLOW-EL: 507.80 BEND: 5 DEG DIA/WIDTH: 4.0 Q-RATIO: 0.04 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE H410 HWI ************************************************,r****************************** 14.00 3 .94 502.60 * 0.012 1 .35 1.37 4.03 4.03 3 .74 3 .94 1.87 CB 68 . 104 LF - 24"CP @ 0 .50� OUTLET: 498.66 INLET: 499.18 INTYP: 5 JLTNC NO. 4: OVERFLOW-EL: 505.19 BEND: 5 DEG DIA/WIDTH: 4.0 Q-RATIO: 0_02 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI ***************************+***********************,r************,r************** 13 .46 3 .91 503 . 09 * 0.012 1.33 1.33 3 . 94 3 . 94 3 .74 3 .91 1 .82 CB 3 . 99 LF - 24"CP @ 0.49� OUTLET: 499.18 INLET: 499 .67 INTYP: 5 JLTNC N0. 5 : OVERFLOW-EL: 504.30 BEND: 5 DEG DIA/WIDTH: 4 .0 Q-RATIO: 0.03 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI ******************************************************************************* , 13 .19 3 .88 503 .55 * 0.012 1.31 1.32 3 .91 3 .91 3 .71 3 .88 1 .80 WW 1_IOOB.DOC Page 1 of 3 WW1 CB 5 . 82 LF - 24"CP @ 0. 50% OUTLET: 499.67 INLET: 500.08 INTYP: 5 JUNC N0. 6: OVERFLOW-EL: 504.86 BEND: 5 DEG DIA/WIDTH: 2 . 0 Q-RATIO: 0 .04 Q(CFS) HW{FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI *******************************.*******************�***************+**,r******** 12 .81 3 .87 503 .95 * 0.012 1.29 1 .28 3 .88 3 .88 3 .70 3 .87 1 .78 CB 6 . 94 LF - 24"CP @ 0.50$ OUTLET: 500.08 INLET: 500.55 INTYP: 5 JLTNC N0. 7: OVERFLOW-EL: 505.83 BEND: 90 DEG DIA/WIDTH: 2. 0 Q-RATIO: 0 .03 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI ************,r******************�**************************************,r******** 12.32 4.08 504.63 * 0.012 1.27 1.25 3 .87 3 .87 3 . 64 4.08 2 . �3 CB 7 . 28 LF - 24"CP @ 0 .50$ OUTLET: 500.55 INLET: 500.69 INTYP: 5 JUNC NO. 8: OVERFLOW-EL: 505.83 BEND: 90 DEG DIA/WIDTH: 2 . 0 Q-RATIO: 0 . 02 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI *****************************************,r******************************,r****** 11.96 4.42 505.11 * 0.012 1.25 1.23 4.08 4.08 4. 01 4.42 1.98 CB 8 . 68 LF - 24"CP @ 0.50$ OUTLET: 500.69 INLET: 501.�3 INTYP: 5 JUNC N0. 9: OVERFLOW-EL: 506.57 BEND: 0 DEG DIA/WIDTH: 2 .0 Q-RATIO: 1 .36 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI *******************************************,r*********************************** 11.72 4.37 505.40 * 0.012 1.23 1.21 4.42 4.42 4.24 4.37 1. 69 CB 37 . 21 LF - 12"CP @ 1. 00� OUTLET: 502.03 INLET: 502 .24 INTYP: 5 � JUNC N0.10: OVERFLOW-EL: 506.12 BEND: 1 DEG DIA/WIDTH: 2 .0 Q-RATIO: 0.06 I Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI � ******************************************************************************* 4.97 3 .93 506.17 * 0.012 0.92 1.00 3 .37 3 .37 3 .51 3 .93 1.74 **************** OVERFLOW ENCOUNTERED AT 4.97 CFS DISCHARGE ***************** ************** ACTUAL OVERFLOti^7 MAY OCCUR AT LESS THI�N 4. 97 CFS ************** ****�*** OVERFL06^d CONDITIONS CALCULATED rSSUMING SURCHARGE CONDITIO�IS ********* CB 38 . 197 LF - 12"CP @ 3 .23� OUTLET: 502 .24 INLET: 508. 60 INTYP: 5 JL7NC N0.11: O�IERFLOW-EL: 513.53 BEND: 90 DEG DIA/WIDTH: 2 .0 Q-RATIO: 0 .04 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI *****,r******************�***�***�*********************************************� 4. 69 2 .25 510 .85 * 0.012 0 .90 0.61 3 . 93 3 .93 0. 90 ***** 2 .25 �'R�1_IOOB.DOC Page 2 of 3 wwi , CB 39 . 21 LF - 12"CP @ 0.76$ OUTLET: 508.60 INLET: 508.76 INTYP: 5 JUNC N0.12: OVERFLOW-EL: 512 .60 BEND: 90 DEG DIA/WIDTH: 2.0 Q-RATIO: 0.12 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI ****************************�***:******,r******:r****:r***************�******+r**** 4.51 3.31 512.07 * 0.012 0.89 1.00 2 .25 2 .25 2 .38 3 .31 2 .15 CB 41 . 136 LF - 12"CP @ 2.18� OiJTLET: 508 .76 INLET: 511 .72 INTYP: 5 JUNC N0.13: OVERFLOW-EL: 515.50 BEND: 1 DEG DIA/WIDTH: 2_0 Q-RATIO: 0_33 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI ********************************************************************,r***,r****** 4.02 2 .28 514.00 * 0.012 0.85 0_63 3 .31 3 .31 1.84 2.28 1.53 CB 43 . 200 LF - 12"CP @ 2 .37$ OUTLET: 511.72 INLET: 516.46 INTYP: 5 JUNC N0.14: OVERFLOW-EL: 520.24 BEND: 1 DEG DIA/WIDTH: 2 .0 Q-RATIO: 0 .50 Q(CFS} HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI *******************************��***************************************,r**,r*** 3 .02 1.18 517 .64 * 0.012 0.75 0.51 2 .28 2.28 0_75 ***** 1.18 CB 45 . 200 LF - 12"CP @ 1 .49$ OUTLET: 516.46 INLET: 519.45 INTYP: 5 JUiVC N0.15 : OVERFLOVd-EL: 523 .23 BEND: 1 DEG �IA/PIIDTH: 2 . 0 Q-RATIO: 0 . 15 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI *****��*�*+****************«+****�******,r��*�*+�**�**��**��***************** 2 . 02 0 .85 520 .30 * 0. �12 0 . 61 0 .46 1 . 18 1. 18 0 .61 ***** 0 . 85 CB 31 . 84 LF - 12"CP @ 0. 67� OUTLET: 519.45 INLET: 520.01 INTYP: 5 JUNC N0.16: OVERFLOW-EL: 524.92 BEND: 1 DEG DIA/WIDTH: 2.0 Q-RATIO: 0.06 Q(CFS) HW{FT) HW ELEV. * N-FAC DC DN TW DO DE HVJO HWI *��*�*************************�*******************+*************************** 1.75 0 .78 520.79 * 0.012 0 . 57 0 . 54 0 . 85 0 .85 0 .57 ***** 0 .78 CB 47 . 52 LF - 12"CP @ 1.13$ OUTLET: 520.01 INLET: 520 .60 INTYP: 5 JUNC N0.17: OVERFLOW-EL: 524.10 BEND: 1 DEG DIA/WIDTH: 2 .0 Q-RATIO: 0.93 4(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI **�*****,r**********************.***********************************�*********** 1. 65 0.80 521.40 * 0.012 0.55 0.45 0 .78 0 .78 0 .55 ***** 0 .80 CB 49 . 164 LF - 12"CP @ 1 .40$ OUTLET: 520. 60 INLET: 522 .89 INTYP: 5 Q(CFS) H��d(FT) HVd ELEV. " N-FAC DC DN �j^J DO DE I-I�VO I-I[�TI ��.*��*�*+:**x*��*��+�*�*****.*�*,**«�***�***�x�*«��*+��*x*+�.��*��***�*��*� 0 . 86 0 . 5� 523 .43 * 0.012 0 .39 0 .30 0 . 80 0 _80 0 .39 ***** 0 . 5� �V��'l_IOOB.DOC Page 3 c�f 3 WW2 BACKWATER COMPUTER PROGRAM FOR PIP�S, 25 year event Pipe data from file:d: \ww2.bwp Surcharge condition at intermediate junctions Tailwater Elevation:500.25 feet Discharge Range:5.2 to 5.2 Step of 0.1 [cfs] Overflow Elevation:528.01 feet Weir:NONE Upstream Velocity:0. feet/sec CB 64 . 28 LF - 18"CP @ 1.00� OUTLET: 507.76 INLET: 508 .04 INTYP: 5 JLINC N0. l: OVERFLOW-EL: 512.54 BEND: 90 DEG DIA/WIDTH: 2 .0 Q-RATIO: 0.06 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI ******************************************************************************* 5 . 20 1.36 509 .�0 * 0.012 0 .88 0 .72 0 . 00 0. 72 0 . 88 ***** 1 . 36 CB o2 . 04 Lr - 18"CP l G .23� UJiLE�: 5G8 .0=� INL.;'I: �09 .�; IidT"'=P: 5 JUNC N0. 2: OVERFLOW-EL: 513 .97 BEND: 90 DEG DIA/WIDTH: 2.0 Q-RATIO: 0.08 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI ***************************************«******,r***********************,r******** 4.91 1.46 510.93 * 0.012 0.86 0.56 1.36 1.36 0 .86 ***** 1.46 CB 60 _ 146 LF - 12"CP @ 1.95� OUTLET: 509 .97 INLET: 512 .82 INTYP: 5 JUNC N0. 3: OVERFLOW-EL: 516.60 BEND: 1 DEG DIA/WIDTH: 2 . 0 Q-RATIO: 0.10 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI ********************************************,r********************************** 4.54 1.61 514.43 * 0.012 0. 89 0.71 0.96 0.96 0.89 ***** 1.61 CB 53 . 196 LF - 12"CP @ 1.76� OUTLET: 512 .82 INLET: 516.26 INTYP: 5 JUNC N0. 4: OVERFLOW-EL: 519.26 BEND: 1 DEG DIA/WIDTH: 2.0 Q-RATIO: 0.11 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI *******************************************�***********************,r*********** 4 . 13 1.45 517 .71 * 0.012 0 .86 0.69 1. 61 1. 61 0.86 ***** 1 .45 CB 54 . 154 LF - 12"CP @ 1.21� OUTLET: 516.26 INLET: 518 .13 INTYP: 5 JUNC NO. 5: OVERFLOW-EL: 521.91 BEND: 1 DEG DIA/WIDTH: 2 .0 Q-RATIO: 0 .55 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI ***************************:r**,r**************:r****************************,r*�*� 3 .72 1.47 519.60 * 0.012 0 .83 0.73 1 .45 1.45 0 .89 1.39 1 .47 �V�b'2_ZSB.DOC' Page l ��f ? WW2 CB 56 . 200 LF - 12��CP @ 1.20� oUT�E�: 518 . 13 �r��E^: 520 .�3 zNTYP: 5 JLTNC N0. 6: OVERFLOW-EL: 524.31 BEND: 1 DEG DIA/WIDTH: 2 .0 Q-RATIO: 0.58 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI ***********************************,r*,r**************,r************************** 2 .40 1 .01 521.54 * 0.012 0 .67 0.54 1 .47 1 .47 0 . 67 ***** 1 . 01 CB 58 . 200 LF - 12"CP @ 1 .00� OUTLET: 520 .53 INLET: 522 .53 INTYP: 5 JUNC NO. 7: OVERFLOW-EL: 526 .31 BEND: 1 DEG DIA/WIDTF�: 2 .0 Q-RATIO: 0. 08 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI **************,r***,r************************************************************ 1 .52 0 .72 523 .25 * 0.012 0 .53 0 .44 1.01 1.01 0 . 53 ***** 0 .72 CB 59 . 28 LF - 12"CP @ 1 . 00� OUTLE^: �22 . 53 =��LE'�: 522 . 81 INTYP: 5 JL�`dC N0. 8 : OVERFLO�f1-EL: 526.31 BEND: 90 DEG DIAi`v7IDTH: 2 . 0 Q-RATIO: 0. 26 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI *�**************************************************************,r******,r******* 1.41 �.74 523.55 * 0.012 0.51 0 .42 0.72 0.72 0 .51 ***** 0.74 CB 34 . 24 LF - 12"CP @ 7 .08$ OUTLET: 522.81 INLET: 524.51 INTYP: 5 Q(CFS) HW(FT) HW ELEV_ * N-FAC DC DN TW DO DE HWO HWI **��***********************+************************************,r************** 1 . 12 0.60 525 . 11 * 0.012 0 .45 0 .23 0 .74 0.74 0 .45 ***** 0 . 60 WVb'2_25B.DOC Page 2 ��f 2 WW2 BACKWATER COMPUTER PROGRAM FOR PIPES, 100 year event Pipe data from file:d:\ww2.bwp Surcharge condition at intermediate junctions Tailwater Elevation:501.84 feet Discharge Range:6.2 to 6.2 Step of 0 .1 [cfs] Overflow Elevation:528.01 feet Weir:NONE Upstream Velocity:0. feet/sec CB 64 . 28 LF - 18"CP @ 1.00$ OUTLET: 507 .76 INLET: 508.04 INTYP: 5 JUNC N0. 1: OVERFLOW-EL: 512.54 BEND: 90 DEG DIA/WIDTH: 2.0 Q-R.ATIO: 0.06 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI ***********************************************************�******************* 6.20 1.56 509.60 * 0.012 0.97 0.79 0.00 0.79 0.97 ***** 1.56 CB 62 . 64 LF - 18"CP @ 2.23$ OUTLET: 508.04 INLET: 509 .47 INTYP: 5 JUNC NO. 2: OVERFLOW-EL: 513 .97 BEND: 90 DEG DIA/WIDTH: 2 .0 Q-RATIO: 0.08 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI ******************************************************************************* 5.85 1.71 511.18 * 0.012 0.94 0.61 1.56 1.56 0.94 ***** 1.71 CB 60 . 146 LF - 12"CP @ 1.95� OUTLET: 509.97 INLET: 512 .82 INTYP: 5 JUNC N0. 3: OVERFLOW-EL: 516.60 BEND: 1 DEG DIA/WIDTH: 2 .0 Q-RATIO: 0.10 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI I ***********************************+******************************************* 5.42 2.00 514.82 * 0.012 0.94 0.83 1.21 1.21 1.00 1.56 2 .00 CB 53 . 196 LF - 12"CP @ 1.76$ OUTLET: 512.82 INLET: 516.26 INTYP: 5 JUNC NO. 4: OVERFLOW-EL: 519.26 BEND: 1 DEG DIA/WIDTH: 2 .0 Q-RATIO: 0.11 , Q(CFS) HW(FT) HW ELEV. '` N-FAC DC DN TW DO DE HWO HWI , ***************************************************,r*************************** i 4.92 2 .24 518.50 * 0.012 0 .92 0.79 2 .00 2 .00 1 .76 2 .24 1.78 ' CB 54 . 154 LF - 12"CP @ 1.21$ OUTLET: 516.26 INLET: 518.13 INTYP: 5 Ji7NC NO. 5: OVERFLOW-EL: 521.91 BEND: 1 DEG DIA/WIDTH: 2.0 Q-RATIO: 0.55 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HVJO HVJI *************************�***************************************************** I 4.44 3.02 521.15 * 0.012 0.89 0.87 2 .24 2 .24 2 .40 3 .02 1.81 WW2_100B.DOC Page 1 of 2 � ww2 CB 56 . 200 LF - 12"CP @ 1.20$ OUTLET: 518.13 INLET: 520 .53 INTYP: 5 JUNC NO. 6 : OVERFLOW-EL: 524.31 BEND: 1 DEG DIA/WIDTH: 2 .0 Q-RATIO: 0.58 Q(CFS} HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI ****************************�**�*********************************************** 2.86 1.98 522 .51 * 0.012 0 .73 0.61 3 .02 3 .02 1.72 1.98 1.14 CB 58 . 200 LF - 12"CP @ 1.00$ OUTLET: 520.53 INLET: 522.53 INTYP: 5 JUNC NO. 7: OVERFLOW-EL: 526.31 BEND: 1 DEG DIA/WIDTH: 2 .0 Q-RATIO: �.08 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI *******************,r********,r**************************************,r*********** 1.81 0.85 523.38 * 0.012 0.58 0.49 1.98 1.98 0.59 0 .85 0 .79 CB 59 . 28 LF - 12"CP @ 1.00$ OUTLET: 522 .53 INLET: 522 .81 INTYP: 5 JUNC NO. 8: OVERFLOW-EL: 526.31 BEND: 90 DEG DIA/WIDTH: 2 . 0 Q-RATIO: 0.26 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI ***********,r****************,r***********«************************************** 1.68 0.84 523 .65 * 0.012 0.56 0.47 0.85 0.85 0.56 ***** 0.84 CB 34 . 24 LF - 12"CP @ 7.08$ OUTLET: 522.81 INLET: 524.51 INTYP: 5 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI ******************,r****************�***********************,r******************* 1.33 0.67 525 .18 * 0.012 0.49 0.25 0.84 0 .84 0.49 ***** 0.67 WW2_100B.DOC Page 2 ��f 2 WW3 BACKWATER COMPUTER PROGRAM FOR PIPES, 25 year event Pipe data from file:d: \ww3.bwp Surcharge condition at intermediate junctions Tailwater Elevation:502.99 feet Discharge Range:6.6 to 6. 6 Step of 0.1 [cfs] Overflow Elevation:529.83 feet Weir:NONE Upstream Velocity:0. feet/sec CB 8A . 65 LF - 18"CP @ 1.66$ OUTLET: 501. 90 INLET: 502 .98 INTYP: 5 JUNC NO. I: OVERFLOW-EL: 507 .26 BEND: 1 DEG DIA/WIDTH: 2 .0 Q-RATIO: 0.11 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI ***************************,r***************************,r*********************** 6.60 1.40 504.38 * 0.012 1.00 0.71 1.09 1.09 1.00 ***** 1.40 CB 9 . 146 LF - 18"CP @ 1.07$ OUTLET: 502 .98 INLET: 504.54 INTYP: 5 JUNC NO. 2_ OVERFLOW-EL: 508.82 BEND: 1 DEG DIA/WIDTH: 2.0 Q-RATIO: 0.14 Q(CFS) HW{FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI **************************************************,r**************************** 5.95 1.33 505.87 * 0.012 0.95 0.76 1.40 1.40 0 .95 ***** 1.33 CB 11 . 155 LF - 18"CP @ 0.63$ OUTLET: 505.54 INLET: 506.51 INTYP: S I'I JLTNC N0. 3 : OVERFLOW-EL: 510.79 BEND: 1 DEG DIA/WIDTH: 2.0 Q-RATIO: 0.23 I, Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI *******,r*********************************************«************************* 5.22 0.96 507.47 * 0.012 0.88 0.82 0_33 0.82 0.88 ***** 0. 96 CB 13 . 200 LF - 12"CP @ 1.50� OUTLET: 507.11 INLET: 510.10 INTYP: 5 JUNC NO. 4: OVERFLOW-EL: 515.51 BEND: 1 DEG DIA/WIDTH: 4.0 Q-RATIO: 0.08 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI ******************************************************************************* 4 .24 1.47 511.57 * 0.012 0 .87 0 .75 0 .36 0 .75 0. 87 ***** 1 .47 CB 15 . 84 LF - 12°CP @ 0. 50� OUTLET: 510.10 INLET: 510.52 INTYP: 5 JL7NC NO. 5: OVERFLOW-EL: 517.78 BEND: 1 DEG DIA/WIDTH: 4.0 Q-RATIO: 0 .30 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI ********************,r********************************************************** 3 . 93 2 .33 512 .85 * 0.012 0 .85 1 .00 1.47 1.47 1 .92 2 .33 1 .49 1b'��`3_2jB_DOC Page 1 �>f ? `'�'`'�'3 CB 16 . 52 LF - 12"CP @ 0 .50� OUTLET: 512 .06 INLET: 512 .32 INTYP: 5 � JUNC N0. 6: OVERFLOW-EL: 517 .50 BEND: 1 DEG DIA/WIDTH: 2 .0 Q-RATIO: 0.31 ' Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI **************,r****************************�***************+******************* 3 .02 1.18 513.50 * 0.012 0.75 1.00 0.79 0_79 0.90 1.18 1. 15 CB 18 . 164 LF - 12"CP @ 3 . 13$ OUTLET: 512 .32 INLET: 517 .46 INTYP: 5 JUNC NO. 7 : OVERFLOW-EL: 521.24 BEND: 1 DEG DIA/WIDTH: 2 .0 Q-RATIO: �.54 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI ***********�****************************,r************************************** 2 .31 0.97 518.43 * 0.012 0.65 0.41 1.18 1.18 0.65 ***** 0.97 CB 20 . 200 LF - 12"CP @ 2 .43� OUTLET: 517 .46 INLET: 522 .32 INTYP: 5 JUNC NO. 8: OVERFLOW-EL: 526 .10 BEND: 1 DEG DIA/WIDTH: 2 .0 Q-RATIO: 0. 25 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI ************************�*******�******************�**,r************************ 1 .50 0 .72 523 .04 * 0.012 0 .52 0 .34 0 .97 0. 97 0.52 ***** 0 . 72 CB 21 . 28 LF - 12"CP @ 1 .00o OUTLET: 522 .32 INLET: 522 . 60 INTYP: 5 JUNC N0. 9: OVERFL04�i-EL: 526.10 BEI�;D: 90 DEG DIA/WIDTH: 2 .0 Q-RATIO: 0.60 Q(CFS) IiLti�(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI *****:r*******�****�********�*************************************************** 1.20 0 .67 523 .27 * 0.012 0.47 0.39 0.72 0.72 0 .47 ***** 0.67 CB 22 . 161 LF - 12"CP @ 1.43$ OUTLET: 522.60 INLET: 524.90 INTYP: 5 JUNC NO.10: OVERFLOW-EL: 528.64 BEND: 90 DEG DIA/WIDTH: 2 .0 Q-RATIO: 0.56 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI ***�********,r*********************************************************,r******** 0 .75 0 . 50 525 .40 * O.Oi2 0 .3? 0 .28 0. 67 0 . 67 0 .3i ***** 0 .50 CB 23 . 35 LF - 12"CP @ 1.00� OUT�ET: 524. 90 INLET: 525 .25 INTYP: 5 JUNC NO.11: OVERFLOW-EL: 528.78 BEND: 90 DEG DIA/WIDTH: 2 .0 Q-RATIO: 0.23 QSCFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI ******************************************************************************* 0.48 0 .39 525 . 64 * 0.012 0 .29 0 .24 0.50 0. 50 0 .29 ***** 0.39 CB 24 . 48 LF - 12"CP @ 0 .50o OliTLET: 525 .25 INLET: 525 .49 INTYP: 5 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI **�*******�*�*��**�*�*�*******�***x***��***********�***�*********************** 0. 39 0.39 525 . 88 * 0.012 0 .26 0 .26 0 .39 0 .39 0 .26 0 .39 0 .35 VV�i'3 25B.DOC Page 2 of 2 WW3 BACKWATER COMPUTER PROGRAM FOR PIPES, 100 year event Pipe data from file:d:\ww3.bwp Surcharge condition at intermediate junctions Tailwater Elevation:505.4 feet Discharge Range:7.9 to 7.9 Step of 0.1 [cfs] Overflow Elevation:529.83 feet Weir:NONE Upstream Velocity:0. feet/sec CB 8A . 65 LF - 18"CP @ 1. 66� OUTLET: 501_90 INLET: 502.98 INTYP: 5 JUNC NO. l: OVERFLOW-EL: 507.26 BEND: 1 DEG DIA/WIDTH: 2 .0 Q-RATIO: 0.11 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI *************,r***************************************************************** 7_90 2 .98 505.96 * 0.012 1.09 0.79 3 .50 3 .50 2 .74 2 .98 1.56 CB 9 . 146 LF - 18"CP @ 1. 07� OUTLET: 502.98 INLET: 504.54 INTYP: 5 JUNC NO. 2 : OVERFLOW-EL: 508.82 BEND: 1 DEG DIA/WIDTH: 2. 0 Q-RATIO: 0.14 Q{CFS) HVJ{FT} HW ELEV. * N-FAC DC DN TW DO DE HWO HWI ***********************,r******************************************************* 7.12 2 .21 506.75 * 0.012 1.04 0.85 2 .98 2 .98 2.00 2.21 1.48 CB 11 . 155 LF - 18"CP @ 1.34$ OUTLET: 505.54 INLET: 507 .61 INTYP: 5 JLINC N0. 3 : OVERFLOW-EL: 510.79 BEND: 1 DEG DIA/WIDTH: 2 .0 Q-RATIO: 0.23 Q(CFS) I-I4V(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI ******************************************************************************* 6.24 1.47 509.08 * 0.012 0.97 0.73 1.21 1.21 0.97 ***** 1.47 CB 13 . 200 LF - 12"CP @ 1.50$ OUTLET: 507.11 INLET: 510 .10 INTYP: 5 ' JUNC N0. 4: OVERFLOW-EL: 515.51 BEND: 1 DEG DIA/WIDTH: 4.0 Q-RATIO: 0. 08 � Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI ***********************************************************�******************* 5 .08 2. 91 513 .01 * 0.012 0.93 0.94 1.97 1.97 2 .44 2 .91 1.82 CB 15 . 84 LF - 12"CP @ 0.50$ OUTLET: 510.10 INLET: 510.52 INTYP: 5 JUNC N0. 5: OVERFLOW-EL: 517.78 BEND: 1 DEG DIA/WIDTH: 4 .0 Q-RATIO: 0 .30 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI ********************************************************,r********************** 4.70 4.32 514.84 * 0.012 0.90 1 .00 2 .91 2.91 3 .74 4.32 1.84 WW3_100B.doc Page 1 of 2 WW3 JUi'vL IvU. o : U"v�Rr�,U6V-`t,L: �l ,' . �U �E.�D: 1 DEI� li_�i6vIDI'I:: � . 0 %�-F��'PiU: 0 .3i Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI ***�**************,r**************************************************,r********* 3 . 62 3 .33 515.65 * 0.012 0.82 1.00 2.78 2 .78 2 .98 3 .33 1.37 CB 18 . 164 LF - 12"CP @ 3.13� OUTLET: 512 .32 INLET: 517 .46 INTYP: 5 JUNC NO. 7: OVERFLOW-EL: 521.24 BEND: 1 DEG DIA/WIDTH: 2 .0 Q-RATIO: 0 .54 Q(CFS) HW{FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI ************,r*******«****************,r*********,r************,r***,r************** 2 .76 1.10 518.56 * 0.012 0.72 0.45 3 .33 3.33 0.72 ***** 1.10 CB 20 . 200 LF - 12"CP @ 2 .43$ OUTLET: 517.46 INLET: 522 .32 INTYP: 5 JUNC NO. 8: OVERFLOW-EL: 526.10 BEND: 1 DEG DIA/WIDTH: 2 .0 Q-RATIO: 0.25 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI ***************,r**,r**,r***«****************«+*************************:r*,r******* 1.79 0.80 523.12 * 0.012 0.57 0.38 1 .10 1.10 0 .57 ***** 0.80 CB 21 . 28 LF - 12"CP @ 1.00� OUTLET: 522.32 INLET: 522.60 INTYP: 5 JUNC NO. 9: OVERFLOW-EL: 526.10 BEND: 90 DEG DIA/WIDTH: 2 .0 Q-RATIO: 0. 60 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI ******************************************************************************* 1.43 0.75 523.35 * 0.012 0.51 0.43 0.80 0.80 0.51 ***** 0.75 CB 22 . 161 LF - 12"CP @ 1.43� OUTLET: 522 .60 INLET: 524.90 INTYP: 5 JUNC NO.10: OVERFLOW-EL: 528.64 BEND: 90 DEG DIA/WIDTH: 2 .0 Q-RATIO: 0.56 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI **************************,r**************************************************** 0.90 0. 56 525.46 * 0.012 0.40 0.30 0.75 0.75 0.40 ***** 0.56 CB 23 . 35 LF - 12"CP @ 1.00$ OUTLET: 524.90 INLET: 525.25 INTYP: 5 JUNC NO. 11: OVERFLOW-EL: 528.78 BEND: 90 DEG DIA/WIDTH: 2.0 Q-RATIO: 0.23 Q(CFS) HW(FT) HW ELEV. '` N-FAC DC DN TW DO DE HWO HWI *****************************,r:r************************************************ 0.57 0.43 525.68 * 0.012 0.32 0.27 0.56 0.56 0.32 ***** 0.43 CB 24 . 48 LF - 12"CP @ 0 .50� OUTLET: 525.25 INLET: 525 .49 INTYP: 5 Q(CFS) I-:Pd(FT) HW ELEV. * N-FAC DC DN TLti' DO DE HVdO HWI �*�*****************�****�*****.��****�***�**�+ **�****�+*�*********�«***��**** 0 .47 0.39 525.88 * 0.012 0 .29 0 .28 0 .43 0.43 0.29 ***** 0 .39 W��'3 100B.du� Pa�e Z of Z : ! _ -_ � _ � ` - ; � ��:� 11814 115th AVE. NE Kirklnad. WA 9803; n (7 208.821.8448 U'^\ 'I � Fez 208.821.34B1 ... .. \\I I �d Su,,,e �•,� rnt ci.0 EnE-, \J Lmd Uee Plmning Pro�ect Ymnac:�,-. ' Imdacepe Archileclwe 31te Desi, I O � : � SCALE: 1" = 150' � : � 0 100 150 300 � 3 � � � Pp, I :: . . .sitr�aois� � uo'• o�s�/rt � :. �:>. � 1 s:;�"t .;%,k:«:in:<::_�„-• � Z ,k;> ..Q �t ��, ... ........... ... ..•-•. ,,. . �, O � Q . . , . � � � o �. W o � � �- 2 i � , �s a��,,� .�•.a��,� - H � � •°' .� �' V 4k1 � � . P . go , �� O � \ i � � ti �,•G+�' � . ao7 aau,�s�r � � r.ro��aao�r s •�a I . . . • . , . . f O ........ .......... ........... .......... ........ � ........... ••• •..... ��_� _ __...,T .... .....` 3 i, . . . .. .._.__�. ._..__.._ .. � ' 1 1 f i 1 t '' I � 1 ' ' � 7 .. _.......... ...... , • f t £ O � `� y ' � 1 � 1 � � : . . . . . . . . . . . . . . ....... . . . , .: , .......... ........... _.�._ . .. . < i ; : : . , _�_ _____ __...� ___..... .......... ..........:.......... .......... ......_. .....__.._ _ __ _ : ...... .......... ....� ; � : : : : .: � � t i � """'j ` MANAGER: � 3 ' ; ; ; � ' `""""' DESIGNED: , ; .... . , , CADD: , ...�. ,....... ....•'. ......3 3 � � ; . �� CHECKED: ; '..... ... ........... ..:....... .....W�. __.._--- .:.._..� 3 ; : DATE: '� '�, � 1 SCALE: HORIZ.: _ ; ' `------- --------- -_....,_.. ..,_._�. ._._.._.. .........�i....._.... ...... , , .......... .._.. ._....... ......._. .�� _... ........... ...... 1 ._.. .�...... .... .......... .......... ...t, Y----. --3 ` , � c 3 i E f..... t ...r....... ..... ..._�._. . . , , i JOB NUMBER , � : : ' ' : � ; : � � � � ; 98-243 { . r � ; < � . SHEET NUMBER . � �_ .....; � � 1 OF 1 . . . . , $ � � I � �� ; �..� , � � • —�. • ��. .� ^''`^\\ � 7RIAD ASSOCIA7'E$ � ' I1814 115th AVE. NE \`� Kirlclnnd, 11A 98034 Tw El. = 498.51, 25yr Z�.Bz�.a4+a � Fnx 208.821.3481 Tw El. = 499.87, 100 ;a;U"P';�, �.�s°`'°�"� � tr+C Project I(�nyemeoc I � : Imdxepe Archileclur< 51te Dal�n i i SCALE: 1" = 150� {FILENAME, �'c) TYP Tw El. = 499.83, 25yr � ; o �5 t so soo "��`��C Tw El. = 501.23, l 00yr = ,........................ ... . , � � � � ' �r � � :�� ,� � � . � 3 � �� WW Tc 1 min = �. � � �� a° �,, a� .._...� eo e .�.............. �� ; �' �" �...�.�...�......_ � � • •�. � �`� :Y.:..'4i� 7.i4 . : �3`�' � � � ��,£� o- �,. �, . € ` �< ��° �� ' � . 4 � �. y,d'' � .:. : .............................� ( .,. � " l � r� � Q� � ._. r.�c �>,� �` � � ;w ., , � ; .:.;.,:: :.� . � �.. :, , . • . :, i • � --�............... ............._. . � ,. . w... .�. . ; . �. :t � � :t- .� $ � r �, . . .� l : �.. :; g �� --��---�........ ........ :. � lara n " ( =��h � B ��Y. � � eF'oA � •� � . � .; . . , $ . , �e ' � � � � , Tc 20. mi , ` ,�, �< �€� Q� ; "��' : ; ; � ......��.......�.... ,. .: :, . Q � # � " � � u J 'r � � �<�� ,�€.� t'J ��`"`'�,, �' I _. V' 4yj O � � F � �� :� � �� N O O �� , � ; �.�� .�� r �m� v� _ � :� � � � � ,3' � ��, � W � � .�..............� � � � � � � � e�� y � ' ..._. . ; . J - . ..�--��--�-�-.. � �� • ~ " ' . ' WZ � � �' `�.o- � � � '� o-�l � � � �� 4 � � a'°swcv� 4 � � • ......_.. ........__.... �o-�l `•.� �..... � �.�0 ie � o-s s ra ; �r : £t � ; '� P a� -�._ ..... . s� Mw.�,, � � t �� itr a�� ` �' � �� ; � (wyy4) ��.... .- � �� • � � �g � � r �� i . Tw El. �= 563.35, :25yr , i CA TCHMENT AREA (TYP) ; _� � 7w El. �= 505.40, ;100yr �� p ` ; ; ; ; ; � Tw E!; = 478.00, f 00yr/ Z : :...... .........( : : W _...._.. '_� ' _..--- `-... TOTAL AREA , Q—RA TIO (TYP) � : i � : . .....t ;...._. ._.___ _.__._.. .......... ........... .......... ........ ..�ASSUMED)._.___ _._..... . i � .. ..,� , . . . _........ ._� . . . �- _ . . � f i.......: � ; TAIL WA TER ELE�A TJOIVS (TY:P) � � �� : � . � � v ; ....... ........... ...�..... ._.......: ....._..._ . . . . . ___._.... ..._...:_. : . . �...... ......: , ., ;; MANAGER: Ei ,...-- �------_ __....- •.......... .......... ..........:E.......... DES[GNED: ...... .......... ...... : � , _.... ......._.. ------ ----- --•--.. ....... .......... ....... ........_ _;._.,. , : ....... . .. . : ... ; . -, -----_- ->--._... ......{ i I - j CADD- � • • • . . , � CHECKED: j < ` ' ' ' ; DATE: . f � 1 j � � . ` SCai.E: HORIZ.� 1�150' � • • . � i VERT.: � ...... ........... .. } i . j ; i � � � . ' , I JOB NUMBER ; ; ,_..... ........, ........-- •9-�__. ._._-,.-. -------- ..�. _ � I ; r . . , . , , I 9�243 SHEET NUMBER 1 OF 1 Section VI : SPECIAL REPORTS AND STUDIES TECHNICAL INFOR1�tATlON REPORT FOR �VINDWOOD-PAGE 33 �� L SUBSURFACE EXPLORATION AND PRELIMINARY GEOTECH1vIICAL ENGINEERING REPORT , RIBERA 28 ACRE5 RENTON, WASHINGTON PREPARED FOR Centex Homes PROJECT NO. G95072A JLTNE 1995 � ASSOCIATED EARTH SCIENCES, INC 911 - 5th Avenue, Suite 100, Kirkland, WA 98033 (206) 827-7701 FAX (206) 827-5424 SUBSURFACE �XPLORATION AND PRELIMINARY GEOTECHNICAL ENGIN�ERING REPORT RIBERA 28 ACRES RENTON, WASHINGTON June 6, 1995 Project No. G95072A I. PROJECT AND SITE CONDITIONS 1.0 INTRODUCTION This report presents the results of our subsurface exploration and preliminary geotechnical engineering study for the proposed residential development of the Ribera 28 acres. Our geotechnical recommendations are preliminary in that building locations and construction details were not available at the time of our study. We understand that Centex wishes to purchase the property for the purpose of constructing single family residences. The location of the property is shown on the attached vicinity map, Figure 1. The approximate locations of the subsurface explorations accomplished for this study are shown on the site and exploration plan, Figure 2. In the event that any changes in the nature of the project are planned, the conclusions and recommendations contained in this report should be reviewed and modified, or verified, as necessary. 1.1 Purpose and Sc�e The purpose of this study was to provide subsurface data for the evaluation, design and construction of the future development of the Ribera project. The study included a review of available geologic literature, and the excavation of exploration pits to assess the type, thickness, distribution and physical properties of the subsurface sediments and shallow ground water conditions at the site. Geotechnical engineering studies were also conducted to determine the types of suitable foundations, floor support recommendations, allowable foundation soil bearing pressures, as well as structural fill, pavement and drainage considerations. This report offers development recommendations based on our understanding of the future development of the property. 1.2 Authorization Written authorization to proceed with this study was granted by Mr. Kevin Simmons of Centex Homes, in a proposal dated March 21, 1995. This report has been prepared for the exclusive use of Centex Homes and their agents, for specific application to this project. Within the limitations of scope, schedule and budget, our services have been performed in accordance with accepted geotechnical engineering and engineering geology practices in effect in this area. No other warranty, expressed or implied, is made. Our observations, findings, and opinions are a means to identify and reduce the inherent risks to the owner. 2.0 PROJECT AND SITE DFSCRIPTION This report was completed with an understanding of the project based on a site map dated May 4, 1995 prepared by Hugh G. Goldsmith and Associates, and a U.S. Geological Survey (USGS) topographic map of the Renton Quadrangle. The subject site was located along the north side � of SE 128th Street, between 148th Avenue SE and 152 Avenue SE in Renton, Washington. The property was rectangular in shape and measured 1925 feet north-south by 655 feet east-west, less a 337-foot by 125-foot parcel removed from the southwest corner of the site (Figure 2). The south side of the propeRy bordered SE 128th Street, the east side bordered pasture, and the west and north sides bordered undeveloped wooded land. A few residential homes were present along � the west central border of the site, and on the parcel at the southwest corner of the property. � An existing home, with sheds and a driveway to SE 128th Street, was rresent in the southeastern portion of the property. Two overhead power lines ran along the south side of the site. Outside of these features, the site was undeveloped. Most of the property was covered by dense stands of alder and cottonwood trees with a thick understory of brush, berry bushes, small saplings and ferns. Prior to our study, wetlands had been delineated in the northeastern and southwestern portions of the property. A crude dozer trail had been cut along most of the perimeter of the site, and overgrown logging trails were present in the central portion of the property. The overall site was relatively flat, bul ihe southwestern portion of the property sloped gently � down to the southwest. A poorly developed drainage swale, with less than 15 feet of relief ' drained to the south in the southwestern portion of the property. A south-flowing drainage ditch was also present along the west central boundary of the property, adjacent to the residential homes. Total topographic relief of the site was less than 25 feet. Development plans were not available at the time of our field study. 3.0 SUBSURFACE EXPLORATION Our field study consisted of excavating a series of 17 exploration pits, utilizing a track-mounted excavator. The pits permitted direct, visual observation of subsurface conditions. The materials encountered were studied and classified in the field by an engineering geologist from our firm. Selected samples were then transported to our laboratory for further visual classification and testing, as necessary. The exploration pits were backfilled immediately after examination and logging. The various types of sediments as well as the depths where characteristics of the sediments changed are indicated on the exploration logs presented in the Appendix. Our explorations were approximately located in the field by measuring from known site features shown on Figure 2. Because of the nature of exploratory work below ground, extrapolation of subsurface conditions between field explorations is necessary. It should be noted that differing subsurface conditions sometimes may be present due to the random nature of deposition and the alteration of topography by past grading and filling. The nature and extent of any variations between the field explorations may not become fully evident until construction. If variations are observed 2 at that time, it may be necessary to re-evaluate specific recommendations in this report and make appropriate changes. 4.0 SUBSURFACE CONDITIOI�IS Subsurface conditions were inferred from the exploration pits, and a visual reconnaissance of the site. This study identified dense glacial sediments at shallow depths across the property. In the area of the existing residence, fill soils (those not naturally placed) coutd also be present ! in drain field area(s) and utiliry trenches. The stratigraphy of the site is discussed in the following section followed by our observations of the hydrology of the site. 4.1 Strati rg, anhv Fill soils were not encountered in any of the exploration pits, but could to be present in the area of the existing residence. The developed area (home) is minor in total area and was not explored by this study. The quality, thickness and compaction of the fill materials may be variable and is undocumented. Therefore, if fill is encountered during construction at the site, it should be considered unsuitable for foundation support. At the surface across the site (beneath a 6-inch- to 2-foot-thick copsoil/organic zone) all 17 of the exploration pits encountered loose to medium dense, moist to wet, yellow brown, mottled, gravelly silty sand, interpreted as weathered till. This weathered zone extended to depths ranging from 2 feet in EP-2, EP-3, EP-7, EP-10, and EP-17, to 3-1/2 feet in EP-1 and EP-5. Beneath this mottled sediment, all of the exploration pits encountered dense, brownish gray, silty sand with gravel, interpreted as lodgement till. The lodgement till extended to below the 7- to 13-foot termination depths of all of the exploration pits. The lodgement till is highly consolidated sediment that was deposited at the sole of an advancing glacial ice sheet. In the Renton area the ice sheet reached an estimated thickness of 3,000 feet, during the Vashon Stade of the Fraser Glaciation about 15,000 years ago. As a result of glacial consolidation (by the weight of the ice), this material possesses high strength, low compressibility, and comparatively low permeability. 4.2 Hydrology No flowing water was observed at the site. Minor standing water was observed in areas mapped as wetland, and in the drainage swale in the southwestern portion of the site. Evidence of temporary standing water was also observed in dried mud puddles in a number of areas near the wetlands. We would expect that most, if not all of these puddles, are the result of precipitation perching atop the relatively impermeable till sediments. Light ground water seepage was encountered in about half of the exploration pits, at depths ranging from near the surface to about 3 feet deep. Moderate seepage was encountered from 2 to 4 feet in EP-10, from 0 to 2-1/2 feet in EP-11, and from 1 to 2-1/2 feet in EP-12. Rapid seepage was also present in a localized zone at 1-1/2 feet in EP-12. The seepages encountered occurred atop and within the mottled, weathered till zone. 3 Fluctuations in the level of the ground water, and subsequent seepage activity can be expected due to the time of the year and variations in rainfall. We would expect that nearly all of the seepage activity encountered is the result of on-site precipitation perching atop and within the weathered lodgement till. 4 June 6, 1995 Project No. G95072A II. PRELIMINARY DESIGN RECOMMENDATIONS 5.0 INTRODUCTION In our opinion, from a geotechnical standpoint, the site is suitable for a residential development, based on the site exploration and visual reconnaissance. A suitable foundation bearing stratum, consisting of lodgement till, occurs near the surface and will be capable of providing foundation support. Conventional spread footing foundations, slab-on-grade floors, and pavement subgrades, may be supported on the natural bearing sediments, or on structural fill that overlies natural bearing sediments. The contractor should understand that although the bearing stratum was relatively shallow in our exploration pits, areas exist that may contain loose soil. In addition, filled areas may be encountered in the vicinity of the existing residence, utility trenches, or drain fields. These areas may require deepened footings or removal and replacement of the loose soil or fill material with structural fill prior to placing foundations. � We should further emphasize that the site is underlain by fine-grained, moisture sensitive soils, which were at or above their optimum moisture content for use as structural fill. Therefore, the � use of the onsite lodgement till soil as structural fill should be limited to the drier times of the year. 6.0 SITE PREPARATION Site preparation of planned building and road/parking areas should include removal of all trees, brush, debris and any other deleterious material. Additionally, the upper organic topsoil should be removed and the remaining roots grubbed. Areas where loose surficial soils exist should be considered as fill and this material should either removed and replaced with structural fill or recompacted. Since the density of soils is variable, random soft/loose pockets may exist, and the depth and extent of stripping can best be determined in the field by the field engineer. Site preparation will also include the demolition of the existing structure. The debris from this operation should be taken to an offsite disposal area and any resulting depression, if beneath a building or road area, should be replaced with structural fill. Existing septic tank(s) should also be removed, and the resultant depression replaced with structural fill. All other areas where loose surf'icial soils exist should be considered as fill and this material should either removed and replaced with structural fill or recompacted to the specified project densities. 5 7.0 STRUCTURAL FILL All fill should be placed in accordance with the recommendations outlined in this section. Prior to filling, topsoil, organics, and loose soils should be excavated from the subgrade as advised by the field engineer. After overexcavation/stripping has been performed to the satisfaction of the geotechnical engineer, the upper 12 inches of exposed ground should be recompacted to at least 90 percent of the modified Proctor maximum density using ASTM:D 1557 as the standard. After recompaction of the exposed ground is tested and approved, structural fill may be placed to attain desired grades. Structural fill is defined as non-organic soil, acceptable to the geotechnical engineer, placed in maximum 8-inch loose lifts with each lift being compacted to 95 percent of the modified Proctor maximum density using ASTM:D 1557 as the standard. The contractor should note that any proposed fill soils must be evaluated by Associated Earth Sciences, Inc. prior to their use in fills. This would require that we have a sample of the material 48 hours in advance to perform a Proctor test and determine its �eld compaction standard. The onsite lodgement till soils contain a significant amount of fine-grained material (smaller than No. 200 sieve) and are considered extremely moisture-sensitive. Use of moisture- sensitive soil in structural fills should be limited to favorable dry weather conditions. If fill is placed during wet weather or if proper compaction cannot be obtained, clean, free-draining gravel and/or sand should be used. Free-draining fill consists of non-organic soil with the amount of fine-grained material limited to 5 percent by weight when measured on the minus No. 4 sieve fraction. A representative from our firm should inspect the stripped subgrade and be present during placement of structural fill to observe the work and perform a representative number of in-place density tests. In this way, the adequacy of the earthwork may be evaluated as filling progresses and any problem areas may be corrected at that time. It is important to understand that taking random compaction tests on a part-time basis will not assure uniformity or acceptable performance of a fill. As such, we are available to aid the owner in developing a suitable monitoring and testing program. 8.0 FOUNDATIONS Spread footings may be used for building support when founded on the medium dense to dense natural glacial sediments, or approved structural �11 (including recompacted natural soils). For building support, structural fill and recompacted natural soils should be compacted to a minimum of 95 percent of the maximum dry density as defined by ASTM:D 1557. Structural fill placement must be inspected by Associated Earth Sciences, Inc. to verify suitable subgrade preparation and compaction. We recommend that an allowable bearing pressure of 2,000 pounds per square foot (ps� be utilized for design of residence footings, including both dead and live loads. An increase of one- third may be used for short-term wind or seismic loading. Perimeter footings should be buried at least 18 inches into the surrounding soil for frost protection; interior footings require only 12 inches burial. However, all footings must penetrate to the prescribed lodgement till bearing stratum and no footing should be founded in or above loose, organic, or existing fill soils. 6 9.0 FLOOR SUPPORT Slab-on-grade floors may be placed over the medium dense to dense natural sediments or approved structural fill. In either case, the upper 12 inches of subgrade must be compacted to a minimum of 90 percent of the modified Proctor maximum density as determined by ASTM:D 1557. A polyethylene plastic vapor barrier and pea gravel capillary break layer should be used under floors likely to receive an impermeable floor finish or where passage of water vapor through the floor is undesirable. Based on American Concrete Institute recommendations, we suggest placing a two to three inch layer of clean sand over the vapor barrier to protect the vapor barrier and to allow some moisture loss through the bottom of the slab to aid in the curing process. Sand should be used to aid in the fine grading process of the subgrade [o provide uniform support under the slab. 10.0 DRAINAGE CONSIDERATIONS At the site, the lodgement till sediments are near the surface. These sediments contain a significant amount of fine grained material, and are considered moisture sensitive. Because the till is relatively impermeable, water will tend to perch atop tliis stratum. Traffic across the till sediments when they are damp or wet will result in disturbance of the otherwise firm stratum. Therefore, prior to site work and construction, the contractor should be prepared to provide drainage and subgrade protection as necessary. All retaining and perimeter footing walls should be provided with a drain at the footing elevation. Drains should consist of rigid, perforated, PVC pipe surrounded by washed pea gravel. The level of the perforations in the pipe should be set approximately 2 inches below the bottom of the footing and the drains should be constructed with sufficient gradient to allow gravity discharge away from the buildings. In addition, retaining walls should be lined with a minimum 12 inch thick washed gravel blanket provided over the full-height of the wall, and which ties into the footing drain. Roof and surface ' runoff should not discharge into the footing drain systems but should be handled by a separate, rigid tightline drains. Because the site does not contain free-draining soils, exterior grades adjacent to walls must be designed to slope downward away from the structures to achieve positive surface drainage. 11.0 PAVEMENT CONSIDERATIONS Areas to be paved should be compacted to a firm, unyielding condition to a minimum of 95 percent of the modified Proctor maximum density using ASTM:D 1557 as the standard. The subgrade surfaces should be slightly crowned to drain to the edges of the paved areas. After compaction, the subgrade should be proof-rolled with a fully loaded, tandem axle dump truck to identify any soft or "pumping" areas. If such areas are observed, they should be overexcavated and back�lled with compacted, free-draining, granular material. Upon completion of the subgrade preparation the leveling course and surface pavement may be placed. The appropriate pavement section will be determined by the anticipated traffic loads and 7 desired pavement life. The pavement base leveling course material should be compacted to 95 percent of Maximum Density as defined by ASTM:D 1557. 12.0 PROJECT DESIGN AND CONSTRUCTION MONITORING At the time of this report, site grading, structural plans, and construction methods have not been completed. We are available to provide additional geotechnical consultation as the project design develops and possibly changes from that upon which this report is based. We recommend that Associated Earth Sciences, Inc., perform a geotechnical review of the plans prior to final design completion. In this way, our earthwork and foundation recommendations may be properly interpreted and implemented in the design. We are also available to provide geotechnical engineering and monitoring services during construction. The integrity of the foundations depends on proper site preparation and construction procedures. In addition, engineering decisions may have to be made in the field in the event that variations in subsurface conditions become apparent. Construction monitoring services are not part of this current scope of work. If these services are desired, please let us know and we will prepare a cost proposal. We have enjoyed working with you on this study and are confident that these recommendations will aid in the successful completion of your project. If you should have any questions, or require further assistance, please do not hesitate to call. Sincerely, ASSOCIATED EARTH SCIENCES, INC. Kirkland, Washington vG� �L YT 4- oF w.�syi . O � _ � �� . �. c George . Bennett, C.P.G. f �- E��yS Engineering Geologist �`` y�"�� - �� 26800 � �G RFG/S7'E�� , � SS�Q`,��"v ExPiaES S yE 1 � �.. .A. Parker, P.G. Bruce L. Blyton, P.E. Principal Senior Engineer GHB/Icpp G9S072A.l WP.6/I/95 Id 8 ML � 1i -- i:� I �90Qi_-� ca � --,i.�"`�u ke�' 1 r. 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I 36 . � I � ,'� I - ; ),I : ;�''� � '✓%._ r i 3t� -T' `�: � %'��'� � i � �^ F� l:� ,T, � � o�nagton / ` � �i' _! � '_6 � 1, -i�' , `' ( / '' , �- (" -- � Me edith "'�'�- � r�. � ( �. nr, T:— /i _ . — •� . � �� , - r r � �, : � � > �r_ � i ,�' i ' I_ . � �'� _ 1 .z.. I � �f I � i - �ti�lYl� REFERENCE: U.S.G.S. 1:100,000 SCALE METPoC TOPOGRAPHIC-BATHYMETRIC MAP 30 X 60 MMUTE QUADRANGLE 'TACOMA, WASHINGTON'. VICINITY MAP NORTH A880CIATED RIBERA - 28 ACRES EARTH RENTON, WASHINGTON S C 1 E N C E 8, I N C G95072A 5/95 FIGURE 1 EP-9 ;-- -- • EP-a0..—�. '�� WETLAND�'B' ' , � �...�, . ' EP-8 -_' S E�F��. ■ �� / WETLANO �A"J r � EP-13 �' , • ' EP-7 EP-12 �� • ■ � EP-15 ■ EP-14 EP-6 ■ � ■ �weruanro ro• .� �` EP-�6 �WETLAND'E' EP-5{ � ..-- EP-17 ■ � .�� • � . �-�--� : �'`:.J�; : '1NETLAND F _ ,,.� � i EP-4 EP-1 ~ EP-3 � • EP-2 ■ SE 128fh Sf. LEGEND NORTH � Approxknate Iocation of exploration pit 0 300 600 SCALE IN FEET SITE AND EXPLORATION PLAN RIBERA - 28 ACRES A680CIATED EARTH RENTON, WASHINGTON 8 C 1 E N C E 8, I N C G95072A 5/95 FIGURE 2 EXPLORATION P IT LOG p _Number EP-1 _ 1"Topsoil and oxidized zone. - Medium dense to dense, moist, yellow-brown, mottled, gravelly, silty SAND. (Weathered Lodgement Till) 5 _ Very dense, moist, brown-gray, gravelly, silty SAND. (Lodgement Till) 10 BOH @ 8-1/2' — Note: Light seepage at 3-1/2; no caving. Terminated due to hard digging. 15 i - � p Number EP-2 I� 6"Topsoil. Loose, moist, dark yellow-brown, gravelly, silty, fine SAND. (Weathered Lodgement Till) Dense, moist, brown-gray, mottled on top 1-1/2', gravelly, silty SAND. (Lodgement Till) 5 _ BOH @ 8' 10 Note: Very light seepage at 3-1/2'; no caving. 15 SubsuAace co�ditions depicted represent our observation at the time and locafio�oi lhis exploratory hole,modified by geologic interpretation,engineering analysis,a�d judgment. They are not necessarily representative of other times and locatio�. We wdI not accept responsibility for the use a interpretation by others d informatio�presenled on this log. Reviewed By � . � �ssociated Earth Sciences, inc. Ribera - 28 Acres :;11 Fifth Avenue, Suite 100 Renton, Washington Kirkland, Washington 98033 Pro ect No. G95072A Phone: 206-827-7701 � Fax: 206-827-5424 M ay 1995 EXPLORATION PIT LOG � _Number EP-3 6"Topsoil. - Loose to medium dense, moist, yellow-brown, mottled, gravelly, silty SAND. (Weathe�ed Lodgement Till) Dense, moist, brown-gray, gravelly, silty SAND. (Lodgement Till) 5 _ BOH@8' 10 _ Note: No seepage; no caving. Terminated due to hard digging. 15 o Number EP-4 6"Topsoil. - Loose, moist, dark yellow-brown, gravelly, silty SAND with many roots. (Weathered Lodgement Till) I 5 - Dense to very dense, moist, brown-gray, mottled to 4', gravelly, silty SAND_ (Lodgement Till) 10 BOH @ 12' - Note: Very light local seepage 4'to 6'; no caving. Terminated due to very hard digging. 15 Subsurface cond'Aions depicted represent our observation at the time and bcation of this exploratory hole,modified by peolopic interpretation,engineering analysis,and judgment. They ere not necessarily representative oi other times and location. We will not accepl responsibility for the use or interpretation by others of iniortnation presented o�this log. Reviewed By � , �ssociated Earth Sciences, �n�. Ribera - 28 Acres ��11 Fifth Avenue, suite �oo Renton, Washington Kirkland, Washington 98033 Project No. G95072A Phone: 206-827-7701 Fax: 206-827-5424 M ay 1995 EXPLORATION PIT L4G � _Number EP-5 i - 8"Topsoil/root zone. Loose to medium dense, moist, dark yellow-brown, gravelly, silty, fine SAND with many roots. (Weathered - Lod ement Till 5 _ Dense to very dense, moist, brown-gray, gravelly, silty SAND. (Lodgement Till) _ BOH @ 8' � 10 Note: No seepage; no caving. ' 15 � Number EP-6 Black topsoil. - Soft/loose, wet to saturated, yellow-brown, gravelly sandy SILT to silty SAND. (Weathered Lodgement Till) 5 Dense, moist to wet, brown-gray, gravelly, sitty SAND. (Lodgement Till) 10 BOH @ 10' Note: Light seepage throughout 1'to 3'; no caving; light sloughing at seepages. 15 Subsuriace condAions depicted represent our observatan at the time end location o(this exploratory hole,modified by gedopic interpretation,engineering a�alysis,and judgment. They are not necessarily representative of ottxr times and location. We will not accept responsibility for the use or interpretation by others M i�(ortnation presented on this log. Reviewed By � � �,ssociated Earth Sciences, �n�. Ribera - 28 Acres �11 Fifth Avenue, suite �oo Renton, Washington Kirkland, Washington 98033 Project No. G95072A Phone: 206-827-7701 Fax: 206-827-5424 May 1995 EXPLORATION PIT L�G � Number EP-7 6"Topsoil. - Loose, moist, dark yellow-brown, gravelly, silty, fine SAND, many roots. Loose to medium dense, moist yellow-brown, mottled, gravelly, silty SAND. (Weathered Lodgement Till) 5 _ Dense, moist, brown-gray, gravelly, silty SAND. (Lodgement Till) BOH @ S' 10 _ Note: No seepage; no caving. 15 � Number EP-8 10"Topsoil/root zone. - Loose to medium dense, moist, yellow-brown, mottled, gravelly, silty SAND. (Weathered Lodgement Till) 5 — Dense, moist, brown-gray, gravelly, silty SAND. (Lodgement Till) 10 BOH @ 9' Note: Very light local seepage at 2-1/2'; no caving. 15 _ Subsu�tace cond'Aions depicted represent our observatan at the time and location of this exploretory hde,modified by yedogic interpretalion,engineering anaysis,and judgment. They are nol necessarily representative of other times and location. We will not accept responsibility for the use or interpretation by others of information presented on this log. Reviewed By � Associated Earth Sciences, �nc. Ribera - 28 Acres �11 Fifth Avenue, suite �oo Renton, Washington Kirkland, Washington 98033 Project No. G95072A Phone: 206-827-7701 Fax: 206-827-5424 May 1995 EXPLORATION P IT LOG � Number EP-9 6"Topsoil. - Loose, moist, dark yellow-brown, silty, fine SAND, some gravel, roots. - Medium dense, moist, light yellow-brown, mottled, gravelly, silty SAND. (Weathered Lodgement Till) 5 __ Dense to very dense, moist, brown-gray, gravelly, silty SAND. (Lodgement Till) 10 BOH @ 8-1/2' — Note: No seepage; no caving. 15 � _ Number EP-10 _ _ Soft, saturated, dark gray, organic rich, silty, fine SAND, some gravel. 5 _ Dense, moist to wet, light brown-gray, mottled to 4', gravelly, silty SAND. (Lodgement Till) - BOH @ 8' 10 _ Note: Light to moderate seepage 0-4'throughout; light sloughing at seepages, no caving. 15 — SubsuRace cond'Aions depicted represent our observation at the time a�d bcation oi this exploratory hole,modified by pedogic inlerpretation,engineering analysis,and judgment. They are not necessarily representative of other times and bcation. We will not accept responsibility for the use or interpretation 6y others of intortnation presented on this log Reviewed By � . �ssociated Earth Sciences, �nc. Ribera - 28 Acres ';11 Fifth Avenue, Suite 100 Renton, Washington Kirkland, Washington 98033 Project No. G95072A Phone: 2o6-s27-7701 Ma 1995 Fax: 206-827-5424 y EXPLORATION PIT L�G p _Number EP-11 Topsoil/muck. Loose to medium dense, saturated, light yellow-brown, gravelly, silty SAND. (Weathered Lodgement Till) Dense to very dense, moist to wet, brown-gray, gravelly, silty SAND. (Lodgement Till) � 5 _ _ BOH@7' Note: Rapid local seepage piping at 1-1/2'; moderate seepage 0 to 2-1/2'; some caving 0 to 2-/12'at - seepages. 10 15 p Number EP-12 Topsoil/muck. Loose to medium dense, saturated, yellow-brown, mottled, gravelly, silty SAND. (Weathered Lodgement Till) 5 _ _ Dense to very dense, moist to wet, gray, gravelly, silty SAND. (Lodgement Till) 10 15 _ BOH@13' Note: Light to moderate seepage 1'to 2-1/2'throughout; no caving. Very hard digging. Subsur(ace co�d"Rions depided represent our observation at the time and location of this exploratory hole,modified by geolopic interpretation,engineeri�g anaysis,and judgment. They are not necessarily representative oi other times end location. We witl not accepl responsib8iry for the use or interpretation by others oi iniormation presented on this log. Reviewed By (�,� •�r7�• � ^�sociated Earth Sciences, �nc. Ribera - 28 Acres �11 Fifth Avenue, suite �oo Renton, Washington Kirkland, Washington 98033 Project No. G95072A Phone: 20fi-827-7701 Fax: 206-827-5424 May 1995 EXPL4RATION PIT LOG � _ Number EP-13 _ 6"Topsoil. Loose to medium dense, moist, dark yellow-brown, silty, fine SAND with some gravel, many roots. (Weathered - Lodqement Till) 5 _ Dense to very dense, moist, brown-gray, gravelly, silty SAND. (Lodgement Till) BOH@7' _ Note: No seepage; no caving. Very hard digging. 10 _ 15 o Number EP-14 8"Topsoil. Loose to medium dense, moist, yellow-brown, mottled, gravelly, silty SAND. (Weathered Lodgement Till) 5 _ Dense to very dense, moist, brown-gray, gravelly, silty SAND. (Lodgement Till) BOH @ 7' - Note: No seepage; no caving. 10 15 _ SubsuAace cond'Aions depicted represent our observatan at the time and location of this exploratory hde,modified by geologic iMerpretation,enginee�ng analysis,and judgment. They ere nol necessarily representative o(other times and locatan. We will not accept responsibility for the use or interpretation by others of i�famation presented o�this log. Reviewed By � . "-.�sociated Earth Sciences, inc. Ribera - 28 Acres �11 Fifth Avenue, Suite 100 Renton, Washington Kirkland, Washington 98033 Project No. G95072A Phone: 206-827-7701 Fax: 206-827-5424 May 1995 EXPLORATION P IT LOG � o _Number EP-15 10"Topsoil/root zone. - Loose to medium dense, moist, yellow-brown, mottled, gravelly, silty SAND. (Weathered Lodgement Till) 5 _ Dense to very dense, moist to wet, gray, gravelly, silty SAND. (Lodgement Till) _ BOH @ 8' �p _ Note: No seepage; no caving. 15 o Number EP-16 10"TopsoiUroot zone. - Loose to medium dense, moist to wet,yellow-brown, mottled, gravelly, silty SAND. (Weathered Lodgement Till) ' Dense to very dense, moist to wet, gray, gravelly, silty SAND. (Lodgement Till) BOH @ 8' - Note: No seepage; no caving. 10 _ 15 _ Subsuriace conditions deqcted represent our observation at 1he lime and location of this enploratory hole,modified by geolopic interpretalion,engineering analysis,and judgment. They are not necessarily representative oi other times and locatan. We will nof accept responsibility lor the use or interpretalion by others o(infortnation presented on this log Reviewed By � �.ssociated Earth Sciences, inc. Ribera - 28 Acres 911 Fifth Avenue, suite �oo Renton, Washington Kirkland, Washington 98033 Pro ect No. G95072A Phone: 206-827-7701 � Fax: 206-827-5424 May 1995 EXPL�RATION PIT LOG � _Number EP-17 3"Sod/topsoil. - Loose to medium dense, moist, yellow-brown, mottled, gravelly, silty SAND. (Weathered Lodgement Till) 5 _ Very dense, moist, brown-gray, gravelly, silty SAND. (Lodgement Till) , _ BOH @ 8' '� 10 Note: No seepage; no caving. 15 _ � Number 5 10 _ 15 _ Subsurface cond'Rions depicted represent our observation at the time end location of this exploratory hole,modified by gedogic interpretation,engineering analysis,and judgment. They are not necessarily representative oi other times and location. We will not accept responsibility for the use or interpretation by others of infortnation presented o�this log. Reviewed By � qssociated Earth Sciences, �nc. Ribera - 28 Acres 911 Fifth Avenue, suite 10o Renton, Washington Kirkland, Washington 98033 Project No. G95072A Phone: 206-827-7701 Fax: 206-827-5424 May 1995 Section VII: BASIN AND COMMUNITY PLANNING AREAS TECHNICAL INFORNtATION REPORT FOR ��'IND�i'OOD-PAGE 34 l;edar Kiver Ylan Jummary, iting �.ounty Yage 1 ot i � King Caunty, Washi ngton . . � ��i.�fi..- �Department of Natiural Resources . WaferQnd Land Resources Division Lower Cedar River Basin Plan Summary Contents: • Introduction . The Basin Planning Area • Problems In The Cedar Basin • O�portunities In The Cedar Basin • What has Already Been Done? • Incentives for Forest Protection • Main Recommendations of the Cedar River Plan • Next Steps • Map of Lower Cedar River features (64k) Introduction The Lower Cedar River Basin and Nonpoint Pollution Action Plan describes current conditions in the basin and proposes solutions to the problems of flooding, property damage and declining salmon and steelhead runs. It also recommends preventive measures to protect and maintain water quality, groundwater supplies and habitat as the basin planning area continues to develop. Preventing problems in the watershed is much more cost- effective in the long term than trying to correct problems once they occur. The recommendations in the Cedar River Basin Plan have been prioritized into a Core Plan that identifies key capital projects and ongoing programs that would, at a minimum, accomplish the Plan's most important goals. This Core Plan would: . Resolve the threat of hazardous flooding for approximately 90 percent of the 130 homes currently a' greatest risk; . Protect the most valuable remaining aquatic habitat sites in the basin planning area, restore those w�.�, the best chance for recovery, and ensure long term productivity of Cedar River salmon and steelhead; and . Maintain the Cedar River's high water quality. The Cedar River Basin Plan presents a unique opportunity and challenge to allow for urban development and to support rural industry and lifestyles,while providing for reduced flood damages, long term salmon and steelhead runs, and high water quality. The Cedar River Basin Plan combines a traditional King County Basin Plan,jointly funded by King County and the City of Renton,with a Nonpoint Source Pollution Action Plan partially funded by the Washington Department of Ecology. The Plan was prepared under the policy direction of the Watershed Management Committee composed of key tribal, state and local government agencies and non-governmental organizations and a Citizens Advisory Committee, made up of area residents. King County's Surface Water Management Division acted as lead in plan preparation. http:l/splash.metrokc.gov/wlr/basins/cedarpin.htm 12/31/98 C;edar K�ver t'lan Jummary, King l;ounty Yage L ot i The Basin Planning Area The Cedar River is one of five major rivers in King County and is the largest tributary to Lake Washington. The river drains an elongated basin of 188 square miles that extends westward from the crest of the Cascades to the southern shore of Lake Washington in the City of Renton. The upper basin, i«,�d,�P which is almost exclusively owned by the City of Seattle, supplies drinking , � - � water for two-thirds of the City of Seattle and its regional customers. It is an ,�:t � unpopulated mountainous area protected from land use change and ��' �'�4`=:�� managed for water quality protection, long term forestry and wildlife habitat. —�<.::�.:��s The Cedar River Basin Plan focuses on the lower third of the basin, where floods and erosion directly impact people and property and where ongoing development threatens fish habitat and the quality and quantity of ground and surface waters. The basin planning area extends from the Landsburg Dam to the river mouth in Renton, a 66 square mile area encompassing both the northem and southern plateaus and the mainstem valley. The lower basin has an extensive water system that includes 15 named tributaries, many high-vafue wetlands, lakes, aquifers and the Cedar River itself. Land uses in the lower basin range from the Renton urban center to adjacent suburbanizing areas to rural and forest zones to the east. The basin planning area is home to a growing population estimated at 55,400 in 1990 and projected to be 93,000 by 2010. Problems In The Cedar Basin ' Flood Hazards During major storms, over 300 homes along the Cedar River are exposed to mainstem flooding. - Y More than 100 of these homes are subject to life- ' threatening flood flows and evacuation routes for - _ .�.��3 - many other homes are impassable. Commercial �r� losses in downtown Renton, especially at the .- ` Renton Munici al Air ort and Boein facilit near _ . J P P 9 Y .�;:. the mouth of the Cedar, have been substantial. �="'''= � , Damage estimates from the November 1990 `} . flood exceeded $11 million. During the November � � .,.�,��.��'~y��,.,� 1995 flood approximately 90 homes and 39 ` •'�E��;:`__ ublic facilities were dama ed. The ublic �� }� '? P 9 P "�-�.�;-�`�:�`: �� facilities damage was estimated at $800,000. Declining Salmon and Steelhead Runs The Cedar River posted a record run of sockeye in 1988, the largest in the contiguous United States. However, natural runs of Lake Washington sockeye, coho, and chinook salmon and steelhead trout have been severely depressed in recent years. The reasons for the declines are not fully understood and vary by species. While the specific reasons for the recent decline remain a topic of study and discussion, it is clear that protection and restoration of the Cedar's aquatic habitat must be a key element in both the recovery and the long term sustainability of salmon and steelhead runs in the Lake Washington system. httpJ/splash.metrokc.�ov/wlr;'basins!cedarpin.htm ]2/31/98 C:edar K�ver Ylan 5ummary, K�ng �;ounty Yage 3 ot 7 Opportunities In The Cedar Basin The Cedar River Basin Plan presents a unique opportunity and challenge to allow for urban development and to support rural industry and lifestyles,while providing for reduced flood damages, long term salmon and steelhead runs, and high water quality. Valuable Aquatic Habitat The Cedar River and its tributaries still contain much of the best remaining aquatic habitat in the Lake Washington system. This basin offers an excellent opportunity to protect and restore high quality habitat while reducing flooding costs, enhancing recreation and scenic values, and protecting water quality. High Water Quality Based on measured data and biological use of the Cedar River, the water quality in the river is generally very good. However, there are some problems, such as sporadic exceedances of the state water quality standard fo�fecal coliform bacteria generated by livestock and failing septic tanks. Also, the urbanized tributaries- Ginger, Maplewood, Molasses and Madsen Creeks-show signs of declining water quality. The Cedar River is the largest and cleanest source of water for Lake Washington, contributing almost 50% of the lake's total inflow. The future of Lake Washington may depend on the Cedar River's flows remaining clean. Typically as river basins become more developed, their phosphorus loadings and other water quality problems increase; this is already occurring in the Cedar River's more urbanized tributaries. Basin residents have the opportunity to correct existing water quality problems in the basin and take preventive steps to reduce the impacts of new development on the water qualiry of the Cedar River and Lake Washington. Important Groundwater Source The basin planning area is an important regional groundwater source.The City of Renton depends on a sole- source aquifer that lies within the rapidly developing basin planning area. In addition, the City of Kent relies on a shallow groundwater source in the Rock Creek subarea for the majority of its municipal water. There are numerous small public and private wells scattered throughout the rural portion of the basin. Future development in the basin planning area may affect the quality and quantity of groundwater available for water supply as well as the amount available to sustain summer base flows to high value wetland and creek habitats. The development that has already occurred in the basin planning area is estimated to have reduced groundwater recharge by 5-10%. It has been well documented by studies in the basin and throughout the country that conversion of forested land to residential, commercial, agricultural and industrial uses reduces groundwater recharge and generates pollutants that can contaminate aquifers. Preventive measures are recommended to reduce the impacts of future development on groundwater quantity and quality. What Has Already Been Done? The Cedar R�v�� - _ �� . . _ accomplishec'. • Elliot Levee Keconstructed - to re-esta��ish t�ood protection an,_ ' � � . Ricardi Buyout-two homes repeatedly damaged by floods were ; : . � . � � floodplain • Madsen Creek Stabilized-a severely eroded ravine that threate � .. � was stabilized . Acquisition of Rock Creek Parcel -98 acres of the highest quality salmonid habitat among the Ce (;edar River Ylan Summary, K�ng (:ounty Yage a oT / • Construction of Spawning Channel-a groundwater fed sockeye spawning channei was const�ucted in conjunction with the Elliot Levee improvement . Lake Washington Studies and Fry Trapping - important ecological investigations being conducted to increase understanding of sockeye needs and population dynamics As called for in the Plan, a group of citizens,tribal and govemment officials started meeting in 1995 to discuss the best ways for government and the community to work together on management of the Cedar River watershed. This Cedar River Watershed Council plans to prioritize spending on Cedar River projects, provide a forum to discuss watershed issues and to coordinate the actions of agencies and public and private interest groups. The Cedar River Basin Steward has also been at work in the basin since 1994, responding to citizen inquiries conceming their watershed, organizing watershed improvement projects and education opportunities and assisting the Cedar River Watershed Council. Volunteers have taken part in numerous small-scale projects that address habitat,water quality,and drainage concems. Partnerships between businesses,civic groups, landowners, schools and local govemment have evolved from some of these projects as a way to protect and restore key areas of the Cedar River. Examples of whaYs been done: • Sand and sand bags delivered to Taylor Creek residents for flood relief by the Basin Steward. . Drainage and flooding concerns addressed at the Lake Desire outlet channel through beaver trapping, debris removal and channel maintenance. • More than 1,000 trees have been planted at Cavanaugh Pond, through the efforts of local residents, service clubs and the Boeing Company. • The Tahoma School DisUict has adopted the new Rock Creek property and is assisting in establishing use and stewardship guidelines for Rock Creek. . The Renton Fish and Game Club monitors Cavanaugh Pond with sponsorship by US West. . Maple Valley Rotary has taken the lead in creating a new riverside park and collaborating with the Tahoma School District for on-site educational opportunities. • Public/private partnership formed to allow annual fish counts and habitat improvements to be done on private property. ' Incentives for Forest Protection ' One of the important goals of the Cedar River Basin Plan is to encourage as much forest cover •,:- . '�.# as possible because it is the best way to ensure �,r��_;;��: , - that the Cedar has clean, stable streams. The � � 'Y �* `-. idea is not to discourage harvesting of �y'''�``�� M-+�� :_ .L �= marketable timber, but to encourage replanting of �� ---_��,�'�,-�: trees after harvesting so the land stays in forest _ - - -- .��, , use over the long term rather than being �,_ �: converted to other uses. Retaining land in forest j� ,� will also protect the quality and quantity of groundwater in the basin, and reduce tributary flooding, erosion, sedimentation and water quality degradation. The initial draft Cedar River Basin Plan called for regulations to meet this goal. This proposal raised concerns from rural residents who feel they are being over-regulated. Staff from King County Surface Water Management met with those concerned about the proposed regulations and with their input crafted an alternative package of incentives to help land owners keep their land in forest use. http://splash.metrokc.gov!wlr/basins!cedarpin.htm 12/31!98 Cedar Kiver Ylan Summary, King County Yage � of 7 By offering this incentive package for retaining forest rather than the previously proposed regulations, King County is challenging the basin community to work in partnership with the County and their neighbors to ensure that this incentive package works.After five years the incentive approach will be evaluated by the Cedar River Watershed Council to see if it is effectively meeting the goal of retaining long-term forest uses and thereby maintaining clean, stable streams in the Cedar basin. The following incentives for�etaining land in forest uses are in the new draft Cedar River Basin Plan: . Tax Relief-Assistance in preparing applications for Timber Land and Public Benefit Rating System tax relief programs and modifying the Public Benefit Rating System to give extra points for forest retention. • Direct Assistance- New forester position to provide technical and tax reduction program information and assist with management plans and site restoration. . Stewardship Classes and Master Forester Program - Offer more low cost forestry classes to help landowners develop their own forest management plan. Develop a program similar to"master gardener" program in which participants learn forest practices then commit to share their knowledge with others. • Demonstration Site-Develop a working forest demonstration site where landowners can see forest practices and economics first hand. . Simplified Permit Processing -Streamline county clearing permit process for landowners with approved forest management plans. Main Recommendations of the Cedar River Plan Flood Damage Reduction The principal flood damage reduction goals of this plan are to eliminate the worst risks that flooding poses to human life and to reduce economic and property damage caused by flooding. Most of the recommended flood damage reduction effo�ts are focused along the Cedar River mainstem rather than in the tributaries because the most severe risks to both human safety and property are located there. Recommendations are designed to lower flood risks and damages,while reducing the Iong-term costs of flood damage and minimizing environmental impacts (consistent with the countywide Flood Hazard Reduction Plan). Key Recommendations: . Voluntary Purchase and Removal of Approximately 112 Residences at 12 locations along the mainstem to reduce flood damage and danger to residents where the most hazardous flood flows occur. . Provide Technical Assistance and Limited Financial Assistance to help floodplain residents and responsible agencies reduce flood damages in the less hazardous areas and improve flood emergency communications. . Study Masonry Dam Operations to determine the feasibility of improving mainstem flood control at the dam. To be done cooperatively by King County, the City of Seattle, the Ciry of Renton and the Muckleshoot Indian Tribe. . Improve Drainage Structures to Reduce Flood Damages along the Tributaries, particula�ly along Taylor Creek, at Lake Desire, and the East Fork of Maplewood Creek. . Re-establish Channel Capacity of the Renton Reach to 100 year flood discharge in order to reduce flood damages. . Modify Levees and Revetments in selected areas to reduce public maintenance costs, restore natural flood storage and help reduce flood damage system-wide. Aquatic Habitat The principal habitat goals of the Plan are to protect and restore stream and wetland habitats critical to the Cedar River's salmon and steelhead runs and to reduce surface water management costs by preserving and http://splash.metrokc.gov/wlr/basins%cedarpin.htm 12/31/98 C:edar K�ver Ylan Jummary, King l.ounty Yage b oi i restoring the overall ecological health of the Cedar/Lake Washington system. Key Recommendations: . Purchase Critical Habitat Sites at 13 mainstem and 11 tributary sites as part of the King County Open Space Program. Tt �► �` � . Restore and Enhance Aquatic Habitat at L�'=�w;=Y�.=:'.�,� f+ �` '�p"i � �, - � 70 mainstem and 14 tributary sites with ,�`,�;��- "�r�� - _�� ..:.�, .�,,��— ,� volunteer labor recruited forthe smaller :�'��`�°�=-•�===��:"' IW�-�r►. ...,,.x,�,- :..��.. ,,rt •-. scale, labor intensive projects. �;,�;. .�`--�.�'T.�:�`'-=' - r �-- . Continue Temporary Sockeye Salmon , �� ^ Hatchery Production and Lake ""' -� �� ` Washington Study to sustain the existing sockeye salmon runs and determine the causes of salmonid declines in the Lake � � Washington system so that long term solutions can be implemented. . Protect Five Regionally Significant Wetlands by requiring expanded buffers, forest retention, retention/detention ponds, infiltration, and seasonal clearing limits in the catchment areas of these wetlands in order to minimize the adverse impacts of future development. (See map on pages 6-7). • Promote Existing Mitigation Bank Program to allow public agencies to fulfill their mitigation obligations for projects such as road widening in large, high quality, off-site mitigation bank sites within the basin,where this mitigation would be more functional than traditional on-site mitigation projects. • Restore Rock Creek Base Flows to address the low flow problems that limit fish use of the lower 1.7 miles of this otherwise high quality habitat by developing a low flow augmentation program with the City of Kent. Water Quality and Groundwater Protection The primary water quality goal of this Plan is to maintain the generally high surFace water and groundwater quality in the basin. These�ecommendations address the basin's most significant water quality problems: total phosphorus loadings into Lake Washington, locally toxic concentrations of urban pollutants, high fecal colifoRn counts, and localized sediment problems. Priority is given to reducing sources of pollution where feasible rather than implementing costly treatment measures. Several recommendations in the Cedar River Basin Plan help protect groundwater quantity and quality while also reducing erosion, phosphorus loadings,tributary flooding, and damage to aquatic resources. Key Recommendations: • Enhance Stormwater Control Measures for New Development by implementing proposed updates to the King County Surface Water Design Manual to reduce surface water n.inoff, treat pollutants and maintain groundwater recharge. . Reduce Sources of Fecal Coliform Bacteria through increased technical assistance to septic tank owners and livestock owners. . Treat Toxic Runoff from existing roads and commercial and residential areas. • Promote Forest Retention using incentives for landowners to keep their land in forest uses such as tax relief and increased technical assistance. . Promote Shared Stormwater Treatment Facilities in the urban areas to minimize costs and land area http://splash.metrokc.gov/wlr/basins/cedarpin.htm 12/31/98 l,eclar x�ver rian �ummary, tting Lounty l'age 7 of 7 required for stormwater control. . Protect Steep Ravines and Slopes of the Cedar River to prevent erosive runoff from new development through a combination of infiltration and enhanced retention/detention facilities. N ext Ste ps Once the Cedar River Basin and Nonpoint Source Pollution Action Plan is finalized, it will be presented to the Metropolitan King County Council and the Renton City Council in early 1996 for their consideration and adoption. Regulatory elements will be adopted as part of the plan. Capital improvement projects will be funded through City and County capital improvement program budgets. New public programs, including the purchase of floodplain property,will be implemented as staff and budgets allow. For more information on the condition of the Cedar River Basin, refer to the Cedar River Current and Future Conditions Report(available at King County Water and Land Resources, 296-6519). For additional information about the Lower Cedar River Basin and Nonpoint Action Plan contact Jean White, King County Water and Land Resources, at 296-1479. Updated: May 29, 1998 King Countv � Natural Resources � Water& Land � News � Services � Comments � Search Links to extemal sites do not constitute endorsements by King County. By visiting this and other King County web pages, you expressly agree to be bound by terms and conditions of the site. The details. k � http:/lsplash.metrokc.gov/wlr/basins/cedarpin.htm 12/31/98 � Section VIII: OTHER PERMITS TECH�IICAL IVFOR�t:�TlO'V REPORT FOR ��'[ND��'OOD- PAGE 35 � �� D�ent of Dev�elopment an Envu�onmental Services 900 Oakesdale Avenue Southwest Renton,WA 98055-1219 i;S �y��I[�`4+( ��l/HwaM�'f- .,.....,. .�V�y� November 18, 1998 Kevin Sunmons Centex Properties 2320— 130�'Avenue Northeast, Suite 200 �ellevue, `Vas�,u�gtoa 9o^COS Re: Windwood Subdivision SWM Variance Request Reconsideration(File No. L98V00391 Deaz Applicant: Thank you for the call requesting reconsideration of the approval conditions for this variance. The Land Use Services Division(LUSD), Engineering Review Section,has completed the reconsideration review for the Windwood subdivision variance request. You are requesting: 1. Revisions to condition ntunber three to include an option of a flow splitter to separate the north and south ditch flow paths of Southeast 128�' Street. 2. Use the 1998 King County Surface Water Design Manual (KCSWDI�pond geomeh-ics. Finding number nine of the approval letter states: The proposal is to collect all flow from the subbasins flowing south to a single detention facility. A flow splitter is proposed at the intersection of Southeast 128�Street and 148�Avenue Southeast. It would be designed to split flows based on the existing area tributary to the flows going west and south at this intersection. As an altemative to a flow splitter it is proposed to limit the release from the detention facility to exisring levels for the flows fr�at go s�utt� from the intersection of Seutheast i28� Street and I4S'� Avenue Southeast. The original proposal was to place a flow splitter at the intersection of Southeast 128�`Street and 148'�Avenue Southeast. T'his was not an acceptable location for the flow splitter as it would not be associated with the detention facility located within the drainage tract of the Windwood subdivision. An alternate proposal is to locate the flow splitter in the Windwood drainage tract with flow directed to the appropriate flow paths on the north and south sides of Southeast 128�' Street at the intersection with 148�Avenue Southeast. Kevin Simmons November 18, 1998 Page 2 The 1998 KCSWDM pond geometrics will provide a facility that meets or exceeds the detention standards of the 1990 KCSWDM. Water Quality requirements of the 1990 Design Manual must still be met. Based on the above findings, we hereby approve the use of the 1998 KCSWDM pond geometrics for detention only and the reconsideration of variance condition number three to: 3. A flow control device that splits the discharge to the flow paths on the north and south sides of Southeast 128m Street may be used. The splitter must be located within the drainage tract of Windwood. The release rates in each path must approximate the existing release rates. As an alternative, a single discharge to the Southeast 128`�Street frontage from the detention facility must equal the release from the existing middle and southern subbasins (identified in finding 4.b. and c. above). If you have any further questions regarding the SWM variance or the design requirements,please contact Richard Lowe at(206)296-7207 or Craig Hislop at(206)296-7195. Sincerely, �.�,__, , (� �\�, ,v Joe Miles, P.E. ONeill Supervising Engineer Site Engineering and Planiung Supervisor Engineering Review Section Building Services Division Land Use Services Division � JM/JO/ch cc: William Goggin, P.E., Triad Associates Curt Crawford, P.E., Supervising Engineer, Local Drainage Services Unit,KCD�ic Richazd E. Lowe,P.E., Senior Engineer, Engineering Review Section, LUSD Bruce Whittaker, Senior Engineer, Engineering Review Section, LUSD Craig Hislop, P.E., Engineer, Engineering Review Section, LUSD i.� � -i✓ � �� Departraent ofDevelopment and Envu�onmental Services 900 Oakesdale Avenue Southwest Renton,WA 98055-1219 � � �� ..�....w�..,._ _�r,.�„�,,,� October 16, 1998 Kevin Simmons Centex Properties 2320— 130m Avenue Northeast, Suite 200 Bellevue,Washington 98005 Re: Windwood Subdivision SWNI Variance Request (File No. L98V00391 Dear Applicant: The Land Use Services Division(LUSD), Engineering Review Section,has completed review of the variance request for the Wind�vood subdivision. You are requesting approval for a variance from the 1990 King County Surface Water Design Manual(KCSWD1Vn Core Requirement No. 1, Section 1.2.1,Discharge at the Natural Location. Our review of the information and a site visit provide the following findings: 1. The proposed Windwood subdivision is located east of the City of Renton. It is located north of Southeast 128'�Street and east of 150`�Avenue Southeast. The 111 lot, 28.09 acre, proposed Windwood subdivision is filed under LUSD File No. L97P0007. 2. The Windwood subdivision is located in the Lower Cedar River Basin and maybe in the May Creek Subbasin of the Newcastle Community Plan. 3. T'he prope��geaer��lly slopes io t��:e s�utihix�es±. R�noffflc��s fr�m ttLree or fo�r s»bb2sins o�'the site. The northeast comer of the property may be part of the May Creek subbasin. Testimony was given at the plat hearing from neighbors indicating some flow may go to May Creek. 4. The remaining subbasins flow to the south or southwest. a. The northern subbasin flows to the western property line then to a ditch in the unopened right of way of 150�Avenue Southeast. At the south end of 150`�Avenue Southeast the runoffenters a twelve inch(12")conveyance system to the west. This system outlets at 148`�Avenue Southeast heading south toward the intersection with Southeast 128�' Street. This runoff does not recombine with the other subbasins until it is over a quarter mile downstream. Kevin Simmons October 20, 1998 Page 2 b. The middle subbasin collects flows near the western property edge in shallow areas that flow across adjoirung properties in a southwesterly direction. This flow enters the ditch on the north side of Southeast 128"'Street and flows west toward the intersection with 148m Avenue Southeast. This runoff is directed south across Southeast 128�' Street to the ditch on the south side of the road. c. The southem subbasin flows to the south and collects in the ditch on the north side of Southeast 128m Street flowing west in the same course as the middle subbasin above. 5. A portion of this site is shown as being in the recharge area of a sole source aquifer. None of the area included for recharge is being diverted. 6. Neighbors to the west that are along drainage 4.a.above have complained about continuous saturated soils and poor sepric performance. They have inquired about additional runoff and connecting to the sewer system. 7. The site will be required to detain to Level 2 of KCRTS (King County Runoff Time Series) continuous model per BW 19 of the Lower Cedar River Basin Plan. 8. The applicant is not proposing to divert flows from the May Creek subbasin to the Cedar River basin. 9. The proposal is to collect all flow from the subbasins flowi.ng south to a single detenrion facility. A flow splitter is proposed at the intersection of Southeast 128�'Street and 148`� Avenue Southeast. It would be designed to split flows based on the existing area tributary to the flows going west and south at this intersection. As an alternarive to a flow splitter it is proposed to limit the release from the detention facility to existing levels for the flows that go south from the intersection of Southeast 128m Street and 148�'Avenue Southeast. I Based on these findings,we hereby approve this variance to allow the diversion of runoff from the exisiing southwesterly flowing subbas:ns to u'�e de�e:.�i�n facility;�ith the follovrina conditions: 1. The site must be surveyed to determine what area drains to the May Creek subbasin. This information must be included in the Technical Information Report at the time of engineering plan submittal. The developed runoff duration(Leve12)must remain the same • as the existing condition. 2. This project is required to use the KCRTS-continuous runoff model Level 2 with a ten percent (10%)volumetric factor of safety added to the facilities. 3. The release from the detention facility must equal the release from the existing middle and � southern subbasins (idenrified in finding 4.b. and c. above). Kevin Simmons October 16, 1998 Page 3 � If you have any further questions regarding the SWM variance or the design requirements,please contact Richard Lowe at(206)296-7207 or Craig Hislop at(206)296-7195. Sincerely, � ' ��.� Joe Miles, P.E. J ONeill Supervising Engineer Site Engineering and Planning Supervisor Engineering Review Section Building Services Division Land Use Services Division JM/JO/ch cc: William Goggin, P.E., Triad Associates Curt Crawford, P.E., Supervising Engineer, Local Drainage Services Unit, KCDNR Richard E. Lowe,P.E., Senior Engineer, Engineering Review Section, LUSD , Bruce Whittaker, Senior Engineer, Engineering Review Section, LUSD Craig Hislop, P.E., Engineer, Engineering Review Section, LUSD � - . - � �'iY�� s�f:<it?:i�:?' ' --.� _i� " •� 224 <n .-t -�,iv" i,:ti '�' . � ;� � ...z.r� � ��a.�e��€1��r�t��+�s� r�f� � �� : :f f . �� :��:�. �� f �:.. a�;: �I r ;�. `�s�:�hz eEt:3yc ic.� tt i>^ �;"., t�..<t >.,£� 'T p'Lu€ e .3��Ei3� . I•K�I �,:..,.�>Cs L{» >>f�-��'��;�'c :2 . f�»i <. :,f�'1�.��fL,�;'Irit Ii ift��E(E I :�� <<�z�i�qu�x�r+��m,�n�s�S�a�t��:��s�=t� �ti:t )tpattmatt oCDtvelopmrnt and Envitoamesstal Suvioes �. £.u r : t�^ > : � =s < `� � n � ei��c�I�� I �td U�e Servltes D(vtslon �<<y �i��f�s �'�� 2 s z a�`s- ,r i .. > ��E 3<2. s.�Ya ��,� :2 : B�< , , �o��A��,�5��.� � f �f.�� '�a r�anc e �2��e qu+�st i� ,s� f��22n<< t:. Ra�tot�Wuhington 980S3-L219 � s s< . ��, e.<� , ,_<�,,. , �, �?! t`;t i{:< s t z. f � 2 � ( u....<...utu(<i.;ti . ......wtii.a,::<h<.::.`:t.�ut�.t.t•�.'.:.twl.......................c..4i.t.. w.uccc.u.2....2iG:t2�.:......i...:2... Project Name: DDES Project File Na DDES EngineedPlanner Name: Windwood L98P0007 I c.g Yo�o s � Project Address: Design Engin . Phone: S.E. 128th St.just west of 148th Ave. Wil am o n, P.E_ 425-821 -8448 ApplipnC Phone: • Signatu : Date: Cent Homes 425-882-3611 Signahue: Date: Engineering Fkm me: � Tria Associates •�'�'•..« C��SW .7.:p C:..;e: Addreas: Giiy,State,'Lip Code: I 232U 130th Ave. NE Ste.200 Bellevue, I 11814 115th Ave.NE Kirkland,WA 98034� I � WA 98005 ! INSTRUCTIONS TO APPLICANTlDESIGN ENGINEER: Pkase be sure to lnclude aU plans,sketcfies,photos and maps which may asslst In compfete review and consideration of this rariance request Fa�ure to prmide ap pertinent infortnation may resutt in detayed pnocessing or dental of your requesi. Please submit this reauest and a�dicable fee to the DDES Intake Counter,at 900 Oakesdale Avenue Southv,r�Renfon,Washington 98055-1219. For add�tonal Information,phone 296-6C00. � ,: , . - . .. :.:..:, -,..:.:. .....: . _ . , a �' RFFER�Q SEGT]ON `i��IN C�iqPTE� i �F TNESi1RFAGE�YATER QES[6ht MANLfAt FOE�Y�iR[ANCES , �: , < � > ..---.... >.:..:.... ....::... .:....... . .....::. :....,..,, . ...:.. .:.>.:, .:. :..:.. : .... . .:..,. ...:,::., .:,..... ...:..:,..> >...::.... . ........ ...:,.::: ^�SCRIPTION OF VARIANCE REQUEST: 0 Standard �Complex 0 Experimental ❑Blanhet 0 Pre-applicatio� Request for approval to divert existing sheet flow from Basin 'A' ' to Basin 'B' (see attachments) . APPLICABLE SECT(ON(S) OF STANDARDS: ��,� KCSWDM - �Core Requirement #� Section 1 .1 .2 � t�'�'""� Discharge at the Natural Locaion �AR 3 01998 JUSTIFICATION PER KCSWDM SECTION 1.4.4 XpSt. See attachments listed below. �i�� `u��`,F; Justif ication As-Bu� �� r ^ r`- �� i�+L��-��Yar� Existing Conditions Map � Vicinity Map Drainage Variance Exhibit AUTHORIZAT(ON S(GNATURES: � DETERMINATiON: O Approval 0 Conditional Appraval(see below) ❑Denial 0 WLRD Approval Signed: �ate: (E�erimental�Blanket variances onty) OOES Sta(f Recommendatkn Signed: Date: 0 a1� CondiGons of Approval: �See attached Memo Dated: � �C' " � ODES DIRECTORIDESIGNEE: DDES,Land Use Services Division,Engineering Review Supervisor. DDES,Bldg.Serv.Div..Site Engineering d,Planning Supervisor. j �- � �(7� 2��`� ��.SL.�J l� �Z.� �� , � �ig�ed: Date: ed: Date: r�cieuis.+onR-s.�pr a�s�v� i. � --- � �� C�� •� TRIAD ASSOCIATES Pro�ect Managemeni Cwil Engineering land Surveying Windwood Land Use Planning Drainage Variance Landscape Architecture Triad Job No. 95-243 Sile Design DDES Project File#L98P0007 REVISED April Z0, 1998 JUSTIFICATION �4 Currently, the Windwood site drainage is split between Basin `A' (10:� On-site Acres) Basin `B' (13.51 On-site Acres) and Basin `C' (4.14 On-site Acres). Basin `A' and Basin `B' flow offsite onto neighboring properties before entering drainage swales along SE 128`� Street. Basin `C' flows directly from the site into the drainage swale along SE 128`� Street. , The proposed development will divert 10 8 yAcres of Basin `A' (7.43 Acres of which will be developed) and 13.51 Acres of Basin`B"(13.13 Acres of which will be developed) into a stormwater detention system. This system will outlet into the drainage swale along SE 128� Street at the point where Basin `C' presently enters the swale. The increased stormwater runoff at the Basin `C' outlet point will be mitigated as descn'bed below. Dowrrstream Description The drainage from Basin `A', which flows overland from the site to 148`� Avenue SE, is directed beneath 148`� Avenue SE at the SE128`� Street intersection, From this intersection, the Basin `A' runoff flows westerly in a swale parallel to SE 128`� Street on the north side (see attached as-built storm plans). Contirn�in� downstream (at approximately the quarter mile point), the runoff from Basin `A' crosses beneath SE 128`h Street and flows toward Tributary O.i07. Basin `B' flows offsite onto property owned by David R & Jennifer Normile (west) and Charles Lackey (southwest corner). The runoff traverses these properties and enters a drainage swale along the north side of SE 128`� Street. Basin `C' also flows into this same drainage swale along the north side of SE 128`� Street at the southwest corner of the site. At the intersection of SE 128'� Street and 148`� Avenue SE, the combined drainage from Basins `B' and `C' is directed beneath SE 128`� Street. From this intersection, the Basin `B' and 'C' runoff flows westerly in a swale pazallel to SE 128`� Street on the south side (see attached as-built storm plans). Continuing downstream (at approxirnately the quarter mile point), the runoff from Basins `B' and `C' REVISED K.C. Variance Request— Windwood — Page 1 of 3 t i�'._ i t5ir A�enue hE KuKia�d Was.��rgi�c 9803»E9�3 Phone a25�'=' 9��8 Toll Free 9�+7 s88�;56 Fax 425 5'� 3a8� Intemet ..v.:v ir��a�;;c,c com combine with the flow from Basin `A'. The combined flow from the site then flows towazd Tnbutary 0307. The following alternatives are being proposed for this King County Surface Water Design Manual Drainage Variance: Aliernative No. 1 The detention pond for the development will be designed to receive flows from existing Basin `C' (4.14 acres) plus diverted runoff from Basins `A' and `B'. The total tributary area of the detention pond will be 23.G5 acres (See Developed Conditions Map). The pond will drain to the Basin `C' outfall point and will be designed to match existing rates for the sum of the existing basins `A', `B' and `C' using the S.B.U.H. method,matching the peak flows from the 2, 10 and 100-year storm events. This volume will be increased by a 30% factor of safety as required by King County. Water quality will be provided using dead storage (water quality storm) and a biofiltration swale. A flow splitter will be provided at the intersection of SE 128�' Street and 148`� Avenue SE. It will be designed to split flows based on the existing conditions area tnbutary to this point. Alternative No. 2 The detention pond for the development will be designed to receive flows from existing Basin `C' (4.14 acres) plus diverted runoff from Basins `A' and `B'. The total tnbutary area of the detention pond will be 23.45 acres (See Developed Conditions Map). The pond will drain to the Basin `C' outfall point and will be designed to match existing rates for the sum of the existing basins `B' and `C' using the S.B.U.H. method, matching the peak flows from the 2, 10 and 100-year storm events. This volume will be increa.sed by a 30% factor of safety as required by King County. Water quality will be provided using � dead storage (water quality storm) and a biofiltration swale. Overdet inin this pond design will ensure that the release rates from the detention pond will not exceed existing rates in the downstream area of Basin `B' and `C'. Since Basins `B' and `C' presently drain into the same swale, no change in runoff in the swale will be realized. No flow splitter at the intersection of SE 128`� Street and 148`� Avenue SE will be required with this alternative. REVISED K.C. Variance Request — Windwood — Page 2 of 3 Summary The on-site azea that is proposed to be diverted from Basins `A' and `B' presently sheet flows across the existing lots located to the southwest of the subject property. Several of the residents in this area have complained about flooding in their basements that occurs on a regulaz basis. Diverting the flow into the on-site detention pond will most likely decrease the frequency of reoccurring flooding problems that occur in this neighborhood. Diverting the flow from Basins `A' and `B', using either of the Alternatives presented above, eliminates the need for additional on-site detention facilities. A single detention facility reduces maintenance requirements for King Counry and may resolve existing flooding probiems in the neighborhood as descnbed above. � REVISED K.C. Variance Request—Windwood — Page 3 of 3 Section IX: EROSION/SEDIMENTATION CONTROL DESIGN The temporary erosion and sedimentation control plan was designed to reduce the discharge of sediment laden runoff from the site. The plan is comprised of temporary measures (rock entrance, filter fence, etc.) as well as permanent measures (hydroseedinQ, etc.). In general, runoff from the residential site will sheet flow across cleared areas into temporary interceptor swales with rock check dams placed approximately every 50 to 150-feet depending on slope. In order to convey the runoff prior to the installation of the residential stormwater pipes and pond, temporary pipes along with portions of the permanent sections of the proposed conveyance system will be installed (see Grading and Erosion Control Plans in the Road and Storm plan set). This system will collect the site runoff during initial clearing and grading, and will convey the water down to the sedimcnt pond at the southern property boundary. The sediment pond is located where the permanent pond will be. Once the permanent stormwater system is functional, the construction drainage will be collected in it, and will flow through the proposed pond prior to discharge downstream. Other erosion control measures include two rock construction entrances located at the west and south entrances to the site, filter fence, and temporary ground cover all constructed per Appendix D on the 1998 KCSWDM. The sediment pond was checked, according to the September 1998 KCSWDM, to verify that adequate storage depth and surface area is provided. Generally, the design water surface area of the pond will be large enough to settle out the design particle (medium silt) at a 2-year inflow rate. The water works output for the developed 10-year, 24-hour design storm event was used to size the pond. A summary of the calculations }�or the sediment pond is included on the fo]lowinQ paQe. TECHNICAL INFORMATION REPORT FOR WINDWOOD-PAGE 36 DEVELOPED SITE Q�o =4.93 (See KCRTS output at the end of Section IV) CN — 0.34x76+0.49x64+1.58x87+1.66x82 _81 2� W 4.07 Sediment Pond Surface Area: Required Surface Area= 2(Q�o)�usED Required Surface Area= 2(4.93)/0.00096 Required Surface Area= 10,270 square feet (minimum) As designed, the sedimerit pond is rectangular shaped and placed in the soutltern end of '� the property, in the proposed future detention/wet pond location. It provides a surface 'i area of approximately 35,000 square feet(conservative) at the design mc�.rimum water surface. The pond will have 2:1 interior side slopes and 6 feet of depth from the top of , the 12" diameter overflow riser to the pond bottom. A mininutm of one foot of freeboard ��I will be provided above the top of the riser. � Overflow Riser: I The overflow riser was designed using Appendix D of the September 1998 King County I Surface Water Design Manual (KCSWDM). Using the 10-year peak pre-developed rate of 2.02 cfs (see water works output in Chapter IV) with 1.0 foot of head, the riser is required to be a minimum of 8.77 inches in diameter. A 12 inch riser is proposed. A 12 inch riser can convey up to 3.78 cfs, with 1.0 foot of head (See figure 5.3.4.H in the Appendix). Qor�face = 3.782 D`'H��'; Q(�fs), D(fI), H(fi) 2.02 = 3.782 D'`(1)�'� D = 8.77 inches, use l? in diameter riser TI+C'l1NIC�U. INFOK1�1:1Tlnl� RI�:YOk"1' FOR 11'['VD1��OOD- P:�GE 37 Overflow Spillway: , The overflow spillway was designed using Equation (5-3) of the September 1998 I� KCSWDM. The spillway was sized to convey the peak rate runoff from the developed 100-year, 24-hour storm event with 0.5 ft of available head. The spillway for the sediment pond is the same as for the permanent detention/wet pond. Q�oo = 9.39 cfs (See KCRTS output at the end of Section IV) L= �Q�oo/ (3.21 H3iz)� — 2.4H li se H = 0.4 feet L= 9 feet Sediment Pond Dewatering Orifice: The overflow spillway was designed using Appendix D of the September 1998 KCSWDM. AS •(2h)0.5 A° 0.5 0.0165sf Dewatering Orifice Area 10.6•3600•T•g AS =35,000 sf,Settling Surface Area h = 3.0 ft,Settling Depth T = 24 Hours,Dewatering Time g = 32.2ft1s2 D = 24• A° = 1.74",Orifice Diameter,use 2" 3.14 The vertical perforated tubing connected to the dewatering orifice will be 4 inches in diameter. TECHNICAL INFOR1�iATION REPORT FOR «�[ND�'��OOD-PAGE 38 Riser Transition H a.00 - �— ------T—; , ---� 3.50 , ; i i --�--� , p I i , ' � � ; , � 3.00 — — ; 2.50 ' ' r-- � r ; � j Orifice'' � I ; i I I _. -r; � z.00 —! . , � �� Input Output , _ � i � j ; ! I ' Q (CfS) 2.02 2.02 � 1.50 - i i � i � , eir � D (in) 0 8.77 �.00 , , � � ; � i ; H (ft) 1.00 1.00 i o.so ;— ' � ' �'I I ; � � ' � � Flow: Orifice Flow o.00 ' 0 10 20 30 40 50 60 70 80 90 100 110 120 130 Diameter(in) Job: Sorensen Description: Sediment Pond Discharge Riser By: Geoff Tamble Date: 12/15/98 Page 1 SECTION 5.3 D�'I'ENTION FACILITIES Riser Overfiow The nomograph in Fi�ure 5.3.4.H can be used to determine the head (in feet) above a riser of given diameter and for a given flow(usually the 100-year peak flow for developed conditions). FIGURE 5.3.4.H RISER INFLOW CURVES �o o , --------------- 72 54 48 � ' � i � 42 � 36 33 30 , 27 i i I I 24 � � 21 = �° w � c � 18 � � d w � � ! � � d ; a � d �� 15 I I w � i U � I I I � v � Q � I I � 2 i � ��'. � � � I � � � 0 � � � I I � � E f �f { t £ � � � � • � � � 0.1 1 1 0 HEAD IN FEET (measured from crest of riser) Qwe�r=9•739 DH��Z 2 1/2 Q,�;�;«=3.782 D H O in cfs, D and H in feet Slope change occurs at weir-orifice transition 9/1/98 1995 Surface�Vater Desi�n Manual � ,Q _ Section X: BOND QUANTITIES `�ORKSHEET TECHNICAL INFORMATION REPORT FOR WIND�i'OOD-PAGE 39 O SIT� IMPROVEMENT 'B ON D'QUANTITY Kin6CoontyDepartmealofDevdopmenlandF.nvironmenWServices � ... W�RKS`HGG'T'. � �� 00 Oak�dale Aventu SW . . . . . � . . . . . . . . .. . . � Rcaitrnt Wasllingtan 9R055•1219 . . . . . . . . .. . ... .. . . . . . . . . . . . . . ProjectName: Windwood SIERRAProjeclNo.: Date: April21,1999 Location: King County Sierra Activity No.: : I: FOR EN71RE PRQJECi uou ! '. :I: Clearing greater than 5000 board feet of timber Pric� ' Unit QueMity Prloe yes no STABILIZATIO WEROSIOWSEDIMENT CONTROL Fence,silt $ 1.30 �F 2400 $ 3120.00 If yes, Hydroseedin .40 sv �2500.0o s,000.00 Forest Practice Permit Number. Jule Meah i.00 sv (RCW 76.09) Mulch,b hand,straw,2"dee .35 SY Mulch,b mechinc,alrew,1'de .40 SY �� Rock Coretructbn Errtrance,50'x 16'x t' 1,030.0o Each Rock Corxtruclion ErArance,t0U x 15'x 1' 1,800.00 Each 1 1,800.00 , G Seedi ,b hand 36 SY W�.h �ry/ V" TESC Pond 1.00 LS 65000 66,000.00 f `1 A � `' � Te .CulveAs 12.00 LF 610 7,320.00 x ..� Irrter tor Svak 5.00 LF 5300 26,600.00 Slraw Beles 10.00 Each 6 60.00 '�� Rock Check�am b0.00 Each 35.00 1,750.00 Z a�2$_ � ESC SUBTOTAL $ 110550.00 �+/�„r��0� VaJ 1 L.�� SfONALF�' EXPtRES '� _�O PAGE $ 110,550.00 KC Bond 1520i99 Page 1 Sierra Projed No. 0 . . . . . . . . . ... ........ . . . .. . . . . . . . . . . . . � . .. . . . . . . . ...... . . . . . . . . . . , . , . . . . . IXISTINO i i FU7UAE PUBLIC i PRIVkTE R7D FACILI7IES AN� i BOF1D REDUCTIONS ' RICiHT-bP.WAY :ROAD : ' IMPFtOVEMENTS:: CONVEYANCE' IMPROYEMENTS §YSTEMS . 4 ' ';',2 ; 3 . . �:Un( :I duanLty i Ouhitlty Cu�ntliY:: . . .. . ::Fr[er �illnit Uu�ntlt I�I Prlo� �. !�usrttlt I Rlo{�:�: Qu�ntlty iRic� Gumtlt �I'Prle� -Itlom I�t��: :Ridr::i..Qomp3�t1 Prlc�l �Com I�a �--Prlo� � GENERALITEMS Clear/Remove Brush,b hand $0.24 SY Clearing/Grubbin iRemoval,trees $6,1b0.00 Acre 7.90 48,585.00 0.07 430.60 1.60 9,840.00 Excavation-bulk 1.10 CY 9075.00 9,982.50 Excavation-tranch 3.00 CV 1351.00 4,053.00 3254.00 9,762.00 � 110.00 330.00 BacMill 8 Com adion-embankment 3.80 CY 1185.00 4,266.00 BacMill R Com adion-trench 5.70 CY 1080.00 6,166.00 2803.00 14,837.10 8d.00 507.60 Fill&Compact-common barrow 11.10 CY Fill&Compact- revel base 15.60 CY 212.00 3,307.20 511.00 7,971.60 17.00 265.20 FIII&Comped-screened topsoil 16.40 CY Gradin ,fine,wfth rader 0.70 SY Grading,fine,b hand 1.30 SY Fencing,cedar,6'high 25.00 LF Fencin ,chain link,5 hl h 920 LF Fencin ,chein Ilnk, ate,20' 880.00 Each Fencin ,tem ora NQPE 1.10 LF 2000.00 2,200.00 Sod 4.82 SY Monumenta,3'lon 84.00 Each 1 84.00 15 1,260.00 Surve ing,lot IocatioNlines 630.00 Acre 28.00 17,640.00 Surve in ,line& rade 610.00 Da 1.00 510.00 3.00 1,530.00 1.00 510.00 Trail,4"crushed cinder 6.50 SY Trell,4'to Couree 6.00 SY Gabbn,3'thick,no earthwork 97.00 SY Wall,retaining,rockery w/earthwork 21.00 SF SUBTOTAL FUR PAGE $ 14,110.20 S 86,145.70 S 18,070.50 $ 25,695.30 KC Bond/520/99 Page 2 Siarre ProJed No. 0 ' IXI671Np FUTUFIE PUBUC'I PRIYATfi Fi/D FACILITIES AND ' BONOIREDUC710NS ' RIGHT-0E-WAY: ! ROAD IMRROVEMENTS i i I CdNVEYANCE i.: ' ! IMPpbUEMENTS I: ' SYSTEMS. . f ' p 3 . � �. . �:�un . . . � . �. ��ou.nnty.:' Cu�nnty � �u■nnty . �. �. . . . . '. �Prb� ��Unit I Ou�ntlt �. '.Prlo� : '��8u�ntl � Prlo�:-: Ou�nUt .Prle� Qu�ntl ' 'Prlo� '.�.Com I�d' '. Prlc� ��. Com 1�U PAu. �. '.Compl�t� � '.Prlor . ROADIMPROVEMENTS AC Orind ,4'mechine 3 7.00 SY AC RemovaliDls osal/Ae air 80.00 SV . Berricade, e III 30.00 LF 120.00 3,600.00 Barricade, e I 20.00 LF Curb,e�Aruded halt 1.b0 LF 1010.00 1,818.00 Curb,extruded concrete 7.80 LF Curb&Outter,rolkd 9.30 LF Curb&6utter,varticel 8.80 LF 600.00 4,080.00 12000.00 81,600.00 DemolitioNDls oeel,curb$ utter 10.30 LF OemolitlorvDk osel,sidewalk 22.50 SV SawcW,as hell,3"d th 1.30 LF Sawcut,concrete, er 1'd th 1.10 LF 11180.00 12,278.00 Sealent 0.70 LF 1860.00 1,302.00 Shoulde�,AC,see AC F1oad 6.60 SY 1800.00 11,700.00 Shoulder, ravel 6.40 SY li Sidewalk,4'thick,veRical curb 20.80 SY 333.00 6,926.40 6667.00 138,673.60 I Sidewalk,5'lhick,rolled curb 23.80 SY I Slr' in ,4'reflectoAzed line 020 LF 5600.00 1,120.00 I Strpin ,per arkl stall 2.90 Each Thickened Ed e 4.70 LF 60.00 376.00 SUBTOTAL FOR PAOE $ 39,222.40 S 223,873.80 S 376.00 KC Bond/520/99 Page 3 Sierre Projed No 0 IXISTINO 'FU7UAE PUBLIC ' PRIVATE WD FACILIT3ES AN� BOND!REDUCTIONS ' ' , qIOHT-b�.WAY: ROAD ,;, , ' IMPFiOVEMENrS'' coNVEYANCE' ' I:IMPROVEM�NTS :, SYST�MS ,7;! 2 3 unt ' ou,�niy i ou.Raty o�.�mr � ' , .:. , , ' � . . 'RWI::-iUnit ��. quintl� � �-�.Rlo� I�I Qu�ntl '�.PN91:: !:Qu�Otlt ��Prle� ��O��dtlt ..Rlw �';CoM Nt�!�: Prlo�:� CoM ft� Prle�. �Compl�U� �� Prlo• - ', ROAD SURFACING i (a"rock=2.6 base S 1.5"to course � AC Overle ,1.5"AC 5.40 SV AC Oveda ,2"AC 6.50 SY i AC Roed,2',4'rodc,First 2500 SY $ 1370 SY 985.00 13,494.50 2500.00 34,250.00 ��I AC Roed,2",4'rock, .over 2500 SY 9.10 SY 8386.00 57,930.60 AC Fioad,3",4'rock,Firet 2500 SY 16.60 SY AC Fioad,3',4'rock, .over 2500 SY 11.00 SY AC Road,5",Flrst 2500 SY 16.30 SY AC Roed,5', .over 2500 SY 10.80 SY AC Road,8',Flrst 2500 SV 19.10 SY AC Roed,6', .over 2500 SY 12.70 SY AspheR Treeted 8ase ATB Aseume 2.05 ton/c 30.00 Ton Gravel Roed,4'rock,First 2500 SY 7.20 SY Gravel Road,4'roCk, .over 2500 SY 4.70 SY PCC Road,b",no base 14.30 SY PCC Road,6',no bese 16.60 SY 516.00 8,565.60 DRAINAGE (CPP=Co� ated Pkstic Pipe,N-12 or equivalent Accese Road,R/D 9.30 SY 600.00 6,580.00 Boilards-flxed 290.00 Each 2 580.00 Bollar�-removeble 475.00 Each 2 950.00 SUBTOTAL Foa PAGE $ 22,060.10 S 9'.,1E0.50 S 711000 KC Bond'S20-99 Fage 4 Sierra Project No. 0 . � � � � . . ''. �' I D(ISTINO . !FUTUAE PUBLIC �-I PRIYATE . ' R7D FACIU7iES AND ' .�I�:: �� ' �BOND�.REDWC710NS � ' � . . . . . .. :: �. �. ::: . . . . , .. . . ... . ... .. . . . . . . . . i I RIGHT-OF'-WAY I!RQAD I IMPROVEMENTSI I CQNVEYANCE ' , iIMPROVEMENTS BY67EMS "1'. 2 3 un ou.naey . ou.nncy ou�nney . . ��PrW �. '.Unit ':Qurotlt� �� Prlc� �� Qu�ntlt� '. Prle�: Qu�ntl :�.Prlc� �'��u�nBt . ' Prlw � ' Com�In�'. Prlo�:: . Compt�t� Pda• � .Compl�t�;�.,�..Prlo• DRAINAOE Con't. (CBs include frame and II CB T e I 850.00 Each 10 8,500.00 55 46,�50.00 CBT eIL 1,000.00 Each 8 8,000.00 CB T e II,48"diemeter 1,300.00 4'dee 7 9,100.00 5 6,500.00 2 2,600.00 lor addltlonel d th over 4' +320.00 +1'de lh 29.00 9,280.00 2.00 640.00 1�.00 5,440.00 CB T e II,54'diameter $1,450.00 4'dee tor additional d lh over 4' +370.00 +1'de th C8 T e II,60"diameter 1,600.00 4'dee for eWltbnel d th ova 4' +410.00 r1'da th CB T e II,�2"dlameter 2,200.00 4'depth lor edditlonel depth over 4' +520.00 +1'de th Throu h-curb Inlet Framework Ad 225.00 Eech 12 2,700.00 Cleenout,PVC,4' 86.00 Each Cleanout,PVC,6" 116.00 Eech Cleanout,PVC,8' 142.00 Eech 55 7,810.00 CuNeA,PVC,4' 4.60 LF CuNert,CPP,6" 9.30 LF CuNert,PVC,6' 6.40 LF CuNeA,CMP,8' 9.50 LF CuNert,concrete,8' 12.90 LF CuNert,CPP,8' 10.00 LF CuNert,PVC,8' 8.00 LF 6800.00 54,400.00 CuNert,CMP,12" 14.60 LF SUBTOTAL Foa PnGE $ 25,ggp.pp 5 sa,s9o.00 S R2,21o.00 $ R,oaoAo KC Bond%520'99 Page 5 Sierra Pro�ed No. 0 IXISTING FUTUAE PUBLIC PRIVATE ' R7D PACIUSIES AN� ' gOND.REDUC710NS �. .:.�: .::i i :i i I I I I! � � : -- � RI�HT-OF-WAY . �.�.:R�CSAD. .. �. � I IMFROVEMENTS i ::'CONVEYANCE�. � � �� . . . � . .. . . . .. . ! i i!' i iI IMPAOYEMENTS ' ii i SY5TEMS I t: 2 3 . �... . . � I Unl.. . . . . . �� .:. �' ' .::: :::: i�� . . ' Oufntlty I .�.. � �Ou�ntlty . . . ::Ov�ntlty' : �. �� PrW► IUnit qurntlt . ::Rlo• ��. Qu�ntl � PflOf i i .:Qu�ptl � �Rlo• ��pu'qq �� Prlw '- cohl Ift�' PrI�� com.�t� ��Prld� ��.Gw�l Itp "Wb� � DRAINAGE Con'l. Cu1veA,concrote,12" 17.90 LF 780.00 13,962.00 Cu1veA,CPP,12" 16.50 LF 455.00 7,507.50 4480.00 73,590.00 32.00 528.00 Culvert,CMP,75' 18J0 LF CuNert,concrote,15' 22.50 LF CuNert,CPP,15" 18,50 LF 64.00 1,184.00 Culvert,CMP,18' 21.90 LF CuNert,concrete,18" 27.60 LF 270.00 7,452.00 131.00 3,615.60 CUNert,CPP,18' 22.00 LF d63.00 18,986.00 643.00 14,148.00 Cubert,CMP 2a" 30.30 LF CuNert,concretq 24' � 39.80 LF CuNert,CPP,24' 29.00 LF 505.00 14,646.00 35.00 1,015.00 CuNert,CMP,30' 38.60 LF CuNert,concrete,30' 64J0 LF CuNert,CMP,36' 62.80 LF CuNert,concrete,36' 83.20 LF Culvert,CPP,36" 39.00 LF � CuNert,concrete,42" 101.80 LF CuNert,CMP,48' 80.60 LF Culvert,concrete,48' 113.00 LF Culverl,CMP,60' 112.00 LF Cubert,concrete,60" 164.00 LF DAching,bare,roadslde 5.40 CY 110.00 594.00 SUBTOTAL Fo� F'nr,L $ 49,685.50 5 102,381A0 S 5,15R.B0 KC Bond/520.'99 Paqe 6 Sierra ProJect No. 0 . . . . . . . .... .... . j EXI571N0 . I FUTUfiE PUBLIC PRIVATE ',', WD FACILITiES AND 90ND'qEDUC710NS. I' ' ! ' I. !I: RICiHT-0F:WAY !RdAD : IMPROVEMENTS I I C4NYEYANCE !!: !IIMPROVEMENTS SY57EMS T! I12 3 . . . . . .. :::� . �. � . .. Unl . . � -:�.�..... .... :-._� . �. �. : .!!! . . ' I Qwntlty �. I . OwntltY �- . . . Ou�ntlty. . . , . . . . . . .Abf �Unit � quMtlt �� .Prlo� � ::Qu�ntl � pf10i��. � Qu�ptlt Prl�� 'OU�htl ' I Prlu ' ICoM I�t�'�. '�. Prlo� �� CWrlpi�t� ��Pr1os � �.Corti let�, , Prlo• DRAINAQE Con't. Flow Dispersal Trench 1,100 base LF 1.00 1,100.00 +15.00 French Orein 12.30 LF Mid-tank Access Riser,36" 700.00 Each Pond O�edlow S�Illwe 4.70 SY 65.00 305.50 Reatrldor/OiIS aretor,�2' 786.00 Each Restnclor/Oil S arator,15" 886.00 Each Restrlctor/OiIS eretor,18' 1,036.00 Eech 1 1,035.00 Hiprap,placed 28.00 CV 15 420.00 Tank End Reducer 400.00 Eech Tresh Rack,12' 160.00 Eech TreshRack,76' 186.00 Eech Trash Rack,18' 210.00 Each Tresh qack,24' 300.00 Eech 1 300.00 PARKINO LOT SUFFACINO 2"A.C.,Y t couree wck R 4"aeled borrow 8.10 SY 1.5"to course rock&2.5"base courae 470 SY 4"select barow 1.75 SV SUBTOTAL Foa P��E $ S 3,160.50 KC Bond/520/99 Page 7 Slerra Projed No. 0 � �. � � � � '�:� '� EXIS7IN�� FUTUfl�PUBLIC�� RRIVATE � �� -R/D FACIUTIES AND �'' '� '�80ND��R6DUC710N5 , , . � � � � � RIGHT-0E-WA:Y ;:ROA4..i i: I IMPRQWEM��TS.;. CONVEYANCE ' I. " IMPPOYEMENTS BY&7EMS �. ' III2 I,3 un , cu■onty ' ' oy■�n�y ou.rynsy . .:::: .::: . . . �. ��.Prlo� .�:unit qu�ntlt ��Prlc� ��-;Qu�nB .:: PtIC�I ' 4uMtl Prlo�� ::Op�pt� ��.Rlw � �'�coln I�t��. �, Prlo�. . � CoM.lt1...�PAo�� cortl:I�t� �Pi'.lo� . . Flow Splltter 4,500.00 EA 1.00 4,500.00 SUBTOTAL(SUM ALL PAGES): S 2e2,soe.2o 5 ss&,no.eo S eo,ese.so S 53,660.60 0,00 0.00 0.00 30%CONTINQENCY&MOBILIZATION: S 7e,752.�5 S �70,�5�2� S 24,�e6.e5 S 16,099.32 0.00 0.00 0.00 TOTAL: S 311,280.88 5 739,fl22.17 S 101,&53.l3 S BD.783.72 0.00 0.00 0.00• �A) (B) (C) SUBTOTAL Foa PA(iE $ E 4,500.00 �r Rond�520�99 PaQe 9 Slerre Pro�ect No. 0 Quan6ties above were completed by: Signature: PE Registration Number: Date: Firm Name: Tried assx�ates Telephone Number: �zoe�e2t-eaae llddf2sS: 11814 115th Avenue NE �� Kirkland,WA 98034 ��I This section to be completed by King County I BOND COMPUTATIONS: PERFORMANCE BOND AMOUNTS MAINTENANCE BOND AMOUNT DEFECT BOND AMOUNT StabilizatioNErosion Sediment Control(ESC) (D) Existing Right-of-Way Improvements (E) Future Public Road Improvements (F) (E+F)x 0.25= Private Improvements FUD Facilities and Conveyance Systems __ _________________ x 0.15= TOTAL (T) PERFORMANCE BOND AMOUNT RIGHT-OF-WAY&SITE RESTORATION BOND (D+E) (First$7,500 of bond shall be cash. (#1) PERFORMANCF BOND TOTAL AFTER BOND REDUCTIONS (T-A,B OR C) (#2) (#3) NOTE. The word"bond"is used to represant Original bond computations Slgnature of Person Preparing 8ond Feduction any linencial guaraMee accepteble to prepared by: Date' King CourAy. N1 Date #2 Date #3 Date NOTE: Total bond emounts remefning afler reductlon shel not be Ips than 30%o}the originel emount or the sum ol th� melntenence end defect emounts shown ebove,whichever ie greeler. H:C Bond:5;20:'99 Fage 9 Section XI: MAINTENANCE AND OPERATIONS MANUAL , Public facility to be maintained by King County. TECE�N[CAL II�FOR11-1ATION REPORT FOR WINDI��OOD- PAGF.40 KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL APPENDIX A MAINTENANCE STANDARDS FOR PRIVATELY MAINTAINED DRAINAGE FACILITIES NO. 1 - DETENTION PONDS Maintenance Defect Conditions When Maintenance Results Expected When Component Is Needed Maintenance Is Performed General Trash&Debris Any trash and debris which exceed 1 cubic foot Trash and debris cleared from site. per 1,000 square feet(this is about equal to the amount of trash it would take to fill up one standard size office garbage can). In general, there should be no visual evidence of dumping. Poisonous Vegetation Any poisonous or nuisance vegetation which No danger of poisonous vegetation may constitute a hazard to County personnel or where County personnel or the the public. public might normally be. (Coordination with Seattle-King County Health Department} Pollution Oil,gasoline,or other contaminants of one No contaminants present other than gallon or more or any amount found that could: a surface fiim. (Coordination with 1)cause damage to plant,animal,or marine life; Seattle/King County Health 2)constitute a fire hazard;or 3)be flushed Departrnent) downstream during rain storms. Unmowed Grass/ If facility is located in private residential area, When mowing is needed, Ground Cover mowing is needed when grass exceeds 18 grass/ground cover should be inches in height. In other areas,the general mowed to 2 inches in height. policy is to make the pond site match adjacent Mowing of selected higher use ground cover and terrain as long as there is no areas rather than the entire slope interference with the function of the facilily. may be acceptable for some situations. Rodent Holes Any evidence of rodent holes if facility is ac6ng Rodents destroyed and dam or as a dam or berm,or any evidence of water berm repaired. (Coordination with piping th�ough dam or berm via rodent holes. SeattteACing County Health Departrnent) Insects When insects such as wasps and homets Insects destroyed or removed from inter(ere with maintenance activities. site. Tree Growth Tree growth does not allow maintenance access Trees do not hinder maintenance or interferes with maintenance activity(i.e.,slope activities. Selectively cultivate trees mowing,silt removal,vactoring,or equipmeni such as alders for firewood. movements). If Vees are not interfering with axess,leave Vees alo�e. Side Slopes of Pond Erosion E�oded damage over 2 inches deep where Slopes should be stabilized by cause of damage is still present or where there using appropriate erosion control is potential for continued erosion. measure(s);e.g.,rock reinforcement,planting of grass, compac6on. Storage Area Sediment Accumulated sediment that exceeds 10°k of the Sediment cieaned out to designed designed pond depth. pond shape and depth;pond reseeded'rf necessary to co�trol erosion. Pond Dikes Settfements Any part of dike which has settled 4 inches lower Oike should be built back to the than the design elevation. design elevation. Emergency Rock Missing Only one layer of rock exists above na6ve soil in Replace rocks to design standards. Overflow/Spillway area five square feet or larger,or any exposure of native soif at the top of out flow path of spillway. Rip-rap on inside slopes need not be replaced. 1998 Surface Water Design h4anual 9/1/98 A-1 APPENDIX A MAINTENANCE STANDARDS FOR PRIVATELY MAINTAINED DRAINAGE FACILTI'IES NO.2-INFlLTRATION Maintenance Defect Conditions When Maintenance Results Expected When Component Is Needed Maintenance Is Pertormed General Trash&Debris See'Ponds'Standard No.1 See'Ponds'Standard No. 1 Pasonous Vegetation See'Ponds'Standard No.1 See'Ponds'Standard No.1 Pollution See'Ponds'Standard No.1 See'Ponds'Standard No.1 Unmowed Grass/ See'Ponds'Standard No. 1 See'Ponds'Standard No.1 Ground Cover Rodent Hdes See'Ponds'Standard No. 1 See'Ponds'Standard No.1 Insects See'Ponds'Standard No.1 See'Ponds'Standard No.1 Storage Area Sediment A percolation test pit or test of facility indicates Sediment is removed and/or facility facility is only working at 90%of its designed is Geaned so that infiltration system capabilities. If two inches or more sediment is works according to design. present,remove. Sheet Cover(If Sheet cover is visible and has more that three Sheet cover repaired or replaced. Applicable) 1/4-inch holes in it. Sump Flled with Any sediment and debris filling vault to 10%of Clean out sump to design depth. Sediment and Debris depth from sump bottom to bottom of outlet pipe (If Applicable) or obstructing flow into the connector pipe. Flter Bags Flled with Sediment Sediment and debris fill bag more than 1/2 full. Replace filter bag or redesign and Debris system. Rock Flters Sediment and Debris By visual inspection,little or no water flows Replace gravel in rock filter. through fifter during heavy rain storms. Side Slopes of Pond Erosion See'Ponds'Standard No.t See'Ponds'Standard No.t Emergency Rock Missing See'Ponds'Standard No.1 Overflow Spillway Settling Ponds and Sediment Remove when 6'or more. `' Vaults � Note: S�ment accumula6on of more than 25 inches per year may i�cate excessive erosion is oacurring upstream of the facility or that conveyance systems are not being propedy mainfained. The coniribu6ng drainage area should be checked for erosion probfems or inadequate maintenance of cbnveyance systems if excessive sedimentation is nofed in an infiltration facility. Check hvice a year during first 2 years of operabon;once a year therea/ter. Gean manholes/catch basins,repair damaged inlets/outlets, dean trash racks. / 9/1/98 1998 Surface Water Design Manual A-2 APPENDIX A MAINTENANCE STANDARDS FOR PRIVATELY MAINTAINED DRAINAGE FACILI'I'IES NO.3-CLOSED DETENTION SYSTEMS(PIPES/TANKS) Maintenance Defect Conditions When Maintenance is Needed Results Expected When Component Mainte�ance is Pertormed Storage Area Plugged Air Vents One-half of ihe cross section of a vent is Wocked at Vents free of debris and any point with debris and sediment sediment Debris and Accumulated sediment depth exceeds 10%of the All sediment and debris Sediment diameter of the storage area for Yz length of storage removed from storage area. � vault or any point depth exceeds 15°k of diameter. Example:72-inch storage tank would require cleaning when sediment reaches depth of 7 inches for more than Kz length of tank. Joints Between Any crack allowing material to be transported into All joint between tank/pipe ! Tank/Pipe Section faality sections are sealed Tank Pipe Bent Any part of tank/pipe is bent out of shape more than Tank/pipe repaired or replaced Out of Shape 10%of iYs design shape to design. Manhole Cover Not in Place Cover is missing or only partially in place.Any open Manhole is closed. manhole requires maintenance. Lodcing Mechanism cannot be opened by one maintenance Mechanism opens with proper Mechanism Not person with proper tools.Bolts into frame have less tools. Working than 3�z inch of thread(may not apply to self-locking lids.) Cover Difficult to One maintenance person cannot remove lid after Cover can be removed and Remo�e applying 801bs of lift. Intent is to keep cover from reinstalled by one maintenance sealing off access to maintenance. person. Ladder Rungs IGng County Safety Office and/or maintenance person Ladder meets design standards Unsafe judges that ladder is unsafe due to missing rungs, allows maintenance person safe misalignment,rust,or cxacks. access. Catch Basins See"Catch Basins"Standarcls No.5 See"Catch Basins"Standards No.5 1998 Surface Water Design Manual 9/1/98 A-3 APPENDIX A MAINTENANCE STANDARDS FOR PRIVATELY MAINTAINED DRAINAGE FAQLTITES NO. 4-CONTROL STRUCTURE/FLOW RESTRICTOR Maintenance Defect Condition When Maintenance is Needed Results Expected When Camponent Maintenance is Pertormed General Trash and Debris Distance between debris build-up and bottom of All trash and debris removed. (Includes Sediment) orifice plate is less than 1-1/2 feet Structural Damage Structure is not securely attached to manhole wall Structure securely attached to and ouUet pipe structure should support at least wall and ouUet pipe. 1,000 Ibs of up or down pressure. Structure is not in upright position(allow up to Structure in correct position. 10%from plumb). Connections to outlet pipe are not watertight and Connections to outlet pipe are show signs of rust. water tigh�structure repaired or replaced and works as designed. Any holes—other than designed holes—in the Structure has no holes other structure. than designed holes. Cleanout Gate Damaged or Missing Cleanout gate is not watertght or is missing. Gate is watertight and works as designed. Gate cannot be moved up and down by one Gate moves up and down easily maintenance person. and is watertight. Chain leading to gate is missing or damaged. Chain is in place and works as designed. Gate is rusted over 50%of its surface area. Gate is repaired or replaced to meet design standards.. Orifice Plate Damaged or Missing Control device is not working properly due to Plate is in place and works as missing,out of place,or bent orifice plate. designed. f Obstructions Any trash,debris,sediment,or vegetation Plate is free of all obstructions blocking the plate. and wortcs as designed. Overflow Pipe Obstructions Any trash or debris blocking(or having the Pipe is free of all obstructions potential of blocking)the overflow pipe. and works as designed. Manhole See"Closed Detention Systems"Standards No.3 See"Closed Detention Systems' Standards No.3 Catch Basin See"Catch Basins"Standards No.5 See'Catch Basins"Standards No.5 �. .� 9/1/98 1998 Surface Water Design Manual A-4 APPENDIX A MAINTENANCE STANDARDS FOR PRIVATELY MAINTAINED DRAIlVAGE FACII,IT�.S NO. 5-CATCH BASINS Maintenance Defect Conditfons When Maintenance is Needed Results Expected When Component Maintenance is pertormed General Trash�Debris Trash or debris of more than 1/2 cubic foot which is No Trash or debris located (Indudes Sediment) located immediately in front of the catch basin immediately in front of catch opening or is blocking capaaty of the basin by basin opening. more than 10% Trash or debris(in the basin)that exceeds 1/3 the No trash or debris in the catch depth from the bottom of basin to invert the lowest basin. pipe into or out of the basin. Trash or debris in any inlet or outlet pipe blocking Inlet and outlet pipes free of more than 1/3 of its height trash or debris. Dead animals or vegetation that could generate No dead animals or vegetation odors that could cause complaints or dangerous present within the catch basin. gases(e.g.,methane). Deposits of garbage exceeding 1 cubic foot in No condition present which volume would attract or support the breeding of insects or rodents. Structure Damage to Comer of frame extends more than 3/4 inch past Frame is even with cufi. Frame and/or Top Slab curb face into the street(If applicable). Top slab has holes larger than 2 square inches or Top slab is free of holes and cracks wider than 1/4 inch(intent is to make sure cracks. aIl material is running into basin). Frame not sitting flush on top slab,i.e.,separation Frame is sitting flush on top of more than 3/4 inch of the frame from the top slab. slab. Cracks in Basin WallsJ Cracks wider than 1/2 inch and longer than 3 feet, Basin replaced or repaired to Bottom any evidence of soil particles entering catch basin design standards. through cracks,or maintenance person judges that sUucture is unsound. Cracks wider than 1/2 inch and longer than 1 foot No cracks more than 1/4 inch at the joint of any inleU outlet pipe or any evidence wide at the joint of inleVoutlet of soil partides entering catch basin through pipe. cracks. SedimenU Basin has setded more than 1 inch or has rotated Basin replaced or repaired to Misalignment more than 2 inches out of aGgnment. design standards. 1998 Surface Water Design Manual 9/1/98 A-5 APPENDIX A MAINTENANCE STANDARDS FOR PRIVATELY MAINTAWED DRAINAGE FACILITIES NO. 5-CATCH BASINS(CONTINUED� Maintenance Defect Conditions When Maintenance is Needed Results Expected When Component Maintenance is pertormed �� c Fire Hazard Presence of chemicals such as natural gas,al and No flammable chemicals gasoline. present. Vegetation Vegetation growing across and blocking more than No vegetation blocking opening 1 U%of the basin opening. to basin. Vegetation growing in inleVoutlet pipe joints that is No vegetation or root growth more than six inches tall and less than six inches present apart- Pollution Nonflammable chemicals of more than t/2 cubic foot No pollution present other than per three feet of basin length. surface film. Catch Basin Cover Cover Not in Place' Cover is missing or only partially in place.Any open Catch basin cover is closed catch basin requires maintenance. Locking Mechanism Mechanism cannot be opened by on maintenance Mechanism opens with proper Not Working person with proper tools.Bolts into frame have less tools. than 1/2 inch of thread. Cover Di�cult to One maintenance person cannot remove lid after Cover can be removed by one Remove applying 80 Ibs.of 6ft;intent is keep cover from maintenance person. sealing off access to maintenance. Ladder Ladder Rungs Ladde�is unsafe due to missing rungs,misalignment, Ladder meets design standards Unsafe rust,cracks,or sharp edges. and albws maintenance person safe access. Metal Grates Grate with opening wider than 7/8 inch. Grate opening meets design (If Applicable) standards. Trash and Debris Trash and debris that is blocking more than 20%of Grate free of trash and debris. � grate surface. � � Damaged or Grate missing or broken member(s)of the grate. Grate is in place and meets I Missing. design standards. I NO. 6 DEBRIS BARRIERS (E.G.,TRASH RACKS) Maintenance Defect Condition When Maintenance is Needed Results Expected When Components Maintenance is Pertormed. General Trash and Debris Trash or debris that is plugging more than 209'0 of Barrier Gear to receive capacity � the openings in the barrier. flow. Metal Damaged/Missing Bars are bent out of shape more than 3 inches. Bars in place with no bends more Bars. tfian 3/4 inch. Bars are missing or entire bartier missing. Bars in place acoording to design. Bars are loose and rust is causing 509'o deterioration Repair or replace barrier to to any part of barrier. design standards. 9/1/98 1998 Surface Water Design Manual A-6 APPEI�IDIX A h9AINTENANCE STANDARDS FOR PRIVATELY MAINT'AINED DRAINAGE FACILI"I'IES NO. 7-ENERGY DISSIPATERS Maintenance Defect Cooditions When Maintenance is Needed Results Expected When Components Maintenance is Pertormed. Extemal: Rock Pad Missing or Moved Oniy one layer of rock exists above native soil in Replace rocks to design Rodc area five square feet or larger,or any exposure of standards. native soil. Dispersion Trench Pipe Plugged with Accumulated sediment that exceeds 20°k of 1he Pipe cleaned/flushed so that it Sediment design depth. matches design. Not Discharging Vlsual evidence of water discharging at Trench must be redesigned or Water Properly concentrated points along trench(nortnal condition rebuilt to standards. is a'sheet flov+l'of water along trench).Intent is to prevent erosion damage. Perforations Over 1/2 of perforations in pipe are plugged with Clean or replace perforated pipe. Plugged. debris and sediment. Water Flows Out Maintenance person observes water flowing out Facility must be rebuilt or Top of'Distributo�' during any storm less than the design storm o�its redesigned to standards. Catch Basin. causing or appears likely to cause damage. Receiving Area Water in receiving area is causing or has potential No danger of landslides. Over-Saturated of causing landslide problems. Intemal: Manhole/Chamber Wom or Damaged Structure d�ssipaUng flow deteriorates to 1/2 or Replace structure to design Post.Baffles,Side original size or any concentrated wom spot standards. of Chamber exceeding one square foot which would make structure unsound. Other Defects See"Catch Basins"Standard No.5 See"Catch Basins"Standard No. 5 1998 Surface Water Design Manual 9/1/98 A-7 APPENDIX A MAINTENANCE STANDARDS FOR PRNATELY MAINTAINED DRAINAGE FACILITTES NO.8-FENCINC Maintenance Defect Conditions When Mainte�ance is Needed Results Expected When Components Maintenance is Pertormed General Missing or Broken Any defect in the fence that permits easy entry Parts i�place to provide adequate Parts to a facil"ity. security. Erosion Erosion more than 4 inches high and 12-18 No opening under the fence that inches wide permitting an opening under a exceeds 4 inches in height. fence. Wire Fences Oamaged Parts Post out of plumb more than 6 inches. Post plumb to within 1-1/2 inches. i Top rails berrt more than 6 inches. Top rail free of bends greater than � 1 inch. Any paR of fence(induding post,top rails,and Fence is aligned and meets design fabric)more than 1 foot out of design alignment. standards. Missing or loose tension wire. Tension wire in place and holding fabric. Missing or toose barbed wire that is sagging Bafied wire in place with less than more ihan 2-1/2 inches between posts. 3/4 inch sag between post. Extension arm missing,broken,or bent out of Extension arm in place with no shape more than 1 1/2 inches. bends larger than 3/4 inch. Deteriorated Paint or Part or parts that have a rusting or scaling Stn�cturally adequate posts or Protecdve Coating condition that has affected structural adequacy. parts with a un'rform protective coating. Openings in Fabric Openings in fabric are such that an 8-inch- No openings in fabric. diameter ball could fit through. �C NO.9-GATES ' Maintenance Defect Conditions When Maintenance is Needed Results Expected When Component Maintenance is Performed General Damaged or Missing Missing gate or locking devices. Gates and Locking devices in Members place. Broken or missing hi�ges such that gate cannot Hinges intact and lubed.Gate is be easily opened and closed by a maintenance woiicing freely. person. Gate is out of plumb more than 6 inches and Gate is aligned and vertcal. more than 1 foot out of design alignment. Missing stretcher bar,stretcher bands,and ties. Stretcher bar,bands and ties in place. Openings in Fabric See"Fencing"Standard No.8 See"Fenang"Standard No.8 _•f` 9/1/98 1998 Surface Water Design Manual A-8 APPENDIX A MAINIENANCE STANDARDS FOR PRIVATELY MAINTAINED DRAINAGE FACILITIES N0. 10-CONVEYANCE SYSTEMS{PfPES & DITCHES) Maintenance Defect Conditions When Maintenance is Needed Results Expected When Component Maintenance is Pertormed Pipes Sediment 8 Debris Accumulated sediment that exceeds 20%of the Pipe cleaned of aIl sediment diameter of the pipe. and debris. Vegetation Vegetation that reduces free movement of water All vegetation removed so water through pipes. flows freely through pipes. Damaged Protecti�e ooating is damaged;rust is causing Pipe repaired or replaced. more than 50%deterioration to any part of pipe. Any dent that decreases tlie cross section area of Pipe repaired or replaced. pipe by more than 20%. Open Ditches Trash 8�Debris Trash and debris exceeds 1 cubic foot per 1,000 Trash and debris cleared from square feet of ditch and slopes. ditches. Sediment Accumulated sediment that exceeds 20°�of ihe Ditch deaned/flushed of all design depih. sediment and debris so that it matches design. Vegetation Vegetation that reduces free movement of water Water flows freely through through ditches. ditches. Erosion Damage to See"Ponds"Standard No.1 See"Ponds"Standard No.1 Slopes Rock Lining Out of Maintenance person can see native soil beneath Replace rocks to design Place or Missing(If the rock lining. standards. Applicable). Catch Basins See"Catch Basins:Standard No.5 See"Catch Basins'Standard No.5 Debris Barriers See"Debris Bamers"Standard No.6 See"Debris Bartiers'Standard (e.g.,Trash Rack) No.6 N0. 11 -GROUNDS(LANDSCAPING) Maintenance Defect Conditions When Maintenance is Needed Results Expected When Component Maintenance is Performed General Weeds Weeds growing in more than 20%of the landscaped Weeds present in less than 5% (Nonpoisonous) area(trees and shn�bs only). of the landscaped area. Safety Hazard Any presence of poison ivy or other poiso�ous No poisonous vegetation vegetation. present in landscaped area. Trash or Litter Paper,cans,bottfes,totaling more than 1 cubic foot Area dear of litter. • witfiin a landscaped area(trees and shrubs only)of t,000 square feet Trees and Shrubs Damaged Limbs or parts of Vees or shrubs that are split or Trees and shrubs with less than b�oken which affect more than 25%of the total 5%of total foliage with split or foliage of the tree or shrub. broken limbs. Trees or shrubs that have been blown down or Tree or shrub in place free of knocked over. injury. Trees w shrubs which are not adequately supported Tree or shrub in place and or are leaning over,causing exposure of the roots. adequately supported;remove any dead or diseased trees. 1998 Surface Water Desigrt Manual 9/1/98 A-9 APPENDIX A MAINTENANCE STANDARDS FOR PRIVATELY MAINTAINED DRAINAGE FACILTITES , NO. 12-ACCESS ROADS/EASEMENTS I Maintenance Defect Condition When Maintenance is Needed Results Expected When .� Component Maintenance is Performed General Trash and Debris Trash and debris exceeds 1 cubic foot per 1,000 Roadway free of debris which square teet i.e.,trash and debris would fitl up could damage tires. one standards size garbage can. ' Blodced Roadway Debris which coutd damage vehide tires(glass Roadway free of debris which or metal). could damage tires. Any obstruction which reduces dearance above Roadway overfiead dear to 14 feet road surface to less than 14 feet high. Any obstruction restricting the access to a 10 to Obstruction removed to allow at � 12 foot width for a distance of more than 12 feet least a 12 foot access. or arry point restricting access to less than a 10 foot width. I Road Surface Settlement,Potholes, When any surface defect exceeds 6 inches in Road surface uniformly smooth Mush Spots,Ruts depth and 6 square feet in area.In general,any with no evidence of settlement, surface defect which hinders or prevents potholes,mush spots,or ruts. maintenance access. Vegetation in Road Weeds growing in the road surface that are Road surface free of weeds taller Surface more than 6 inches tall and less than 6 inches than 2 inches. tall and less than 6 inches apart within a 400- square foot area. Modular Grid Build-up of sediment mildly contaminated with Removal of sediment and disposal Pavement petroleum hydrocarbons. in keeping with Health Department recommendations for mildly contaminated soils or catch basin sediments. Shoulders and Erosion Damage Erosion within 1 foot of the roadway more than 8 Shoulder free of erosion and � Ditches inches wide and 6 inches deep. matching the surrounding road. :f Weeds and Brush Weeds and brush exceed 18 inches in height or Weeds and brush cut to 2 inches hinder maintenance aocess. in height or deared in such a way as to allow maintenance access. � 9/1/98 1998 Surface Water Design Manual A-10 APPENDIX A MAINTENANCE STANDARDS FOR PRIVATELY MAINTAINED DRAINAGE FACILTI'IES N0. 13-WATER QUALITY FACILITIES A.) Biofiltration Swale Maintenance Detect Condition When Maintenance is Needed Results Expected When Component Maintenance is Performed Biofiftration swale Sediment Accumulation Sediment depth exceeds 2-inches No sediment deposits on grass on Grass Layer layer of the bio-swale,which would impede filtration of nmoff. Vegetation When the grass becomes excessively tall Vegetation is mowed or nuisance (greater than 10-inches);when nuisance weeds vegetation is eradicated,such that and other vegetation starts to take over. flow not impeded.Grass should be mowed to a height between 4 inches and 9 inches. Inlet OuUet Pipe InIeU outlet pipe dogged with sediment and/or No dogging or blockage in the inlet debris. and outlet piping. Trash and Debris Trash and debris aocumulated in the bio-swale. Trash and debris removed from Accumulation bioswale. ErosioN Scouring Where the bio-swale has eroded or scoured Bioswale should be re-graded and the bottom due to flow channelization,or higher re-seeded to speafication,to flows. eliminated channeled flow. Overseeded when bare spots are evident. NO. 13-WATER QUALITY FACILITIES (CONTINUED� B.) Grasslined Filter Strips Maintenance Defect Condition When Maintenance is Needed Results Expected When Component Maintenance is Performed Flter Strip Sediment Accumulation Sediment depth exceeds 2 inches. No sediment deposits on grass on Grass Layer layer of the filter strip,which would impede fittration runoff. Vegetation When the grass becomes excessively tatl Vegetation is mowed or nuisance (greater than 10-inches);when nuisance weeds vegetation is eradicated,such that and other vegetaGon starts to take over. flow not impeded.Grass should be mowed to a height between 4 inches and 9 inches. Trash and Debris Trash and debris accumulated on the filter Trash and Debris removed from Aocumulation strip. filter. ErosioN Scouring Where the filter strip has eroded or scoured SVip should be re-graded and re- due to flow channelization,or higher flows. seeded specification,to eliminate channeled flow.Overseeded when bare spots are evident. V-Notch Pipe Weir When the V-Notch pipe becomes damaged or Cleaned and properiy functioning clogged with sedimenU debris. weir,such that flows uniformly spread. 1998 Surface Water Design Manual 9/1/98 A-11 APPENDIX A MAINTENANCE STANDARDS FOR PRIVATELY MAINTAINED DRAINAGE FACILITIES C.)Wetponds Mai�tenance Defect Condition When Maintenance is Needed Hesults Expected When """` Component Maintenance is Pertormed � Wetpond Vegetation Vegetation such as grass and weeds need to be Vegetation should be mowed to mowed when it starts to impede aesthe6cs of pond. 4 to 5 inches in height. Trees Mowing is generally required when height exceeds and bushes should be removed 18-inches.Mowed vegetabon should be removed where they are interfering with from areas where it could enter the pond,either pond maintenance acfivities. when ihe pond level rises,or by rainfall runoff. Trash and Debris Accumulation that exceeds 1 CF per 1000-SF of Trash and debris removed from pond area. pond. InleU Outlet Pipe InIeU OuBet pipe clogged with sediment and/or No dogging or blockage in the debris material. inlet and outlet piping. Sediment Sediment accumulations in pond bottom that Remo�al of sediment from pond Accumulation in Pond exceeds the depth of sediment zone plus 6-inches, bottom. Bottom usually the first cell. Oil Sheen on Water Prevalent and visible oil sheen. Removal of sediment from pond bottom. Erosion Erosion of the pond's side slopes and/or scouring of Slopes should be stabilized by the pond bottom,that exceeds 6-inches,or where using proper erosion control continued erosion is prevalent. measures,and repair methods. Settlement of Pond Any part of these components that has settled 4- Dike/berm is repaired to Dike/BeRn inches or lower than the design elevation,or specifications. inspector determines dikel beRn is unsound. Rock Window Rodc window is clogged with sediment. wndow is free of sediment and debris. 2 Overflow Spillway Rodc is missing and soil is exposed at top of Replace rocks to specifications. ;3 spillway or outside slope. 9/1/98 1998 Surface Water Design Manual A-12 APPENDIX A MAIN7'ENANCE STANDARDS FOR PRIVATELY MAINTAINED DRAINAGE FACILITIES N0. 13-WATER QUALlTY FACILIIIES(CONTIIVUE� D.)Wetvaults � Maintenance Defect Condition When Maintenance is Needed Results Expected When Compone�t Mai�tenance is Performed Wetvault Trash/Debris Trash and debris accumulated in vault,pipe or Trash and debris removed from Accumulation inleV outlet,(ncludes floatables and non- vault. floatables). Sediment Accumulation Sediment accumulation in vautt bottom that Removal of sediment from vault. in Vault exceeds the depth of the sediment zone plus 6- inches. Damaged Pipes InIeU outlet piping damaged or broken and in Pipe�epaired and/or replaced. need of repair. Access Cover Cover cannot be opened or removed,especially Pipe�epaired or replaced to Damaged/Not Worlting by one person. proper worlcing specifications. Vault Structure Vault:Cracks wider than 1/2-inch and any No cracks wider than 1/4-inch at Damaged evidence of soil particles entering the structure the joint of the inleU outlet pipe. through the cracks,or maintenance/inspection Vault is detertnined to be personnet determines that the vault is not sVucturally sound. shucturally sound. Baffles Baffles corroding,cracking,warping and/or Repair or replace baffles to showing signs of failure as determined by speafications. maintenance!inspection staff. Access Ladder Damage Ladder is corroded or deteriorated,not functioning l.a.dder replaced or repaired to properly,missing rungs,has cradcs and/or speafica6ons,and is safe to misaligned. use as determined by inspection personnel. 1998 Surface Water Design Manual 9/1/98 A-13 APPENDIX A MAINTENANCE STANDARDS FOR PRIVATELY MAINTAIi�1ED DRAINAGE FACILITIES N0. 13-WATER QUALITY FACILfiIES (CONTINUED� E.) Sand Filters Maintenance Defect Condition When Maintenance is Needed Results Expected When ' Component Maintenance is Performed Above Ground Sediment Sediment depth exceeds 1/2-inch. No sediment deposit on grass Accumulation on Grass layer of sand filter which would l.ayer impede permeability of the filter section. Trash and Debris Trash and debris accumulated on sand filter bed. Trash and debris removed from Accumulations sand filter bed. SedimenV Debris in When the yard drain CB's and Gean-out become Sediment,material from the Yard Drains/Clean- full or partially plugged with sediment and/or CB's and dean-outs removed. Outs] debris. Vegetation When the grass becomes excessively tall(greater Vegetation is mowed or than 6-inches);when nuisance weeds and other nuisance vegetation is vegetation starts to take over. eradicated,such that flow is not impeded. Sand Filter Media Drawdown of water through the sand filter media, Usually requires replacement of takes longer tfian 24hours,and/or flow through top 6 to 12-inches of inedia. the overflow pipes occurs frequently. May require replacement of entire sand filter section, depending on section. Prolonged flows Sand is saturated for prolonged periods of time Limit the low,continuous 8ows (several weeks)and does not dry out between to a small portion of the facility stortns due to continuous base flow or prolonged by using a low wooden divider or flows from detention facilities. slighUy depressed sand surface. Short Circuiting When ilows become concentrated over the sand Flow and percolation of water filter rather than dispersed. through the sand fifte�is un'rform and dispersed across the filter section. � �' Erosion Darnage to Erosion over 2-inches deep where cause of Slopes should be stabilized by Slopes damage is prevalent or potential for con6nued using proper erosion control erosion is evident. measures. Rock Pad Missing or Soil beneath the rock is visible. Replace or rebuild the rock pad Out of Place to design specifications. V-Notch Pipe Weir When the V-Notch pipe becomes damaged or Clean and properly functioning clogged with sedimenU debris. weir,such that ftows unifortnly spread. Damaged Pipes Any part of the piping that is crushed or deformed Pipe repaired.or replaced. more than 20%or any other failure to the piping. Below Ground Sediment Sediment depth exceeds 1/2-inch. No sediment deposits on sand Vault. Accumulation on Sand filter section,which would Media Section impede peRneabitity of the filter section. Sediment Sediment depth exceeds 6-inches in vault bottom. No sediment deposit in the first Accumulation in Vault chamber of the vault. Trash/Debris Trash and debris accumulated in vault,or pipe Trash and debris removed from Accumulation inleV outlet,floatables and non-floatables vault,and inleU ouUet piping. Sediment in Drain When drain pipes,cleanouts,and yard drains Remove the material from the Pipes/Yard Drains/ become full with sediment and/or debris. faalities. Cleanouts , � 911/98 1998 Surface Water Design Manual A-14 APPENDIX A MAINTENANCE STANDARDS FOR PRIVATELY MAINTAINED DRAINAGE FACII.,ITIES N0. 13-WATER GIUALITY FACILITIES(CONTINUED� E.) Sand Filters (Continued) Maintenance Defect Conditions When Maintenance is Needed Results Expected When Component Maintenance is Pertormed Below Ground Short Circui6ng When seepage/flow occurs along the vault walis Sand fitter media section re-laid Vault(Continued) and comers. and compacted along perimeter of vautt to form a semi-seal. Vertical Riser Pipes Plugged,failure due to cracking defortna6on.Flows Clean out the riser pipe;replace tend to back-up in first chamber of the vault pipe as needed. Damaged Pipes Inlet or outlet piping damaged or broken and in Pipe repaired and/or replaced. need of repair. Access Cover Cover cannot be opened,one person cannot open Cover repaired to proper Damaged/Not the cover,ooRosioN defortnation of cover. woricing specifications or Working replaced. Vault Structure Cracks wider than 1/2-inch and any evidence of soil Vautt replaced or repaired to Damaged;InGudes partides ente�ng the stn�cture through the cracks, design specifications. Cracks in Walls, or maintenance/inspection personnel detertnines Bottom, Damage to that the vault is not structurally sound. Frame and/or Top Slab. Cracks wider than 1/2-inch at the jants of any inleU No cracks more than 1/4-inch outlet pipe or any evidence of soil particles entering wide at the joint of Uie inleV the vault through the walls. outlet pipe. Baffles Baffles corroding,cradang,warping and/or showing Repair or replace baffles to signs of failure as determined by maintenance/ specifications. inspection person. Access Ladder Ladder is corroded or deteriorated,not functioning Ladder replaced or repaired to Damaged properiy,missing rungs,cracks,and misaligned. speafications,and is safe to use as determined by inspection personnel. 1998 Surface Water Design Manual 9I1/98 A-15 APPENDIX A MAINTENANCE STANDARDS FOR PRIVATELY MAINTAINED DRAINAGE FACILTTIES N0. 13-WQTER QUALITY FACILlTiES(CONTINUFD� F.) Leaf Compost Filters Maintenance Defect Conditions When Maintenance is Needed Results Expected When � Component Maintenance is Pertormed Above Ground Sediment Sediment depth exceeds 0.25-inches. No sediment deposits on fabric Open Swale accumulation on Geo- layer which would impede Textile/media permeability of the fabric. Trash and debris Trash and debris accumulated on compost filter Trash anci debris removed from accumulations bed. . compost filter bed. SedimenU debris in When the yard drain CB's and clean-0uts become Remove the accumulated drain/yard drains/ full of sediment and/or debris. material from the facility. clean-outs. Vegetation VegetaUon impending flow through section,or Vegetation is mowed or encroaching into compost media. eradicated such that flow is no longer impeded. Leaf Compost Media Drawdown of water through the leaf compost, Replace media with new to takes longer than 12-hours,and/or flow through design specifications,in addition the overflow pipes occurs frequently. to replacing fabric. Short-Circuiting When Channeled flow occurs over the leaf inedia; Flow is un'rform over the entire and where flow perks through the media at the width of the media section,and baffles. ooncentrated percolation does not occur at the baffle walls. Media needs to be graded and re-set at the baffles to foRn a seal.Weir plate may need to be ; adjusted in addition. Erosion Damage to Eroded damage over 2-inches deep where cause Slopes should be stabilized by Slopes of damage is prevalent or potential for continued using proper erosion conVol � erosion is prevalent. measures. ': > Damaged Geo-Textile When fabric is tom,deteriorated,raveled,etc. Fabric replaced as necessary. Fabric. Rock Pad Missing or Soil beneath the pad is visible. Replace or rebuild the rock pad out of place to design standards. Damaged Pipes Any part of the pipe system that is crushed, Pipe repaired or replaced. damage due to corrosion,and!or settlement V-Notch Weir Flow is not being un'rformly spread over filter Clean,repair or replace the weir Assemblies media. systems. Below Ground Sediment Sediment depth exceeds 0.25-inches. No sediment deposits on fabric Vault Accumulation on Geo- layer which would impede Textile/Media. permeability of the fabric and compost media. Sediment SedimeM depth exceeds 6-inches in first chamber. No sediment deposits in vault Accumuiation in Vault bottom of first chamber. Trash/Debris Trash and debris aocumulated on compost filter Trash and debris removed from Accumulation bed. the compost filter bed. Sediment in Drain When drain pipes,dean-outs,yard drains become Remove the accumulated Pipes/Yard Drains/ full with sediment and/or debris. material from the facilities. Clean-Outs � 9/1/98 1998 Surface Water Design Manual A-16 APPENDIX A MAIMENANCE STANDARDS FOR PRIVATELY MAINTAINED DRAINAGE FACILTITES N0. 13-WATER QUALITY FACILIIIES(CONT1111UED� F.) Leaf Compost Filter(Continued) Maintenance Defect Condition When Maintenance is Needed Results Expected When Component Maintenance is Pertormed Below Ground Leaf Compast Media Drawdown of water through the leaf compost,takes Replace media with new longer than 12fiours,and/or overflow occurs compost to specifications,in frequently. addition to replaang fabric. Short Circuiting When seepage occurs along the vault wall and Percolation of water occurs comers axur. along tfie walls and comers and not through the media section. Media needs to be re-set along the vault wall and comers to fortn a semi-seal. Plugged/Damaged Flow tends to backup unusually high in the first Clean out the elbow fittings and/ Elbows chamber of the vault. or replace if damaged. Damaged Geo-Textile Fabric is tom,deteriorated,raveled,etc. Fabric replaced as necessary. Fabric Rock Pad Missing or Sal beneath the pad is visible. Replace or rebuild tfie rock pad Out of Place to design standards. Damaged Pipes Any part of the pipes that are crushed,damaged Pipe repaired and/or replaced. due to corrosion and/or settlement. Aocess Cover Cover cannot be opened,one person cannot open Cover repaired to proper Damaged/Not the cover,corrosion/deformatio�of cover. working specifica6ons or Worfcing replaced. V-Notch Weir Flow dces not spread un"rformly over filter media by Clean,repair and/or replace the Assemblies weir section. weir plate section,or adjust height. Vault Structure Cracks wider tl�an 112-inch and any evidence of soil Vault replaced or repaired to Includes Cracks in partides entering the structure through the cracks, design specifications. Wall,Bottom, or maintenance/inspection personnel determines Damage to Frame that the vauft is not structurally sound. and/or Top Slab Baffles Baffles coRoding,cracking warping,and/or showing Repair or replace baffles to signs of failure as determined by maintenance/ specification. inspection person. Access Ladder Ladder is corroded or deteriorated,not functioning Ladder replaced or repaired and Damaged property,missing rungs,cracks,and misaligned. meets specifications,and is safe to use as determined by inspection personnel. Cracks wider than 1/2-inch at the joint of any No cracks more than 1/4-inch inleVoutlet pipe or any evidence of soil partides wide at the joint of the inleU entering the vault through the walls. oudet pipe. i 1998 Surface Water Desigrt Manual 9/1/98 A-17 APPENDIX A MAINTENANCE STANDARDS FOR PRIVAT'ELY MAINTAINED DRAINAGE FACILITIES N0. 13-WATER QUALITY FACIL111ES(CONTINUED� G.) Infiltration Ponds Maintenance Defect Condition When Maintenance is Needed Results Expected When Component Maintenance is Pertormed . Infiltration Pond Vegetation Vegetation such as grass and weeds needs to be Vegetation should be mowed to mowed when it starts to impede infiltra6on function. 2-inches in height.Trees and Mowing is generally required when height exceeds bushes should be removed 12 inches. where they impact ihe infittrating area of the pond. Sand Flter Layer Sand filter layer has sediment deposits that exceeds Remove sediment and top layer 1/2-inch or the infiltration rate of the sand layer is of sand,and replace in kind per less than 2 in/hr. specification. Sediment Sediment accumulations in pond bottom that Removal of sediment from pond Accumulation in exceeds 1/2-incli in depth or percolation test of the bottom. Pond Bottom pond indicates facility is only working at 90'/0 of iYs design percola6on rate. Trash and Debris Accumulation that exceeds 1-CF per 1,000-SF of Trash and Debris removed from pond area. pond. InIeU Outlet Pipe InIeU oubet pipe clogged with sediment and/or No clogging or blockage in the debris material. inlet and outlet piping. Erosion E�osion of the pond's side slope and/or scouring of Slopes should be stabilized by the pond bottom,that exceeds 2-inches,or where using proper erosion control potential for continued erosion is prevalent measures and repair methods. Sediment of Pond Any part of these components that has settled 4- Slopes should be stabifized by Dike/Berm inches or lower ihan the design elevation,or where using proper erosion control ' potential for oontinued erosion is prevalent. measures and repair methods. Rock Wi�dow Rock window is clogged with sediment Window is free of sediment and debris. Overflow Sp�llway Rock is missing and soil is exposed Replace rocks to specifications. / Infiltration VauIV Sediment Tanks:Sediment depth exceeds 6-inches in depth. No sediment deposits in tank Tank Accumulation in bottom. Vault Trash and Debris Trash and debris accumulated in tank,vault or Trash and debris removed from Accumulation connecting pipe.Includes floatables and non- each facility. floatables. Access Cover Cover cannot be opened or removed,especially by Cover�epaired or replaced to Damaged/Not one person. proper working specifications or Wor{cing replaced. Tank or Vau1t Tank:Joints between tank sections failing,such that Tank replaced or repaired to Structure Damaged leakage occurs and.or material being washed design specifications. • through into facility;or maintenance/inspec6on person determines the tank is not structurally sound. f 9/1/98 1998 Surface Water Design Manual A-18 APPENDIX A MAINTENANCE SfANDARDS FOR PRIVATELY MAINTAINED DRAINAGE FACII.ITIFS N0. 13-WATER QUALITY FACILIl1ES(CONTINUED� G.) Infiltration Ponds (Continuea� Malntenance Defect Conditions When Maintenance is Needed Results Expected When Component Maintenance is Pertormed Infiltration VauiU Tank or Vault Structural Vault:Cracks wider than 1/2-inch and any Tank replaced or repaired to Tank Damage evidence of soil partides entering the structure design specifications. through the cracks,or maintenance inspection personnel determines that the vault is not structurally sound. Access Ladder Damaged Ladder is comoded or deteriorated,not Ladder replaced or repaired to functioning properiy,missing rungs,has cracks speafications,and is safe to and!or misatigned. use as detertnined by inspection personnel. 1998 Surface Water Design Manual 9/1/98 A-19 APPENDIX A MAINTENANCE STANDARDS FOR PRIVATELY MAINTAINED DRAINAGE FACILIT'�S N0. 14-OIL CONTROL FACILIIIES A.) OiV Water Separators Maintenance Defect Condition When Maintenance is Needed Results Expected When Component Maintenance is Pertormed. API Type OWS Monitoring Inspection of discharge water for obvious signs Effiuent discharge from vault of poor water quality. should be dear with out thick visible sheen. Sediment Accumulation Sediment depth in bottom of vault exceeds 6- No sediment deposits on vault inches in depth. bottom which would impede flow through the vault and separation � efficiency. Trash and Debris Trash and debris accumulation in vault,or pipe Trash and debris removed from Accumulation inleU outlet,floatables and non-floatables. vault,and infeV outlet piping. Oil Accumulation Oil accumulations that exceed 1-inch,at 1he Extract al from vault by � surface of the water vactoring.Disposal in accordance with state and local rules and regutations. Damaged Pipes Inlet or outlet piping damaged or broken and in Pipe repaired or replaced. need of repair. Access Cover Damaged/ Cover cannot be opened,one person cannot Cover repaired to proper Not Working open the cover,corrosioN deformation of cover. worlcing specifications or replaced. Vauft Structure Damage- Cracks wider than 1/2-inch and any evidence of Vault replaced or repaired to Includes Cracks in Walls soil partides entering the structure through the design specifications. Bottom,Damage to cracks,or maintenancel inspeckion personnel Frame and/or Top Slab determines that the vault is not structurally sound. Baffles Baffles corroding,cracking,warping and/or Repair or replace baffles to showing signs of failure as detertnined by specifications. maintenance/inspection person. '' Access Ladder Damaged Ladder is corcoded or deteriorated,not Ladder replaced or repaired and funcdoning properly,missing rungs,cracks,and meets specifications,and is misaligned. safe to use as determined by inspection personnel. Cracks wider than 1/2-inch at the joint of any No cracks more than 1/4-inch inleU outlet pipe or any evidence of soit particles wide at the joint of the inleU entering the vault through the walls. outlet pipe. CPS-Type OWS Monitoring Inspection of discharge water for obvious signs Effluent discharge from vauft of poor water quality. should be dear with no thick visible sheen. Sediment Accumulation Sediment depth in bottom of vault exceeds 6- No sediment deposits on vault inches in depth and/or visible signs of sediment bottom and plate media,which on plates. would impede flow through the vault and separation efficiency. Trash and Debris Trash and debris accumulated in vautt,or pipe Trash and debris removed from Accumulabon inleV outlet,floatables and non-floatables. vault,and inleU outlet piping. Oil Accumulation Oil accumulation that exceeds 1-inch at the Extract oil from vault by water surtace. vactoring methods.Clean coalescing plates by thoroughly rinsing and flushing.Should be no visible oil depth on water. 9!1/9R �„y� � i r:i�e i� [er ii_•�i_�n \l:t:iu.:l �-?f) APPENDIX A MAINTENANCE STANDARDS FOR PRIVATELY MAINTAINED DRAINAGE FACII.ITIES N0. 14-OIL CONTROL FAC[U71ES(CONTINUED� A.) OiV Water Separators(Continued) Maintenance Defect Condition When Maintenance is Needed Results Expected When Component Maintenance is Pertortned Damaged Coalescing Plate media broken,deformed,cradced and/or Replace that portion of inedia Plates showing signs of failure. pack or entire plate pack depending on severity of failure. Damaged Pipes Inlet or outlet piping damaged or broken and in need Pipe repaired and or replaced. of repair. Baffles Baffles corroding,cradang,warping and/or showing Repair or reptace baffles to signs of failure as determined by maintenance/ specifica6ons. inspection person. Vault Structure Cracks wider than 1/2-inch and any evidence of soil Vault replaced or repaired to Damage-Indudes partides entering the structure through the cradcs, design specifications. Cracks in Walls, or maintenance inspection personnel determines Bottom,Damage to that the vauft is not structurally sound. ' Frame and/or Top Slab Access Ladder Ladder is corroded or deteriorated,not functioning Ladder replaced or repaired and Damaged property,missing rungs,cracks,and misaligned. meets specifications,and is safe to use as determined by inspection personnel. Cracks wider than 1/2-inch at the jant of any inleU No cracks more than 1/4-inch ouUet pipe or any evidence of soil partiGes entering wide at the joint of the inleV the vault through the walls. outlet pipe. B.) Catch Basin Inserts Maintenance Defect Conditions When Maintenance is Needed Results Expected When Component Maintenance is Pertormed Catch Basin Sediment When sediment forms a cap over the insert media of No sediment cap on the insert Accumulation the insert and/or unit media and iYs unit. Trash and Debris Trash and debris accumulates on insert unit creating Trash and debris removed from Accumulation a blockage!restric6on. insert unit.Runoff freely flows into catch basin. Inspection Inspection of inedia insert is required. Effluent water from media inser is fre� � � . sheer Media lnsert-Water Catch basi�insert is saturated with water,which no Remc.� �:,,. ., ...� . . Saturated longer has the capacity to absorb. insert Media lnsert-Oil Media oil saturated due to petroleum spill that drains Remove and replace media Saturated into catch basin. insert. General Regular interval replacement due to typical average Remove and replace media at life of inedia insert product regular intervals,depending on insert product. 1998 Surface Water Design Manual 9/1/98 A-21 I�1 F�I A � W � a � _ �r�r 7S-z �3 October 15, 1998 OFFICE OF THE HEARING EXAMINER KING COUNTY, WASHINGTON c 850 Union Bank of California Building , ��``t 900 Fourth Avenue Seattle, Washington 98164 �+� Telephone(206)296-4660 Facsimile(206)296-1654 ' REPORT AND DECISION ON APPLICATION FOR PRELIlI�IINARY PLAT APPROVAL. SUBJECT: Department of Development and Environmental Services File No. L98P0007 i WINDWOOD Preliminary Plat Application Locarion: Generally between 150th Avenue SE and 155th Avenue SE, � off SE 128th Street , Applicant: Kevin Simmons ' Centex Properties 2320- 130th Avenue NE,Suite 200 Bellevue,WA 98005 Represented by Larry Smith Attorney At Law 1420 Fifth Avenue, 33rd Floor Seattle, WA 98101-2390 SUIVIl�iARY OF RECOMMENDATIONS: Department's Preliminary: Approve,subject to condirions Department's Final: Approve, subject to condirions(modified) Examiner: Approve, subject to condirions(modified) PRELIMINARY MA'ITERS: Application or petition submitted: February 13, 1998 Complete application: March 13, 1998 EXAMINER PROCEEDINGS: Hearing Opened: October 6, 1998, 9:30 a.m. Hearing Closed: October 6, 1998, 12:50 p.m. Participants at the public hearing and the exhibits offered and entered are listed in the attached minutes. A verbatim recording of the hearing is available in the office of the King County Hearing Examiner. Windwood L98P0007 Page 2 ISSLTES/TOPICS ADDRESSED: • Bus stops • Trees • Density(subdivision) • Street trees • Maximum density • Surface water conveyance • Fire protecrion • Surface water drainage • Road improvements • Public sewer availability • Recreation areas • Wetlands • Traffic impacts • Road standards • Traffic impact mitigations FINDINGS,CONCLUSIONS &DECISION: Having reviewed the record in this matter, the Examiner now makes and enters the following: FINDINGS: 1. GeneralInformation. Owner/Developer: Kevin Simmons,Centex Properties 2320- 130th Avenue NE, Suite 200 Bellevue,WA 98005 Engineer: Bill Dunlap,Triad Associates 11814- 115th Avenue NE Kirkland, WA 98034 Location: Generally between 150th Avenue SE and 155th Avenue SE,aff SE 128th Street STR: 11-23-OS Zoning: R-4 Acreage: 28.09 Number of Lots: 111 Density: 3.95 units/acre Typical Lot Size: 5,340 square feet Proposed Use: Detached single-family residences Sewage Disposal: City of Renton Water Supply: Water District 90 Fire District: #25 , School District: Issaquah ', Complete Application Date: March 13, 1998 �I Revised Site Plan Received: September 16, 1998 2. Proposal. Centex Properties(the "Applicant")proposes to divide a 28.09-acre parcel (classified R 4) into 111 single-family residenrial building lots. Lot sizes average approximately 5,340 square feet. Using the "base density" method of density calcularion as established by KCC 21A.12.070, the Applicant stays below the 4.00-unit-per-acre average density for the enrire property, accomplishing 3.98 units per acre. Windwood L98P0007 Page 3 3. SEPA.On August 7, 1998, the Deparbment withdrew a previously-issued Determination of Non- � Significance(DNS),and concurrently issued a Mitigated Determinarion of Non•Significance (MDNS). An MDNS is a declaration that the proposed development will not impose a significant adverse impact upon the environment,provided that certain mitigating measures are taken. In this case, the mitigating measures contained in the MDNS require the Applicant to accomplish certain ingress/egress controls at the proposed entrance to the proposed plat of Windwood.Those mitigating measures are quoted in Finding No. 7.b,below.No person, agency,or tribe appealed the NIDNS. The environmental documents reviewed by the Department arc incorporated in this hearing record and have been subject to this public review. 4. Preliminary Report Errata.On October 6, 1998, the Department of Development and Environmental Services("DDES",or the "Department") issued its Preliminary Report to the Hearing Examiner(Exhibit No. 2). In the public hearing, the Department made the following correcrions to that Report: a. Section F.3,Natural Environment; Hydrography/Mapped Sensitive Areas: There are sir wetlands on-site,not f ve. b. Section J.l.d,Public Services/School Access: The school bus pick-ups will be located at the intersection of SE 124th and 148th Ave�ue SE(not 124th Avenue sE). Any errata having regulatory content or implication will be addressed in the changes to the Department's recommendation in Finding No. 5, following. 5. Department Recommendallon.In its Preliminary Report(Exhibit No.2),the Department recommends granring preliminary approval to the proposed plat of Windwood,subject to 18 conditions of final plat approval stated on pages 6 through 10 of that Report, as modified by these changes: a. Public Sewer Service. In its preliminary rccommendation,the Departiment recommended that the Applicant be required to secure public sewage disposal service � from the City of Renton.Having heard all testimony,the Deparomcnt now suggests Chat the sewer service may be obtained from either City of Renton or Water District No. 90. The Applicant has obtained certificates of sewer service availability from both the City and the District b. Fire Protection. In response to a suggestion from the Applicant, the Department agrees that all language regarding lots 35,000 square feet in size or more should be deleted �om Recommended Condirion No. 6. c. Drainage. In Recommended Condition No. 8, the Department clarifies its intenrion to recommend a retention/detention standard that shall be Level 2 per Basin Policy BW 19. d. King County Road Standards(KCRS) Improvement Requirements. Recommended Condition No. 10.a refers to improvemenLs made on 153rd Avenue SE. Although this street number designation is consistent with some written text in the hearing record, the Applicant's drawings refer to the boulevard entrance segment of this same street as Windwood L98P0007 Page 4 154th Avenne SE.The Department aclmowledges this distinction. This distincrion is important because the entrance segment of the street is subject to neighborhood collector standard, whcreas the remainder(which provides internal subdivision traffic circularion) � is subject to a less rigorous standard(urban sub-access). e. Improvement to 153rd Avenue SE. DDES also agrees with the Applicant's request to idenrify the "urban sub-access standard" that applies to only that portion of 153rd Avenue SE located between SE 124th Street and SE 127th Street, for the same reason as indicated in Finding S.d,preceding. f. School District Improvement Reqaests.Having heard all testimony,the Depamnent amends its recommendarion for a"safe waiting azea with bus pull-out" to include also the language or as otherwue required by the School Dutrict. g. Frontage Improvement Requirements Clarification.The Department seeks to clarify frontage improvement requirements by adding additional language to its recommendarion which would require: The frontage along SE 128th Street(north side)shall be improved to the urban principal arterial standard,with provisions for a bike lane. Incidentally,this improvement standard also requires curb and gutter drainage control and sidewalks. h. Suitable Recreadon Space. There are three changes from Recommended Condition Il�i No. 16 as it is stated on page 9 of the Department's Preliminary Report(Exhibit No. 2): I • The Applicant asks that the King County Parks Uepartment approval of its I recreation facility plan be postponed from the rime of engineering plan approval to the final plat approval, in order to avoid possible delays.The Department agrees,but suggests that a conceptua!recreation plan be submitted at the time that engineering plans are submitted. • The Applicant has proposed moving a temporary cul-de-sac turn-around shown on Exhibit No. 7 (Applicant's Preliminary Plat Drawing) from the terminus of(proposed) 151 st Avenue SE southward approximately 100 feet.This change would reduce the amount of recreational open space in proposed Tract J by approximately 3,500 square feet.The Department agrees to this proposed change,which is illustrated by Exhibit No. 21. This loss of recrearional open space will not jeopardize the Windwood proposal's compliance with the suitable recrearional space and facility requirements of KCC 21 A.14.180 and-.190. • At 390 square feet per lot, the correct suitable open space requirement should be 43,290 square feet,not 52,237 square feet, as indicated in Recommended Condirion No. 16 on page 9 of Exhibit No. 2. Windwood L98P0007 Page S i. Street Tree Planting Requirements. Recommended Condition No. 18 requires the Applicant to plant street trees consistent with several standards, including King County � Road Standards and Metro Service Planning Standards. The Applicant asks for language which assures that these street tree planting requirements apply only to the project site, not to any off-site project work.The DepaRment agrees. As stated in the Depardment's Preliminary Report(Exhibit No. 2),Recommended Condition No. 18 also requires a street tree species selecrion and plan approval by King County Department of Natural Resources. In its fmal recommendation, DDES asks that these references to the Department of Natural Resources be deleted. j. Sensitive Area Impact Mitigation; ClarificaHon.The Department amends its Recommended Condition No. l l.h as stated in its Preliminary Report by suggesting language which clarifies that sensitive area impact mirigation for this project must be. completed prior to final plat approval. 6. Applicant's Acceptaace of Preliminary Repart Correctlons.The Applicant accepts the Department's final recommendation as described by Finding No.4,preceding. 7. Neighborhood Concerns. Correspondence and testimony brought forward the following issues for review: a. Drainage Basin.The Applicant obtained an inter-basin transfer variance from the King County Water and Land Resources Division(WLRD).This appears to have created some misunderstanding regarding basin boundaries within the project. Expert testimony indicates that all of the property is within the Cedar River Basin,except Wetland A, which is located in the May Creek Drainage Basin. It will continue to do so following complete development of Windwood. However,the rooftop-driveway drainage from homes abutting proposed Wetland A will be conveyed to the principal drainage system; then will join the surface water flows of the remainder of Windwood, flowing downstream eventually to the Cedar River.This inter-basin transfer will probably affect no more than nine,perhaps ten,homesites. WLRD and DDES will require the final detailed drainage engineering plans to maintain pre-development wetland levels. b. Tra�c on SE 128th Street.The subject property abuts, and will obtain its principal access from, SE 128th Street. In order to provide ingress/egress compatible with SE 128th Street traffic flows, the MDNS prepared pursuant to the State Environmental Policy Act(SEPA)mandates the following: SE 128th Street is currently a four-lane road with no center turn lane in the vicinity of 154th Avenue SE.To accommodate left-turn tuming movements to and from 154th Avenue SE,the Applicant will provide an eastbound left-turn lane and refuge/merge lane on SE 128th Street at 154th Avenue SE. As noted above, (proposed) 154th Avenue SE will serve as the principal entrance to W indwood. Windwood L98P0007 Page 6 Nearby, SE 128th Street intersects with 148th Avenue SE.The MDNS further mandates: This intersection is an unsignalized"T" intersecrion, with a southbound shared right-and left-turn lane on 148th Avenue SE. To reduce adverse impacts on the intersecrion, the Applicant will provide a separate southbound right and tum lane on 148th Avenue SE at SE 128th Stree� Some neighboring property owners express concern that the proposed development will adversely affect tra�c flows and volumes in the viciniry to a greater degree than indicated in the DDES Preliminary Report to the Hearing Examiner or by Roads Division testimony. Traffic analysis for Windwood was prepared by Transportation Planning and Engineering, Inc., ("TPE")and reviewed by the King County Roads Division. "Burnstead" and"Morrison" development proposals,nearby, aze figured into the traffic analysis for this proposed development as "background traffic".The TPE analysis provides the following informarion: • Although the level of service(LOS) for the 148th Avenue SFJSE 128th Street intersection is "A" overall, the southbound 148th Avenue SE leg of that intersecrion operates at LOS F with 68 seconds of delay. It is this information which provides the basis for the IvIDNS requirement to construct a southbound shared right-and left-turn lane on 148th Avenue SE. • King County Accident Rate data does not indicate unusual accident acrivity in the vicinity of the subject properiy. • Based upon the 111 single-family unit construction plans and on Insritute of Transportation Engineers(TI'E)Trip Generarion Standards, 1,072 average weekday trips are expected to be generated, including mail delivery, urility vehicles,postal service, and so on.This trip generarion rate suggests a p.m.peak hour trip generarion of 113. • Entering sight distance(ESD)and stopping sight distance(SSD)at the proposed Windwood entrance at(proposed) SE 154th Street exceed County minimum standards in both the east and west directions. c. School Access. Issaquah School District Assistant Superintendent Doug Snyder has indicated to DDES Staff that all future students from this subdivision will be bused to school(elementary,junior high, and high school).The school bus pick-ups will be located at the intersecrion of SE 124th Street and 148th Avenue SE, and at the SE 128th Streed 154th Avenue SE intersecrion.Sidewalks to the bus pick-ups and safe waiting areas will be provided. A neighboring property owner notes that nearby Apollo Elementary School has a 100%bused student enrollment due to, she testifies,traffic conditions in the area.The School District has chosen to locate Apollo Elementary on a designated principal arterial street,which intersects nearby with a collector artenal. Typically, elementary schools are not placed on arterials for precisely the reasons Windwood L98P0007 Page 7 indicated in the neighborhood testimony regarding Windwood. In this case, DDES has recommended,and the Applicant has accepted, extensive &ontage and off-site sidewalk improvements that address these pedestrian safety concerns. d. Sewer Service. Apparently, some dispute exists between City of Renton and Water District No. 90 regarding who shall provide sewer service in the vicinity of the subject �I, property, according to the testimony of some hearing participants. Water District No. 90 , has an approved comprehensive plan which anricipates service to the area. City of ' Renton also is developing such a plan, soon to be submitted to the King County Utilitites Technical Review Committee for recommendarion to the King County Council, according to testimony. The Applicant has obtained cenificates of'sewer availability from both purveyors(City of Renton, Exhibit No. 1; Water District No.90, Fxhibit No. 25). DDES has no preference as to which purveyor provides sewer service.The Department's Preliminary Report to the Examiner(Exhibit No. 2)indicates that service will be provided by City of Renton only because the Departmcnt was unawaze of the Water District 90 Certificate of Sewer Service Availability at the time the Department prepared it. The proposed development will not be allowed to proceed to corrstruction in the � absence of a final plat approval which includes authorization to connect to the sewer service purveyor. Before a sewer or wattr utility may put a shovel to the ground within a King County right-of-way, it must have a right-of-way construcrion permit(KCC 14.44). Before a sewer or water utility purveyor/contractor can obtain a right-of-way construcrion permit, ' it must have a franchise to operate within the County right-of-way in quesrion (KCC 6.27). Before the sewer or water purveyor can obtain a franchise, it must have Comprehensive Plan approval by the King County Council(KCC 13.24).Recommended Condition No.4,below,requires that the Applicant must obtain final approval from the King Counry Health Department before final plat recording. In order to obtain that Health Department approval,the Applicant must secure public sewage disposal service from either Water District No.90 or City of Renton.Required sewer system improvements, including a sewer trunk line extension and an on-site collecrion system,will require a Sewer Comprehensive Plan amendment if the connection is to be made to Renton. e. Density Calculation.A neighboring property owner questions how the proposed development could be slightly less than four dwelling units per acre when the lots are small enough to achieve a higher density.The answer, in short, is that the entire property is considered when calculating density.The recrearional open space, retention/detenrion pond, streets,and wetland areas are a part of the entire property and aze thus included in the calcularion. Property azea divided by number of units equals densiry expressed as dwelling units per acre.This method of calculating residential development density is consistent with the dcnsity calculation procedure established by KCC 21A.12.070 (Ordinance 10870, Secrion 344, as amended by Ordinance 11927, Secrion 1). f. Long-Term School Enrollment Impact. Windwood will be served by Apollo Elementary School, Maywood Middle School, and Liberty High School, all located within the Issaquah School Dis�-ict.The Issaquah School Board has adopted capacity figures that indicate their abiliry to accommodate additional studtnts.The figures reveal the Distnct has adequate capaciry to accommodate the anricipated students generated by Windwood L98P0007 Page 8 this proposal through 2001. The Issaquah School District presrntly imposes an impact fee of$2,797 per lot to fund school system improvements. Beyond 2041,predicrion of ' school enrollment and enrollment capaciry becomes remote and speculative,due to - inability to predict future cconomic climate(and therefore the rate of residenrial build-out j within the District), future bond levies and bond levy results,acrions takcn in the State legislature,boundary adjustments,etc. g. Construction Traffic. Development of Windwood will not be permitted to proceed without DDES approval of the Applicant's construcrion traffic control plan. 8. Department Report Adopted. Except as noted above, the facts and analysis contained in the Land Use Services Division Preliminary Report dated October 6, 1998 are correct and aze incorporated here by reference.A copy of the Land Use Services Division report will be attached to those copies of the ezaminer's report which are submitted to the King County Council. CONCLUSIONS: 1. Based upon the whole record, and according substantial weight to the determinarion of environmental significance made by the Land Use Services Division, it is concluded that approval of this subdivision as recommended below would not consritute a major action significantly affecting the quality of the cnvironment.All evidence of environmental impact relating to the proposed action and reasonable altematives to the proposed action have been included in the review and consideration of this action. 2. If approved subject to the condirions recommended below,the proposed subdivision will comply , with the goals and objecrives of the Comprehensive Plan,Newcastle Community Plan, ', Subdivision and Zoning Codes,and other official land use controls and policies of King County. ' 3. If approved subject to the conditions recommended below, this proposed subdivision will make appropriate provision for the public health, safety and general welfaze and for drainage ways, streets, other public ways,water supply,and sanitary wastes; and it will serve the public use and interest. 4. The conditions recommended in the Land Use Services Division's Preliminary Report as amended below are in the public interest and are reasonable requirements. DECISION: GRANT preliminary approval to the proposed plat of WINDWOOD, as described by the Applicant's preliminary plat drawing(Exhibit No. 7),as amended by the relocation of the 151st Avenue SE cul-de- sac (Exhibit No. 19); SUBJECT to the following conditions of fmal plat approval: 1. Compliance with all platting provisions of Title 19 of the King County Code. 2. All persons having an ownership interest in the subject property shall sign on the face of the final plat a dedication that includes the language set forth in King County Council Motion No. 5952. Windwood L98P0007 Page 9 3. The plat shall meet thc basc density(and minimum density)of the R4 zone classificarion. All lots � , shall meet the minimum dimensional requirements of the R4 zone classification or shall be as shown on the face of the approved preliminary plat, whichever is largcr. Minor revisions to the � plat that do not result in substanrial changes may be approved at the discretion of the Department ' of Development and Environmental Services. 4. The applicant must obtain final approval from the King Counry Health Deparnnent. Prior to final � recording of the plat, the applicant must secure public sewage disposal service for the plat from � the City of Renton or King County Water District#t90.Annexation of the site or approval by the BRB will be necessary,and the required sewer system improvements(including a sewer trunk ' line extension and an on-site collecrion system) will require a sewer comprehensive pan I amendment. 5. All construction and upgrading of public and private roads shall be done in accordance with the King County Road Standards established and adopted by Ordinance No. 11187,as amended. 6. The applicant must obtain the approval of the King County Fire Protecrion Engineer for the adequacy of the fire hydrant,water main, and fire flow standards of Chapter 17.08 of the King County Codc. � . 7. Final plat approval shall require full compliance with drainage provisions set forth in King County Code 9.04 and the storm drainage requirements and guidelines as established by the Surface Water Management Division.Compliance may result in reducing the number and/or location of lots as shown on the preliminary approved plat.The following condirions represent portions of the Code and requirements and shall apply to all plats. a. Drainage plans and analysis shall comply with the 1990 King County Surface Water Design Manual and updates which were adopted by Public Rule effective January 1, 1995. DDES approval of the drainage and roadway plans is required prior to any construcrion. b. Current standard plan notes and ESC notes,as established by DDES Engineering Review,shall be shown on the engineering plans. c. The following note shall be shovm on the final recorded plat: "All building downspouts, footing drains, and drains from all impervious surfaces such as parios and driveways shall be connected to the permanent storm drain outlet as shown on the approved construction drawings# on file with DDES and/or the Department of Public Works.This plan shall be submitted with the application of any building permit.All connecrions of the drains must be constructed and approved prior to the final building inspecrion approval. For those lots that are designated for individual lot infiltrarion systems,the systems shall be constructed at the time of the building petmit and shall comply with plans on file." Windwood L98P0007 Page 10 8. The drainage design shall be in accordance with the Cedar River Basin Plan.The retenrion/ , detention standard shall be Leve12 per BW 19 and the water quality trcatment design shall be the Basic Treatment per BW 12(see Maplewood and Orting Hill Subbasins MW3). 9. An exisring drainage course exists along the west site boundary adjoining proposed lots 91 through 98 (in 150�Avenue SE nght-of-way). This drainage course shall be analyzed at engineering plan submittal for capacity per the 1994 King County Surface Water Design Manual, to ensure no drainage impacts following development of the Windwood site. Onsite or offsite improvements may be required to achieve adequate drainage conve}+ance. 10. The following road improvements are required with this subdivision to be constructed according to 1993 King County Road Standards (KCRS): (Metro wants bus improvements.) a. 154th Avenue SE(between the entrance and SE 127�Street)and SE 124�Street shall be improved to the full-width urban neighborhood collector standard. . b. OFFSTTE: On the south side, SE 124�►Street from the west site boundary to 148� Avenue SE shall be improved to the urban neighborhood collector standard.The north side shall also be im�roved per DDES approval,but not to the full urban neighborhood collector standard. Plans for this improvement shall be submitted at engineering plan submittal. � c. SE 127�Street shall be improved to the urban subcollector standard. SE 127�Street shall extend east to the east property boundary. d. 151St Avenue SE, 152nd Avenue SE(between SE 124th Street to SE 126�StreP�� I 126th Street,and 153rd Avenue SE(from SE 124�to SE 127�Street) shall be improved to the urban subaccess standard. e. 152nd Avenue SE(from SE 124�Street, north to cul-de-sac) shall be improved to the urban minor acccss standard. f. Access Tract H shall be impr�ved to the private access road standard per Section 2.09 KCRS. . g. Access Tract L shall be improved to the joint use driveway standard per Secrion 3.01 KCRS. h. Modificarions to the above road condirions may be considered according to the provisions of Section 1.08 KCRS. i. A safe waiting area and shelter footing will be provided for school bus and METRO bus pickup at the project entrance(154�Avenue SE and SE 128�). If requested by the Issaquah School District,a bus pullout will also be provided at or near the Windwood entrance. Also, a safe waiting area for school bus pickup will be provided at 148� Avenue SE and SE 124�Street. Windwood L98P0007 Page 11 j. The Windwood property frontage along the north side of SE 128�Street shall be � improved to the�an principal arterial standard, with provision for a bike lane. i l. Preliminary plat review has identified the following specific sensitive area requirements which apply to this project. All other applicable requirements from KCC 21A.24 shall also be addressed by the applicant: a. The Class II wetlands shall have a buffer width of 50 feet, measured from the wetland edge. Buffer averaging is acceptable so long as the provisions of KCC 21A.24.320B are sarisfied. b. The Class III wetlands(except unregulated wetlands)shall have a buffer width of 25 feet, measured from the wetland edge. c. One Class III wetland,Wetland F, is proposed to be filled.This is acceptable per KCC 21A.24.330.K, with appropriate mitigation as specified in subsection g.below. d. The wetlands and their respective buffers shall be placed in Sensitive Area Tracts(SA'I). e. A minimum building setback line of 15 feet shall be required from the edge of the SAT. f. The wetland and sensirive area tract(s)shall be delineated and signed in accordance with KCC 21A.24.160.The sign details shall be shown on the engineering plans. I g. A final enhancemenbmirigarion plan must be submitted for review and approval by DDES �, along with the engineering plans for this proposal.The plan must include proposed final grades, hydrology,construcrion and monitoring notes and a detailed planring plan, showing species, site locarion. h. Mitigation required pursuant to this project must be completed prior to final plat approval. If this is not possible,due to seasonal requirements or othcr circumstances beyond the applicant's control,the applicant may post a performance bond that guarantees that all required mirigarion measures will be completed within one-yeaz of plat construction. i. Once mirigation work is completed to DDES's sarisfaction,the performance bond may be replaced by a maintenance bond in a form and amount sufficient to guarantee sarisfactory worlananship, materials and performance of the approved plan for a period of five years. j. Upon satisfactory complerion of the final monitoring inspection, DDES staff shall release the maintenance bond. If the project has not met the established performance standards at the end of the monitoring period,the applicant shall be responsible for the prepararion and implementarion of a contingency plan to remedy the situarion. 12. The proposed subdivision shall comply with the Sensirive Areas Ordinance as outlined in KCC 21A.24. Permanent survey marking,and signs as specified in KCC 21A.24.160 shall also be addressed prior to final plat approval. Temporary marking of sensirive areas and their buffers (e.g., with bright orange construction fencing) shall be placed on the site and shall remain in place until all construction activities are completed. Windwood L98P0007 Page 12 13. The following note shall be shown on the final engineering plan and recorded plat: RESTRICTIONS FOR SENSITNE AREA TRACTS AND SENSITTVE AREAS AND BUFFERS Dedication of a sensirive area tract/sensitive area and buffer conveys to the public a beneficial interest in the land within the tracdsensitive area and buffer.This interest includes the preservarion of native vegetarion for all purposes that benefit the public health, safety and welfare, including control of surface water and erosion,maintenance of slope stability, and protection of plant and animal habitat.The sensitive azea tracdsensirive area and buffer imposes upon all present and future owners and occupiers of the land subject to the tracdsensitive area and buffer the obligation,enforceable on behalf of the public by King County,to leave undisturbed all trees and other vegetarion within the tracdsensitive area and buffer.The vegetarion within the tracdsensirive area and buffer may not be cut,pnuied,covered by fill,removed or damaged without approval in writing from the King County Department of Development and Environmental Services or its successor agency, unless otherwise provided by law. � The common boundary between the tracdsensirive area and buffer and the area of development activity must be marked or otherwise flagged to the sarisfaction of King County prior to any clearing, grading,building construction or other development activity on a lot subject to the sensirive area tracdsensitive azea and buffer.The required marldng or flagging shall remain in place until all development proposal activities in the vicinity of the sensitive area are completed. No building foundations are allowed beyond the required 15-foot building setback line,unless otherwise provided by law. 14. All utilities within proposed rights-of-way must be included within a franchise approved by the King County Council prior to final plat recording. 15. The applicant or subsequent owner shall comply with King County Code 14.75,Mirigation Payment System(MPS), by paying the required MPS fee and administration fee as determined by the applicable fee ordinance. The applicant has the option to either: (1)pay the MPS fee at final plat recording, or(2)pay the MPS fee at the time of building permit issuance. If the first oprion is chosen, the fee paid shall be the fee in effect at the rime of plat application and a note shall be placed on the face of the plat that reads, "All fees required by King County Code 14.75, � Mirigation Payment System(MPS),have been paid." If the second option is chosen,the fee paid shall be the amount in effect as of the date of building permit application. 16. Suitable recreation space shall be provided consistent with the requirements of KCC 21A.14.180 and KCC 21A.14.190.The applicant will provide at least 43,290 square feet of recrearion space within Tracts D,F,J, and K.A conceptual recreation facilities plan shall be submitted prior to engineering plan approval.The applicant shall obtain DDES and King County Parks Department approval of the detailed recreational facilities plan before final plat approval will be granted. 17. A homeowners'association shall be established to the satisfacrion of DDES in order to maintain the recreation facilities and associated landscaping, and sensitive areas. Windwood L98P0007 Page 13 18. Street trees shall be provided on-site as follows: I a. At a muumum, trees shall be planted at a rate of one tree for every 40 feet of frontage along SE 128�Street,SE 124�Street, and 154�Avenue SE. Spacing may be modified to accommodate sight distance requirements for driveways and intecsections. b. Trees shall be located within the street right-of-way and planted in accordance with Drawing No. 5-009 of the 1993 King County Road Standards,unless King County Public Works determines that trees should not be located in the street right-of-way. c. If Public Works determines that the required street trees should not be located within the right-of-way,they shall be located no morc than 20 feet from the street right-of-way line. d. The trees shall be owned and maintained by the abutting lot owners or the homeowners' association or other workable organization unless thc County has adopted a maintenance program.This shall be notcd on the face of the fmal recorded plat. e. The species of trees shall be approved by DDES if located within the right-of-way, and shall not include poplar,cottonwood,soft maplcs,gum,any fruit-bearing trees,or any other tree or shrub whose roots aze likely to obstruct sanitary or storm sewers,or that is not compatible with overhead urility lines. f. The applicant shall submit a s�eet tree plan and bond quantity sheet for review and approval by DDES prior to enginecring plan approval. g. The applicant shall contact Metro Service Planning at(206)684-1622 to determine if SE 128� Street is on a bus route. If SE 128�Street is a bus route,the street tree plan shall also be reviewed by Metro. h. The street trees must be installed and inspected,or a performance bond posted prior to recording of the pla�If a performanco bond is posted, the strcet trees must be installed and inspected within one year of recording of the plat.At the time of inspecrion, if the trees are found to be installed per the approved plan,a maintenance bond must be . submitted or the performance bond replaced with a maintenance bond, and held for one year. After one year,the maintenance bond may be released after DDES has completed a second inspecrion and determined that the trees have been kcpt healthy and thriving. A$538 landscape inspection fee shall also be submitted prior to plat recording.The inspection fee is subject to change based on the current County fees. OR.DERED this 15� day of October, 1998. , R. S. Ti ury King G Heazing Examiner Windwood L98P4407 Page 14 T'RANSMITTED this 15t°day of October, 1998,to the following parties and interested persoas: Steve Bedc Kevin 3immons - Scott Brovm Larry J.Smith Sue Burgemeister Eric&Auturtu�Tomlinson Sydney Cheung Gary Weisser Jeffrey Cox Steve�Johanna Craig Keri Akers Carolyn Crawforc! G�eg Borba Ginger Dickson Kim Gaussen Claudia�Michael Donnelly Nidc Gillen Roger porstad Shirley Gdl Wiliam Dunlap,Jr King Conservation Distrid Vnce Gegiia Seattle-King County F{eaith Departrnent Nom�an&Cynfhia Green King Co Prosearting Attomeys Offioe Merty Allen Hamblin Michaelene Manion Unda Matlodc • Aileen MdNanus Aaron McMichael Carol Rogets Ardyce Menager Gary Samek Eleanor Moon Steven C.Townsend Richard Munro Larty West Roger Paulsen Caroline Whalen Mr&Mrs Harold Reynolds Bruce Whittaker Robert Rhoades Oiana Lee Ribera John Riley Sharon Scott NOTICE OF RIGHT TO APPEAL In order to appeal the decision of the Examiner,written notice of appcal must be filed with the Clerk of the King County Council with a fee of$125.00(check payable to King County Of�ice of Finance)on or before October 29, 1998.If a norice of appeal is filed,the original aad six(6)copies of a written appeal statement specifying the basis for the appeal and argument in support of the appeal must be filed with the Clerk of the King County Council on or before November 5,1998.Appeal statements may refer only to facts contained in the hearing record;ncw facts may not be presented on appeal. Filing requires actual delivery to the Office of the Clerlc of the Council,Room 403,King County Courthouse,�rior to the close of business(430 p.m.)on the date duc. Prior mailing is not suf�icient if actual receipt by the Clerk does aot occur withia the applicable time period.The Examiner dces not have authority to extend the time period unless the Office of the Cletk is not open on the specificd closing date,in which event delivery prior to tho close of business on , the next business day is sufficient to meet the filing requirement. If a written notice of appeal and filing fee are not filed within fourteen(14)calendaz days of the date of this report,or � if a written appeal statemeat and argument aze not filed within twenty-one(21)calendar days of the date of this report, I the decision of the hearing examiner contained herein shall be the final decision of King County without the need for further acrion by the Council. MINUTES OF TF�OCTOBER 6, 1998 PUBLIC HEARING ON DEPARTMENT OF DEVELOPMENT& � ENVIRONMENTAL SERVICES FILE NO. L98P0007-WII�IDWOOD: R.S.Titus was the Heariag Examiner in this matter.Participating in the hearing were Keri Akers,Bruce Whittaker, I Ailcen McManus,Larry Smith,Jeffrey Cox,Bill Dunlap,lr.,Susan Burgcmeister,Vince Geglia,Ginger Dicicson, Aaron McMichael,Claudia Donnelly,Norman Green.Ardyce Menager,and Mary Ellen Hamblin. The following exhibits were offered and entered into the record: I Exhibit No. 1 Dcpartment of Development and Enviroamental Services File No. L98P0007 Exhibit No. 2 Depaztrnent of Devclopment and Enviroamental Services Preliminary Report to the Hearing Examiner for the October 6, 1998 public hearing Exhibit No.3 Application dated February 13, 1998 Exhibit No.4 Environmental Checklist dated Febcuary 13, 1998 Exhibit No. 5 Mitigated Dcclaration of Non-Significance dated August 7, 1998 Exhibit No.6 �davit of Posting indicating March 27, 1998 as date of posting and April 1, 1998 as date �davit was received by DDFS ' Exhibit No. 7 Plat map dated Scptember 16, 1998 � Exhibit No. 8 Land use map,Kroll page 806W Exhibit No. 9 Assessor map SW 11-23-OS I Exhibit No. 10 Level Oae Drainage Analysis,July 9, 1998 Exhibit No. 11 SWDM Variance Application,Mazch 30, 1998 Exhibit No. 12 Wetland Analysis Report,April 1, 1998 Exhibit No. 13 Preliininary Gcotech Rcport,June 1995 (received February 13, 1998) Exhibit No. 14 Traffic Impact Analysis,Apri129, 1998 Exhibit No. 15 Conceptual Road Widening Plan,September 16, 1998 Exhibit No. 16 Letter from J.Loan to K Simmons dated April 15, 1998 Exhibit No. 17 Conceptual Drainage Plan,Febcuary 13, 1998 ' Exhibit No. 18 DDES Staf�'s Proposed Additioas W Recommended Condition No. 10 Exhibit No. 19 Applicant's Proposed Changes to Staff Recommended Conditioas Exlubit No.20 Color-coded proliminary plat drawing Exhibit No. 21 Illustration of Applicant's proposed alteration to cul de sac at Lot 80 Exhibit No. 22 Statement by Claudia Donaelly Exhibit No.23 Statement by Normaa Green Exhibit No. 24 DDES Staffs Recommended Addition to Condition No. 10 Exhibit No. 25 Certification of Sewer Availability from Water Dis�ict 90 RST:gb/vam/gb . platsV98pu98p0007 rpt