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Home My WebLink AboutTHE SAVOY - FDP230012 - SUBMITTAL DOCUMENTS - ROUND 3 - DRAINAGE REPORT FINAL DRAINAGE REPORT THE SAVOY FORT COLLINS, COLORADO SEPTEMBER 20, 2023 NORTHERNENGINEERING.COM 970.221.4158 FORT COLLINS GREELEY This Drainage Report is consciously provided as a PDF. Please consider the environment before printing this document in its entirety. When a hard copy is necessary, we recommend double-sided printing. NORTHERNENGINEERING.COM | 970.221.4158 FINAL DRAINAGE REPORT: THE SAVOY (514-003) FORT COLLINS | GREELEY COVER LETTER September 20, 2023 City of Fort Collins Stormwater Utility 700 Wood Street Fort Collins, CO 80526 RE: FINAL DRAINAGE REPORT FOR THE SAVOY (514-003) Dear Staff: Northern Engineering is pleased to submit this Final Drainage Report for your review. This report accompanies the Preliminary Development Review submittal for The Savoy. 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 The Savoy multi-family project. We understand review by the City of Fort Collins is to assure general compliance with standardized criteria contained in the FCSCM. If you should have any questions as you review this report, please feel free to contact us. Sincerely, NORTHERN ENGINEERING SERVICES, INC. BLAINE MATHISEN, PE Project Manager NORTHERNENGINEERING.COM | 970.221.4158 FINAL DRAINAGE REPORT: PROJECT NAME FORT COLLINS | GREELEY TABLE OF CONTENTS TABLE OF CONTENTS GENERAL LOCATION AND DESCRIPTION .......................................................... 1 DRAIN BASINS AND SUB-BASINS ..................................................................... 3 DRAINAGE DESIGN CRITERIA .......................................................................... 4 DRAINAGE FACILITY DESIGN ........................................................................... 8 CONCLUSIONS ............................................................................................ 10 REFERENCES .............................................................................................. 11 TABLES AND FIGURES FIGURE 1 - VICINITY MAP ..................................................................................................1 FIGURE 2 - AERIAL PHOTO ................................................................................................2 FIGURE 3 - FIRMETTE MAP 08069C0994F .........................................................................3 TABLE 1 - LE FEVER INLET SUMMARY ..............................................................................6 TABLE 2 - LID SUMMARY TABLE ..................................................................................... 10 APPENDICES APPENDIX A – HYDROLOGIC COMPUTATIONS APPENDIX B – HYDRAULIC CALCULATIONS APPENDIX C –WATER QUALITY/LID COMPUTATIONS APPENDIX D – EROSION CONTROL REPORT APPENDIX E – EXCERPTS FROM PREVIOUS REPORTS AND USDA SOILS REPORT MAP POCKET DR1 – DRAINAGE EXHIBIT NORTHERNENGINEERING.COM | 970.221.4158 FINAL DRAINAGE REPORT: THE SAVOY FORT COLLINS | GREELEY 1 | 11 GENERAL LOCATION AND DESCRIPTION A. LOCATION Vicinity Map The Savoy 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 project site (refer to Figure 1) is bordered to the west, east, and south by other multi-family complexes and to the north by a vacant lot. There are no major drainageways located adjacent to the project site. B. DESCRIPTION OF PROPERTY The Savoy project is comprised of ±8.34 acres plus some additional right-of-way dedications. The site is currently vacant with native grasses. The existing on-site runoff generally drains from the north-to-south across flat grades (e.g., <2.00%) into either Brookfield Drive or Precision Drive. Once runoff has entered the right-of- way, it is routed to a 15' Type R inlet at the northwest corner of the Brookfield Drive and Precision Drive intersection. From there, the drainage is routed to Detention Pond A – Brookfield via a series of RCP pipes. The Savoy is proposing to alter this existing drainage pattern to align with the master planning put forth with the Banner Medical Center and Brookfield projects. The site will be split, with roughly 5.94 acres routed north to the ODP Pond, associated with Banner Medical Center. The remaining runoff (3.30 acres) will be routed to Detention Pond A – Brookfield. Additional information regarding these changes will be Figure 1 - Vicinity map NORTHERNENGINEERING.COM | 970.221.4158 FINAL DRAINAGE REPORT: THE SAVOY FORT COLLINS | GREELEY 2 | 11 provided in the following sections. In addition, excerpts from both drainage reports have been provided in Appendix F for further clarification. According to the United States Department of Agriculture (USDA) Natural Resources Conservation Service (NRCS) Soil Survey website: http://websoilsurvey.nrcs.usda.gov/app/WebSoilSurvey.aspx), the site consists entirely of Nunn clay loam (Hydrologic Soil Group C). According to “Geological and Preliminary Geotechnical Investigation – The Savoy” dated November 17, 2021 by CTL Thompson shows that groundwater at this location is roughly 20’ deep. There is no major drainageway within or adjacent to the project site. However, Fossil Creek Reservoir Inlet Ditch runs adjacent to the ODP Pond and Detention Pond A – Brookfield. The proposed development will consist of eight multi-family buildings containing a total of 240 units. Other proposed improvements include a clubhouse, new concrete drive aisles, new sidewalks, and new landscaping. The proposed land use is multi-family dwellings. This use is permitted in the Harmony Corridor District (H-C). Figure 2 - Aerial Photo NORTHERNENGINEERING.COM | 970.221.4158 FINAL DRAINAGE REPORT: THE SAVOY FORT COLLINS | GREELEY 3 | 11 C. FLOODPLAIN The subject property is not located in a FEMA regulatory floodplain. In particular, the project site is not located within a FEMA-designated 100-year floodplain per Map Number 08069CO994F (Effective date: December 19, 2006). Additionally, the project site is not located in a City of Fort Collins regulated floodplain. DRAIN BASINS AND SUB-BASINS A. MAJOR BASIN DESCRIPTION The Savoy Project is located within the City of Fort Collins McClelland's major drainage basin. Specifically, the project site is situated in the eastern third of this major drainage basin. This basin is located in southeast Fort Collins and has a drainage area of approximately 3.4 square miles and includes drainage originating near the College and Harmony intersection and draining through the Oakridge, Willow Springs, Stetson Creek, and Harvest Park developments. The McClelland's major drainage basin generally drains from northwest to southeast. Runoff from the major drainage basin drains to the Fossil Creek Reservoir. Figure 3 - FIRMette Map 08069C0994F NORTHERNENGINEERING.COM | 970.221.4158 FINAL DRAINAGE REPORT: THE SAVOY FORT COLLINS | GREELEY 4 | 11 B. SUB-BASIN DESCRIPTION There are two separate outfalls for the project. However, both outfalls are routed to the Fossil Creek Reservoir Inlet Ditch. The existing subject site can be defined with one (1) major sub-basins that encompasses the entire project site and the adjacent ROW. The existing site runoff generally drains from northwest to southeast and into either Precision Drive or Brookfield Drive. An existing 15' Type R inlet is routing all the runoff to Detention Pond A – Brookfield via a series of RCP pipes. The project site does not receive runoff from contiguous off-site properties. DRAINAGE DESIGN CRITERIA A. ORIGINAL PROVISIONS AND PREVIOUS STUDIES There are no optional provisions outside of the FCSCM proposed with The Savoy. The Savoy project site has been included in several drainage studies for this area. The "East Harmony Portion of McClelland's Creek Master Drainage Plan Update" (ICON Engineering, Inc., August 1999), "Final Drainage Report for Brookfield" (TST, Inc. Consulting Engineers, December 2001), "Final Drainage and Erosion Control Report Banner Health Medical Campus" (Northern Engineering, September 2013), "Final Drainage and Erosion Control Report for Presidio Apartments" (Northern Engineering, December 2009), and "Final Drainage Report for Milestone Apartments" (Northern Engineering, May 2014). All these reports were reviewed before the preparation of this report. It is noted, City Stormwater previously agreed the off-site ODP Pond and Detention Pond A – Brookfield were to provide all water quality and detention requirements for The Savoy project site. Per "Final Drainage Report and Erosion Control Report Banner Health Medical Campus," the ODP Pond is responsible for detaining 5.90 acres of The Savoy project site. Basin O-2 from the Banner Health Medical Campus Master Drainage Exhibit depicts this. During the design of the ODP Pond, Basin O-2 was assumed to be 85% impervious. Per "Final Drainage Report for Brookfield," Detention Pond A – Brookfield was designed to detain and treat 9.93 acres, with an assumed impervious of 85%, of The Savoy project site. Basins D9 and D5 from the "Final Drainage Report for Brookfield" are the basins associated with The Savoy project site. The "Final Drainage and Erosion Control Report Banner Health Medical Campus" and "Final Drainage Report for Brookfield" contradict one another regarding which pond is responsible for detaining and treating The Savoy site. Banner Health Medical Campus specifies the ODP Pond, north of the project site, is responsible for detaining and treating 5.90 acres of The Savoy project site. However, Brookfield specifies Detention Pond A – Brookfield is responsible for detaining and treating 9.93 acres of the project site and adjacent rights-of- way. Because "Final Drainage and Erosion Control Report Banner Health Medical Campus" was published after "Final Drainage Report for Brookfield," The Savoy will be relying on the ODP Pond to detain 5.94 acres of the project site, while the remaining portion of the site is routed towards Detention Pond A – Brookfield for detention and traditional water quality. After reviewing all the reports mentioned above, it became clear that The Savoy would be responsible for providing on-site Low Impact Development (LID) methods to treat stormwater quality to bring the site into compliance with FCSCM. LID will be provided via NORTHERNENGINEERING.COM | 970.221.4158 FINAL DRAINAGE REPORT: THE SAVOY FORT COLLINS | GREELEY 5 | 11 Stormtech isolator chambers and a rain garden. Additional information on LID sizing will be provided below. Please refer to Appendix F for excerpts from previous drainage studies. Complete copies can be provided at request. B. STORMWATER MANAGEMENT STRATEGY The overall stormwater management strategy employed with The Savoy utilizes the "Four Step Process" to minimize adverse impacts of urbanization on receiving waters. The following is a description of how the proposed development has incorporated each step. Step 1 – Employ Runoff Reduction Practices. Several techniques have been utilized with the proposed development to facilitate the reduction of runoff peaks, volumes, and pollutant loads as the site is developed from the current use of implementing multiple Low Impact Development (LID) strategies, including: · Providing vegetated open areas throughout the site to reduce the overall impervious area and to minimize directly connected impervious areas. · Routing runoff through the drain rock within the Stormtech system and rain garden to increase concentration-time and promote infiltration. Step 2 – Implement BMPs that Provide a Water Quality Capture Volume (WQCV) with Slow Release. The efforts taken in Step 1 will help to minimize excess runoff from frequently occurring storm events; however, urban development of this intensity will still have stormwater runoff leaving the site. Water quality treatment will occur in the Stomtech Isolator chambers on the north side of the site and a rain garden on the site's south side. Step 3 – Stabilize Drainageways. As stated in Section I. B. 5. above, there is no major drainageway adjacent to the subject site. While this step may not seem applicable to The Savoy, the proposed project indirectly helps achieve stabilized drainageways, nonetheless. Once again, site selection has a positive effect on stream stabilization. Developing an infill site with existing stormwater infrastructure, combined with LID strategies, reduces the likelihood of bed and bank erosion. Furthermore, this project will pay one-time stormwater development fees and ongoing monthly stormwater utility fees, both of which help achieve Citywide drainageway stability. Step 4 – Implement Site Specific and Other Source Control BMPs. This step typically applies to industrial and commercial developments. However, localized trash enclosures with gates will reduce the potential impacts of garbage making its way downstream. C. DEVELOPMENT CRITERIA REFERENCE AND CONSTRAINTS The subject property is part of an Overall Development Plan (ODP) drainage study or similar "development/project" drainage master plan. Refer to Section III. A. and Appendix F for a list of all previous drainage studies that include The Savoy project site. The site plan is constrained on all four sides by public streets. It is bound by Cinequefoil Lane to the west, Le Fever Drive to the north, Brookfield Drive to the east, and Precision Drive to the south. NORTHERNENGINEERING.COM | 970.221.4158 FINAL DRAINAGE REPORT: THE SAVOY FORT COLLINS | GREELEY 6 | 11 D. HYDROLOGICAL CRITERIA The City of Fort Collins Rainfall Intensity-Duration-Frequency Curves, as depicted in Figure 3.4-1 of the FCSCM, serves as the source for all hydrologic computations associated with The Savoy development. Tabulated data contained in Table 3.4-1 has been utilized for Rational Method runoff calculations. The Rational Method has been employed to compute stormwater runoff utilizing coefficients contained in Tables 3.2-1 and 3.2-2 of the FCSCM. The Rational Formula-based Federal Aviation Administration (FAA) procedure has not been utilized for detention storage calculations since detention is provided off-site at the ODP Pond or Detention Pond A – Brookfield. Three separate design storms have been utilized to address distinct drainage scenarios. The first event analyzed is the "Minor" or "Initial" Storm, with a 2-year recurrence interval. The second event considered is the "Major Storm," which has a 100-year recurrence interval. The final event analyzed was the 10-year recurrence interval for comparative analysis only. E. HYDRAULIC CRITERIA The drainage facilities proposed with The Savoy project are designed in accordance with criteria outlined in the FCSCM and/or the Mile High Flood District's (UDFCD) Urban Storm Drainage Criteria Manual. Inlets A3-2 and A3-1.1 were designed using FCSCM. Both inlets are sized to be 10’ Type R inlets. Below is a summary of the inlet required capacities and designed capacities. Inlet ID Required 100-yr capacity (CFS) Designed capacity (cfs) A3-1.1 3.8 9.7 A3-2 7.6 9.7 Table 1 - Le Fever Inlet Summary Inlets A3-2 and A3-1.1 are located in Le Fever Drive which is classified as Collector Local. Runoff encroachment was verified to meet requirments set forth in Chapter 9 Section 2.1 of FCSCM. Per “Table 2.1-1:Street Encroachment Standards for the Minor (2-year) Storm” the minor storm has a maximum encroachment of no-curb-overtopping and flow may spread to the crown of street. Per “Table 2.1-2:Street Encroachment Standards for the Major (100-year)” the most restrictive maximum encroachment is based on depth for Le Fever Drive, which is 12” at flowline for the major event. For a detailed summary and comprehensive calculation see Appendix B “Le Fever Street Capactiy”. Additionally, elevation lables have been included on the Drainage Exhibit at Inlet A3-2, Inlet A3-1.1, the crown, and the adjacant utility easement for additional clarity. During the minor event Le Fever Drive has a capacity of 11.8 cfs which is 6.5 times greater than the required 1.8 cfs. During the major event Le Fever Drive has a max capacity of 107.1 cfs which is 14 times greater than the required 7.6 cfs. Therefore, it has been shown that Le Fever Drive meets all the requirments set forth by the FCSCM. Refer to Appendix B for additional information. NORTHERNENGINEERING.COM | 970.221.4158 FINAL DRAINAGE REPORT: THE SAVOY FORT COLLINS | GREELEY 7 | 11 As stated in Section I. C. 1. above, the subject property is not located within a FEMA or a City of Fort Collins designated floodplain. Storm drains are designed to convey 100-year flow rates. F. FLOODPLAIN REGULATIONS COMPLIANCE As stated in Section I. C. 1. above, the subject property is not located within a FEMA or a City of Fort Collins designated floodplain. G. MODIFICATIONS OF CRITERIA No formal modifications are requested at this time. However, as previously stated, The Savoy will not provide detention on-site. Two regional detention ponds will provide detention and extended water quality for a portion of the runoff. H. CONFORMANCE WITH WATER QUALITY TREATMENT CRITERIA City Code requires 100% of runoff from a project site to receive water quality treatment. This project proposes to provide water quality treatment by using an underground infiltration gallery (aka – underground chambers) located at the north end of the project and a rain garden at the south end of the site. Stormtech isolator chambers are considered a LID treatment method. Due to the physical constraints associated with an infill project of this nature and the prohibition of providing water quality facilities within the public right-of-way, some areas around the perimeter of the project cannot be captured and adequately routed to either the rain garden or the Stormtech chambers. However, these areas have been accounted for within the ODP Pond and Detention Pond A – Brookfield to receive water quality. Additionally, when the ODP Pond was installed, it did meet the current LID requirements set forth by the FCSCM at the time of approvals. The ODP Pond has a sand filter along the entire length of the bottom. However, the ODP Pond is also used for detention, and thus that is why it no longer meets current LID standards. I. CONFORMANCE WITH LOW IMPACT DEVELOPMENT (LID) The project site will conform with the requirement to treat a minimum of 75% of the site using a LID technique. Please see Appendix C for LID design information, table, and exhibit(s). As shown in the LID table provided in the appendix, 75.03% of the proposed site, including adjacent right-of-way, will receive LID Treatment, which meets the minimum required. J. SIZING OF LID FACILITIES The Stormtech isolator chambers were sized by determining the required water quality capture volume (WQCV) for Major Basin A. A 12-hour drain time was used in this calculation. Once the WQCV was identified, the minimum number of vaults needed to achieve this volume was calculated. The required WQCV for Major Basin A is 5,343 cf. The number of MC-7200 chambers required is 23. However, in order to simplify the installation process 24 MC-7200 units have been specified, which provides 6,148 cf of WQCV. Each isolator row will have an inspection port and a Nyloplast basin at the end for easy maintenance and cleanout. NORTHERNENGINEERING.COM | 970.221.4158 FINAL DRAINAGE REPORT: THE SAVOY FORT COLLINS | GREELEY 8 | 11 Additionally, the major events will bypass the isolator rows via a manifold system. Please refer to the Subgrade Plan within the Utility Plans for additional information. The rain garden was sized by determining the required water quality capture volume for Major Basin B. The Mile High Flood District's criteria and online tools yielded a required WQCV of 1,843 cf. The Savoy proposes installing a rain garden with a total WQCV of 1,903 cf. A volume calculation utilizing the WQ flow rate into the chamber and the calculated release rate through the fabric was completed. The number of chambers has been increased as needed to confirm the resulting volume is provided within the empty volume of the underground chambers. This is intended to ensure the chambers do not become overwhelmed in the water quality storm event before "discharging" flows into the surrounding aggregates. For additional clarification, please refer to Appendix C. DRAINAGE FACILITY DESIGN A. GENERAL CONCEPT The main objective of The Savoy drainage design is to bring the project site into compliance with existing drainage studies the site is associated with. No notable off-site runoff passes directly through the project site. A list of tables and figures used within this report can be found in the Table of Contents at the front of this document. The tables and figures are located within the sections to which the content best applies. Drainage for the project site has been analyzed using four (4) Major Drainage Basins, designated as Basins A, B, ODP, and BF. Basins A, B, and ODP all have associated sub-basins. The drainage patterns anticipated for the basins are further described below. Major Basin A Major Basin A has twelve (12) sub-basins (A1-A12) associated with the north side of The Savoy site. Major Basin A has a total area of 4.67 acres and an impervious value of 80%. All runoff generated within Major Basin A is routed via a combination of overland flow, storm line conveyance, and curb and gutter routing to the Stormtech system. Major Basin A will receive LID treatment within the Stormtech system. Once treated or any event greater than the WQ event, the runoff will be routed via storm pipes to the ODP Pond for detention. Major Basin B Major Basin B has six (6) sub-basins (B1-B6) and is associated with the south side of The Savoy site. Major Basin B has a total area of 2.27 acres and an impervious value of 72%. All runoff generated within Major Basin B is routed via a combination of overland flow, storm line conveyance, and curb and gutter routing to the rain garden at the southeast corner of the site. An overflow inlet will be set at the WQCV water surface elevation (WSEL) to allow storm events larger than the WQ event to bypass the rain garden without draining across public sidewalks. All runoff from Major Basin B will be routed to the existing 15' Type R Inlet at the northwest corner of the Brookfield Drive and Precision Drive intersection via an existing 36” RCP stub into the back of the inlet. This existing inlet has been acting as the "interim" outfall location for the entire Savoy property. Once runoff has been routed to the existing Type R inlet, it is conveyed to Detention Pond A – Brookfield via a series of RCP pipes gradually upsized as it moves downstream. NORTHERNENGINEERING.COM | 970.221.4158 FINAL DRAINAGE REPORT: THE SAVOY FORT COLLINS | GREELEY 9 | 11 Major Basin ODP Major Basin ODP has three (3) sub-basins (ODP1-ODP3) and is associated with the area along the north side of the property that cannot be captured and treated for LID on The Savoy project site but is being routed to the ODP Pond. Sub-Basin ODP1 is associated with the north side of Le Fever Drive and, therefore, it is not counted toward any of The Savoy's LID requirements or detention requirements. Sub-Basin ODP2 is on the south side of the Le Fever Drive, and, therefore, The Savoy would be responsible for detaining and treating this basin if it had not been included in the ODP Pond calculations. Sub-Basin ODP3 is associated with a small portion of the east side of Cinequefoil Lane. Existing drainage patterns for Sub- Basin ODP3 are being maintained with The Savoy Development. Water quality and detention for Sub-Basin ODP3 are being provided in the ODP Pond. As previously stated in Section III. A., per "Final Drainage Report and Erosion Control Report Banner Health Medical Campus", the ODP Pond is responsible for detaining and treating 5.90 acres of The Savoy project site. Basin O-2 from the Banner Health Medical Campus Master Drainage Exhibit depicts this. During the design of the ODP Pond, Basin O-2 was assumed to be 85% impervious. The Savoy proposes utilizing the ODP Pond for 5.82 acres with an impervious value of 76%. The 5.82 ac (4.67+0.90+0.25=5.82) acres come from Major Basin A (4.67 ac) plus Sub-Basin ODP2 (0.90 ac) and Sub-Basin ODP3 (0.25 ac). The discrepancy between 5.82 acres and 5.90 is negligible. Additionally The Savoy is 9% under the assumed impervious value from the “Final Drainage Report and Erosion Control Report Banner Health Medical Campus” will offset the 0.03-acre difference. Sub-Basin ODP1 was not included in this calculation because it is on the north side of Le Fever Drive and thus not associated with Basin O-2, but rather Basin O-3 per "Final Drainage Report and Erosion Control Report Banner Health Medical Campus." Therefore, The Savoy is meeting the requirements set forth by "Final Drainage Report and Erosion Control Report Banner Health Medical Campus." Major Basin BF1 Major Basin BF1 has no sub-basins and is associated with the area along the east, west, and south sides of The Savoy property that cannot be brought into the project site for LID treatment. Major Basin BF1 has an area of 1.16 acres and an impervious value of 54%. Major Basin BF1 will maintain existing runoff patterns, with all runoff being routed to the existing 15' Type R Inlet at the northwest corner of the Brookfield Drive and Precision Drive intersection. Runoff generated in Major Basin BF1 will be detained and treated within Detention Pond A – Brookfield. As previously stated in Section III. A., per "Final Drainage Report for Brookfield," Detention Pond A – Brookfield was designed to detain and treat 9.93 acres, with an assumed impervious of 85% of The Savoy project site. Basins D9 and D5 from the "Final Drainage Report for Brookfield" are the basins associated with The Savoy project site. However, The Savoy project is proposing to route 3.43 acres, with an impervious value of 66%, to Detention Pond A – Brookfield. The remaining portion of the site will be routed to the ODP Pond. A full-size copy of the Drainage Exhibit can be found in the Map Pocket at the end of this report. In addition, excerpts from earlier drainage reports referenced in this Section can be found in Appendix E. NORTHERNENGINEERING.COM | 970.221.4158 FINAL DRAINAGE REPORT: THE SAVOY FORT COLLINS | GREELEY 10 | 11 B. SPECIFIC DETAILS Since detention is not required with this site, the existing impervious area has not been considered in determining allowable release from the property. Instead, the site was designed to send roughly 5.90 acres to the ODP Pond while the rest of the runoff would be routed to Detention Pond A – Brookfield. The Savoy was able to successfully route 5.82 acres to the ODP Pond. LID treatment will be provided for Major Basin A and Major Basin B. Major Basin ODP will be treated in the ODP Pond, and Major Basin BF1 will be treated in Detention Pond A – Brookfield. LID SUMMARY TABLE Area treated by Stormtech LID Pond (ac) 4.67 Area treated by Rain Garden (ac) 2.27 Total LID (ac) 6.94 *Total Drainage Area (ac) 9.25 % Treated by LID 75.03% % Treated by ODP Pond and Detention Pond A - Brookfield 24.97% *Includes Major Basin A, Major Basin B, Basin BF1, Sub-Basin ODP2, and Sub-Basin ODP3. Excludes Sub-Basin ODP1. CONCLUSIONS A. COMPLIANCE WITH STANDARDS The design elements comply without the need for variances and meet all LID requirements. The drainage design proposed for The Savoy complies with the City of Fort Collins Master Drainage Plan, "Final Drainage Report and Erosion Control Report Banner Health Medical Campus," and "Final Drainage Report for Brookfield." Excerpts from referenced reports can be found in Appendix F. There are no FEMA regulatory floodplains associated with The Savoy development. The drainage plan and stormwater management measures proposed with The Savoy project are compliant with all applicable State and Federal regulations governing stormwater discharge. B. DRAINAGE CONCEPT The drainage design proposed with this project will effectively limit potential damage associated with its stormwater runoff. The Savoy project will provide on-site LID treatment for runoff but will not be detaining any flows. Detention is provided either in the ODP Pond or Detention Pond A- Brookfield. The Savoy development will not impact the Master Drainage Plan recommendations for the McClelland Major Drainage Basin. Table 2 - LID Summary Table NORTHERNENGINEERING.COM | 970.221.4158 FINAL DRAINAGE REPORT: THE SAVOY FORT COLLINS | GREELEY 11 | 11 REFERENCES 1. City of Fort Collins Landscape Design Guidelines for Stormwater and Detention Facilities, November 5, 2009, BHA Design, Inc. with City of Fort Collins Utility Services. 2. Fort Collins Stormwater Criteria Manual, City of Fort Collins, Colorado, adopted by Ordinance No. 159, 2018, and referenced in Section 26-500 of the City of Fort Collins Municipal Code. 3. Soils Resource Report for Larimer County Area, Colorado, Natural Resources Conservation Service, United States Department of Agriculture. 4. Urban Storm Drainage Criteria Manual, Volumes 1-3, Urban Drainage and Flood Control District, Wright-McLaughlin Engineers, Denver, Colorado, Revised April 2008. 5. Final Drainage Report for Milestone Apartments, Northern Engineering, Fort Collins, Colorado, May 2014. 6. Final Drainage and Erosion Control Report Banner Health Medical Campus, Northern Engineering, Fort Collins, Colorado, September 2013. 7. Final Drainage and Erosion Control Report for Presidio Apartments, Northern Engineering, Fort Collins, Colorado, December 2009. 8. Final Drainage Report for Brookfield, TST, Inc. Consulting Engineers, Fort Collins, Colorado, December 2001. 9. East Harmony Portion of McClelland's Creek Master Drainage Plan Update Final Report, ICON Engineering, Inc., Englewood, Colorado, August 1999. 10. Geological and Preliminary Geotechnical Investigation, CTL Thompson, Fort Collins, Colorado, November 2021 NORTHERNENGINEERING.COM | 970.221.4158 PRELIMINAY DRAINAGE REPORT: THE SAVOY FORT COLLINS | GREELEY APPENDIX APPENDIX A HYDROLOGIC COMPUTATIONS CHARACTER OF SURFACE1: Percentage Impervious 2-yr Runoff Coefficient 10-yr Runoff Coefficient 100-yr Runoff Coefficient Developed Asphalt .…………………………..……………………………………………….…………………………..……………………………………………….…………………………..……………………………………………….…………………………..………………………………………………100%0.95 0.95 1.00 Concrete .…………………………..……………………………………………….…………………………..……………………………………………….…………………………..……………………………………………….…………………………..………………………………………………100%0.95 0.95 1.00 Rooftop .…………………………..……………………………………………….…………………………..……………………………………………….…………………………..……………………………………………….…………………………..………………………………………………90%0.95 0.95 1.00 Gravel .…………………………..……………………………………………….…………………………..……………………………………………….…………………………..……………………………………………….…………………………..………………………………………………40%0.50 0.50 0.63 Pavers .…………………………..……………………………………………….…………………………..……………………………………………….…………………………..……………………………………………….…………………………..………………………………………………40%0.50 0.50 0.63 Landscape or Pervious Surface Playgrounds .…………………………..……………………………………………….…………………………..……………………………………………….…………………………..……………………………………………….…………………………..………………………………………………25%0.35 0.35 0.44 Lawns Clayey Soil .…………………………..……………………………………………….…………………………..……………………………………………….…………………………..……………………………………………….…………………………..………………………………………………2%0.25 0.25 0.31 Lawns Sandy Soil .…………………………..……………………………………………….…………………………..……………………………………………….…………………………..……………………………………………….…………………………..……………………………………………….…………………………..……………………………………………….…………………………..………………………………………………2%0.15 0.15 0.19 Notes: Basin ID Basin Area (ac) Area of Asphalt (ac) Area of Concrete (ac) Area of Rooftop (ac) Area of Gravel (ac) Area of Pavers (ac) Area of Playgrounds (ac) Area of Lawns (ac) Composite % Imperv. 2-year Composite Runoff Coefficient 10-year Composite Runoff Coefficient 100-year Composite Runoff Coefficient A1 0.11 0.00 0.00 0.08 0.00 0.00 0.00 0.03 65% 0.75 0.75 0.94 A2 0.52 0.00 0.37 0.09 0.00 0.00 0.00 0.06 87% 0.87 0.87 1.00 A3 0.68 0.00 0.49 0.09 0.00 0.00 0.00 0.11 83% 0.84 0.84 1.00 A4 0.12 0.00 0.00 0.08 0.00 0.00 0.00 0.04 63% 0.74 0.74 0.93 A5 0.27 0.00 0.01 0.20 0.00 0.00 0.00 0.05 74% 0.82 0.82 1.00 A6 0.22 0.00 0.01 0.13 0.00 0.00 0.00 0.08 61% 0.71 0.71 0.89 A7 0.24 0.00 0.23 0.00 0.00 0.00 0.00 0.01 95% 0.92 0.92 1.00 A8 0.52 0.00 0.47 0.00 0.00 0.00 0.00 0.05 91% 0.88 0.88 1.00 A9 0.63 0.00 0.21 0.18 0.00 0.00 0.00 0.23 61% 0.69 0.69 0.86 A10 0.51 0.00 0.45 0.00 0.00 0.00 0.00 0.06 89% 0.87 0.87 1.00 A11 0.60 0.00 0.46 0.00 0.00 0.00 0.00 0.14 77% 0.79 0.79 0.99 A12 0.24 0.00 0.00 0.20 0.00 0.00 0.00 0.04 77% 0.85 0.85 1.00 ODP1 0.45 0.27 0.00 0.00 0.00 0.00 0.00 0.18 60% 0.67 0.67 0.84 ODP2 0.86 0.27 0.09 0.21 0.00 0.00 0.00 0.30 64% 0.71 0.71 0.89 ODP3 0.29 0.04 0.05 0.10 0.00 0.00 0.00 0.11 61% 0.70 0.70 0.88 B1 0.25 0.00 0.01 0.13 0.00 0.00 0.00 0.11 51% 0.64 0.64 0.80 B2 0.63 0.00 0.56 0.00 0.00 0.00 0.00 0.06 90% 0.88 0.88 1.00 B3 0.58 0.00 0.48 0.00 0.00 0.00 0.00 0.10 82% 0.82 0.82 1.00 B4 0.25 0.00 0.00 0.20 0.00 0.00 0.00 0.04 75% 0.83 0.83 1.00 B5 0.39 0.00 0.01 0.26 0.00 0.00 0.00 0.11 65% 0.75 0.75 0.94 B6 0.17 0.00 0.01 0.00 0.00 0.00 0.00 0.17 7% 0.29 0.29 0.36 BF1 1.14 0.00 0.44 0.17 0.00 0.00 0.00 0.53 53% 0.63 0.63 0.79 MAJOR BASIN A, ODP2, and ODP3 5.83 0.31 2.87 1.35 0.00 0.00 0.00 1.29 76% 0.79 0.79 0.99 MAJOR BASIN A 4.68 0.00 2.79 1.05 0.00 0.00 0.00 0.84 80% 0.82 0.82 1.00 MAJOR BASIN B & BF1 3.41 0.00 1.52 0.77 0.00 0.00 0.00 1.13 65% 0.72 0.72 0.90 MAJOR BASIN B 2.27 0.00 1.07 0.60 0.00 0.00 0.00 0.60 72% 0.77 0.77 0.96 DEVELOPED BASIN % IMPERVIOUSNESS AND RUNOFF COEFFICIENT CALCULATIONS 2) Runoff Coefficients are taken from the Fort Collins Stormwater Criteria Manual, Chapter 3. Table 3.2-1 and 3.2-2 1) Percentage impervious taken from the Fort Collins Stormwater Criteria Manual, Chapter 5, Table 4.1-2 and Table 4.1-3 Combined Basins Overland Flow, Time of Concentration: Channelized Flow, Time of Concentration: Total Time of Concentration : T c is the lesser of the values of Tc calculated using T c = T i + T t C2 C100 Length, L (ft) Slope, S (%) Ti2 Ti100 Length, L (ft) Slope, S (%) Roughness Coefficient Assumed Hydraulic Radius Velocity, V (ft/s) Tt (min)Tc (Eq. 3.3-5) Tc2 = Ti +Tt Tc100 = Ti +Tt Tc2 Tc100 a1 A1 0.75 0.94 25 4.00%2.1 1.0 0 N/A N/A N/A N/A N/A 10.1 2.1 1.0 5.0 5.0 a2 A2 0.87 1.00 50 2.00%2.4 1.0 205 0.60%0.013 0.15 2.52 1.4 11.4 3.8 2.4 5.0 5.0 a3 A3 0.84 1.00 50 2.00%2.7 1.0 210 0.60%0.013 0.15 2.50 1.4 11.4 4.1 2.5 5.0 5.0 a4 A4 0.74 0.93 25 4.00%2.1 1.0 0 N/A N/A N/A N/A N/A 10.1 2.1 1.0 5.0 5.0 a5 A5 0.82 1.00 25 4.00%1.6 0.6 25 5.00%0.030 0.40 6.03 0.1 10.3 1.7 0.7 5.0 5.0 a6 A6 0.71 0.89 25 4.00%2.3 1.3 25 5.00%0.030 0.40 6.03 0.1 10.3 2.4 1.3 5.0 5.0 a7 A7 0.92 1.00 50 2.00%1.9 1.0 140 1.57%0.013 0.15 4.06 0.6 11.1 2.5 1.6 5.0 5.0 a8 A8 0.88 1.00 50 2.00%2.3 1.0 140 2.00%0.013 0.15 4.58 0.5 11.1 2.8 1.6 5.0 5.0 a9 A9 0.69 0.86 50 2.00%4.3 2.5 0 N/A N/A N/A N/A N/A 10.3 4.3 2.5 5.0 5.0 a10 A10 0.87 1.00 35 2.00%2.0 0.9 145 1.59%0.013 0.15 4.08 0.6 11.0 2.6 1.5 5.0 5.0 a11 A11 0.79 0.99 35 2.00%2.7 1.0 145 0.60%0.013 0.15 2.51 1.0 11.0 3.7 2.0 5.0 5.0 a12 A12 0.85 1.00 25 4.00%1.5 0.6 0 N/A N/A N/A N/A N/A 10.1 1.5 0.6 5.0 5.0 odp1 ODP1 0.67 0.84 13 5.77%1.6 1.0 467 0.50%0.016 0.19 2.18 3.6 12.7 5.2 4.6 5.2 5.0 odp2 ODP2 0.71 0.89 15 0.67%3.2 1.8 467 0.50%0.016 0.19 2.18 3.6 12.7 6.8 5.3 6.8 5.3 odp3 ODP3 0.70 0.88 50 4.00%3.3 1.9 134 0.75%0.016 0.19 2.66 0.8 11.0 4.2 2.7 5.0 5.0 b1 B1 0.64 0.80 25 4.00%2.7 1.8 0 N/A N/A N/A N/A N/A 10.1 2.7 1.8 5.0 5.0 b2 B2 0.88 1.00 35 2.00%1.9 0.9 289 1.09%0.013 0.15 3.38 1.4 11.8 3.4 2.3 5.0 5.0 b3 B3 0.82 1.00 35 2.00%2.5 0.9 200 2.00%0.013 0.15 4.58 0.7 11.3 3.2 1.6 5.0 5.0 b4 B4 0.83 1.00 25 4.00%1.6 0.6 0 N/A N/A N/A N/A N/A 10.1 1.6 0.6 5.0 5.0 b5 B5 0.75 0.94 25 4.00%2.1 1.0 25 6.00%0.030 0.40 6.60 0.1 10.3 2.1 1.0 5.0 5.0 b6 B6 0.29 0.36 50 12.00%4.7 4.3 0 N/A N/A N/A N/A N/A 10.3 4.7 4.3 5.0 5.0 bf1 BF1 0.63 0.79 25 0.67%5.0 3.3 935 0.63%0.013 0.15 2.57 6.1 15.3 11.1 9.4 11.1 9.4 ODP Pond MAJOR BASIN A, ODP2, and ODP3 0.79 0.99 35 2.00% 2.7 1.0 385 0.60% 1.30% 15.00% 0.25 25.7 12.3 28.4 26.6 12.3 12.3 STORMTECH MAJOR BASIN A 0.82 1.00 35 2.00% 2.5 0.9 385 0.60%1.30% 15.00% 0.25 25.7 12.3 28.1 26.5 12.3 12.3 BROOKFIELD POND MAJOR BASIN B & BF1 0.72 0.90 25 0.68% 4.0 2.1 935 0.02% 1.30% 15.00% 0.04 347.1 15.3 351.1 349.2 15.3 15.3 RAIN GARDEN MAJOR BASIN B 0.77 0.96 25 0.68% 3.5 1.5 935 0.02% 1.30% 15.00% 0.04 347.1 15.3 350.6 348.6 15.3 15.3 Combined Basins DEVELOPED DIRECT TIME OF CONCENTRATION Channelized Flow Design Point Basin Overland Flow Time of Concentration Frequency Adjustment Factor: (Equation 3.3-2 FCSCM) (Equation 5-5 FCSCM) (Equation 5-4 FCSCM) (Equation 3.3-5 FCSCM) Table 3.2-3 FCSCM Therefore Tc2=Tc10 Rational Method Equation: Rainfall Intensity: a1 A1 0.11 5.0 5.0 0.75 0.94 2.85 4.87 9.95 0.24 0.42 1.07 a2 A2 0.52 5.0 5.0 0.87 1.00 2.85 2.85 9.95 1.29 1.29 5.16 a3 A3 0.68 5.0 5.0 0.84 1.00 2.85 2.85 9.95 1.64 1.64 6.80 a4 A4 0.12 5.0 5.0 0.74 0.93 2.85 2.85 9.95 0.25 0.25 1.07 a5 A5 0.27 5.0 5.0 0.82 1.00 2.85 2.85 9.95 0.62 0.62 2.65 a6 A6 0.22 5.0 5.0 0.71 0.89 2.85 2.85 9.95 0.45 0.45 1.97 a7 A7 0.24 5.0 5.0 0.92 1.00 2.85 2.85 9.95 0.64 0.64 2.43 a8 A8 0.52 5.0 5.0 0.88 1.00 2.85 2.85 9.95 1.32 1.32 5.22 a9 A9 0.63 5.0 5.0 0.69 0.86 2.85 2.85 9.95 1.24 1.24 5.41 a10 A10 0.51 5.0 5.0 0.87 1.00 2.85 2.85 9.95 1.27 1.27 5.08 a11 A11 0.60 5.0 5.0 0.79 0.99 2.85 2.85 9.95 1.36 1.36 5.93 a12 A12 0.24 5.0 5.0 0.85 1.00 2.85 2.85 9.95 0.59 0.59 2.41 odp1 ODP1 0.45 5.0 5.0 0.67 0.84 2.85 2.85 9.95 0.87 0.87 3.78 odp2 ODP2 0.86 5.3 5.3 0.71 0.89 2.85 2.85 9.95 1.75 1.75 7.63 odp3 ODP3 0.29 5.0 5.0 0.70 0.88 2.85 2.85 9.95 0.58 0.58 2.53 b1 B1 0.25 5.0 5.0 0.64 0.80 2.85 2.85 9.95 0.45 0.45 1.96 b2 B2 0.63 5.0 5.0 0.88 1.00 2.85 2.85 9.95 1.57 1.57 6.23 b3 B3 0.58 5.0 5.0 0.82 1.00 2.85 2.85 9.95 1.36 1.36 5.78 b4 B4 0.25 5.0 5.0 0.83 1.00 2.85 2.85 9.95 0.59 0.59 2.47 b5 B5 0.39 5.0 5.0 0.75 0.94 2.85 2.85 9.95 0.83 0.83 3.64 b6 B6 0.17 5.0 5.0 0.29 0.36 2.85 2.85 9.95 0.14 0.14 0.63 bf1 BF1 1.14 9.4 9.4 0.63 0.79 2.30 2.30 8.03 1.66 1.66 7.24 ODP Pond MAJOR BASIN A, ODP2, and ODP3 5.83 12.3 12.3 0.79 0.99 2.05 2.05 7.16 9.44 11.81 41.24 STORMTECH MAJOR BASIN A 4.68 12.3 12.3 0.82 1.00 2.05 2.05 7.16 7.86 9.59 33.50 BROOKFIELD POND MAJOR BASIN B & BF1 3.41 15.3 15.3 0.72 0.90 1.87 1.87 6.52 4.59 5.74 20.02 RAIN GARDEN MAJOR BASIN B 2.27 15.3 15.3 0.77 0.96 1.87 1.87 6.52 3.26 4.08 14.22 Combined Basins Tc100 (min) Intensity, i2 (in/hr) Intensity, i100 (in/hr) DEVELOPED RUNOFF COMPUTATIONS Design Point Basin(s)Area, A (acres) Tc2 (min) Flow, Q2 (cfs) Flow, Q100 (cfs) C2 C100 IDF Table for Rational Method - Table 3.4-1 FCSCM Intensity, i10 (in/hr) Flow, Q10 (cfs) ()()()AiCCQf= BASIN TOTAL AREA (acres) Tc2 (min) Tc100 (min) C2 C100 Q2 (cfs) Q100 (cfs) A1 0.11 5.0 5.0 0.75 0.94 0.24 1.07 A2 0.52 5.0 5.0 0.87 1.00 1.29 5.16 A3 0.68 5.0 5.0 0.84 1.00 1.64 6.80 A4 0.12 5.0 5.0 0.74 0.93 0.25 1.07 A5 0.27 5.0 5.0 0.82 1.00 0.62 2.65 A6 0.22 5.0 5.0 0.71 0.89 0.45 1.97 A7 0.24 5.0 5.0 0.92 1.00 0.64 2.43 A8 0.52 5.0 5.0 0.88 1.00 1.32 5.22 A9 0.63 5.0 5.0 0.69 0.86 1.24 5.41 A10 0.51 5.0 5.0 0.87 1.00 1.27 5.08 A11 0.60 5.0 5.0 0.79 0.99 1.36 5.93 A12 0.24 5.0 5.0 0.85 1.00 0.59 2.41 ODP1 0.45 5.0 5.0 0.67 0.84 0.87 3.78 ODP2 0.86 5.3 5.3 0.71 0.89 1.75 7.63 ODP3 0.29 5.0 5.0 0.70 0.88 0.58 2.53 B1 0.25 5.0 5.0 0.64 0.80 0.45 1.96 B2 0.63 5.0 5.0 0.88 1.00 1.57 6.23 B3 0.58 5.0 5.0 0.82 1.00 1.36 5.78 B4 0.25 5.0 5.0 0.83 1.00 0.59 2.47 B5 0.39 5.0 5.0 0.75 0.94 0.83 3.64 B6 0.17 5.0 5.0 0.29 0.36 0.14 0.63 BF1 1.14 9.4 9.4 0.63 0.79 1.66 7.24 MAJOR BASIN A, ODP2, and ODP3 5.83 12.3 12.3 0.79 0.99 9.44 41.24 MAJOR BASIN A 4.68 12.3 12.3 0.82 1.00 7.86 33.50 MAJOR BASIN B & BF1 3.41 15.3 15.3 0.72 0.90 4.59 20.02 MAJOR BASIN B 2.27 15.3 15.3 0.77 0.96 3.26 14.22 Rational Flow Summary | Developed Basin Flow Rates Combined Basins 6/26/20238:12 AM P:\514-003\Drainage\Hydrology\514-003_Proposed Rational Calcs (FCSCM)\Summary Tables NORTHERNENGINEERING.COM | 970.221.4158 PRELIMINARY DRAINAGE REPORT: THE SAVOY FORT COLLINS | GREELEY APPENDIX APPENDIX B HYDRAULIC CALCULATIONS – FOR FUTURE USE Storm Drains A, A3, A3-1, D, D1, D4, E, & E1 Storm Drain A (pipes 1- 6) Storm Drain A (pipes 6 - 9)