The URL can be used to link to this page

Home My WebLink AboutDrainage Reports - 08/02/2012ty of Ft Collins v Plans July 24, 2012 Mr. Glen Schlueter Fort Collins Utilities — Stormwater 700 Wood Street Fort Collins RE: 1801 S. College Ave. Renovation Drainage Memo JVA PN: 1952c Dear Glen: JVA, Incorporated 25 Old Town Square Suite 200 Fort Collins, CO 80524 Ph: 970.225.9099 Fax: 970.225.6923 Toll Free: 877.444.1951 Web site: www.jvajva.com E-mail: info@jjvajva.com This letter is prepared to summarize the changes in impervious area and the stormwater quality improvements associated with the site improvements for the renovation of the facility at 1801 S. College Ave. Proiect Description 1801 S. College Ave. is located at the southwest comer of Stuart Street and South College Avenue and was previously occupied by a Maytag appliance retail store and a granite shop. The property has been recently purchased and is proposed to be renovated to be mixed use commercial with a combination of retail and restaurant occupancies. In general, as part of this renovation project, the proposed site improvements will consist of modifications to the east and west parking areas, grading modifications to accommodate a recessed sitting plaza adjacent to the west side of the building, a potential sitting plaza space north of the existing building, incorporation of ramps and stairs along the west side of the existing building for access to the lower and upper levels of the building, and incorporation of additional landscape and stormwater quality areas. Existing Drainage Patterns The proposed drainage patterns are to remain similar to current patterns. Currently, all of the western property drains to three inlets within the parking and service/loading area. See Figure 1 attached. The existing storm drain piping and inlets draining this site were recently improved with the Choice Center project and are proposed to be utilized with these improvements. An existing 42" reinforced concrete pipe (RCP) storm drain crosses the site, draining north to south. An existing 48" RCP storm drain exits the site from the existing southern manhole and ultimately daylights into Spring Creek. Two existing 18" RCP pipes connect to the 42" storm drain line, draining the two area inlets adjacent to the west side of the building. The amount of runoff going to the two inlets will be reduced with the modifications for the recessed plaza area. Due to the close proximity of these inlets to the lower level of the building, Tideflex Checkmate check valves are being proposed to be installed in these two inlets to reduce the chance of a storm event surcharging these inlets. An existing inlet and a 14"x23" HERCP (horizontal elliptical) storm drain connects to the 42"storm drain line, currently draining the remaining western parking lot. This inlet will remain and will be utilized for the storm drain connection for the porous landscape detention area along the western BOULDER I FORT COLLINS I WINTER PARK 1801 S. College Ave. Renovation 7/24/2012 2 of 3 property line. See Figure 2 attached. The existing manhole rims and inlet grates will need to be adjusted to the proposed final grades. The east parking area currently drains north to Stuart Street and south to College Avenue. Some grading modifications are needed to improve accessibility from Stuart Street to the front of the building. This slightly increases the area draining to Stuart Street, while reducing the area draining to College Ave. The drainage is currently, and is proposed to be conveyed offsite via surface flows and ultimately to Spring Creek. Impervious Areas The weighted historic and developed percent impervious was calculated based on the current City of Fort Collins Stormwater Criteria Manual and the Urban Storm Drainage Criteria Manual. The weighted percent impervious and composite runoff coefficient calculations, along with the rational calculations are attached for reference. The existing site has an overall percent impervious of 90.6%, and the proposed improvements will slightly decrease the percent impervious to 86.3%. The decrease in impervious area is due to the increase in proposed landscape and the incorporation of water quality areas. Water Ouality Improvements The water quality improvements will be achieved within the proposed landscape areas. Due to the limited area within the east parking lot and the existing drainage patterns, site runoff is not able to be directed to landscape areas. It should be noted that the amount of overall impervious area has decreased by approximately 10% with an increased landscape area along the east side of the property. The west parking area will utilize a porous landscape detention (PLD) area, located along the west property edge, for water quality improvements. The curb and gutter along the west edge of the park area will have l' curb cuts at every parking stripe (every 8.5' to 9') and will drain into the PLD. The PLD will have 18" of growing media to promote and maintain plantings. Below the growing media, a perforated pipe, with a minimum of 6" of drainage filter gravel over the pipe, will convey infiltrated runoff from drainage basin Al to the area drain located within the PLD area. The area drain then conveys runoff to the existing inlet within the parking lot. To improve the effectiveness of the PLD, the existing inlet and surrounding grades within the parking lot have been slightly raised to direct flows around the inlet to the PLD. In the event that the area drain within the PLD becomes clogged, the inlet in the parking lot would act as a secondary outlet. The outlet pipe from the PLD area drain is sized at 12" with a full flow capacity of 3.27 cfs which is greater than the 100 year flow rate from drainage basin Al of 1.68 cfs. See calculations attached. Due to the proximity of the PLD to the retaining wall on the Choice Center site, it is proposed that an impervious membrane be installed to limit water infiltrating against the foundation of the wall. The roof drainage will be conveyed to landscape areas prior to entering the existing storm drain. There are two roof drain locations, one along the north side of the existing building, and one in the southwest corner of the building. The north roof drain will daylight to the landscape area along the BOULDER I FORT COLLINS I WINTER PARK 1801 S. College Ave. Renovation 7/24/2012 3 of 3 north side of the building. The runoff will be conveyed across the landscape area to a sidewalk chase that drains to Stuart Street. The runoff will continue south to the existing inlet on the south side of Stuart and ultimately to Spring Creek. The southwest roof drain will daylight into a landscape area surrounding the site's southernmost existing storm manhole. The runoff will be conveyed across the landscape area and is proposed to drain into this existing manhole. The manhole cover is proposed to be replaced with beehive grate. All roof drains that are conveyed to the landscape areas will have a 5' long splash block directing stormwater away from the building foundation. Erosion and Sediment Control During construction there will be temporary erosion and sediment control practices used to limit soil erosion. These temporary erosion control devices include a vehicle tracking control/construction entrance, a concrete washout area, inlet protection around all storm sewer inlets, curb rock socks along Stuart Street, and sediment control logs along the boundary of the site. Additional details have been provided on the plans including the Stormwater Management Plan (SWMP). Based on the included information, the proposed improvements and adjusted impervious areas, the overall imperviousness of the site has decreased by approximately 4.3% compared to existing conditions. Minor topographic changes are proposed within the floodplain, but are considered to have no adverse impacts due to minor allowed disturbance within the assumed ineffective flow area. Please feel free to contact JVA to discuss any questions you may have. Sincerely, JVA, INCORPORATED Charles R. Hager, IV, P.E. Vice President Enclosure: Figure 1 - Historic Drainage Map Figure 2 - Developed Drainage Map Composite Runoff Coefficient Calculations Drainage Basin Summary Table PLD Sizing Calculations CC: Vaught Frye Larson architects Ripley Design, Inc. Imago Enterprises Lester Kaplan DO REgi;>"/ ••....•# � R HgC`9�0 37146 'J3 e 7/24/12 r BOULDER I FORT COLLINS I WINTER PARK I 1 ` — � T o0 E)(IST 42m RCP SD I � EXIST 14"x 23" EXIST SD MH 'I HERCP SD EXIST SD 1 AREA INLET EXIST 42" RCP SD � 09 0.17 1 1 � � I I EXIST SD MH i 1 � IEXIST 48" RCP SD Liu I I I �TUAR� TREET :<' �..� 01 0.07 EXIST 18" RCP SID o.7 02 O i � o 2 EXIST SID AREA INLET I z � Z m 0 1801 0 "� � o S. COLLEGE AVE. o� all o 1 (EXISTING BUILDING) G C5 EXIST 18" RCP SD 100-YR FLOODPLAIN G , EXIST SD AREA INLET " ml / - HIKErpf ..y� �� 6 CIAYI n .. Wx..H i OOrwme J rsa}tlnn `I . J 11 ! E {I(1 ' 1' wCE Wf!'AiLL � 1?hI,IIC CAP J e_1^ri. GONCRCIE .y(mlmI cVMKING i53194i WIH,'oul f"cllV l LEGEND PROPOSED INDEX CONTOUR M PROPOSED DRAINAGE BASIN BOUNDARY (MAJOR BASIN) PROPOSED DRAINAGE BASIN BOUNDARY (SUB BASIN) PROPOSED INTERMEDIATE CONTOUR DIRECTION OF FLOW (HISTORIC) EXIST INDEX CONTOUR 1.0%i DIRECTION OF FLOW AND SLOPE (DEVELOPED) �1 EXIST INTERMEDIATE CONTOUR BASIN DESIGN POINT q A = DEVELOPED BASIN DESIGNATION 5 1.0 DRAINAGE BASIN IDENTIFICATION BUBBLE .5 = 100-YR RUNOFF COEFFICIENT 1.0 = AREA ACRES 20 0 20 40 SCALE IN FEET SUMMARY RUNOFF TABLE I BASIN DESIGN AREA 5 YR 100 YR POINT (ACRES) RUNOFF PEAK (CFS) (CFS) H1 1 0.17 0.55 1.49 H2 2 028 0.72 2.06 H3 3 0.07 0.18 0.50 H4 4 0.11 0.32 0.87 S-.rE ND FIG-1 a 0 Lm-m-mH•qm-Q�H•Ht �7Y� V Al Ob 0 1 18" SD INLET — EXIST 14"x 23" HERCP SD LROUS LANDSCAPE TENTION AREA GNG WALL �T1, r14 0STREET - \ 7 C4N- -�� -- —� R4 -- Z 1 X-�\tw EXIST 42' RCP SD \ -EXIST SD MH - V \ C EXIST SD \ AREA INLET EXIST 42" RCP SD oor EXIST SD MH REPLACE EXIST COVER WITH BEEHIVE GRATE IEXIST 48" RCP SD LEGEND PROPOSED INDEX CONTOUR PROPOSED INTERMEDIATE CONTOUR EXIST INDEX CONTOUR EXIST INTERMEDIATE CONTOUR PUST,C GP J LLt, R a F •I.tUiING 'M�N� IFlM t:Vl'l SIDEWALK CHASE ROOF DRAIN A2 EXIST 18" RCP SD I 09102D EXIST SD AREA INLET INSTALL TIDEFLEX CHECKMATE CHECK I VALVE IN INLET 12"x 12" AREA INLET I - PROPOSED RETAINING WALL 100-YR FLOODPLAIN EXIST 18" RCP SD EXIST SD AREA INLET INSTALL TIDEFLEX CHECKMATE CHECK VALVE IN INLET ROOF DRAIN / FOiI U.Vifl OIIFI.'.N (INIMV' J 00 11 A3 i 1 OB 0.11 1 1 \ 1cn 88 1 I I I 88 I I C6 I 11 A4 _ I 0.7 0.09 11 I II I I 4 11 11 . I I 0o SIDEWALK CHASE 11 1 `��1ygi 0 'NIUI J {{I11I ! "JIOE N^lflll p:l 1. �nCP2TC �� "INI(=PMIIIN(f A.",.. i:f IIIt YC LL 'CN !./. 4Y JI1lEN (INIV' PROPOSED DRAINAGE BASIN BOUNDARY (MAJOR BASIN) — PROPOSED DRAINAGE BASIN BOUNDARY (SUB BASIN) DIRECTION OF FLOW (HISTORIC) —� DIRECTION OF FLOW AND SLOPE (DEVELOPED) �1 BASIN DESIGN POINT A A = DEVELOPED BASIN DESIGNATION 5 1.0 DRAINAGE BASIN IDENTIFICATION BUBBLE .5 = 100-YR RUNOFF COEFFICIENT 1.0 = AREA ACRES �= Olklj INI SCALE IN FEET SUMMARY RUNOFF TABLE E BASIN DESIGN AREA 5 YR 100 YR POINT (ACRES) RUNOFF PEAK (CFS) (CFS) Al 1 022 0.60 1.68 A2 2 0.20 0.55 1.54 A3 1 3 1 0.11 023 0.70 A4 1 4 1 0.09 022 0.63 a w U) Q d d Q z 2 w z z w o or Cl w Lu CD o_ w p J J o "> U 0 Fwt-T NO FIG-2 1801 S. College Ave. PROPOSED COMPOSITE C AND IMPERVIOUS AREA CALCULATION Design Engineer. D.Douvas Design Finn: JVA, Inc. Project Number. 1952c Date: February 29, 2012 DESIGN CRITERIA: JVA, Incorporated 25 Old Town Sq, Suite 200 Fort Collins, CO 80524 Ph: 970.225.9099 Fax: 970.225.6923 Urban Storm Drainage Criteria Manual by Urban Drainage and Flood Control District, June 2001 (Revised April 2008) City of Fort Collins Stormwater Criteria Manual (Ordinance No. 174, 2011) BASINS: % Impervious values from Table RO-3 and C Values obtained from Table RO-5 in the Urban Storm Drainage Criteria Manual for Hydrologic Soil Classification B Land Use % Impervious C VALUE C2 Cs C1w Roofs 90.0% 0.71 0.73 0.81 Parks 5.0% 0." 0.10 0.38 Streets 100.0% 0.89 0.90 0.96 Drives & Walks 90.0% 0.71 0.73 0.81 Lawns 0.0% 0.02 0.08 0.35 Sub -basin Designation At�w (acres) Air (acres) Aqft (acres) APe ed (acres) A,.aa (acres) Aa. (acres) Weighted % Impervious COMPOSITE , C2 Cs C7oo H1 0.17 0.00 0.01 0.16 0.00 0.00 96.8% 0.82 0.84 0.90 H2 O.28 0.14 0.02 0.10 0.01 0.00 96.3% 0.65 0.67 0.76 H3 0.07 0.00 0.01 0.04 0.02 0.00 98.4% 0.68 0.70 0.79 H4 0.11 0.00 0.01 0.08 0.02 0.00 93.4% 0.76 0.78 0.85 Historic overall 0.62 0.14 0.04 0.39 0.04 0.00 90.6% 0.72 0.74 0.82 Al 0.22 0.00 1 0.02 1 0.18 1 0.01 1 0.00 1 89.6% 1 0.70 1 0.72 1 0.80 A2 0.20 0.14 10.00 0.00 0.05 0.00 90.3% 0.71 0.73 0.81 A3 0.11 0.00 0.02 0.05 0.04 0.00 75.3X 0.51 0.54 0.68 A4 0.09 0.00 1 0.01 1 0.06 0.02 1 0.00 1 93.3% 1 0.61 0.63 0.73 1 Proposed Overdl 0.61 0.14 0.06 1 0.29 0.12 1 0.00 86.3% 1 0.65 0.67 0.77 c Proposed Rabonal.)dsx - COMPOSITE C Page 1 of 1 JVA, Inc. 1801 S. College Ave. PROPOSED DRAINAGE SUMMARY Design Engineer. D.Douvas Design Finn: JVA, Inc. Project Number. 1952c Date: February 29, 2012 DRAINAGE BASIN SUMMARY TABLE JVA, Incorporated 25 Old Town Sq, Suite 200 Fort Collins, CO 80524 Ph: 970.225.9099 Fax: 970.225.6923 DESIGN POINT TRIBUTARY SUB -BASIN AREA (acres) Cx CS C1os tx (min) 02 (cfs) 45 (cfs) 4100 (cfs) DRAINAGE REMARKS 1 H1 0.17 0.82 0.84 0.90 5.00 0.39 0.55 1.49 2 H2 O.28 0.65 0.67 0.76 5.00 0.50 0.72 2.06 3 H3 0.07 0.68 0.70 0.79 5.00 0.12 0.18 0.50 4 H4 0.11 0.76 0.78 0.85 5.00 0.22 0.32 0.87 Historic Overall 0.62 0.72 0.74 0.82 1.24 1.77 4.92 1 At 0.22 0.70 0.72 0.80 5.20 0.42 0.60 1.68 2 A2 0.20 0.71 0.73 0.81 5.00 0.39 0.55 1.54 3 A3 0.11 0.51 0.54 0.66 5.00 0.15 0.23 1 0.70 4 A4 0.09 0.61 0.63 0.73 5.65 0.15 0.22 1 0.63 Proposed Overall 0.61 0.65 0.67 0.77 1.11 1.59 1 4.54 c Proposed Rational.xisx - Summary Page 1 of 1 JVA, Inc. Worksheet Worksheet for Circular Channel Project Description Worksheet SD sizing for west porus landscape detention Flow Element Circular Channel . Method Manning's Formula Solve For Full Flow Capacity Input Data Mannings Coefficient 0.010 Channel Slope 0.005000 ft/ft Diameter 12.0 in Results Depth 12.0 in Discharge 3.27 cfs .4 Flow Area 0.8 ft' Wetted Perimeter 3.14 ft Top Width 0.00 ft Critical Depth 0.77 ft Percent Full 100.0 % Critical Slope 0.005589 ft/ft Velocity 4.17 We Velocity Head 0.27 ft Specific Energy 15.2 in Froude Number 0.00 Maximum Discharge 3.52 cfs Discharge Full 3.27 cfs Slope Full 0.005000 ft/ft Flow Type N/A Drainage Basin Al has a 100-year flow rate of 1.68 cfs 3.27 cfs > 1.68 cfs O.K. Project Engineer: Kevin Tone untitled.fm2 JVA, Inc FlowMaster v7.0 [7.00051 03/01/12 04:13:41 PM m Haestad Methods, Inc. 37 Brookside Road Waterbury, CT 06708 USA +1-203-755-1666 Page 1 of 1 Design Procedure Form: Rain Garden (RG) Sheet 1 of 2 Designer: D. Hamer Company: JVA Consulting Engineers Date: March 28, 2012 Project: 1952c 1801 S. Colleg Ave. Location: 1801 S. Colleg Ave., Fort Collins, CO 1 Basin Storage Volume A) Effective Imperviousness of Tributary Area, I, I, = 89.6 % (100% if all paved and roofed areas upstream of rain garden) B) Tributary Area's Imperviousness Ratio (i = I.M 00) 1 = 0.896 C) Water Quality Capture Volume (WQCV) for a 12-hour Drain Time WQCV = 0.32 watershed inches (WQCV= 0.8' (0.91• i3- 1.19' i'+ 0.78' 1) D) Contributing Watershed Area (including rain garden area) Area = 9.583 sq ft E) Water Quality Capture Volume (WQCV) Design Volume Vwocv = cu ft Vol = (WQCV / 12)' Area F) For Watersheds Outside of the Denver Region, Depth of da = 0.82 in Average Runoff Producing Storm G) For Watersheds Outside of the Denver Region, Vwocv OTHER = 485.0 cu ft Water Quality Capture Volume (WQCV) Design Volume H) User Input of Water Quality Capture Volume (WQCV) Design Volume VWOCV USER = OU It (Only if a different WQCV Design Volume is desired) 2. Basin Geometry Total surface area A)WQCV Depth (12-inch maximum) Owocv= 0 in provided is greater than B) Rain Garden Side Slopes (Z = 4 min., hor¢. dirt per unit vertical) Z = 0.00 ft/ ft required (Use "0" if rain garden has vertical walls) C) Mimimum Flat Surface Area A,,= 323 sq ft Due to limited grade, no additional storage Volume D) Actual Flat Surface Area Aa= 424 sq It has been achieved above E) Area at Design Depth (Top Surface Area) AT. = 424 sq ft the growing media F) Rain Garden Total Volume VT= 0 cu ft (VT=((Arm+Aa )/2)'Depth) 3. Growing Media Choose One Q 18" Rain Garden Growing Media O Other (Explain): 4. Underdrain System A) Are underdrains provided? Choose One _7 (9) YES O NO B) Underdrain system orifice diameter for 12 hour drain time i) Distance From Lowest Elevation of the Storage y= 0.0 ft Volume to the Center of the Orifice ii) Volume to Drain in 12 Hours V0112 = N/A cu ft III) Orifice Diameter, 3/8" Minimum Do = N/A in 1952c PLD System - UD-BMP_v3_Ot.xisx, RG 3/2812012, 11:51 AM Design Procedure Form: Rain Garden (RG) Sheet 2 of 2 Designer: D. Hamer Company: JVA Consulting Engineers Date: March 28, 2012 Project: 1952c 1801 S. Colleg Ave. Location: 1901 S. Colleg Ave., Fort Collins, CO 5. Impermeable Geomembrane Liner and Geotextile Separator Fabric Choose One * YES A) Is an impermeable liner provided due to proximity ONO of structures or groundwater contamination? PROVIDE A 30 MIL (MIN) PVC LINER WITH COOT CLASS B GEOTEXTILE ABOVE IT. USE THE SAME GEOTE7(TILE BELOW THE LINER IF THE SUBGRADE IS ANGULAR 6. Inlet / Outlet Control Choose One * Sheet Flow- No Energy Dissipation Required A) Inlet Control 0 Concentrated Flow- Energy Olssipabon Provided Choose One 7. Vegetation O Seed (Plan for frequent weed control) * PlantIngs 10 Sand Grown or Other High Infiltration Sod S. Irrigation Choose One O YES A) Will the rain garden be irigated? O NO Notes: 1952c PLD System - UD-BMP_v3_Ot.xisx, RG 3128/2012, 11,51 AM