HomeMy WebLinkAbout613 S MELDRUM ST CARRIAGE HOUSE - FDP200028 - DOCUMENT MARKUPS - ROUND 4 - DRAINAGE REPORT
KEEFE CIVIL, INC
3125 Crockett Street
Fort Collins, Colorado 80526
(970) 215-6808
meg@keefecivil.com
June 17, 2021 Keefe Civil Project Number: 2021-006
Matt Simpson
Development Review Engineer
Water Utilities Engineering
City of Fort Collins
700 Wood Street
Fort Collins, Colorado 80522
RE: 613 South Meldrum Street Drainage Memo
FDP200028
Dear Matt:
The purpose of this letter is to describe the proposed site improvements and potential drainage
impacts at 613 South Meldrum (Exhibit A). The 0.217-acre project site is a developed single-
family residential lot with established landscaping located on South Meldrum Street between
Myrtle Street and Laurel Street in Fort Collins, Colorado. The site is located within the Old Town
drainage basin. Current conditions at the site include a single-story house, a small garden shed,
flagstone pathways, concrete and wood patio areas, established trees, several garden areas, and a
brick driveway.
The lot is bound by existing single-family residential properties on the north and south lot lines,
South Meldrum Street right-of-way to the east, and a dirt alley way to the west. Per the NRCS Soil
Survey of Larimer County (Exhibit B), the site entirely consists of Fort Collins loam and is
classified as being within hydrologic soil group C. These soils are anticipated to have a slow
infiltration rate when thoroughly wet and a slow rate of water transmission.
Per the flood insurance rate map, the lot is located within Zone X. Zone X is defined as an area of
minimal flood hazard and does not have a base flood elevation associated with it. Also, the site is
outside of all City of Fort Collins mapped floodplains. (Exhibit C)
Historically, site stormwater has drained with gentle slopes from the west to east into South
Meldrum Street right-of-way, when not infiltrated into established landscaping (historic basin A).
Based on field survey and visual inspections, the alley drains north from a high point located
adjacent to the southwest corner of the site. Historic and developed drainage basins are shown in
Exhibit D.
The proposed site improvements include a two-story carriage house with a basement and an
attached garage with access off the alley. The proposed driveway shall be constructed with gravel
and the existing garden shed will be removed prior to construction. All carriage house roof drains,
aside from one, are proposed to drain towards South Meldrum Street right-of-way, minimizing
stormwater flows to the alley way. A small drainage basin (<350 sf adjusted impervious area) west
of the carriage house is proposed to drain into the existing alley.
Composite Runoff Coefficient Calculations639 Smith Street, Fort Collins, COArea (sf)Minor (2- and 10-yr) Composite C2Major (100-yr) Composite C3Area (sf)Minor (2- and 10-yr) Composite C2Major (100-yr) Composite C3Area (sf)Minor (2- and 10-yr) Composite C2Major (100-yr) Composite C3Area (sf)Minor (2- and 10-yr) Composite C2Major (100-yr) Composite C3Area (sf)Minor (2- and 10-yr) Composite C2Major (100-yr) Composite C3Area (sf)Minor (2- and 10-yr) Composite C2Major (100-yr) Composite C3Hardscape or Hard SurfaceConcrete0.955001000115160500Rooftop0.951,54080001,4651,540Gravel0.5004400000Patio and Pavers0.501,150020130565720Total Impervious Area3,190 620202452,1902,760Landscape or Pervious SurfaceLawns, Clayey Soil, Flat Slope < 2% 0.20 6,2520445001,500Lawns, Clayey Soil, Average Slope 2-7% 0.25 0280001,1150Lawns, Clayey Soil, Steep Slope >7% 0.35 00027000Total9,442 0.40 0.50 900 0.51 0.64 465 0.21 0.27 515 0.52 0.65 3,3050.64 0.80 4,260 0.61 0.76Notes:Developed Drainage Basin EDeveloped Drainage Basin A Developed Drainage Basin B Developed Drainage Basin C Developed Drainage Basin DSurface TypeRunoff Coefficients1Historic Drainage Basin A3. Frequency adjustment factor per Fort Collins Stormwater Criteria Manual Table 3.2-3.1. Runoff coefficients per Fort Collins Stormwater Criteria Manual Table 3.2-2.2. Composite runoff coefficient per Fort Collins Stormwater Criteria Manual Equation 5-1.613 Meldrum - drainage.xlsx
Drainage Basin Runoff Calculations 639 Smith Street, Fort Collins, COLength (ft)Slope (%)Minor to (min)Major to (min)Length (ft)Slope (%)Channel TypeVelocity (fps)tt (min)Minor Tc (min)Major Tc (min)2-yr 10-yr 100-yr 2-yr 10-yr 100-yrA 0.217 0.40 0.50 180 2 14.0 12.0 NA 14.0 12.0 1.93 3.30 7.42 0.17 0.29 0.80A 0.021 0.51 0.64 20 4 3.1 2.4 NA 5.0 5.0 2.85 4.87 9.95 0.03 0.050.13B 0.011 0.21 0.27 5 10 1.7 1.6 NA 5.0 5.0 2.85 4.87 9.95 0.01 0.010.03C 0.012 0.52 0.65 10 33 1.1 0.8 NA 5.0 5.0 2.85 4.87 9.95 0.02 0.03 0.08D 0.076 0.64 0.80 12 5 7.5 1.2 155 2% swale 2.1 1.2 8.7 5.0 2.33 3.98 9.95 0.11 0.19 0.60E 0.098 0.61 0.76 120 2 8.0 5.5 NA 8.0 5.5 2.41 4.12 9.69 0.14 0.25 0.72Notes:3. Per Fort Collins Stormwater Criteria Manual Section 3.3.4. A minimum Tc of 5 minutes is required.4. Per IDF Table for Rational Method, Table 3.4-1 Fort Collins Stormwater Criteria Manual.1. Per Fort Collins Stormwater Criteria Manual Section 3.3.2.2. Per Fort Collins Stormwater Criteria Manual Section 3.3.3.Initial/Overland Time1Travel Time2HistoricDevelopedFinal Tc3Intensity (in/hr)4BasinArea (acres)Minor Composite CMajor Composite CBasin Flow (cfs)55. Per Fort Collins Stormwater Criteria Manual Equation 5-1.613 Meldrum - drainage.xlsx