The URL can be used to link to this page

Home My WebLink AboutENCLAVE AT REDWOOD - PDP210004 - DOCUMENT MARKUPS - ROUND 4 - DRAINAGE REPORT PRELIMINARY DRAINAGE REPORT FOR ENCLAVE AT REDWOOD Fort Collins, CO 80524 Date: August 18, 2021 Revised: October 19, 2021 Prepared for: 9555 South Kingston Court Denver, CO 80112 Phone: 303-488-0061 Prepared by: Mark A. West, P.E., C.F.M. 1120 Lincoln Street, Suite 1000 Denver, CO 80203 Ph.: 303-623-6300, Fax: 303-623-6311 Harris Kocher Smith Project No. 201013 Enclave at Redwood Table of Contents October 19, 2021 TABLE OF CONTENTS I. GENERAL LOCATION AND DESCRIPTION ................................................................................................... 4 A. Site Location ....................................................................................................................................... 4 B. Description of Property ...................................................................................................................... 4 II. MASTER DRAINAGE BASIN DESCRIPTION .................................................................................................. 5 A. Floodplain........................................................................................................................................... 5 B. Master Drainage Basin ....................................................................................................................... 5 III. DRAINAGE DESIGN CRITERIA ................................................................................................................. 6 A. Regulations and Previous Studies ...................................................................................................... 6 B. Four-Step Process .............................................................................................................................. 6 C. Hydrologic Design Criteria ................................................................................................................. 7 D. Hydraulic Design Criteria .................................................................................................................... 9 E. Variances .......................................................................................................................................... 10 F. Erosion Control ................................................................................................................................ 10 IV. PROPOSED DRAINAGE SYSTEMS .......................................................................................................... 10 A. General Concept .............................................................................................................................. 10 B. Proposed Basins ............................................................................................................................... 11 C. Specific Details ................................................................................................................................. 13 V. CONCLUSIONS ......................................................................................................................................... 17 A. Compliance with Standards ............................................................................................................. 17 B. Drainage Concept ............................................................................................................................. 17 VI. REFERENCES ......................................................................................................................................... 18 VII. APPENDICES ......................................................................................................................................... 19 Appendix A – Vicinity Map, FIRM, Geotechnical Engineering Report ....................................................... A Appendix B - Portions from Relevant Previous Studies ............................................................................ B Appendix C – Subcatchment Hydrology .................................................................................................... C Appendix D – Detention Storage Sizing ..................................................................................................... D Appendix E – SWMM Model and Results .................................................................................................. E Appendix F – Low Impact Development ................................................................................................... F Appendix G – Drainage Map ..................................................................................................................... G Enclave at Redwood Engineer Certification October 19, 2021 Engineer Certification I hereby attest that this report for the preliminary drainage design for the Enclave at Redwood 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. __________________________________ _______________________ Mark A. West, P.E., C.F.M. Date State Of Colorado Registration No. 38561 On Behalf of Harris Kocher Smith Enclave at Redwood Page 4 October 19, 2021 I. GENERAL LOCATION AND DESCRIPTION A. Site Location The proposed Enclave at Redwood development (hereinafter referred to as “Site”) is located in the southeast ¼ of Section 1, Township 7 north, Range 69 west of the sixth Principal Meridian, City of Fort Collins, County of Larimer, State of Colorado. The Site is bounded by Redwood Street to the west and East Suniga Road to the south. A small portion of the Site exists south of East Suniga Road. Adjacent developments include the Meadows at Redwood PUD Phase 1 (Redwood Meadows) to the west, Northfield to the east and southeast, and Evergreen Park 3rd (Evergreen) to the north. Lake Canal exists as an irrigation ditch adjacent to the Site to the east and southeast, and Redwood Channel lies adjacent to the Site to the north. The Site will connect to Redwood St to the southwest, Lupine Dr in Redwood Meadows to the west, Steeley Dr in Northfield to the southeast, and Collamer Dr in Northfield to the east. See Appendix A for the Vicinity Map. The Site exists entirely within the Dry Creek master drainage basin. B. Description of Property The Site is approximately 29.66 acres of undeveloped land. The undeveloped land is made up of various native trees and grasses. The Site generally slopes from west to east at grades between roughly 0.3% and 1% towards Lake Canal. Lake Canal is an irrigation ditch and discharging stormwater from the developed Site to this ditch will require approval from the ditch ownership. Redwood Pond is an existing regional pond to the northwest of the Site, it historically outfalls east into the Redwood Channel drainage ditch that exists north of the Site. The proposed development of the Site will feature mutli- family housing, public and private roadways, walks, parks, a clubhouse with pool, landscaped areas, four on-Site detention facilities and low-impact-development systems. Cole Garner Geotechnical has prepared a Geotechnical Engineering Report for Enclave at Redwood Residential Development on August 11, 2021. This report details existing soils information for the Site. Ten borings were drilled on-Site to examine subsurface conditions in February of 2021. Groundwater was encountered in all borings at the time of drilling and approximately two weeks after drilling at depths ranging from 8 to 12 feet below existing Site grades. In order to account for seasonal groundwater fluctuations, Cole Garner measured groundwater levels in the aforementioned borings again in September of 2021. It was found that three of the ten borings saw no change in groundwater elevation, six of the ten borings saw a rise in groundwater of less than 1.5 feet, and one of the borings saw a rise in groundwater of 4 feet. The drainage design of the Site will consider the readings from September to be the more accurate reading indicative of the wet season. Due to shallow groundwater concerns, construction dewatering may be required. All drainage facilities will be located at least 24 inches above groundwater or feature a detailed underdrain system. Please see Appendix A for relevant portions of the Geotechnical Engineering Report and a table of the groundwater readings taken in September of 2021. Enclave at Redwood Page 5 October 19, 2021 II. MASTER DRAINAGE BASIN DESCRIPTION A. Floodplain The Site is shown on the Federal Emergency Agency’s (FEMA) Flood Insurance Rate Map (FIRM) Community Panel Numbers 08069C0977G and 08069C0981G, effective June 17, 2008. Lake Canal is partially located within Zone X (0.2% annual chance flood hazard) and therefore the Site is partially within this zone. Because the development of the Site will not involve altering of Lake Canal, no floodplain modifications are necessary. Please refer to Appendix A for more details. B. Master Drainage Basin The Site exists in the Dry Creek Master Drainage Basin, but according to the City of Fort Collins, the Dry Creek Master Drainage Plan is outdated and not specific to the Site. The North East College Corridor Outfall Design Report prepared by Ayres Associates in August 2009 (NECCO) will be utilized to impose drainage conditions on the Site instead of the Dry Creek Master Drainage Plan. Please see Appendix B for relevant portions from the NECCO report. This report details the design and construction of a regional pond that conveys a large amount of runoff from the Dry Creek basin in a new storm main beneath E Suniga St running from west to east. This report also contains design plans to revise the existing Redwood Pond’s grading and change its outfall location from the Redwood Channel drainage ditch north of the Site to the NECCO storm main beneath E Suniga St south of the Site. The Redwood Pond changes detailed in the NECCO report have not been constructed, and therefore the A2 lateral outlined in the NECCO report has not been constructed either. The Site will require design and construction of the proposed Redwood Pond outlet structure and the A2 lateral storm line that are detailed in the NECCO report. No other proposed changes to the Redwood Pond will be constructed as part of this development, as the Site contributes no runoff to the Redwood Pond. The A2 lateral storm line will connect to an existing stub from the NECCO main and will act as the ultimate outfall of the developed Site. The basins from the NECCO report that were analyzed for this report include basins 113, 213, 313, 413, and 812. The Site exists in basins 113, 313, and 413. Basin 413 will remain undeveloped and thus the A3 lateral detailed in the NECCO report will not be constructed, and runoff from this basin will continue to follow historic patterns and release into Lake Canal undetained and untreated. The NECCO report calls for future on-Site detention for basins 113 and 313, which will each require a 100-year release rate of 0.2 cubic-feet-per-second (CFS) per acre. Basin 213 consists of the Redwood Meadows development and would require water quality treatment but no detention if redeveloped in the future. The Site will provide inlets at various points between the border of the Redwood Meadows development and the Site boundary in order to capture all runoff from basin 213 and route it to the A2 lateral storm line. Basin 812 consists of the Redwood Pond, which the NECCO report details as requiring regrading and redesign to allow for a 100-year detention volume of 7.70 acre-feet (ac-ft) and an additional 2.16 ac-ft of storage for water quality. The redesign would entail adding additional pond facilities such as trickle channels and forebays, as well as plugging the existing outlet, but leaving the existing berm and overflow spillway. As stated above, because the Site will not contribute runoff to the Redwood Pond, only the outlet structure and storm lateral A2 will be designed and constructed as part of this development. Please see Section IV of this report for more information on the proposed redesign of the Redwood Pond. The on-Site detention facilities will meet the release rate constraint of 0.2 CFS/acre imposed by the NECCO Report. Enclave at Redwood Page 6 October 19, 2021 Also provided for the development of drainage for the Site was an existing conditions SWMM model featuring the constructed NECCO storm main under E Suniga St and the regional pond designed in the NECCO Report. This model included a significant number of elements not pertinent to the Site development and elements that were pertinent to the Site development featured parameters based on outdated LIDAR data. Because of these issues, it was decided to wait to incorporate the Site into the existing conditions NECCO model that was received until the Site design is further developed. As such, a Site-specific SWMM model was developed for preliminary drainage analysis. In order to account for the existing conditions model ahead of the Site model’s insertion, the elements contributing runoff to the Redwood Pond upstream of the Site have been brought into the Site model, and tailwater data from the existing conditions model has been inserted into the outfall of the Site model, which is the NECCO main A2 lateral stub. The Site SWMM model will be incorporated into the existing conditions NECCO SWMM model upon final drainage analysis in a future version of this drainage report. Please see Appendix E for the tailwater time series and upstream elements that were brought from the existing conditions model to the Site model. Historic drainage analysis of the Site shows that the entirety of the Site (29.66 acres) discharges into Lake Canal existing along the Site boundary running from the southeast to the northeast. The existing Site has an imperviousness of 2% and an approximate 100-year runoff of 14 CFS, all of which discharges into Lake Canal. Any stormwater discharging from the developed Site into Lake Canal will require approval from the ditch ownership. The Site will contribute some undetained and untreated runoff to Lake Canal due to the Site’s existing drainage patterns. Please see Section IV of this report for approximate 100-year runoff values discharging to Lake Canal from the developed Site. Please note the approximate runoff stated here and in Section IV is calculated using SWMM’s hydrologic calculator, more accurate runoff calculations using the Rational Method will be included in a later version of this report. III. DRAINAGE DESIGN CRITERIA A. Regulations and Previous Studies The principal design criteria used for this report was the Fort Collins Stormwater Criteria Manual, revised December 2018 (FCSCM). In addition, Mile High Flood District’s (MHFD) Urban Storm Drainage Criteria Manual, Volumes 1-3 revised August 2018, September 2017, and January 2021 respectively, were used (USDCM). The NECCO report from above also provides a certain level of drainage criteria for the Site that must be met. B. Four-Step Process a. Step 1: Employ Runoff Reduction Practices The Site will feature numerous open areas dedicated for low-impact-development (LID), parks, and above ground detention. Wherever possible, vegetated swales will be used to convey runoff to area inlets and roof drains will be used to convey flow to these swales, directly to LID implements, or to storm sewer structures. Enclave at Redwood Page 7 October 19, 2021 b. Step 2: Implement BMPs That Provide a WQCV with Slow Release There are four LID systems incorporated on-Site, all of them being isolator rows for underground infiltration. These implements are utilized to treat over 75% of newly added impervious are with the development of the Site per the FCSCM. A majority of the remainder of the Site’s impervious areas will be treated in the above ground on-Site detention pond. c. Step 3: Stabilize Streams The Site will be far upstream of Dry Creek and the NECCO report has already considered developed release rates from the Site entering Dry Creek. There will be no need to provide stream stabilization of Dry Creek with the development of the Site. d. Step 4: Implement Site Specific and Other Source Control BMPs Because the Site is not a new development or redevelopment of an industrial or commercial zone this step is not applicable to the Site. C. Hydrologic Design Criteria Design Frequencies – For the Site, the minor storm will be the 2-year and the major storm will be the 100-year. For detention volume and release rates, the WQCV and 100-year storm events have been analyzed. Rainfall Data - Fort Collins varies by runoff calculation method. For the purpose of this preliminary drainage report, only SWMM was used in calculating runoff. Below is Table 4.1-4 which presents rainfall intensity values for use in SWMM modelling. Enclave at Redwood Page 8 October 19, 2021 Hydrologic Computation Method – As stated above, only EPA SWMM 5.1 was used to calculate runoff for this preliminary drainage design. As of now the basins tributary to each of the ponds have not been broken into smaller sub-basins for the purpose of inlet calculations. For future iterations of this report, the rational method will be utilized. SWMM uses basin imperviousness, slope, area, and width along with several default parameters to calculate runoff. SWMM inputs can be found in Appendix E as well as Section IV of this report. The rational method uses weighted “C” coefficients based upon surface type and a time of concentration to determine runoff. Fort Collins rational method IDF table and “C” coefficient table can be found in Appendix C along with SWMM subcatchment default parameters and imperviousness by surface type tables. A summary of SWMM results for each subcatchment can be found in Appendix C as well. The rational method “C” coefficient and water quality event rainfall intensities were utilized in the Modified FAA Procedure to calculate the WQCV for the isolator rows. It should be noted that imperviousness values used were rounded up from exact calculated values for this preliminary drainage design. Detention Volume Computation Method – For project sizes greater than 20 acres, SWMM is required for detention calculation. SWMM storage nodes are used to represent the ponds and require storage curves (depth-area), SWMM then computes a volume based on these tables. SWMM outlet links are used to represent a ponds outlet structure and require rating curves (depth-release). SWMM can also utilize orifice, weir, or conduit links for a pond’s outlet structure. A mix of these different links were utilized for the Site’s SWMM modelling. More discussion on pond modelling in the Site SWMM model can be found in Section IV of this report, and all calculations relating to detention ponds and facilities can be found in Appendix D. The FCSCM requires that the WQCV be added to the 100-year storage volume as opposed Enclave at Redwood Page 9 October 19, 2021 to being included in said volume, thus the WQCV has been included in the SWMM model’s storage nodes as an initial water depth value. Please see below for more information on computation of the WQCV. See Appendix E for SWMM output results of storage nodes. Water Quality Control Volume Calculation – The only LID systems implemented on-Site are isolator rows featuring underground infiltration. Three of these systems are included as part of an underground detention chamber system, and one other features isolator row chambers solely. For these isolator row systems, a spreadsheet received from Advanced Drainage Systems (ADS) was used to determine the number of chambers needed based on product choice, chamber volume, and required WQCV. For the sizing of these systems, two different WQCV values are compared to determine which results in a higher number of required chambers. The first is 120% of the WQCV based on a 12-hour drain time, which can be calculated using UD-BMP’s rain garden tab and multiplying that value by 1.2. The second is the WQCV calculated from the modified FAA procedure, which uses a weighted “C” coefficient, tributary area, and maximum flow out of the chamber system. Whichever WQCV results in more chambers based on the received spreadsheet discussed above is the utilized WQCV. The required WQCV for the above ground on-Site detention pond was found using the UD-BMP extended detention basin tab. This tab computes a WQCV based on a 40-hour drain time, which is then multiplied by a factor of 1.2 to meet the 120% of the WQCV requirement from the FCSCM. See Appendix D for the calculation of the WQCV for the above ground pond, and Appendix F for the calculation of the WQCV and chamber requirements for the isolator rows. D. Hydraulic Design Criteria Detention Pond Infrastructure Sizing - Express Hydraflow will be used to calculate vegetated swale and emergency overflow spillway capacities for the Site. The FCSCM requires that overflow spillway design flow depth be no greater than 0.5 feet. UD-BMP will be used to size trickle channels, forebays, and forebay notches for the above ground pond. Outlet structures for the Redwood Pond and on-Site above ground detention pond have been preliminarily designed, and only the Redwood Pond will feature a rating curve in SWMM to act as an outlet. The on-Site above ground detention pond has been designed in SWMM using multiple orifice and weir links instead of a rating curve. This pond and the three underground detention chamber systems do not feature rating curves and instead feature conduits with their maximum flow values set at the 0.2 CFS/acre release rate criteria. This ensures the facilities will have enough volume without needing to fully design their outlet structure (box height, restrictor plates, orifice plates). These detention facilities’ outlet structures will be designed fully in a future version of this report using stage-storage-discharge tables that result in a developed rating curve. The MHFD spreadsheet “SDI_Design_Data_v1.08.xlsm” released January 2017 will be used to confirm that pond release rates meet Colorado drain time criteria. For preliminary drainage design, meeting the release rate criteria took precedent over drain time criteria, thus the SDI data sheets included with this version of the report should only be used to check 100-year drain times. For final drainage design, rating curves will be used to develop more accurate drain times and show proper conformance. Spillways, preliminary SDI data sheets, and stage-area tables can be found in Appendix D. Street Capacity Calculation – Street sections upstream of proposed inlets will be analyzed using the MHFD spreadsheet “MHFD-Inlet v5.01” released April 2021. These calculations will be presented in a later version of this report. Storm Sewer Sizing – Inlet sizing will be performed using the MHFD-Inlet spreadsheet. For the preliminary layout of the storm network inlet sizes were estimated based on contributing area. Inlet Enclave at Redwood Page 10 October 19, 2021 Type 16 curb and valley inlets, Type R curb inlets, and Type C and D areas inlets were utilized for this Site. Storm pipe sizing and vertical alignment will be analyzed using Bentley StormCAD CONNECT. StormCAD computes losses and velocities and produces accurate HGLs and EGLs to prove the storm sewer network works hydraulically. Inlet sizing calculations and StormCAD pipe sizing calculations will be provided in a later version of this report. E. Variances The drainage design for the Site will not require any variance from criteria put forth in the FCSCM, USDCM, and NECCO Report. F. Erosion Control The following drainage design will comply with all erosion control criteria put forth in the USDCM, FCSCM, and NECCO Report. All erosion control materials will be provided with the final drainage report. IV. PROPOSED DRAINAGE SYSTEMS A. General Concept The Site will include outlet structure design for the Redwood Pond to the northwest of the Site as detailed in the NECCO report. For the preliminary drainage design of the Site, the outlet structure has been designed to attempt to meet the parameters presented in the NECCO report without regrading. The Site will include development of the NECCO A2 storm lateral, which runs from the new Redwood Pond outlet structure to an existing stub off of the NECCO main line under E Suniga Rd. There are three proposed underground detention chamber facilities and one proposed above ground detention pond, all of which will feature some level of water quality treatment. All four of these facilities will feature an outlet structure to be designed in a later version of this report. The above ground pond will bypass a portion of the 100-year runoff routed to it to one of the underground chamber facilities downstream. All four of these ponds will meet the 0.2 CFS/ac release rate criteria, and release to the NECCO A2 storm lateral. For the purpose of this preliminary drainage design, all four ponds are shown to be capturing 100% of runoff from the Site in order to size them conservatively. For the final drainage design of the Site, each of these ponds tributary areas will be refined and their required volumes will decrease. Site runoff will be conveyed to these ponds via roof drains, swales, inlets and storm sewer pipes, and landscape drains, all to be designed in a later version of this report. Runoff from basin 213 consisting of Redwood Meadows will be captured by proposed on-Site inlets and routed directly into the NECCO A2 storm lateral. Further breakdown of the ponds and a summary table can be found below. The Site will feature four LID systems all of which being underground infiltration isolator rows. Three of these systems will be included in the three underground detention chambers mentioned above. The fourth system will be directly upstream of the above ground detention pond and will not feature any 100-year detention. These LID features are designed to treat at least 75% of the Site’s impervious areas for the WQCV. Unlike the detention facilities mentioned above, these LID systems are only designed to capture the areas actual tributary to them and have been sized as such. The systems are conservatively sized by rounding up the calculated imperviousness of their tributary areas for use in calculations. Enclave at Redwood Page 11 October 19, 2021 Runoff will be routed to these systems via roof drains, swales, inlets and storm sewer pipes, and landscape drains, all to be designed in a later version of this report. Any on-Site runoff that is not practicable to route to a stormwater facility will leave the Site untreated, however more LID facilities may be added in a future revision to the Site’s drainage design to reduce the amount of area leaving the Site untreated. The above ground detention pond features water quality detention but does not treat for any areas already accounted for by LID facilities. Further breakdown of the LID areas and a summary table can be found below. For the SWMM analysis included in this preliminary drainage design report only seven subcatchments were used, and the only storm line included was the NECCO A2 storm lateral that receives the outfall from all five ponds and runoff from basins 213 and 413. This is a high-level analysis of the Site’s drainage and the SWMM subcatchments will be further refined for the final drainage report. Below is a breakdown of the seven subcatchments as well as a table featuring their SWMM input parameters. Also found below is a table summarizing SWMM model results. See Appendix C for summary of subcatchments and SWMM input parameters. See Appendix D for underground detention chamber layouts, stage-area tables for all ponds, SDI data sheets for all ponds, and any other pond calculations and information. See Appendix E for SWMM schematic, input report and output results. See Appendix F for LID calculations, summary table, and exhibit showing areas and locations of facilities. See Appendix G for drainage map showing pond locations, basins, drainage patterns, and storm layout. B. Proposed Basins Below is Table 1 featuring a summary of all basin input parameters for SWMM and other calculated parameters. Table 1: Pond Subcatchment Summary Table Basin Area (ac) Imperviousness (%) Width (ft) Slope (%) 2-Year Peak Runoff (CFS) 100- Year Peak Runoff (CFS) 113_1 4.28 55 1863.8 0.75 6.65 36.15 113_2 7.86 50 1342.2 0.50 9.93 50.32 113_3 9.75 65 2831.8 0.80 17.21 84.07 113_4 5.58 68 2432.3 0.60 10.51 50.65 213 7.82 75 1946.5 0.40 14.41 67.65 413 2.19 7 374.3 1.00 0.45 6.62 812 3.75 2 544.5 0.50 0.22 7.21 Basin 113_1 lies on-Site and encompasses the southwestern portion of the Site. This basin consists of multi-family housing, walks, roadways, alleys, open space and underground detention system UD1. Runoff from this basin will be conveyed to UD1 in the southern portion of this basin via roof drains, Enclave at Redwood Page 12 October 19, 2021 swales, storm sewer systems, and landscape drains. It is assumed that some potions of this basin will flow off-Site undetained and untreated into Redwood St or Lake Canal, but all of this basin is tributary to UD2 for the purpose of this preliminary drainage analysis. Basin 113_2 lies on-Site and encompasses the eastern portion and border of the Site. This basin consists of multi-family housing, walks, roadways, alleys, open space, portions of Lake Canal irrigation ditch and underground detention system UD2. Runoff from this basin will be conveyed to UD2 in the southwestern portion of the basin via roof drains, swales, storm sewer systems, and landscape drains. It is assumed that some portions of this basin will flow off-Site undetained and untreated into Lake Canal or the Northfield development, but all of this basin is tributary to UD2 for the purpose of this preliminary drainage analysis. Basin 113_3 lies on-Site and encompasses the middle portion of the Site spanning from the Redwood Meadows property boundary to the west to the northeastern corner of the Site. This basin consists of multi-family housing, walks, roadways, alleys, open space, isolator rows, and above ground detention pond Pond1. A majority of the runoff from this basin will be conveyed to the isolator row system IR1 in the middle of the basin via roof drains, swales, storm sewer systems, and landscape drains. All other runoff from this basin will be conveyed directly into Pond1 instead of being routed through IR1. The area Pond1 takes up will also be utilized as an open space park. It is assumed that some portions of this basin will flow undetained and untreated into inlets meant to capture basin 213, but all of this basin is tributary to Pond1 for the purpose of this preliminary drainage analysis. Basin 113_4 lies on-Site and encompasses the northern portion of the Site. This basin is consisting of multi-family housing, walks, roadways, alleys, open space, and underground detention system UD3. Runoff from this basin will be conveyed to UD3 in the northwestern portion of the basin via roof drains, swales, storm sewer systems, and landscape drains. It is assumed some portions of this basin will contribute runoff north off-Site undetained and untreated into the Redwood Channel drainage ditch, but all of this basin is tributary to UD3 for the purpose of this preliminary drainage analysis. Basin 213 lies off-Site to the west of the Site. This basin consists of the Redwood Meadows development featuring walks, single-family homes, roadways, and open spaces. Runoff from this basin will not need detained but will need to be conveyed to the NECCO A2 storm lateral. Two at-grade inlets are proposed at the connection of Lupine Dr and the Site to collect runoff from the roadways of this basin. An area inlet and swale are also proposed sitting just east of the Redwood Meadows development meant to collect any runoff from this basin that is not collected by the roadways within the basin. This basin slopes from the south to the northwest generally. This basins imperviousness was assumed to be 75% for conservative analysis but may decrease to a more exact value for the Final Drainage Report. Basin 413 lies on-Site south of E Suniga St. This basin will remain undeveloped and consists entirely of open space. Runoff from this basin will continue to follow historic patterns and discharge into Lake Canal. The NECCO report details an additional storm lateral A3 for this basin but will not be constructed because this lot will remain undeveloped. Basin 812 lies off-Site to the northwest of the Site. This basin consists of the existing Redwood Pond. Runoff from this basin will be collected by the Redwood Pond. Preliminary analysis was done to determine the amount of undetained and untreated flow leaving the Site. Note that for the final drainage design more of these areas may be picked up by on-Site storm Enclave at Redwood Page 13 October 19, 2021 sewer systems or LID facilities. Approximately 5.58 acres of the Site currently contributes flow off-Site untreated and undetained, with 0.21 acres being captured by the NECCO A2 storm lateral, 0.28 acres discharging into the Northfield development, 0.04 acres discharging into Redwood St, 0.60 acres discharging into Redwood Channel, and 4.45 acres discharging into Lake Canal. Note that runoff discharging from the developed Site into Lake Canal and Redwood Channel is mostly coming from open space. Further analysis of these areas will be conducted with the final drainage design of the Site. C. Specific Details The Redwood Pond outlet structure has been preliminarily designed as two modified Type C inlet boxes and grates as detailed in the NECCO report. The NECCO report calls for a pond bottom invert of 4953.10, so the proposed outlet structure will be buried until the Redwood Pond is regraded. Because the structure will be buried the only thing controlling the release rate in this preliminary design are the grates at the top of the structure. The release rate for the pond from the Site’s SWMM model can be ignored for the preliminary design of the Site, as final design of the outlet structure will be coordinated with the City. The pond’s berm and spillway will remain the same at an elevation of 4962.10, and the existing outlet pipe into Redwood Channel will be plugged as part of the ultimate condition for this pond. The stage-storage-discharge table presented in Appendix D for this pond was put together in order to not have any blank information in the SWMM model and begin design of the outlet structure, as long as the inaccurate release rates did not cause flooding in the SWMM model. The final release rate for this pond will be equal to or less than 15.96 CFS, as presented in the NECCO report. Pond1 is located in the middle portion of the Site and features a depth of 4.27 ft and a pond bottom elevation of 4957.48. The spillway has a crest elevation of 4960.25 and a length of 76 ft. The spillway is situated on the northern edge of the pond and will discharge runoff above the 100-year event into public roadway. Basin 113_3 (9.75 ac) is tributary to this pond, allowing for a release rate of 1.95 CFS for the 100-year storm event. Most of the runoff from basin 113_3 will be captured and treated for water quality by the isolator row LID facility named IR1 directly upstream of the pond. All runoff from this basin not treated by IR1 will be treated via standard practices in Pond1. Pond1 has a WQCV water surface elevation (WSEL) of 4958.65, modelled as an initial depth of 1.17 ft in the SWMM model. This pond will feature varying side slopes and aesthetically pleasing design. Due to this design and maintaining the open space this pond lies within as a usable park, the available storage volume (given a 0.5 ft spillway design flow depth and 1 ft of freeboard) is not large enough to capture and detain the full 100-year runoff while meeting the required release rate of 1.95 CFS. A dual outlet box structure has been preliminarily designed to release 1.95 CFS to the NECCO A2 storm lateral while bypassing the necessary extra 100-year runoff to detention facility UD2 in order to not cause overtopping of the spillway during the 100-year storm. The main outlet box will feature orifice holes and a weir grate as typical to treat the WQCV, and a restrictor plate to be designed during final drainage design that limits the release rate to 1.95 CFS. The secondary outlet box will feature a rectangular orifice with an invert above the WQCV WSEL and a pipe at the bottom of the box that will route undetained and untreated runoff to UD2. The volume of runoff bypassed to UD2 is approximately 2.02 ac-ft with a flow rate around 35 CFS. The minimum groundwater depth below this pond is 6.60 ft, with an elevation of 4950.88. Please see the table below for SWMM computed results for this pond. Underground detention system UD1 is located in the southwestern portion of the Site and features an invert elevation of 4951.40. This system will be comprised of 288 ADS MC-4500 Stormtech chambers with 9 inches of stone below the chambers and 12 inches of stone above the chambers. The total height of the system is 6.75 ft, putting the top of stone at an elevation of 4958.15. The minimum finished grade Enclave at Redwood Page 14 October 19, 2021 above the system is 4960.81 which is more than the 1 ft of required cover above the top of the system. The maximum groundwater elevation below the system is 4949.40, which is 24 inches below the bottom of the facility, meeting FCSCM criteria. Basin 113_1 (4.28 ac) is tributary to this system, allowing for a release rate of 0.86 CFS for the 100-year storm event. The system releases directly into the NECCO A2 storm lateral. The outlet manhole design to be included for final drainage design will feature an orifice plate, weir, and restrictor plate to hold the release rate to 0.86 CFS. Please see the table below for SWMM computed results for this system. The WQCV for this system will be treated entirely by isolator rows included in the system, see below for more information on these chambers. Underground detention system UD2 is located in the southwestern portion of the Site and features an invert elevation of 4946.76. This system will be comprised of 790 ADS MC-4500 Stormtech chambers with 54 inches of stone below the chambers and 12 inches of stone above the chambers. The total height of the system is 10.5 ft, putting the top of stone at an elevation of 4957.26. The minimum finished grade above the system is 4958.26 which is exactly the 1 ft of required cover above the top of the system. The maximum groundwater elevation around the system is 4948.42, which is 1.66 ft above the invert of the system. In order to effectively lower the groundwater around the system and meet FCSCM criteria a geotextile liner will be placed around the entirety of the system and an underdrain system will be placed around the bottom of the system. This underdrain system will be designed in a later version of this report. Basin 113_2 (7.86 ac) is tributary to the system, allowing for a release rate of 1.57 CFS for the 100-year storm event. The system releases directly into the NECCO A2 storm lateral. The outlet manhole design to be included for final drainage design will feature an orifice plate, weir, and restrictor plate to hold the release rate to 1.57 CFS. Please see the table below for SWMM computed results for this system. The WQCV for this system will be treated entirely by isolator rows included in the system, see below for more information on these chambers. Underground detention system UD3 is located in the northeastern portion of the Site and features an invert elevation of 4955.81. This system will be comprised of 363 ADS MC-3500 Stormtech chambers with 9 inches of stone below the chambers and 12 inches of stone above the chambers. The total height of the system is 5.50 ft, putting the top of stone at an elevation of 4961.31. The minimum finished grade above the system is 4961.81 which is exactly the 0.5 ft of required cover above the top of the system. The maximum groundwater elevation below the system is 4953.81, which is 24 inches below the bottom of the facility, meeting FCSCM criteria. Basin 113_4 (5.58 ac) is tributary to this system, allowing for a release rate of 1.12 CFS for the 100-year storm event. The system releases directly into the NECCO A2 storm lateral. The outlet manhole design to be included for final drainage design will feature an orifice plate, weir, and restrictor plate to hold the release rate to 1.12 CFS. Please see the table below for SWMM computed results for this system. The WQCV for this system will be treated entirely by isolator rows included in the system, see below for more information on these chambers. See below for Table 2 showing a summary of pond results from SWMM. The WQCV presented in this table for the underground detention systems is from the LID isolator rows to be discussed below. The WQCV for the above ground pond does not include any volume already treated by LID systems. The WQCV WSELs have been inputted into SWMM and not computed. Enclave at Redwood Page 15 October 19, 2021 Table 2: Detention Pond Summary Table Pond 100- Year Volume (cu-ft) 100- Year Volume (ac-ft) 100-Year WSEL WQCV (cu-ft) WQCV WSEL Max Release Rate (CFS) 100-Year Runoff Bypassing Detention Facility (ac-ft) UD1 43,219 0.992 4956.71 3252.00* 4952.15 0.86 N/A UD2 177,384 4.072 4957.26 3414.60* 4947.09 1.57 N/A Pond1 30,488 0.700 4960.25 1,812.10 4958.65 1.95 2.03** UD3 60,510 1.389 4960.41 5250.00* 4956.48 1.12 N/A *WQCV in Underground Chamber Systems Explored Further in LID Exhibit and Calculations Found in Appendix F of Preliminary Drainage Report **Pond1 Outlet Structure Configured Preliminarily to Detain and Release Maximum of 1.95 CFS, and Bypass Additional 100-Year Runoff to UD2. SWMM Model, Inputs, and Outputs Found in Appendix E of Preliminary Drainage Report Isolator rows IR1 are located in the middle portion of the Site, just upstream of Pond1. The sizing process for these chambers is located above in Section III. The result is 42 ADS MC-3500 Stormtech chambers. These chambers will have a release rate of 1.51 CFS. This system has a total height of 5.50 ft, requiring 2 ft below the system clear of groundwater, and 0.5 ft above the system for cover. The minimum groundwater depth for this system is approximately 11.50 ft, giving this system more than enough vertical clearance both ways. The 100-year runoff entering this system will bypass the system undetained and into Pond1. Isolator rows IR2, IR3, and IR4 are located within underground detention systems UD1, UD2, and UD3 respectively. These isolator row chambers will match the inverts and dimensions of the systems they are within. IR2 located within UD1 will feature 20 chambers, IR3 located within UD2 will feature 21 chambers, and IR4 located within UD3 will feature 30 chambers. Table 3 below features a summary of the LID systems for the Site including tributary area, imperviousness, impervious area, calculated WQCV, and provided WQCV. Enclave at Redwood Page 16 October 19, 2021 Table 3: Table 4 below features a summary of the SWMM results for nodes. Table 5 below features a summary of the SWMM results for links. See Appendix E for a schematic calling out the nodes summarized below. Table 4: SWMM Node Results Summary Table Node Type Maximum Depth (ft) Maximum HGL (ft) Maximum Total Inflow (CFS) A2_1 JUNCTION 3.57 4950.26 72.65 A2_2 JUNCTION 3.97 4950.97 71.12 A2_3 JUNCTION 3.51 4952.00 71.81 A2_4 JUNCTION 3.64 4952.91 72.45 A2_5 JUNCTION 4.01 4953.58 73.03 A2_6 JUNCTION 4.17 4954.21 72.38 A2_7 JUNCTION 3.32 4955.40 75.66 A2_8 JUNCTION 3.75 4956.29 76.09 A2_9 JUNCTION 3.52 4956.34 27.12 A2_10 JUNCTION 6.26 4959.36 29.71 NECCO_Stub OUTFALL 2.58 4949.16 79.1 Pond_Redwood STORAGE 2.34 4959.34 33.23 Pond1 STORAGE 2.66 4960.14 84.07 Pond1_Bypass JUNCTION 1.75 4959.23 35.88 Pond1_Outlet JUNCTION 2.65 4960.13 6.26 UD1 STORAGE 5.31 4956.71 36.15 UD2 STORAGE 10.50 4957.26 83.48 UD3 STORAGE 4.60 4960.41 50.65 Enclave at Redwood Page 17 October 19, 2021 Table 5: SWMM Link Results Summary Table Link Type Maximum Flow (CFS) Maximum Velocity (fps) Maximum/Full Flow Maximum/Full Depth A2_1 CONDUIT 72.65 7.07 0.83 0.77 A2_2 CONDUIT 71.08 5.84 0.69 0.93 A2_3 CONDUIT 70.26 5.84 0.69 0.92 A2_4 CONDUIT 71.81 6.38 0.71 0.88 A2_5 CONDUIT 72.45 5.97 0.71 0.94 A2_6 CONDUIT 71.08 5.68 0.7 0.99 A2_7 CONDUIT 72.38 6.16 0.71 0.92 A2_8 CONDUIT 75.66 6.66 0.74 0.87 A2_9 CONDUIT 27.01 5.43 0.85 1 A2_10 CONDUIT 26 10.81 3.53 1 Pond1_Bypass CONDUIT 25.76 9.63 0.73 0.89 Pond1_Outfall CONDUIT 1.95 3.46 0.13 1 Redwood_Outlet DUMMY 29.71 UD1_Outlet CONDUIT 0.86 3.44 0.04 1 UD2_Outlet CONDUIT 1.57 1.87 0.65 1 UD3_Outlet CONDUIT 1.12 4.11 0.1 1 V. CONCLUSIONS A. Compliance with Standards The drainage design is prepared in compliance with the FCSCM and the USDCM Volumes 1, 2, and 3. As stated before, the NECCO report details utilizing a release of less than 15.96 CFS for the Redwood Pond and less than 0.2 CFS/ac for the three on-Site ponds. This criteria has been met for the proposed preliminary drainage design. B. Drainage Concept The drainage design as described herein; if properly constructed and maintained, will effectively control stormwater runoff in accordance with the criteria. The proposed development will provide water quality and detention for the 100-year event with associated outlets and spillway overflow. This drainage design for the proposed development does not have any impact on the NECCO report design. The drainage design for this Site will have no adverse effects to any upstream or downstream adjacent properties. Enclave at Redwood Page 18 October 19, 2021 VI. REFERENCES 1. National Flood Hazard Layer FIRMette, City of Fort Collins, Colorado, Map No. 08069C0977G, Map No. 08069C0981G, June 17, 2008, Federal Emergency Management Agency. 2. Geotechnical Engineering Report for Enclave at Redwood Residential Development, Cole Garner Geotechnical, August 11, 2021. 3. Fort Collins Stormwater Criteria Manual, City of Fort Collins, revised December 2018. 4. Urban Storm Drainage Criteria Manual Vol. 1, Mile High Flood District, revised August 2018. 5. Urban Storm Drainage Criteria Manual Vol. 2, Mile High Flood District, revised September 2017. 6. Urban Storm Drainage Criteria Manual Vol. 3, Mile High Flood District, revised November 2010 with updates from January 2021. 7. North East College Corridor Outfall (NECCO) Design Report, Ayres Associates, August 2009. Enclave at Redwood Page 19 October 19, 2021 VII. APPENDICES Appendix A Vicinity Map, FIRM, Geotechnical Engineering Report Appendix B Portions from Relevant Previous Studies Appendix C Subcatchment Hydrology Appendix D Detention Storage Sizing Appendix E SWMM Model and Results Appendix F Low Impact Development Appendix G Drainage Map PROPOSED LID CALCULATIONSProject:Enclave at RedwoodDate:8/16/2021Date Revised:10/19/2021By:JMRBasinArea (sq-ft)Calculated Imperviousness (%)*Utilized Imperviousness (%)Impervious Area (sq-ft)120% WQCV (12-Hour Drain Time) (cu-ft)FAA WQCV (cu-ft)LID TreatmentProvided Volume in LID (cu-ft)IR-1305956.7371.1275217596.437331.484322.62Isolator Rows 17350IR-2143024.9065.597093810.033146.891787.29Isolator Rows 2 - UD13252IR-3141648.4172.5375102737.593394.251935.36Isolator Rows 3 - UD23414.6IR-4198045.5479.2980157030.315201.782408.87Isolator Rows 4 - UD35250Total LID Treated Area788675.5872.42571174.36Total Site Area1292085.4351.91670721.55Standard WQCV Treatment Area100771.7031.5431783.3985.16%Total LID Treated Impervious Area/Total Site Impervious Area (Must be > 75%)LOW IMPACT DEVELOPMENT SUMMARY TABLE**Isolator Rows were sized by comparing 120% of the WQCV based on a 12-Hour drain time and the City of Fort Collins Modified FAA Method*In some cases imperviousness was rounded up to be more conservative in sizing LID facilities, exact imperviousness was used to prove 75% of new impervious areas treated by LID IR1 ISOLATOR ROW VOLUME CALCULATION: MODIFIED FAA METHOD FROM FORT COLLINS IDF Project #201013 Project Name Enclave at Redwood *Unused Designer JMR Date 10/12/2021 0.7549 7.0238 1.51 Time (min)WQCV Intensity (1/2 of 2-Year Intensity) (in/hr) Volume In (cu-ft) Out Factor* Adjusted Release (CFS) Volume Out (cu-ft) Storage (cu-ft) 5 1.425 2266.719 1.00 1.5100 453.000 1813.72 10 1.105 3515.403 1.00 1.5100 906.000 2609.40 15 0.935 4461.857 1.00 1.5100 1359.000 3102.86 20 0.805 5121.990 0.95 1.4345 1721.400 3400.59 25 0.715 5686.681 0.86 1.2986 1947.900 3738.78 30 0.65 6203.652 0.80 1.2080 2174.400 4029.25 35 0.585 6513.835 0.76 1.1476 2409.960 4103.87 40 0.535 6808.110 0.73 1.1023 2645.520 4162.59 45 0.495 7086.479 0.70 1.0570 2853.900 4232.58 50 0.46 7317.128 0.68 1.0268 3080.400 4236.73 55 0.435 7611.404 0.66 0.9966 3288.780 4322.62 60 0.41 7826.146 0.65 0.9815 3533.400 4292.75 65 0.39 8064.748 0.64 0.9664 3768.960 4295.79 70 0.365 8128.375 0.63 0.9513 3995.460 4132.91 75 0.35 8351.070 0.62 0.9362 4212.900 4138.17 80 0.33 8398.790 0.61 0.9211 4421.280 3977.51 85 0.32 8653.299 0.61 0.9211 4697.610 3955.69 90 0.305 8732.833 0.60 0.9060 4892.400 3840.43 95 0.29 8764.647 0.59 0.8909 5078.130 3686.52 100 0.28 8907.808 0.59 0.8909 5345.400 3562.41 105 0.27 9019.156 0.59 0.8909 5612.670 3406.49 110 0.26 9098.690 0.58 0.8758 5780.280 3318.41 115 0.255 9329.338 0.58 0.8758 6043.020 3286.32 120 0.245 9353.198 0.58 0.8758 6305.760 3047.44 4322.62 Qout (From ADS maximum chamber flow rate)(CFS) FAA Method Table Maximum Storage Represents Required WQCV C (From Fort Collins Storm Criteria Manual) Area (ac) ABC DEFGHIJKLMNVAULT IDTOTAL REQUIRED WQCV(CF)WQ FLOW (CFS)CHAMBER TYPERELEASE RATE/CHAMBER(CFS)CHAMBER VOLUME(CF)CHAMBER VOLUME + AGGREGATE(CF)NUMBER OF CHAMBERSCOMBINED RELEASE RATE WQCV METHOD(CFS)FAA REQUIRED STORAGE VOLUME (CF)NUMBER OF CHAMBERS (FAA)TOTAL VOLUME (CHAMBERS ONLY)(CF)COMBINED RELEASE RATE FAA METHOD (CFS)TOTAL NUMBER OF CHAMBERS REQUIREDTOTAL SYSTEM VOLUME (CF)7331.4840MC-35000.036109.9175.0421.514322.624043961.43427350CONFIRMCONFIRMAMHFD Rain Garden UD-BMP WQCV * 120%B1/2 of the 2-year developed flow rate for the basin being sizedCChamber type based on site constraintsDFlwo rate thru the bottom of the isolator row chamber which is equal to the area of the bottom of the chamber multiplied by the flow rate per unit area (see calculations below)EVolume within chamber only, not accounting for void spaces in surrounding aggregate (standard spec)FVolume includes chamber and void space (40%) in surrounding aggregate , per chamber unit. (standard spec)GNumber of chambers required to provide full WQCV within total installed system, include aggregate = A / FHRelease rate per chamber times number of chambers = D * G IFAA calc based on Flow, WQ and Total Release RateJNumber of chambers required to provide required FAA staorage volume stored within the chamber only (no aggregate stone) = I / EKVolume provided in chambers only (no aggregate storage). This must meet or excheed the required FAA storage volume. Greater of G or J * E LRelease rate per chamber times number of chambers = D * J MTotal number of chambers (Greater of J or G)NTotal system volume. Includes number of chambers plus aggregate. This must meet or exceed required WQCVMC-4500MC-3500SC-740SC-310SC-160LP60.045.030.016.012.0100.077.051.034.025.048.386.085.485.485.433.546.030.220.214.8106.5109.985.914.76.9162.6175.074.931.015.0CHAMBER FLOW RATE CONVERSION (GPM/SF TO CFS)0.35GPM/SF1 CF=7.48052GAL1 GALLON=0.133681CF 1 GPM=0.002228CFS*FLOW RATE BASED ON 1/2 OF NOV 07 QMAX IN FIGURE 17 OF UNH TESTING REPORTMC-4500MC-3500SC-740SC-310SC-160LP0.02620.0360.0240.0160.012(COLUMN D)FLOW RATE / CHAMBER (CFS)STORMTECH CHAMBER VOLUME AND RELEASE RATE CALCULATIONSFLOOR AREA (SF)CHAMBER VOLUME (CF)CHAMBER/AGGREGATE VOLUME (CF)STORMTECH CHAMBER DATAFLOW RATE*CHAMBER FLOW RATECHAMBER DIMENSIONSWIDTH (IN)INSTALLED LENGTH (IN)HEIGHT (IN) UD1 ISOLATOR ROW VOLUME CALCULATION: MODIFIED FAA METHOD FROM FORT COLLINS IDF Project #201013 Project Name Enclave at Redwood *Unused Designer JMR Date 10/12/2021 0.7089 3.2834 0.52 Time (min)WQCV Intensity (1/2 of 2-Year Intensity) (in/hr) Volume In (cu-ft) Out Factor* Adjusted Release (CFS) Volume Out (cu-ft) Storage (cu-ft) 5 1.425 995.050 1.00 0.5200 156.000 839.05 10 1.105 1543.200 1.00 0.5200 312.000 1231.20 15 0.935 1958.677 1.00 0.5200 468.000 1490.68 20 0.805 2248.464 0.95 0.4940 624.000 1624.46 25 0.715 2496.353 0.86 0.4472 780.000 1716.35 30 0.65 2723.295 0.80 0.4160 936.000 1787.29 35 0.585 2859.459 0.76 0.3952 1092.000 1767.46 40 0.535 2988.641 0.73 0.3796 1248.000 1740.64 45 0.495 3110.840 0.70 0.3640 1404.000 1706.84 50 0.46 3212.091 0.68 0.3536 1560.000 1652.09 55 0.435 3341.273 0.66 0.3432 1716.000 1625.27 60 0.41 3435.541 0.65 0.3380 1872.000 1563.54 65 0.39 3540.283 0.64 0.3328 2028.000 1512.28 70 0.365 3568.214 0.63 0.3276 2184.000 1384.21 75 0.35 3665.974 0.62 0.3224 2340.000 1325.97 80 0.33 3686.922 0.61 0.3172 2496.000 1190.92 85 0.32 3798.647 0.61 0.3172 2652.000 1146.65 90 0.305 3833.561 0.60 0.3120 2808.000 1025.56 95 0.29 3847.527 0.59 0.3068 2964.000 883.53 100 0.28 3910.372 0.59 0.3068 3120.000 790.37 105 0.27 3959.251 0.59 0.3068 3276.000 683.25 110 0.26 3994.165 0.58 0.3016 3432.000 562.17 115 0.255 4095.416 0.58 0.3016 3588.000 507.42 120 0.245 4105.890 0.58 0.3016 3744.000 361.89 1787.29 Qout (From ADS maximum chamber flow rate)(CFS) FAA Method Table Maximum Storage Represents Required WQCV C (From Fort Collins Storm Criteria Manual) Area (ac) ABC DEFGHIJKLMNVAULT IDTOTAL REQUIRED WQCV(CF)WQ FLOW (CFS)CHAMBER TYPERELEASE RATE/CHAMBER(CFS)CHAMBER VOLUME(CF)CHAMBER VOLUME + AGGREGATE(CF)NUMBER OF CHAMBERSCOMBINED RELEASE RATE WQCV METHOD(CFS)FAA REQUIRED STORAGE VOLUME (CF)NUMBER OF CHAMBERS (FAA)TOTAL VOLUME (CHAMBERS ONLY)(CF)COMBINED RELEASE RATE FAA METHOD (CFS)TOTAL NUMBER OF CHAMBERS REQUIREDTOTAL SYSTEM VOLUME (CF)3146.8920MC-45000.026106.5162.6200.521787.291718110.44203252CONFIRMCONFIRMAMHFD Rain Garden UD-BMP WQCV * 120%B1/2 of the 2-year developed flow rate for the basin being sizedCChamber type based on site constraintsDFlwo rate thru the bottom of the isolator row chamber which is equal to the area of the bottom of the chamber multiplied by the flow rate per unit area (see calculations below)EVolume within chamber only, not accounting for void spaces in surrounding aggregate (standard spec)FVolume includes chamber and void space (40%) in surrounding aggregate , per chamber unit. (standard spec)GNumber of chambers required to provide full WQCV within total installed system, include aggregate = A / FHRelease rate per chamber times number of chambers = D * G IFAA calc based on Flow, WQ and Total Release RateJNumber of chambers required to provide required FAA staorage volume stored within the chamber only (no aggregate stone) = I / EKVolume provided in chambers only (no aggregate storage). This must meet or excheed the required FAA storage volume. Greater of G or J * E LRelease rate per chamber times number of chambers = D * J MTotal number of chambers (Greater of J or G)NTotal system volume. Includes number of chambers plus aggregate. This must meet or exceed required WQCVMC-4500MC-3500SC-740SC-310SC-160LP60.045.030.016.012.0100.077.051.034.025.048.386.085.485.485.433.546.030.220.214.8106.5109.985.914.76.9162.6175.074.931.015.0CHAMBER FLOW RATE CONVERSION (GPM/SF TO CFS)0.35GPM/SF1 CF=7.48052GAL1 GALLON=0.133681CF 1 GPM=0.002228CFS*FLOW RATE BASED ON 1/2 OF NOV 07 QMAX IN FIGURE 17 OF UNH TESTING REPORTMC-4500MC-3500SC-740SC-310SC-160LP0.02620.0360.0240.0160.012(COLUMN D)FLOW RATE / CHAMBER (CFS)STORMTECH CHAMBER VOLUME AND RELEASE RATE CALCULATIONSFLOOR AREA (SF)CHAMBER VOLUME (CF)CHAMBER/AGGREGATE VOLUME (CF)STORMTECH CHAMBER DATAFLOW RATE*CHAMBER FLOW RATECHAMBER DIMENSIONSWIDTH (IN)INSTALLED LENGTH (IN)HEIGHT (IN)