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Home My WebLink About209 TROUTMAN PAINT BOOTH ADDITION - MINOR AMENDMENT - MA190088 - SUBMITTAL DOCUMENTS - ROUND 4 - DRAINAGE REPORTDenver • Steamboat Springs • Golden • Colorado Springs • Loveland Corporate Office: 112 North Rubey Drive, Suite 210; Golden, Colorado 80403 June 20th, 2023 Development Review Center 281 North College Ave, Fort Collins, CO 80524 RE: Lot A, Troutman PUD Phase 1 —Drainage Memo This memo details the stormwater considerations that went into the design of this site, as well as how the proposed site complies with the Fort Collins Stormwater Criteria Manual (FCSCM) dated December 2018. The property is located at the west end cul-de-sac at 209 West Troutman Parkway. Big O Tires exists between the site and South Mason St on the east. On the west is the Max Guideway route running north/south. On the south is the Casey’s Wash & Detail Center. According to the Fort Collins Stormwater Master Planning basin map, the site lies within the Mail Creek Basin. The proposed site, Lot A, is a 0.67 acre portion of the subdivision, of which approximately 0.22 acres will be disturbed in construction. Improvements to the site will include a 1980 SF building addition, new concrete paving, a concrete drainage pan, a sidewalk extension and expansion of the asphalt parking lot. Stormwater runoff will follow historic drainage patterns from west to east via overland and gutter flow until it leaves the property. From this point, runoff will be directed via gutters and storm sewer networks on West Troutman Parkway and South Mason Ave. Following typical flows for the Mail Creek Basin, runoff will be directed towards Fossil Creek Reservoir. Onsite detention facilities are not planned. In order to ensure compliance with the Fort Collins Stormwater Criteria manual, an analysis of imperviousness differences regarding the improvements to the site was conducted. MHFD UD-Rational sheets were used to calculate the imperviousness. The Rational Method was utilized to calculate proposed runoff per Chapter 5: Hydrology Standards of the FCSCM. Per the results in Table 1 below, site improvements are not expected to significantly change runoff and will not require further analysis. Calculations are included in the Attachments Table 1: Site Imperviousness Comparison Weighted Impervious and C Values AREA (ACRE)Runoff (CFS) Basin Area Imperv. % C2 C100 Paved Roofs Soils C2 C100 EX 0.67 88.5 0.87 1.00 0.43 0.18 0.06 1.62 6.5 PR 0.67 89.4 0.89 1.00 0.40 0.22 0.05 1.66 6.5 Page| 2 A report from the USDA Web Soil Survey shows that the entire site is covered by Altvan-Satanta loams, which is rated as Hydrologic Soil Group B. According to the FEMA Flood Map Service Center the site falls within Zone X, an area of minimal flood hazard. As this project property and total disturbance area are less than one acre, an erosion control report is not required per Sec. 6.1.4 of the FCSCM. Sediment and erosion control is projected to be minimal since the majority of work is being completed over existing hardscape, but a number of control measures will be provided to protect surrounding properties during construction. These will include silt fence or similar barrier on the north side of the site landscaped area, a stockpile area within the site, vehicle tracking from the entrance on W Troutman Pkwy, a concrete washout structure, and regular street sweeping to handle any dust or dirt that gets tracked past the vehicle tracking control. These measures should adequately protect neighboring properties without interrupting commerce in the area. Based on the information presented in this narrative along with the supporting data attached, the proposed site will comply with the Fort Collins Stormwater Criteria Manual. A 1% increase in imperviousness will not create a notable difference in stormwater runoff. No stormwater infrastructure improvements are proposed. The existing drainage design will remain sufficient for handling flows from this site with the proposed improvements while maintaining current protection for off-site properties. Please reach out to us if you have any questions or require further information. Sincerely, Jeremy Goetsch, P.E. Attachments Soil Report FEMA Firmette Rational Method Calculations Drainage Plan Hydrologic Soil Group—Larimer County Area, Colorado (209 W Troutman Pkwy) Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 6/20/2023 Page 1 of 4448635044863604486370448638044863904486400448641044864204486430448635044863604486370448638044863904486400448641044864204486430493170493180493190493200493210493220 493170 493180 493190 493200 493210 493220 40° 31' 43'' N 105° 4' 50'' W40° 31' 43'' N105° 4' 47'' W40° 31' 40'' N 105° 4' 50'' W40° 31' 40'' N 105° 4' 47'' WN Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 13N WGS84 0 20 40 80 120 Feet 0 5 10 20 30 Meters Map Scale: 1:436 if printed on A portrait (8.5" x 11") sheet. Soil Map may not be valid at this scale. MAP LEGEND MAP INFORMATION Area of Interest (AOI) Area of Interest (AOI) Soils Soil Rating Polygons A A/D B B/D C C/D D Not rated or not available Soil Rating Lines A A/D B B/D C C/D D Not rated or not available Soil Rating Points A A/D B B/D C C/D D Not rated or not available Water Features Streams and Canals Transportation Rails Interstate Highways US Routes Major Roads Local Roads Background Aerial Photography The soil surveys that comprise your AOI were mapped at 1:24,000. Warning: Soil Map may not be valid at this scale. Enlargement of maps beyond the scale of mapping can cause misunderstanding of the detail of mapping and accuracy of soil line placement. The maps do not show the small areas of contrasting soils that could have been shown at a more detailed scale. Please rely on the bar scale on each map sheet for map measurements. Source of Map: Natural Resources Conservation Service Web Soil Survey URL: Coordinate System: Web Mercator (EPSG:3857) Maps from the Web Soil Survey are based on the Web Mercator projection, which preserves direction and shape but distorts distance and area. A projection that preserves area, such as the Albers equal-area conic projection, should be used if more accurate calculations of distance or area are required. This product is generated from the USDA-NRCS certified data as of the version date(s) listed below. Soil Survey Area: Larimer County Area, Colorado Survey Area Data: Version 17, Sep 7, 2022 Soil map units are labeled (as space allows) for map scales 1:50,000 or larger. Date(s) aerial images were photographed: Jul 2, 2021—Aug 25, 2021 The orthophoto or other base map on which the soil lines were compiled and digitized probably differs from the background imagery displayed on these maps. As a result, some minor shifting of map unit boundaries may be evident. Hydrologic Soil Group—Larimer County Area, Colorado (209 W Troutman Pkwy) Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 6/20/2023 Page 2 of 4 Hydrologic Soil Group Map unit symbol Map unit name Rating Acres in AOI Percent of AOI 4 Altvan-Satanta loams, 3 to 9 percent slopes B 0.7 98.2% 74 Nunn clay loam, 1 to 3 percent slopes C 0.0 1.8% Totals for Area of Interest 0.8 100.0% Description Hydrologic soil groups are based on estimates of runoff potential. Soils are assigned to one of four groups according to the rate of water infiltration when the soils are not protected by vegetation, are thoroughly wet, and receive precipitation from long-duration storms. The soils in the United States are assigned to four groups (A, B, C, and D) and three dual classes (A/D, B/D, and C/D). The groups are defined as follows: Group A. Soils having a high infiltration rate (low runoff potential) when thoroughly wet. These consist mainly of deep, well drained to excessively drained sands or gravelly sands. These soils have a high rate of water transmission. Group B. Soils having a moderate infiltration rate when thoroughly wet. These consist chiefly of moderately deep or deep, moderately well drained or well drained soils that have moderately fine texture to moderately coarse texture. These soils have a moderate rate of water transmission. Group C. Soils having a slow infiltration rate when thoroughly wet. These consist chiefly of soils having a layer that impedes the downward movement of water or soils of moderately fine texture or fine texture. These soils have a slow rate of water transmission. Group D. Soils having a very slow infiltration rate (high runoff potential) when thoroughly wet. These consist chiefly of clays that have a high shrink-swell potential, soils that have a high water table, soils that have a claypan or clay layer at or near the surface, and soils that are shallow over nearly impervious material. These soils have a very slow rate of water transmission. If a soil is assigned to a dual hydrologic group (A/D, B/D, or C/D), the first letter is for drained areas and the second is for undrained areas. Only the soils that in their natural condition are in group D are assigned to dual classes. Rating Options Aggregation Method: Dominant Condition Hydrologic Soil Group—Larimer County Area, Colorado 209 W Troutman Pkwy Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 6/20/2023 Page 3 of 4 Component Percent Cutoff: None Specified Tie-break Rule: Higher Hydrologic Soil Group—Larimer County Area, Colorado 209 W Troutman Pkwy Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 6/20/2023 Page 4 of 4 National Flood Hazard Layer FIRMette 0 500 1,000 1,500 2,000250 Feet Ü SEE FIS REPORT FOR DETAILED LEGEND AND INDEX MAP FOR FIRM PANEL LAYOUT SPECIAL FLOOD HAZARD AREAS Without Base Flood Elevation (BFE) Zone A, V, A99 With BFE or DepthZone AE, AO, AH, VE, AR Regulatory Floodway 0.2% Annual Chance Flood Hazard, Areas of 1% annual chance flood with average depth less than one foot or with drainage areas of less than one square mileZone X Future Conditions 1% Annual Chance Flood HazardZone X Area with Reduced Flood Risk due to Levee. See Notes.Zone X Area with Flood Risk due to LeveeZone D NO SCREEN Area of Minimal Flood Hazard Zone X Area of Undetermined Flood HazardZone D Channel, Culvert, or Storm Sewer Levee, Dike, or Floodwall Cross Sections with 1% Annual Chance 17.5 Water Surface Elevation Coastal Transect Coastal Transect Baseline Profile Baseline Hydrographic Feature Base Flood Elevation Line (BFE) Effective LOMRs Limit of Study Jurisdiction Boundary Digital Data Available No Digital Data Available Unmapped This map complies with FEMA's standards for the use of digital flood maps if it is not void as described below. The basemap shown complies with FEMA's basemap accuracy standards The flood hazard information is derived directly from the authoritative NFHL web services provided by FEMA. This map was exported on 6/20/2023 at 1:14 PM and does not reflect changes or amendments subsequent to this date and time. The NFHL and effective information may change or become superseded by new data over time. This map image is void if the one or more of the following map elements do not appear: basemap imagery, flood zone labels, legend, scale bar, map creation date, community identifiers, FIRM panel number, and FIRM effective date. Map images for unmapped and unmodernized areas cannot be used for regulatory purposes. Legend OTHER AREAS OF FLOOD HAZARD OTHER AREAS GENERAL STRUCTURES OTHER FEATURES MAP PANELS 8 B 20.2 The pin displayed on the map is an approximate point selected by the user and does not represent an authoritative property location. 1:6,000 105°5'8"W 40°31'56"N 105°4'31"W 40°31'28"N Basemap Imagery Source: USGS National Map 2023 Project Area Designer:Company:2-yr 5-yr 10-yr 25-yr 50-yr 100-yr 500-yrDate:1-hour rainfall depth, P1 (in) =0.82 1.40 2.86Project:abcLocation:Rainfall Intensity Equation Coefficients =28.50 10.00 0.7862-yr 5-yr 10-yr 25-yr 50-yr 100-yr 500-yrOverland Flow LengthLi (ft)U/S Elevation(ft)(Optional)D/S Elevation(ft)(Optional)Overland Flow SlopeSi (ft/ft)Overland Flow Timeti (min)Channelized Flow LengthLt (ft)U/S Elevation(ft)(Optional)D/S Elevation(ft)(Optional)Channelized Flow SlopeSt (ft/ft)NRCS Conveyance Factor KChannelized Flow VelocityVt (ft/sec)Channelized Flow Timett (min)Computedtc (min)Regionaltc (min)Selectedtc (min)2-yr 5-yr 10-yr 25-yr 50-yr 100-yr 500-yr 2-yr 5-yr 10-yr 25-yr 50-yr 100-yr 500-yr0.73 0.76 0.78 0.81 0.83 0.84 0.860.89 0.89 1.005.00 2.78 4.75 9.70 1.66 2.83 6.500.72 0.75 0.77 0.80 0.82 0.84 0.860.87 0.87 1.005.00 2.78 4.75 9.70 1.62 2.77 6.50EX 0.67Cells of this color are for calculated results based on overridesGCTBaseline Corporation6/20/2023Ft Collins Collision209 W Troutman PkwyVersion 2.00 released May 2017B 88.5Rainfall Intensity, I (in/hr) Peak Flow, Q (cfs)Calculation of Peak Runoff using Rational MethodOverland (Initial) Flow Time Channelized (Travel) Flow Time Time of ConcentrationRunoff Coefficient, CSubcatchment NameArea(ac)NRCS Hydrologic Soil GroupPercent ImperviousnessPR 0.67 B 89.4Select UDFCD location for NOAA Atlas 14 Rainfall Depths from the pulldown list OR enter your own depths obtained from the NOAA website (click this link)Cells of this color are for required user-inputCells of this color are for optional override valuesI𝑖𝑛/ℎ𝑟 ൌa∗Pଵb൅tୡୡt୧ൌ0.3951.1െ CହL୧S୧଴.ଷଷt୲ൌL୲60KS୲ൌ L୲60V୲Computed tୡൌt୧൅t୲Regional tୡൌ26െ 17i ൅ L୲6014i൅ 9S୲Selected tୡൌmaxt୫୧୬୧୫୳୫ ,minComputed tୡ ,Regional tୡ t୫୧୬୧୫୳୫ൌ5 (urban) t୫୧୬୧୫୳୫ൌ10 (non‐urban)Q𝑐𝑓𝑠 ൌ CIA FCSCM CH. 5 Hydrology Standards: