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HomeMy WebLinkAboutSWP272091 TUDOR ENGINEERING COMPANY Consulting Engineers and Planners Norton Building 801 Second Avenue, Suite 516 Seattle, Washington 98104 (206) 6824915 Fax: (206)467-8632 February 25, 1991 Mr. Joe Armstrong City of Renton Department of Public Works 200 Mill Avenue South File: 1346.220 Renton, Washington 98055 Ser.: 4853 Subject: South 43rd Street Drainage This letter is intended to provide a response to Ron Straka's comments of January 28, 1991 regarding drainage issues related to the South 43rd Street Project. We hope the following responses will prove sufficient for all concerned. Core Requirement No. 3: As was identified in our previous letter of January 16, 1991 the existing drainage system discharges into a well defined channel with a maximum slope of approximately 3%. After traversing a distance of approximately 20 feet from point of discharge this well defined channel (with a cross section as shown in "Typical Bottom Section" on the attached sheet) disperses into the southern marshes of the Panther Creek Wetlands (with a minimum bottom width as shown in "Typical General Section" also on the attached sheet). The "Typical General Section" also applies to the first 20 feet downstream from the point of discharge and should be considered as stacked on top of the "Typical Bottom Section" for that distance. We have analyzed the existing area we consider suitable for biofiltration in conformance with Section 4.6.3 of the King County Surface Water Design Manual (KCSWDM) and are able to make the following conclusions for the 2 year storm: 1. Normal water depth for first 20 feet = 1.2' > 8". 2. Water velocity for fast 20 feet = 0.65 ft/s < 1.5 ft/s. 3. Normal water depth after first 20 feet = 0.54' < 8". 4. Water velocity after first 20 feet = 0.36 ft/s < 1.5 ft/s. As is illustrated above, after the first 20 feet of channelized flow, the existing conditions meet the KCSWDM requirements. A further requirement for biofiltradon is that the length be 200 feet which is met by the existing area. (Actual distance of the marsh is greatly in excess of 200 feet.) CORPORATE OFFICE 1800 Harrison St.,Oakland,CA 94612 P.O.Box 23210,Oakland,CA 94623 (415)268-6100 Mr. Joe Armstrong TUDOR ENGINEERING COMPANY February 25, 1991 Page 2 Core Requirement No. 3: (cont.) The last item we checked was to assure that the maximum velocity for a 100 year storm would be less than 5 ft/sec. Our calculations indicate a maximum velocity of 1.24 ft/s. In conclusion we anticipate that the information supplied above, in conjunction with the attached calculations, should resolve any outstanding issues on this topic. Core Requirement No. 5 It is now our intention to show the location of proposed silt fences on the construction sequencing plans. Also to be shown on the construction sequencing plans is the use of the tunnel area as a sedimentation pond. At the suggestion of Ron Straka we will insert a payment item for 'Erosion and Sedimentation Control" into the Special Provisions. It is our intention to make this item payable on a lump sum basis. We hope that the information outlined above will resolve any outstanding issues. If you have any questions, please do not hesitate to contact myself or Attila Laszlo. Very truly yours, TUDOR ENGINEERING COMPANY j° &/Ao/ - Peter G. De Boldt, P.E. Project Manager Attachments rjab u �^^��✓.. i �i u� [ivVu�[[FU lv l� LVIV,YHIV l BY DATE �� PROJECT �67vTr� -S. ¢,�� SHEET NO. OF CHKD. BY DATE JOB NO. C F=X/ST/�G �o.vo it�.Nrr - ,ZD OF WALL D6i'FiN� /.PAPC tOwOAt CyN/✓NbZ O.f',Cid /NT3 ,2 ewz4 i✓C L y Disi /cr SEc?-*AV R&R T*�—a fdLGrWiNCv S�criy�s N/gX;Mcuv .scco-;bF /s 3% ram. ,o,P oiS�Qs..,/G 78 .SLYITHEir,,/ of /v/JN/7/.EiQ Ci?rFf_. T/c 7YP/c9L BpJTOM SECrro%1 %kA^/.3iTicrJ3 �o7p�eTe�Y Tv c GfN�itAt- S6GTio.I ~ /JFTd2 Zo � I IYRcAL 1 0OTM-A SECr',4I 'TYRu1L G�c`�lE4AL SECT/J.J T CAWAI ND PMs1G Z C--,o J,/ A.VQ VEL oci ry ¢ �9N✓/.vl,S %/ •, &VC O. A.vA> A �'LDPE pF Z�1u j= 149 r�t/ccr TYP/GlJL $o�r�,Y/ SECnrn/ Gn4Si.' -7 c7� zj u uL6-Z/ \��u\�, tMUIN KKIN,C, COMPANY �j BY �f� DATE�JL�C7L�PROJECT-6E�— S' '�3� 577 SHEET NO. 2 _OF� CHKD. BY DATE _JOB NO. CrEC.r %YPic.aL Ge�/CRac^ sw�r.a...r , Z Vie.Z'S' 7- All CY6 /rows AMP T.✓E �?Eu/fwrLY .SNCL/ Zgzv,Gry GF 7W 777'�4cwt is 7,r�M secrn,�j O,v-y ThE "Tt/Pic,i- GEn/,6tgc 5EC`o✓ '•' G/sue w= O.io Pc a?D ! 3jo io ao �p,/o p , j (,got :roc v..Jc roe 31a3F� CITY OF RENTON MEMORANDUM DATE: January 28, 1991 TO: Joe Armstrong FROM: Randall Parsons t STAFF CONTACT: Ron Straka ; iv 1 SUBJECT: S. 43rd Street Improvements Drainage Report We have reviewed Tudor Engineering's response to our January 10, 1991 comments regarding their drainage report submitted for the S. 43rd Street Improvements. The supplemental information satisfies our comments regarding Core Requirements #2 and #4. In our comments regarding the project's conformance with Core Requirement #3, we were requesting that the consultant actually size the amount of biofiltration needed for the project. This would provide us with information which we could compare the existing biofiltration area to what is actually required and allow us to determine if the existing biofiltration is adequate. We have contacted the consultant requesting this information on January 21, 1991, but have not received anything yet. It is important to understand that, per the City Storm and Surface Water Drainage Ordinance, if a project proposes to release runoff from an increase of impervious surface area of more than 5,000 square feet, which is subject to vehicular use, then the runoff must be treated prior to discharge from the project site by on-site biofiltration measures. The only way we can waive this requirement is if it can be shown that the existing biofiltration meets the criteria as specified in Section 4.6.3 in Chapter 4 of the City adopted King County Surface Water Design Manual. It was our understanding that your Division would have the consultant prepare a temporary erosion and sedimentation control plan in accordance with the City's Storm and Surface Water Drainage Ordinance and as required per the SEPA Determination of Non-Significance - Mitigated, Condition Number 9. In our phone conversation with the consultant on January 21, 1991, it was learned that erosion control requirements would be incorporated into the Construction Contract Specifications Special Provisions and no actual temporary erosion and sedimentation control plan would be developed. Core Requirement #5 of the City adopted King County Surface Water Design Manual specifies that "All engineering plans for projects that propose to construct new or modify existing drainage facilities shall include an erosion/sedimentation control plan." An erosion/sedimentation control plan is a requirement by Ordinance and we feel if there is an erosion/sedimentation control plan, the contractor is more likely to implement the proper controls. I£ a pay item for erosion/sedimentation is included in the project schedule of prices, the City will have a mechanism for requiring the contractor to implement the erosion/sedimentation control plan. A contractor is also more likely to do erosion control if there will be payment for the activity. J � Joe Armstrong January 28, 1991 Page Two In conclusion, we expect the consultant to provide us with the biofiltration sizing calculations which we can use to determine if the existing biofiltration area is equal to or greater than the biofiltration area required for the project per the City adopted King County Surface Water Design Manual. We also expect for a project of this magnitude that an erosion/sedimentation control plan would be prepared and be in conformance with the City Storm and Surface Water Drainage Ordinance. This plan must be reviewed and approved prior to the advertisement for construction to allow the contractor to have a plan to review in order to estimate the cost for erosion and sedimentation control for inclusion into the contractor's bid. If you have any questions, or need additional information, please contact Ron Straka at Ext. 5547. S-43RD/RLP:R3S:If , CITY OF RENTON MEMORANDUM DATE: January 16, 1990 TO: Ron Straka Lge FROM: Joe Armstrong SUBJECT: S. 43rd LID 329 D Please find attached Tudor Engineers response to your comments of January 10, 1990. Please review as soon as possible so our consultant can respond in a timely manner. THANK YOU TUDOR ENGINEERING COMPANY Consulting Engineers and Planners Norton Building 801 Second Avenue, Suite 516 Seattle, Washington 98104 (206) 682-4915 Fax: (206)467-8632 January 16, 1991 Mr. Joe Armstrong City of Renton Department of Public Works 200 Mill Avenue South File: 1346.220 Renton, WA 98055 Ser.: 4808 Subject: South 43rd Street Drainage This letter is intended to provide a response to Ron Straka's comments of January 10, 1991 regarding drainage issues related to the South 43rd Street Project. We hope the following responses will prove sufficient for all concerned. Core Requirement No. 2: The existing drainage system discharges into the southern end of the Panther Creek Wetlands. From the point of discharge the flow is through a naturally grass lined swale for an approximate distance of 20 feet at an approximate slope of 3%. From that point flow disperses into the southern reaches of the Panther Creek Wetlands typified by a wide area with a minimal slope and shallow water depth. Present are extensive cattails, some grass, limited brush and alder trees which are slowly dying because of the saturated soils. Eventually the water flows under SR167 in the 24" and 30" culverts a total of approximately 700 feet from the point of discharge. Graphical explanation of the downstream site as well as the upstream tributary drainage area are provided on the attached Figure 1. Based on the Santa Barbara Unit Hydrography Analysis contained in our original submittal an anticipated flow increase of 0.3 cfs is expected for a 100 year storm due to the proposed project. It is our opinion that this minimal increase will not significantly increase any flooding downstream that you have identified as presently occurring. Core Requirement No. 3: The existing drainage system discharges into a grass lined swale extending approximately 20 feet from point of discharge in a well defined channel of slope approximately equal to 3%. At that point the flow disperse into the southern marshes of the Panther Creek Wetlands. It is our opinion that the biofiltration provided by this existing, natural system would only be impaired by any construction activity downstream of the drainage system CORPORATE OFFICE 1800 Harrison St.,Oakland,CA 94612 P.O.Box 23210,Oakland,CA 94623 (415)268-6100 TUDOR ENGINEERING COMPANY discharge. We would like to emphasize that the existing system does not lend itself to direct analysis for sizing described in section 4.6.3 of the King County Surface Water Design Manual because it is a natural system with a non-uniform cross-section. The runoff coefficient anticipated for the area east of the Talbot Road which was excluded from the project drainage was estimated to be 0.2. The associated time of concentration was estimated to be an additional 10 minutes to that contained in the report. Based on the above assumtions we estimated a peak flow of 16.8 cfs for the 25 year storm when this area was included. Without including this area the peak flow was 22.1 cfs for the 25 year storm. Core Requirement No. 4: The pipe size will be increased to 27" diameter. Core Requirement No. 5: It is our intent that a Wetpond be maintained on the north side of 43rd street at the approximate location of the future tunnel. The Wetpond will have a minimum capacity of 300 c.f. for exceeding the volume requirement) but a surface area of approximately 300 square feet as opposed the required area of approximately 3,500 square feet. Water shall be pumped from the settling pond to the existing storm drain system during the construction period. The Wetpond will be shown on the Construction Sequencing Plans to fulfill this requirement. We hope that the information provided above is sufficient in detail to alleviate your concerns regarding this project. If you have any questions, please do not hesitate to contact me. Very truly yours, TUDOR ENGINEERING COMPANY Peter G. De Boldt, P.E. Project Manager mcs Su ♦ .aI i I a• • I �.. � 1� r.. 'E Ili I R ma-� Track ;tip' Ii •1,' Jh I -- r� 1 8 Reservoir M. r OBM too I'm. 25 B.30 I' fir,i li • • `r., r BM n1� EK15TIr�IG `•.• •� 7 t 'C : 1 ---- - r -____ -- - - 17 34 .Orillla ' _ ;I••i / •1 1• li ? i 1 JR 1 i. I 36 BMm 23� 117 ••� i .w^ 4�8 •. i �E114.1 :I Q. All Drive-in' 01 J.. 1 FII _Srt�6� c +.�c. p' b 11 I ..�•- Tzr fivTlta , MAp SoutCE : 4TUND SCALE CITY OF RENTON MEMORANDUM DATE: January 10, 1991 TO: Harold Adams FROM: Randall Parsons STAFF CONTACT: Ron Straka SUBJECT: SOUTH 43RD STREET IMPROVEMENTS(LID 329) DRAINAGE STUDY BY TUDOR ENGINEERING COMPANY The Storm Water Utility staff has reviewed the South 43rd Street Improvement (LID 329) Drainage Study prepared by Tudor Engineering. The study was reviewed for conformance with the City Storm and Surface Water Drainage Ordinance and particularly King County Surface Water Design Manual Core Requirement # 1, 2, 3, 4, and 5 and Special Requirement #5 and 6. These are the requirements we discussed in our 12/5/90 meeting with your Section and the consultant. The following is our comments regarding the drainage study and the projects conformance with the specified requirements: Core Requirement #1: This requirement is satisfied. Core Requirement #2: The downstream analysis describes the existing pipe system adequately, but fails to be very specific about where the drainage goes once discharged from the existing pipe system. The study says the outfall empties into a wetland which extends northward to the Panther Creek Wetland. We know of a 30" and 24" culvert crossings of SR 167 near Nendels Vain Inn. We would like to know if the drainage discharged from the site will enter these culverts. We know of existing flooding problems on the west side of SR 167 as a result of drainage from these culverts. The Level 1 off- site analysis must describe the general condition of the downstream drainage system for a minimum of f miles, and the upstream tributary drainage areas to the site and the downstream system must be delineated on a map (minimum USGS 1:24000 Quadrangle Topographic Map). The narrative describing the upstream tributary drainage area and downstream system should be contained in its own section of the report. Harold Adams South 43rd Street Improvements (LID 329) Drainage Study Page 2 Core Requirement #3: The post-developed peak runoff rate for the 100 year, 24 hour storm event is less than 0.5 CFS (0.26 actually) greater than the pre-developed peak runoff for the same storm event. Therefore, on-site detention is not required. The proposed project will increase the impervious surface subject to vehicular use by 0.5 acres. If a project proposes to release runoff from more than 5,000 square feet of impervious surface, subject to vehicular use, then the runoff must be treated prior to discharge from the project site by on-site biofiltration measures. The study indicates that the existing drainage system discharges into a grass-lined area with a very shallow slope which provides biofiltration and also is a wetland. The consultant should verify that this existing biofiltration area conforms to the requirements described in Section 4.6.3 in Chapter 4 of the Design Manual. The consultant decided to exclude runoff from a large undeveloped area east of Talbot Road from the study since the contributing drainage was estimated to have a large time of concentration and a low coefficient of runoff. This would produce a lower peak runoff than that of the smaller, but highly developed areas in the site vicinity. This is probably correct and the consultant should include the estimated values used in making the decision. Core Requirement #4: The proposed drainage system was correctly analyzed in conformance with the Design Manual requirements. The backwater analysis on the proposed system for a 100 year, 24 hour storm event shows that the presently proposed 18" storm lines from CB 03 to the connection with the existing 27" system, would result in a water surface elevation approximately 3' above the rim elevation of CB #3 and would cause the entire tunnel to be flooded. The consultant determined that a 27" storm line would have adequate capacity to accommodate the flows and recommended that the construction drawings be revised to show a 27" pipe instead of an 18" pipe. We concur with this recommendation and suggest that you advise the consultant preparing the construction plans to make this revision. Core Requirement #5: A Temporary Erosion and Sedimentation Control Plan is required and must conform with the requirements specified in Chapter 5 of the Design Manual and must satisfy this core requirement. The Erosion and Sedimentation Control Plan must be approved prior to the pre-construction conference. Special Requirement #5: The project will not construct more than one acre of impervious surface that will be subject to vehicular use, therefore, the project is exempt from Special Requirement #5. Special Requirement #6: The project is not constructing more than five acres of impervious surface subject to high vehicular use and, therefore, Special Requirement #6 does not apply. Harold Adams South 43rd Street Improvements (LID 329) Drainage Study Page 3 This concludes the Storm Water Utility review of the South 43rd Street Improvements (LID #329) Drainage Study prepared by Tudor Engineering Company. We request that the consultant revise the study to addresss our comments, particularly the adequacy of the existing biofiltration area and a clearer Level 1 off-site analysis in detail and format. We also suggest that the construction drawing be revised to show a 27 inch storm system from CB 03 to connection with the existing system instead of the presently proposed 18" storm system. If you have any questions, please contact Ron Straka at X-5547. 91-032:RIS:ps CC: Richard Anderson Ran Straka TUDOR ENGINEERING COMPANY Consulting Engineers and Planners Norton Building 801 Second Avenue, Suite 516 Seattle, Washington 98104 (206) 682-4915 Fax: (206)467-8632 January 3, 1991 Mr. Joe Armstrong City of Renton Dept. of Public Works 200 Mill Ave. S. Renton, WA 98055 File: 1346.220 Ser.: 4802 Subject: S. 43rd St. Drainage Dear Joe: Please find attached our drainage analysis and report for the subject project. We would like to highlight the following points contained in the report: • From the tunnel to the connection with the existing 27 inch diameter pipe a 24 inch diameter pipe should be utilized instead of the 18 inch pipe originally contained in the contract documents. • The existing outfall of the storm drain system is into a grass-lined area with a very shallow slope which provides biofiltration. Because of this condition it is our opinion that additional biofiltration is not required. • Because of the very limited additional impervious area that will be added, and the long time of concentration for the existing system, on-site detention is not recommended. If you have any questions regarding the attached material, please do not hesitate to contact me. Very truly yours, TUDOR ENGINEERING COMPANY Peter G. De Boldt, P.E. Project Manager Enclosure CORPORATE OFFICE 1800 Harrison St.,Oakland,CA 94612 P.O.Box 23210,Oakland,CA 94623 (415)268-6100 DRAINAGE REPORT South 43rd. Street Improvements LID 329 Renton, WA. ------------------------------- GENERAL: The Project entails widening of South 43rd. Street from Talbot Road So. to the SR 167 access ramps, construction of a tunnel access from Davis Avenue So. to the Valley General Hospital, and widening of Talbot Road So. north from the intersection with So. 43rd. Street for about 300 feet. The widening of So. 43rd. Street and access to the tunnel will create about one-half acre of new impervious ground cover. Runoff generated from the Project site will be conveyed to an existing outfall through new stormdrain construction (453 feet) and an existing stormdrain system that currently serves the Project area. The purpose of this drainage study is threefold :- i) To provide hydrology and hydraulic information on which to base design of the new stormdrain. ii) To analyze downstream portions of the existing stormdrain system and determine if sufficient capacity exists for conveyance of additional runoff caused by the Project (25-year storm). iii) To perform a hydrograph analysis (Santa Barbara Unit Hydrograph) of existing and proposed conditions at the Project site and determine if on-site detention is required as per surface water management requirements. EXISTING DRAINAGE: Existing drainage facilities that are impacted by the proposed Project are those that convey storm runoff into and away from the Project site. These include : i) A 12 inch system that runs north on Talbot Road to the intersection with So. 43rd. Street, and then west on So. 43rd. Street into the Project area. This system also serves a ditch that runs along the east side of Talbot Road from as far away as 600 feet south of So. 45th. Place. The ditch picks up runoff from Talbot Road as well as from a large undeveloped area east of Talbot Road and south of 45th. Place. For this study, a decision was made to exclude this undeveloped area from the contributing drainage at the Project site since the long time of concentration and low runoff coefficient was estimated to produce a lower peak than that of the smaller but highly developed area in the site vicinity. ii) A 12 inch stormdrain system that drains the north end of Davis Avenue, including a large parking lot (for hospital employees) between Davis Avenue and the SR 167 corridor. This system joins the stormdrain described in (i) above within the Project site, and conveys the total runoff into the hospital stormdrain system described below. iii) A 27 inch system, with 42 inch outfall, that serves the Valley General Hospital site. The outfall does not discharge into a well defined channel, but rather into a broad wetland area that extends northwards to the Panther Creek wetlands. Runoff in the stormdrains described in (i) and (ii) above discharge into this system. HYDROLOGY: For the purposes of this study, estimates of peak discharge for the 25-year and 100-year storm runoff were computed at two points of interest : i) At So. 43rd. St. where runoff in the Talbot Road system and the Davis Avenue system combine and enter the proposed new stormdrain construction. This new construction serves the proposed tunnel and access ramps, and, because of the low tunnel invert elevation, replaces the existing connection into the 27 inch outfall system. As previously stated, a large portion of undeveloped area was excluded from the area contributing to the Talbot Road system. Based on field observations, the Talbot Road right-of-way (ROW) and an area extending 250 feet east and as far south as 45th. Place, and the So. 43rd. Street ROW from Talbot Road to Davis Avenue, for a total area of 6.6 acres, were included in the calculations. The Davis Avenue system included the Davis Avenue ROW, the parking lot to the west, and the majority of the area between Davis Street and Talbot Road, for a total area of 5.1 acres. A small portion of the area adjacent to Talbot Road and 45th. Place was assumed to drain into the 45th. Place stormdrain system (with outfall to the south). The two stormdrain systems combine to provide a total drainage area of 11.7 acres at the proposed tunnel. Using a conservative estimate of impervious area, a weighted runoff coefficient "C" of 0.70 for the drainage area was computed. Based on the topography of the drainage area, and the in-place existing stormdrains, a time of concentration of 6 minutes was estimated. Using the criteria in Chapter 4, and the isopluvial information in Figure 3.5.1 of the King County Surface Water Design Manual, a rainfall intensity of 2.7 inches/hour and 3.2 inches/hour was derived for the 25-year and 100-year storm runoff, respectively. Plugging these parameters into the equation Q=CiA resulted in peak discharges of 22.1 cubic feet per second (cfs) and 26.2 cfs for the 25-year and 100-year storm, respectively. ii) A second point of interest for runoff analysis is at the connection of the proposed new construction and the existing 27 inch stormdrain system. The additional drainage area at this point is comprised entirely of the Valley General Hospital buildings and parking lot, and is estimated to be 9.9 acres. Based on an estimated 75 percent impervious and 25 percent pervious surface treatment, the weighted runoff coefficient "C" was computed to be 0.74. The weighted "C" for the entire drainage area to this point is computed to be 0.72. The travel time in the new stormdrain from the tunnel invert to this point was calculated to be about 4 minutes. This was added to the 6 minutes at So. 43rd. Street for a total time of concentration of 10 minutes. Rainfall intensities of 2.04 inches/hour and 2.4 inches/hour were calculated for the 25-year and 100-year, respectively. Plugging these values into the equation Q=CiA, with the total contributing area equal to 21.6 acres, resulted in peak discharges of 31.7 cubic feet per second (cfs) and 37.3 cfs for the 25-year and 100-year storm, respectively. HYDRAULICS: The new stormdrain construction is designed to take the 25-year peak discharge of 22.1 cfs at full flow. From the connection in So. 43rd. Street to the invert of the tunnel, an 18 inch RCP with a minimum slope of 3.8 percent is required. From the tunnel invert to the existing 27 inch stormdrain there is minimal head available, consequently, a 24 inch RCP with a minimum slope of 0.85 percent is required. A check was made to determine if the proposed system can convey the 100-year discharge under pressure flow without overflowing the catchbasins. Calculations show that the catchbasin in the tunnel invert (CB #3) will overflow during the 100-year storm if a 24 inch stormdrain is used. If a 27 inch stormdrain is used then the 100-year peak discharge will be conveyed without the headwater exceeding the grate elevation in the tunnel, Le no overflow. The minimum slope of the existing 27 inch stormdrain is 3.2 percent. This slope provides for a capacity of 60 cfs at full flow. Therefore, the existing outfall system can safely convey the estimated 25-year and 100-year storm runoff discharged from the Project area. HYDROGRAPH ANALYSIS: A hydrograph analysis using the Santa Barbara Unit Hydrograph methodology, as prescribed in the King County Surface Water Design Manual, was performed to estimate additional runoff volumes and to provide a basis for on-site detention. The results of the analysis are presented in the attached computer printout. 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BY DATE Lab Eaq JOB NO. 2 L � elev.- vim_ . -= . fa3 l + 0. h L = � 434� ,O,OrZ� �27ZZ �. �.•3) �0•G�� 2 �2� CZ�Zz)(o56a�''� �w, cp a + �ev. vv J . ♦+<wuu wl a .a.au a.rc.a arju .a...b w,��, ....0 Site Design Criteria : Standard Conditions -------------------------------------------------------- KIN3 CC7fIINPY Surface Water Managwent Division Department of Public Works 701 Dexter-Horton Building Seattle, WA. 98104 ___________________<under license from:PBP>-----------________ ----------- So. 43rd. Street Improvements LID 329 P0TI %I, WA. Date/Time : 12-19-1990/20:21:23 STCF M DURATION = 24 Hours DISTRIBUTICK CtRVE = SCS Type IA ----------------------------------+ Storm Frequency Rainfall Depth 2-Year 2.00" 1 10-Year 2.90" ; 100-Year 3.90" NCIVISFR OF MEROIA3IC OPERATIONS = 1 File Name: "43RDST" ------------------------------------------------------------ ------------------------------------------------------------ STEP NO. 1 DERIVE HAPH Sub-Basin I.D : H5D1 Drainage Area = 11.70 Acres EKISfIN3 DEVELOPED Time of Concentration (Mins): 6 6 Pervious Parcel (Acres) 4.10 3.60 Curve Number 80 80 Impervious Parcel (Acres) 7.60 8.10 Curve Number 98 98 -------------------[2][10] [100-Yr]----------------- Peak Discharge (Cfs) : [4.0][6.5][9.4] [4.2][6.8][9.7] Time to Peak Mrs) : [7.8] [7.8] [7.8] [7.8][7.8] [7.81 Excess Rainfall (Ins) : [1.3][2.11[3.1] [1.4][2.2)[3.1] ________________End of Hydrologic Operations=====___________ FIYCROIOCIC OPERATIONS ST[M - SU MARY +______________________<outflow hydrograph>====_________________+ Existing Condition Developed Condition 1 --------------------;-------------------1 mQUIRED ; RE1UI Peak I Volume ; Peak ; Volume I bZt"RAGE STUM 1 (Cfs) 1 (Ac-Ft) (Cfs) 1 (Ac-Ft) ; (Cu-Ft) 1---------+---------+----------+---------+- -----+-------- 2-Yr 1 4.05 1.32 1 4.25 1.37 ; 297 1 1 10-Yr 1 6.52 2.09 1 6.75 2.15 2022 1 100-Yr 1 9.40 2.99 9.66 3.06 ; 2148 Storage Requirements based on "Standard Conditions" �Y" • 1 �� `, LiR�. r ♦ T np:- M IS IS IKE E T I t, IT VAS AVAILED FROn III l SOURCES 'IT IS TIK R (I IERA RWIOH AVA,&y. IT THIS OF MD SIIpi1lD IS USED SP OEHERAL VOIDANCE Ok THE CITY 4< REHIS li HOT RESPONSIBLE FOR ENGIN RI OIOSSIfWi VHCH THIS ARE T n0TMK IS USED FOR,, ENGINEERING PLDIPOSC; DESIGNERS ARE TO R0.0 VERIFY TMS )NfpRHAT](h SEE SHEET 26 f avne auLi-1 %Di . SV {LtT ST rfM AVE :E a6N-JI a00-] kD ' . aecat a kD acm D IK 1 AL.LFY g CAE NERAL I INOSPITAL, N QRD J60H ST aR o - aW_1 ao u J6C`{ aCU-1 ,TYDhi J6Drt ]OLH •• .. cim aREH ]OLD-] aVh! d.••rc• ���.�.�. a3Gh •• JYLI�Z DAvK�AVE JAL ROAD SYS17E M r �F SYS aar.. D.oh ': ' S. I Aams a '+� I OVA i {SiN R 1 N aysr H i a.s>-1, zra-u �O14tN Waao-u aam+ ano-u W Dva u aofa a awJ '�1 aon-� aes>-n 'w IuiDua-u aors-D F all ]arc-, _ _ _ ]ox-a aaec-e aorJ-I � CITY OF RENTON MEMORANDUM DATE: June 14, 1990 TO: Dick Anderson, Utility Systems Manager FROM: Randall Parsons, Supervisor Storm Water/Waste Water Utility ec ion STAFF CONTACT: Kim Scattarella, Storm Water Utility Section / SUBJECT: EROSION CONCERNS FROM STATE OF WASHINGTON PROPERTY The property at the south end of S. Smithers, just off S.W. 43rd (see attached map) was inspected for erosion control. As a result of this inspection, I would like to recommend the following measures for future mitigation: 1) straw mulching and additional hydroseeding on exposed slopes; and 2) placement of silt fence to prevent fill from washing down into system on S.W. 43rd. A photograph from January 9, 1990, that shows the exposed slopes of this site is attached. It should be noted that this area has been hydroseeded and has stabilized since then, but still poses a potential downstream erosion problem. Let us know if you would like a letter prepared to WSDOT on this matter. 90-075:KSJS Enclosure cc: David Martin,special Projects Manager 346A 1, r,32 F 6 33 'w Q,;-�. �' .r"• .l0 ry s5 a 0.16Z � y. ''�.Gc' *S. 177TH ST. 0 34 - h� 146.98 laa/ ae.la r vV � 8 h 50 j5 4 (C) I3ea4 a '- IO 0 2 35 e 1 177/0 7 ris WS 12 I r �� 36 3 Ronald SIS 37 W. Sco-- S a � 14' < N� 5"(B�N aryl 78 4 e c a5 N 5. c I0c �L e 40. >'EO/CAC 152_6a r / . B� II l &9 CEN16 N Q 1 e - 3 rsBo �qo a� V_m? �' M241 9I Ni540 4I ' 42'z o /.. 170 i $$,' Q. 130 178 J511� aA 23 a, 2 1 r 29 e p �-'122 iP 50 a 67 4 m w- ^. 60• CSYI 7 •1.O I? S\ . — . 6�J!'i'...130� i00 3).ajrP 45 P, 44 .r> Q ® S.P. 1276056 R S.P 1282043 N� ti s (2) + ' ® (2) p S.P. 213-78 p xs p) i ® i .2s ®I I I. b 54 01.13 83. 1 $/t9y? =ST. .. d-_ Z44.61 310 SB W I I S j::: 112.54 ❑ 016 I� � F- N a li f 4� it NI (2) 0o � t� l o0 J a � •I, o LJ ;�o r',� State of ashington Ms. Springbrook Y ;I 28AC. +� lt11 j � ___ zr_n«rrr �._r Iir• 22i24 �'�I ypl I�$ (2) 4s30 2.50 Ac. /,�ao s (4) x S.P. 074-85 Valle yy Villa 'A (I) ` - Convalescent �� 2.31 Ac: ��� SP. 459.79 7 62. 41 y� 63I.32 45 Lvl 190:32 . 481 0 � _ 1 a0 B [1.6 W. Shegrud i PL. r 69 94 60 --1 0.10= = 480.99 =Iongvil'le � State of Washington r: Jack B. Sparks t.63Ac. I , 63 y14 Syr K f Sr +t D {to�m4r'aQheL{ On Sal n 9i /y