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HomeMy WebLinkAboutBROOKFIELD SECOND FILING, TRACTS D & E - PDP/FDP - FDP150025 - REPORTS - DRAINAGE REPORT (3)301 N. Howes Street, Suite 100, Fort Collins, CO 80521 970.221.4158 www.northernengineering.com 1 City of Fort Collins Stormwater Utility 700 Wood Street Fort Collins, Colorado 80521 January 25, 2016 RE: Drainage Memorandum Brookfield Second Replat, Lots 1‐12, Tract E and a portion of Tract D Fort Collins, Colorado Project Number: 374‐020 Dear Staff: Northern Engineering Services is pleased to submit this Drainage Memorandum for Brookfield for your review. Brookfield Second Replat is located within Lots 1‐12, Tract E and a portion of Tract D of the Plat of Brookfield. The Brookfield project is a proposed multi‐family residential site. The site is located in the Northeast Quarter of Section 4, Township 6 North, Range 68 West of the 6th Principal Median, City of Fort Collins, Larimer County, Colorado. The site is bounded on the north, east, and west by undeveloped area. The site is bounded on the south by Brookfield Phase 1, a multi‐family site. Fossil Creek Reservoir Inlet Ditch (FCRID) flows north‐west to south and is located east of the site outside of the project boundary. The proposed 10’ pedestrian trail along the east side of the site is more than 50’ west from the FCRID water surface elevation and minimal grading is proposed within this area as shown on the Drainage Exhibit. Southeast of the Site is Detention Pond A constructed as part of Brookfield Phase 1 development that currently detains flows from Brookfield development Phase 1. Detention Pond A was designed for future development of Brookfield including this site. The site falls within the East Harmony Portion of McClellands Creek Master Drainage Basin. This Drainage Memorandum has been prepared in compliance with technical criteria set forth in the City of Fort Collins Storm Drainage Design Criteria, Urban Drainage and Flood Control District Criteria Manual (UDFCDCM) and City of Fort Collins Amendments to the UDFCDCM. The Brookfield project consists of approximately 6 acres. The development will consist of 12 multi‐family buildings with approximately 68 units. The buildings will be two story with the possibility of basements. Parking will be provided by on street parking, parking stalls off the alleys, attached garages, and detached garages. The streets within the multi‐family tracts will 301 N. Howes Street, Suite 100, Fort Collins, CO 80521 970.221.4158 www.northernengineering.com 2 be private and will be maintained privately. Public streets bound the tract. The proposed site has been a part of many different drainage plans and studies in the past. The most recent drainage plan, Final Drainage Report for Brookfield by TST dated December 14, 2001 covers the entire Brookfield development including already constructed phases, the proposed site, and future development. The TST drainage report for Brookfield references two previously completed Drainage Reports that are a part of the McClellands Drainage Basin: Final Drainage Report for Willow Brook by TST, Inc. Consulting Engineers, dated October, 2000 and East Harmony Portion of McClellands Creek Master Drainage Plan Update by ICON Engineering, Inc. dated August, 1999. The proposed site closely matches the original proposed development as part of the TST Brookfield Utility Plans and TST Brookfield Drainage Report and is in compliance with the original TST Brookfield Drainage Report. The calculations presented in the original report for all of Brookfield including proposed and future developments has an Imperviousness of 73% and the area corresponding to the current proposed Site has an Imperviousness of 71%. The current proposed Site has an Imperviousness of 53%. A Comparison Table with drainage basins and imperviousness values for the original Brookfield plan and the current Site is included herein. Drainage Basins are named to match the original Basin names of the TST Drainage Report for ease of comparison. Several constraints have been identified from the original report including the maximum runoff allowable into existing inlets and drainageways. Specifically, the Brookfield Drainage Plan divided the site into two basins. The interior of the site drains to an existing storm sewer system. The north and east perimeter areas drain offsite to the existing FCRID. This Drainage Plan incorporated the 100‐yr maximum release rate from the Brookfield site as 0.5 cfs per acre. The site currently sheet flow from west to east with an average slope of 0.5‐1.0%. Currently most of the Site is discharged into the FCRID. The southern portion of the sites flows into an existing curb inlet on Precision Drive and into the storm sewer system that flows into Pond A. The existing land onsite is currently undeveloped and consists of loose soils with no vegetation. Most of the Brookfield site (constructed and future phases) is graded to Detention Pond A. This water quality detention pond was sized based on SDDC and Urban Drainage criteria and has a release rate of 0.5 cfs/ac. The pond was constructed with an orifice plate with multiple orifices to provide for an extended drainage time. The water quality volume was based on a 2‐ yr storm, with the 100‐yr storm overtopping the control structure and entering the discharge pipe. The pond was provided with an orifice plate on the discharge pipe to control the 100‐yr discharge from the pond. If the pond were to overtop, it will spill in a historic eastward direction and into the FCRID. No structures will be inundated if overtopping occurs. The required volume of the detention pond is 9.01 ac‐ft. Offsite sheet flow from the west in Drainage Basin D‐5/9 is proposed to be intercepted by a drainage swale and into a storm sewer system that goes to Pond A. Offsite flows north of Le Fever Drive are channelized in a grass swale that flows into the FCRID. Offsite flows from the eastern portion of the site include the bank above the FCRID, proposed 10’ wide trail, retaining 301 N. Howes Street, Suite 100, Fort Collins, CO 80521 970.221.4158 www.northernengineering.com 3 walls and graded slopes. As this area will be vegetated and closely match undeveloped conditions it is proposed to release undetained. This undetained release will not be accounted for in the design of the detention pond since it will be at historic rates. All developed subbasins are proposed to discharge from the site at a release rate of 0.5 cfs per acre as dictated by the master plan after passing through the Pond A. The overall stormwater management strategy employed with the Brookfield Second Replat is to closely match the original design while incorporating current LID practices to minimize adverse impacts of urbanization on receiving waters. Several techniques have been utilized with the proposed development to facilitate the reduction of runoff peaks, volumes, and pollutant loads as the site is developed from the current use by implementing multiple Low Impact Development (LID) strategies including: Providing permeable paver areas with underground detention area to increase time of concentration promote infiltration and provide water quality. Providing a Drywell to promote infiltration and water quality for a portion of the site. Providing a Rain Garden and Bio Swale with Soft Bottom to slowly release the flood control volume in an area and removes pollutants by treatment processes of sedimentation, filtering, adsorption, evapotranspiration and biological uptake of constituents. A Snout and settling basin within an area inlet for water treatment prior to flows entering the subsurface infiltration galleries and storm systems. I. NCLUSS The overall stormwater management strategy employed with the Brookfield Second Replat is in compliance with the following standards: City of Fort Collins’ Stormwater Criteria Manual. Final Drainage Report for Brookfield by TST There are no regulatory floodplains associated with the development. The drainage plan and stormwater management measures proposed with the development are compliant with all applicable State and Federal regulations governing stormwater discharge. Included herein are Rain Garden calculations showing compliance with Colorado Statute §37‐92‐602 (8). The Rain Garden meets the criteria listed in the statute including continuously releasing and infiltrating at least 97% of all runoff from a rainfall event that is less than or equal to a 5‐year storm within 72 hours and releasing and infiltrating at least 99% of the runoff from a rainfall event greater than a 5‐year storm within 120 hours. The site achieves the requirements set forth by the City of Fort Collins for Low Impact Development (LID) by providing 25.8% of total paved areas as permeable pavers and providing 59.3% of total impervious areas as being treated through an LID treatment. A LID Conformance Report is attached to this Memo that includes LID sizing and exhibit. 301 N. Howes Street, Suite 100, Fort Collins, CO 80521 970.221.4158 www.northernengineering.com 4 The drainage design proposed with this project will effectively comply with previous studies and will limit any potential damage or erosion associated with its stormwater runoff. Inlets located in the alleys are designed to collect the 100‐year flows; capacity calculations are included herein. The proposed curb inlet (Design Point D3A) located on Northern Lights Drive is designed to convey the majority of the 2‐year flow with 0.1cfs by‐pass to the existing downstream curb inlet located on Precision Drive (Design Point 43). Design Point D3A matches the TST Drainage Report, Design Point 55. The TST Drainage Report had a runoff of 2.32 cfs for the 2‐year flow that was proposed to runoff to the curb inlet on Precision Drive (Design Point 43); therefore a reduction of 2.22 cfs is conveyed to the existing inlet on Precision Drive. All existing downstream drainage facilities are expected to not be impacted negatively by this development The drainage design is anticipated to be very conservative. We have omitted any runoff reduction that will manifest due to infiltration from drywells and pervious pavement. This is currently unable to be calculated with available soils data. If you have any questions, please feel free to contact me at your earliest convenience. Sincerely, NORTHERN ENGINEERING SERVICES, INC. Amber Morse, PE Project Engineer ATTACHMENTS: ATTACHMENT A Hydrologic Computations and Drainage Exhibit ATTACHMENT B Inlet Calculations ATTACHMENT C Storm Sewer Calculations (Hydraflow) ATTACHMENT D Imperviousness Comparison Table ATTACHMENT E Low Impact Development Conformance Report ATTACHMENT F Rain Garden – Compliance with Colorado Statute §37-92-602 (8) ATTACHMENT A HYDRAULIC COMPUTATIONS AND DRAINAGE EXHIBIT 374-020 Brookfield Second Replat CHARACTER OF SURFACE 1 : Runoff Coefficient Percentage Impervious Project: 374-020 Brookfield Streets, Parking Lots, Roofs, Alleys, and Drives: Calculations By: A. Morse Asphalt ……....……………...……….....…...……………….…………………………… 0.95 100% Date: December 7, 2015 Concrete …….......……………….….……….………………..….……………………… 0.95 90% Gravel (packed) ……….…………………….….…………………………..…………… 0.50 40% Roofs …….…….………………..……………….………………………………………… 0.95 90% Pavers…………………………...………………..………………………………………… 0.40 22% Lawns and Landscaping Sandy Soil Flat <2% ……………………………………………………………………………… 0.10 0% Average 2% to 7% ……………………………………………………………………… 0.15 0% Steep >7% ……………………………………………………………………………… 0.20 0% Clayey Soil Flat <2% ……………………………………………………………………………… 0.20 0% Average 2% to 7% ……………………………………………………………………… 0.25 0% Steep >7% ……………………………………………………………………………… 0.35 0% 2-year Cf = 1.00 10-year Cf = 1.00 100-year C f = 1.25 Runoff Coefficients are taken from the Fort Collins Stormwater Criteria Manual, Table RO-11 Sub-Basin ID Sub- BasinBasin Area (ac) Area of Asphalt (ac) Area of Concrete (ac) Area of Pavers (ac) Area of Roofs (ac) Soil Type and Average Slope Area of Lawns and Landscaping (ac) 2-year Composite Runoff Coefficient 10-year Composite Runoff Coefficient 100-year Composite Runoff Coefficient Composite % Imperv. 374-020 Brookfield Second Replat Overland Flow, Time of Concentration: 374-020 Brookfield Gutter/Swale Flow, Time of Concentration: Tt = L / 60V Tc = Ti + Tt (Equation RO-2) Velocity (Gutter Flow), V = 20·S½ Velocity (Swale Flow), V = 15·S½ NOTE: C-value for overland flows over grassy surfaces; C = 0.25 Is Length >500' ? C*Cf (2-yr Cf=1.00) C*Cf (10-yr Cf=1.00) C*Cf (100-yr Cf=1.25) Ti 2-yr (min) Ti 10-yr (min) Ti 100-yr (min) Velocity, V (ft/s) Tt (min) 2-yr Tc (min) 10-yr Tc (min) 100-yr Tc (min) D2A OF-1 & D-2A Yes 0.82 0.82 1.00 18.0 18.0 6.5 1.31 5.3 23.2 23.2 11.8 45 D-2B No 0.63 0.63 0.79 N/A N/A N/A 1.57 4.2 5.0 5.0 5.0 42 D-2B & D-2C (not a part) No 0.80 0.80 1.00 N/A N/A N/A 1.34 6.6 6.6 6.6 6.6 D3A D-3A No 0.74 0.74 0.93 N/A N/A N/A 1.71 3.7 5.0 5.0 5.0 43 D-3B No 0.77 0.77 0.96 N/A N/A N/A 1.60 6.5 6.5 6.5 6.5 D3C D-3C No 0.62 0.62 0.78 61.5 61.5 41.6 1.53 2.3 63.8 63.8 43.9 44 D-5/92 Yes 0.28 0.28 0.36 43.3 43.3 39.5 1.30 5.7 49.0 49.0 45.2 46 D-7 No 0.71 0.71 0.89 N/A N/A N/A 2.13 1.1 5.0 5.0 5.0 51 D-7.1 No 0.74 0.74 0.93 N/A N/A N/A 1.89 0.6 5.0 5.0 5.0 52 D-7.2 No 0.85 0.85 1.00 N/A N/A N/A 2.17 1.7 5.0 5.0 5.0 47 D-8 No 0.77 0.77 0.97 N/A N/A N/A 1.98 1.3 5.0 5.0 5.0 48 D-8.1 No 0.84 0.84 1.00 N/A N/A N/A 1.23 0.7 5.0 5.0 5.0 54 D-10 No 0.72 0.72 0.91 N/A N/A N/A 1.64 1.4 5.0 5.0 5.0 56 D-11a No 0.87 0.87 1.00 N/A N/A N/A 1.41 1.2 5.0 5.0 5.0 374-020 Brookfield Second Replat Rational Method Equation: Project: 374-020 Brookfield Calculations By: Date: Rainfall Intensity: D2A OF-1 & D-2A 0.27 23 23 12 0.82 0.82 1.00 1.49 2.55 7.29 0.33 0.57 1.97 45 D-2B 0.53 5 5 5 0.63 0.63 0.79 2.85 4.87 9.95 0.94 1.61 4.12 42 D-2B & D-2C (not a part) 0.77 7 7 7 0.80 0.80 1.00 2.60 4.44 9.06 1.61 2.75 6.98 D3A D-3A 0.44 5 5 5 0.74 0.74 0.93 2.85 4.87 9.95 0.93 1.59 4.07 43 D-3B 1.27 6 6 6 0.77 0.77 0.96 2.67 4.56 9.31 2.60 4.45 11.35 D3C D-3C 0.61 64 64 44 0.62 0.62 0.78 0.79 1.34 3.54 0.30 0.51 1.67 44 D-5/92 9.94 49 49 45 0.28 0.28 0.36 0.95 1.61 3.46 2.67 4.55 12.22 46 D-7 0.30 5 5 5 0.71 0.71 0.89 2.85 4.87 9.95 0.61 1.05 2.68 51 D-7.1 0.33 5 5 5 0.74 0.74 0.93 2.85 4.87 9.95 0.70 1.19 3.04 52 D-7.2 0.33 5 5 5 0.85 0.85 1.00 2.85 4.87 9.95 0.80 1.37 3.27 47 D-8 0.33 5 5 5 0.77 0.77 0.97 2.85 4.87 9.95 0.72 1.23 3.14 48 D-8.1 0.33 5 5 5 0.84 0.84 1.00 2.85 4.87 9.95 0.79 1.34 3.25 54 D-10 0.10 5 5 5 0.72 0.72 0.91 2.85 4.87 9.95 0.20 0.35 0.89 56 D-11a 0.36 5 5 5 0.87 0.87 1.00 2.85 4.87 9.95 0.89 1.52 3.58 11b D-11b 0.10 5 5 5 0.89 0.89 1.00 2.85 4.87 9.95 0.25 0.43 0.98 60 OF-1 0.44 51 51 46 0.31 0.31 0.39 0.91 1.56 3.41 0.12 0.21 0.58 OF2 OF-2 0.15 5 5 5 0.70 0.70 0.88 2.85 4.87 9.95 0.30 0.51 1.30 December 7, 2015 Intensity, i10 (in/hr) C10 Area, A (acres) Intensity, i2 (in/hr) 100-yr Tc (min) PROPOSED RUNOFF COMPUTATIONS C100 Design Point Flow, Q100 (cfs) Flow, Q2 (cfs) 10-yr Tc (min) 2-yr Tc (min) C2 Flow, Q10 (cfs) Intensity, i100 H Y D X X X S H Y D H Y D D D D C.O. D D C.O. D D C.O. C.O. C.O. VAULT CABLE CTV CTV CTV UD UD UD UD 12" W 12" W 12" W 12" W 12" W 12" W 12" W CINQUEFOIL LANE NORTHERN LIGHTS DRIVE PRECISION DRIVE STEELHEAD STREET BROOKFIELD DRIVE X X X X GM EM EM GM EM EM 12" W 12" W 12" SS 12" SS E E/FO/CTV E/FO/CTV G G G ATTACHMENT B INLET CALCULATIONS Project = Inlet ID = Design Information (Input) MINOR MAJOR Type of Inlet Inlet Type = Local Depression (additional to continuous gutter depression 'a' from 'Q-Allow') alocal = 2.00 2.00 inches Number of Unit Inlets (Grate or Curb Opening) No = 1 1 Water Depth at Flowline (outside of local depression) Flow Depth = 3.5 9.0 inches Grate Information MINOR MAJOR Length of a Unit Grate Lo (G) = 3.00 3.00 feet Width of a Unit Grate Wo = 1.73 1.73 feet Area Opening Ratio for a Grate (typical values 0.15-0.90) Aratio = 0.43 0.43 Clogging Factor for a Single Grate (typical value 0.50 - 0.70) Cf (G) = 0.50 0.50 Grate Weir Coefficient (typical value 2.15 - 3.60) Cw (G) = 3.30 3.30 Grate Orifice Coefficient (typical value 0.60 - 0.80) Co (G) = 0.60 0.60 Curb Opening Information MINOR MAJOR Length of a Unit Curb Opening Lo (C) = N/A N/A feet Height of Vertical Curb Opening in Inches Hvert = N/A N/A inches Height of Curb Orifice Throat in Inches Hthroat = N/A N/A inches Angle of Throat (see USDCM Figure ST-5) Theta = N/A N/A degrees Side Width for Depression Pan (typically the gutter width of 2 feet) Wp = N/A N/A feet Clogging Factor for a Single Curb Opening (typical value 0.10) Cf (C) = N/A N/A Curb Opening Weir Coefficient (typical value 2.3-3.6) Cw (C) = N/A N/A Curb Opening Orifice Coefficient (typical value 0.60 - 0.70) Co (C) = N/A N/A MINOR MAJOR Total Inlet Interception Capacity (assumes clogged condition) Qa = 0.9 4.9 cfs Inlet Capacity IS GOOD for Minor and Major Storms (>Q PEAK) Q PEAK REQUIRED = 0.7 3.1 cfs INLET IN A SUMP OR SAG LOCATION Brookfield Second Replat - Project no. 374-020 Design Point 47 - Private Alley with Type 13 Inlet at Sump CDOT/Denver 13 Valley Grate H-Vert H-Curb W Lo (C) Lo (G) Wo WP 374-020 - Alley - Design Point 47 - Type 13-Single - UD Inlet 3.1.xlsm, Inlet In Sump 8/27/2015, 3:04 PM Project = Inlet ID = Design Information (Input) MINOR MAJOR Type of Inlet Inlet Type = Local Depression (additional to continuous gutter depression 'a' from 'Q-Allow') alocal = 2.00 2.00 inches Number of Unit Inlets (Grate or Curb Opening) No = 2 2 Water Depth at Flowline (outside of local depression) Flow Depth = 3.5 9.0 inches Grate Information MINOR MAJOR Length of a Unit Grate Lo (G) = 3.00 3.00 feet Width of a Unit Grate Wo = 1.73 1.73 feet Area Opening Ratio for a Grate (typical values 0.15-0.90) Aratio = 0.43 0.43 Clogging Factor for a Single Grate (typical value 0.50 - 0.70) Cf (G) = 0.50 0.50 Grate Weir Coefficient (typical value 2.15 - 3.60) Cw (G) = 3.30 3.30 Grate Orifice Coefficient (typical value 0.60 - 0.80) Co (G) = 0.60 0.60 Curb Opening Information MINOR MAJOR Length of a Unit Curb Opening Lo (C) = N/A N/A feet Height of Vertical Curb Opening in Inches Hvert = N/A N/A inches Height of Curb Orifice Throat in Inches Hthroat = N/A N/A inches Angle of Throat (see USDCM Figure ST-5) Theta = N/A N/A degrees Side Width for Depression Pan (typically the gutter width of 2 feet) Wp = N/A N/A feet Clogging Factor for a Single Curb Opening (typical value 0.10) Cf (C) = N/A N/A Curb Opening Weir Coefficient (typical value 2.3-3.6) Cw (C) = N/A N/A Curb Opening Orifice Coefficient (typical value 0.60 - 0.70) Co (C) = N/A N/A MINOR MAJOR Total Inlet Interception Capacity (assumes clogged condition) Qa = 1.3 10.4 cfs Inlet Capacity IS GOOD for Minor and Major Storms (>Q PEAK) Q PEAK REQUIRED = 0.9 3.6 cfs INLET IN A SUMP OR SAG LOCATION Brookfield Second Replat - Project no. 374-020 Maximum Flow - Design Point 56 - Private Alley with Type 13 Inlet-Double at Sump CDOT/Denver 13 Valley Grate H-Vert H-Curb W Lo (C) Lo (G) Wo WP 374-020 - Alley - Design Point 56 - UD Inlet 3.1.xlsm, Inlet In Sump 8/27/2015, 2:27 PM Project: Inlet ID: Design Information (Input) MINOR MAJOR Type of Inlet Type = Local Depression (additional to continuous gutter depression 'a' from 'Q-Allow') aLOCAL = 2.0 2.0 inches Total Number of Units in the Inlet (Grate or Curb Opening) No = 1 1 Length of a Single Unit Inlet (Grate or Curb Opening) Lo = 3.00 3.00 ft Width of a Unit Grate (cannot be greater than W from Q-Allow) Wo = 2.00 2.00 ft Clogging Factor for a Single Unit Grate (typical min. value = 0.5) Cf-G = 0.50 0.50 Clogging Factor for a Single Unit Curb Opening (typical min. value = 0.1) Cf-C = 0.10 0.10 Street Hydraulics: OK - Q < maximum allowable from sheet 'Q-Allow' MINOR MAJOR Total Inlet Interception Capacity Q = 0.8 2.1 cfs Total Inlet Carry-Over Flow (flow bypassing inlet) Qb = 0.1 1.9 cfs Capture Percentage = Qa/Q o = C% = 90 52 % INLET ON A CONTINUOUS GRADE Brookfield Second Replat - Project no. 374-020 Northern Lights Drive (Local Street) with Combination Inlet - Design Point D3A CDOT/Denver 13 Combination 374-020 - Design Point D3A - Northern Lights - UD Inlet 3.1.xlsm, Inlet On Grade 8/27/2015, 2:49 PM ATTACHMENT C STORM SEWER CALCULATIONS (HYDRAFLOW) ATTACHMENT D IMPERVIOUSNESS COMPARISON TABLE 374-020 Brookfield Second Replat DESIGN POINT BASIN ID AREA (acres) % Impervious BASIN ID AREA (acres) % Impervious D2A OF-1 & D-2A 0.27 79% 45 D-2B 0.53 51% 42 D-2B & D-2C (not a part) 0.77 73% D3A D-3A 0.44 66% 43 D-3B 1.27 69% D3C D-3C 0.61 49% 44 D-5/92 - - D5, D9 46 D-7 0.30 57% D7 0.25 86% 51 D-7.1 0.33 65% D7.1 0.22 86% 52 D-7.2 0.33 68% D7.2 0.79 86% 47 D-8 0.33 63% D8 0.29 83% 48 D-8.1 0.33 70% D8.1 0.22 83% 54 D-10 0.39 59% D10 0.32 86% 56 D11a & D11b 0.46 68% D11 0.14 86% 60 OF-1 0.44 8% OF2 OF-2 0.15 58% Totals: 6.94 53% Totals: 6.58 71% (1) - Drainage Memorandum for Brookfield Second Replat by Northern Engineering dated December 7, 2015 (2) - Final Drainage Report for Brookfield by TST dated December 14, 2001 Not a Part of Site Not a Part of Site Proposed Future Commercial Northern Engineering Drainage Memo (1) TST Drainiage Report (2) IMPERVIOUSNESS COMPARISON TABLE D3 2.73 67% D2 1.62 81% D:\Projects\374-020\Drainage\Hydrology\374-020_Proposed_Rational_Calcs.xlsx 12/7/2015 ATTACHMENT E LOW IMPACT DEVELOPMENT CONFORMANCE REPORT 301 N. Howes Street, Suite 100, Fort Collins, CO 80521 970.221.4158 www.northernengineering.com LID Conformance Report Date: January 25, 2016 Project: Brookfield Second Replat, Lots 1-12, Tract E and a portion of Tract D Project No. 374-020 Fort Collins, CO Attn: Stormwater Staff City of Fort Collins Stormwater Utility 700 Wood Street Fort Collins, CO 80521 Stormwater Staff: This letter serves to document conformance of the above referenced project with City of Fort Collins Low Impact Development (LID) requirements. In particular, the project is meeting Section 3.1 of the Fort Collins Stormwater Amendments to the Urban Drainage and Flood Control District Criteria Manual, including Section 3.1 (a)(1) requiring that no less than 50% of any newly added impervious area be treated using one or more LID techniques and Section 3.1(a)(2) requiring that no less than 25% of all new paving use a permeable pavement technology that is considered an LID technique. Section 3.1(a)(1) The project as a whole is proposing 2.997 acres of new on-site impervious area. This results in a minimum required LID treatment area of 1.498 acres. The project is treating 0.740 acres of on-site impervious area by pavers (directly or indirectly). The project is treating 0.260 acres of on-site impervious areas and 0.113 acres of off-site impervious areas using a Bio Swale with Soft Bottom. Runoff from the east half of a portion of Brookfield Drive flows along the curb and gutter to a 4’ concrete chase under the sidewalk and into the Bio Swale. Low flows along the gutter will flow into the north side of the Bio Swale by the concrete chase and high flows will continue south along the curb and gutter as historically designed. The Bio Swale with Soft Bottom is designed with an underdrain perforated pipe, two clean-outs and a 12-inch grate inlet to keep ponding to the designed depth of 0.1-feet. During a major storm event flows will bypass the 12-inch grate inlet and will flow out a 2’ metal chase under the sidewalk on the south side of the Bio Swale. The project is treating 0.835 acres of on-site impervious areas and 0.407 acres of off-site impervious areas using a treatment train of pavers, inlet snout, rain garden, forebay and dry well. Runoff from the north half of Le Fever Drive flows along the curb and gutter to a 4’ concrete chase under the sidewalk and into a 3-feet deep concrete forebay before entering the Rain Garden. Low flows along the gutter will flow into the Rain Garden by the concrete chase and high flows will continue south along the curb and gutter as historically designed. The Rain Garden is designed with an underdrain perforated pipe, two clean-outs and a 12-inch grate inlet. Water quality capture volume is 466-cubic feet and a design depth of 0.44-feet. During a major storm event flows will bypass the 12-inch grate inlet and will flow out the 4-feet concrete chase under the sidewalk and down the curb and gutter south along Northern Lights Drive. Runoff from the south half of Le Fever Drive flows along the curb and gutter to a curb inlet on Northern Lights Drive. Surface flow upstream of the permeable pavers is captured by an underdrain and into the storm sewer line. Flow within the storm sewer line will be treated by a snout that will remove floating debris and oil at the area inlet located in the 301 N. Howes Street, Suite 100, Fort Collins, CO 80521 970.221.4158 www.northernengineering.com driveway. Low flows within the storm sewer line will flow to a Dry Well located east of the rain garden. High flows within the storm sewer line will flow south along Northern Lights Drive within the proposed storm sewer line and outlet to Pond A. The Dry Well will receive low flows from the storm sewer line and flows from the underdrain in the Rain Garden. The Dry Well has a capacity of 1395 cubic feet; calculations are included herein. The total on-site project area treated by LID techniques is 1.776 acres, which is 59.3% of the total new impervious area. Section 3.1(a)(2) The project as a whole is proposing 0.944 acres of new impervious paving. This results in a minimum required permeable paving area of 0.236 acres. The project has evaluated various areas for pavers to provide LID treatment to multiple areas of the Site. The total area of permeable pavers provided by the project is 0.243 acres, which is 25.8% of the total new paving. An exhibit has been provided to illustrate the topics outlined, and calculations supporting the LID techniques. Please feel free to contact me if you have any questions. Sincerely, Amber Morse Project Engineer ATTACHMENTS: Low Impact Development (LID) Treatment Exhibit Bio Swale with Soft Bottom Calculation Rain Garden Calculation Rain Garden Stage Storage Drywell Detail Drywell Capacity Calculation Low Flow Pipe to Dry Well Flow Calculation X UD UD UD FOSSIL CREEK RESERVOIR INLET DITCH WETLAND RAIN GARDEN REQUIRED WQCV = 466 CF DESIGN VOLUME = 1,300 CF PERMEABLE PAVEMENT SOUTHEAST PERMEABLE PAVEMENT SOUTH CENTER PERMEABLE PAVEMENT NORTH PERMEABLE PAVEMENT SOUTHWEST BIO SWALE W/ SOFT-BOTTOM DRY WELL WQCV VOLUME = 1286 CF DESIGN VOLUME = 1395 CF OFF-SITE IMPERVIOUS AREA CURB INLET AREA INLET WITH SNOUT BROOKFIELD DRIVE NORTHERN LIGHTS DRIVE LE FEVER DRIVE PRECISION DRIVE 4' CONCRETE CHASE LOW FLOW INTO BIO SWALE 2' METAL CHASE HIGH FLOW TO STREET 4' CONCRETE CHASE LOW FLOW INTO RAIN GARDEN HIGH FLOW TO STREET MH A5 LOW FLOW T TO DRY WELL HIGH FLOW CONTINUES IN STORM SEWER 8-INCH PVC 2.71 CFS FULL-FLOW CAPACITY 12" GRATE 12" GRATE KEYMAP COVERED ENTRY ENTRY COVERED DECK COVERED COVERED ENTRY ENTRY COVERED ENTRY DECK DECK DECK DECK Sheet 1 of 1 Designer: Company: Date: Project: Location: 1. Design Discharge for 2-Year Return Period Q2 = 0.30 cfs 2. Hydraulic Residence Time A) : Length of Grass Swale LS = 140.0 ft B) Calculated Residence Time (based on design velocity below) THR= 6.5 minutes 3. Longitudinal Slope (vertical distance per unit horizontal) A) Available Slope (based on site constraints) Savail = ft / ft B) Design Slope SD = 0.010 ft / ft 4. Swale Geometry A) Channel Side Slopes (Z = 4 min., horiz. distance per unit vertical) Z = 4.00 ft / ft B) Bottom Width of Swale (enter 0 for triangular section) WB = 8.00 ft 5. Vegetation A) Type of Planting (seed vs. sod, affects vegetal retardance factor) 6. Design Velocity (0.467 ft / s maximum for desirable 5-minute residence time) V2 = 0.36 ft / s 7. Design Flow Depth (1 foot maximum) D2 = 0.10 ft A) Flow Area A2 = 0.8 sq ft B) Top Width of Swale WT = 8.8 ft C) Froude Number (0.50 maximum) F = 0.20 D) Hydraulic Radius RH = 0.10 E) Velocity-Hydraulic Radius Product for Vegetal Retardance VR = 0.03 F) Manning's n (based on SCS vegetal retardance curve E for seeded grass) n = 0.080 G) Cumulative Height of Grade Control Structures Required HD = 0.00 ft AN UNDERDRAIN IS 8. Underdrain REQUIRED IF THE (Is an underdrain necessary?) DESIGN SLOPE < 2.0% 9. Soil Preparation (Describe soil amendment) 10. Irrigation Notes: Design Procedure Form: Grass Swale (GS) A. Morse Northern Engineering December 7, 2015 Brookfield 374-020 Bio Swale with Soft Bottom Choose One Temporary Permanent Choose One Grass From Seed Grass From Sod Choose One YES NO 374-020_RG_UD.xlsm, GS 12/7/2015, 11:14 AM Brookfield 374-020 374-020 City of Fort Collins, CO A. Morse Date: 1/21/2016 Pond No.: Rain Garden 2-yr acft Design Storm WQCV Required Volume= 466 ft3 4897.33 ft. Contour Elevation (Y- values) Contour Area Depth Column Not Used Incremental Volume Total Volume Total Volume ft2 ft. ft3 ft3 ft3 acre-feet 4,896.90 937.50 0.00 0 0 0 0 4,897.00 1007.30 0.10 97 97 0.00 4,897.20 1155.41 0.20 216 313 0.01 4,897.40 1311.36 0.20 246 559 0.01 4,897.60 1464.95 0.20 277 836 0.02 4,897.80 1631.62 0.20 309 1146 0.03 4,898.00 1827.14 0.20 345 1491 0.03 Design Point Design Storm Require Volume= Stage - Storage Calculation Project Number: Project Location: Calculations By: Required Volume Water Surface Elevation (WSE) 1/21/20168:34 AM D:\Projects\374-020\Drainage\LID\374-020__RG Stage Storage.xlsm\Stage_Storage_RG Sheet 1 of 2 Designer: Company: Date: Project: Location: 1. Basin Storage Volume A) Effective Imperviousness of Tributary Area, Ia I a = 63.0 % (100% if all paved and roofed areas upstream of rain garden) B) Tributary Area's Imperviousness Ratio (i = Ia/100) i = 0.630 C) Water Quality Capture Volume (WQCV) for a 12-hour Drain Time WQCV = 0.20 watershed inches (WQCV= 0.8 * (0.91* i 3 - 1.19 * i 2 + 0.78 * i) D) Contributing Watershed Area (including rain garden area) Area = 28,320 sq ft E) Water Quality Capture Volume (WQCV) Design Volume VWQCV = 466 cu ft Vol = (WQCV / 12) * Area F) For Watersheds Outside of the Denver Region, Depth of d6 = in Average Runoff Producing Storm G) For Watersheds Outside of the Denver Region, VWQCV OTHER = 0.0 cu ft Water Quality Capture Volume (WQCV) Design Volume H) User Input of Water Quality Capture Volume (WQCV) Design Volume VWQCV USER = cu ft (Only if a different WQCV Design Volume is desired) 2. Basin Geometry A) WQCV Depth (12-inch maximum) DWQCV = 12 in B) Rain Garden Side Slopes (Z = 4 min., horiz. dist per unit vertical) Z = 4.00 ft / ft (Use "0" if rain garden has vertical walls) C) Mimimum Flat Surface Area AMin = 310 sq ft D) Actual Flat Surface Area AActual = 936 sq ft E) Area at Design Depth (Top Surface Area) ATop = 1800 sq ft F) Rain Garden Total Volume VT= 1,368 cu ft (VT= ((A Top + AActual ) / 2) * Depth) 3. Growing Media 4. Underdrain System A) Are underdrains provided? B) Underdrain system orifice diameter for 12 hour drain time i) Distance From Lowest Elevation of the Storage y = ft Volume to the Center of the Orifice ii) Volume to Drain in 12 Hours Vol12 = N/A cu ft iii) Orifice Diameter, 3/8" Minimum DO = N/A in Design Procedure Form: Rain Garden (RG) A. Morse Northern Engineering December 7, 2015 Brookfield 374-020 Rain Garden Choose One Choose One 18" Rain Garden Growing Media Other (Explain): YES NO 374-020_RG_UD.xlsm, RG 12/7/2015, 11:54 AM Sheet 2 of 2 Designer: Company: Date: Project: Location: 5. Impermeable Geomembrane Liner and Geotextile Separator Fabric A) Is an impermeable liner provided due to proximity of structures or groundwater contamination? 6. Inlet / Outlet Control A) Inlet Control 7. Vegetation 8. Irrigation NO SPRINKLER HEADS ON FLAT SURFACE A) Will the rain garden be irrigated? Notes: Design Procedure Form: Rain Garden (RG) A. Morse Northern Engineering December 7, 2015 Brookfield 374-020 Rain Garden Choose One Choose One Choose One Sheet Flow- No Energy Dissipation Required Concentrated Flow- Energy Dissipation Provided Plantings Seed (Plan for frequent weed control) Sand Grown or Other High Infiltration Sod Choose One YES NO YES NO 374-020_RG_UD.xlsm, RG 12/7/2015, 11:54 AM Project: Pipe ID: Design Information (Input) Pipe Invert Slope So = 0.0500 ft/ft Pipe Manning's n-value n = 0.0130 Pipe Diameter D = 8.00 inches Design discharge Q = 0.72 cfs Full-flow Capacity (Calculated) Full-flow area Af = 0.35 sq ft Full-flow wetted perimeter Pf = 2.09 ft Half Central Angle Theta = 3.14 radians Full-flow capacity Qf = 2.71 cfs Calculation of Normal Flow Condition Half Central Angle (0<Theta<3.14) Theta = 1.27 radians Flow area An = 0.11 sq ft Top width Tn = 0.64 ft Wetted perimeter Pn = 0.85 ft Flow depth Yn = 0.23 ft Flow velocity Vn = 6.56 fps Discharge Qn = 0.72 cfs Percent Full Flow Flow = 26.57% of full flow Normal Depth Froude Number Frn = 2.79 supercritical Calculation of Critical Flow Condition Half Central Angle (0<Theta-c<3.14) Theta-c = 1.77 radians Critical flow area Ac = 0.22 sq ft Critical top width Tc = 0.65 ft Critical flow depth Yc = 0.40 ft Critical flow velocity Vc = 3.29 fps Critical Depth Froude Number Frc = 1.00 CIRCULAR CONDUIT FLOW (Normal & Critical Depth Computation) 374-020 Brookfield Low Flow Pipe to Dry Well from MH A5 - 2-YR Flow is 0.72 cfs 374-020_Low Flow Pipe to DW_UD-Culvert.xls, Pipe 12/3/2015, 12:19 PM ATTACHMENT F RAIN GARDEN – COMPLIANCE WITH COLORADO STATUTE §37-92-602 (8) Stormwater Facility Name: Facility Location & Jurisdiction: User (Input) Watershed Characteristics User Defined User Defined User Defined User Defined Discharge Watershed Slope = 0.005 ft/ft Stage [ft] Area [ft^2] Stage [ft] Discharge [cfs] Method Watershed Length‐to‐Width Ratio = 2.66 L:W 0.00 938 0.00 0.00 Watershed Area =1.58acres 0.10 1,007 0.10 0.05 4in Slotted Pipe Watershed Imperviousness = 71.0% percent 0.30 1,155 0.30 0.05 4in Slotted Pipe Percentage Hydrologic Soil Group A =0.0%percent 0.50 1,311 0.50 0.05 4in Slotted Pipe Percentage Hydrologic Soil Group B = 50.0% percent 0.70 1,465 0.70 0.64 12" Grate Percentage Hydrologic Soil Groups C/D = 50.0% percent 0.90 1,632 0.90 0.85 12" Grate 1.10 1,827 1.00 0.96 12" Grate 1.10 8.80 12" Grate & 4' Chase to Gutter User Input: Detention Basin Characteristics WQCV Design Drain Time = 12.00 hours After completing and printing this worksheet to a pdf, go to: https://maperture.digitaldataservices.com/gvh/?viewer=cswdif, create a new stormwater facility, and attach the pdf of this worksheet to that record. Routed Hydrograph Results Design Storm Return Period = WQCV 2 Year 5 Year 10 Year 25 Year 50 Year 100 Year Two‐Hour Rainfall Depth = 0.53 0.98 1.36 1.71 2.31 2.91 3.67 in Calculated Runoff Volume = 0.029 0.088 0.135 0.179 0.259 0.338 0.442 acre‐ft OPTIONAL Override Runoff Volume = acre‐ft Inflow Hydrograph Volume = 0.029 0.088 0.134 0.178 0.259 0.338 0.442 acre‐ft Time to Drain 97% of Inflow Volume = 555 5443 hours Time to Drain 99% of Inflow Volume = 6666655 hours Maximum Ponding Depth = 0.57 0.99 1.02 1.03 1.07 1.08 1.09 ft Maximum Ponded Area = 0.031 0.039 0.040 0.040 0.041 0.041 0.042 acres Maximum Volume Stored = 0.015 0.030 0.031 0.031 0.033 0.033 0.034 acre‐ft Workbook Protected Worksheet Protected Stormwater Detention and Infiltration Design Data Sheet Brookfield ‐ 374‐020 January 25, 2016 Rain Garden 374‐020_SDI_Design_Data_FC_Rainfall.xlsm, Design Data 1/21/2016, 9:20 AM Doing_Clear_FoYes CountA= 1 0123 #N/A #N/A 0123 #N/A #N/A Check Data Set 1 Check Data Set 1 Area Discharge Stormwater Detention and Infiltration Design Data Sheet 0 1 2 3 4 5 6 7 8 9 0.1 1 10 FLOW [cfs] TIME [hr] 100YR IN 100YR OUT 50YR IN 50YR OUT 25YR IN 25YR OUT 10YR IN 10YR OUT 5YR IN 5YR OUT 2YR IN 2YR OUT WQCV IN WQCV OUT 0 0.2 0.4 0.6 0.8 1 1.2 0.1 1 10 100 PONDING DEPTH [ft] DRAIN TIME [hr] 100YR 50YR 25YR 10YR 5YR 2YR WQCV 374‐020_SDI_Design_Data_FC_Rainfall.xlsm, Design Data 1/21/2016, 9:20 AM Channel Report Hydraflow Express Extension for Autodesk® AutoCAD® Civil 3D® by Autodesk, Inc. Monday, Jan 4 2016 374-020 - Rain Garden - 4in Slotted PVC Pipe Circular Diameter (ft) = 0.25 Invert Elev (ft) = 100.00 Slope (%) = 0.40 N-Value = 0.015 Calculations Compute by: Q vs Depth No. Increments = 10 Highlighted Depth (ft) = 0.25 Q (cfs) = 0.048 Area (sqft) = 0.05 Velocity (ft/s) = 0.99 Wetted Perim (ft) = 0.79 Crit Depth, Yc (ft) = 0.14 Top Width (ft) = 0.00 EGL (ft) = 0.27 0 1 Elev (ft) Section 99.75 100.00 100.25 100.50 100.75 101.00 Reach (ft) 3130 Verona Avenue • Buford, GA 30518 (866) 888-8479 / (770) 932-2443 • Fax: (770) 932-2490 © Nyloplast Inlet Capacity Charts June 2012 0.00 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60 0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50 0.55 0.60 0.65 0.70 0.75 0.80 0.85 0.90 0.95 1.00 1.05 1.10 Capacity (cfs) Head (ft) Nyloplast 12" Drop In Grate Inlet Capacity Chart Weir Report Hydraflow Express Extension for Autodesk® AutoCAD® Civil 3D® by Autodesk, Inc. Monday, Jan 4 2016 374-020 - Rain Garden - Overflow Weir to Gutter Rectangular Weir Crest = Sharp Bottom Length (ft) = 4.00 Total Depth (ft) = 0.70 Calculations Weir Coeff. Cw = 3.33 Compute by: Q vs Depth No. Increments = 10 Highlighted Depth (ft) = 0.70 Q (cfs) = 7.801 Area (sqft) = 2.80 Velocity (ft/s) = 2.79 Top Width (ft) = 4.00 0 .5 1 1.5 2 2.5 3 3.5 4 4.5 5 Depth (ft) 374-020 - Rain Garden - Overflow Weir to Gutter Depth (ft) -0.50 -0.50 0.00 0.00 0.50 0.50 1.00 1.00 Weir W.S. Length (ft) ENTRY COVERED COVERED ENTRY DECK COVERED ENTRY COVERED ENTRY COVERED ENTRY DECK DECK DECK COVERED ENTRY ENTRY COVERED DECK COVERED ENTRY COVERED ENTRY COVERED ENTRY DECK DECK DECK COVERED ENTRY ENTRY COVERED DECK COVERED COVERED ENTRY COVERED ENTRY ENTRY DECK DECK DECK DECK COVERED ENTRY ENTRY COVERED DECK COVERED ENTRY COVERED ENTRY COVERED ENTRY DECK DECK DECK DECK COVERED ENTRY ENTRY COVERED DECK COVERED ENTRY COVERED COVERED ENTRY ENTRY DECK DECK DECK DECK LEGEND: 5013 PROPOSED CONTOUR 93 EXISTING CONTOUR EXISTING STORM SEWER LID BOUNDARY PROPOSED STORM SEWER FOR LID REVIEW ONLY NOT FOR CONSTRUCTION ( IN FEET ) 0 1 INCH = 70 FEET 70 70 140 210 ENGINEER ING N O R T H E RN 2016.01.21 D:\PROJECTS\374-020\DWG\EXHIBITS\374-020_LID.DWG LOW IMPACT DEVELOPMENT (LID) TREATMENT EXHIBIT FORT COLLINS, CO BROOKFIELD LID-1 PERMEABLE PAVERS RUN-ON AREA FOR PERMEABLE PAVERS OFF-SITE IMPERMEABLE AREA TREATED BY LID E/CTV TRACT F PLAT OF BROOKFIELD MORNINGSIDE VILLAGE CONDOS FOSSIL CREEK RESERVOIR INLET DITCH WETLAND POND A DIRT TRAIL BROOKFIELD DRIVE NORTHERN LIGHTS DRIVE LE FEVER DRIVE PRECISION DRIVE 47 D-8 D-8.1 0.39 AC 0.33 AC 48 52 D-7.2 0.79 AC D-3C 0.61 AC D-7.1 0.33 AC 51 46 D-7 0.30 AC 43 D-5/9 9.94 AC 44 OF2 0.15 AC OF2 D11a 0.36 AC 56 D-10 0.39 AC 54 D-2B 0.53 AC 45 OF1 0.44 AC 60 D-3A 0.44 AC D-2A 0.27 AC D-3B 1.27 AC D-2C 0.77 AC 42 D3A D3C D2A WIDTH VARIES HABITAT BUFFER ZONE D11b 0.10 AC 11b BIO SWALE WITH SOFT BOTTOM RAIN GARDEN DRY WELL INLET WITH SNOUT WIDTH VARIES HABITAT BUFFER ZONE WIDTH VARIES NORTH POUDRE IRRIGATION COMPANY DITCH ROAD AND MAINTENANCE EASEMENT FCRID TOP OF BANK 50' KEYMAP FOX DEN BUFFER ZONE NORTHERN LIGHTS DRIVE BROOKFIELD DRIVE COVERED ENTRY ENTRY COVERED DECK COVERED COVERED ENTRY ENTRY COVERED ENTRY DECK DECK DECK DECK COVERED ENTRY ENTRY COVERED COVERED ENTRY COVERED ENTRY COVERED ENTRY COVERED ENTRY ENTRY COVERED DECK COVERED ENTRY COVERED ENTRY COVERED ENTRY DECK DECK DECK DECK COVERED ENTRY ENTRY COVERED DECK COVERED ENTRY COVERED ENTRY COVERED ENTRY DECK DECK DECK DECK COVERED ENTRY ENTRY COVERED COVERED ENTRY COVERED ENTRY COVERED ENTRY COVERED ENTRY ENTRY COVERED COVERED ENTRY COVERED ENTRY COVERED ENTRY No. Revisions: By: Date: REVIEWED BY: R. Banning DESIGNED BY: DRAWN BY: SCALE: DATE: January 25, 2016 PROJECT: 374-020 Sheet Of 36 BROOKFIELD SECOND REPLAT These drawings are instruments of service provided by Northern Engineering Services, Inc. and are not to be used for any type of construction unless signed and sealed by a Professional Engineer in the employ of Northern Engineering Services, Inc. NOT FOR CONSTRUCTION REVIEW SET 01/25/16 E N G I N E E R I N G N O R T H E RN 301 North Howes Street, Suite 100 Fort Collins, Colorado 80521 PHONE: 970.221.4158 www.northernengineering.com LEGEND: 5013 PROPOSED CONTOUR 93 EXISTING CONTOUR PROPERTY BOUNDARY EXISTING STORM SEWER 1.THE SIZE, TYPE AND LOCATION OF ALL KNOWN UNDERGROUND UTILITIES ARE APPROXIMATE WHEN SHOWN ON THESE DRAWINGS. IT SHALL BE THE RESPONSIBILITY OF THE CONTRACTOR TO VERIFY THE EXISTENCE OF ALL UNDERGROUND UTILITIES IN THE AREA OF THE WORK. BEFORE COMMENCING NEW CONSTRUCTION, THE CONTRACTOR SHALL BE RESPONSIBLE FOR LOCATING ALL UNDERGROUND UTILITIES AND SHALL BE RESPONSIBLE FOR FOR ALL UNKNOWN UNDERGROUND UTILITIES. 2.REFER TO THE DRAINAGE MEMORANDUM BROOKFIELD SECOND REPLAT BY NORTHERN ENGINEERING, DATED AUGUST 28, 2015 FOR ADDITIONAL INFORMATION. 3.HABITAT BUFFER ZONE IS TO BE MAINTAINED IN A NATIVE LANDSCAPE. SEE SECTION 3.4.1 OF THE LAND USE CODE FOR ALLOWABLE USES WITHIN THE BUFFER ZONE.{ HABITAT BUFFER ZONE IS BETWEEN THE LOT LINE AND EASTERN EDGE OF PEDESTRIAN TRAIL.} { } NOTES: DRAINAGE BASIN BUBBLE A 144 ac DESIGN POINT A BASIN BOUNDARY PROPOSED STORM SEWER FOR DRAINAGE REVIEW ONLY NOT FOR CONSTRUCTION City Engineer Date Date Date Date Date Stormwater Utility Parks & Recreation Traffic Engineer Date APPROVED: CHECKED BY: CHECKED BY: CHECKED BY: CHECKED BY: CHECKED BY: Water & Wastewater Utility City of Fort Collins, Colorado UTILITY PLAN APPROVAL Environmental Planner DR1 DRAINAGE EXHIBIT R. Banning A. Boese 1"=60' 24 ( IN FEET ) 0 1 INCH = 60 FEET 60 60 120 180 PERMEABLE PAVERS (in/hr) Sub-Basin(s) A. Morse Rainfall Intensity taken from the Fort Collins Stormwater Criteria Manual (FCSCM), Tables RA-7 and RA-8 Q = C f (C )( i )(A ) 12/7/2015 9:56 AM D:\Projects\374-020\Drainage\Hydrology\374-020_Proposed_Rational_Calcs.xlsx\Runoff 11b D-11b No 0.89 0.89 1.00 N/A N/A N/A 1.90 0.4 5.0 5.0 5.0 60 OF-1 Yes 0.31 0.31 0.39 51.4 51.4 46.3 N/A N/A 51.4 51.4 46.3 OF2 OF-2 No 0.70 0.70 0.88 4.8 4.8 2.7 N/A N/A 5.0 5.0 5.0 * Time of Concentrations are calculated for the entire basin and used for both the Impervious and Pervious portions of the basins. PROPOSED TIME OF CONCENTRATION COMPUTATIONS A. Morse December 7, 2015 Design Point Sub-Basin(s) Overland Flow Gutter/Pipe Flow Time of Concentration (Equation RO-4) () 3 1 1 . 87 1 . 1 * S Ti C Cf L − = 12/7/2015 9:56 AM D:\Projects\374-020\Drainage\Hydrology\374-020_Proposed_Rational_Calcs.xlsx\Tc D-2A 0.27 0.15 0.07 0.00 0.00 Clayey | Average 2% to 7% 0.049 0.82 0.82 1.00 79% D-2B 0.53 0.12 0.09 0.00 0.07 Clayey | Average 2% to 7% 0.241 0.63 0.63 0.79 51% D-2C2 0.77 0.11 0.29 0.00 0.22 Clayey | Average 2% to 7% 0.160 0.80 0.80 1.00 73% TOTAL BASIN D2 1.57 0.38 0.45 0.00 0.29 Clayey | Average 2% to 7% 0.450 0.75 0.75 0.94 67% D-3A 0.44 0.12 0.08 0.00 0.11 Clayey | Average 2% to 7% 0.131 0.74 0.74 0.93 66% D-3B 1.27 0.36 0.30 0.00 0.28 Clayey | Average 2% to 7% 0.335 0.77 0.77 0.96 69% D-3C 0.61 0.06 0.07 0.00 0.19 Clayey | Average 2% to 7% 0.287 0.62 0.62 0.78 49% TOTAL BASIN D3 2.32 0.54 0.45 0.00 0.58 Clayey | Average 2% to 7% 0.753 0.72 0.72 0.90 63% D-5/92 9.94 0.41 0.07 0.00 0.00 Clayey | Average 2% to 7% 9.456 0.28 0.28 0.36 5% D-7 0.30 0.00 0.06 0.05 0.11 Clayey | Average 2% to 7% 0.138 0.71 0.71 0.89 57% D-7.1 0.33 0.00 0.02 0.05 0.20 Clayey | Average 2% to 7% 0.079 0.74 0.74 0.93 65% D-7.2 0.79 0.00 0.24 0.00 0.36 Clayey | Average 2% to 7% 0.421 0.85 0.85 1.00 68% D-8 0.39 0.00 0.10 0.05 0.15 Clayey | Average 2% to 7% 0.180 0.77 0.77 0.97 63% D-8.1 0.33 0.00 0.07 0.00 0.19 Clayey | Average 2% to 7% 0.141 0.84 0.84 1.00 70% D-10 0.39 0.00 0.07 0.07 0.15 Clayey | Average 2% to 7% 0.167 0.72 0.72 0.91 59% D-11a 0.36 0.00 0.13 0.00 0.14 Clayey | Average 2% to 7% 0.221 0.87 0.87 1.00 68% D-11b 0.10 0.00 0.04 0.00 0.03 Clayey | Average 2% to 7% 0.067 0.89 0.89 1.00 68% TOTAL BASIN D 16.82 1.33 1.71 0.23 2.19 Clayey | Average 2% to 7% 12.074 0.48 0.48 0.60 29% OF-12 0.44 0.03 0.01 0.00 0.00 Clayey | Average 2% to 7% 0.399 0.31 0.31 0.39 8% OF-2 0.15 0.00 0.02 0.00 0.08 Clayey | Average 2% to 7% 0.053 0.70 0.70 0.88 58% 1. Table RO-11 | Rational Method Runoff Coefficients for Composite Analysis 2. Sub-Basin outside of Project Boundary Composite Runoff Coefficient with Adjustment PROPOSED COMPOSITE % IMPERVIOUSNESS AND RUNOFF COEFFICIENT CALCULATIONS 12/7/2015 9:55 AM D:\Projects\374-020\Drainage\Hydrology\374-020_Proposed_Rational_Calcs.xlsx\Composite C