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Home My WebLink AboutBachus and Schanker Law Office Building - fdp200031 - - DRAINAGE REPORT2900 South College Avenue, Ste. 3D Fort Collins, CO 80525 303-740-9393 • Fax: 303-721-9019 www.jrengineering.com Memorandum To:Matt Simpson From:JR Engineering Date:12/16/2020 Subject:Lot 1 of the Warren Federal Credit Union – East Drake – Final Drainage Report 1ST Amendment This memo has been prepared to summarize that drainage and the proposed improvements for the re-plat of lot 1 of the Warren Federal Credit Union –East Drake is in compliance with the Lot 1, 3 and Tract A, Warren Federal Credit Union – East Drake - Final Drainage Report as prepared by Interwest Consulting Group. Introduction: The site, lot 1 of the Warren Federal Credit Union – East Drake, is located in the northwest quarter of Section 29, Township 7 North, Range 68 West of the 6th Principal Meridian, in the City of Fort Collins, Larimer County, Colorado. Refer to the attached Vicinity Map. The site is bounded north by East Drake Road, Illinois Dive to the west, Lot 2 of the Warren Federal Credit union to the south, and the existing parking lot of the Warren Federal Credit Union – East Drake development to the east. The total area of the site is 0.25 acres of land. The proposed development includes the construction of an office building and a future commercial/retail building, walks, patios, and a landscape area. A walk going north-south has been proposed to connect to an existing walk within the East Drake Road ROW. Existing Conditions: The site is within a property that is part of the approved Warren Federal Credit – East Drake – Final Drainage Report. Detention for the site has been provided by an off-site existing water quality and detention pond as stated in the Final Drainage Report for Rigden Farm Northwest Roads as prepared by JR Engineering. The site is currently undeveloped and is composed primarily of dry vegetation, with the exception of an existing drainage pan on the site. The site is located in a FEMA flood zone X in the non-published FIRM panel 08069C1000F, dated 12/19/2006. The soils on the site are primary composed of type B soils - with Satanta loam, 3 to 5 % making up 94.7% of the site. A minority of the soils on the site are characterized as type C soils – with Nunn clay loam, 3 to 5% slopes making up 5.3% of the overall site. For additional information on the soil-groups, refer to the attached Hydrologic soil group map. 2900 South College Avenue, Ste. 3D Fort Collins, CO 80525 303-740-9393 • Fax: 303-721-9019 www.jrengineering.com Proposed Development: Lot 1 of the Warren Federal Credit Union - East Drake will be re-plated into two separate lots. Lot 1 will be developed into the Bachus and Schanker law office building, and lot 2 will be developed into a commercial/retail building. Basin 1A is 0.15 Acres and 58.9 % impervious, includes lot 1 of the re-plat, the Bachus and Schanker law office building, proposed walk, landscape area. Runoff from basin 1A is collected with nyloplast landscape drains and roof drains, and drains to design point 2, as shown in the attached Bachus and Schanker Office Building Drainage Plan. Basin 2A is 0.02 Acres and 37.0% impervious, includes lot 1 of the re-plat, an existing concrete pan, and landscape area. Basin 2A drains into the existing parking lot at design point 1, as shown in the attached Bachus and Schanker Office Building Drainage Plan. The runoff is then treated by LID pervious pavers and drains into an inlet represented as design point b2 in the attached Interwest drainage map. Basin 1B is 0.09 Acres and 58.7% imperious, includes lot 2 of the re-plat designated to be a future office/ commercial/retail building. Basin 2B drains to design point 3, as shown in the attached Bachus and Schanker Office Building Drainage Plan. Runoff from basin 1B is confluences with the upstream runoff from basin 1A at design point 3.1. The runoff is ultimately conveyed into an existing manhole and is represented as design point C as shown within the attached Interwest drainage map. Basins 1A, 2A, and 1B are part of basins C and B2 from the Interwest drainage report. Additional impervious area will be added to basin B2 from the site connection to the existing sidewalk along the East Drake ROW and walks along the building(s) frontage access. The net percent impervious of the proposed improvements to the site is 57.1 % percent. The impervious is well below the Interwest percent impervious values for basin B2 72% impervious, and basin C, 73% impervious. Therefore the proposed additions to the site are anticipated to not adversely affect the LID measures put in place during the development of the East Warren Federal Credit Union subdivision or the downstream stormwater infrastructure. Low Impact Development Approved LID measures were designed by Interwest to treat 51% of the runoff, as shown in the attached Interwest LID exhibit. The sidewalk extension to the East Drake Road ROW within Basin 2A is tributary to the LID pervious pavers. The required LID treatment determined by Interwest was 30,130 sq-ft. The provided treatment area was for 30,477 sq-ft. of total impervious area. The new walk adds 236 sq-ft. of impervious area, and the LID treatment measures remain at over 50%, as shown in the attached Interwest LID exhibit. Conclusion Improvements to the site remain in continuity with the approved Lot 1, 3 and Tract A, Warren Federal Credit Union – East Drake - Final Drainage Report. 2900 South College Avenue, Ste. 3D Fort Collins, CO 80525 303-740-9393 • Fax: 303-721-9019 www.jrengineering.com References 1.) Lot 1, 3 and Tract A, Warren Federal Credit Union – East Drake - Final Drainage Report, Interwest …Consulting Group, March, 2016 2.) Final Drainage and Erosion Control Report for Rigden Farm – Northwest Roads”, JR Engineering, April …2005 Attachments: 1.) Vicinity Map 2.) Soils Map 3.) Interwest Drainage Map 4.) Interwest LID exhibit 4.) Interwest Drainage Calcs 5.) Proposed Drainage Calcs 6.) Proposed Drainage Map A Westrian Company Hydrologic Soil Group—Larimer County Area, Colorado Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 11/25/2020 Page 1 of 4448902844890344489040448904644890524489058448906444890704489076448902844890344489040448904644890524489058448906444890704489076496899496905496911496917496923496929496935 496899 496905 496911 496917 496923 496929 496935 40° 33' 8'' N 105° 2' 11'' W40° 33' 8'' N105° 2' 10'' W40° 33' 7'' N 105° 2' 11'' W40° 33' 7'' N 105° 2' 10'' WN Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 13N WGS84 0 10 20 40 60 Feet 0 3 7 14 21 Meters Map Scale: 1:263 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 Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 11/25/2020 Page 2 of 4 Hydrologic Soil Group Map unit symbol Map unit name Rating Acres in AOI Percent of AOI 73 Nunn clay loam, 0 to 1 percent slopes C 0.0 5.3% 96 Satanta loam, 3 to 5 percent slopes B 0.3 94.7% Totals for Area of Interest 0.3 100.0% 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. Rating Options Aggregation Method: Dominant Condition Hydrologic Soil Group—Larimer County Area, Colorado Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 11/25/2020 Page 3 of 4 Component Percent Cutoff: None Specified Tie-break Rule: Higher Hydrologic Soil Group—Larimer County Area, Colorado Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 11/25/2020 Page 4 of 4                                                                                                          Subdivision:East Warren Federal Credit Union Project Name:Bachus and Schanker Location:Fort Collins Project No.: Calculated By:ARJ Checked By:0 Date:12/9/20 1A 0.15 100%0.01 7.3%90%0.09 50.9%2%0.06 0.7%58.9% 2A 0.02 100%0.01 35.7%90%0.00 0.0%2%0.01 1.3%37.0% 1B 0.09 100%0.003 3.6%90%0.05 54.3%2%0.03 0.7%58.7% Total 0.26 57.1% 39792.00 COMPOSITE % IMPERVIOUS CALCULATIONS Weighted % Imp. Basins Total Weighted % Imp.Basin ID Total Area (ac) % Imp.Area (ac) Lawns % Imp. Area (ac)Weighted % Imp. Paved Surface Roofs Weighted % Imp.% Imp. Area (ac) X:\3970000.all\3979200\Excel\Drainage\Drainage_Calcs_Template_v2.07.xlsm Page 1 of 2 12/15/2020 Subdivision:East Warren Federal Credit Union Project Name:Bachus and Schanker Location:Fort Collins Project No.: Calculated By:ARJ Checked By:0 Date:12/9/20 1A 0.15 0.95 0.01 0.07 0.09 0.95 0.09 0.54 0.67 0.25 0.06 0.09 0.11 0.70 0.87 2A 0.02 0.95 0.01 0.34 0.42 0.95 0.00 0.00 0.00 0.25 0.01 0.16 0.20 0.50 0.62 1B 0.09 0.95 0.00 0.03 0.04 0.95 0.05 0.57 0.72 0.25 0.03 0.09 0.11 0.70 0.87 Total 0.26 0.68 0.85 COMPOSITE RUNOFF COEFFICIENT CALCULATIONS Basin ID Area (ac) 10- YEAR C 100 - YEAR C Runoff Coefficient Area (ac)10- YEAR C 100 - YEAR C 39792.00 Total Area (ac)Runoff Coefficient Area (ac) 10 - YEAR C 100 - YEAR C Basins Total Weighted 100 YEAR C Runoff Coefficient Paved Surface Roofs Lawns Basins Total Weighted 2 YEAR C X:\3970000.all\3979200\Excel\Drainage\Drainage_Calcs_Template_v2.07.xlsm Page 1 of 1 12/15/2020 Project Name:Bachus and Schanker Subdivision:East Warren Federal Credit Union Project No.: Location:Fort Collins Calculated By:ARJ Design Storm:Checked By:0 Date: TRAVEL TIME STREET Design PointBasin IDArea (Ac)Runoff Coeff.tc (min)C*A (Ac)I (in/hr)Q (cfs)tc (min)C*A (ac)I (in/hr)Q (cfs)Qstreet (cfs)C*A (ac)Slope (%)Qpipe (cfs)C*A (ac)Slope (%)Pipe Size (inches)Length (ft)Velocity (fps)tt (min)REMARKS 1 2A 0.02 0.50 7.0 0.01 4.31 0.0 drains to pan Bachus and Schanker office 2 1A 0.15 0.70 10.0 0.11 3.78 0.4 roof drains and surrounding building into inlet(s) Retail/commercial office 3 1B 0.09 0.70 11.0 0.06 3.63 0.2 roof drains and surrounding building into inlet(s) Bachus and Schanker office, retail/commercial office 3.1 11.0 0.17 3.63 0.6 roof drains and surrounding building into inlet(s) Notes: Street and Pipe C*A values are determined by Q/i using the catchment's intensity value. DIRECT RUNOFF TOTAL RUNOFF STREET PIPE STANDARD FORM SF-3 STORM DRAINAGE SYSTEM DESIGN (RATIONAL METHOD PROCEDURE) 10-Year 39792.00 12/9/20 X:\3970000.all\3979200\Excel\Drainage\Drainage_Calcs_Template_v2.07.xlsm Page 1 of 1 12/15/2020 Project Name:Bachus and Schanker Subdivision:East Warren Federal Credit Union Project No.: Location:Fort Collins Calculated By:ARJ Design Storm:Checked By:0 Date: TRAVEL TIME STREET Design PointBasin IDArea (ac)Runoff Coeff.tc (min)C*A (ac)I (in/hr)Q (cfs)tc (min)C*A (ac)I (in/hr)Q (cfs)Qstreet (cfs)C*A (ac)Slope (%)Qpipe (cfs)C*A (ac)Slope (%)Pipe Size (inches)Length (ft)Velocity (fps)tt (min)REMARKS 1 2A 0.02 0.62 7.0 0.01 8.80 0.1 drains to pan Bachus and Schanker office 2 1A 0.15 0.87 10.0 0.13 7.72 1.0 roof drains and surrounding building into inlet(s) Retail/commercial office 3 1B 0.09 0.87 11.0 0.08 7.42 0.6 roof drains and surrounding building into inlet(s) Bachus and Schanker office, retail/commercial office 3.1 11.0 0.21 7.42 1.6 roof drains and surrounding building into inlet(s) Notes: Street and Pipe C*A values are determined by Q/i using the catchment's intensity value. STORM DRAINAGE SYSTEM DESIGN STANDARD FORM SF-3 (RATIONAL METHOD PROCEDURE) 39792.00 PIPE 100-Year DIRECT RUNOFF TOTAL RUNOFF 12/9/20 STREET X:\3970000.all\3979200\Excel\Drainage\Drainage_Calcs_Template_v2.07.xlsm Page 1 of 1 12/15/2020 A Westrian Company Know what'sbelow.before you dig.CallR