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Home My WebLink AboutHILL SINGLE-FAMILY - FDP210005 - SUBMITTAL DOCUMENTS - ROUND 2 - DRAINAGE REPORT KEEFE CIVIL, INC 3125 Crockett Street Fort Collins, Colorado 80526 (970) 215-6808 meg@keefecivil.com May 6, 2021 Keefe Civil Project Number: 2020-016 Water Utilities Engineering City of Fort Collins 700 Wood Street Fort Collins, Colorado 80522 RE: Hill Single-Family Drainage Memo FDP210005 To Whom it May Concern: The purpose of this letter is to describe the proposed improvements and potential drainage impacts associated with the Hill Single-Family FDP210005 project (Appendix A). The 4.011-acre project site is located 0.3 mile east of South Timberline Road, on the north side of Kechter road. The lot is undeveloped pastureland and is bound by a Stetson Creek PUD Second Filing concrete drainage channel and single-family residential lots to the north, and urban estate residential properties to the south, west, and east. The site is located within the McClellands drainage basin. The McClellands Basin Master Drainage Plan assumed 35% imperviousness. Per the NRCS Soil Survey of Larimer County (Appendix B), the site consists of ~57% Fort Collins loam and ~43% Nunn clay loam, which has a hydrologic soil group C classification. 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. (Appendix C) Historically, site stormwater (historic basin A) has drained with gentle slopes from the southwest to northeast into offsite flood irrigation channels on the upstream edge of Blehm Subdivision Lot 6 to the east and conveyed north to the Stetson Creek PUD Second Filing concrete drainage channel, which discharges into McClellands drainageway. Historic and developed drainage basins are shown in Appendix D. An excerpt from the Stetson Creek PUD Second Filing Drainage Report (Northern Engineering 1996) is included in Appendix E. The proposed site improvements include a two-story house with a basement, attached garage, a gravel driveway with access off Kechter Road, and a detached barn. There will be minimal concrete surrounding the house and barn. The homeowner intends to revegetate with native plant material and turf. The gravel driveway and turnaround shall be made of compacted road base material meeting Poudre Fire Authority standards. The lot’s total adjusted impervious area will increase by 15,152 square feet (sf), as indicated in calculations shown below. The total proposed impervious area is 11% for this project. Hill Single-Family Drainage Memo Keefe Civil Project No.: 2020-016 Page 2 of 2 May 6, 2021 Hardscape or Hard Surface Historic Site Area (sf) Adjusted Historic Area (sf) Developed Site Area (sf) Adjusted Developed Area (sf) Concrete 845 845 2,090 2,090 Rooftop (90%) 2,380 2,142 10,210 9,189 Gravel Driveway (40%) 0 0 17,150 6,860 Total Impervious Area 3,225 3,225 29,450 18,139 Adjusted Site Imperviousness 15,152 The composite runoff coefficient and drainage basin runoff calculations for the historic and developed site are included in the enclosed tables (Appendix F). Using the Fort Collins Stormwater Criteria Manual (2018), the proposed stormwater runoff will increase slightly towards McClellands drainageway, but the site improvements will remain below the 35% imperviousness used in the McClellands Basin Master Drainage Plan. 2-year 10-year 100-year Basin A Historic Runoff 1.77 cfs 3.02 cfs 7.95 cfs Basin B Historic Runoff 1.75 cfs 2.97 cfs 5.08 cfs Basin A Developed Runoff 1.59 cfs 2.71 cfs 7.20 cfs Basin B Developed Runoff 1.33 cfs 2.27 cfs 7.73 cfs Basin C Developed Runoff 0.37 cfs 0.63 cfs 1.68 cfs In my professional opinion, the additional runoff generated by this development will not cause adverse impacts to downstream private properties. Therefore, Keefe Civil respectfully requests no detention and water quality requirements be imposed on this development. Based on the enclosed design, it is my professional opinion the additional runoff generated by these site improvements will not cause adverse impacts to downstream private properties. I hereby attest that this letter for the final drainage design for the Hill Single-Family FDP210005 project was prepared by me or under my direct supervision, in accordance with the provisions of the Fort Collins Stormwater Criteria Manual. I understand that the City of Fort Collins does not and will not assume liability for drainage facilities designed by others. Thank you for the opportunity to submit this drainage memo. Please do not hesitate to reach out to me if you have any questions or comments regarding the above items. Best regards, Megan L. Keefe, PE / Manager Keefe Civil, Inc. Enclosures Cc: Chris Hill, Property Owner APPENDIX A COMMON AREA CKECHTER CROSSING M.L.D.RS RSKECHTER ROAD CENTERLINE4 OF 11 LOT 2 4.011 ACRES LOT 1 2.385 ACRES FORT COLLINS, COLORADOSHEET KEEFE CIVIL, INC3125 CROCKETT STREETFORT COLLINS, CO 80526(970) 215-6808MEG@KEEFECIVIL.COMLOT 2, BLEHM SUBDIVISION 2ND FILING, BEING A REPLAT OFLOT 5, BLEHM SUBDIVISION UTILITY PLANSGRADING & EROSION CONTROL PLANMATCHLINE - SEE SHEET 5ABBREVIATION LEGEND: LEGEND: BMP CONTROLS: SF SP VTC PSPS CWA PS VTC SF RS LOT 6BLEHM SUBDIVISIONSTETSON CREEK P.U.D.FORT COLLINS, COLORADOSHEET KEEFE CIVIL, INC3125 CROCKETT STREETFORT COLLINS, CO 80526(970) 215-6808MEG@KEEFECIVIL.COMLOT 2, BLEHM SUBDIVISION 2ND FILING, BEING A REPLAT OFLOT 5, BLEHM SUBDIVISION UTILITY PLANS5 OF 11 LOT 2 4.011 ACRES SWEETWATERCREEK DRIVEGRADING & EROSION CONTROL PLANABBREVIATION LEGEND: LEGEND:MATCHLINE - SEE SHEET 4BMP CONTROLS: SF SP VTC PSPS CWA PS PS PS SF SP CWA SP CWA APPENDIX B Hydrologic Soil Group—Larimer County Area, Colorado (Hill Single-Family) Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 5/6/2021 Page 1 of 44484390448442044844504484480448451044845404484570448460044846304484660448469044843904484420448445044844804484510448454044845704484600448463044846604484690497080497110497140497170497200497230497260497290 497080 497110 497140 497170 497200 497230 497260 497290 40° 30' 46'' N 105° 2' 4'' W40° 30' 46'' N105° 1' 54'' W40° 30' 36'' N 105° 2' 4'' W40° 30' 36'' N 105° 1' 54'' WN Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 13N WGS84 0 50 100 200 300 Feet 0 20 40 80 120 Meters Map Scale: 1:1,500 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 15, Jun 9, 2020 Soil map units are labeled (as space allows) for map scales 1:50,000 or larger. Date(s) aerial images were photographed: Aug 11, 2018—Aug 12, 2018 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 (Hill Single-Family) Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 5/6/2021 Page 2 of 4 Hydrologic Soil Group Map unit symbol Map unit name Rating Acres in AOI Percent of AOI 35 Fort Collins loam, 0 to 3 percent slopes C 1.1 26.0% 36 Fort Collins loam, 3 to 5 percent slopes C 1.3 31.0% 76 Nunn clay loam, wet, 1 to 3 percent slopes C 1.8 43.0% Totals for Area of Interest 4.3 100.0% 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. Hydrologic Soil Group—Larimer County Area, Colorado Hill Single-Family Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 5/6/2021 Page 3 of 4 Rating Options Aggregation Method: Dominant Condition Aggregation is the process by which a set of component attribute values is reduced to a single value that represents the map unit as a whole. A map unit is typically composed of one or more "components". A component is either some type of soil or some nonsoil entity, e.g., rock outcrop. For the attribute being aggregated, the first step of the aggregation process is to derive one attribute value for each of a map unit's components. From this set of component attributes, the next step of the aggregation process derives a single value that represents the map unit as a whole. Once a single value for each map unit is derived, a thematic map for soil map units can be rendered. Aggregation must be done because, on any soil map, map units are delineated but components are not. For each of a map unit's components, a corresponding percent composition is recorded. A percent composition of 60 indicates that the corresponding component typically makes up approximately 60% of the map unit. Percent composition is a critical factor in some, but not all, aggregation methods. The aggregation method "Dominant Condition" first groups like attribute values for the components in a map unit. For each group, percent composition is set to the sum of the percent composition of all components participating in that group. These groups now represent "conditions" rather than components. The attribute value associated with the group with the highest cumulative percent composition is returned. If more than one group shares the highest cumulative percent composition, the corresponding "tie-break" rule determines which value should be returned. The "tie-break" rule indicates whether the lower or higher group value should be returned in the case of a percent composition tie. The result returned by this aggregation method represents the dominant condition throughout the map unit only when no tie has occurred. Component Percent Cutoff: None Specified Components whose percent composition is below the cutoff value will not be considered. If no cutoff value is specified, all components in the database will be considered. The data for some contrasting soils of minor extent may not be in the database, and therefore are not considered. Tie-break Rule: Higher The tie-break rule indicates which value should be selected from a set of multiple candidate values, or which value should be selected in the event of a percent composition tie. Hydrologic Soil Group—Larimer County Area, Colorado Hill Single-Family Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 5/6/2021 Page 4 of 4 APPENDIX C 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 3/22/2021 at 4:11 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°2'18"W 40°30'48"N 105°1'41"W 40°30'21"N Basemap: USGS National Map: Orthoimagery: Data refreshed October, 2020 APPENDIX D COMMON AREA CKECHTER CROSSING M.L.D.LOT 6BLEHM SUBDIVISIONLOT 4BLEHM SUBDIVISIONSTETSON CREEK P.U.D.1 OF 1SWEETWATER CREEK DRIVEFORT COLLINS, COLORADOSHEET KEEFE CIVIL, INC3125 CROCKETT STREETFORT COLLINS, CO 80526(970) 215-6808MEG@KEEFECIVIL.COMFORT COLLINS - LOVELAND WATER DISTRICT SOUTH FORT COLLINS SANITATION DISTRICT Mr. Chris Matkins, District Manager Date All changes, addendums, additions, deletions and modifications to these drawings must be approved, in writing, by the Fort Collins-Loveland Water District and the South Fort Collins Sanitation District.LOT 2, BLEHM SUBDIVISION 2ND FILING, BEING A REPLAT OFLOT 5, BLEHM SUBDIVISION UTILITY PLANSHISTORIC DRAINAGE EXHIBITLEGEND: FOR DRAINAGE REVIEW ONLY NOT FOR CONSTRUCTIONFUTURE SAGE CREEK ROADKECHTER ROAD1 1 2 LOT 6BLEHM SUBDIVISIONLOT 4BLEHM SUBDIVISIONSTETSON CREEK P.U.D.FORT COLLINS, COLORADOSHEET KEEFE CIVIL, INC3125 CROCKETT STREETFORT COLLINS, CO 80526(970) 215-6808MEG@KEEFECIVIL.COMLOT 2, BLEHM SUBDIVISION 2ND FILING, BEING A REPLAT OFLOT 5, BLEHM SUBDIVISION UTILITY PLANS8 OF 11 LOT 2 4.011 ACRES SWEETWATERCREEK DRIVEDRAINAGE EXHIBITLEGEND: FOR DRAINAGE REVIEW ONLY NOT FOR CONSTRUCTION LOT 1 FUTURE SAGE CREEK ROAD2 1 1 3 BLEHM SUBDIVISION LOT 6 BLEHM SUBDIVISION LOT 4 APPENDIX E This unofficial copy was downloaded on Aug-11-2020 from the City of Fort Collins Public Records Website: http://citydocs.fcgov.com For additional information or an official copy, please contact City of Fort Collins Utilities 700 Wood Street Fort Collins, CO 80524 USA This unofficial copy was downloaded on Aug-11-2020 from the City of Fort Collins Public Records Website: http://citydocs.fcgov.com For additional information or an official copy, please contact City of Fort Collins Utilities 700 Wood Street Fort Collins, CO 80524 USA This unofficial copy was downloaded on Aug-11-2020 from the City of Fort Collins Public Records Website: http://citydocs.fcgov.com For additional information or an official copy, please contact City of Fort Collins Utilities 700 Wood Street Fort Collins, CO 80524 USA This unofficial copy was downloaded on Aug-11-2020 from the City of Fort Collins Public Records Website: http://citydocs.fcgov.com For additional information or an official copy, please contact City of Fort Collins Utilities 700 Wood Street Fort Collins, CO 80524 USA This unofficial copy was downloaded on Aug-11-2020 from the City of Fort Collins Public Records Website: http://citydocs.fcgov.com For additional information or an official copy, please contact City of Fort Collins Utilities 700 Wood Street Fort Collins, CO 80524 USA This unofficial copy was downloaded on Aug-11-2020 from the City of Fort Collins Public Records Website: http://citydocs.fcgov.com For additional information or an official copy, please contact City of Fort Collins Utilities 700 Wood Street Fort Collins, CO 80524 USA This unofficial copy was downloaded on Aug-11-2020 from the City of Fort Collins Public Records Website: http://citydocs.fcgov.com For additional information or an official copy, please contact City of Fort Collins Utilities 700 Wood Street Fort Collins, CO 80524 USA This unofficial copy was downloaded on Aug-11-2020 from the City of Fort Collins Public Records Website: http://citydocs.fcgov.com For additional information or an official copy, please contact City of Fort Collins Utilities 700 Wood Street Fort Collins, CO 80524 USA This unofficial copy was downloaded on Aug-11-2020 from the City of Fort Collins Public Records Website: http://citydocs.fcgov.com For additional information or an official copy, please contact City of Fort Collins Utilities 700 Wood Street Fort Collins, CO 80524 USA This unofficial copy was downloaded on Aug-11-2020 from the City of Fort Collins Public Records Website: http://citydocs.fcgov.com For additional information or an official copy, please contact City of Fort Collins Utilities 700 Wood Street Fort Collins, CO 80524 USA This unofficial copy was downloaded on Aug-11-2020 from the City of Fort Collins Public Records Website: http://citydocs.fcgov.com For additional information or an official copy, please contact City of Fort Collins Utilities 700 Wood Street Fort Collins, CO 80524 USA V\T>7NX-..~x.\X\X,\ \»\\N>\\x# » A .||fFT^Aillksss\s,sAtil!u\It'.■V./■nw *l***'■) I'•Si*(•■■I «iia«BBa>PHitPOND■—.A^,S.c_r:NmAattEC Ol/\v\w\.\V\v: ■■•I*\7TT4*ri\)M .♦*iI1✓# Xj-:Iils'*• >ivII14r\.♦H1►«VI\tIOXV♦011Vr)Dit>24J-Xi♦iiiri.♦.♦.♦V.♦i✓i *\✓ "♦V.7Q\♦i✓<i♦\ii■o*•/*\02i03xXm♦SLEGEND:mA♦.29.131,17.497;imm*\\i\#HIr**— iEXISTING STORM SEWERi\SCHELLER(SUBDIVISIONi.♦i--.h'XEXISTING STORM SEWER INlEII 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PR ATT SM AN: ACAP IfrCPAWCQ: 05/Q7/99 ~ISh<»ls> APPENDIX F Composite Runoff Coefficient Calculations 2400 Kechter Road, Fort Collins, CO Area (sf) Minor (2- and 10-yr) Composite C2 Major (100-yr) Composite C3 Area (sf) Minor (2- and 10-yr) Composite C2 Major (100-yr) Composite C3 Area (sf) Minor (2- and 10-yr) Composite C2 Major (100-yr) Composite C3 Area (sf) Minor (2- and 10-yr) Composite C2 Major (100-yr) Composite C3 Area (sf) Minor (2- and 10-yr) Composite C2 Major (100-yr) Composite C3 Hardscape or Hard Surface Concrete 0.95 675 845 2,825 0 110 Rooftop 0.95 6,310 2,380 8,169 8,545 2,185 Gravel Driveway 0.50 7,700 0 15,430 1,150 8,270 Total Impervious Area 14,685 3,225 26,424 9,695 10,565 Landscape or Pervious Surface Lawns, Clayey Soil, Average Slope 2-7%0.15 0 0 0 3,400 4,875 Undeveloped Greenbelts, Agriculture 0.20 242,770 176,600 131,511 241,880 24,910 Total 257,455 0.23 0.29 179,825 0.21 0.27 157,935 0.28 0.35 254,975 0.23 0.28 40,350 0.30 0.37 Notes: 3. 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. Surface Type Runoff Coefficients1 Historic Drainage Basin H1 Historic Drainage Basin H2 Developed Drainage Basin CDeveloped Drainage Basin A Developed Drainage Basin B 2400 Kechter Road - drainage.xlsx Drainage Basin Runoff Calculations 2400 Kechter, Fort Collins, CO Length (ft) Slope (%) Minor to (min) Major to (min) Length (ft) Slope (%) Channel Type Velocity (fps) tt (min) Minor Tc (min) Major Tc (min)2-yr 10-yr 100-yr 2-yr 10-yr 100-yr 1 H1 5.910 0.23 0.29 240 1 25.2 23.6 400 1%swale 1.5 4.4 29.7 28.0 1.31 2.23 4.69 1.77 3.02 7.95 2 H2 4.128 0.21 0.27 230 1 25.1 23.6 475 1%swale 1.5 5.3 30.4 28.9 1.29 2.19 4.61 1.75 2.97 5.08 1 A 3.626 0.28 0.35 120 1 16.8 15.3 400 1%swale 1.5 4.4 21.2 19.8 1.55 2.66 5.65 1.59 2.71 7.20 2 B 5.853 0.23 0.28 240 1 25.3 23.7 400 1%swale 1.5 4.4 29.8 28.1 1.31 2.22 4.68 1.33 2.27 7.73 3 C 0.926 0.30 0.37 230 1 22.7 20.6 475 1%swale 1.5 5.3 28.0 25.9 1.34 2.29 4.88 0.37 0.63 1.68 Notes:Notes: 2. Per Fort Collins Stormwater Criteria Manual Section 3.3.3. Initial/Overland Time1 Travel Time2 Historic Developed Final Tc 3 Intensity (in/hr)4 Basin Area (acres) Minor Composite C Major Composite C Basin Flow (cfs)5 5. Per Fort Collins Stormwater Criteria Manual Equation 5-1. Design Point 3. Per Fort Collins Stormwater Criteria Manual Section 3.3.4. A minimum T c 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. 2400 Kechter Road - drainage.xlsx