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Home My WebLink AboutNORTHFIELD COMMONS - MJA210001 - SUBMITTAL DOCUMENTS - ROUND 2 - DRAINAGE REPORT PRELIMINARY DRAINAGE REPORT FOR Northfield Commons Prepared by: Highland Development Services 6355 Fairgrounds Ave, Suite 100 Windsor, Colorado 80550 Phone: 970.674.7550 Prepared for: Mercy Housing 1600 Broadway, Suite 200 Denver, CO 80202 Phone: 303.830.3470 June 9, 2021 Job Number 21-1037-00 6355 FAIRGROUNDS AVE, SUITE 100, WINDSOR, COLORADO 80550 | PHONE 970.674.7550 June 9, 2021 Mr. Dan Mogen Fort Collins Utilities 700 Wood Street Fort Collins, CO 80522 RE: Preliminary Drainage Report for Northfield Commons Dear Dan, We are pleased to submit for your review, the Preliminary Drainage Report for the Northfield Commons, an amendment to the “Final Drainage Report for Northfield” prepared by Highland Development Services, dated February 26, 2020. This report describes the drainage design intent to be in accordance with the criteria in the City of Fort Collins Storm Drainage Manual. I appreciate your time and consideration in reviewing this submittal. Please call if you have any questions. Sincerely, Adele McKenna, EI Jason T. Claeys, P.E., LEED AP Highland Development Services Page i TABLE OF CONTENTS Table of Contents ............................................................................................................................. i Engineer’s Certification Block ..........................................................................................................ii General Description and Location .................................................................................................. 1 Site Description and Location ...................................................................................................... 1 Site Soils ....................................................................................................................................... 1 Previous Studies .......................................................................................................................... 2 Storm Drainage Criteria .................................................................................................................. 3 Hydrologic Criteria ....................................................................................................................... 3 Hydraulic Criteria ......................................................................................................................... 3 Drainage Basins ............................................................................................................................... 4 Drainage Facility Design .................................................................................................................. 5 Drainage Conveyance Design ...................................................................................................... 5 Detention/Water Quality Pond Design ....................................................................................... 5 Low Impact Development ............................................................................................................... 6 Stormwater Pollution Prevention ................................................................................................... 8 Conclusions ..................................................................................................................................... 9 References .................................................................................................................................... 10 Appendix ....................................................................................................................................... 11 Appendix A – Site Descriptions, Characteristics, & References .................................................. A Appendix B – Rational Calculations ............................................................................................. B Appendix C – Low Impact Development Calculations ................................................................. C Page ii ENGINEER’S CERTIFICATION BLOCK I hereby attest that this report for the Preliminary Drainage Design for Northfield Commons was prepared by me (or under my direct supervision) in accordance with the provisions of the Fort Collins Stormwater Criteria Manual for the owners thereof. I understand that the City of Fort Collins does not and will not assume liability for drainage facilities designed by others. ________________________________________ Jason T. Claeys, PE Registered Professional Engineer State of Colorado No. 42122 Page 1 GENERAL DESCRIPTION AND LOCATION SITE DESCRIPTION AND LOCATION Northfield Commons (NFC) is located in the Southeast Quarter of Section 1, Township 7 North, Range 69 West of the Sixth Principal Meridian, City of Fort Collins, County of Larimer, within the State of Colorado. NFC is located west of the Alta Vista Subdivision, north of the Rocky Mountain Raptor Center, south of the proposed Suniga Road, and southeast of the Lake Canal irrigation ditch. More specifically, NFC is located within the replat of Tracts U & V of Northfield, with the areas of water quality and detention being provided for these proposed improvements within Northfield Tract W. The project site is approximately 6.45 acres and is currently undeveloped agricultural land. The site appears to be vegetated with grasses harvested for livestock feed. The site generally slopes from the northwest to the southeast at about 0.5% slope. This area is part of the approved improvements associated with Northfield and the improvements described within are considered an amendment to the approved plans and repo rts. The overall Northfield site is currently under construction though there are no existing surface improvements currently on the property. The property is proposed to be replatted into a multi-family development. NFC will consist of 7 apartment buildings and 4 condominium buildings, along with the associated utility and access infrastructure. The NFC improvements are located within the FEMA Zone X, area of 0.2% annual chance of flood hazard as shown on FEMA FIRM map numbers LOMR 19-08-0715P (effective June 15, 2020). The site is located within the Cache la Poudre River 500-yr floodplain. Critical facilities are prohibited within the 100-yr and/or 500-yr floodplains. Critical facilities include facilities for at-risk populations (daycares, schools, nursing homes, etc) and emergency service facilities (urgent care, hospitals, fire stations, police stations, etc). SITE SOILS The NFC site consists of Loveland clay loam and Nunn clay loam and are classified as Type C hydrologic group. According to USDA/Natural Resource Conservation Group, this soil has a slow infiltration rate when thoroughly wet. These soils consist chiefly of soils having a layer that impedes the downward movement of water or soils of moderately fine texture or fine texture. These soils have a slow rate of water transmission. Page 2 Per the “Preliminary Subsurface Exploration and Groundwater Report – Schlagel Property”, prepared be Earth Engineering Consultants (EEC), dated August 16, 2017: Vegetation growth and topsoil was encountered at the surface of each boring. Underlying the topsoil/vegetation layer was a zone of cohesive subsoils classified lean to fat clay with varying amounts of sand and clayey sand to approximate depths of 2 to 5-1/2 feet. Underlying the cohesive subsoils was a granular layer of poorly to well graded sand with silt and gravel extending to the depths explored at approximately 14 to 21-1/2 feet or to underlying bedrock. It appears that below the lean to fat clay, there is a granular materials layer that would exhibit more moderate infiltration rates than the surface materials. Groundwater was also observed during the subsurface soil exploration: Groundwater and/or the presence of a piezometric water surface, was generally observed at depths ranging from approximately 3 to 7 feet below ground surface as indicated on the enclosed boring logs. A permanent dewatering system has been installed with the Northfield project and the groundwater is anticipated to be maintained approximately 9 to 10 feet below the exi sting grades. Supporting figures can be found in Appendix A. PREVIOUS STUDIES The Northfield Subdivision originally included the Northfield Commons project site as part of the drainage design. In the approved Northfield Utility Plans and Final Drainage Report, the NFC site was broken into sub-basins and analyzed using rational calculations for inlet sizing and EPA SWMM for pond and conveyance element sizing. These results, along with the LID calculations, are referenced to provide confirmation that the proposed NFC improvements are within the previously assumed improvements determined to size the stormwater infrastructure accordingly. The inlets and storm drains in NFC will be sized to accommodate the proposed improvements. Detention, water quality, and LID calculations will be updated as necessary. Page 3 STORM DRAINAGE CRITERIA This report was prepared to meet or exceed the City of Fort Collins storm water criteria. The City of Fort Collin’s Stormwater Criteria Manual was referenced as guidelines for this design. HYDROLOGIC CRITERIA The rational method was performed to calculate the peak runoff rates for each basin. Percent imperviousness and runoff coefficients were calculated for each basin using the surface characteristics of each basin. The time of concentration was calculated using City of Fort Collins initial time of concentration and the intensity was calculated using the corresponding storm rainfall depth and the City of Fort Collins’ Intensity-Duration-Frequency Curve. HYDRAULIC CRITERIA The NFC storm drainage system has been analyzed to verify conformance with the drainage system design of Northfield. The NFC system is to be designed to convey the minor and major storm events through the combination of private drives, inlets, storm sewer pipes, and pans. The NFC peak basin runoff flows from the rational calculations will be used to size area inlets and confirm private drive capacities. For the purposes of this preliminary study, the rational and attenuated rational calculations have been prepared to confirm the proposed improv ements are within, and not exceeding, the original assumptions of the Northfield Final Drainage Report. The Northfield drainage design utilized EPA SWMM to model the captured flows and size conveyance elements and detention ponds. It is assumed that the inlets are free of clogging debris and capturing the maximum amount of runoff. The program accounts for head losses within manholes and bends and head losses associated with pipe friction. The SWMM model will be updated for the final report. All pipe outlets are protected with buried riprap or suitable erosion protection methods. Storm sewer pipe outlets are protected using the requirements set by the USDCM for the protection downstream of culverts. All supporting calculations for runoff rates, street sections, and inlets are located in the Appendix. Page 4 DRAINAGE BASINS The Northfield Commons (NFC) project site is located within Northfield Drainage System D. Drainage System D outfalls into the existing Northeast College Corridor Outfall (NECCO) storm system. The descriptions within are an amendment to Northfield’s Drainage System D and described below: Drainage System D: Drainage System D consists of 9.18 acres of improvements within the area south of Suniga Road. Runoff from basins in the D system drain to an extended detention basin, Pond D. Sub-basin D1 consist of 3.05 acres of apartment buildings, private drives, and open space. Runoff is conveyed via roof downspouts, roadways, and concrete pans, and is captured by a Type 13 and a Type C inlet, ultimately discharged to detention Pond D and treated for standard water quality. Sub-basins D2 thru D3 consist of 0.15 acres of public roadway. This basin includes portions of Steeley Drive. Runoff from these basins is conveyed along roadways and is captured by two on-grade 5’ Type R curb inlets, ultimately discharging to detention Pond D and treated for standard water quality. Sub-basin D4 consist of 0.24 acres of open space and concrete sidewalk. Runoff is conveyed via sheet flow to area inlets and is ultimately discharged to detention Pond D and treated for standard water quality. Sub-basins D5 thru D8 consist of 3.15 acres of apartment buildings, condominiums, private drives, and open space. Runoff from these basins is conveyed via roof downspouts, roadways, concrete pans and storm pipes, ultimately discharging to LID facility, Rain Garden D1. Sub-basin D9 consists of 2.50 acres of open space encompassing detention Pond D. This basin’s detention requirements allows a release rate equal to the current/historic run off rates and is accounted for in the Pond D detention volume calculations. An outlet structure in Pond D has been designed as part of the Northfield subdivision to limit discharge into the NECCO storm system as well as treat for standard water quality enhancement. Page 5 DRAINAGE FACILITY DESIGN DRAINAGE CONVEYANCE DESIGN Storm infrastructure to convey runoff will include concrete trickle pans, inlets, storm sewer and culverts. Stormwater detention and water quality enhancement will be achieved through the use of Northfield Pond D and Northfield Rain Garden D1. Storm inlets, storm sewers and the roadway culverts have been appropriately sized to convey the minor and major storms. DETENTION/WATER QUALITY POND DESIGN Below is an excerpt of the detention and water quality design from the “Final Drainage Report for Northfield” prepared by Highland Development Services as it pertains to the amended Northfield Commons development: EPA SWMM 5.0 has been utilized for the final drainage design. UDFCD is referenced for the standard water quality capture volume (WQCV) with a 40-hr drain time and the LID rain gardens and infiltration galleries WQCV with a 12-hr drain time. Below is a brief summary of the proposed design for each pond: Pond D: Extended detention basin for all area south of Suniga Road, with LID rain garden and standard water quality treatment via the outlet structure located at the north center of the pond. An 4-3/4” 100-yr orifice plate maximizes volume in the pond and restricts release rate into the NECCO system. The rain garden includes a concrete forebay sized for 1% of the surface area for WQCV with a rock embankment to dissipate flows before entering the media material. Large storm events in excess of the rain garden capacity will spill over a turf mat reinforced berm and down into Pond D. The 100-yr water surface elevation is 4949.54 feet, with a maximum depth in the pond of 3.92 feet, with another 1.46 feet of additional volume available. Should the pond outlet become clogged, overtopping will occur along the east side near design point D15, spilling over the sidewalk across a length of 120 feet at a depth of 0.32 feet (spill elevation = 4951.75), into Lemay Ave public ROW. As stated, the ultimate outfall for the Northfield site is the existing NECCO storm drain system. A portion of the area south of Suniga Road (delineated as sub-basins D13-D15) is allowed to release at a rate equal to current undeveloped/historic rates with the remaining area (delineated as sub-basins D1-D12) restricted to the 0.2 cfs/acre rate. Page 6 LOW IMPACT DEVELOPMENT The City of Fort Collins updated the Low Impact Development ordinance in 2016 (Ordinance No. 007, 2016) to require: • Treat at least 75% of any newly developed or redeveloped impervious area using one or a combination of LID techniques, or • Treat at least 50% of any newly developed or redeveloped impervious area using one or a combination of LID techniques when 25% of private driveable surfaces are permeable. To satisfy the required implementation of Low Impact Development (LID) techniques, Northfield Commons will utilize bioretention pond/Rain Garden D1 that was previously designed as part of the Northfield subdivision. Impervious calculations for the tributary areas to the rain garden and standard water quality facility have been updated for the amended site layout. LID treatment requirements for the entire Northfield subdivision are still exceeded, achieving approximately 104% of the required impervious area treatment in the rain gardens and infiltration galleries. The water quality capture volume needed within the rain garden (LID) is 1,995 cu-ft and the pond (standard WQCV) is 0.090 ac-ft. Both are less than the Northfield design for the rain garden and pond which are 2,384 cu-ft and 0.092 ac-ft respectively, and therefore will not require redesign. Below is a description of the 4-step process for selecting structural BMPs: Urban Drainage and Flood Control District (UDFCD) recommends a Four Step Process for receiving water protection that focuses on reducing runoff volumes, treating the water quality capture volume (WQCV), stabilizing drainageways and implementing long-term source controls. The Four Step Process applies to the management of smaller, frequently occurring events. Step 1: Employ Runoff Reduction Practices To reduce runoff peaks, volumes, and pollutant loads from urbanizing areas, implement Low Impact Development (LID) strategies, including Minimizing Directly Connected Impervious Areas (MDCIA). Captured runoff from strategic areas are routed through bioretention pond/rain gardens. Rain gardens will slow runoff, promote infiltration, and filter runoff prior to being released into the adjacent storm drain system. Page 7 Step 2: Implement BMPs that Provide a Water Quality Capture Volume with Slow Release The bioretention pond/rain gardens are designed to provide water quality capture volume per Urban Drainage’s recommendations and calculations. The captured runoff is designed for a 12- hr drain time. Step 3: Stabilize Drainageways Natural Drainageways are subject to bed and bank erosion due to increases in frequency, duration, rate and volume of runoff during and following development. Because the site will drain to an existing storm system, bank stabilization is unnecessary with this project. Riprap and turf reinforcement mats are utilized throughout for onsite permanent stabilization. Step 4: Implement Site Specific and Other Source Control BMPs The proposed project amendment will improve upon site specific source controls compared to historic conditions by providing localized trash enclosures within the development for disposal of solid waste; Snouts, and rain gardens for water treatment prior to flows entering storm systems; and additional water quality measures to protect and prolong the design life of BMPS delineated in Step 1. Page 8 STORMWATER POLLUTION PREVENTION Erosion and sedimentation will be controlled on-site by use of sediment control logs, silt fencing, inlet protection, gravel construction entrances, temporary sediment basins, seeding, mulch, and turf. The measures are designed to limit the overall sediment yield increase due to construction as required by the City of Fort Collins. During overlot and final grading the soil will be roughened and furrowed perpendicular to the prevailing winds. During the performance of the work required by these specifications or any operations appurtenant thereto, whether on right-of-way provided by the City or elsewhere, the contractor shall furnish all labor, equipment, materials, and means required. The Contractor shall carry out proper efficient measures wherever and as necessary to reduce dust nuisance, and to prevent dust nuisance that has originated from his operations from damaging crops, orchards, cultivated fields, and dwellings, or causing naissance to persons. The Contractor will be held liable for any damage resulting from dust originating from his operations under these specifications on right-of-way or elsewhere. It is unlawful to track or cause to be tracked mud or other debris onto city streets or rights-of- way. Wherever construction vehicles access routes or intersect paved public roads, previsions must be made to minimize the transport of sediment by runoff or vehicles tracking onto the paved surface. Stabilized construction entrances are required with base material consisting of 6” coarse aggregate. The contractor will be responsible for clearing mud tracked onto city streets on a daily basis. All temporary and permanent erosion and sediment control practices must be maintained and repaired as needed to assure continued performance of their intended function. Silt fence and sediment control logs will require periodic replacement. Maintenance is the responsibility of the contractor. All disturbed areas must be seeded and mulched within 30 days of project start. Vegetation shall not be considered established until a ground cover is achieved which is demonstrated to be mature enough to control soil erosion to the satisfaction of the City Inspector and to survive severe weather condition. Page 9 CONCLUSIONS This Preliminary Drainage Report for Northfield Commons has been prepared to comply with the stormwater criteria set by the City of Fort Collins. The proposed drainage system presented in this report adheres to the overall Northfield subdivision design. The system conveys the developed peak storm water runoff through the site to the existing storm drain system and to the development’s LID features, detention and water quality facilities. The peak flows for the amended design are less than the original design (Exhibit B02) and therefore no updated design is required for the street capacities and inlet sizing. This drainage report anticipates the implementation of best management practices for erosion control, temporary and permanent, and on-site construction facilities. It can therefore be concluded that development of Northfield Commons complies with the storm water jurisdictional criteria and will not adversely affect the adjacent properties, streets, storm drain system and/or detention/water quality facilities. Controlling the developed runoff from these improvements will improve the situations currently existing on the site. Page 10 REFERENCES 1. Urban Storm Drainage Criteria Manual (Volumes 1, 2, and 3), Urban Drainage and Flood Control District, June 2001, Revised January 2016. 2. Fort Collins Stormwater Criteria Manual, Fort Collins Utilities, City of Fort Collins, Colorado, Dated December 2018, Adopted January 2019. 3. “Hydrologic Group Rating for Larimer County Area, Colorado”, USDA-Natural Resources Conservation Service, National Cooperative Soil Survey. Web Soil Survey URL: http://websoilsurvey.nrcs.usda.gov. [12/06/2017] 4. “Preliminary Subsurface Exploration and Groundwater Report – Schlagel Property”, prepared by Earth Engineering Consultants, LLC, Dated August 16, 2017 5. “Flood Insurance Rate Map, Larimer County, Colorado – LOMR 19-08-0751P”, Federal Emergency Management Agency, Map Revised June 15, 2020. 6. “Final Drainage Report for Northfield”, prepared by Highland Development Services, Dated February 26, 2020. Page 11 APPENDIX Appendix A – Site Descriptions, Characteristics, & References Appendix B – Rational Calculations Appendix C – Low Impact Development Calculations Appendix A APPENDIX A – SITE DESCRIPTIONS, CHARACTERISTICS, & REFERENCES SITE Vicinity Map Scale: 1" = 1000' PROJECT DATUM: NAVD88 CITY OF FORT COLLINS BENCHMARK #43-97 ON THE SOUTH END OF THE WEST HEADWALL OF THE LAKE CANAL BRIDGE AT NORTH LEMAY AVENUE, 200 FEET SOUTH OF THE INTERSECTION OF LEMAY AVENUE AND CONIFER STREET ELEV= 4960.11 CITY OF FORT COLLINS BENCHMARK #12-07 SOUTH SIDE OF VINE DRIVE ON THE SOUTH HEADWALL OF THE BRIDGE OVER DRY CREEK BASIN 0.4 MILES EAST OF NORTH LEMAY AVENUE ELEV= 4947.86 BASIS OF BEARINGS: PLEASE NOTE: THIS PLAN SET IS USING NAVD88 FOR A VERTICAL DATUM. SURROUNDING DEVELOPMENTS HAVE USED NGVD29 UNADJUSTED DATUM (PRIOR CITY OF FORT COLLINS DATUM) FOR THEIR VERTICAL DATUMS. IF NGVD29 UNADJUSTED DATUM (PRIOR CITY OF FORT COLLINS DATUM) IS REQUIRED FOR ANY PURPOSE, THE FOLLOWING EQUATIONS SHOULD BE USED: NGVD29 UNADJUSTED DATUM (PRIOR CITY OF FORT COLLINS DATUM) = 4960.11 (NAVD88 DATUM) - 3.17' NGVD29 UNADJUSTED DATUM (PRIOR CITY OF FORT COLLINS DATUM) = 4947.86 (NAVD88 DATUM) - 3.18' N W E S NORTHFIELD COMMONS Hydrologic Soil Group—Larimer County Area, Colorado (NorthField) Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 12/6/2017 Page 1 of 444941304494220449431044944004494490449458044946704494130449422044943104494400449449044945804494670494350494440494530494620494710494800494890494980495070495160 494350 494440 494530 494620 494710 494800 494890 494980 495070 495160 40° 36' 11'' N 105° 4' 2'' W40° 36' 11'' N105° 3' 23'' W40° 35' 52'' N 105° 4' 2'' W40° 35' 52'' N 105° 3' 23'' WN Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 13N WGS84 0 200 400 800 1200 Feet 0 50 100 200 300 Meters Map Scale: 1:4,140 if printed on A landscape (11" x 8.5") sheet. Soil Map may not be valid at this scale. MAP LEGEND MAP INFORMATION Area of Interest (AOI) Area of Interest (AOI) Soils Soil Rating Polygons A A/D B B/D C C/D D Not rated or not available Soil Rating Lines A A/D B B/D C C/D D Not rated or not available Soil Rating Points A A/D B B/D C C/D D Not rated or not available Water Features Streams and Canals Transportation Rails Interstate Highways US Routes Major Roads Local Roads Background Aerial Photography The soil surveys that comprise your AOI were mapped at 1:24,000. Warning: Soil Map may not be valid at this scale. Enlargement of maps beyond the scale of mapping can cause misunderstanding of the detail of mapping and accuracy of soil line placement. The maps do not show the small areas of contrasting soils that could have been shown at a more detailed scale. Please rely on the bar scale on each map sheet for map measurements. Source of Map: Natural Resources Conservation Service Web Soil Survey URL: Coordinate System: Web Mercator (EPSG:3857) Maps from the Web Soil Survey are based on the Web Mercator projection, which preserves direction and shape but distorts distance and area. A projection that preserves area, such as the Albers equal-area conic projection, should be used if more accurate calculations of distance or area are required. This product is generated from the USDA-NRCS certified data as of the version date(s) listed below. Soil Survey Area: Larimer County Area, Colorado Survey Area Data: Version 12, Oct 10, 2017 Soil map units are labeled (as space allows) for map scales 1:50,000 or larger. Date(s) aerial images were photographed: Mar 20, 2015—Oct 15, 2016 The orthophoto or other base map on which the soil lines were compiled and digitized probably differs from the background imagery displayed on these maps. As a result, some minor shifting of map unit boundaries may be evident. Hydrologic Soil Group—Larimer County Area, Colorado (NorthField) Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 12/6/2017 Page 2 of 4 Hydrologic Soil Group Map unit symbol Map unit name Rating Acres in AOI Percent of AOI 64 Loveland clay loam, 0 to 1 percent slopes C 11.9 20.9% 73 Nunn clay loam, 0 to 1 percent slopes C 16.6 29.2% 76 Nunn clay loam, wet, 1 to 3 percent slopes C 28.3 49.9% Totals for Area of Interest 56.7 100.0% Description Hydrologic soil groups are based on estimates of runoff potential. Soils are assigned to one of four groups according to the rate of water infiltration when the soils are not protected by vegetation, are thoroughly wet, and receive precipitation from long-duration storms. The soils in the United States are assigned to four groups (A, B, C, and D) and three dual classes (A/D, B/D, and C/D). The groups are defined as follows: Group A. Soils having a high infiltration rate (low runoff potential) when thoroughly wet. These consist mainly of deep, well drained to excessively drained sands or gravelly sands. These soils have a high rate of water transmission. Group B. Soils having a moderate infiltration rate when thoroughly wet. These consist chiefly of moderately deep or deep, moderately well drained or well drained soils that have moderately fine texture to moderately coarse texture. These soils have a moderate rate of water transmission. Group C. Soils having a slow infiltration rate when thoroughly wet. These consist chiefly of soils having a layer that impedes the downward movement of water or soils of moderately fine texture or fine texture. These soils have a slow rate of water transmission. Group D. Soils having a very slow infiltration rate (high runoff potential) when thoroughly wet. These consist chiefly of clays that have a high shrink-swell potential, soils that have a high water table, soils that have a claypan or clay layer at or near the surface, and soils that are shallow over nearly impervious material. These soils have a very slow rate of water transmission. If a soil is assigned to a dual hydrologic group (A/D, B/D, or C/D), the first letter is for drained areas and the second is for undrained areas. Only the soils that in their natural condition are in group D are assigned to dual classes. Hydrologic Soil Group—Larimer County Area, Colorado NorthField Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 12/6/2017 Page 3 of 4 Rating Options Aggregation Method: Dominant Condition Component Percent Cutoff: None Specified Tie-break Rule: Higher Hydrologic Soil Group—Larimer County Area, Colorado NorthField Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 12/6/2017 Page 4 of 4 National Flood Hazard Layer FIRMette 0 500 1,000 1,500 2,000250 Feet Ü SEE FIS REPORT FOR DETAILED LEGEND AND INDEX MAP FOR FIRM PANEL LAYOUT SPECIAL FLOOD HAZARD AREAS Without Base Flood Elevation (BFE) Zone A, V, A99 With BFE or DepthZone AE, AO, AH, VE, AR Regulatory Floodway 0.2% Annual Chance Flood Hazard, Areas of 1% annual chance flood with average depth less than one foot or with drainage areas of less than one square mileZone X Future Conditions 1% Annual Chance Flood HazardZone X Area with Reduced Flood Risk due to Levee. See Notes.Zone X Area with Flood Risk due to LeveeZone D NO SCREEN Area of Minimal Flood Hazard Zone X Area of Undetermined Flood HazardZone D Channel, Culvert, or Storm Sewer Levee, Dike, or Floodwall Cross Sections with 1% Annual Chance 17.5 Water Surface Elevation Coastal Transect Coastal Transect Baseline Profile Baseline Hydrographic Feature Base Flood Elevation Line (BFE) Effective LOMRs Limit of Study Jurisdiction Boundary Digital Data Available No Digital Data Available Unmapped This map complies with FEMA's standards for the use of digital flood maps if it is not void as described below. The basemap shown complies with FEMA's basemap accuracy standards The flood hazard information is derived directly from the authoritative NFHL web services provided by FEMA. This map was exported on 4/23/2021 at 10:39 AM and does not reflect changes or amendments subsequent to this date and time. The NFHL and effective information may change or become superseded by new data over time. This map image is void if the one or more of the following map elements do not appear: basemap imagery, flood zone labels, legend, scale bar, map creation date, community identifiers, FIRM panel number, and FIRM effective date. Map images for unmapped and unmodernized areas cannot be used for regulatory purposes. Legend OTHER AREAS OF FLOOD HAZARD OTHER AREAS GENERAL STRUCTURES OTHER FEATURES MAP PANELS 8 B 20.2 The pin displayed on the map is an approximate point selected by the user and does not represent an authoritative property location. 1:6,000 105°4'9"W 40°36'2"N 105°3'32"W 40°35'35"N Basemap: USGS National Map: Orthoimagery: Data refreshed October, 2020 FORT COLLINS STORMWATER CRITERIA MANUAL Hydrology Standards (Ch. 5) 3.0 Rational Method 3.4 Intensity-Duration-Frequency Curves for Rational Method Page 8 Table 3.4-1. IDF Table for Rational Method Duration (min) Intensity 2-year (in/hr) Intensity 10-year (in/hr) Intensity 100-year (in/hr) Duration (min) Intensity 2-year (in/hr) Intensity 10-year (in/hr) Intensity 100-year (in/hr) 5 2.85 4.87 9.95 39 1.09 1.86 3.8 6 2.67 4.56 9.31 40 1.07 1.83 3.74 7 2.52 4.31 8.80 41 1.05 1.80 3.68 8 2.40 4.10 8.38 42 1.04 1.77 3.62 9 2.30 3.93 8.03 43 1.02 1.74 3.56 10 2.21 3.78 7.72 44 1.01 1.72 3.51 11 2.13 3.63 7.42 45 0.99 1.69 3.46 12 2.05 3.50 7.16 46 0.98 1.67 3.41 13 1.98 3.39 6.92 47 0.96 1.64 3.36 14 1.92 3.29 6.71 48 0.95 1.62 3.31 15 1.87 3.19 6.52 49 0.94 1.6 3.27 16 1.81 3.08 6.30 50 0.92 1.58 3.23 17 1.75 2.99 6.10 51 0.91 1.56 3.18 18 1.70 2.90 5.92 52 0.9 1.54 3.14 19 1.65 2.82 5.75 53 0.89 1.52 3.10 20 1.61 2.74 5.60 54 0.88 1.50 3.07 21 1.56 2.67 5.46 55 0.87 1.48 3.03 22 1.53 2.61 5.32 56 0.86 1.47 2.99 23 1.49 2.55 5.20 57 0.85 1.45 2.96 24 1.46 2.49 5.09 58 0.84 1.43 2.92 25 1.43 2.44 4.98 59 0.83 1.42 2.89 26 1.4 2.39 4.87 60 0.82 1.4 2.86 27 1.37 2.34 4.78 65 0.78 1.32 2.71 28 1.34 2.29 4.69 70 0.73 1.25 2.59 29 1.32 2.25 4.60 75 0.70 1.19 2.48 30 1.30 2.21 4.52 80 0.66 1.14 2.38 31 1.27 2.16 4.42 85 0.64 1.09 2.29 32 1.24 2.12 4.33 90 0.61 1.05 2.21 33 1.22 2.08 4.24 95 0.58 1.01 2.13 34 1.19 2.04 4.16 100 0.56 0.97 2.06 35 1.17 2.00 4.08 105 0.54 0.94 2.00 36 1.15 1.96 4.01 110 0.52 0.91 1.94 37 1.16 1.93 3.93 115 0.51 0.88 1.88 38 1.11 1.89 3.87 120 0.49 0.86 1.84 FORT COLLINS STORMWATER CRITERIA MANUAL Hydrology Standards (Ch. 5) 3.0 Rational Method 3.4 Intensity-Duration-Frequency Curves for Rational Method Page 9 Figure 3.4-1. Rainfall IDF Curve – Fort Collins Figure 2. Depth to groundwater over time at Northfield monitoring points (in feet). Date MW-1 MW-2 PZ-1 PZ-2 PZ-3 PZ-4 PZ-5 PZ-6 PZ-7 7/27/2017 3.8 5.3 4.7 4.6 5.1 5.0 6.0 6.8 7.2 9/19/2017 4.0 5.7 5.2 4.7 5.8 5.3 7.0 6.7 7.3 10/19/2017 4.0 5.6 5.0 4.6 5.9 5.1 7.1 6.6 7.3 2/12/2018 5.7 7.0 6.8 6.2 7.5 6.5 8.8 8.0 8.9 6/7/2018 3.7 5.2 4.4 4.6 4.4 5.3 5.1 7.2 7.0 2/15/2019 6.5 7.4 7.6 7.3 9.7 6/6/2019 3.8 5.5 4.5 4.4 5.3 6.9 7.5 0 1 2 3 4 5 6 7 8 9 10 6/1/2017 8/31/2017 11/30/2017 3/1/2018 6/1/2018 8/31/2018 11/30/2018 3/2/2019 6/1/2019 8/31/2019 Depth to Water (feet) Date MW-1 MW-2 PZ-1 PZ-2 PZ-3 PZ-4 PZ-5 PZ-6 PZ-7 6/25/2019 Miller Groundwater Engineering, LLC C2-10C100tc2 yr (min)tc100-yr (min)I2(in/hr)I100(in/hr)Q2(cfs)Q100(cfs)DESIGN POINTRunoff CoefficientTime of ConcentrationRainfall IntensityAREA (acres)TRIBUTARY SUB-BASINPeak RunoffB7B7 0.27 0.81 1.00 5.00 5.00 2.85 9.95 0.62 2.64B8B8 0.40 0.78 0.98 5.27 5.00 2.74 9.95 0.86 3.90B9B9 2.29 0.81 1.00 5.00 13.07 1.87 6.90 1.93 8.89B10B10 0.48 0.66 0.82 5.00 5.00 2.85 9.95 0.90 3.91B11B11 2.47 0.73 0.91 11.21 8.85 2.11 8.09 3.82 18.29B12B12 0.41 0.26 0.33 6.00 5.57 2.64 9.40 0.28 1.27B13B13 0.38 0.87 1.00 5.00 5.00 2.85 9.95 0.95 3.81B14B14 0.36 0.86 1.00 5.00 5.00 2.85 9.95 0.88 3.59B15B15 0.89 0.80 1.00 6.29 5.67 2.60 9.36 1.86 8.31B16B16 0.54 0.91 1.00 5.00 5.00 2.85 9.95 1.41 5.38B17B17 0.35 0.79 0.99 5.40 5.00 2.72 9.95 0.76 3.48B18B18 0.43 0.67 0.84 8.49 6.56 2.36 8.96 0.68 3.24B19B19 0.43 0.69 0.87 8.25 6.26 2.38 9.09 0.71 3.38B20B20 2.94 0.34 0.43 21.24 19.62 1.56 5.67 1.57 7.12B Total 19.4828.44 126.55C1C1 1.30 0.45 0.56 14.81 10.70 2.05 7.52 1.41 6.48C2C2 0.14 0.53 0.67 12.07 5.00 2.85 9.95 0.10 0.42C3C3 0.83 0.25 0.31 5.00 6.12 2.38 9.15 1.39 6.66C4C4 0.22 0.70 0.88 8.23 5.00 2.85 9.95 0.47 2.07C5C5 1.20 0.77 0.96 5.00 10.27 2.11 7.64 1.05 4.74C Total 3.684.42 20.37D1AD1A 0.70 0.57 0.71 7.86 6.93 2.41 8.80 0.70 3.18D1D1 0.73 0.42 0.52 6.39 5.00 2.59 9.95 1.40 6.75D2D2 0.65 0.42 0.52 7.94 5.00 2.77 9.95 1.57 6.50D3D3 0.45 0.25 0.31 5.00 6.81 2.42 8.85 0.61 2.81D4D4 0.16 0.61 0.76 8.39 5.00 2.85 9.95 0.33 1.42D5D5 0.43 0.87 1.00 5.07 6.88 2.36 8.82 0.61 2.85D6D6 0.10 0.70 0.87 5.00 5.00 2.59 9.95 0.20 0.94D7D7 0.09 0.73 0.92 6.38 5.00 2.85 9.95 0.21 0.87D8D8 0.72 0.63 0.78 11.58 5.00 2.69 9.95 1.67 7.15D9D9 0.61 0.83 1.00 5.00 9.99 2.09 7.72 0.79 3.67D10D10 0.16 0.65 0.81 11.91 5.00 2.68 9.95 0.28 1.30D11D11 0.88 0.89 1.00 5.83 10.39 2.06 7.61 1.17 5.42D12D12 0.76 0.86 1.00 5.61 5.04 2.66 9.67 1.80 7.3718-1000-00 Rational Calcs (FC).xlsx Page 18 of 19Highland Development ServicesAREA MATCHESPROPOSED BASIN D1AREA MATCHESPROPOSED BASIN D2-D3AREA MATCHESPROPOSED BASIN D5-D7NORTHFIELD RATIONAL CALCS SUMMARY SHEET C2-10C100tc2 yr (min)tc100-yr (min)I2(in/hr)I100(in/hr)Q2(cfs)Q100(cfs)DESIGN POINTRunoff CoefficientTime of ConcentrationRainfaill IntensityAREA (acres)TRIBUTARY SUB-BASINPeak RunoffD13D13 0.28 0.67 0.83 5.72 5.00 2.85 9.95 0.24 1.06D14D14 2.50 0.31 0.39 5.00 13.75 1.89 6.75 1.33 5.90D15D15 0.44 0.72 0.89 14.39 5.53 2.61 9.42 0.84 3.80D Total 9.6513.75 60.99E1E1 0.48 0.28 0.35 14.39 5.11 2.56 9.63 1.01 4.62E2E2 0.66 0.82 1.00 6.61 5.33 2.53 9.52 1.43 6.32E3E3 1.55 0.85 1.00 6.88 13.92 1.92 6.71 2.50 10.42E4E4 1.95 0.84 1.00 13.92 15.22 1.75 6.43 2.50 11.50E5E5 0.58 0.73 0.91 17.04 6.38 2.40 9.03 1.16 5.28E6E6 0.56 0.83 1.00 8.05 6.18 2.42 9.12 1.13 5.15E7E7 0.75 0.83 1.00 7.87 6.94 2.34 8.80 1.31 6.19E8E8 0.60 0.75 0.93 8.67 7.42 2.28 8.61 0.97 4.58E9E9 0.39 0.71 0.89 9.31 5.15 2.85 9.95 0.91 3.58E10E10 0.24 0.81 1.00 5.00 5.00 3.82 13.32 0.80 3.24E Total 7.7913.74 60.88Overall 58.7087.03 387.81*NOTE - Flows represented above are to the design point and do not account for any excess flow from another basin. Please refer to the Inlet Summary Sheet for overflow.18-1000-00 Rational Calcs (FC).xlsx Page 19 of 19Highland Development ServicesAREA MATCHESPROPOSED BASIN D8AREA MATCHESPROPOSED BASIN D9 A11A12A14A15A18A3A4A6A9B1B10B11B12B17B18B19B2B20B3B4B6B8B9C1C2C3C4C5D13D14D3D4D5D6D7D1AD1OPA1OPA3OPA4OPB1OPB2OPB3OP-MHA4OP-MHA6OP-MHA7OP-MHB2OP-MHB5PA1PA10PA11PA12PA13PA14PA15PA16PA17PA2PA3PA4PA5PA6PA7PA8PB1PB10PB11PB12PB13PB14PB15PB16PB17PB18PB19PB2PB20PB3PB4PB5PB6PB7PB8PB9PC1PC2PC3PC4PC5PC6PC7PD5PD6PD7PD8PD11PD12PD13PE1PE2PA9PD9PD10PD1PD2PD3PD4OutB2OutA4OutA3OutB3OutB1OutD1OutC1OutA1IA1IA2IA3IA4IA5IA6IB1IB10IB11IB2IB3IB4IB5IB6IB7IB8IB9IC1IC2IC3IC4ID3ID4ID5ID6IE1IE2MHA1MHA2MHA3MHA5MHB1MHB3MHB4MHB6MHC1MHC2MHD2MHD4MHD5OA2OA3-Stage1OA3-Stage2OA4-Stage1OA4-Stage2OB1-Stage1OB1-Stage2OB2-Stage1OB2-Stage2OB3-Stage1OB3-Stage2OC1OD1MHD3ID1AID1ID2MHD1OA1-Stage1OA1-Stage2Out2Out1Out3MHB2MHA4MHB5MHA7MHA6VB3VB2VB1VA2VA1VC1VD1CoFC_100-yr03/11/2019 00:05:00SWMM 5.1Page 1A11A12A14A15A18A3A4A6A9B1B10B11B12B17B18B19B2B20B3B4B6B8B9C1C2C3C4C5D13D14D3D4D5D6D7D1AD1OPA1OPA3OPA4OPB1OPB2OPB3OP-MHA4OP-MHA6OP-MHA7OP-MHB2OP-MHB5PA1PA10PA11PA12PA13PA14PA15PA16PA17PA2PA3PA4PA5PA6PA7PA8PB1PB10PB11PB12PB13PB14PB15PB16PB17PB18PB19PB2PB20PB3PB4PB5PB6PB7PB8PB9PC1PC2PC3PC4PC5PC6PC7PD5PD6PD7PD8PD11PD12PD13PE1PE2PA9PD9PD10PD1PD2PD3PD4OutB2OutA4OutA3OutB3OutB1OutD1OutC1OutA1IA1IA2IA3IA4IA5IA6IB1IB10IB11IB2IB3IB4IB5IB6IB7IB8IB9IC1IC2IC3IC4ID3ID4ID5ID6IE1IE2MHA1MHA2MHA3MHA5MHB1MHB3MHB4MHB6MHC1MHC2MHD2MHD4MHD5OA2OA3-Stage1OA3-Stage2OA4-Stage1OA4-Stage2OB1-Stage1OB1-Stage2OB2-Stage1OB2-Stage2OB3-Stage1OB3-Stage2OC1OD1MHD3ID1AID1ID2MHD1OA1-Stage1OA1-Stage2Out2Out1Out3MHB2MHA4MHB5MHA7MHA6VB3VB2VB1VA2VA1VC1VD1CoFC_100-yrA11A14A15A18A3A4A6A9B1B10B11B12B17B18B19B2B20B3B4B6B8B9C1C2C3C4C5D14D3D4D5D6D7D1AD1A12D9D10D12E6E8OPA4OPA2OPA1OPB3OPB2OPB1OP-MHA4OP-IA03OP-IA01OP-MHB05OP-MHB01PA14PA07PA06PA05PA17PA03PA02PA01PA04PA13PA12PA15PA11PA10PA16PA09PB11PB15PB14PB13PB12PB04PB03PB02PB20PB18PB19PB10PB01PB109PB08PB07PB06PB16PB17PB05PC1PC2PC3PC4PC5PC6PC7PD5PD6PD7PD8PD11PD12PD13PE1PE2PA08PD9PD10PD1PD2PD3PD4PD14PD15PD16PD17OutB2OutA1OutA2OutB1OutD1OutC1OutA4OutB3IA07IA06IA08IA09IA04IA02IB06IB11IB12IB05IB04IB03IB09IB10IB08IB07IB13FESC01IC01IC03IC02ID04ID03ID02ID01IE02IE01MHA04MHA03MHA02MHA01MHB06MHB03MHB02MHB04FESC02MHC02MHD04MHD02MHD01OA3OA2-Stage1OA2-Stage2OA1-Stage1OA1-Stage2OB3-Stage1OB3-Stage2OB2-Stage1OB2-Stage2OB1-Stage1OB1-Stage2OC1OD1MHD03ID09ID08ID05MHD05OA4-Stage1OA4-Stage2IA05IA03IA01IB01IB02FESD06ID06FESD05MHD01AOut2Out1Out3VB3VB2VB1VA2VA1VC1VD1CoFC_100-yrPROPOSEDNORTHFIELDCOMMONS SITE Northfield SWMM Output_2019-10-15.rpt FESD06 JUNCTION 9.23 9.23 0 00:40 0.107 0.107 -0.016 ID06 JUNCTION 1.21 10.28 0 00:40 0.0119 0.119 0.024 FESD05 JUNCTION 11.14 11.14 0 00:40 0.132 0.132 0.005 MHD01A JUNCTION 0.00 20.23 0 00:40 0 0.25 -0.004 Out2 OUTFALL 0.00 7.49 0 05:08 0 1.08 0.000 Out1 OUTFALL 0.00 4.55 0 00:31 0 0.613 0.000 Out3 OUTFALL 0.00 19.63 0 00:40 0 0.365 0.000 VB3 STORAGE 11.44 57.73 0 00:40 0.162 0.65 0.910 VB2 STORAGE 2.26 18.07 0 00:40 0.0223 0.11 0.015 VB1 STORAGE 6.57 48.96 0 00:36 0.146 1.24 0.240 VA2 STORAGE 19.99 49.73 0 00:40 0.238 0.52 0.082 VA1 STORAGE 8.84 49.86 0 00:40 0.162 1.15 4.181 VC1 STORAGE 5.30 20.73 0 00:40 0.0728 0.25 0.252 VD1 STORAGE 4.91 44.51 0 00:42 0.128 0.619 0.250 ********************** Node Surcharge Summary ********************** Surcharging occurs when water rises above the top of the highest conduit. --------------------------------------------------------------------- Max. Height Min. Depth Hours Above Crown Below Rim Node Type Surcharged Feet Feet --------------------------------------------------------------------- IA07 JUNCTION 1.17 3.186 0.374 IA06 JUNCTION 1.92 3.743 0.417 IA08 JUNCTION 1.09 4.173 0.027 IA09 JUNCTION 5.48 3.104 0.186 IA04 JUNCTION 5.53 3.299 4.381 IA02 JUNCTION 5.45 4.904 0.206 IB06 JUNCTION 5.47 3.325 0.345 IB11 JUNCTION 5.33 1.830 1.470 IB12 JUNCTION 5.25 1.498 1.152 IB05 JUNCTION 5.48 3.945 1.105 IB04 JUNCTION 5.48 3.411 1.229 IB03 JUNCTION 5.48 3.615 1.785 IB09 JUNCTION 5.47 3.462 0.048 IB10 JUNCTION 2.74 0.352 2.848 IB08 JUNCTION 3.90 4.295 0.695 IB07 JUNCTION 3.11 3.974 0.696 IC01 JUNCTION 1.17 0.131 2.669 IC02 JUNCTION 1.57 0.200 3.300 IE02 JUNCTION 0.12 0.241 3.459 IE01 JUNCTION 0.60 0.398 3.502 MHA04 JUNCTION 1.25 3.277 0.713 MHA03 JUNCTION 1.24 3.156 1.294 MHA02 JUNCTION 5.48 3.828 1.892 MHA01 JUNCTION 5.54 3.737 4.923 MHB06 JUNCTION 5.48 3.824 2.476 MHB03 JUNCTION 5.55 4.237 5.163 MHB02 JUNCTION 5.57 4.972 2.448 MHB04 JUNCTION 5.38 2.319 4.481 FESC02 JUNCTION 2.61 0.420 2.380Page 7PEAK FLOW FOR NORTHFIELDSUB-BASINS D1-D14NORTHFIELD EPA SWMM OUTPUT REDWOOD STREETDRY CREEKLA K E CA NA L D I TC H FUTURE LEMAY AVENUEN. LEMAY AVENUECOLLAMER DRIVEPIONEER TRAIL ROADSTEELEY DRIVELANDMARK WAY N. LEMAY AVENUE RAINGARDEND1SC H LAG E L S T R E E T FUTURESUNIGAROADPOND B3POND A2POND A1POND B2POND CPOND B1POND DRAIN GARDEN B1E. SUNIGA ROADSUNIGA ROAD AREADETENTION / LANDSCAPE AREAPROPOSED SINGLE FAMILY AREAPROPOSED MULTI-FAMILY AREAAREA CONTRIBUTING TO LID TREATMENTLEGEND0100'20010050100SCALE: 1" = REVISIONNO.BY DATE HIGHLAND DEVELOPMENT SERVICES 6355 FAIRGROUNDS AVENUE, SUITE 100 | WINDSOR, CO 80550 PHONE: 970.674.7550 | FAX: 970.674.7568 | www.Highland-DS.comPREPARED BY OR UNDER THEDIRECT SUPERVISION OF:FOR AND ON BEHALF OF HIGHLANDDEVELOPMENT SERVICESREVIEW SETNOT FORCONSTRUCTIONOFSHEETDRAWN BYCHECKED BYDATESCALE (H)HDS PROJECT #SCALE (V)NORTHFIELD LID & WQ TREATMENT AREAS EXHIBIT10/15/191" = 100'N/AKRBJTC18-1000-00----11NWESPROPOSED COMMERCIAL AREAAREA CONTRIBUTING TO EXTENDEDDETENTION BASIN WATER QUALITY TREATMENTAREA CONTRIBUTING TO SNOUT HOODWATER QUALITY TREATMENT Design Engineer: Design Firm: Project Number: Date: DESIGN CRITERIA Low Impact Development Summary Sq-Ft Acres Impervious Area (sq-ft) % of Impervious Area Requiring Treatment Impervious Area Requiring Treatment 537,816 12.35 330,931 50% 165,465 1,189,400 27.30 794,336 75% 595,752 40,986 0.94 20,720 75% 15,540 304,148 6.98 248,720 0% N/A 445,251 10.22 0 0% N/A 2,517,600 57.80 1,394,707 - 776,757 LID Facility Contributing Basins Area Drainage to LID (sq-ft) % Impervious Impervious Area Treated (sq-ft) WQCV12-hr (watershed inches) WQCV12-hr (cu-ft) Treatment Method A2 A1+…+A12 427,599 66.5% 302,122 0.21 7,414 Infiltration Gallery B1 B13+…B17 110,074 79.3% 93,219 0.26 2,378 Rain Garden B2 B10+…+B12 146,450 55.7% 86,485 0.18 2,173 Infiltration Gallery B3 B1+…+B9 426,521 54.7% 251,577 0.18 6,243 Infiltration Gallery D1 D8+…+D13 148,227 61.5% 98,626 0.19 2,384 Rain Garden EDB Pond Contributing Basins Drainage Area (sq-ft) Drainage Area (sq-ft)% Impervious WQCV40-hr (watershed inches) WQCV40-hr (ac-ft) Pond A A18 131,657 3.022 12.5% 0.08 0.024 Pond B B18+…+B20 165,673 3.803 22.5% 0.13 0.048 Pond C C1+…+C5 160,137 3.676 38.2% 0.18 0.064 Pond D D1+…+D7+D14 253,037 5.809 32.5% 0.16 0.092 776,757 832,029 107.1% Area (sq-ft) Area (acres) Treatment Ratio 1,258,871 28.90 50.0% 710,504 16.31 28.2% 322,629 7.41 12.8% 126,940 2.91 5.0% 2,418,944 55.53 96.1% 98,790 2.27 3.9% 2,517,734 57.80 Total Area unable to be Treated (Basins A13, A14, portion of A16, & A17) Total Treated Area Total Improvement Area Water Quality Area Treatment Summary Description Total Area Treated by Snout (Lemay - Basins A15 & D15) Standard Water Quality Areas Total Area Treated by LID Total Area Treated by EDB Total Area Treated by Snout (Suniga) Description Single Family Area Multifamily Area Commercial Area Suniga Road (no LID treatment) Northfield Low Impact Development Total % Treatment Development Area Breakdown City of Fort Collins - Ordinance No. 007, 2016 - Treat at least 75% of any newly developed or redeveloped impervious area using one or a combination of LID techniques, or - Treat at least 50% of any newly developed or redeveloped impervious area using one or a combination of LID techniques when 25% of private driveable surfaces are permeable. Total Impervious Area Treated (sq-ft) Total Impervious Area Required for LID Treatment (sq-ft) LID Treatment Summary LID Treatment Areas Detention / Landscape Areas (no LID treatment) J.Claeys Highland Development Services 18-1000-00 October 15, 2019 Urban Storm Drainage Criteria Manual by Urban Drainage and Flood Control District, June 2001 (Revised January 2016) Totals Appendix B APPENDIX B – RATIONAL CALCULATIONS Design Engineer:Design Firm:Project Number:Date:POND D SUMMARY TABLENF Approved (D1-D14)NFC Proposed (D1-D9)NF ApprovedNFC ProposedNF ApprovedNFC ProposedPOND D 9.21 9.18 41.3% 37.9% 44.51 28.94Notes: 1. Northfield sub-basins D1-D14 correlate to Northfield Commons sub-basins D1-D9.2. Northfield Approved area and % Impervious taken from Northfield Rational Calcs, dated October 15, 2019. 3. Northfield Peak Runoff was obtained from the EPA SWMM model output in the "Final Drainage Report for Northfield" dated February 26, 2020.4. Northfield Commons Peak Runoff was obtained from Attenuated Flows spreadsheet included in this report.Northfield CommonsDEVELOPED PEAK RUNOFFArea (acres) % ImperviousD. EggerHighland Development Services21-1037-00April 21, 2021Peak Runoff (cfs)21-1037-00 Rational Calcs (FC).xlsx Page 5 of 6Highland Development Services Design Engineer:Design Firm:Project Number:Date:%ImperviousRunoff Coefficient CReturn PeriodFrequency Adjustment Factor (Cf)100% 0.952-year to 10-year1.0090% 0.95 100-year 1.2590% 0.9540% 0.500% 0.25C2 to C10C100D1 137,252 3.151 30,572 29,347 8,661 0 68,67147.2% 0.60 0.75D2 3,228 0.074 3,228 0 0 0 0100.0% 0.95 1.00D3 3,219 0.074 3,219 0 0 0 0100.0% 0.95 1.00D4 10,255 0.235 0 0 2,007 0 8,24817.6% 0.39 0.48D5 35,323 0.811 959 13,174 1,044 0 20,14538.9% 0.55 0.69D6 6,832 0.157 517 2,669 0 0 3,64642.7% 0.58 0.72D7 83,097 1.908 40,019 17,887 762 0 24,42968.4% 0.74 0.93D8 11,992 0.275 0 0 1,007 0 10,9857.6% 0.31 0.39D9 108,741 2.496 0 0 4,743 0 103,9983.9% 0.28 0.35Overall 399,938 9.181 78,514 63,077 18,224 0 240,12337.9% 0.53 0.66Northfield CommonsDEVELOPED IMPERVIOUS AREA CALCULATIONDESIGN CRITERIA:Fort Collins Stormwater Criteria ManualBASINS:Highland Development ServicesD. Egger21-1037-00April 21, 2021Land UsePavedRoofWalksGravel/PaversLawns(Heavy, 2-7% Slope)Sub-basinDesignationAtotal(sq feet)Atotal(acres)Weighted % ImperviousCOMPOSITEApaved(sq feet)Aroof(sq feet)Awalk(sq feet)Agravel/pavers(sq feet)Alawn(sq feet)21-1037-00 Rational Calcs (FC).xlsxPage 1 of 6Highland Development Services Design Engineer:Design Firm:Project Number:Date:City of Fort Collins Stormwater Criteria ManualOverland Flow Equations for City of Fort Collins Stormwater Criteria ManualEQUATIONS:-Equation 5-3-Equation 5-4-Urbanized Check Equation 3.3-5- CoFC Overland FlowCONSTRAINTS:300ft - Overland flow shall not exceed for developed condition500ft - Overland flow shall not exceed for undeveloped conditionFinal tc = minimum of ti + tt and urbanized basin checkrecommended minimum tc = 5 min for urbanized basinsTime of Concentration (2-yr to 10-yr) D1 D1 47.2% 0.60 3.151 101 0.0485 5.55 480 0.0064 0.10 0.016 1.61 4.98 10.54 581 13.2310.54D2 D2 100.0% 0.95 0.074 24 0.0195 1.10 89 0.0177 0.10 0.016 2.67 0.56 5.00 113 10.635.00D3 D3 100.0% 0.95 0.074 24 0.0208 1.08 89 0.0174 0.10 0.016 2.65 0.56 5.00 113 10.635.00D4 D4 17.6% 0.39 0.235 43 0.0418 5.43 263 0.0050 0.10 0.016 1.42 3.09 8.52 306 11.708.52D5 D5 38.9% 0.55 0.811 19 0.1021 2.06 575 0.0050 0.10 0.016 1.42 6.76 8.82 594 13.308.82D6 D6 42.7% 0.58 0.157 40 0.0200 4.92 132 0.0156 0.10 0.016 2.51 0.88 5.79 172 10.965.79D7 D7 68.4% 0.74 1.908 40 0.0248 3.11 735 0.0069 0.10 0.016 1.67 7.35 10.46 775 14.3110.46D8 D8 7.6% 0.31 0.275 15 0.0200 4.55 29 0.0050 0.10 0.016 1.42 0.34 5.00 44 10.245.00D9 D9 3.9% 0.28 2.496 37 0.0200 7.40 593 0.0050 0.10 0.016 1.426.97 14.36 630 13.5013.50April 21, 2021Northfield CommonsDEVELOPED TIME OF CONCENTRATIOND. Egger21-1037-00Highland Development ServicesLENGTH(ft)DESIGN CRITERIA:SUB-BASIN DATAINITIAL/OVERLAND TIME (ti)TRAVEL TIME (tt)tc=ti+tt(min)Urban CheckFinaltc(min)DESIGN POINTSub-basin%ImperviousC2-10AREA (acres)tt(min)OVERALL LENGTH(ft/ft)tc(min)SLOPE(ft/ft)ti(min)LENGTH(ft)SLOPE(ft/ft)VELOCITY(ft/s)HYDRAULIC RADIUS(ft)ROUGHNESS COEFFICIENTticttt+=VLtt60=1.871.1 10180+=LtcV.R2/3S 1/221-1037-00 Rational Calcs (FC).xlsxPage 2 of 6Highland Development Services Design Engineer:Design Firm:Project Number:Date:City of Fort Collins Stormwater Criteria ManualOverland Flow Equations for City of Fort Collins Stormwater Criteria ManualEQUATIONS:-Equation 5-3-Equation 5-4-Urbanized Check Equation 3.3-5- CoFC Overland FlowCONSTRAINTS:300ft - Overland flow shall not exceed for developed condition500ft - Overland flow shall not exceed for undeveloped conditionFinal tc = minimum of ti + tt and urbanized basin checkrecommended minimum tc = 5 min for urbanized basinsTime of Concentration (100-yr) D1 D1 47.2% 0.75 3.151 101 0.0485 3.89 480 0.0064 0.10 0.016 1.61 4.98 8.87 581 13.238.87D2 D2 100.0% 1.00 0.074 24 0.0195 0.73 89 0.0177 0.10 0.016 2.67 0.56 5.00 113 10.635.00D3 D3 100.0% 1.00 0.074 24 0.0208 0.72 89 0.0174 0.10 0.016 2.65 0.56 5.00 113 10.635.00D4 D4 17.6% 0.48 0.235 43 0.0418 4.69 263 0.0050 0.10 0.016 1.42 3.09 7.78 306 11.707.78D5 D5 38.9% 0.69 0.811 19 0.1021 1.55 575 0.0050 0.10 0.016 1.42 6.76 8.30 594 13.308.30D6 D6 42.7% 0.72 0.157 40 0.0200 3.56 132 0.0156 0.10 0.016 2.51 0.88 5.00 172 10.965.00D7 D7 68.4% 0.93 1.908 40 0.0248 1.48 735 0.0069 0.10 0.016 1.67 7.35 8.83 775 14.318.83D8 D8 7.6% 0.39 0.275 15 0.0200 4.10 29 0.0050 0.10 0.016 1.42 0.34 5.00 44 10.245.00D9 D9 3.9% 0.35 2.496 37 0.0200 6.77 593 0.0050 0.10 0.016 1.426.97 13.73 630 13.5013.50April 21, 2021Northfield CommonsDEVELOPED TIME OF CONCENTRATIOND. Egger21-1037-00Highland Development ServicesLENGTH(ft)DESIGN CRITERIA:SUB-BASIN DATAINITIAL/OVERLAND TIME (ti)TRAVEL TIME (tt)tc=ti+tt(min)Urban CheckFinaltc(min)DESIGN POINTSub-basin%ImperviousC2-10AREA (acres)tt(min)OVERALL LENGTH(ft/ft)tc(min)SLOPE(ft/ft)ti(min)LENGTH(ft)SLOPE(ft/ft)VELOCITY(ft/s)HYDRAULIC RADIUS(ft)ROUGHNESS COEFFICIENTticttt+=VLtt60=1.871.1 VLtt60=10180+=LtcV.R2/3S 1/221-1037-00 Rational Calcs (FC).xlsxPage 3 of 6Highland Development Services Design Engineer:Design Firm:Project Number:Date:EQUATIONS:Qn = n-yr peak discharge (cfs)Cn = n-yr runoff coefficientIn = n-yr rainfall intensity (in/hr) An = Basin drainage area (ac)tc (min)Runoff Coeff(C2-10)C(A) (acres)Intensity (in/hr)Q (ft3/s)tc (min)Runoff Coeff(C2-10)C(A) (acres)Intensity (in/hr)Q (ft3/s)tc (min)Runoff Coeff. (C100)C(A) (acres)Intensity (in/hr)Q (ft3/s)D1D1 3.151 10.54 0.60 1.89 2.174.1010.54 0.60 1.89 3.707.008.87 0.75 2.36 8.0819.09D2D2 0.074 5.00 0.95 0.07 2.850.205.00 0.95 0.07 4.870.345.00 1.00 0.07 9.950.74D3D3 0.074 5.00 0.95 0.07 2.850.205.00 0.95 0.07 4.870.345.00 1.00 0.07 9.950.74D4D4 0.235 8.52 0.39 0.09 2.350.218.52 0.39 0.09 4.020.377.78 0.48 0.11 8.470.96D5D5 0.811 8.82 0.55 0.45 2.321.048.82 0.55 0.45 3.971.778.30 0.69 0.56 8.284.62D6D6 0.157 5.79 0.58 0.09 2.670.245.79 0.58 0.09 4.550.415.00 0.72 0.11 9.951.12D7D7 1.908 10.46 0.74 1.42 2.173.0910.46 0.74 1.42 3.715.278.83 0.93 1.77 8.1014.37D8D8 0.275 5.00 0.31 0.09 2.850.245.00 0.31 0.09 4.870.415.00 0.39 0.11 9.951.06D9D9 2.496 13.50 0.28 0.70 1.951.3713.50 0.28 0.70 3.332.3313.50 0.35 0.88 6.805.9510-yr Peak Runoff100-yr Peak RunoffNorthfield CommonsDEVELOPED PEAK RUNOFFCity of Fort Collins Stormwater Criteria ManualDESIGN CRITERIA:Design PointSub-basin Area (acres)D. EggerHighland Development Services21-1037-00April 21, 20212-yr Peak RunoffnnnnAICQ=21-1037-00 Rational Calcs (FC).xlsxPage 4 of 6Highland Development Services Northfield Commons Attenuated Flows Design Engineer: Design Firm: Project Number: Date: DESIGN CRITERIA: EQUATIONS: -Equation 5-3 -Equation 5-4 -CoFC Overland Flow CONSTRAINTS: 300 ft - Overland flow shall not exceed for developed condition Final t c = minimum of t i + t t and urbanized basin check 500 ft - Overland flow shall not exceed for undeveloped condition recommended minimum t c = 5 min for urbanized basins Qn = n -yr peak discharge (cfs)I = rainfall intensity (in/hr) Cn = n -yr runoff coefficient P1 = one-hour point rainfall depth (in) In = n -yr rainfall intensity (in/hr) tc = time of concentration (min) A = drainage area (ac)P1-1/2 2yr =0.41 in. P1-2yr =0.82 in. P1-100yr =2.86 in. BASINS: DP/Manhole D9 Contributing Basins D1-D9 Contributing Area (acres)9.18 C2 C100 Runoff Coefficients 0.53 0.66 Overland Flow Time Length (ft)101 Slope (%)4.85 2-yr 100-yr ti (min)6.33 4.86 Travel Time Length (ft) Slope (%) Hydraulic Radius (ft) Roughness Coefficient Velocity (ft/s)tt (min) 480 0.64%0.10 0 1.61 4.98 67 3.80%0.10 0 3.91 0.29 pipe conveyance 799 0.34%0.10 0 1.17 11.38 pipe conveyance 124 0.22%0.10 0 0.94 2.20 pipe conveyance 154 4.25%0.10 0 4.14 0.62 pipe conveyance 227 0.50%0.10 0 1.42 2.67 Total Time 22.14 Final Time of Concentration - tc (min) 2-yr 100-yr 28.47 27.00 Intensities (in/hr) 1/2 2-yr 2-yr 100-yr 0.66 1.32 4.76 Discharge (cfs) 1/2 2-yr 2-yr 100-yr 3.22 6.44 28.94 D. Egger Highland Development Services 21-1037-00 April 26, 2021 Fort Collins Stormwater Criteria Manual ( ) 786.0 1 10 5.28 ct PI + =AICQnnn= ticttt+= V Ltt60 == 1.87 1.1 − . V=.R2/3 S 1/2 21-1037-00 Attenuated Flows.xlsx - D1-D9 1 of 1 JVA, Inc. Appendix C APPENDIX C – LOW IMPACT DEVELOPMENT CALCULATIONS Design Engineer: Design Firm: Project Number: Date: DESIGN CRITERIA Low Impact Development Summary Sq-Ft Acres Impervious Area (sq-ft) % of Impervious Area Requiring Treatment Impervious Area Requiring Treatment 537,816 12.35 330,931 50% 165,465 1,189,400 27.30 794,336 75% 595,752 40,986 0.94 20,720 75% 15,540 304,148 6.98 248,720 0% N/A 445,251 10.22 0 0% N/A 2,517,600 57.80 1,394,707 - 776,757 LID Facility Contributing Basins Area Drainage to LID (sq-ft) % Impervious Impervious Area Treated (sq-ft) WQCV12-hr (watershed inches) WQCV12-hr (cu-ft) Treatment Method A2 A1+…+A12 427,599 66.5% 302,122 0.21 7,414 Infiltration Gallery B1 B13+…B17 110,074 79.3% 93,219 0.26 2,378 Rain Garden B2 B10+…+B12 146,450 55.7% 86,485 0.18 2,173 Infiltration Gallery B3 B1+…+B9 426,521 54.7% 251,577 0.18 6,243 Infiltration Gallery D1 D5+...+D8 137,244 54.2% 78,037 0.17 1,995 Rain Garden EDB Pond Contributing Basins Drainage Area (sq-ft) Drainage Area (sq-ft)% Impervious WQCV40-hr (watershed inches) WQCV40-hr (ac-ft) Pond A A18 131,657 3.022 12.5% 0.08 0.024 Pond B B18+…+B20 165,673 3.803 22.5% 0.13 0.048 Pond C C1+…+C5 160,137 3.676 38.2% 0.18 0.064 Pond D D1+…+D4+D9 262,694 6.031 29.4% 0.15 0.090 776,757 811,440 104.5% Area (sq-ft) Area (acres) Treatment Ratio 1,247,888 28.65 49.6% 720,162 16.53 28.6% 323,951 7.44 12.9% 126,940 2.91 5.0% 2,418,940 55.53 96.1% 98,790 2.27 3.9% 2,517,730 57.80 Northfield Commons Low Impact Development Total % Treatment Development Area Breakdown City of Fort Collins - Ordinance No. 007, 2016 - Treat at least 75% of any newly developed or redeveloped impervious area using one or a combination of LID techniques, or - Treat at least 50% of any newly developed or redeveloped impervious area using one or a combination of LID techniques when 25% of private driveable surfaces are permeable. Total Impervious Area Treated (sq-ft) Total Impervious Area Required for LID Treatment (sq-ft) LID Treatment Summary LID Treatment Areas Detention / Landscape Areas (no LID treatment) D. Egger Highland Development Services 21-1037-00 April 27, 2021 Urban Storm Drainage Criteria Manual by Urban Drainage and Flood Control District, June 2001 (Revised January 2016) Totals Standard Water Quality Areas Total Area Treated by LID Total Area Treated by EDB Total Area Treated by Snout (Suniga) Description Single Family Area Multifamily Area Commercial Area Suniga Road (no LID treatment) Total Area unable to be Treated (Basins A13, A14, portion of A16, & A17) Total Treated Area Total Improvement Area Water Quality Area Treatment Summary Description Total Area Treated by Snout (Lemay - Basins A15 & D15)