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HomeMy WebLinkAboutBALFOUR SENIOR LIVING - PDP220001 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORT PRELIMINARY DRAINAGE REPORT FOR THE OVERLANDER BY BALFOUR EAST HARMONY ROAD AT CINQUEFOIL LANE FORT COLLINS, COLORADO Prepared for: BALFOUR SENIOR LIVING 183 S. Taylor Avenue, Suite 155 Louisville, Colorado 80027 Prepared by: BOWMAN CONSULTING GROUP 1526 Cole Boulevard, Suite 100 Lakewood, Colorado 80401 Contact: Adrian Todsen, P.E. Phone: 303.801.2910 January 26, 2022 Bowman Project No. 020452-02-001 Preliminary Drainage Report The Overlander by Balfour January 26, 2022 City of Fort Collins Planning and Development Services 281 N. College Ave. Fort Collins, Colorado 80524 RE: Preliminary Drainage Report for The Overlander by Balfour Dear Staff: Bowman is pleased to submit this Preliminary Drainage Report for your review. This report accompanies the Project Development Plan (PDP) submittal for the subject development. This report has been prepared in accordance with the Fort Collins Stormwater Criteria Manual (FCSCM) and serves to document the stormwater impacts associated with the proposed project. We understand that review by City is to assure general compliance with standardized criteria included in the FCSCM. If you have any questions or require additional information, please feel free to reach me by phone at (303) 801-2910 or by email at atodsen@bowman.com. Thank you, Adrian Todsen, P.E. Assistant Project Manager Bowman Consulting Preliminary Drainage Report The Overlander by Balfour Table of Contents I. GENERAL LOCATION AND DESCRIPTION ....................................................... 1 A. Location ................................................................................................... 1 B. Description of Property ............................................................................. 2 C. Floodplain Designation ............................................................................. 2 II. DRAINAGE BASINS AND SUB-BASINS ............................................................. 3 A. Major Basin Description ........................................................................... 3 B. Sub-Basin Description .............................................................................. 3 III. DRAINAGE DESIGN CRITERIA .......................................................................... 4 A. Regulations .............................................................................................. 4 B. Four Step Process ................................................................................... 4 C. Development Criteria and Constraints ...................................................... 5 D. Hydrologic Criteria .................................................................................... 5 E. Hydraulic Criteria ...................................................................................... 6 F. Floodplain Regulation Compliance ........................................................... 6 G. Modifications of Criteria ............................................................................ 6 IV. DRAINAGE FACILITY DESIGN ........................................................................... 6 A. General Concept ...................................................................................... 6 B. Master Drainage Concepts ....................................................................... 6 C. Specific Details ........................................................................................ 7 V. CONCLUSION ..................................................................................................... 8 A. Compliance with Standards ...................................................................... 8 B. Drainage Concept .................................................................................... 9 VI. REFERENCES .................................................................................................... 9 APPENDICES A. Proposed Site Plan and Drainage Area Map B. Hydrology Calculations C. Preliminary Detention Calculations Preliminary Drainage Report The Overlander by Balfour Preliminary Drainage Report Page 1 I. GENERAL LOCATION AND DESCRIPTION A. Location The Overlander by Balfour (the Project) is located within the City of Fort Collins, Colorado at the southeast corner of East Harmony Road and Cinquefoil Lane, as shown in Figure 1 below. Figure 1: Vicinity Map The project site is located in the northeast quarter of Section 4, Township 6 North, Range 68 West of the 6th Principal Meridian, City of Fort Collins, County of Larimer, State of Colorado. The tract is bordered by East Harmony Road to the North, Cinquefoil Lane to the West, Fossil Creek Reservoir Inlet Ditch to the East, and undeveloped land to the South. Surrounding developments include the Banner Fort Collins Medical Center to the west across Cinquefoil Lane, a Hewlett-Packard corporate campus to the north across East Harmony Lane, and a multifamily residential development to the east across the Fossil Creek Reservoir Inlet Ditch. This site lies within the McClellands Creek Master Drainage Basin. Per the “East Harmony Portion of the McClellands Creek Master Drainage Plan Update”, by Icon Engineering, August 1999 (Ref. 3), onsite detention is required with a release rate of 0.5 cfs per acre in the 100-year storm event. Preliminary Drainage Report The Overlander by Balfour Preliminary Drainage Report Page 2 B. Description of Property The subject property is approximately 5.0 acres and is presently zoned Harmony Corridor District (H-C). The site consists of primarily undeveloped land with some abandoned agricultural buildings and driveways. Existing slopes on the site vary from 1 to 10%. General topography on the site falls from west to east and drains toward the Fossil Creek Reservoir Inlet Ditch. Figure 2: Soil Map According to the United States Department of Agriculture (USDA) Natural Resources Conservation Service (NRCS) Soil Survey (see Figure 2 above), the site consists of a combination of Larimer-Stoneham complex with 3 to 10 percent slopes (Hydrologic Soil Group B) and Nunn clay loam with 0 to 3 percent slopes (Hydrologic Soil Group C). See Appendix A for the complete Web Soil Survey. The Project will develop the entirety of the site and consists of a senior care community. Parking areas, associated utilities, and detention/water quality structures will be included in the construction. The Fossil Creek Reservoir Inlet Ditch is an irrigation canal that feeds into the Fossil Creek Reservoir and runs along the east side of the site. C. Floodplain Designation The site is located within Zone “X” as shown on the FEMA Flood Insurance Rate Map (FIRM) Map No. 08069C0994F (see Figure 3 below and Appendix A), dated December 19, 2006, and revised by Case No. 14-08-0580P, effective December 15, 2014. Preliminary Drainage Report The Overlander by Balfour Preliminary Drainage Report Page 3 Figure 3: FEMA Floodplain Map The Cache La Poudre River 100-year floodplain lies approximately 800 feet offsite to the east. No portion of the project location is encroached by any City or FEMA jurisdictional floodplain. The vertical benchmark used for site survey data is NGS Benchmark Y401 (Elevation = 4971.96, NAVD 88). II. DRAINAGE BASINS AND SUB-BASINS A. Major Basin Description The Project falls within the East Harmony portion of the McClellands Creek Master Drainage Basin. The McClellands basin encompasses approximately 3.4 square miles in southeast Fort Collins and conveys flows from the upper end of the basin to the downstream discharge point along the Fossil Creek Reservoir Inlet Ditch, located along the east side of the project site. A majority of the basin is developed or currently being developed with residential and commercial land uses. B. Sub-Basin Description The site historically drains toward the Fossil Creek Reservoir Inlet Ditch located directly east of the site. Each proposed sub-basin within the site boundary will be retained or detained before being released into the Fossil Creek Reservoir Inlet Ditch. Drainage from East Harmony Road to the North of the site is currently Preliminary Drainage Report The Overlander by Balfour Preliminary Drainage Report Page 4 conveyed via a roadside ditch along the south side of the road to an existing outfall into the Fossil Creek Reservoir Inlet Ditch. Drainage on Cinquefoil Lane follows the curb and gutter down to East Harmony Road. The undeveloped area to the south generally flows from west to east to the existing detention pond constructed south of the site, which also outfalls to the Fossil Creek Reservoir Inlet Ditch. No offsite flows are anticipated for this site. III. DRAINAGE DESIGN CRITERIA A. Regulations This report is being prepared based on the regulations and guidelines set forth by the Fort Collins Stormwater Criteria Manual (FCSCM). No modifications to the criteria are being proposed at this time. B. Four Step Process This site was evaluated using the “Four Step Process” in order to minimize adverse impacts of urbanization to receiving waters. Chapter 1, Section 2.3.7 of the FCSCM requires that at least 75% of all newly added or impervious area shall be treated by low-impact development (LID) techniques. As shown in the proposed drainage areas, we are currently proposing to treat 100% of the new impervious areas through LID systems. A summary of the Four Step Process for this project is outlined below: Step 1 – Employ runoff reduction practices Several methods have been implemented with this project in order to reduce runoff peaks and volumes and utilize LID techniques including: - Providing significant landscaping and vegetated areas along the East Harmony Road corridor and throughout the site to reduce impervious cover - Installing several bioretention filters for the northern portion of the site for stormwater capture to provide initial water quality control - Installing underground detention with isolation chambers for drainage of the southern portion of the site prior to outfall for water quality control Step 2 – Implement best management practices (BMPs) that provide a water quality capture volume with slow release and/or infiltration All stormwater runoff from the site will ultimately be routed to one of three detention methods depending on the drainage area that all include outlet control structures: - Oversized storm sewer pipes to provide detention storage up to and including the 100-year, 2-hour storm event for areas that drain through bioretention filters - Above-ground filtration ponds on the north side of the site to capture and treat sheet flow prior to being detained in the oversized storm sewer - Underground detention storage with isolation chambers for drainage areas on the south side of the site Preliminary Drainage Report The Overlander by Balfour Preliminary Drainage Report Page 5 Step 3 – Stabilize drainageways During construction, temporary erosion control measures will be continually maintained to minimize erosion along the Fossil Creek Reservoir Inlet Ditch. Outlet structures into the ditch will incorporate permanent erosion control measures as required. The development of this site will also provide water quality where none was previously provided and will reduce the amount of direct drainage area, and therefore erosion potential, into the Fossil Creek Reservoir Inlet Ditch. Step 4 – Implement site specific and other source control BMPs: Maintenance of the bioretention filters, detention ponds, and outlet structures will be provided to ensure drainage capability and reduce pollution into the stormwater runoff system. The site will also include a trash enclosure for the disposal of waste products from the development. C. Development Criteria and Site Constraints The subject tract is bounded by existing public roadways to the north and west and by the Fossil Creek Reservoir Inlet Ditch to the east. Certain considerations have been taken based on these constraints: - Existing elevations along the perimeter of the site will generally be maintained. - Existing drainage patterns on the site will be maintained by draining east to the Fossil Creek Reservoir Inlet Ditch. - The peak outfall release rate from the site into the Fossil Creek Reservoir Inlet Ditch during a 100-year storm is limited to 0.5 cfs/acre in accordance with the “East Harmony Portion of the McClellands Creek Master Drainage Plan Update” by Icon Engineering, August 1999, and confirmed with the North Poudre Irrigation Company, the owner of the irrigation ditch. D. Hydrological Criteria Since the size of the subject tract is exactly 5 acres, the Rational Method was chosen as the basis for all hydrologic calculations in this report, in accordance with Chapter 5, Section 3.0 of the FCSCM. Composite runoff coefficients were calculated for each drainage area based on the surface type in accordance with Chapter 5, Section 3.2 of the FCSCM. The two-hour Fort Collins Intensity-Duration-Frequency (IDF) Curves as presented in Table 3.4-1 of the FCSCM serve as the basis for all hydrologic calculations. The 2-year, 10-year and 100-year design storms were analyzed to examine various drainage scenarios depending on the intensity of the rain event. The 2- year storm event is considered the “Minor” storm and has a 50th percentile probability of occurring in any given year. The 10-year storm event has a probability of occurring in the 90th percentile in any given year and was analyzed for reference purposes. Preliminary Drainage Report The Overlander by Balfour Preliminary Drainage Report Page 6 E. Hydraulic Criteria As previously mentioned, existing drainage patterns on the site will be maintained. Drainage facilities are designed in accordance with criteria outlined in the FCSCM. The subject tract is not located within a FEMA regulatory floodplain. The proposed improvements do not propose to alter any natural drainageways. F. Floodplain Regulation Compliance All structures are located outside of any FEMA 100-year floodplain. Therefore, the structures are not subject to any floodplain regulations. G. Modifications of Criteria We are not proposing to request any modifications to the criteria at this time. IV. DRAINAGE FACILITY DESIGN A. General Concept The project is divided into several sub-basins. The proposed drainage will generally follow the existing drainage patterns and flows from west to east. These are generally grouped into a northern and southern basin, with each basin having an outfall into Fossil Creek Reservoir Inlet Ditch. Calculations associated with the sub-basins are included in the Appendices. B. Master Drainage Concepts The intent of the overall detention concept is to provide all detention on-site for the 100-year, 2-hour storm event through various methods of underground storage. Sizing of these detention areas was completed using the Modified FAA Method in accordance with Chapter 6, Section 2.3 of the FCSCM. Tabular data for detention storage is included in the Appendix of this report. Table below summarizes the results. Table 1: Detention Summary Detention Method Outfall Location Receiving Area Detention Required Detention Provided 100-Year Peak Release Rate Oversized Pipe No. 1 N 1.26 AC 6,621 cf 6,676 cf 0.39 cfs Oversized Pipe No. 2 N 0.87 AC 4,640 cf 4,653 cf 0.94 cfs Underground Chambers (1) S 2.66 AC 24,050 cf 25,340 cf (2) 1.17 cfs TOTAL 4.79 AC 35,311 cf 36,669 cf 2.50 cfs (3) 1 Preliminary Drainage Report The Overlander by Balfour Preliminary Drainage Report Page 7 Notes: (1) Final design and layout to be done by ADS and will be provided for review prior to FP approval. (2) Approximate detention storage based on available footprint and previous iterations from ADS. (3) Total tract area is 5.00 acres. A portion of the east side of the site will grade down to the existing maintenance berm along the Fossil Creek Reservoir Ditch and does not include any impervious area but was included in the allowable release rate for the site. C. Specific Details A summary of the surface types and drainage patterns for each of the sub-basins within the site is listed below: Sub-Basin DA-1 (0.30 AC) This sub-basin consists of some historical structures that will remain on-site, sidewalks, a pickleball court, and landscaping/lawn area. This area drains through a bioretention filter and into proposed Detention Pipe No. 1. Sub-Basin DA-2 (0.17 AC) This sub-basin consists of a portion of a historical structure that will remain on-site, sidewalks, and landscaping/lawn area and drains through a bioretention filter to proposed Oversized Pipe No. 1. Sub-Basin DA-3 (0.11 AC) This sub-basin consists of a portion of a historical structure that will remain on-site, sidewalks, and landscaping/lawn area and drains through a bioretention filter to proposed Oversized Pipe No. 1. Sub-Basin DA-4 (0.69 AC) This sub-basin consists of landscaping/lawn area, sidewalks, and rooftop along East Harmony Road and will drain through a filtration pond and into proposed Oversized Pipe No. 1. Sub-Basin DA-5 (0.24 AC) This sub-basin consists of landscaping/lawn area, sidewalks, and rooftop and will drain through a filtration pond and into Oversized Pipe No. 2. Sub-Basin DA-6 (0.73 AC) This sub-basin consists of paved parking areas, sidewalks, rooftop and landscaping and drains through a curb inlet into the proposed Underground Chamber Storage. Sub-Basin DA-7 (0.64 AC) This sub-basin consists of rooftop, a courtyard area and landscaping and drains into landscape inlets, through a bioretention filter and into Oversized Pipe No. 2. Preliminary Drainage Report The Overlander by Balfour Preliminary Drainage Report Page 8 Sub-Basin DA-8 (0.31 AC) This sub-basin consists of rooftop and landscaping/lawn area and drains through landscape inlets directly into the proposed Underground Chamber Storage. Sub-Basin DA-9 (0.27 AC) This sub-basin consists of paved parking areas, sidewalks, rooftop and landscaping and drains through a grate inlet and into the proposed Underground Chamber Storage. Sub-Basin DA-10 (0.50 AC) This sub-basin consists of paved parking areas, sidewalks, rooftop and landscaping and drains through a grate inlet and into the proposed Underground Chamber Storage. Sub-Basin DA-11 (0.71 AC) This sub-basin consists of paved parking areas, sidewalks, rooftop and landscaping and drains through a grate inlet and into the proposed Underground Chamber Storage. Sub-Basin DA-12 (0.13 AC) This sub-basin consists of rooftop and landscaping/lawn area and drains through landscape inlets directly into the proposed Underground Chamber Storage. A copy of the drainage area map is included at the end of the report. Water quality treatment is being provided exclusively through the various LID features on the site, including bioretention filters, filtration ponds, and isolation chambers. Final design and sizing of the LID features will be provided prior to FP approval. A separate grading and erosion control report and plans will be provided in a future submittal. This project shall be in compliance will all erosion control measures and details as required and included in the final plans. V. CONCLUSION A. Compliance with Standards This preliminary drainage report has established that the proposed development is in compliance with City of Fort Collins design criteria through the FCSCM. The drainage design is in compliance with the “East Harmony Portion of the McClellands Creek Master Drainage Plan Update”, by Icon Engineering, August 1999 (Ref. 6). There are no regulatory floodplains within the proposed development. The stormwater management measures proposed shall be in compliance with all applicable State and Federal regulations regarding stormwater discharge. Preliminary Drainage Report The Overlander by Balfour Preliminary Drainage Report Page 9 B. Drainage Concept The drainage design proposed within this report has been shown to provide sufficient detention storage and water quality treatment in order to limit adverse effects of the proposed development up to and including the 100-year, 2-hour storm event in accordance with the FCSCM. VI. REFERENCES 1. Fort Collins Stormwater Criteria Manual, City of Fort Collins, Colorado, as adopted by Ordinance No. 159, 2018, and referenced in City Code Section 26-500. 2. Soils Resource Report for Larimer County Area, Colorado, Natural Resources Conservation Service, United States Department of Agriculture. 3. East Harmony Portion of the McClellands Creek Master Drainage Plan Update, Icon Engineering, August 1999. Preliminary Drainage Report The Overlander by Balfour APPENDIX A PROPOSED SITE PLAN AND DRAINAGE AREA MAP PRELIMINARY DRAINAGE AREA MAP ANDDETENTION STORAGE LOCATIONSTHE OVERLANDER BY BALFOUREX-4 FORT COLLINSCOLORADO020452-01-001 1/26/2022 1" = 50'Phone: (303) 801-2900www.bowman.com1526 Cole Blvd, Suite 100Lakewood, CO 80401REVISIONS© 2021 Bowman Consulting Group Ltd Preliminary Drainage Report The Overlander by Balfour APPENDIX B HYDROLOGY CALCULATIONS Sub-Basin Area (acres)2-yr (cfs) 10-yr (cfs) 100-yr (cfs) Design Point Contributing Basins Area (acres) 2-yr (cfs) 10-yr (cfs) 100-yr (cfs) DA-1 0.30 0.46 0.79 2.02 1 DA-1 0.30 0.46 0.79 2.02 DA-2 0.17 0.24 0.41 1.06 2 DA-2 0.17 0.24 0.41 1.06 DA-3 0.11 0.14 0.23 0.59 3 DA-3 0.11 0.14 0.23 0.59 DA-4 0.69 0.78 1.32 3.38 4 DA-4 0.69 0.78 1.32 3.38 DA-5 0.24 0.32 0.55 1.39 5 DA-5 0.24 0.32 0.55 1.39 DA-6 0.73 1.71 2.93 7.48 6 DA-6 0.73 1.71 2.93 7.48 DA-7 0.64 1.43 2.44 6.24 7 DA-7 0.64 1.43 2.44 6.24 DA-8 0.31 0.42 0.71 1.81 8 DA-8 0.31 0.42 0.71 1.81 DA-9 0.27 0.67 1.14 2.91 9 DA-6, 9 1.01 2.38 4.07 10.38 DA-10 0.50 1.08 1.84 4.70 10 DA-6, 9, 10 1.51 3.46 5.91 15.08 DA-11 0.71 1.59 2.72 6.96 11 DA-6, 9, 10, 11 2.21 5.05 8.63 22.04 DA-12 0.13 0.12 0.21 0.53 12 DA-12 0.13 0.12 0.21 0.53 SUMMARY OF SITE HYDROLOGY DESIGN POINT SUMMARY TABLEBASIN SUMMARY TABLE Designer:ART Company:Bowman Runoff Coeff Total Area (ac) 4.80 Date:1/26/2022 0.20 Composite C 0.65 Project:Balfour 0.95 Location:Fort Collins, CO 0.95 1 From Table 3.2-2 in FCSCM Area (ac) % Area (ac) % Area (ac) % DA-1 0.299 0.163 54.4%0.076 25.5%0.060 20.2% 0.54 DA-2 0.171 0.103 60.4%0.049 28.9%0.018 10.6% 0.50 DA-3 0.105 0.069 66.2%0.014 13.8%0.021 20.0% 0.45 DA-4 0.688 0.509 74.0%0.087 12.7%0.092 13.3% 0.40 DA-5 0.237 0.151 63.7%0.028 11.9%0.058 24.4% 0.47 DA-6 0.734 0.128 17.4%0.330 45.0%0.276 37.5% 0.82 DA-7 0.637 0.138 21.7%0.076 11.9%0.423 66.4% 0.79 DA-8 0.312 0.201 64.3%0.016 5.2%0.095 30.5% 0.47 DA-9 0.274 0.036 13.0%0.209 76.4%0.029 10.7% 0.85 DA-10 0.498 0.127 25.5%0.258 51.7%0.114 22.8% 0.76 DA-11 0.707 0.150 21.2%0.325 46.0%0.232 32.8% 0.79 DA-12 0.133 0.112 83.9%0.002 1.4%0.020 14.7% 0.32 Lawns, Sandy Soil Summary POST-DEVELOPMENT C VALUES Sub-Basin Name Area (ac) Composite Runoff Coefficient (C) Lawns Asphalt, Concrete Roof Global Parameters1 Land Use Roof Asphalt, Concrete Designer:ART Company:Bowman Date:1/26/2022 Project:Balfour Location:Fort Collins, CO Basin Area Coeff Tc C*A I Cf Q Tc Sum Area Sum C*A I Cf Q Design (ac) C (min) (ac)(in/hr)(cfs)(min) (ca) (ac)(in/hr) (cfs) DA-1 0.299 0.54 5.00 0.16 2.85 1.00 0.46 1 DA-1 5.00 0.30 0.16 2.85 1.00 0.46 DA-2 0.171 0.50 5.00 0.08 2.85 1.00 0.24 2 DA-2 5.00 0.17 0.08 2.85 1.00 0.24 DA-3 0.105 0.45 5.00 0.05 2.85 1.00 0.14 3 DA-3 5.00 0.11 0.05 2.85 1.00 0.14 DA-4 0.688 0.40 5.00 0.27 2.85 1.00 0.78 4 DA-4 5.00 0.69 0.27 2.85 1.00 0.78 DA-5 0.237 0.47 5.00 0.11 2.85 1.00 0.32 5 DA-5 5.00 0.24 0.11 2.85 1.00 0.32 DA-6 0.734 0.82 5.00 0.60 2.85 1.00 1.71 6 DA-6 5.00 0.73 0.60 2.85 1.00 1.71 DA-7 0.637 0.79 5.00 0.50 2.85 1.00 1.43 7 DA-7 5.00 0.64 0.50 2.85 1.00 1.43 DA-8 0.312 0.47 5.00 0.15 2.85 1.00 0.42 8 DA-8 5.00 0.31 0.15 2.85 1.00 0.42 DA-9 0.274 0.85 5.00 0.23 2.85 1.00 0.67 9 DA-6, 9 5.00 1.01 0.83 2.85 1.00 2.38 DA-10 0.498 0.76 5.00 0.38 2.85 1.00 1.08 10 DA-6, 9, 10 5.00 1.51 1.21 2.85 1.00 3.46 DA-11 0.707 0.79 5.00 0.56 2.85 1.00 1.59 11 DA-6, 9, 10, 11 5.00 2.21 1.77 2.85 1.00 5.05 DA-12 0.133 0.32 5.00 0.04 2.85 1.00 0.12 12 DA-12 5.00 0.13 0.04 2.85 1.00 0.12 STORM DRAINAGE SYSTEM DESIGN - 2-YEAR DESIGN STORM DESIGN POINT STREET/ CONTRIBUTING BASINS DIRECT RUNOFF TOTAL RUNOFF Designer:ART Company:Bowman Date:1/26/2022 Project:Balfour Location:Fort Collins, CO Basin Area Coeff Tc C*A I Cf Q Tc Sum Area Sum C*A I Cf Q Design (ac) C (min) (ac)(in/hr)(cfs)(min) (ca) (ac)(in/hr)(cfs) DA-1 0.299 0.54 5.00 0.16 4.87 1.00 0.79 1 DA-1 5.00 0.30 0.16 4.87 1.00 0.79 DA-2 0.171 0.50 5.00 0.08 4.87 1.00 0.41 2 DA-2 5.00 0.17 0.08 4.87 1.00 0.41 DA-3 0.105 0.45 5.00 0.05 4.87 1.00 0.23 3 DA-3 5.00 0.11 0.05 4.87 1.00 0.23 DA-4 0.688 0.40 5.00 0.27 4.87 1.00 1.32 4 DA-4 5.00 0.69 0.27 4.87 1.00 1.32 DA-5 0.237 0.47 5.00 0.11 4.87 1.00 0.55 5 DA-5 5.00 0.24 0.11 4.87 1.00 0.55 DA-6 0.734 0.82 5.00 0.60 4.87 1.00 2.93 6 DA-6 5.00 0.73 0.60 4.87 1.00 2.93 DA-7 0.637 0.79 5.00 0.50 4.87 1.00 2.44 7 DA-7 5.00 0.64 0.50 4.87 1.00 2.44 DA-8 0.312 0.47 5.00 0.15 4.87 1.00 0.71 8 DA-8 5.00 0.31 0.15 4.87 1.00 0.71 DA-9 0.274 0.85 5.00 0.23 4.87 1.00 1.14 9 DA-6, 9 5.00 1.01 0.83 4.87 1.00 4.07 DA-10 0.498 0.76 5.00 0.38 4.87 1.00 1.84 10 DA-6, 9, 10 5.00 1.51 1.21 4.87 1.00 5.91 DA-11 0.707 0.79 5.00 0.56 4.87 1.00 2.72 11 DA-6, 9, 10, 11 5.00 2.21 1.77 4.87 1.00 8.63 DA-12 0.133 0.32 5.00 0.04 4.87 1.00 0.21 12 DA-12 5.00 0.13 0.04 4.87 1.00 0.21 STORM DRAINAGE SYSTEM DESIGN - 10-YEAR DESIGN STORM DESIGN POINT STREET/ CONTRIBUTING BASINS DIRECT RUNOFF TOTAL RUNOFF Designer:ART Company:Bowman Date:1/26/2022 Project:Balfour Location:Fort Collins, CO Basin Area Coeff Tc C*A I Cf Q Tc Sum Area Sum C*A I Cf Q Design (ac) C (min) (ac)(in/hr)(cfs)(min) (ac) (ac)(in/hr)(cfs) DA-1 0.299 0.54 5.00 0.16 9.95 1.25 2.02 1 DA-1 5.00 0.30 0.16 9.95 1.25 2.02 DA-2 0.171 0.50 5.00 0.08 9.95 1.25 1.06 2 DA-2 5.00 0.17 0.08 9.95 1.25 1.06 DA-3 0.105 0.45 5.00 0.05 9.95 1.25 0.59 3 DA-3 5.00 0.11 0.05 9.95 1.25 0.59 DA-4 0.688 0.40 5.00 0.27 9.95 1.25 3.38 4 DA-4 5.00 0.69 0.27 9.95 1.25 3.38 DA-5 0.237 0.47 5.00 0.11 9.95 1.25 1.39 5 DA-5 5.00 0.24 0.11 9.95 1.25 1.39 DA-6 0.734 0.82 5.00 0.60 9.95 1.25 7.48 6 DA-6 5.00 0.73 0.60 9.95 1.25 7.48 DA-7 0.637 0.79 5.00 0.50 9.95 1.25 6.24 7 DA-7 5.00 0.64 0.50 9.95 1.25 6.24 DA-8 0.312 0.47 5.00 0.15 9.95 1.25 1.81 8 DA-8 5.00 0.31 0.15 9.95 1.25 1.81 DA-9 0.274 0.85 5.00 0.23 9.95 1.25 2.91 9 DA-6, 9 6.12 1.01 0.83 9.95 1.25 10.38 DA-10 0.498 0.76 5.00 0.38 9.95 1.25 4.70 10 DA-6, 9, 10 7.81 1.51 1.21 9.95 1.25 15.08 DA-11 0.707 0.79 5.00 0.56 9.95 1.25 6.96 11 DA-6, 9, 10, 11 8.98 2.21 1.77 9.95 1.25 22.04 DA-12 0.133 0.32 5.00 0.04 9.95 1.25 0.53 12 DA-12 5.00 0.13 0.04 9.95 1.25 0.53 STORM DRAINAGE SYSTEM DESIGN - 100-YEAR DESIGN STORM DESIGN POINT STREET/ CONTRIBUTING BASINS DIRECT RUNOFF TOTAL RUNOFF Preliminary Drainage Report The Overlander by Balfour APPENDIX C PRELIMINARY DETENTION CALCULATIONS Preliminary Detention Calculations Oversized Storm Sewer Pipe Contributing Sub-Basins: DA-1, DA-2, DA-3 and DA-4 Designer:ART Company:BOWMAN Vi = C*I*A(60T)SUB-BASIN AREA (AC) C VALUE Date:1/26/2022 Vo = Qout(60T)DA-1 0.299 0.54 Project:Balfour Vs = Vi - Vo DA-2 0.171 0.50 Location:Ft Collins, CO DA-3 0.105 0.45 DA-4 0.688 0.40 BASIN AREA (AC)1.263 COMPOSITE C 0.45 FREQ FACTOR (Cf)1.25 C VALUE USED 0.56 100-YR RUNOFF AREA INFLOW ALLOWABLE OUTFLOW REQUIRED DURATION (T) INTENSITY (I) COEFF (C) (A) VOLUME (Vi)DISCHARGE (Qout)VOLUME (Vo)STORAGE (Vs) MIN IN/HR AC CF CFS CF CF 5 9.95 0.56 1.263 2,125 0.39 117 2,008 10 7.72 0.56 1.263 3,297 0.39 234 3,063 15 6.52 0.56 1.263 4,177 0.39 351 3,826 20 5.60 0.56 1.263 4,783 0.39 468 4,315 25 4.98 0.56 1.263 5,317 0.39 585 4,732 30 4.52 0.56 1.263 5,791 0.39 702 5,089 35 4.08 0.56 1.263 6,098 0.39 819 5,279 40 3.74 0.56 1.263 6,389 0.39 936 5,453 45 3.46 0.56 1.263 6,649 0.39 1,053 5,596 50 3.23 0.56 1.263 6,897 0.39 1,170 5,727 55 3.03 0.56 1.263 7,117 0.39 1,287 5,830 60 2.86 0.56 1.263 7,328 0.39 1,404 5,924 65 2.71 0.56 1.263 7,523 0.39 1,521 6,002 70 2.59 0.56 1.263 7,743 0.39 1,638 6,105 75 2.48 0.56 1.263 7,943 0.39 1,755 6,188 80 2.38 0.56 1.263 8,131 0.39 1,872 6,259 85 2.29 0.56 1.263 8,313 0.39 1,989 6,324 90 2.21 0.56 1.263 8,494 0.39 2,106 6,388 95 2.13 0.56 1.263 8,642 0.39 2,223 6,419 100 2.06 0.56 1.263 8,797 0.39 2,340 6,457 105 2.00 0.56 1.263 8,968 0.39 2,457 6,511 110 1.94 0.56 1.263 9,113 0.39 2,574 6,539 115 1.88 0.56 1.263 9,233 0.39 2,691 6,542 120 1.84 0.56 1.263 9,429 0.39 2,808 6,621 6,621 0.152 340 59.75 60 6,676 0.153 REQUIRED PIPE DIAMETER (IN): SELECTED PIPE DIAMETER (IN): PROVIDED STORAGE (CF): PROVIDED STORAGE (AC-FT): COMPOSITE RUNOFF COEFFICIENT REQUIRED STORAGE (CF): REQUIRED STORAGE (AC-FT): TOTAL PIPE LENGTH (LF): Preliminary Detention Calculations Oversized Storm Sewer Pipe Contributing Sub-Basins: DA-5 and DA-7 Designer:ART Company:BOWMAN Vi = C*I*A(60T)SUB-BASIN AREA (AC) C VALUE Date:1/26/2022 Vo = Qout(60T)DA-5 0.237 0.47 Project:Balfour Vs = Vi - Vo DA-7 0.637 0.79 Location:Ft Collins, CO BASIN AREA (AC)0.874 COMPOSITE C 0.70 FREQ FACTOR (Cf)1.25 C VALUE USED 0.88 100-YR RUNOFF AREA INFLOW ALLOWABLE OUTFLOW REQUIRED DURATION (T) INTENSITY (I) COEFF (C) (A) VOLUME (Vi)DISCHARGE (Qout)VOLUME (Vo)STORAGE (Vs) MIN IN/HR AC CF CFS CF CF 5 9.95 0.88 0.874 2,293 0.94 282 2,011 10 7.72 0.88 0.874 3,559 0.94 564 2,995 15 6.52 0.88 0.874 4,508 0.94 846 3,662 20 5.60 0.88 0.874 5,163 0.94 1,128 4,035 25 4.98 0.88 0.874 5,739 0.94 1,410 4,329 30 4.52 0.88 0.874 6,251 0.94 1,692 4,559 35 4.08 0.88 0.874 6,583 0.94 1,974 4,609 40 3.74 0.88 0.874 6,896 0.94 2,256 4,640 45 3.46 0.88 0.874 7,177 0.94 2,538 4,639 50 3.23 0.88 0.874 7,445 0.94 2,820 4,625 55 3.03 0.88 0.874 7,682 0.94 3,102 4,580 60 2.86 0.88 0.874 7,910 0.94 3,384 4,526 65 2.71 0.88 0.874 8,120 0.94 3,666 4,454 70 2.59 0.88 0.874 8,357 0.94 3,948 4,409 75 2.48 0.88 0.874 8,574 0.94 4,230 4,344 80 2.38 0.88 0.874 8,777 0.94 4,512 4,265 85 2.29 0.88 0.874 8,973 0.94 4,794 4,179 90 2.21 0.88 0.874 9,169 0.94 5,076 4,093 95 2.13 0.88 0.874 9,328 0.94 5,358 3,970 100 2.06 0.88 0.874 9,496 0.94 5,640 3,856 105 2.00 0.88 0.874 9,680 0.94 5,922 3,758 110 1.94 0.88 0.874 9,837 0.94 6,204 3,633 115 1.88 0.88 0.874 9,966 0.94 6,486 3,480 120 1.84 0.88 0.874 10,178 0.94 6,768 3,410 4,640 0.107 237 59.91 60 4,653 0.107PROVIDED STORAGE (AC-FT): COMPOSITE RUNOFF COEFFICIENT PROVIDED STORAGE (CF): SELECTED PIPE DIAMETER (IN): REQUIRED PIPE DIAMETER (IN): TOTAL PIPE LENGTH (3-BARREL) (LF): REQUIRED STORAGE (CF): REQUIRED STORAGE (AC-FT): Preliminary Detention Calculations Underground Storage - ADS Stormtech with Isolation Chambers Contributing Sub-Basins: DA-6, DA-8, DA-9, DA-10, DA-11 and DA-12 Designer:ART Company:BOWMAN Vi = C*I*A(60T)SUB-BASIN AREA (AC) C VALUE Date:1/26/2022 Vo = Qout(60T)DA-6 0.734 0.82 Project:Balfour Vs = Vi - Vo DA-8 0.312 0.47 Location:Ft Collins, CO DA-9 0.274 0.85 DA-10 0.498 0.76 BASIN AREA (AC)2.658 DA-11 0.707 0.79 COMPOSITE C 0.74 DA-12 0.133 0.32 FREQ FACTOR (Cf)1.25 C VALUE USED 0.92 100-YR RUNOFF AREA INFLOW ALLOWABLE OUTFLOW REQUIRED DURATION (T) INTENSITY (I) COEFF (C) (A) VOLUME (Vi)DISCHARGE (Qout)VOLUME (Vo)STORAGE (Vs) MIN IN/HR AC CF CFS CF CF 5 9.95 0.92 2.658 7,317 1.17 351 6,966 10 7.72 0.92 2.658 11,354 1.17 702 10,652 15 6.52 0.92 2.658 14,384 1.17 1,053 13,331 20 5.60 0.92 2.658 16,472 1.17 1,404 15,068 25 4.98 0.92 2.658 18,311 1.17 1,755 16,556 30 4.52 0.92 2.658 19,943 1.17 2,106 17,837 35 4.08 0.92 2.658 21,002 1.17 2,457 18,545 40 3.74 0.92 2.658 22,002 1.17 2,808 19,194 45 3.46 0.92 2.658 22,899 1.17 3,159 19,740 50 3.23 0.92 2.658 23,752 1.17 3,510 20,242 55 3.03 0.92 2.658 24,510 1.17 3,861 20,649 60 2.86 0.92 2.658 25,238 1.17 4,212 21,026 65 2.71 0.92 2.658 25,907 1.17 4,563 21,344 70 2.59 0.92 2.658 26,665 1.17 4,914 21,751 75 2.48 0.92 2.658 27,356 1.17 5,265 22,091 80 2.38 0.92 2.658 28,003 1.17 5,616 22,387 85 2.29 0.92 2.658 28,628 1.17 5,967 22,661 90 2.21 0.92 2.658 29,253 1.17 6,318 22,935 95 2.13 0.92 2.658 29,760 1.17 6,669 23,091 100 2.06 0.92 2.658 30,297 1.17 7,020 23,277 105 2.00 0.92 2.658 30,886 1.17 7,371 23,515 110 1.94 0.92 2.658 31,386 1.17 7,722 23,664 115 1.88 0.92 2.658 31,797 1.17 8,073 23,724 120 1.84 0.92 2.658 32,474 1.17 8,424 24,050 24,050 0.552 25,340 0.582 COMPOSITE RUNOFF COEFFICIENT REQUIRED STORAGE (CF): REQUIRED STORAGE (AC-FT): EST. PROVIDED STORAGE (CF) EST. PROVIDED STORAGE (AC-FT): PRELIMINARY DRAINAGE AREA MAP ANDDETENTION STORAGE LOCATIONSTHE OVERLANDER BY BALFOUREX-4 FORT COLLINSCOLORADO020452-01-001 1/26/2022 1" = 50'Phone: (303) 801-2900www.bowman.com1526 Cole Blvd, Suite 100Lakewood, CO 80401REVISIONS© 2021 Bowman Consulting Group Ltd