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Home My WebLink AboutDrainage Reports - 11/08/2018 (2) Page 1 of 1 D:\Projects\207-023\Drainage\Reports\Drainage Report\1281-001_Drainage-Letter.docx Drainage Letter Report Date: October 23, 2018 Project: Collindale Industrial Park – Minor Amendment Project No. 1281-001 Fort Collins, Colorado Attn: Mr. Wes Lamarque City of Fort Collins Stormwater Utility 700 Wood Street Fort Collins, Colorado 80521 Dear Wes: This letter serves to address the stormwater impacts of the above referenced project. This project is located at the southwest corner of the intersection of Timberline Road and Danfield Court. The site currently consists of rooftop, concrete walks and patio, asphalt parking areas, trees, and other vegetation. The site presently drains west to east via overland flow into a series of area and curb inlets located in the center of the parking lot and drive aisles. Only one inlet is getting relocated which is in the landscaping area to the west side of the building. It’s going to be placed within the new flowline, but the historic flows will still be getting routed to it. The rest of the inlets are going to remain exactly where they are and at the same elevation to preserve historic drainage patterns. The inlets release into the City’s storm sewer system within Timberline Road. Historic drainage patterns will generally be preserved. The total impervious area within the project boundary of the existing site is approximately 247,996 square-feet with a composite percent impervious of 97%. The proposed redevelopment will be removing some parking islands, an associated storage building, a portion of some sidewalks, and some asphalt associated with the parking lots. The new project is proposing to modify the parking lot to increases parking count as well as adding some additional sidewalks and associated landscaping amenities. The new project intends to maintain existing drainage patterns as well as utilizing all the existing storm infrastructure except for relocating one inlet. The total impervious area within the project boundary of the proposed redevelopment is roughly 241,181 square-feet with a composite percent impervious of 97%. Therefore, these improvements are reducing the overall impervious area for the site. Due to the reduction in impervious area there will not be any detention or water quality provided with this improvement. For additional clarification on these calculations please see the attached Runoff Coefficient Calculations at the back of this letter. Northern Engineering was unable to locate any previous drainage reports associated with the existing development. However, existing percent impervious and drainage patters were maintained so no adverse impacts will occur with downstream infrastructure. Therefore, no additional drainage analysis or infrastructure is needed for this minor amendment. If there are any concerns or questions, please give Northern Engineering a call. Cody N. Snowdon, PE Project Manager Blaine Mathisen, EI Project Engineer 10.23.18 CHARACTER OF SURFACE: PercentageImperviousProject:MadwireStreets, Parking Lots, Roofs, Alleys, and Drives:Calculations By:B. MathisenAsphalt ……....……………...……….....…...……………….…………………………………..100%Date:Concrete …….......……………….….……….………………..….…………………………………90%Gravel ……….…………………….….…………………………..………………………………..40%Roofs …….…….………………..……………….…………………………………………….. 90%Pavers…………………………...………………..……………………………………………..22%Lawns and LandscapingSandy Soil ……..……………..……………….……………………………………………..0%Clayey Soil ….….………….…….…………..……………………………………………….0%2-year Cf = 1.00100-year Cf = 1.25Basin IDBasin Area(s.f.)Basin Area(ac)Area ofAsphalt(ac)Area ofConcrete(ac)Area ofGravel (ac)Area ofLawns andLandscaping(ac)2-yearComposite RunoffCoefficient10-yearComposite RunoffCoefficient100-yearComposite Runoff CoefficientComposite% Imperv.Existing3283777.543.750.360.001.850.750.750.9473%Proposed3283777.543.780.330.012.000.740.740.9271%Existing (Impervious)2479965.693.750.360.000.000.950.951.0097%Existing (Pervious)803811.850.000.000.001.850.150.150.190%Proposed (Impervious)2411815.543.780.330.010.000.950.951.0097%Proposed (Pervious)871962.000.000.000.002.000.150.150.190%Proposed Pervious Area Only Impervious Area BreakdownOverall AreaExisting Impervious Area OnlyProposed Imperverious Area OnlyExisting Pervious Area OnlyCOMPOSITE % IMPERVIOUSNESS AND RUNOFF COEFFICIENT CALCULATIONSNotesOverall AreaOctober 3, 201810-year Cf = 1.00**Soil Classification of site is Sandy Loam**Runoff Coefficients are taken from the City of Fort Collins Storm Drainage Design Criteria and Construction Standards, Table 3-3. % Impervious taken from UDFCD USDCM, Volume I.Page 1 of 1D:\Projects\BD-18-011\Drainage\Hydrology\1281-001_Rational-Calcs.xlsx\Hist-C-Values VAULT F.O. VAULT F.O. S MH MH F.O. CONTROL IRR MH D VAULT F.O. DD DCTFO VAULT F.O.HY DT VAULT F.O. MH MH MH MH GX XXXXXXXXXXXXXXXXXX X X X XXW TIMBERLINE RD.DANFIELD CT. E N G I N E E R N GI EHTRON R N 09.06.2018 D:\PROJECTS\BD-18-011\DWG\DRNG\1281-001_EXSTDRNG.DWG ( IN FEET ) 0 1 INCH = 80 FEET 80 80 Existing (sf)Proposed (sf) Asphalt 163455 164130 Concrete 15873 14273 Roofs 68668 61894 Gravel 0 399 Landscaping 80381 87682 Total 328377 328377 Composite Impervious 73%71% EXISTING PERVIOUS V. IMPERVIOUS EXHIBIT A1 FORT COLLINS, CO COLLINDALE INDUSTRIAL PARK - MINOR AMENDMENT REFER TO THE DRAINAGE LETTER REPORT ASSOCIATED WITH THE COLLINDALE INDUSTRIAL PARK MINOR AMENDMENT BY NORTHERN ENGINEERING FOR ADDITIONAL CLARIFICATION AND MORE DETAILED CALCULATIONS. CONTROL IRR CONTROL IRR CONTROL IRR VAULT F.O. VAULTF.O. S F.O. IRRIRRIRRIRR CONTROL IRR CONTROL IRR VAULT F.O. CT CONTROL IRR FO VAULTF.O. T VAULT F.O. CONTROL IRR CONTROL IRR G CONTROL IRR CONTROLIRR CONTROLIRR CONTROLIRR CONTROLIRR XXXXXXXXXXXXXXXXXX X X X XXW CONTROL IRR CONTROL IRR CONTROL IRR CONTROL IRR CONTROL IRR CONTROL IRR T T TIMBERLINE RD.DANFIELD CT. PROPOSED PERVIOUS V. IMPERVIOUS EXHIBIT A2 FORT COLLINS, CO COLLINDALE INDUSTRIAL PARK - MINOR AMENDMENT E N G I N E E R N GI EHTRON R N 10.03.2018 D:\PROJECTS\BD-18-011\DWG\DRNG\1281-001_DRNG.DWG Existing (sf)Proposed (sf) Asphalt 163455 164616 Concrete 15873 14273 Roofs 68668 61894 Gravel 0 399 Landscaping 80381 87196 Total 328377 328377 Composite Impervious 73%71% ( IN FEET ) 0 1 INCH = 80 FEET 80 80 REFER TO THE DRAINAGE LETTER REPORT ASSOCIATED WITH THE COLLINDALE INDUSTRIAL PARK MINOR AMENDMENT BY NORTHERN ENGINEERING FOR ADDITIONAL CLARIFICATION AND MORE DETAILED CALCULATIONS.