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Home My WebLink AboutFOOTHILLS MALL MULTI-FAMILY - MAJOR AMENDMENT - MJA150002 - REPORTS - DRAINAGE REPORTDesign Procedure Form: Rain Garden (RG) Sheet 2 of 2 Designer: Daniel Hull Company: Olsson Associates Date: April 24, 2015 Project: Major Amendment to a Portion of Foothills Mall Redevelopment Planning Area 3 Location: Modified Rain Garden 33 Choose One 5. Impermeable Geomembrane Liner and Geotextile Separator Fabric 0 YES A) Is an impermeable liner provided due to proximity O NO of structures or groundwater contaminator? Choose One 6. Inlet I Outlet Control Q Sheet Flow- No Energy Dissipation Required A) Inlet Control ® Concentrated Flats Energy Dissipation Provided 7. Vegetation p Seed (Plan for frequent weed control) 40 Plantings Sand Grown or Other High Infiltration Sod Choose One B. Irrigation Q YES A) Will the rain garden be irrigated? ® NO Notes: Exhibit F Modified Rain Garden, RG33 lot 2 Rain Garden 33.0 Calcs.xism, RG 4/24/2015, 1 57 PM Design Procedure Form: Rain Garden (RG) Sheet 1 of 2 Designer: Daniel Hull Company: Olsson Associates Date: April 24, 2015 Project: Major Amendment to a Portion of Foothills Mall Redevelopment Planning Area 3 Location: Modified Rain Garden 33 1. Basin Storage Volume A) Effective Imperviousness of Tributary Area, I, 1„ = 68.0 % (100% 4 all paved and roofed areas upstream of rain garden) B) Tributary Area's Imperviousness Ratio (i = Idl OO) = 0.680 C) Water Quality Capture Volume (WQCV) for a 12-hour Drain Time WQCV = 0.21 watershed inches (WQCV= 0.8' (0.91' it- 1.19' i'+ 0.78' i) D) Contributing Watershed Area (including rain garden area) Area = 68,348 sq it E) Water Quality Capture Volume (WQCV) Design Volume Vwocv = 1,213 cu ft Vol = (WQCV / 12)' Area F) For Watersheds Outside of the Denver Regan, Depth of dS = 0.00 in Average Runoff Producing Storm G) For Watersheds Outside of the Denver Region, Vwxv 0TWR = DA cu ft Water Quality Capture Volume (WQCV) Design Volume H) User Input of Water Quality Capture Volume (WQCV) Design Volume VWOCV USER = cu ft (Only it a different WQCV Design Volume is desired) 2. Basin Geometry A) WQCV Depth (12-inch maximum) Dwmv = 12 in 8) Rain Garden Side Slopes (Z = 4 min., horiz. dist per unit vertical) Z = 4.00 ft / ft (Use "0" 1 rain garden has vertical walls) C) Mimimum Flat Surface Area AMA, = 809 sq ft 0) Actual Flat Surface Area AAd, W = 993 sq ft E) Area at Design Depth (Top Surface Area) AT,p = 1692 sq ft F) Rain Garden Total Volume VT= 1,343 cu ft (VT= ((Arm + Anm,x) / 2) ' Depth) 3. Growing Media LhOoSe ne Q 18" Rain Garden Growing Medal 10 Other (Explain): 4. Underdrain System ChOO5e One A) Are underdrains provided? r YES 0 NO NO B) Underdrain system orifice diameter for 12 hour drain time i) Distance From Lowest Elevation of the Storage y = 60.0 N Volume to the Center of the Orifice ii) Volume to Drain in 12 Hours Vold= 1,213 cu ft iii) Orifice Diameter, 3/8" Minimum Dr, = 0.40 in Exhibit F Modified Rain Garden, RG33 1 of 2 Rain Garden 33.0 Calcs.xl5m, RG 412412015, 1.57 PM 5285 McWhinney Boulevard 160 Foothills Mall Multi -Family Exhibit E OAOLSSON Loveland, te CO 80538 Revised Rain Garden RG-33 ASSOCIATES TEL 970.431.7733 Existing Design Lot Area (SF) AREA (AC) Landscape Paved Roof Walks Porous Paving Percent Impervious Imperviousness 0% 100% 90% 90% 90% NA 3 170,929 3.92 47,519 47,007 58,191 18,212 0 68% 4 112,588 2.58 36,461 1,162 66,796 8,169 0 61% 5 101,716 2.34 is,199 1,782 68,600 16,135 1 0 77% 6 134,248 3.08 33,514 2,263 89,864 8,607 0 68% Total 519,481 8.84 132,693 52,214 283,451 51,123 1 0 68% Proposed Design Lot Area (SF) AREA (AC) Landscape Paved Roof Walks Porous Paving Percent Impervious Imperviousness 0% 100% 90% 90% 90% NA 3 170,929 3.92 49,881 47,583 59,234 2,515 11,716 67% 4 112,588 2.58 39,200 2S,094 32,372 8,583 7,339 61% 5 101,716 2.34 27,416 27,917 34,096 4,396 7,891 68% 6 134,248 3.08 27,217 48,433 41,840 3,884 1 12,874 75% Total 519,481 8.84 143,714 149,027 167,542 19,378 39,820 68% Foothills Mall Multi-Famliy Exhibit D Percent Imperviousness 5285 McWhinney Boulevard Suite 160 OLSSON 9i Loveland, C080538 ASSOCIATES TEL 970.431, 7733 4 rurowe r— "'A x RT OTN(r IEFILLER 1 I G I li nllli \ _ j ! LOT 3 ' I IRIIIII�IIIIIf1 SAI f s : RAIN ERORONO CURIS99 TO GARDEN 33.0 xuow RUROFF ro aM TO Ru-(NROER Irm) VA" Wall, I .� lyl� IA, ✓ e r ice.. r -.r-- SAND FILTER 1.0 FOOTHILLS REDEVELOPMENT F-.,^_',;—"`—. xr v .awe �v inonm?swRRee�o- RR'ein�in°hCMol�uenluiw. Cry aF roxl cawu.oaMlTa uxMen. mnn or rmaueo ._+.- xLRV I1YFI FOL �!• PLANNING AREA 3 • ""' THIS NJNGAAWN OKY FINAL PLANS o ••. � WILT IN vp RUSE NAY 22. 2014MV1 ARS H RAIN RESIoeNnaL GARDEN 31.0 I $, R l00 OPY111C WAX — / tool slq Arx: n.a.o« TopIAI0. TTO W)IorOwMy --"_ _ 9MR: EO.iwsaw, Er DRAINAGE PLAN BMP VOLUME SUMMARY �).r�n ;w url • cx LA. Sm+th Nh L 1..: SM ;itl Rl w d) ,x -y R.uwnrrcx v rs ,xe rk r F O O T H I L L S e))^ sMc c'alslxucrFn uvnR r� MY.Q. nu o�R Rws REDEVELOPMENT cwsrwclro waFR ant � e. I n r c e LEGEND WALTON )' uu rwnmux autrnxa td sw nme .M unoRwnrl wn ao�oRwt Uval� lnu 9[ D4, IC-Wl MMq+ nFlp IG F oraEep �� -a.r ■ ' 1730 M9rM MAlIn; ]C AWpi )Imll) .f9W9.1/I./i iW�, x1�lIY Y! NA ISM. r, y, RMY6 A AtCM101.1rf WO-001 C-3 2302 Exhibit C 5285 McWlenneV Boulevard E Foothills Mall Multi -Family O�OLSSON Suite 160 Lot Map ® TEL Lovef9 311..n33g ASSOCIATES 35 F 5 201 � 17 (PS r to3 8 2sI 49 ~ T 37 — - \ Map taken from Storm Water Management Plan for Foothills Redevelopment, r .prepared by R.A. Smith National, dated Revised December 5, 2013 5285 McWhinney Boulevard Foothills Mall Multi-Famil Exhibit B Suite 160 y ICAOLSSON .'. Loveland. Co 80538 Existing Drainage Basins ASSOCIATES TEL 970.431.7733 E. DRAVE RD 0 J Lot 3, 4, 5 and 61 PRINCIPAL Ac �; SITE OUTLET Lu E. SwN.I w RD (UNNAMED) ( r SITE i - L1MI TS OF J FOOTHILLS LARIMER COUNTY LL BASIN DI TCH NO 2 MONROE - - - E. HO TOOTH RD Map taken from Storm Water Management Plan for Foothills Redevelopment, prepared by R.A. Smith National, dated Revised December 5, 2013 5285 McWNnney Boulevard Swim160 Foothills Mall Multi -Family Exhibit A O#kOLSSON Loveland. CO 80538 Vicinity Map ASSOCIATES TEL 970.431,7733 Addendum 1 Drainage Analysis for the Major Amendment to a Portion of Foothills Mall Redevelopment Planning Area 3 (Lots 3, 4, 5, and 6 of Foothills Mall Redevelopment) Page 2 The following calculations and supporting material are attached for your reference: • Exhibit A — Vicinity Map • Exhibit B — Existing Drainage Basins • Exhibit C — Percent Imperviousness • Exhibit D — Lot Map (Rain Garden Locations) • Exhibit E — Revised Rain Garden, RG-33 • Exhibit F — Revised Rain Garden, RG33, Calculations If you have any questions or need additional information, please contact me. Sincerely, Olsson Associates Oti0?S 39337 ' FSsroniPkl � Daniel Hull, PE Senior Project Engineer Enclosures CAOLSSON A S S O C I A T E S September 30, 2015 Stormwater Engineering City of Fort Collins 281 North College Avenue Fort Collins. CO 80524 RE: Addendum 1 Drainage Analysis for the Major Amendment to a Portion of Foothills Mall Redevelopment Planning Area 3 (Lots 3, 4, 5. and c of Foothills Mall Redevelopment) Dear Sir or Madam: Olsson has completed an analysis of the drainage design for Lot 3, 4, 5 a--, 6 of Foothills Mall Redevelopment to determine the changes from the original to the proposed design. The original design is defined within the following drainage report: Storm Water Management Plan for Foothills Redevelopment, prepared by R.A. Smith National, dated Revised December 5, 2013 (existing drainage report). The lots fall within Basin 25 of the Existing Drainage Report. The original basin's imperviousness was compared to the imperviousness of the proposed design to determine if further analysis would be required. The original design's overall composite percent imperviousness was determined to be 68 percent. The percent imperviousness of the proposed design was calculated to be 6E percent. Based on the calculations, a reduction of the developed runoff would be anticipated. See attached calculations and supporting material. Since the intended drainage patterns will remain the same, detailed analysis will not be required. In addition, the runoff for original design was intended to drain to sand filters and rain gardens within the Foothills Mall Redevelopment: Sand Filters SF-1.0, SF-2.0. and SF-4.0; and Rain Gardens RG-29 and RG-31. These drainage systems have been designed per the existing drainage report and are being constructed as part of the Foothills Redevelopment Planning Area 2 Final Plans. The rain garden and sand filter design's assumed the contributing area was 90 percent imperviousness. Based on that assumption, additional analyses will not be required. Since rain garden RG-33 was being constructed as part of Foothills Redevelopment Planning Area 3 Final Plans, analysis of the rain garden was completed for the proposed design. Based on the analysis a rain garden will be provided in the northeast corner of Lot 3 meeting the original intent. 5285 McWhinney Blvd., Suite 160 TEL 303.237.2072 Loveland, CO 80538 FAX 303.237,2659 www.olssonassociates.com