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HomeMy WebLinkAboutMASON PLACE - MAJOR AMENDMENT - MJA180003 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE RELATED DOCUMENTApril 26, 2018 Heather McDowell, P.E. City of Fort Collins Utilities – Stormwater Engineering 700 Wood Street Fort Collins, CO 80521 RE: Mason Place, 3750 South Mason Street - Drainage Letter JVA Job No. 2873c Dear Heather: This letter has been prepared to summarize the drainage concept, solutions and changes in impervious area associated with the site improvements for the Mason Place redevelopment project located at 3750 South Mason Street in the City of Fort Collins. Existing Drainage Patterns The existing site, platted as Lot 5A and adjoining Lot 6 (same owner), is predominantly paved asphalt and consists of the existing Midtown Arts Center building, drive aisles, and parking areas. The existing ground surface is relatively flat, generally sloping either northwest or southwest at grades ranging from 0.5% to 2.0%. The majority of stormwater runoff is conveyed via surface flow either to the northwest into an existing curb inlet in the north parking area (into a private storm system that serves the northern portion of the site and its eastern neighbors), or to the southwest across the Lot 6 parking lot, through a curb cut and over public sidewalk and into the public storm drainage system in South Mason Street via a curb inlet. See Figure 1: Historic Drainage Map. The site is located outside FEMA and City of Fort Collins mapped 100-year and 500-year floodplains, per FEMA Flood Risk Map Panel number 08069C0987G, effective date 05/02/2012. Proposed Drainage Patterns Proposed drainage patterns are to remain generally the same as the current, but will utilize landscaped areas, concrete pans, sidewalk chases, and inlets to capture and treat the majority of runoff before discharging into the public storm system without flowing over driveway approaches or sidewalks and into the street. In general, the proposed redevelopment of the site consists of reusing the existing building, reconfiguring the north parking area, relocating the access driveway on Mason Street further to the south, and constructing a courtyard and greenspaces on the west side of the existing building along within new storm infrastructure to improve the drainage characteristics of the site. The site has been divided into four hydrologic basins for analysis. Basins A and B represent the majority of roof drainage from the existing building and runoff from the north parking area and the west courtyard. These areas will be collected and treated via grassed swales and captured in area inlets before being discharged into the existing public storm system. Basin C represents the runoff from the remainder of the redeveloped site, draining to the south past the new Mason curb cut via a concrete pan and into a proposed curb inlet in the Lot 6 parking area. Basin OS1 represents a strip of sidewalk and landscaping along the east edge of the building that drains east into the neighboring curb & gutter, and is then captured into the same private storm system that Mason Place Drainage Letter April 26, 2018 2 of 2 runs through the north side of the Mason Place property and discharges into the Mason Street public storm system. All four basins eventually convey stormwater to Fossil Creek. It follows that the proposed improvements will substantially decrease the total impervious area on the site, from 84.2% to 67.9%. See Figure 2: Developed Drainage Map for the drainage basin boundaries, runoff calculations, and a summary of the existing and proposed impervious areas. Chapter 2 of the Urban Drainage and Flood Control District’s Urban Storm Drainage Criteria Manual Volume 3 (USDCM) provides guidelines for the selection of appropriate structural BMPs for a site that is to be developed or redeveloped. Mason Place is best characterized as a “conventional redevelopment” with just over 1 acre of impervious area on the project site. The BMP decision tree for such sites is provided in Figure 2-2 of the USDCM. The site and surrounding vicinity is comprised of hydrologic soil group Type C & D soils, per the NRCS soil survey. Permeable pavement (with partial or no infiltration) and/or the use of a “green roof” or grass swale/buffer are the recommended runoff reduction practices for this scenario. The proposed grass swales along the west side of the property will perform this function for the majority of the runoff generated on the site by capturing and treating runoff from Basins A & B. The impervious area for Basins A & B account for 76.6% of the total site impervious area, thus satisfying the City of Fort Collins Low Impact Development (LID) requirements. These landscaped features will facilitate sedimentation and filtration while limiting erosion, providing both treatment and slowed release of the water quality capture volume. The proposed redevelopment of this site will serve to reduce water quality and quantity impacts to natural drainageways by decreasing the frequency, rate, duration, and volume of runoff. Erosion and Sediment Control During construction, temporary erosion and sediment control practices will be used to limit soil erosion and sediment discharge off the site. Please feel free to contact me to discuss any questions you may have. Sincerely, JVA, INCORPORATED By: ________________________________ Karen Brigman, CFM . Senior Project Engineer Enclosures: Figure 1: Historic Drainage Map, Figure 2: Developed Drainage Map, Rational Calculations CC: Kristin Fritz, Housing Catalyst HISTORIC DRAINAGE MAP FIG 1 NO. DATE DES'D D'WN REVISION DESCRIPTION DESIGNED BY: DRAWN BY: CHECKED BY: JOB #: DATE: © JVA, INC. HOUSING CATALYST MASON PLACE FORT COLLINS, CO SHEET NO. 2873c APRIL 2018 CRH EJK EJK JVA, Inc. 213 Linden Street, Suite 200 www.jvajva.com Fort Collins, CO 80524 970.225.9099 Boulder ● Fort Collins ● Winter Park Glenwood Springs ● Denver PROPOSED DRAINAGE MAP FIG 2 NO. DATE DES'D D'WN REVISION DESCRIPTION DESIGNED BY: DRAWN BY: CHECKED BY: JOB #: DATE: © JVA, INC. HOUSING CATALYST MASON PLACE FORT COLLINS, CO SHEET NO. 2873c APRIL 2018 CRH EJK EJK JVA, Inc. 213 Linden Street, Suite 200 www.jvajva.com Fort Collins, CO 80524 970.225.9099 Boulder ● Fort Collins ● Winter Park Glenwood Springs ● Denver JVA Incorporated Job Name: Mason Place I% C2 C5 C10 C100 213 Linden St, Suite 200 Job Number: 2873c Streets Paved 100% 0.95 0.00 0.95 1.00 Fort Collins, CO 80524 Date: 4/24/18 Concrete Drives/Walks 90% 0.95 0.00 0.95 1.00 Ph: (970) 225 9099 By: KRB Roof 90% 0.95 0.00 0.95 1.00 Gravel 40% 0.50 0.00 0.50 0.63 Landscaping (B soil) 0% 0.15 0.00 0.15 0.19 Mason Place Landscaping (C/D soil) 0% 0.25 0.00 0.25 0.31 Historic Runoff Coefficient & Time of Concentration Calculations Playground 10% 0.11 0.00 0.11 0.14 Location: Fort_Collins Artificial Turf 25% 0.20 0.00 0.20 0.25 Minor Design Storm: 2 Major Design Storm: 100 Soil Type: C/D Basin Design Data I (%) = 100% 90% 90% 40% 10% 25% 0% 0% I (%) tc Comp tc Final Basin Name Design Point Apaved streets (sf) Adrives/co nc (sf) Aroof (sf) Agravel (sf) Aplygnd (sf) Aart. turf (sf) Alscape (B soil) (sf) Alscape (C/D soil) (sf) ATotal (sf) ATotal (ac) Imp (%) C2 C5 C10 C100 Upper most Length (ft) Slope (%) ti (min) Length (ft) Slope (%) Type of Land Surface K Velocity JVA Incorporated Job Name: Mason Place I% C2 C5 C10 C100 213 Linden St, Suite 200 Job Number: 2873c Streets Paved 100% 0.95 0.00 0.95 1.00 Fort Collins, CO 80524 Date: 4/24/18 Concrete Drives/Walks 90% 0.95 0.00 0.95 1.00 Ph: (970) 225 9099 By: KRB Roof 90% 0.95 0.00 0.95 1.00 Gravel 40% 0.50 0.00 0.50 0.63 Landscaping (B soil) 0% 0.15 0.00 0.15 0.19 Mason Place Landscaping (C/D soil) 0% 0.25 0.00 0.25 0.31 Composite Runoff Coefficient Calculations Playground 10% 0.11 0.00 0.11 0.14 Location: Fort_Collins Artificial Turf 25% 0.20 0.00 0.20 0.25 Minor Design Storm: 2 Major Design Storm: 100 Soil Type: C/D Basin Design Data I (%) = 100% 90% 90% 40% 10% 25% 0% 0% I (%) Basin Name Design Point Apaved streets (sf) Adrives/c onc (sf) Aroof (sf) Agravel (sf) Aplygnd (sf) Aart. turf (sf) Alscape (B soil) (sf) Alscape (C/D soil) (sf) ATotal (sf) ATotal (ac) Imp (%) C2 C5 C10 C100 A 1 8,620 3,537 8,810 6,993 27,960 0.64 70.6% 0.77 0.00 0.77 0.83 B 2 3,494 4,559 5,506 13,559 0.31 53.5% 0.58 0.00 0.58 0.62 C 3 2,954 5,354 1,005 9,313 0.21 80.3% 0.85 0.00 0.85 0.90 OS2 4 655 156 811 0.02 72.7% 0.77 0.00 0.77 0.81 Runoff Coeff's 2873c - Rational Calculations.xlsx Developed C Page 2 of 5 JVA Incorporated Job Name: Mason Place 213 Linden St, Suite 200 Job Number: 2873c Fort Collins, CO 80524 Date: 4/24/18 Ph: (970) 225 9099 By: KRB Mason Place Time of Concentration Calculations Location: Fort_Collins Minor Design Storm: 2 Major Design Storm: 100 Soil Type: C/D Sub-Basin Data tc Comp tc Final Basin Name Design Point ATotal (ac) C5 Upper most Length (ft) Slope (%) ti (min) Length (ft) Slope (%) Type of Land Surface Cv Velocity (fps) tt (min) Time of Conc ti + tt = tc Total Length (ft) tc =(L/180)+ 10 (min) Min tc A 1 0.64 0.00 105 2.0% 16.4 50 2.0% Grassed waterway 15 2.1 0.4 16.8 155 10.9 10.9 B 2 0.31 0.00 40 2.0% 10.1 80 2.0% Grassed waterway 15 2.1 0.6 10.8 120 10.7 10.7 C 3 0.21 0.00 5 2.0% 3.6 20 1.5% Paved areas & shallow paved swales 20 2.4 0.1 3.7 25 10.1 5.0 OS2 4 0.02 0.00 5 2.0% 3.6 5 1.5% Paved areas & shallow paved swales 20 2.4 0.0 3.6 10 10.1 5.0 Initial Overland Time (ti JVA Incorporated Job Name: Mason Place 213 Linden St, Suite 200 Job Number: 2873c Fort Collins, CO 80524 Date: 4/24/18 Ph: (970) 225 9099 By: KRB Mason Place Developed Storm Runoff Calculations Design Storm : 100 Year Point Hour Rainfall (P1) : 2.86 Basin Name Design Point Area (ac) Runoff Coeff tc (min) C*A (ac) I (in/hr) Q (cfs) Total tc (min) ΣC*A (ac) I (in/hr) Q (cfs) Inlet Type Q intercepted Q carryover Q bypass Pipe Size (in) or equivalent Pipe Material Slope (%) Pipe Flow (cfs) Max Pipe Capacity (cfs) Length (ft) Velocity (fps) tt (min) Total Time (min) Notes A 1 0.64 0.83 10.90 0.53 7.45 3.96 10.90 0.53 7.45 3.96 B 2 0.31 0.62 10.70 0.19 7.51 1.44 10.70 0.19 7.51 1.44 C 3 0.21 0.90 5.00 0.19 9.95 1.91 5.00 0.19 9.95 1.91 OS2 4 0.02 0.81 5.00 0.02 9.95 0.15 5.00 0.02 9.95 0.15 Direct Runoff Total Runoff Inlets Pipe Pipe/Swale Travel Time 2873c - Rational Calculations.xlsx Q100 Page 4 of 5 JVA Incorporated Job Name: Mason Place 213 Linden St, Suite 200 Job Number: 2873c Fort Collins, CO 80524 Date: 4/24/18 Ph: (970) 225 9099 By: KRB Mason Place Developed Storm Runoff Calculations Design Storm : 2 Year Point Hour Rainfall (P1) : 0.82 Basin Name Design Point Area (ac) Runoff Coeff tc (min) C*A (ac) I (in/hr) Q (cfs) Total tc (min) ΣC*A (ac) I (in/hr) Q (cfs) Inlet Type Q intercepted Q carryover Q bypass Pipe Size (in) or equivalent Pipe Material Slope (%) Pipe Flow (cfs) Max Pipe Capacity (cfs) Length (ft) Velocity (fps) tt (min) Total Time (min) Notes A 1 0.64 0.77 10.90 0.50 2.14 1.06 10.90 0.50 2.14 1.06 B 2 0.31 0.58 10.70 0.18 2.15 0.39 10.70 0.18 2.15 0.39 C 3 0.21 0.85 5.00 0.18 2.85 0.52 5.00 0.18 2.85 0.52 OS2 4 0.02 0.77 5.00 0.01 2.85 0.04 5.00 0.01 2.85 0.04 Direct Runoff Total Runoff Inlets Pipe Pipe/Swale Travel Time 2873c - Rational Calculations.xlsx Q Minor Page 5 of 5 ) Travel Time (tt ) tt =Length/(Velocity x 60) tc Urbanized Check ON 2873c - Rational Calculations.xlsx Developed Tc Page 3 of 5 (fps) tt (min) Time of Conc ti + tt = tc Total Length (ft) tc=(L/180)+ 10 (min.) Min tc A 1 13,497 2,299 8,810 2,832 27,438 0.63 85.6% 0.88 0.00 0.88 0.93 5 2.0% 3.6 150 1.3% Paved areas & shallow paved swales 20 2.3 1.1 4.7 155 10.9 5.0 B 2 7,580 3,207 9,911 2,696 23,394 0.54 82.9% 0.87 0.00 0.87 0.92 5 2.0% 3.6 190 1.8% Paved areas & shallow paved swales 20 2.7 1.2 4.8 195 11.1 5.0 OS1 3 655 156 811 0.02 72.7% 0.82 0.00 0.82 0.87 5 2.0% 3.6 5 1.5% Paved areas & shallow paved swales 20 2.4 0.0 3.6 10 10.1 5.0 0 0.00 Paved areas & shallow paved swales 20 0 10.0 0 0.00 Paved areas & shallow paved swales 20 0 10.0 TOTAL SITE 21,077 6,161 18,721 0 0 0 0 5,684 51,643 1.19 84.2% 0.87 0.00 0.87 0.92 Basin Name Design Point Time of Conc (tc) C2 C5 C10 C100 2 5 10 100 ATotal (sf) ATotal (ac) Q2 Q5 Q10 Q100 A 1 5.0 0.88 0.00 0.88 0.93 2.85 0.00 4.87 9.95 27,438 0.63 1.58 0.00 2.69 5.82 B 2 5.0 0.87 0.00 0.87 0.92 2.85 0.00 4.87 9.95 23,394 0.54 1.33 0.00 2.27 4.92 OS1 3 5.0 0.82 0.00 0.82 0.87 2.85 0.00 4.87 9.95 811 0.02 0.04 0.00 0.07 0.16 0 0 0 0.00 0 0 0 0.00 TOTAL SITE 51,643 1.19 2.95 0.00 5.04 10.90 Initial Overland Time (ti) Travel Time (tt) tt=Length/(Velocity x 60) tc Urbanized Check ON Runoff Coeff's Rainfall Intensities (in/hr) Area Flow Rates (cfs) Runoff Coeff's 2873c - Rational Calculations.xlsx Historic Page 1 of 5