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HomeMy WebLinkAboutEx06_Drainage_Report6162 S. Willow Drive, Suite 320 Greenwood Village, CO 80111 303.770.8884 •GallowayUS.com May 11th, 2020 Mr. Justin Johnson Community & Economic Development Civil Construction 1055 South Grady Way Renton, WA 98057 RE: Drainage Conformance Letter for Technical Information Report – Retail Expansion – Walmart Store #2516-240 Dear Mr. Johnson, The purpose of this letter is to demonstrate that the drainage characteristics of the Online Grocery Pickup (OGP) expansion improvements for the Walmart Supercenter, Store #2516 in Renton, WA is in conformance with the Technical Information Report – Retail Expansion dated February 25th, 2010 (per stamp date) by Pac Land. SUMMARY The subject property is located at 743 Rainier Ave S, Renton, WA 98057, a previously developed lot (part of the previous Walmart expansion) that consists of an existing Walmart with associated paved parking, totaling an area of 13.65 Acres. It is bound to the north by SW 7th Street, east by Rainier Ave S, and south & west by adjacent businesses. The project area consists of approximately 0.33 Acres. The existing area is comprised of paved parking lot, sidewalk, and landscape islands. Improvements to the site include the addition of an OGP building expansion (1,350 SF), conversion of landscape islands to pavement (1,425 SF), installation of an OGP canopy, re-striping of existing parking lot, and relocation of existing waterline and hydrant. DRAINAGE BASIN PATTERNS Improvements to the site will not change the existing drainage basin areas and drainage shall follow the existing drainage patterns for basins 2a and 2b outlined in the Technical Information Report – Retail Expansion report (Note: these areas are indicated as proposed conditions within the existing report). Landscape areas in proposed drainage basins 2a and 2b are being modified as part of this project and will become impervious pavement. Total additional areas for basins 2a and 2b are 949 SF and 476 SF respectively. In addition to the changes illustrated above, 1,350 SF of existing impervious area (sidewalk and pavement) will be removed and replaced by the proposed building expansion within basin 2a. Roof drains from the proposed building expansion will splash to surface and follow the existing drainage patterns. Existing basin and Proposed Basin areas are shown in the tables on the following page. RECEIVED 06/09/2020 amorganroth PLANNING DIVISION EXHIBIT 6 DocuSign Envelope ID: 1C3D0486-3D78-416B-94DE-E64EA6106C25 Wal-Mart Stores Inc. Walmart #2516 OGP Expansion 05-11-2020 Galloway & Company, Inc.Page 2 of 4 Existing basin areas per Technical Information Report – Retail Expansion report. (Note: These are listed as Proposed Sub-Basins areas in Table 2 of the above-mentioned report.) Proposed basin areas based on new construction. SITE HYDROLOGY Existing drainage patterns outlined in the Technical Information Report – Retail Expansion shall remain unchanged with the current improvements.Existing basins 2a and 2b were broken down from the existing report and runoff rates can be found below. Proposed drainage patterns will follow the existing drainage patterns. Drainage basin 2a will maintain the same area as noted previously, however, pervious areas (landscape island areas) will be exchanged for impervious pavement areas and building roof area in exchange for pavement areas. Drainage basin 2b will also maintain the same area, however, pervious area (landscape island area) 1 2a 2b 3 Roof 150,244 0 0 0 Garden Center 0 4,701 0 0 Landscaping 0 51,795 8,783 5,112 Pavement (PGIS)2,548 276,524 27,496 37,433 Sidewalk 0 24,430 3,560 1,927 Gravel 0 0 0 0 Total 152,792 357,450 39,839 44,472 Surface Existing Sub-Basins 1 2a 2b 3 Roof 150,244 1,350 0 0 Garden Center 0 4,701 0 0 Landscaping 0 50,846 8,307 5,112 Pavement (PGIS)2,548 276,333 27,972 37,433 Sidewalk 0 24,220 3,560 1,927 Gravel 0 0 0 0 Total 152,792 357,450 39,839 44,472 Surface Proposed Sub-Basins Event Peak Q Rate (CFS) 2-year - 24 Hr 3.3167 10-year 5.113 100-year 7.0847 Ex. Basin 2a Runoff Rates SBUH Method Event Peak Q Rate (CFS) 2-year - 24 Hr 0.3479 10-year 0.5482 100-year 0.7686 Ex. Basin 2b Runoff Rates SBUH Method DocuSign Envelope ID: 1C3D0486-3D78-416B-94DE-E64EA6106C25 Wal-Mart Stores Inc. Walmart #2516 OGP Expansion 05-11-2020 Galloway & Company, Inc.Page 3 of 4 will be exchanged for impervious pavement areas. The changes in the proposed drainage basins produced the following flow information. Detailed calculations can be found in Appendix B of this Report. RETENTION/DETENTION ANALYSIS As dictated in the Retention/Detention System section of the Technical Information Report – Retail Expansion, unless the 24-hour storm increases by more than 0.50 cfs from the pre-developed peak runoff rate, the project is exempt from runoff control. Given that basin 2a only increases by 0.0056 cfs and basin 2b only increases by 0.0029 cfs, this project is exempt under the provision. BIOSWALE TREATMENT The existing biofiltration swale in the northwestern portion of the site will still maintain the treatment of the basin 2a area. As noted in the Technical Information Report – Retail Expansion report, additional water quality was provided for the additional pavement area. This bioswale outlined in the New PGIS section of the Technical Information Report – Retail Expansion report, shall facilitate in providing the additional water quality. Per the existing report, the bioswale for basin 2b was overdesigned for the required conditions and given the minimal increase in flow rates, the existing bioswale will suffice in providing the required water quality for the proposed development. The existing bioswale design was verified using the following parameters: The resultant swale design requires a minimum bottom width of 7.63 feet and a minimum treatment length of 91 feet. Given that the swale was designed with an 8 foot bottom width and a 115 foot treatment length, with a 1.0% longitudinal slope, the swale design fits into the parameters. Calculations showing the existing bioswale characteristics accommodating the additional flows can be found in Appendix C. CONCLUSIONS Given the minor increase in flows, 0.0056 cfs for basin 2a and 0.0029 cfs for 2b, and the fact that the bioswale can accommodate the additional flow rates as designed. The improvements outlined in this conformance letter comply with the existing drainage report and therefore no additional modifications are necessary. Event Peak Q Rate (CFS) 2-year - 24 Hr 3.3223 10-year 5.1181 100-year 7.0893 Prop. Basin 2a Runoff Rates SBUH Method Event Peak Q Rate (CFS) 2-year - 24 Hr 0.3508 10-year 0.551 100-year 0.7712 Prop. Basin 2b Runoff Rates SBUH Method Criteria Value 2-yr, 24-hr flow 0.3508 cfs Design Flow Depth 0.25 feet Mannings Coeff 0.35 Residence Time 9 minutes Side Slope 3.0 H:V Bioswale Design Criteria - Single Event DocuSign Envelope ID: 1C3D0486-3D78-416B-94DE-E64EA6106C25 Wal-Mart Stores Inc. Walmart #2516 OGP Expansion 05-11-2020 Galloway & Company, Inc.Page 4 of 4 Sincerely, GALLOWAY Brandon D. Alley, PE Principal - Galloway US BrandonAlley@gallowayUS.com NOTE: See attached documents for further drainage information: Addendum A: Drainage Map Addendum B: Drainage Detention Calculations Addendum C: Bioswale Calculations DocuSign Envelope ID: 1C3D0486-3D78-416B-94DE-E64EA6106C25 APPENDIX A PROPOSED DRAINAGE MAP DocuSign Envelope ID: 1C3D0486-3D78-416B-94DE-E64EA6106C25 1 inch = 60 ft. ( IN FEET ) GRAPHIC SCALE 060 60 120 24030 SHEET JOB No. SCALE DATE CHECKED DRAWN REVISIONS BY RHA002516.20 05/11/20 AS NOTED JES DMPNOTFORCONS TRUCTIONH:\RHA\WA, Renton - RHA002516.20 - 743 Rainier Ave. S\3 Permit CDs\3.04 Grading-Drainage Studies\3.04.2 Proposed Drainage Reports-Info\RHA2516_Drainage Map - 2019-02-11 - Ryan James DocuSign Envelope ID: 1C3D0486-3D78-416B-94DE-E64EA6106C25 APPENDIX B DRAINAGE DETENTION CALCULATIONS DocuSign Envelope ID: 1C3D0486-3D78-416B-94DE-E64EA6106C25 Appended on: Wednesday, May 29, 2019 8:29:09 PM Ex Basin 2a Event Summary Record Id: Ex Basin 2a Licensed to: Engenious Systems, Inc. Event Peak Q (cfs)Peak T (hrs)Hyd Vol (acft)Area (ac)Method 2 yr 24 hr 3.3167 8.00 1.0941 8.21 SBUH 10 year 5.113 8.00 1.6972 8.21 SBUH 100 year 7.0847 8.00 2.3738 8.21 SBUH All results based on storm duration of 24.0 hours. This is ok if all precipitations are appropriate for the storm duration. If some design event precipitations are for different duration storms, those results are incorrect Design Method SBUH Rainfall type TYPE1A.RAC Hyd Intv 10.00 min Peaking Factor 484.00 Storm Duration 24.00 hrs Abstraction Coeff 0.20 Pervious Area 8.21 ac DCIA 0.00 ac Pervious CN 96.26 DC CN 0.00 Pervious TC 5.00 min DC TC 0.00 min Pervious CN Calc Description SubArea Sub cn Impervious surfaces (pavements, roofs, etc)7.02 ac 98.00 Open spaces, lawns,parks (>75% grass)1.19 ac 86.00 Pervious Composited CN (AMC 2)96.2607 Pervious TC Calc Type Description Length Slope Coeff Misc TT Sheet Smooth Surfaces.30.00 ft 2.0%0.011 0.00 in 0.585 min Int Channel CMP pipe (n=0.024)200.00 ft 0.5%0.024 2.2202 min Pervious TC 2.8052 min Page 1 of 1 5/29/2019file:///C:/Users/sid_biddle/Stormshed/StormShed3G/Basin%202a.html DocuSign Envelope ID: 1C3D0486-3D78-416B-94DE-E64EA6106C25 Appended on: Wednesday, May 29, 2019 8:33:27 PM Ex Basin 2b Event Summary Record Id: Ex Basin 2b Licensed to: Engenious Systems, Inc. Event Peak Q (cfs)Peak T (hrs)Hyd Vol (acft)Area (ac)Method 2 yr 24 hr 0.3479 8.00 0.1149 0.91 SBUH 10 year 0.5482 8.00 0.1811 0.91 SBUH 100 year 0.7686 8.00 0.2557 0.91 SBUH All results based on storm duration of 24.0 hours. This is ok if all precipitations are appropriate for the storm duration. If some design event precipitations are for different duration storms, those results are incorrect Design Method SBUH Rainfall type TYPE1A.RAC Hyd Intv 10.00 min Peaking Factor 484.00 Storm Duration 24.00 hrs Abstraction Coeff 0.20 Pervious Area 0.91 ac DCIA 0.00 ac Pervious CN 95.36 DC CN 0.00 Pervious TC 5.00 min DC TC 0.00 min Pervious CN Calc Description SubArea Sub cn Impervious surfaces (pavements, roofs, etc)0.71 ac 98.00 Open spaces, lawns,parks (>75% grass)0.20 ac 86.00 Pervious Composited CN (AMC 2)95.3626 Pervious TC Calc Type Description Length Slope Coeff Misc TT Sheet Smooth Surfaces.30.00 ft 2.0%0.011 0.00 in 0.585 min Int Channel CMP pipe (n=0.024)200.00 ft 0.5%0.024 2.2202 min Pervious TC 2.8052 min Page 1 of 1 5/29/2019file:///C:/Users/sid_biddle/Stormshed/StormShed3G/Basin%202a.html DocuSign Envelope ID: 1C3D0486-3D78-416B-94DE-E64EA6106C25 Appended on: Wednesday, May 29, 2019 8:35:46 PM Pro Basin 2b Event Summary Record Id: Pro Basin 2b Licensed to: Engenious Systems, Inc. Event Peak Q (cfs)Peak T (hrs)Hyd Vol (acft)Area (ac)Method 2 yr 24 hr 3.3223 8.00 1.096 8.21 SBUH 10 year 5.1181 8.00 1.6993 8.21 SBUH 100 year 7.0893 8.00 2.376 8.21 SBUH All results based on storm duration of 24.0 hours. This is ok if all precipitations are appropriate for the storm duration. If some design event precipitations are for different duration storms, those results are incorrect Design Method SBUH Rainfall type TYPE1A.RAC Hyd Intv 10.00 min Peaking Factor 484.00 Storm Duration 24.00 hrs Abstraction Coeff 0.20 Pervious Area 8.21 ac DCIA 0.00 ac Pervious CN 96.29 DC CN 0.00 Pervious TC 5.00 min DC TC 0.00 min Pervious CN Calc Description SubArea Sub cn Impervious surfaces (pavements, roofs, etc)7.04 ac 98.00 Open spaces, lawns,parks (>75% grass)1.17 ac 86.00 Pervious Composited CN (AMC 2)96.2899 Pervious TC Calc Type Description Length Slope Coeff Misc TT Sheet Smooth Surfaces.30.00 ft 2.0%0.011 0.00 in 0.585 min Int Channel CMP pipe (n=0.024)200.00 ft 0.5%0.024 2.2202 min Pervious TC 2.8052 min Page 1 of 1 5/29/2019file:///C:/Users/sid_biddle/Stormshed/StormShed3G/Basin%202a.html DocuSign Envelope ID: 1C3D0486-3D78-416B-94DE-E64EA6106C25 Appended on: Wednesday, May 29, 2019 8:37:33 PM Prop Basin 2a Event Summary Record Id: Prop Basin 2a Licensed to: Engenious Systems, Inc. Event Peak Q (cfs)Peak T (hrs)Hyd Vol (acft)Area (ac)Method 2 yr 24 hr 0.3508 8.00 0.1158 0.91 SBUH 10 year 0.551 8.00 0.1821 0.91 SBUH 100 year 0.7712 8.00 0.2568 0.91 SBUH All results based on storm duration of 24.0 hours. This is ok if all precipitations are appropriate for the storm duration. If some design event precipitations are for different duration storms, those results are incorrect Design Method SBUH Rainfall type TYPE1A.RAC Hyd Intv 10.00 min Peaking Factor 484.00 Storm Duration 24.00 hrs Abstraction Coeff 0.20 Pervious Area 0.91 ac DCIA 0.00 ac Pervious CN 95.49 DC CN 0.00 Pervious TC 5.00 min DC TC 0.00 min Pervious CN Calc Description SubArea Sub cn Impervious surfaces (pavements, roofs, etc)0.72 ac 98.00 Open spaces, lawns,parks (>75% grass)0.19 ac 86.00 Pervious Composited CN (AMC 2)95.4945 Pervious TC Calc Type Description Length Slope Coeff Misc TT Sheet Smooth Surfaces.30.00 ft 2.0%0.011 0.00 in 0.585 min Int Channel CMP pipe (n=0.024)200.00 ft 0.5%0.024 2.2202 min Pervious TC 2.8052 min Page 1 of 1 5/29/2019file:///C:/Users/sid_biddle/Stormshed/StormShed3G/Basin%202a.html DocuSign Envelope ID: 1C3D0486-3D78-416B-94DE-E64EA6106C25 APPENDIX C BIOSWALE CALCULATIONS DocuSign Envelope ID: 1C3D0486-3D78-416B-94DE-E64EA6106C25 5/29/2019 JSB RCJ Step# P-1 0.3508 cfs Water Quality Design Flow P-2 0.01 ft/ft Swale Slope < 2%, underdrains required P-3 D-1 0.25 ft D-2 0.35 D-3 3 H:V D-4a 7.62 ft D-4b 9.12 ft D-5 2.09 sf 90.6 = Length (Feet) Required D-6 0.17 fps 90.9 = Length (Feet) w/ 9 min rest time (this is still long enough) D-7 Yes Okay - V<1.5 fps proceed to SC-1 D-8 D Table III-6.2 (D or E) D-9 1.70 Table III - 6.6, n =nwq from step D-2 D-10 -ft D-11 - D-12 -% D-13 -fps D-14 -sf D-15a -ft D-15b -ft D-16 If biofiltration swale is still to wide, see DOE page III-6-17 for more info and options Step# SC-1 0.77 cfs BIOSWALE DESIGN Date Designer Project Manager WMT OGP Expansion #2516 RHA002516.20 On-Site (Redev) Project Name Project Number Swale Title Channel Width T=b+2*y*z Qwq (100-yr - 24-Hr) Actual V V=(VR/R) Channel X-Sec Area A=Q/A New Swale Bottom Width (b) b=(A/y)-Z*y First Approx for VR Hydraulic Radius R=(V*R)/Vmax Actual VR VR=(1.486*(R1.6668)*S0.5)/n % Difference A=(b*y)+(Z*y2) Flow Velocity v=Q/A Is Design Adequate Degree of retardence Design Steps (D) Stability Check Steps (SC) Design Flow Depth (y) Mannings Roughness Coeff (ᶯwq) Side Slope (Z) Swale bottom width (b) b=(Q*n)/(1.486*y1.667*s0.5)-(Z*y) Top width (T) T=b+2*y*z Area (A) Qwq (2-yr, 24-Hr) Slope of Swale (s) Select Vegetation to be used Grass Legume Mix Preliminary Steps (P) DocuSign Envelope ID: 1C3D0486-3D78-416B-94DE-E64EA6106C25 SC-2a Good (Good or Fair) SC-2b 0.25 ft SC-3 D Table III-6.2 (D or E) SC-4 3.00 fps Table III-6.3 SC-5 0.043 (Good initial choice 0.04) SC-6 2.70 Table III - 6.6 SC-7 0.9 ft SC-8 2.90 SC-9 7.38%% SC-10 3.22 fps SC-11 0.24 sf SC-12 Yes Swale is Stable 1.2 ft 8.00 ft 15.2 ft SC-13 1.2 ft 115 SC-14 2.2 ft SC-15 1.16 ft SC-16a 32.12 sf SC-16b 15.06 cfs Okay, Capacity > 100-yr, 24-Hr Storm R=((b*y*t)+(Z*y*t2))/(b+2yt*(Z2+1)0.5) Channel X-Sec Area Channel Capacity Q=(1.486*A*R0.677*s0.5)/n T=b+2*y*z Depth of Flow y=(t-b)/2z Total Swale Depth yt = y+1 Hydraulic Radius A=Q/V Compare A with Orig New y = New b = b=(Q*n)/(1.486*y1.667*s0.5)-(Z*y) New T = Actual VR VR=(1.486*R1.667*s0.5)/n % difference Actual V V=VR/R X-Sec Area Degree of Retardance Max allowed Velocity Trial Mannings n First Approx for VR Hydraulic Radius R=(V*R)/Vmax Condition of vegetation Height of grass @ first storm DocuSign Envelope ID: 1C3D0486-3D78-416B-94DE-E64EA6106C25