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Home My WebLink About01-011 t t Regional Communications and Emergency Coordination Center Drainage Report P�o AN®�R�G 4z 30791 �'�taNAL�G p EXPIRES 4/4/ 43 Prepared by: SYMO N DSI 1601 Second Avenue, Suite 1000 Seattle,Washington 98101 i)EVFLOPNIE NT Proj ect No. 01-011 Cln.OF F EL� MG July zoos Jul 2 0 200, PLy 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 K.G. DEPT of coOT. & Ff 11— MGM' RC& ECC Address Location ADMl'N 8L06, 500 FOUR?�l � Township ?_3 N Phone Range 5 F Project En ineer ./Z....Section I G BKON AratDER6UR G Company 5 C E Address/Phone 2-O6 g 4 i- t 8.5 5 Part 3 TYPE OF PERMIT Part 4 OTHER REVIEWS AND PERMITS APPLICATION 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 SITE COMMUNITY AND DRAINAGE BASIN Community CITY OF RENTON Drainage Basin CEDAR RIVER Part 6 SITE CHARACTERISTICS River Floodplain Wetlands Stream Seeps/Springs Critical Stream Reach High Groundwater Table Depressions/Swales Groun=Recharge Lake Other Steep Slopes Part 7 SOILS Soil Type Slopes Erosion Potential Erosive Velcoties Additional Sheets Attached Part 8 DEVELOPMENT LIMITATIONS REFERENCE LIMITATION/SITE CONSTRAINT Ch. 4—Downstream Analysis Additional Sheets Attached Part9 ESC REQUIREMENTS MINIMUM ESC REQUIREMENTS MINIMUM ESC REQUIREMENTS DURING CONSTRUCTION AFTER CONSTRUCTION Sedimentation Facilities Stabilize Exposed Surface Stabilized Construction Entrance Remove and Restore Temporary ESC Facilities Perimeter Runoff Control Clean and Remove All Silt and Debris Clearing and Graing Restrictions Ensure Operation of Permanent Facilities Cover Practices Flag Limits of SAO and open space Construction Sequence preservation areas Other Other 7 t Part 10 SURFACE WATER SYSTEM Method of Analysis Grass Lined Tank 11nf=tratlon 5 B U H Channel Vault Depression [�V Pipe System Compensation/Mitigati Energy Dissapator Flow Dispersal on of Eliminated Site Open Channel Wetland Waiver Storage Dry Pond Stream Regional =WetPond Detention Brief Description of System Operation PIA V( n�(�1"��OW to r.�P�eht lOh 00r) Facility Related Site Limitations Reference Facility Limitation NONE KNOWN Part 11 STRUCTURAL ANALYSIS Part 12 EASEMENTS/TRACTS Cast in Place Vault Drainage Easement Retaining Wall Access Easement Rockery> 4' High Native Growth Protection Easement Structural on Steep Slope Tract Other Other Part 13 SIGNATURE OF PROFESSIONAL ENGINEER I or a civil engineer under my supervision my supervision have visited the site. Actual site conditions as observed were incorporated into this worksheet and the attachments. To the best of my knowledge the information provided here is accurate. Si ned/Date T Table of Contents Regional Communications and Emergency Coordination Center Section 1 Project Overview .............................................................................. 1 1.1 Project Description .......................................................................... 1 1.2 Existing Conditions......................................................................... 1 1.3 Developed Conditions...................................................................... 1 1.4 Challenging Site Parameters.......................................................... 2 Section 2 Core and Special Requirements........................................................ 3 2.1 Core Requirements.......................................................................... 3 2.1.1 Core Requirement#1 ........................................................3 2.1.2 Core Requirement#2........................................................3 2.1.3 Core Requirement#3........................................................4 2.1.4 Core Requirement#4........................................................4 2.1.5 Core Requirement#5........................................................4 2.2 Special Requirements......................................................................4 2.2.1 Special Requirement#1....................................................4 2.2.2 Special Requirement#2....................................................5 2.2.3 Special Requirement#3....................................................5 2.2.4 Special Requirement#4.................................................... 5 2.2.5 Special Requirement#5....................................................5 2.2.6 Special Requirement#6.................................................... 5 2.2.7 Special Requirement#7....................................................6 2.2.8 Special Requirement#8....................................................6 2.2.9 Special Requirement#9....................................................6 2.2.10 Special Requirement#10................................................6 2.2.11 Special Requirement#11 .................................................6 2.2.12 Special Requirement#12................................................7 2.2.13 Special Requirement#13 ................................................8 Section 3 Offsite Analysis.................................................................................9 3.1 Field Inspection...............................................................................9 Section 4 Infiltration and Water Quality Sizing Criteria and Results.......... 11 4.1 Infiltration Ponds .......................................................................... 11 4.2 Water Quality Ponds..................................................................... 12 4.3 Filter Strips ................................................................................... 12 Section 5 Conveyance System Analysis and Design..................................... 13 5.1 Conveyance System....................................................................... 13 i Drainage Report 07/17/01 Svmonds Consulting Engineers Table of Contents t ' Regional Communications and Emergency Coordination Center List of Appendices Appendix A....................................................... Contributing Area Maps Appendix B.............................................. Infiltration Pond Calculations Appendix C .........................................Water Quality Pond Calculations Appendix D.......................................................Filter Strip Calculations Appendix E ......................................... Conveyance System Calculations ii Drainage Report 07/17/01 Symonds Consulting Engineers r Regional Communications and Emergency Coordination Center Section 1 Project Overview 1.1 Project Description The proposed King County Regional Communications and Emergency Coordination Center in Renton, WA, is intended to accommodate a full-time regional communications staff, as well as an emergency coordination center for temporary management of emergency response and communications. The Center will consist of a single-story building with appurtenant parking and an approximately 200-foot high communications tower. It is anticipated that approximately 4.40 acres of existing surface area will be affected, resulting in 0.58 acres of new roadway, 0.39 acres of landscaping, and 3.44 acres of new impervious surface (including parking areas and the new building). The project is located within Zone 2 of an Aquifer Protection Area within the City of Renton, and as such will comply.with the requirements and regulations set forth by the City of Renton Municipal Code, and the King County Surface Water Design Manual (1990). The project includes the installation of storm drainage pipes, filter strips, water quality ponds, and infiltration ponds to convey and treat the stormwater from the new impervious roadways, parking areas, and rooftops. 1.2 Existing Conditions The existing property is located within the City of Renton in the vicinity of 2°d Avenue NE and Monroe Avenue NE, southeast of the County maintenance facilities. The site was apparently used as tank testing grounds during World War II, and is currently used by King County Road Services Division as a storage and paint-stripe testing area. The site is relatively flat, though the southern portion of the site is the crest of a 250-foot high slope that descends toward the Cedar River. Much of the site is currently wooded and overgrown with heavy vegetation. An existing paved roadway cuts through the site. There are also several gravel foot paths across the site. The storm drainage from this property does not appear to leave the site via overland flow. Field visits have indicated, and the geotechnical report have confirmed, that the surface water infiltrates completely into the soil. Section 3: Offsite Analysis contains a description of the downstream drainage conditions, and Section 2.2.12 describes the results of the Geotechnical Report prepared for this site. 1.3 Developed Conditions ,In the developed condition, the property will have approximately 0.58 acres of new roadway, 0.39 acres of landscaping, and 3.44 acres of new impervious surface (including parking areas and the new building). Runoff from the roadway will be treated for water quality in filter strips, and will be infiltrated via drainage swales. 07/17/01 1 Drainage Report Symonds Consulting Engineers Regional Communications and Emergency r r Coordination Center Runoff from the new parking areas will be directed to water quality ponds through storm drain pipes, and will then be infiltrated via infiltration ponds. Runoff from the roof of the proposed building will be routed directly to the infiltration ponds, as pretreatment is not required. 1.4 Challenging Site Parameters There are two site parameters that affect the location and size of the proposed infiltration ponds. First, there are two existing 50-foot wide easements directly east of the project site which accommodate a 16-inch and a 20-inch oil pipeline, owned by Olympic Pipeline. The design of the eastern infiltration pond is intended to prevent any changes in the groundwater elevation in the soil surrounding these pipelines. Secondly, the steep slope to the south of the site is within 200 feet of the eastern infiltration pond. Due to the high permeability of the existing soils and the existing infiltration patterns of stormwater, the proximity of this western pond to the slopes south of the site is not anticipated to affect the stability of the slope. See Section 2.2.11 for a discussion of the Geotechnical Report prepared for this site and the infiltration pond locations near a steep slope. 07/17/01 2 Drainage Report Symonds Consulting Engineers Regional Communications and Emergency Coordination Center Section 2 Core and Special Requirements 2.1 Core Requirements 2.1.1 Core Requirement#1: Discharge at Natural Location Requirement: All surface and storm water runoff from a project must be discharged at the natural location so as not to be diverted onto or away from downstream properties, except that surface and storm runoff from new or existing impervious surfaces subject to vehicular use or storage of chemicals should be discharged at the location and in the manner which will provide the most protection to the aquifer. The manner in which runoff is discharged from the project site must not create a significant adverse impact to downhill properties or drainage systems. There is no existing concentrated drainage flow away from the project site. Currently, stormwater that falls on the site is infiltrated into the ground. The design for the proposed stormwater management facilities is to install infiltration ponds which will mimic the existing infiltration process. Runoff will not be diverted onto any downstream properties, nor will any existing runoff be diverted away from downstream properties. Runoff from the proposed impervious surfaces that are subject to vehicular use or storage of chemicals will be routed to a treatment water quality pond prior to infiltration. The water quality pond will be lined in order to prevent infiltration into the aquifer during the treatment stage. The project is not located within a Landslide Hazard Drainage Area, nor is it adjacent to or containing Sensitive Areas Ordinance (SAO)-defined landslide, steep slope, or erosion hazard areas. The project is located within Zone 2 of an Aquifer Protection Area as defined by City ordinance, and the methods of analysis and design are in compliance with those standards set forth in Special Requirement#13: Aquifer Recharge and Protection Areas. 2.1.2 Core Requirement#2: Offsite Analysis Requirement: All proposed projects must submit an offsite analysis report that assesses potential offsite drainage impacts associated with development of the project site and proposes appropriate mitigations of those impacts. See Section 3 for an Offsite Analysis of the proposed project area. 07/17/01 3 Drainage Report Symonds Consulting Engineers Regional Communications and Emergency Coordination Center 2.1.3 Core Requirement#3: Runoff Control Requirement: Proposed projects must provide runoff control through a combination of peak rate runoff control and on-site biofiltration. Proposed project runoff resulting from more than 5,000 sf of impervious surface, and subject to vehicular use or storage of chemicals, shall be treated prior to discharge from the project site by on-site biofiltration measures as described in Section 4.6.3. of the KCSWDM Peak rate runoff control will be provided through infiltration ponds in order to mimic the existing natural drainage condition of the site, designed in accordance with KCSWDM Section 4.5.2. Runoff resulting from areas subject to vehicular use or storage of chemicals will be pretreated using water quality ponds as described in Section 4.6 of the KCSWDM. See Section 4: Infiltration and Water Quality Sizing Criteria and Results. 2.1.4 Core Requirement#4: Conveyance System Requirement: All conveyance systems for proposed projects must be analyzed, designed and constructed for existing tributary off-site runoff and developed on-site runoff from the proposed project. . See Section 5: Conveyance System Analysis and Design conveyance system design criteria and calculations. 2.1.5 Core Requirement#5: Temporary Erosion and Sedimentation Control Requirement: TESC measures shall be provided that minimize the transport of sediment to drainage facilities, water resources, and adjacent properties. A Temporary Erosion and Sediment Control Plan has been prepared for this project, and is included in the Design Drawings. 2.2 Special Requirements 2.2.1 Special Requirement#1: Critical Drainage Area Threshold: Proposed project lies within a designated Critical Drainage Area as indicated on Critical Drainage Area maps at the BALD Division Permit Center. N/A. Project does not meet threshold criteria. 07/17/01 4 Drainage Report Symonds Consulting Engineers Regional Communications and Emergency Coordination Center 2.2.2 Special Requirement #2: Compliance With an Existing Master Drainage Plan Threshold: Proposed project lies within an area covered by an approved Master Drainage Plan as listed at the BALD Division Permit Center.. N/A. Project does not meet threshold criteria. 2.2.3 Special Requirement#3: Conditions Requiring a Master Drainage Plan Threshold: Proposed project is a Master Planned Development, a Planned Unit Development, or will clear an area more than 500 acres within a contiguous drainage subbasin. N/A. Project does not meet threshold criteria. 2.2.4 Special Requirement#4: Adopted Basin or Community Plans Threshold: Proposed project lies within an area with an adopted Basin or Community Plan as listed at the BALD Division Permit Center. N/A. Project does not lie within an area with an adopted Basin or Community Plan as listed at the BALD Division Permit Center 2.2.5 Special Requirement#5: Special Water Quality Controls Threshold: Discharge area contains more than I acre of new impervious surface that will be subject to vehicular use or storage of chemicals and (a)proposes direct discharge of runoff to a regional facility, receiving water, lake, wetland, or closed depression without on-site peak rate runoff control; or(b)proposes discharge of runoff through overland flow or on-site infiltration into a Class 1 or 2 stream, or Class 1 wetland, within one mile radius downstream from the project site. N/A. Project proposes to discharge to on-site infiltration ponds that will provide peak rate runoff control for 100-year, 24-hour and 100-year, 7-day storms. 2.2.6 Special Requirement#6: Coalescing Plate Oil/Water Separators Threshold: Proposed project will construct more than 5 acres of impervious surface in any threshold discharge area that will be subject to (a)petroleum storage or transfer, or (b) high vehicular use, or(c) heavy equipment use, storage or maintenance. N/A. Site does not meet threshold criteria. 07/17/01 5 Drainage Report Symonds Consulting Engineers Regional Communications and Emergency Coordination Center 2.2.7 Special Requirement#7: Closed Depressions Threshold: Proposed project will discharge runoff to an existing closed depression that has greater than 5,000 sf of water surface area at overflow elevation. N/A. Project does not meet threshold criteria. 2.2.8 Special Requirement#8: Use of Lakes,Wetlands or Closed Depressions for Peak Rate Runoff Control Threshold: Project proposes to use a lake, wetland or closed depression for peak rate runoff control, to receive a direct discharge, or to increase the volume of runoff to an off-site closed depression. N/A. Project does not meet threshold criteria. 2.2.9 Special Requirement#9: Delineation of 100-year Floodplain Threshold: Proposed project contains or abuts a stream, lake, wetland, or closed depression, or if other King County regulations require study of flood hazards. The project site does contain closed depressions, as there is no overland flow path in evidence within the proposed site area. However, the infiltration rates through these soils and the depth of the water table suggests that there would be no standing water on the site during a 100-year storm event. See Section 2.2.12 for a description of the Geotechnical Report findings for the project site. 2.2.10 Special Requirement#10: Flood Protection Facilities for Type 1 and 2 Streams Threshold: Proposed project contains or abuts a Class 1 or 2 stream that has an existing flood protection facility, or proposes to construct a new, or modify an existing, flood protection facility. N/A. Project does not meet threshold criteria. 2.2.11 Special Requirement#11: Geotechnical Analysis and Report Threshold: Proposed project will construct (1)a pond or infiltration system within 200 feet from the top of a steep slope, or on a slope with a gradient steeper than 15%, or using a berm higher than 6 feet, or(2) modifies an existing flood protection facility. The proposed project will construct an infiltration pond approximately 130 feet from the top of the steep slope south of the project area. This slope is inclined at approximately 2H:1V. A Geotechnical Report was prepared for this site by HWA GeoSciences, Inc., as is described in Section 2.2.12. In regards to the proximity of the steep slope, the results of their analysis were summarized in a correspondence from the geotechnical engineer as follows: 07/17/01 6 Drainage Report Symonds Consulting Engineers ' Regional Communications and Emergency Coordination Center Infiltrated water will seep down through the permeable recessional outwash until it encounters the relatively impermeable glacial till/drift, and will then seep in the direction of gravity along this contact. Our borings indicate that the top of the Glacial Till/Drift, below the proposed facilities, slopes down to the northwest as illustrated in our Figure 6 [of the Geotechnical Report]. Thus, water seepage from the easterly infiltration pond is not likely to flow toward the south slope. It is our opinion, therefore, that storm water infiltration at either infiltration pond location will not result in a reduction of the stability of the south slope. The location of the infiltration ponds is not anticipated to have any adverse impacts on the steep slope. 2.2.12 Special Requirement#12: Soils Analysis and Report Threshold: Soils underneath proposed project have not been mapped, or the existing soils maps are in error or not of sufficient resolution to allow the proper engineering analysis of the proposed site to be performed. A geotechnical report was prepared for this project by HWA GeoSciences, entitled Geotechnical Report• King County Regional Communications and Emergency Coordination Center• Renton Washington (June 20, 2001). This report is still in the draft stage. The Geotechnical Report results indicate that the receptor soils in the areas of the proposed ponds are unsaturated recessional outwash soils which exhibit "high permeability," with a groundwater table at a depth of approximately 20 feet. According to the field investigation included in Appendix A of the Geotechnical Report, infiltration testing was performed with the following results: HWA completed a single pilot infiltration test (PIT) in the proposed easterly infiltration area in general accordance with Draft Ecology guidelines (Ecology, 2000)...The relatively large-scale test was conducted at a depth of approximately 6 feet below the ground surface, or approximate elevation 327 feet. The test pit was excavated with a bottom area of approximately 10 feet by 10 feet, and the sidewalls were trimmed to about 1%H:1V. A 2-inch diameter fire hose with a flow meter and butterfly valve were attached to a nearby hydrant located in the City of Renton maintenance facility. The free end of the hose was inserted into a 6-inch rigid pipe and splash bucket anchored to the test pit bottom. A 6-inch pipe marked with 1-inch increments was installed vertically in the bottom of the test pit to measure the water level. Water was added to the test pit at a maximum flow rate of about 125 gallons per minute for 22% hours. The cumulative volume and 07/17/01 7 Drainage Report Symonds Consulting Engineers Regional Communications and Emergency Coordination Center instantaneous flow rate were recorded every 30 minutes for the duration of the test. Approximately 20,000 cubic feet of water flowed into the pit over the 22%2 hour test. There was no accumulation of standing water in the pit throughout the entire test. The results of this test indicate that the high permeability of the soil would preclude saturated soil as an antecedent condition to a precipitation event, and that standing water would not be an issue on the site. 2.2.13 Special Requirement#13: Aquifer Recharge and Protection Area Threshold: Proposed project lies within an Aquifer Recharge and/or Protection Area as defined and designed by City ordinance and as indicated on the Aquifer Recharge and Protection Map at the City permit Counter. Proposed project lies within Zone 2 of an Aquifer Protection Area as indicated on the Aquifer Protection Map. Infiltration pond and water quality pond analyses, sizing, and liners have been designed in accordance with the special requirements, methods of analysis and design standards as outlined in the KCSWDM and the City of Renton Municipal Code, as modified for infiltration within Zone 2 of an Aquifer Protection Area. See Section 4: Infiltration and Water Quality Sizing Criteria and Results. 07/17/01 8 Drainage Report Symonds Consulting Engineers Regional Communications and Emergency Coordination Center Section 3 Offsite Analysis 3.1 Field Inspection The site includes the King County Roads campus along with the area south of the City of Renton Shops site. Also included are the steep slopes that drop down towards the Maplewood area at the bottom of the valley. At the time that this report was printed, the King County parcel was being subdivided. For the purpose of this report, the site includes the full, roughly 100-acre parcel owned by King County. Following subdivision, the subject project will occupy a lot of roughly 5 acres. Along with the primary site, two off-site areas were visited,'the Sunnydale Community, entrance located at 375 Union Ave. SE and Leisure Estates located at 201 Union Ave. SE. The site was examined during a visit on January 5, 2001. The following surface water features were observed: There is an existing depression immediately north of the proposed easterly pond. The depression is fed by an existing 12-inch corrugated metal flume about 70 feet long that crosses diagonally over the Olympic Pipeline Company easement on the east edge of the subject property. At the upstream end of the flume are two pipes, one 18-inch diameter the other 12-inch diameter. These pipes appear to originate in the RV storage lot that is shared by the mobile home parks. The flume was running about one inch deep or less at the time of the site visit. Weather at the time was intermittent rain. Based on the.City of Renton's stormwater map, number F5, the area tributary to the closed depression is about 5 acres. It is probable that most of the rainfall originating in the tributary area is intercepted by the storm drainage system in the Sunnydale Mobile home park. The Sunnydale system conveys the stormwater to a moderately large detention pond that is a prominent feature on map number F5. It is interesting to note that the outfall pipe downstream of this pond is slated for replacement within the next year. The existing deteriorated CMP pipe will be abandoned. A new on-grade HDPE pipe will convey flows from the pond down the steep slope to the Cedar River Valley. The other surface water feature observed was the ephemeral stream that parallels the existing deteriorated pipe mentioned above. This stream was followed upstream to its source which proved to be a series of seeps emanating from the steep slopes due south of the building site. The seeps were located about 20 or 30 vertical feet down from the top of the slope. Approximately 3 or 4 were seen arrayed along the head of the ravine, each at roughly the same elevation. Based on conversations with the geotechnical engineer, it is believed that the elevation of the seeps corresponds with the top of the existing glacial till soil that is shown on Figure 7 in the geotechnical report. When the seeps were again observed on March 14th of 2001, they had nearly dried up. 07/17/01 9 Drainage Report Symonds Consulting Engineers Regional Communications and Emergency Coordination Center (This page deliberately blank) 07/17/01 10 Drainage Report Symonds Consulting Engineers Regional Communications and Emergency Coordination Center Section 4 Infiltration and Water Quality Sizing Criteria and Results 4.1 Infiltration Ponds Peak rate runoff control for the proposed project will be achieved through infiltration ponds within the project site. Runoff from the project area will be directed to one of three infiltration ponds. The contributing areas to these ponds are indicated in Appendix A. The infiltration ponds were sized according to the requirements of KCSWDM Section 4.5.2, using the StormShed"` Stormwater Analysis software as developed by Engenious Systems, Inc. StormShed utilizes the Santa Barbara Urban Hydrograph (SBUH) method of runoff analysis. The following table summarizes the contributing areas and hydrologic flow characteristics for the developed site. Complete calculations have been included in Appendix B. Im ervious Area ac Pervious Peak Flow Rate Peak Volume PGIS Non-PGIS Area (ac) (Qpeak, cfs) (Vpeak, ac-ft) Western Pond 1.29 0.71 0.13 1.90 0.635 Eastern Pond 1.28 0.18 0.21 1.46 0.487 Central Pond - 0.23 - 0.23 0.070 Table 4-1 Hydrological Characteristics 100-year, 24-hour storm event The infiltration ponds were preliminarily sized to infiltrate the 100-year 24-hour storm and the 100-year 7-day storm, using infiltration only through the bottom area. Rather than provide for an overflow conveyance system downstream from the ponds, an additional factor of safety of two (2) is applied to the infiltration rate in the event that the infiltration areas become plugged, effectively doubling the calculated size of the ponds. The pond sizing is summarized in the following table. Initial Peak Peak Outflow, Active Min. Bottom Bottom Stage (ft) Infiltration Volume Dimension, Area (ft2) (cfs) (ac-ft) (ftxft) Western Pond 1625 3.02 0.28 0.13 99 x 33 Eastern Pond 1200 3.03 0.21 0.14 85 x 28 Central Pond 300 0.97 0.05 0.01 60x10 Table 4.2 Infiltration Pond Characteristics 07/17/01 11 Drainage Report Symonds Consulting Engineers Regional Communications and Emergency , Coordination Center 4.2 Water Quality Ponds The proposed project will result in an increase of pollution generating impervious surfaces (PGIS) for the areas contributing to the western and eastern ponds. These areas will be pretreated using water quality ponds, sized and designed according to the KCSWDM Section 4.6. The ponds will act as water quality facilities to improve the quality of the stormwater prior to the infiltration ponds. The ponds will be lined in order to prevent infiltration of untreated surface water into the ground. Water quality pond volumes are designed, at minimum, to contain the total volume of runoff from the water quality design storm, having a total precipitation of one- third of the 2-year, 24-hour design storm. The surface area of the pond is, at minimum, one percent of the impervious surface area in the drainage sub-basin contributing to the facility. Only that portion of impervious surface within the sub- basin that is pollution generating is routed through the water quality ponds. The following table summarizes the design parameters for the water quality ponds. Complete calculations have been included in Appendix C. Contributing Peak Flow Peak Min. Surface Min. Surface Area, PGIS Rate (cfs) Volume Area @ 3' Dimension (ft x ft2) (ft3) de th (ft2) ft Western 56,320 0.170 2182 727 15 x 49 Pond Eastern 55,657 0.169 2164 721 15 x 48 Pond Table 4.3 Water Quality Pond Characteristics The Central Pond will not have a water quality pond prior to infiltration since none of the contributing area is pollution generating. 4.3 Filter Strips Runoff from the proposed roadway will be treated for water quality with a filter strip along the western edge of the roadway. The width of the filter strip is a fraction of the tributary area draining to the strip. For the 24-foot wide roadway proposed for this project, the filter strip must be a minimum of 5.5 feet wide. See Appendix D for filter strip sizing calculations. 07/17/01 12 Drainage Report Symonds Consulting Engineers Regional Communications and Emergency Coordination Center Section 5 Conveyance System Analysis and Design 5.1 Conveyance Design They conveyance system was preliminarily sized using the Manning's equation, assuming a minimum slope of 1%. The conveyance pipes are 12-inch diameter, and are of adequate capacity to convey the 25-year 24-hour storm, as well as the 100- year 24-hour storm without overtopping. See Appendix E for preliminary conveyance sizing calculations. 07/17/01 13 Drainage Report Symonds Consulting Engineers S APPENDIX A CONTRIBUTING AREA MAPS nllNY1L RMSiDF fo1V: ot1MlAtt-MyttmJlLM!'-0vM rlOf pt}C 0!/t eOt 15Df f°t(t t.t W/m M nw Jp M2 @ p07peyW _ PPP-SS-TTTT e.. �''20' '" '" CITY OF King County Regional Communications oe of .Y., RENTON and Emergency Coordination Center Rm 'NM Plannlnq/Building/Public Works Dept. GRADING AND Z GreggZimmerman P.E., Administrator C3' N0. REVISION BY DATE APPR �- �� DRAINAGE PLAN WEST tk Ala. 0° _ Wit---- -� \ o \ o 33o 5 339.4 \� - 0 - ----- ----- ' WESTERN POND ----- �8=---1i -- °----� Aimp= 2 . 71 acres o\ \ \ \` ^.-,� R --� r----- --�;- I A Per:- 0 . es 13 acres (� \ •'� 'b- J Y _ I I I----- ----- 340. 340.5 TO 340.0 X S33\ \ x 33 33 .1 k Cb 1 t 339.2 CB \ t I I L___ RE- 33 .2 I B EE � pp _ I 333.6-41 11 _ .. E= R37 ----- -----BJ 1 -- 339.4 3 .9 \ x X J 3 x t---- I 1 I 40.6 339.6 339.1 3a7.4 O® r----- z-- 0- 1 B -----�J L�----- --- NVA X TP9 C-----7 r----- -- �- 'i33 0 339. ® I 8 .--------- ------ 338.6 -----------11 . -- -- _ 1 `-----------� N ----- RE- \ \ T o J --� BI IB � I I j �\ PLTR AZA � ° --7 ----- ----- 1341. D \ ----� 339. 1 j 339.4 _ I �� --I ---34 -- I \ 340.7 ` 34C.1t \ WATER FEATURE � I u) i- w....1...... M RAIN LEADER ` I \ U) \\\ 340.O-BOW r=Tl Ln ° \ !1 ~�j \ 0 �� V 0 f i k ETTLIN POND ^' \ MP WA LITY POND \ !J/ ✓ \ BOTTOM 330.4 �T Z o o �\ i \ ° Z 38.0 0 NECT}Na� ° ° INFILTRATION ° q � o POND o ° RAMP INISTION E PON \ ° BOTTOM V- 330. o ° 0 ° ° \ '�36.5 336. O \. a ° \ o 0 0 ° \` \ \ CENTRAL POND ° Aimp 0 . 23 acres o Q, \ ° o \ ° o 0 0 ° N r o ° o o 0 0 ✓ o "\ o 1 0 0 rtDwC Rltbl.tteeo AIM. oft-nvAl,-�sA>>mJ7.L.q,!'-0v..r nm Dim ea/,Wet nm ruL• ,., Pon wvm vY mft a a m aanoww r _ PPP-SS-TTTT - a• 1'-20' "" �� CITY OF King County Regional Communications O! D1 BY RENTON and Emergency Coordinartion Center ZM DATUM •R=b Planning/Building/Public Works Dept GRADING AND C3,0 N0, REVISION BY DATE APPR ••� ��-� Gregg Zimmerman P.E., Administrator DRAINAGE PLAN EAST \ ' ° 0 S 9'00'5 E 643.35__ • • � ° • 0 o /( / r10 ( \ - ° o I o 330 `l • o o • ECOLOGY ` _ 0 - o \ BLOCK 1 '� 0 °o WALL 1 ' .0 x 39.p� 16 33 5 CB ^� I CB • a RE- 338.2 \ RE- 338.9 E_ ❑ 1 / IE- 336.4 \ , 338.6 9.9 40.2 • o\• \ \ '\ x 338.7 \ ` ! 33 FlL R if i \ 339.9 j x ° \ 40 ° 74 /` � CB \ \ 33 .3 x 9. 339.4 ` �' o� RE- 3 0 � 3 0.2 l 339.9 \ IE- 3 4 • \ 339.7 3Q o\ FRENCH ®RAIN CURBA \ - - - - x 339. 33). • • \CB 339.9 339.9 .9 RE= 341.4 - - -- - - + - - _° \ IE= 339.4 33TP FlL //R I l \ PARKING tV I O M 6 __ \ I m E 3 000 IE = 334 7 H2 341.1x \ 41.1f 71 4, r f( . Cri 3 9.5 I CB / ° I I o _ RE- � / ` POND BOTTO ° 33 0 ,q ° B 33�. "3 8 36.8 0 PEiRgLEUM , o \ODUCTS PIPELINE�-- o 339.7 GTP4 W \ 339.7 x 340.1 W W z \ W W a oa ono a / Wnn Al O III _ z - - - EASTERN POND Aimp= 1 ..46 acres PREFERRED SURFACE' O�wo A =per 0. 21 acres J \ _ ACCESS ROAD , 3440 ° u o i � o t APPENDIX B INFILTRATION POND CALCULATIONS RC&ECC Infiltration Pond Project No.01-011 Western Pond CLEARHIS RLPCOMPUTE [ROUTING] SUMMARY 100yr 7day MatchQ=PeakQ= 0.9748 cfs Peak Out Q: 0.2821 cfs - Peak Stg` 102.40 ft-Active Vol: 0.13 acft 100 yr 2 4 hr. MatchQ=PeakQ= 1.9005 cfs Peak Out Q: 0.2821 cfs - Peak Stg: 103.02 ft- Active Vol: 0.18 acft ; Running P:\2001\01011\Civil\StormShed\ROUTING Report.pgm on Tuesday, July 10, 2001 ---------- Summary Report of all RI-Pool Data Project Precips [2 yr] 2.10 in [5 yr] 3.10 in [10 yr] 3.65 in [25 yr] 4.50 in [100 yr] 3.89 in [100yr 7day] 9.75 in ---- HYDLIST SUMMARY [7DAY- 100yr 7day] [24HR- 100 yr] [7day Pond] [24hr Pond) LSTEND HydID Peak Q Peak T Peak Vol Cont Area ------- (cfs) (hrs) (ac-ft) (ac) Z�L 7DA-100yr 7day 0.97 55.00 1.6706 2.1300 " 24HR- 100 yr 1.90 8.00 0.6348 2.1300 7day Pond 0.28 50.33 1.6713 2.1300 24hr Pond 0.28 4.00 0.6348 2.1300 STORLIST "y '4 LSTEND[POND] \\DATASVR\PROJECT\2001\01011\Civil\StormShed\PondWest.doc 1 of 2 07/10/01 RC&ECC Infiltration Pond Project No. 0 1-0 11 - Western Pond Node ID: POND Desc: Infiltration Pond Start EI: 100.0000 ft Max El: 108.0000 ft Contrib Basin: Contrib Hyd: Length ss1 ss2 Width ss3 ss4 65.0000 ft 3.00h:1 v 3.00h:1 v 25.0000 ft 3.00h:1 v 3.00h:1 v Bottom area only with infiltration DISCHLIST [POND] LSTEND Control Structure ID: POND -Infiltration control structure Descrip: Infiltration Pond Start El Max El Increment 100.0000 ft 108.0000 ft 0.10 Infil: 7.50 in/hr Multiplier: 1.00 \\DATASVR\PROJECT\2001\01011\Civil\StormShed\PondWest.doc 2 of 2 07/10/01 RC&ECC Infiltration Pond 01-011 Western Pond Contributing Area Impervious Area APGIS = 1.29 acres AROOF= 0.53 acres APLAZA= 0.18 acres ATOTAL IMP= 2.00 acres impervious Pervious Area AP,A = 0.13 acres pervious TOTAL AREA AMP= 2.00 acres Aper= 0.13 acres Design Storm Per NOAA iso luvial maps 400-year 24-hour storm: P= 3.89 in 100- ear 7-day storm: P=9.75 in Soil Type Everett Material, Type B per Geotech email, 3/21/01 Infiltration Rate t I = 15 in/hr per Geotech Technical Memorandum, 1/17/01 I = 0.0003 ft/sec Per KCSWDM pg 4.5.2-2, apply Factor of Safety of 2.0 1 = 0.00017 ft/sec Curve Number Per KCSWDM Table 3.5.26 CN pery= 85 CN imp= 98 Time of Concentration (tj Assume 10 minute time of concentration. P:/2001/01011/Civil/DrainageWest.x1s:90 KCSWDM 1 of 1 7/10/01 RC&ECC Infiltration Pond Project No. 0 1-0 11 Eastern Pond CLEARHIS RLPCOMPUTE [ROUTING] SUMMARY 100 yr MatchQ=PeakQ= 1.4553 cfs Peak Out Q: 0.2083 cfs - Peak Stg: 103.03 ft -Active Vol: 0.14 acft 100yr 7day MatchQ=PeakQ= 0.7591 cfs Peak Out Q: 0.2083 cfs - Peak Stg: 102.49 ft-Active Vol: 0.11 acft Running P:\2001\01011\Civil\StormShed\ROUTING Report.pgm on Monday, July 09, 2001 Summary Report of all RLPool Data Project Precips [2 yr] 2.10 in [5 yr] 3.10 in [10 yr] 3.65 in [25 yr] 4.50 in [100 yr] 3.89 in [100yr 7day] 9.75 in HYDLIST SUMMARY [24HR- 100 yr] [7DAY- 100yr 7day] [24 hr out] [7 day out] LSTEND HydlD Peak Q Peak T Peak Vol Cont Area ------- (cfs) (hrs) (ac-ft) (ac) 24HR- 100 yr 1.46 8.00 0.4860 1.6700 7DAY- 100yr 7day 0.76 55.00 1.2954 1.6700 24 hr out 0.21 4.17 0.4864 1.6700 7 day out 0.21 50.33 1.2954 1.6700 STORLIST [POND] LSTEND P:\2001\01011\Civil\StormShed\PondEast.doc 1 of 2 07/09/01 RC&ECC Infiltration Pond Project No. 0 1-0 11 Eastern Pond Node ID: POND Desc: Infiltration Pond Start El: ..100.0QU". Max El: 104.0000 ft Contrib Basin: Contrib Hyd: Length ssl ss2 Width ss3 ss4 60.0000 ft 3.00h:1 v 3.00h:1 v 20.0000 ft 3.00h:1 v 3.00h:1 v Bottom area only with infiltration DISCHLIST [POND] LSTEND Control Structure ID: POND - Infiltration control structure Descrip: Infiltration Pond Start El Max El Increment 100.0000 ft 104.0000 ft 0.10 Infil: 7.50 in/hr Multiplier: 1.00 P:\2001\01011\Civil\StormShed\PondEast.doc 2 of 2 07/09/01 RC&ECC Infiltration Pond 01-011 Eastern Pond Contributing Area Impervious Area APcis = 1.28 acres AROOF= 0.18 acres ATOTAL IMP= 1.46 acres impervious Pervious Area ALANDscAPiNc= 0.21 acres pervious TOTAL AREA Aimp= 1.46 acres AI.= 0.21 acres Design Storm Per NOAA isopluvial maps 100-year 24-hour storm: P=3.89 in 100- ear 7-day storm: P=9.75 in Soil Type Everett Material, T e B per Geotech email, 3/21/01 Infiltration Rate I = 15 in/hr per Geotech Technical Memorandum, 1/17/01 1 = 0.0003 ft/sec Per KCSWDM pg 4.5.2-2, apply Factor of Safety of 2.0 1 = 0.00017 ft/sec Curve Number Per KCSWDM Table 3.5.2E CN pery= 85 CN imp= 98 Time of Concentration (tj Assume 10 minute time of concentration P:/2001/01011/Civil/DrainageEast.xls:90 KCSWDM 1 of 1 7/10/01 RC&ECC Infiltration Pond Project No. 0 1-0 11 Central Pond CLEARHIS RLPCOMPUTE [ROUTING] SUMMARY 100yr 7day MatchQ=PeakQ= 0.1060 cfs Peak Out Q: 0.0521 cfs - Peak Stg: 100.70 ft-Active Vol: 273.06 cf 100 yr MatchQ=PeakQ= 0.2343 cfs Peak Out Q: 0.0521 cfs- Peak Stg: 100.97 ft-Active Vol: 417.53 cf Running P:\2001\01011\Civil\StormShed\ROUTING Report.pgm on Wednesday, July 11, 2001 Summary Report of all RLPool Data Project Precips [2 yr] 2.10 in [5 yr] 3.10 in [10 yr] 3.65 in [25 yr] 4.50 in [100 yr] 3.89 in [100yr 7day] 9.75 in HYDLIST SUMMARY [7DAY- 100yr 7day] [24HR- 100 yr] [7DAY- 100yr 7day] [24HR - 100 yr] [7day Pond] [24hr Pond] LSTEND HydID Peak Q Peak T Peak Vol Cont Area ------- (cfs) (hrs) (ac-ft) (ac) 7DAY-100yr 7day 0.11 55.00 0.1823 0.2300 24HR-100 yr 0.23 7.83 0.0701 0.2300 7day Pond 0.05 52.50 0.1822 0.2300 24hr Pond 0.05 6.83 0.0701 0.2300 STORLIST [POND] LSTEND \\DATASVR\PROJECT\2001\01011\Civil\StormShed\PondCentral.doc 1 of 07/11/01 RC&ECC Infiltration Pond Project No. 0 1-0 11 Central Pond Node ID: POND Desc: Infiltration Pond Start El: 100.0000 ft Max El: 108.0000 ft Contrib Basin: Contrib Hyd: Length ss1 ss2 Width ss3 ss4 30.0000 ft 3.00h:1 v 3.00h:1 v 10.0000 ft 3.00h:1 v 3.00h:1 v Bottom area only with infiltration DISCHLIST [POND] LSTEND Control Structure ID: POND - Infiltration control structure Descrip: Infiltration Pond Start El Max El Increment 100.0000 ft 108.0000 ft 0.10 Infil: 7.50 in/hr Multiplier: 1.00 \\DATASVR\PROJECT\2001\01011\Civil\StormShed\PondCentral.doc 2 of 2 07/11/01 RC&ECC Infiltration Pond 01-011 Central Pond Contributing Area Impervious Area AROOF= 0.23 acres ATOTAL.IMP= 0.23 acres impervious TOTAL,AREA ^imP= 0.23 acres Design Storm Per NOAA iso luvial maps 100-year 24-hour storm: P=3.89 in 100- ear 7-day storm: P=9.75 in Soil Type Everett Material, Type B per Geotech email, 3/21/01 Infiltration Rate I = 15 in/hr per Geotech Technical Memorandum, 1/17/01 1 = 0.0003 ft/sec Per KCSWDM pg 4.5.2-2, apply Factor of Safety of 2.0 I = 0.00017 ft/sec Curve Number Per KCSWDM Table 3.5.26 CN imp= 98 Time of Concentration (tj Assume 10 minute time of concentration P:/2001/01011/Civil/DrainageCentral.x1s:90 KCSWDM 1 of 1 7/10/01 IM Mims Im Von ��w, �!►=.-OL ON Rai S %, Tl • J �, ut �`► 11 1 • • t 1 � � ►.1�, ��1, � yell �� I 1 KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL TABLE 3.5.213 SCS NVESTERN WASHINGTON RUNOFF CURVE NUMBERS SCS WESTERN WASHINGTON RUNOFF CURVE NUMBERS (Published by SCS in 1982) Runoff curve numbers for selected agricultural, suburban and urban land use for Type 1A rainfall distribution, 24-hour storm duration. CURVE NUMBERS BY HYDROLOGIC SOIL GROUP LAND USE DESCRIPTION A B C D Cultivated land(1): winter condition 86 91 94 95 Mountain open areas: low growing brush and grasslands 74 82 89 92 Meadow or pasture: 65 78 85 89 Wood or forest land: undisturbed or older second growth 42 64 76 81 Wood or forest land: young second growth or brush 55 72 81 86 Orchard: with cover crop 81 88 92 94 Open spaces, lawns, parks, golf courses, cemeteries, landscaping. good condition: grass cover on 75% or more of the area 68 80 86 90 fair condition: grass cover on 50% to 75% of the area 77 85 90 92 Gravel roads and parking lots 76 85 89 91 Dirt roads and parking lots 72 82 87 89 Impervious surfaces, pavement, roofs, etc. 98 g 98 98 Open water bodies: lakes, wetlands, ponds, etc. 100 00 100 100 Single Family Residential (2) Dwelling Unit/Gross Acre % Impervious (3) 1.0 DU/GA 15 Separate curve number 1.5 DU/GA 20 shall be selected 2.0 DU/GA 25 for pervious and 2.5 DU/GA 30 impervious portion 3.0 DU/GA 34 of the site or basin 3.5 DU/GA 38 4.0 DU/GA 42 4.5 DU/GA 46 5.0 DU/GA 48 5.5 DU/GA 50 6.0 DU/GA 52 6.5 DU/GA 54 7.0 DU/GA 56 a�— Planned unit developments, % impervious condominiums, apartments, must be computed commercial business and industrial areas. (1) For a more detailed description of agricultural land use curve numbers refer to National Engineering Handbook, Section 4, Hydrology, Chapter 9, August 1972. (2) Assumes roof and driveway runoff is directed into street/storm system. (3) The remaining pervious areas (lawn) are considered to be in good condition for these curve numbers. 3.5.2-3 11/92 APPENDIX C WATER QUALITY POND CALCULATIONS RC&ECC Infiltration Pond Project No. 01-011 Wet Ponds CLEARHIS East Event Summary: BasinID Peak Q Peak T Peak Vol Area Method Raintype Event ------- (cfs) (hrs) (ac-ft) ac /Loss East 0.17 7.83 0.0497 1.28 SBUH/SCS User1 WQ Drainage Area: East Hyd Method: SBUH Hyd Loss Method: SCS CN Number Peak Factor: 484.00 SCS Abs: 0.20 Storm Dur: 24.00 hrs Intv: 10.00 min Area CN TC Pervious 0.0000 ac 78.00 0.00 hrs Impervious 1.2800 ac 98.00 0.08 hrs Total 1.2800 ac Supporting Data: Impervious CN Data: PGIS 98.00 1.2800 ac Impervious TC Data: Flow type: Description: Length: Slope: Coeff: Travel Time Fixed PGIS 0.00 ft 0.00% 5.0000 5.00 min West Event Summary: BasinlD Peak Q Peak T Peak Vol Area Method Raintype Event ------- (cfs) (hrs) (ac-ft) ac /Loss West 0.17 7.83 0.0501 1.29 SBUH/SCS User1 WQ Drainage Area: West Hyd Method: SBUH Hyd Loss Method: SCS CN Number Peak Factor: 484.00 SCS Abs: 0.20 Storm Dur: 24.00 hrs Intv: 10.00 min Area CN TC Pervious 0.0000 ac 78.00 0.00 hrs Impervious 1.2900 ac 98.00 0.08 hrs Total 1.2900 ac Supporting Data: Impervious CN Data: PGIS 98.00 1.2900 ac Impervious TC Data: Flow type: Description: Length: Slope: Coeff: Travel Time Fixed PGIS 0.00 ft 0.00% 5.0000 5.00 min WetPond.doc 1 of 1 07/10/01 SYMONDS 1601 Second Ave. - Suite 1000 - Seattle, WA 98101-1541 P: 206/441-1855 F: 206/448-7167 Project �� , job No. _ j Pagc l of Client Bev 1 ,_ �� Date Subject Checked Date � UJI✓�� Sfioti�� L ) TG = r.i, Ct,a,�t✓I/�fib`/ . WIN 1.4 krol. RIMA VA ■r_ f OM � • ♦ 1 ON HIM y Q !{ IF 1 FA •1 APPENDIX D FILTER STRIP CALCULATIONS SYMONDS 1601 Second Ave. - Suite 1000 • Seattle,WA 98101-1541 pp d� P: 206/441-1855 •F: 206/448-7167 Project job No. 0 Page f of Client By !/, Date I o I Subject L/7'F1'-. r'�Y .I n 'FI tn 1{s Cheched Date APPENDIX E CONVEYANCE SYSTEM CALCULATIONS SYMONDS1601 Second Ave. - Suite 1000• Seattle,WA 98101-1541 Q�+LV"TJLL-A P: 206/441-1855 F: 206/448-7167 Project �i Job No. 0' — o I I Page I of Client By '/ / Date 113 p Subject CAV(,4 Checked V „I Date I�ws A/1. ?7)^�, Mfir-j l ,/ t4� W( An,-vt1 c�✓s TU 's (2�--yZ-- INS-► L fy CAL J �in1P 1.Y6 �� C� rM(o = 4� 5: V.Q-- -M fix, = 3. � C� � �t9��+-�/U v� �-a it.�,., ✓�i. KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL FIGURE 4.3.4A NOMOGRAPH FOR SIZING CIRCULAR DRAINS FLOWING FULL 1000 900 800 .0001 700 2.0 600 .0002 500 Minimum .0003 Allowable 400 .0004 .0001 Velocity .0006 (Flowing 3.0 300 120 .0008 .0002 Full) o .001 108 .0003 0 200 96 11 .0004 90 c .002 .0005 4.0 84 cc .0006 z O .003 .0008 66 w 004 .001 v�hk y, f� J 005 / 5.0 100 60 O .006 N 0 90 54 .008 .002 O 80 48 .01 w 6.0 70 N 003 � w c N 60 = 42 .004- u: Z_ 36 .02 .005 U 7.0 50 .00 LL CL U z 33 .03 08 LU w 8.0 Z 40 w 30 .04 10 O w w a 27 0 � Z 9.0 FL 6 - Q 30 w 24 .06 .020 } 10.0 2 O 21 ~ 10 w .030 UO 20 w 18 .040 w g .050 Q 15 E 060 p080 12 .100 10 10 9 8 SAMPLE USE f'. 7 ' 8 24" dia. CMP @ 2% slope yields 20.0 6 17cfs @ 5.2 FPS velocity (n = 0.024) 5 6 4 Values per Manning's Equation �hvk l 3 n ° 30.0 3" g This table can be converted to other"n" values b applying Y 2 formula.- 40.0 01 n1 Q2 n2 1 4.3.4-18 1/90 RC&ECC Conveyance Capacity Check Project No. 0 1-0 11 ` 25-yr 24-hr design storm WESTERN POND CONVEYANCE CAPACITY CHECK 24HR Event Summary: BasinlD Peak Q Peak T Peak Vol Area Method Raintype Event ------- �(cl* (hrs) (ac-ft) ac /Loss ,�- 24HR 1.67 8.00 0.5574 2.13 SBUH/SCS User1 25 yr Drainage Area: 24HR Hyd Method: SBUH Hyd Loss Method: SCS CN Number Peak Factor: 484.00 SCS Abs: 0.20 Storm Dur: 24.00 hrs Intv: 10.00 min Area CN TC Pervious 0.1300 ac 85.00 0.17 hrs Impervious 2.0000 ac 98.00 0.17 hrs Total 2.1300 ac Supporting Data: Pervious CN Data: On-Site Pervious 85.00 0.1300 ac Impervious CN Data: On-Site Impervious 98.00 2.0000 ac Pervious TC Data: Flow type: Description: Length: Slope: Coeff: Travel Time Fixed On-Site Pervious 0.00 ft 0.00% 10.0000 10.00 min Impervious TC Data: Flow type: Description: Length: Slope: Coeff: Travel Time Fixed On-Site Impervious 0.00 ft 0.00% 10.0000 10.00 min Conveyance Capacity.doc 1 of 2 07/13/01 RC&ECC Conveyance Capacity Check Project No. 0 1-0 11 4 25-yr 24-hr design storm EASTERN POND CONVEYANCE CAPACITY CHECK 24HR Event Summary: BasinlD Peak Q Peak T Peak Vol Area Method Raintype Event ------- (cfs) (hrs) (ac-ft) ac /Loss - 24HR 1.28 8.00 0.4259 1.67 SBUH/SCS Used 25 yr Drainage Area: 24HR Hyd Method: SBUH Hyd Loss Method: SCS CN Number Peak Factor: 484.00 SCS Abs: 0.20 Storm Dur: 24.00 hrs Intv: 10.00 min Area CN TC Pervious 0.2100 ac 85.00 0.17 hrs Impervious 1.4600 ac 98.00 0.17 hrs Total 1.6700 ac Supporting Data: Pervious CN Data: On-Site Pervious 85.00 0.2100 ac Impervious CN Data: On-Site Impervious 98.00 1.4600 ac Pervious TC Data: Flow type: Description: Length: Slope: Coeff: Travel Time Fixed On-Site Pervious 0.00 ft 0.00% 10.0000 10.00 min Impervious TC Data: Flow type: Description: Length: Slope: Coeff: Travel Time Fixed On-Site Impervious 0.00 ft 0.00% 10.0000 10.00 min Conveyance Capacity.doc 2 of 2 07/13/01 • 1�j�rw�r�r�� , .