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Home My WebLink About301 PARKER STREET - TWO FAMILY - FDP210026 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORT NORTHERNENGINEERING.COM | 970.221.4158 FORT COLLINS | GREELEY 1 | 2 DATE: November 9, 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 along the southeast quarter of the lot is provided along the east lot line to convey stormwater to the alley. The alley will be regraded along the rear frontage to better collect and convey stormwater to Mathews Street curb and gutter. The total proposed impervious area for the lot is 2,315 square feet. This is a net increase of 996 square feet. 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. NORTHERNENGINEERING.COM | 970.221.4158 FORT COLLINS | GREELEY 2 | 2 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. 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:November 9, 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 400 100%400 Asphalt 0 100%0 Pavers 0 40%0 Gravel 1,107 40%443 Landscaping 3,882 0%0 Total 6,861 34%2,315 996 IMPERVIOUS AREA CALCULATIONS Historic Impervious Areas Developed Impervious Areas Net Increase in Impervious Area NORTHERNENGINEERING.COM | 970.221.4158 FORT COLLINS | GREELEY XT X X XX XXXXXXXXXVAULT ELEC X X XT 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 2,315TOTAL= 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 NOV 9, 2021 PROJECT 1892-001 DR-A1 DRAWINGSCALE 1"=20' LANDSCAPE GRAVEL 784 40%314 LANDSCAPE 5,072 0%0 ASPHALT 896 109 0 0 1,472 400 0 0 100% 100% 100% 40% 1,107 40%443 3,882 0%0 1,472 400 0 0 TOTAL PERCENT IMPERVIOUS = 19%TOTAL PERCENT IMPERVIOUS = 34%