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Home My WebLink About301 PARKER STREET - TWO FAMILY - FDP210026 - SUBMITTAL DOCUMENTS - ROUND 2 - DRAINAGE REPORT NORTHERNENGINEERING.COM | 970.221.4158 FORT COLLINS | GREELEY 1 | 2 DATE: December 22, 2021 PROJECT: 301 Parker Street Fort Collins, Colorado PROJECT NO. 1892-001 ATTENTION: Stormwater Staff City of Fort Collins Stormwater 700 Wood Street Fort Collins, CO 80521 Stormwater Staff This letter serves to document the proposed drainage impacts for improvements at 301 Parker Street in Fort Collins, Colorado. The site is in the Old Prospect Neighborhood, and it is bounded by Parker Street to the north, an unpaved alley to the south, and single-family homes to the east and west. The project site is Lot 8 and a portion of Lot 9, Block 1, Alpert Subdivision. Project Overview The proposed project is to replace a single-family home with a duplex with walkways and a gravel parking lot in the back. Walkways towards the front of the lot will be concrete. Walkways towards the rear of the lot will be crusher fines. The developer proposed to keep an existing honey locus tree on the property. Existing Site/Drainage The existing site functions as a “B” lot, with runoff first sheet flowing out from the home to the side lot lines, which then convey the drainage to both the front and back of the lot. Existing grades in the front yard range between 4% to 15%, and the grades in the back of the rear yard vary between 0.5% to 3.0%. There are some small steep areas of 5:1 to 4:1 slope in the southwest corner of the lot, along the alley. In addition to the existing home, the existing lot consists of a gravel driveway in the front and a detached shed in the rear. There is a 2.5’ wide concrete path from the gravel driveway to the existing home, and some bare spots around the detached shed. The remainder of the site is Kentucky Bluegrass lawn with several mature trees. The alley is bare dirt with the flowline in the center conveying runoff west towards the Mathews Street curb and gutter. The total existing impervious area for the lot is 1,319 square feet. Proposed Site/Drainage The proposed site will continue to function as a “B” lot, with drainage from the new duplex being directed to the side lot lines, then to both the front and back of the via swales. A swale along the west lot line is proposed to collect and convey drainage to the front and rear without impacting the neighboring properties. Because of the flat grades, a valley pan and curb along the southeast quarter of the lot is provided along the east lot line to convey stormwater to the alley. The curb is required to protect the neighbor’s garage along the east property line. The total proposed impervious area for the lot is 2,205 square feet. This is a net increase of 887 square feet. There will be an increase of 0.04 cfs and 0.16 cfs during the 2-Year and 100-Year storm events respectively within the Parker Street curb and gutter from the increased impervious area. There will be an increase of 0.02 cfs and 0.06 cfs during the 2-Year and 100-Year storm events respectively within the alley from the increased impervious area. The additional 0.06 cfs results in a negligible increase of the flowrate and flow depth within the alley. NORTHERNENGINEERING.COM | 970.221.4158 FORT COLLINS | GREELEY 2 | 2 Basin Existing Flowrate (cfs) Proposed Flowrate (cfs) Net Increase (cfs) 2-Year 100-Year 2-Year 100-Year 2-Year 100-Year Front 0.05 0.21 0.09 0.37 0.04 0.16 Rear 0.11 0.52 0.13 0.58 0.02 0.06 Detention According to Fort Collins Stormwater requirements, an increase of less than 1,000 square feet are not required to provide detention, water quality, and LID improvements. The attached exhibit documents the existing vs. proposed impervious areas for the site. Water Quality Water quality for the site is being provided by releasing concentrated flows from the roof into landscaped areas allowing stormwater to infiltrate into the surrounding soils. Stormwater unable to infiltrate is slowly passed through vegetated areas, further removing stormwater contaminates before leaving the property. Erosion and Sediment Control During construction, the contractor will follow the appropriate and applicable Fort Collins standards for erosion and sediment control. Even though the project will disturb less than 10,000 square feet, the contractor will be required to sweep and maintain the site to prevent dirt, saw cuttings, concrete wash, trash and debris, landscape materials and other pollutants from leaving the site. City inspectors may require the installation of erosion and sediment control measures dependent on site inspections or neighbor complaints. Floodplains There are no regulatory floodplains associated with the project. Conclusions The proposed grading concept closely matches the original drainage patterns and comply with the City of Fort Collins Stormwater Manual. There will be no adverse impacts to downstream properties and City of Fort Collins infrastructure from the proposed improvements for 301 Parker Street. Please feel free to contact me if you have any questions. Sincerely, NORTHERN ENGINEERING SERVICE, INC. Frederick S. Wegert, PE Project Engineer Project Number:1892-001 Calc. By:F. Wegert Project Name:301 Parker St Date:December 22, 2021 Project Location:Fort Collins, Colorado Description Surface Area (ft2)Percent Impervious Impervious Area (ft2) Rooftop 896 100%896 Concrete 109 100%109 Asphalt 0 100%0 Pavers 0 40%0 Gravel 784 40%314 Landscaping 5,072 0%0 Total 6,861 19%1,319 Description Surface Area (ft2)Percent Impervious Impervious Area (ft2) Rooftop 1,472 100%1,472 Concrete 437 100%437 Asphalt 0 100%0 Pavers 0 40%0 Gravel 741 40%296 Landscaping 4,211 0%0 Total 6,861 32%2,205 887 IMPERVIOUS AREA CALCULATIONS Historic Impervious Areas Developed Impervious Areas Net Increase in Impervious Area NORTHERNENGINEERING.COM | 970.221.4158 FORT COLLINS | GREELEY XW T X X XX XXXXXXXXXVAULT ELEC X X XW T XXXXXXXXVAULT ELEC X X ROOFTOP CONCRETE ASPHALT PAVERS SURFACE AREA (SF)% IMPERV.IMPERV. AREA (SF) 896 109 0 0 100% 100% 100% 40% TOTALS 6,861 1,319TOTAL= ROOFTOP CONCRETE PAVERS GRAVEL SURFACE AREA (SF)% IMPERV.IMPERV. AREA (SF) TOTALS 6,861 2,205TOTAL= EXISTING PROPOSED P:\1892-001\DWG\DRNG\1892-001_IMPV.DWG301 PARKER STREET FORT COLLINS COLORADO Fort Collins: 301 N. Howes St., Ste. 100, 80521 Greeley: 820 8th Street, 80631 E N G I N E E R N GI EHTRON R N PHONE: 970.221.4158 www.northernengineering.com DESCRIPTION EXISTING VS. PROPOSED IMPERVIOUS AREA - BASIN B1 DRAWN BY F. WEGERT DATE DEC 22, 2021 PROJECT 1892-001 DR-A1 DRAWINGSCALE 1"=20' LANDSCAPE GRAVEL 784 40%314 LANDSCAPE 5,072 0%0 ASPHALT 896 109 0 0 1,472 437 0 0 100% 100% 100% 40% 741 40%296 4,211 0%0 1,472 437 0 0 TOTAL PERCENT IMPERVIOUS = 19%TOTAL PERCENT IMPERVIOUS = 32% Runoff Coefficient1 Percent Impervious1 Project: Location: 0.95 100%Calc. By: 0.95 90%Date: 0.50 40% 0.50 40% 0.20 2% 0.20 2% Basin ID Basin Area (sq.ft.) Basin Area (acres) Asphalt, Concrete (sq.ft.)Rooftop (sq.ft.)Gravel (sq.ft.)Pavers (sq.ft.) Undeveloped: Greenbelts, Agriculture (sq.ft.) Lawns, Clayey Soil, Flat Slope < 2% (sq.ft.) Percent Impervious C2*Cf Cf = 1.00 C5*Cf Cf = 1.00 C10*Cf Cf = 1.00 C100*Cf Cf = 1.25 Front 2,773 0.06 1.43 0.00 691.53 0.00 0.00 2,080.33 12%0.28 0.28 0.28 0.34 Rear 4,088 0.09 108.07 896.17 91.99 0.00 0.00 2,991.49 40%0.50 0.50 0.50 0.63 Total 6,861 0.16 109.50 896.17 783.52 0.00 0.00 5,071.82 40%0.50 0.50 0.50 0.63 2) Composite Runoff Coefficient adjusted per Table 3.2-3 of the Fort Collins Stormwater Manual (FCSM). Lawns, Clayey Soil, Flat Slope < 2% USDA SOIL TYPE: C Undeveloped: Greenbelts, Agriculture Composite Runoff Coefficient2 1) Runoff coefficients per Tables 3.2-1 & 3.2 of the FCSM. Percent impervious per Tables 4.1-2 & 4.1-3 of the FCSM. Combined Basins EXISTING RUNOFF COEFFICIENT CALCULATIONS Asphalt, Concrete Rooftop Gravel Pavers Streets, Parking Lots, Roofs, Alleys, and Drives: Character of Surface:301 Parker Street Fort Collins F. Wegert December 22, 2021 Lawns and Landscaping: Page 1 of 3 Where: Length (ft) Elev Up Elev Down Slope (%) Ti 2-Yr (min) Ti 10-Yr (min) Ti 100-Yr (min) Length (ft) Elev Up Elev Down Slope (%)Surface n Flow Area3 (sq.ft.) WP3 (ft)R (ft)V (ft/s) Tt (min) Max. Tc (min) Comp. Tc 2-Yr (min) Tc 2-Yr (min) Comp. Tc 10-Yr (min) Tc 10-Yr (min) Comp. Tc 100- Yr (min) Tc 100-Yr (min) front Front 57 90.80 87.00 6.67%6.19 6.19 5.67 N/A Swale (8:1)0.04 8.00 16.12 N/A N/A 0.00 10.32 6.19 6.19 6.19 6.19 5.67 5.67 rear Rear 50 90.80 90.40 0.80%8.55 8.55 6.77 61 90.40 89.40 1.64%Swale (8:1)0.04 8.00 16.12 0.50 3.42 0.30 10.62 8.84 8.84 8.84 8.84 7.06 7.06 Notes S = Longitudinal Slope, feet/feet R = Hydraulic Radius (feet) n = Roughness Coefficient V = Velocity (ft/sec)WP = Wetted Perimeter (ft) EXISTING TIME OF CONCENTRATION COMPUTATIONS Location: Maximum Tc:Overland Flow, Time of Concentration: Channelized Flow, Velocity:Channelized Flow, Time of Concentration: 301 Parker Street Fort Collins F. Wegert December 22, 2021 Project: Calculations By: Date: Design Point Basin ID Overland Flow Channelized Flow Time of Concentration (Equation 3.3-2 per Fort Collins Stormwater Manual)𝑅𝑖=1.87 1.1 −𝐶∗𝐶𝑓𝐿 𝑅ൗ13 𝑉=1.49 𝑛∗𝑅2/3 ∗𝑅(Equation 5-4 per Fort Collins Stormwater Manual) 𝑅𝑐=𝐿 180 +10 (Equation 3.3-5 per Fort Collins Stormwater Manual) 𝑅𝑡=𝐿 𝑉∗60 (Equation 5-5 per Fort Collins 1)Add 4900 to all elevations. 2) Per Fort Collins Stormwater Manual, minimum Tc = 5 min. 3) Assume a water depth of 6" and a typical curb and gutter per Larimer County Urban Street Standard Detail 701 for curb and gutter channelized flow. Assume a water depth of 1', fixed side slopes, and a triangular swale section for grass channelized flow. Assume a water depth of 1', 4:1 side slopes, and a 2' wide valley pan for channelized flow in a valley pan. Page 2 of 3 Tc2 Tc10 Tc100 C2 C10 C100 I2 I10 I100 Q2 Q10 Q100 front Front 0.06 6.2 6.2 5.7 0.3 0.3 0.3 2.7 4.6 9.6 0.05 0.08 0.21 rear Rear 0.09 8.8 8.8 7.1 0.5 0.5 0.6 2.4 4.0 8.8 0.11 0.19 0.52 Design Point Basin Intensity, I, from Fig. 3.4.1 Fort Collins Stormwater Manual. Rational Equation: Q = CiA (Equation 6-1 per MHFD) Area (acres) Runoff CTc (Min)Intensity (in/hr)Flow (cfs) 301 Parker Street F. Wegert December 22, 2021Date: Fort Collins Project: Location: Calc. By: EXISTING DIRECT RUNOFF COMPUTATIONS Page 3 of 3 Runoff Coefficient1 Percent Impervious1 Project: Location: 0.95 100%Calc. By: 0.95 90%Date: 0.50 40% 0.50 40% 0.20 2% 0.20 2% Basin ID Basin Area (sq.ft.) Basin Area (acres) Asphalt, Concrete (sq.ft.)Rooftop (sq.ft.)Gravel (sq.ft.)Pavers (sq.ft.) Undeveloped: Greenbelts, Agriculture (sq.ft.) Lawns, Clayey Soil, Flat Slope < 2% (sq.ft.) Percent Impervious C2*Cf Cf = 1.00 C5*Cf Cf = 1.00 C10*Cf Cf = 1.00 C100*Cf Cf = 1.25 Front 2,805 0.06 252.12 736.00 0.00 0.00 0.00 1,817.24 34%0.46 0.46 0.46 0.58 Rear 4,056 0.09 185.19 736.00 741.19 0.00 0.00 2,393.72 40%0.50 0.50 0.50 0.63 Total 6,861 0.16 437.31 1,472.00 741.19 0.00 0.00 4,210.97 40%0.50 0.50 0.50 0.63 2) Composite Runoff Coefficient adjusted per Table 3.2-3 of the Fort Collins Stormwater Manual (FCSM). Lawns, Clayey Soil, Flat Slope < 2% USDA SOIL TYPE: C Undeveloped: Greenbelts, Agriculture Composite Runoff Coefficient2 1) Runoff coefficients per Tables 3.2-1 & 3.2 of the FCSM. Percent impervious per Tables 4.1-2 & 4.1-3 of the FCSM. Combined Basins DEVELOPED RUNOFF COEFFICIENT CALCULATIONS Asphalt, Concrete Rooftop Gravel Pavers Streets, Parking Lots, Roofs, Alleys, and Drives: Character of Surface:301 Parker Street Fort Collins F. Wegert December 22, 2021 Lawns and Landscaping: Page 1 of 3 Where: Length (ft) Elev Up Elev Down Slope (%) Ti 2-Yr (min) Ti 10-Yr (min) Ti 100-Yr (min) Length (ft) Elev Up Elev Down Slope (%)Surface n Flow Area3 (sq.ft.) WP3 (ft)R (ft)V (ft/s) Tt (min) Max. Tc (min) Comp. Tc 2-Yr (min) Tc 2-Yr (min) Comp. Tc 10-Yr (min) Tc 10-Yr (min) Comp. Tc 100- Yr (min) Tc 100-Yr (min) front Front 25 91.30 90.48 3.28%4.00 4.00 3.27 67 90.48 87.60 4.30%Swale (4:1)0.04 4.00 8.25 0.48 5.45 0.20 10.51 4.21 5.00 4.21 5.00 3.48 5.00 rear Rear 25 91.30 90.79 2.04%4.42 4.42 3.50 117 90.79 89.40 1.19%Valley Pan 0.04 6.00 10.25 0.59 3.25 0.60 10.79 5.02 5.02 5.02 5.02 4.10 5.00 Notes S = Longitudinal Slope, feet/feet R = Hydraulic Radius (feet) n = Roughness Coefficient V = Velocity (ft/sec)WP = Wetted Perimeter (ft) DEVELOPED TIME OF CONCENTRATION COMPUTATIONS Location: Maximum Tc:Overland Flow, Time of Concentration: Channelized Flow, Velocity:Channelized Flow, Time of Concentration: 301 Parker Street Fort Collins F. Wegert December 22, 2021 Project: Calculations By: Date: Design Point Basin ID Overland Flow Channelized Flow Time of Concentration (Equation 3.3-2 per Fort Collins Stormwater Manual)𝑅𝑖=1.87 1.1 −𝐶∗𝐶𝑓𝐿 𝑅ൗ13 𝑉=1.49 𝑛∗𝑅2/3 ∗𝑅(Equation 5-4 per Fort Collins Stormwater Manual) 𝑅𝑐=𝐿 180 +10 (Equation 3.3-5 per Fort Collins Stormwater Manual) 𝑅𝑡=𝐿 𝑉∗60 (Equation 5-5 per Fort Collins 1)Add 4900 to all elevations. 2) Per Fort Collins Stormwater Manual, minimum Tc = 5 min. 3) Assume a water depth of 6" and a typical curb and gutter per Larimer County Urban Street Standard Detail 701 for curb and gutter channelized flow. Assume a water depth of 1', fixed side slopes, and a triangular swale section for grass channelized flow. Assume a water depth of 1', 4:1 side slopes, and a 2' wide valley pan for channelized flow in a valley pan. Page 2 of 3 Tc2 Tc10 Tc100 C2 C10 C100 I2 I10 I100 Q2 Q10 Q100 front Front 0.06 5.0 5.0 5.0 0.5 0.5 0.6 2.9 4.9 10.0 0.09 0.15 0.37 rear Rear 0.09 5.0 5.0 5.0 0.5 0.5 0.6 2.9 4.9 10.0 0.13 0.23 0.58 Design Point Basin Intensity, I, from Fig. 3.4.1 Fort Collins Stormwater Manual. Rational Equation: Q = CiA (Equation 6-1 per MHFD) Area (acres) Runoff CTc (Min)Intensity (in/hr)Flow (cfs) 301 Parker Street F. Wegert December 22, 2021Date: Fort Collins Project: Location: Calc. By: DEVELOPED DIRECT RUNOFF COMPUTATIONS Page 3 of 3 Channel Report Hydraflow Express Extension for Autodesk® Civil 3D® by Autodesk, Inc.Tuesday, Dec 21 2021 Existing 100-Year Flowrate in Alley from 301 Parker Street Trapezoidal Bottom Width (ft) = 12.00 Side Slopes (z:1) = 5.00, 3.00 Total Depth (ft) = 0.25 Invert Elev (ft) = 100.00 Slope (%) = 7.60 N-Value = 0.022 Calculations Compute by: Known Q Known Q (cfs) = 0.52 Highlighted Depth (ft) = 0.03 Q (cfs) = 0.520 Area (sqft) = 0.36 Velocity (ft/s) = 1.43 Wetted Perim (ft) = 12.25 Crit Depth, Yc (ft) = 0.04 Top Width (ft) = 12.24 EGL (ft) = 0.06 0 2 4 6 8 10 12 14 16 18 Elev (ft)Depth (ft)Section 99.75 -0.25 100.00 0.00 100.25 0.25 100.50 0.50 100.75 0.75 101.00 1.00 Reach (ft) Channel Report Hydraflow Express Extension for Autodesk® Civil 3D® by Autodesk, Inc.Tuesday, Dec 21 2021 Developed 100-Year Flowrate in Alley from 301 Parker Street Trapezoidal Bottom Width (ft) = 12.00 Side Slopes (z:1) = 5.00, 3.00 Total Depth (ft) = 0.25 Invert Elev (ft) = 100.00 Slope (%) = 7.60 N-Value = 0.022 Calculations Compute by: Known Q Known Q (cfs) = 0.58 Highlighted Depth (ft) = 0.03 Q (cfs) = 0.580 Area (sqft) = 0.36 Velocity (ft/s) = 1.60 Wetted Perim (ft) = 12.25 Crit Depth, Yc (ft) = 0.05 Top Width (ft) = 12.24 EGL (ft) = 0.07 0 2 4 6 8 10 12 14 16 18 Elev (ft)Depth (ft)Section 99.75 -0.25 100.00 0.00 100.25 0.25 100.50 0.50 100.75 0.75 101.00 1.00 Reach (ft)