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Home My WebLink AboutBROOKFIELD SECOND FILING, TRACTS D & E - PDP/FDP - FDP150025 - REPORTS - DRAINAGE REPORT301 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 August 27, 2015 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. 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 be private and will be maintained privately. Public streets bound the tract. 301 N. Howes Street, Suite 100, Fort Collins, CO 80521 970.221.4158 www.northernengineering.com 2 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 the 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 76%. The current proposed Site has an Imperviousness of 63%. 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 walls and graded slopes. As this area will be vegetated and closely match undeveloped 301 N. Howes Street, Suite 100, Fort Collins, CO 80521 970.221.4158 www.northernengineering.com 3 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 Drywells to promote infiltration and water quality throughout the site. Providing a Rain Garden and Grass Swale 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. Snouts and settling basins 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. The site achieves the requirements set forth by the City of Fort Collins for Low Impact Development (LID) by providing 25% of total paved areas as permeable pavers and providing 54% of total impervious areas as being treated through an LID treatment. LID and Porous Pavement Calculation Tables are provided herein. 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 301 N. Howes Street, Suite 100, Fort Collins, CO 80521 970.221.4158 www.northernengineering.com 4 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 374-020 Brookfield Second Replat CHARACTER OF SURFACE1: Runoff Coefficient Percentage Impervious Project: 374-020 Brookfield Streets, Parking Lots, Roofs, Alleys, and Drives: Calculations By: A. Morse Asphalt ……....……………...……….....…...……………….…………………………… 0.95 100% Date: August 27, 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. 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% 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) Length, L (ft) Up Stream Elevation Down Stream Elevation Slope, S (%) Ti 2-yr (min) Ti 10-yr (min) Ti 100-yr (min) Length, L (ft) Up Stream Elevation Down Stream Elevation Slope, S (%) Velocity, V (ft/s) Tt (min) 2-yr Tc (min) 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 0.36 5 5 5 0.76 0.76 0.95 2.85 4.87 9.95 0.78 1.33 3.40 56 D-11 0.36 5 5 5 0.87 0.87 1.00 2.85 4.87 9.95 0.89 1.52 3.58 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 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 (in/hr) Sub-Basin(s) A. Morse Rainfall Intensity taken from the Fort Collins Stormwater Criteria Manual (FCSCM), Tables RA-7 and RA-8 August 27, 2015 Intensity, 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 UD 12" W 12" W 12" W 12" W 12" W 12" W 12" W CINQUEFOIL LANE NORTHERN LIGHTS DRIVE PRECISION DRIVE STEELHEAD STREET 20' DRAINAGE EASEMENT 20' DRAINAGE EASEMENT 20' DRAINAGE EASEMENT 20' DRAINAGE EASEMENT BROOKFIELD DRIVE GM EM EM GM EM EM 12" W 12" W 12" SS 12" SS E E/FO/CTV E/FO/CTV G G G 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 X X UD UD UD BROOKFIELD DRIVE MORNINGSIDE VILLAGE CONDOS FOSSIL CREEK RESERVOIR INLET DITCH WETLAND 1 2 3 4 5 6 7 8 9 10 11 12 13 14 RAIN GARDEN PERMEABLE PAVEMENT PERMEABLE PAVEMENT PERMEABLE PAVEMENT PERMEABLE PAVEMENT GRASS SWALE DRY WELL KEYMAP LEGEND: 5013 PROPOSED CONTOUR 93 EXISTING CONTOUR EXISTING STORM SEWER LID AREA 1 LID BOUNDARY PROPOSED STORM SEWER FOR LID REVIEW ONLY NOT FOR CONSTRUCTION ( IN FEET ) 0 1 INCH = 70 FEET 70 70 140 210 N O R T H E RN 2015.06.23 D:\PROJECTS\374-020\DWG\EXHIBITS\374-020_LID.DWG LOW IMPACT DEVELOPMENT (LID) AREAS FIGURE 1 374-020 Brookfield Second Replat LID ID LID Area (ac) Area of Concrete (ac) Area of Pavers (ac) Area of Roofs (ac) Area of Lawns and Landscaping (ac) 2-year Composite Runoff Coefficient 10-year Composite Runoff Coefficient 100-year Composite Runoff Coefficient Composite % Imperv. Impervious Area (ac) Basin Treated thru LID? LID Treated Impervious Area (ac) LID Treated Type 1 0.22 0.08 0.00 0.11 0.03 0.86 0.86 1.00 78% 0.17 YES 0.17 Curb Inlet to Dry Well 2 0.35 0.07 0.00 0.19 0.16 0.81 0.81 1.00 66% 0.23 YES 0.23 Dry Well 3 0.39 0.10 0.05 0.15 0.18 0.77 0.77 0.97 63% 0.24 YES 0.24 Permeable Pavement, Dry Well 4 0.46 0.07 0.00 0.19 0.20 0.65 0.65 0.81 51% 0.23 YES 0.23 Grass Swale 5 0.82 0.24 0.00 0.36 0.44 0.84 0.84 1.00 66% 0.54 NO N/A N/A 6 0.32 0.02 0.00 0.15 0.15 0.62 0.62 0.78 48% 0.15 NO N/A N/A 7 0.36 0.02 0.05 0.20 0.12 0.71 0.71 0.89 60% 0.22 YES 0.22 Permeable Pavement 8 0.31 0.04 0.07 0.11 0.13 0.65 0.65 0.82 52% 0.16 YES 0.14 Permeable Pavement 9 0.23 0.02 0.00 0.13 0.08 0.70 0.70 0.87 58% 0.14 NO N/A N/A 10 0.15 0.02 0.00 0.08 0.06 0.69 0.69 0.87 57% 0.09 YES 0.09 Rain Garden 11 0.37 0.13 0.00 0.14 0.23 0.85 0.85 1.00 66% 0.24 NO N/A N/A 12 0.13 0.01 0.00 0.07 0.04 0.70 0.70 0.88 58% 0.07 NO N/A N/A 13 0.52 0.12 0.07 0.18 0.26 0.74 0.74 0.92 58% 0.30 YES 0.30 Permeable Pavement 14 1.55 0.15 0.00 0.08 1.32 0.35 0.35 0.44 13% 0.21 NO N/A N/A TOTAL: 6.17 2.99 1.61 LID Requirements Total Proposed Impermeable Area(ac)= 2.99 Total Impermeable Area Treated with LID(ac)= 1.61 Percent Treated with LID= 54% LOW IMPACT DEVELOPMENT (LID) CALCULATIONS 8/27/2015 3:18 PM D:\Projects\374-020\Drainage\Hydrology\374-020_Proposed_Rational_Calcs.xlsx\LID 374-020 Brookfield Second Replat LID ID LID Area (ac) New Area of Pavement (ac) New Area of Pavers (ac) Basin Treated by Porous Pavement? 1 0.22 0.00 0.00 NO 2 0.35 0.07 0.00 NO 3 0.39 0.09 0.05 YES 4 0.46 0.00 0.00 NO 5 0.82 0.23 0.00 NO 6 0.32 0.00 0.00 NO 7 0.36 0.02 0.05 YES 8 0.31 0.04 0.07 YES 9 0.23 0.00 0.00 NO 10 0.15 0.00 0.00 NO 11 0.37 0.13 0.00 NO 12 0.13 0.00 0.00 NO 13 0.52 0.12 0.07 YES 14 1.55 0.00 0.00 NO TOTAL: 0.70 0.24 Porous Pavement Requirements New Areas of Pavement including Pavers (ac)= 0.94 Total Porous Pavement (ac)= 0.24 Percent Porous Pavement= 25% POROUS PAVEMENT CALCULATIONS 8/27/2015 3:20 PM D:\Projects\374-020\Drainage\Hydrology\374-020_Proposed_Rational_Calcs.xlsx\Porous Pavement 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 67% 43 D-3B 1.27 66% D3C D-3C 0.61 69% 44 D-5/92 - - D5, D9 46 D-7 0.30 63% D7 0.25 86% 51 D-7.1 0.33 5% D7.1 0.22 86% 52 D-7.2 0.33 57% D7.2 0.79 86% 47 D-8 0.33 65% D8 0.29 83% 48 D-8.1 0.33 68% D8.1 0.22 83% 60 OF-1 0.36 63% OF2 OF-2 0.36 70% Totals: 6.22 63% Totals: 6.12 76% (1) - Drainage Memorandum for Brookfield Second Replat by Northern Engineering dated August 28, 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 Drainiage Memo (1) TST Drainiage Report (2) IMPERVIOUSNESS COMPARISON TABLE D3 2.73 67% D2 1.62 81% E/CTV TRACT F PLAT OF BROOKFIELD MORNINGSIDE VILLAGE CONDOS FOSSIL CREEK RESERVOIR INLET DITCH WETLAND POND A 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 D11 0.36 AC 56 D-10 0.49 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 0.0% 50' HABITAT BUFFER ZONE 50' HABITAT BUFFER ZONE KEYMAP FOX DEN BUFFER ZONE NORTHERN BROOKFIELD LIGHTS DRIVE 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: August 28, 2015 PROJECT: 374-020 Sheet Of 34 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 08/28/15 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. { } NOTES: FLOW PATH 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 PLAN R. Banning A. Boese 1"=60' 24 ( IN FEET ) 0 1 INCH = 60 FEET 60 60 120 180 i10 (in/hr) C10 Q = C f (C )( i )(A ) 8/27/2015 3:16 PM D:\Projects\374-020\Drainage\Hydrology\374-020_Proposed_Rational_Calcs.xlsx\Runoff 10-yr Tc (min) 100-yr Tc (min) D2A OF-1 & D-2A Yes 0.82 0.82 1.00 700 4.56 1.47 0.44% 18.0 18.0 6.5 412 100.60 98.84 0.43% 1.31 5.3 23.2 23.2 11.8 45 D-2B No 0.63 0.63 0.79 0 0.00 0.00 N/A N/A N/A N/A 395 98.84 96.42 0.61% 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 0 0.00 0.00 N/A N/A N/A N/A 525 98.34 96.00 0.45% 1.34 6.6 6.6 6.6 6.6 D3A D-3A No 0.74 0.74 0.93 0 0.00 0.00 N/A N/A N/A N/A 375 100.96 98.23 0.73% 1.71 3.7 5.0 5.0 5.0 43 D-3B No 0.77 0.77 0.96 0 0.00 0.00 N/A N/A N/A N/A 626 99.63 95.60 0.64% 1.60 6.5 6.5 6.5 6.5 D3C D-3C No 0.62 0.62 0.78 160 1.00 0.99 0.01% 61.5 61.5 41.6 210 100.86 99.63 0.59% 1.53 2.3 63.8 63.8 43.9 44 D-5/92 Yes 0.28 0.28 0.36 660 104.10 99.21 0.74% 43.3 43.3 39.5 440 99.85 98.00 0.42% 1.30 5.7 49.0 49.0 45.2 46 D-7 No 0.71 0.71 0.89 0 0.00 0.00 N/A N/A N/A N/A 135 98.25 96.72 1.13% 2.13 1.1 5.0 5.0 5.0 51 D-7.1 No 0.74 0.74 0.93 0 0.00 0.00 N/A N/A N/A N/A 68 98.68 98.07 0.90% 1.89 0.6 5.0 5.0 5.0 52 D-7.2 No 0.85 0.85 1.00 0 0.00 0.00 N/A N/A N/A N/A 225 100.14 97.50 1.17% 2.17 1.7 5.0 5.0 5.0 47 D-8 No 0.77 0.77 0.97 0 0.00 0.00 N/A N/A N/A N/A 150 100.14 98.67 0.98% 1.98 1.3 5.0 5.0 5.0 48 D-8.1 No 0.84 0.84 1.00 0 0.00 0.00 N/A N/A N/A N/A 50 0.37 0.18 0.38% 1.23 0.7 5.0 5.0 5.0 54 D-10 No 0.76 0.76 0.95 0 0.00 0.00 N/A N/A N/A N/A 210 98.45 97.09 0.65% 1.61 2.2 5.0 5.0 5.0 56 D-11 No 0.87 0.87 1.00 0 0.00 0.00 N/A N/A N/A N/A 105 98.45 97.93 0.50% 1.41 1.2 5.0 5.0 5.0 60 OF-1 Yes 0.31 0.31 0.39 700 4.56 1.47 0.44% 51.4 51.4 46.3 0 0.00 0.00 N/A N/A N/A 51.4 51.4 46.3 OF2 OF-2 No 0.70 0.70 0.88 70 98.97 97.40 2.24% 4.8 4.8 2.7 0 0.00 0.00 N/A N/A N/A 5.0 5.0 5.0 PROPOSED TIME OF CONCENTRATION COMPUTATIONS A. Morse August 27, 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 − = 8/27/2015 3:12 PM D:\Projects\374-020\Drainage\Hydrology\374-020_Proposed_Rational_Calcs.xlsx\Tc 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 0.49 0.00 0.12 0.07 0.18 Clayey | Average 2% to 7% 0.234 0.76 0.76 0.95 61% D-11 0.36 0.00 0.13 0.00 0.14 Clayey | Average 2% to 7% 0.221 0.87 0.87 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 8/27/2015 3:13 PM D:\Projects\374-020\Drainage\Hydrology\374-020_Proposed_Rational_Calcs.xlsx\Composite C