Stormwater Drainage Design Report. Reeve & Associates, Inc. Maverik, Inc. 88th Avenue and Pecos Street. Thornton, CO

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1 88th Avenue and Pecos Street Stormwater Drainage Design Report Reeve & Associates, Inc. Solutions You Can Build On for Maverik, Inc. 88th Avenue and Pecos Street Thornton, CO submitted to Reeve & Associates, Inc. Contact: Nate Reeve, PE 920 Chambers Street, Suite 14 Ogden, Utah Fax www. reeve-assoc.com City of Thornton 9500 Civic Center Drive Thornton, CO PH: (303) June 2, 2016 Ref:

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4 Stormwater Drainage Design Report 1.0 Introduction 1.1 Purpose The purpose of this drainage report is to reflect proposed changes to the current drainage patterns associated with the proposed Maverik and subdivision. Proposed changes to the property include construction of a 5,518 sq. ft. Maverik convenience store with fuel pumps and associated utility service connections. The detention basin and associated facilities have been designed for a full build-out scenario. 1.2 General Property Description At the request of Thornton City, Reeve & Associates has prepared the following Storm Drainage Design Report for the proposed Maverik located at 88 th Avenue and Pecos Street in Thornton, Colorado. The site is located in the southeast quarter of section 21, township 2 south, range 68 west. See Figure 1 for a general location map that shows the proposed location and surrounding properties. A private storm sewer system will collect stormwater runoff from the proposed development. The storm sewer system will discharge into a private detention pond located on the eastern side of the property. An outlet pipe from the detention pond will outlet to the public right of way located along the north side of W. 88 th Avenue. The proposed development includes an access road and vacant land for future development. The detention basin and outlet structures are sized for a full buildout scenario for all future developments. 1.3 Pre-developed Drainage Characteristics The existing site is currently undeveloped and consists mostly of dry weeds and sandy loam with the soil type being C/D. The existing runoff from this property is divided into two subbasins (EX-1 and EX-2) but sheet flows primarily from the north to the south and into the curb and gutter on 88 th Avenue as outline in this section and depicted on the predevelopment drainage plan located in the Appendix; with design point Z being the outfall of these existing basins. There is a third drainage basin (EX-3) on the north east corner of the site that sheet flows to the north east and into the Orchard Hill Senior Apartment Complex with design point Y being the outfall of this basin. 4

5 Stormwater Drainage Design Report The property is bordered to the north by residential property to the west by Pecos Street and Water World Amusement Park, to the south by 88 th Ave, and to the east by Orchard Hill Senior Apartments. The pre-developed stormwater runoff leaves the site without the use of engineered quality or detention facilities. 1.4 Post-developed Drainage Characteristics The proposed site will operate as a Maverik Convenience Store with vehicle fueling stations. The entire parcel sits on 6.35 acres. The site will contain 197,154 s.f. of undeveloped area, 54,546 s.f. of hard surface area, 19,880 s.f. of landscaped area and 5,518 s.f. of building area. Note that the detention basin has been sized to accommodate future developments on the site to tie into the detention basin. The proposed grading will divide the site into twelve drainage basins and seven design points as outlined in this section and depicted on the developed drainage plan located in the Appendix. Basin R-1 encompasses 0.43 acres of sidewalk and landscape between the onsite curb and gutter and Pecos Street and W. 88 th Avenue right of way. Stormwater generated in this basin will sheet flow undetained into the curb and gutter within the right-of-way and into the southeast corner of the lot. Basin R-2 encompasses 0.23 acres of sidewalk and landscape between the onsite curb and gutter and W. 88 th Avenue right of way. Stormwater generated in this basin will sheet flow undetained into the curb and gutter within the right-of-way and into the southeast corner of the lot. Basin R-3 encompasses 0.02 acres of asphalt paving on the southeast corner of the lot. Stormwater generated in this basin will sheet flow undetained into the curb and gutter within the right-of-way in W. 88th. Basin R-4 encompasses 0.02 acres of asphalt paving on the northwest corner of the lot. Stormwater generated in this basin will sheet flow undetained into the curb and gutter within the right-of-way on Pecos and follow the curb and gutter to the southeast corner of the lot. Basin B-1 encompasses 0.63 acres of parking and drive aisles of the proposed convenience store. Stormwater generated in this basin will sheet flow to a low point on the curb with an inlet box titled A. The water will be conveyed by a private storm sewer system to the private detention pond. Basin B-2 encompasses 0.02 acres of parking and drive aisles of the proposed convenience store. Stormwater generated in this basin will sheet flow to a low 5

6 Stormwater Drainage Design Report point on the curb with an inlet box titled d B. The water will be conveyed by a private storm sewer system to the private detention pond. Basin B-3 encompasses 0.14 acres of parking and drive aisles of the proposed convenience store. Stormwater generated in this basin will sheet flow to a low point on curb with an inlet box titled C. The water will be conveyed by a private storm sewer system to the private detention pond. Basin B-4 encompasses 0.57 acres of parking and drive aisles, the building and canopy for the proposed convenience store. Stormwater generated in this basin will sheet flow to a low point on curb with an inlet box titled D. The water will be conveyed by a private storm sewer system to the private detention pond. Basin B-5 encompasses 0.40 acres of parking and drive aisles, the building and canopy for the proposed convenience store. Stormwater generated in this basin will sheet flow to a low point on curb with an inlet box titled E. The water will be conveyed by a private storm sewer system to the private detention pond. Basin B-6 encompasses 0.35 acres of parking and drive aisles, the building and canopy for the proposed convenience store. Stormwater generated in this basin will sheet flow to a low point on curb with an inlet box titled F and G. The water will be conveyed by a private storm sewer system to the private detention pond. Basin B-7 encompasses 0.82 acres of detention pond. This has been sized to detain the 100-year storm event per COT code with an outlet structure and orifice plates for the WQCV, EURV and 100-year storm event. It will be landscaped per COT code. Basin F-1 encompasses 2.73 acres and will be developed at a later date. However, the detention basin design has included this area in a full build-out scenario. Future developments will convey their storm water to the proposed private detention pond. Pipe P1 conveys the stormwater from Basin B-2 from the inlet box B. Pipe P2 conveys the stormwater from Basin B-1 from the inlet box A. This pipe also carries the water from Basin B-2. Pipe P3 conveys the stormwater from Basin B-3 from the inlet box C. Pipe P4 conveys the stormwater from Basin B-4 from the inlet box D. This pipe also carries the water from Basin B-2 and B-1. Pipe P5 conveys the stormwater from B-5 from the inlet box E. This pipe also carries the water from Basin B-4, B-3, B-2 and B-1. 6

7 Stormwater Drainage Design Report Pipe P6 conveys the stormwater from B-6 from the inlet box F. This pipe also carries the water from Basin B-5, B-4, B-3, B-2 and B-1. Pipe P7 also conveys the stormwater from B-6 from the inlet box G. This pipe also carries the water from Basin B-5, B-4, B-3, B-2 and B-1. Ultimately, all storm water runoff from this site is conveyed to the South Platte River. In a fully developed scenario, 1% or cfs and 0.17 cfs will exit the site at each access untreated during the 5-yr and 100-yr storms respectively. The remaining storm water from hard surface areas will be directed to a private detention pond that is sized for the WQCV, EURV and 100-yr volumes. It will release 0.5 cfs and 8.90 cfs into the 88 th Ave right-of-way during the 5-year and 100-year storm events respectively. 1.5 Water Quality A private water quality facility will be provided for the full build-out at this time. Post-development stormwater runoff will be collected via curb and gutter and private combination curb inlets throughout the property. A private storm sewer system will convey storm water flows to the private detention pond facility located along the northeast property line. The detention pond will provide storage for the water quality capture volume of acre-feet or 6,926 c.f. with a water surface elevation of and the EURV storage has also been provided with a volume of acre-feet or 13,765 c.f. with an elevation of An outlet structure within the detention pond will provide water quality and staged release of stored stormwater that meets the City of Thornton Storm Drainage Design requirements. Because the 5-yr, and 100-yr design storm event developed flows are larger than the pre-developed site runoff totals, the detention pond outlet structure also reduces the release rates of the post-developed flows to the pre-developed rates. The pond will provide storage for the 5-yr design storm event and the water quality volume of acre-feet or 21,867 c.f. with a water surface elevation of The pond will also provide storage for the 100-yr, design storm event and the water quality volume of acre-feet or 35,240 c.f. with a water surface elevation of During the 100-yr design storm event, the pond outlet structure will provide a release rate of 8.9 cfs which is less than the predeveloped outflow of 9.7 cfs provided the UD-Detention analysis of the detention pond volume. A private 24 RCP pipe will connect to the outlet structure and release into a sidewalk chase drain and into the curbline along the north side of W. 88 th Avenue. 7

8 Stormwater Drainage Design Report See Hydraulic Calculations located in the Appendix for more details regarding detention pond design. 1.6 Hydrology Calculations The City of Thornton Storm Drainage Design, Grading, and Water Quality Technical Criteria within the City of Thornton Standards and Specifications was used to perform hydrology calculations. The Rational Method has been used to compute storm water runoff, as preferred for drainage areas less than 100-acres. Design storms with the 5-yr, and 100-yr, occurrence intervals were used. Weighted or composite C values for the site were calculated using the following formula. 5-year, and 100-yr, flows for the proposed site are summarized in the Appendix. Table 1 shows a comparison between pre-development discharges and postdevelopment discharges from the project site. Tablie 1: Peak Discharge Comparison Pre-Development Discharge (cfs) Post-Development Discharge (cfs) Discharge Difference (cfs) Q5 Pecos Q100 Pecos Q5 88th Q100 88th NE Corner NE Corner Pipe and inlet capacity calculations were performed at each design point as shown on the drainage plan. Storm sewer for this project was designed to convey the required 10-yr storm even with a surcharge hydraulic grade line not less than one foot below finished grade. Hydrologic and hydraulic calculations are located in the Appendix. All assumptions shall be field verified by the contractor prior to commencing construction, and discrepancies shall be reported to the engineer immediately for review. 8

9 Stormwater Drainage Design Report 1.7 Floodplain Statement According to the Federal Emergency Management Agency (FEMA), as depictured on Flood Insurance Rate Map (FIRM) 08001C0582H with an effective date of March 5, 2007, the site lies within areas determined to be outside the 500- year floodplain. 1.8 Erosion Control It is respectfully requested that an erosion control plan be submitted in conjunction with the final grading plan and not be required to be submitted with this drainage report. 1.9 Summary Developed runoff generated from the project site during the 100-yr. design storm event are anticipated to be less than or equal to the pre-developed runoff rates. Prior to being released off-site, runoff will be treated via a private detention pond and water quality facility, while a small percentage of the site s runoff will discharge (un-detained) to the adjacent right-of-way or adjacent properties. Downstream of the detention pond, a private 24 RCP pipe and sidewalk chase drain will convey treated runoff into the W. 88 th Avenue right of way. A series of private combination inlets will collect runoff in multiple locations on site and convey the runoff to the proposed private detention pond east of the Maverik building. The storm sewer has been designed to handle developed flows in the required 10-yr. design storm event condition within minimal surcharge. Since the site s anticipated developed runoff rate is less than the allowed predevelopment runoff rate, development on this site as described in the enclosed drainage plan is not anticipated to adversely impact downstream stormwater infrastructure. Upon the completion of construction, if conditions or outfall locations differ from the assumptions stated within this drainage study, an amendment to this report must be completed. Maverik Inc. will be responsible for any maintenance on the drainage facilities. 9

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12 Stormwater Drainage Design Report Figure 1 Vicinity Map 88 th Avenue and Pecos Street Project Site The project site is located at 88 th Avenue and Pecos Street in Thornton, CO. 12

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20 Stormwater Drainage Design Report Allowable Capacity for one-half of Street (Minor & Major) 20

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29 DETENTION BASIN STAGE-STORAGE TABLE BUILDER Project: 88th & Pecos Maverik Fueling Station Basin ID: Full Build-Out Detention Basin Depth Increment = 0.1 ft Optional Optional Example Zone Configuration (Retention Pond) Stage - Storage Stage Override Length Width Area Override Area Volume Volume Description (ft) Stage (ft) (ft) (ft) (ft^2) Area (ft^2) (acre) (ft^3) (ac-ft) Required Volume Calculation Media Surface , Selected BMP Type = No BMP Flood Control Only , Watershed Area = 6.35 acres , , Watershed Length = 762 ft , , Watershed Slope = ft/ft , , Watershed Imperviousness = 75.00% percent , , Percentage Hydrologic Soil Group A = 0.0% percent , , Percentage Hydrologic Soil Group B = 15.0% percent , , Percentage Hydrologic Soil Groups C/D = 85.0% percent , , Desired WQCV Drain Time = N/A hours Zone 1 (WQCV) , , Location for 1-hr Rainfall Depths = UDFCD Default , , Water Quality Capture Volume (WQCV) = acre-feet Optional User Input , , Excess Urban Runoff Volume (EURV) = acre-feet 1-hr Precipitation , , yr Runoff Volume (P1 = 0.95 in.) = acre-feet inches , , yr Runoff Volume (P1 = 1.34 in.) = acre-feet inches , , yr Runoff Volume (P1 = 1.64 in.) = acre-feet inches , , yr Runoff Volume (P1 = 2.02 in.) = acre-feet inches , , yr Runoff Volume (P1 = 2.32 in.) = acre-feet inches , , yr Runoff Volume (P1 = 2.61 in.) = acre-feet inches , , yr Runoff Volume (P1 = 3.29 in.) = acre-feet inches , , Approximate 2-yr Detention Volume = acre-feet , , Approximate 5-yr Detention Volume = acre-feet , , Approximate 10-yr Detention Volume = acre-feet , , Approximate 25-yr Detention Volume = acre-feet , , Approximate 50-yr Detention Volume = acre-feet Zone 2 (EURV) , , Approximate 100-yr Detention Volume = acre-feet , , , , Stage-Storage Calculation , , Zone 1 Volume (WQCV) = acre-feet , , Zone 2 Volume (EURV - Zone 1) = acre-feet , , Zone 3 Volume (100-year - Zones 1 & 2) = acre-feet , , Total Detention Basin Volume = acre-feet , , Initial Surcharge Volume (ISV) = N/A ft^ , , Initial Surcharge Depth (ISD) = N/A ft , , Total Available Detention Depth (H total) = 3.39 ft , , Depth of Trickle Channel (H TC) = 0.50 ft , , Slope of Trickle Channel (S TC) = ft/ft Zone 3 (100-year) , , Slopes of Main Basin Sides (S main) = 4 H:V , , Basin Length-to-Width Ratio (R L/W) = , , , , Initial Surcharge Area (A ISV) = 0 ft^ , , Surcharge Volume Length (L ISV) = 0.0 ft , , Surcharge Volume Width (W ISV) = 0.0 ft , , Depth of Basin Floor (H FLOOR) = 0.00 ft , , Length of Basin Floor (L FLOOR) = ft , , Width of Basin Floor (W FLOOR) = 61.8 ft , , Area of Basin Floor (A FLOOR) = 7,649 ft^ , , Volume of Basin Floor (V FLOOR) = 0 ft^ , , Depth of Main Basin (H MAIN) = 3.39 ft , , Length of Main Basin (L MAIN) = ft , , Width of Main Basin (W MAIN) = 89.0 ft , , Area of Main Basin (A MAIN) = 13,416 ft^ , , Volume of Main Basin (V MAIN) = 35,249 ft^ , , Calculated Total Basin Volume (V total) = acre-feet , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , UD-Detention_v3.02.xlsm, Basin 6/9/2016, 3:32 PM

30 DETENTION BASIN STAGE-STORAGE TABLE BUILDER User Defined Stage-Area Boolean for Message Equal Stage-Area Inputs Watershed L:W 1 CountA 0 Calc_S_TC H_FLOOR L_FLOOR_OTHER Length, Width (ft.) ISV 0.00 ISV 0.00 Floor 0.00 Floor 0.84 Zone 1 (WQCV) 0.84 Zone 1 (WQCV) 2.21 Zone 2 (EURV) 2.21 Zone 2 (EURV) Area (sq.ft.) 3.39 Zone 3 (100-yea 3.39 Zone 3 (100-year) Stage (ft) Length (ft) Width (ft) Area (sq.ft.) Area (acres) Volume (ac-ft) Stage (ft.) Area (acres) Volume (ac-ft) UD-Detention_v3.02.xlsm, Basin 6/9/2016, 3:32 PM

31 Detention Basin Outlet Structure Design Project: 88th & Pecos Maverik Fueling Station Basin ID: Full Build-Out Detention Basin4 Stage (ft) Zone Volume (ac-ft) Outlet Type Zone 1 (WQCV) Orifice Plate Zone 2 (EURV) Orifice Plate Zone 3 (100-year) Weir&Pipe (Circular) Example Zone Configuration (Retention Pond) Total 24 User Input: Orifice at Underdrain Outlet (typically used to drain WQCV in a Filtration BMP) Calculated Parameters for Underdrain Underdrain Orifice Invert Depth = N/A ft (distance below the filtration media surface) Underdrain Orifice Area = N/A ft 2 Underdrain Orifice Diameter = N/A inches Underdrain Orifice Centroid = N/A feet User Input: Orifice Plate with one or more orifices or Elliptical Slot Weir (typically used to drain WQCV and/or EURV in a sedimentation BMP) Calculated Parameters for Plate Invert of Lowest Orifice = 0.00 ft (relative to bottom of basin at Stage = 0 ft) WQ Orifice Area per Row = 2.083E-02 ft 2 Depth at top of Zone using Orifice Plate = 2.21 ft (relative to bottom of basin at Stage = 0 ft) Elliptical Half-Width = N/A feet Orifice Plate: Orifice Vertical Spacing = 8.80 inches Elliptical Slot Centroid = N/A feet Orifice Plate: Orifice Area per Row = 3.00 sq. inches (diameter = 1-15/16 inches) Elliptical Slot Area = N/A ft 2 User Input: Stage and Total Area of Each Orifice Row (numbered from lowest to highest) Row 1 (required) Row 2 (optional) Row 3 (optional) Row 4 (optional) Row 5 (optional) Row 6 (optional) Row 7 (optional) Row 8 (optional) Stage of Orifice Centroid (ft) Orifice Area (sq. inches) Stage of Orifice Centroid (ft) Orifice Area (sq. inches) Row 9 (optional) Row 10 (optional) Row 11 (optional) Row 12 (optional) Row 13 (optional) Row 14 (optional) Row 15 (optional) Row 16 (optional) User Input: Vertical Orifice (Circular or Rectangular) Calculated Parameters for Vertical Orifice Not Selected Not Selected Not Selected Not Selected Invert of Vertical Orifice = N/A N/A ft (relative to bottom of basin at Stage = 0 ft) Vertical Orifice Area = N/A N/A ft 2 Depth at top of Zone using Vertical Orifice = N/A N/A ft (relative to bottom of basin at Stage = 0 ft) Vertical Orifice Centroid = N/A N/A feet Vertical Orifice Diameter = N/A N/A inches User Input: Overflow Weir (Dropbox) and Grate (Flat or Sloped) Calculated Parameters for Overflow Weir Zone 3 Weir Not Selected Zone 3 Weir Not Selected Overflow Weir Front Edge Height, Ho = 2.21 N/A ft (relative to bottom of basin at Stage = 0 ft) Height of Grate Upper Edge, H t = 3.59 N/A feet Overflow Weir Front Edge Length = 2.00 N/A feet Over Flow Weir Slope Length = 5.67 N/A feet Overflow Weir Slope = 4.00 N/A H:V (enter zero for flat grate) Grate Open Area / 100-yr Orifice Area = N/A should be > 4 Horiz. Length of Weir Sides = 5.50 N/A feet Overflow Grate Open Area w/o Debris = 7.94 N/A ft 2 Overflow Grate Open Area % = 70% N/A %, grate open area / total area Overflow Grate Open Area with Debris = 3.97 N/A ft 2 Debris Clogging % = 50% N/A % User Input: Outlet Pipe w/ Flow Restriction Plate (Circular Orifice, Restrictor Plate, or Rectangular Orifice) Calculated Parameters for Outlet Pipe w/ Flow Restriction Plate Zone 3 Circular Not Selected Zone 3 Circular Not Selected Depth to Invert of Outlet Pipe = 3.40 N/A ft (distance below bottom of basin at Stage = 0 ft) Outlet Orifice Area = 0.73 N/A ft 2 Circular Orifice Diameter = N/A inches Outlet Orifice Centroid = 0.48 N/A feet Half-Central Angle of Restrictor Plate on Pipe = N/A N/A radians User Input: Emergency Spillway (Rectangular or Trapezoidal) Calculated Parameters for Spillway Spillway Invert Stage= 4.40 ft (relative to bottom of basin at Stage = 0 ft) Spillway Design Flow Depth= 0.89 feet Spillway Crest Length = 8.00 feet Stage at Top of Freeboard = 6.29 feet Spillway End Slopes = 4.00 H:V Basin Area at Top of Freeboard = 0.45 acres Freeboard above Max Water Surface = 1.00 feet Routed Hydrograph Results Design Storm Return Period = WQCV EURV 2 Year 5 Year 10 Year 25 Year 50 Year 100 Year 500 Year One-Hour Rainfall Depth (in) = Calculated Runoff Volume (acre-ft) = OPTIONAL Override Runoff Volume (acre-ft) = Inflow Hydrograph Volume (acre-ft) = Predevelopment Unit Peak Flow, q (cfs/acre) = Predevelopment Peak Q (cfs) = Peak Inflow Q (cfs) = Peak Outflow Q (cfs) = Ratio Peak Outflow to Predevelopment Q = N/A N/A N/A Structure Controlling Flow = Plate Plate Plate Overflow Grate 1 Overflow Grate 1 Overflow Grate 1 Overflow Grate 1 Outlet Plate 1 Outlet Plate 1 Max Velocity through Grate 1 (fps) = N/A N/A N/A Max Velocity through Grate 2 (fps) = N/A N/A N/A N/A N/A N/A N/A N/A N/A Time to Drain 97% of Inflow Volume (hours) = Time to Drain 99% of Inflow Volume (hours) = Maximum Ponding Depth (ft) = Area at Maximum Ponding Depth (acres) = Maximum Volume Stored (acre-ft) =

32 Detention Basin Outlet Structure Design FLOW [cfs] YR COUNTA IN for Basin Tab = 1 Ao Dia WQ Plate Type Vert Orifice 1 Vert Orifice 2 500YR Count_Underdrain OUT = eter = 3/8 inch) YR INCount_WQPlate = ter = 7/16 inch) 100YR OUT Count_VertOrifice1 = eter = 1/2 inch) Outlet Plate 1 Outlet Plate 2 Drain Time Message Boolean 50YR IN Count_VertOrifice2 = ter = 9/16 inch) 2 1 5yr, <72hr 0 50YR OUT 25YR IN Count_Weir1 = eter = 5/8 inch) >5yr, <120hr 0 25YR OUT Count_Weir2 = er = 11/16 inch) Max Depth Row 10YR Count_OutletPipe1 IN = eter = 3/4 inch) WQCV 77 Watershed Constraint Check 10YR Count_OutletPipe2 OUT = er = 13/16 inch) 2 Year 164 Slope YR IN COUNTA_2 (Standard FSD Setup)= eter = 7/8 inch) EURV 204 Shape YR OUT MaxPondDepth_Error? FALSE 0.67 er = 15/16 inch) 5 Year 233 2YR IN Hidden Parameters & Calculations 0.76 meter = 1 inch) 10 Year 267 Spillway Depth 2YR OUT /16 inches) 25 Year EURV IN WQ Plate Flow at 100yr depth = = 1-1/8 inches) 50 Year 316 EURV OUT CLOG #1= 35% /16 inches) 100 Year Z1_Boolean WQCV IN C dw #1 = = 1-1/4 inches) 500 Year Z2_Boolean WQCV OUT C do #1 = /16 inches) Zone3_Pulldown Message 1 Z3_Boolean Overflow Weir #1 Angle = = 1-3/8 inches) 1 Opening Message CLOG #2= #VALUE! /16 inches) Draintime Running C dw #2 = #VALUE! 1.73 = 1-1/2 inches) Outlet Boolean Outlet Rank Total (1 to 4) C do #2 = #VALUE! /16 inches) Vertical Orifice Overflow Weir #2 Angle = #VALUE! 2.03 = 1-5/8 inches) Vertical Orifice Boolean Underdrain Q at 100yr depth = /16 inches) Overflow Weir Max Depth 0.1 VertOrifice1 Q at 100yr depth = = 1-3/4 inches) Overflow 1 Weir yr Depth 10 VertOrifice2 Q at 100yr depth = /16 inches) TIME [hr] Outlet Pipe Freeboard PONDING DEPTH [ft] EURV_draintime_user = 2.72 = 1-7/8 inches) Outlet Pipe Spillway 4.5 Count_User_Hydrographs /16 inches) 0 Spillway Length 500YR CountA_3 (EURV & 100yr) = eter = 2 inches) Button Visibility Boolean 100YR 4 CountA_4 (100yr Only) = 50YR gular openings) 1 Button_Trigger 0 Underdrain 25YR YR 1 WQCV Plate 5YR 0 EURV-WQCV Plate 3 2YR EURV WQCV 0 EURV-WQCV VertOrifice 1 Outlet 90% Qpeak 0 Outlet Undetained DRAIN TIME [hr] AREA [ft^2], VOLUME [ft^3] User Area [ft^2] Interpolated Area [ft^2] Volume [ft^3] Outflow [cfs] 5, , , , , , , , , OUTFLOW [cfs] PONDING DEPTH [ft]

33 Detention Basin Outlet Structure Design Outflow Hydrograph Workbook Filename: Storm Inflow Hydrographs The user can override the calculated inflow hydrographs from this workbook with inflow hydrographs developed in a separate program. SOURCE WORKBOOK WORKBOOK WORKBOOK WORKBOOK WORKBOOK WORKBOOK WORKBOOK WORKBOOK WORKBOOK Time Interval TIME WQCV [cfs] EURV [cfs] 2 Year [cfs] 5 Year [cfs] 10 Year [cfs] 25 Year [cfs] 50 Year [cfs] 100 Year [cfs] 500 Year [cfs] 5.19 min 0:00: :05: Hydrograph 0:10: Constant 0:15: :20: :25: :31: :36: :41: :46: :51: :57: :02: :07: :12: :17: :22: :28: :33: :38: :43: :48: :54: :59: :04: :09: :14: :20: :25: :30: :35: :40: :45: :51: :56: :01: :06: :11: :17: :22: :27: :32: :37: :42: :48: :53: :58: :03: :08: :14: :19: :24: :29: :34: :39: :45: :50: :55: :00: :05: :11: :16: :21: :26: :31: :37: :42: :47: :52: :57: :02: :08: :13:

34 Reference Figures and Equations Circular Pipe with Restrictor Plate WQ Elliptical Slot Weir (Alternative to WQ Orifice Plate for Large Watersheds) Watershed Runoff Volume Calculations Where WQCV is the water quality capture volume (acre-ft), EURV is the excess urban runoff volume (acre-ft), V #yr is the volume for the given return period (acre-ft), a is a coefficient corresponding to WQCV drain time (1.0 for 40 hours, 0.9 for 24 hours, and 0.8 for 12 hours), P 1 is the one-hour rainfall depth (in), A is the contributing watershed area (acres), I is the percentage imperviousness (expressed as a decimal), A%, B%, and CD% are the percent of each hydraulic soil group (expressed as a decimal). Initial Surcharge Volume: Basin Volume Calculations Where ISV is the initial surcharge volume (ft 3 ), A ISV is ISV surface area (ft 2 ), ISD is the initial surcharge depth (ft, typically 0.33 to 0.50), and L ISV and W ISV are the length and width of the ISV (ft). Basin Floor Volume: Where L floor and W floor (ft) are the length and width of the basin floor section at the point where the top of the basin floor section meets the toe of the basin main section, H floor is the depth of the basin floor section (ft), S TC is the trickle channel slope (ft/ft), S main is the side slope of the basin main section (H:V; e.g., 4 if the horizontal:vertical ratio is 4:1), R L:W is the basin length:width ratio (e.g., 2 if the basin length is twice the basin width), A floor is top area of the basin floor section (ft 2 ), and V floor is volume of the basin floor section (ft 3 ). Main Basin Volume: Where L main and W main (ft) are the length and width of the main basin section at the point at the top of the basin, H main is the depth of the main basin section (ft), A main is top area of the main basin section (ft 2 ), and V main is volume of the main basin section (ft 3 ). Total Basin Volume: Where V- total is the volume of the total basin (ft 3 ) and D TC is the depth of the trickle channel (ft). UD-Detention_v3.02.xlsm, Reference 6/9/2016, 3:32 PM

35 1 2 6/2/2015 7:10:47 AM A B C D 0" 1" 2" SEAL DATE STATUS DATE REVISION PROJECT NUMBER????? FILE DRAWN BY R. Hansen CHECKED BY J.Nate Reeve, P.E. SCALE As indicated PRE-DEVELOPED DRAINAGE MAP THORNTON MAVERIK 88TH AVENUE & PECOS STREET THORNTON, COLORADO

36 1 2 6/2/2015 7:10:47 AM A B C D 0" 1" 2" SEAL DATE STATUS DATE REVISION PROJECT NUMBER????? FILE DRAWN BY R. Hansen CHECKED BY J.Nate Reeve, P.E. SCALE POST - DEVELOPED DRAINAGE MAP As indicated THORNTON MAVERIK 88TH AVENUE & PECOS STREET THORNTON, COLORADO

37 D 0" 1" 2" US PATENT # ADDITIONAL PATENTS PENDING BMP, INC. 53 MT. ARCHER ROAD, LYME, CT (800) FAX: (860) C 18F SNOUT OIL & DEBRIS STOP 09/14/99 NONE 18F B 36" MIN. *NOTE- SUMP DEPTH OF 36" MIN. FOR < OR= 12" DIAM. OUTLET. FOR OUTLETS >OR= 15", DEPTH = 2.5-3X DIAM. THORNTON MAVERIK 88TH AVENUE & PECOS STREET THORNTON, COLORADO SEAL NOTES: 1. ALL HOODS AND TRAPS FOR CATCH BASINS AND WATER QUALITY STRUCTURES SHALL BE AS MANUFACTURED BY: BEST MANAGEMENT PRODUCTS, INC. 53 MT. ARCHER RD. LYME, CT (860) , (860) FAX TOLL FREE: (800) OR (888) WEB SITE: OR PRE-APPROVED EQUAL 2. ALL HOODS SHALL BE CONSTRUCTED OF A GLASS REINFORCED RESIN COMPOSITE WITH ISO GEL COAT EXTERIOR FINISH WITH A MINIMUM 0.125" LAMINATE THICKNESS. 3. ALL HOODS SHALL BE EQUIPPED WITH A WATERTIGHT ACCESS PORT, A MOUNTING FLANGE, AND AN ANTI-SIPHON VENT AS DRAWN. (SEE CONFIGURATION DETAIL) 4. THE SIZE AND POSITION OF THE HOOD SHALL BE DETERMINED BY OUTLET PIPE SIZE AS PER MANUFACTURER'S RECOMMENDATION. 5. THE BOTTOM OF THE HOOD SHALL EXTEND DOWNWARD A DISTANCE EQUAL TO 1/2 THE OUTLET PIPE DIAMETER WITH A MINIMUM DISTANCE OF 6" FOR PIPES <12" I.D. 6. THE ANTI-SIPHON VENT SHALL EXTEND ABOVE HOOD BY MINIMUM OF 3" AND A MAXIMUM OF 24" ACCORDING TO STRUCTURE CONFIGURATION. ANCHOR W/ BOLT (SEE DETAIL A) 1/2 D GASKET COMPRESSED BETWEEN HOOD AND STRUCTURE (SEE DETAIL B) FOAM GASKET W/ PSA BACKING (TRIM TO LENGTH) MOUNTING FLANGE DETAIL B INSTALLATION NOTE: POSITION HOOD SUCH THAT BOTTOM FLANGE IS A DISTANCE OF 1/2 OUTLET PIPE DIAMETER (MIN.) BELOW THE PIPE INVERT. MINIMUM DISTANCE FOR PIPES < 12" I.D. IS 6". DETAIL A DATE DATE STATUS REVISION A 6/2/2015 7:10:47 AM 7. THE SURFACE OF THE STRUCTURE WHERE THE HOOD IS MOUNTED SHALL BE FINISHED SMOOTH AND FREE OF LOOSE MATERIAL. 8. THE HOOD SHALL BE SECURELY ATTACHED TO STRUCTURE WALL WITH 3/8' STAINLESS STEEL BOLTS AND OIL-RESISTANT GASKET AS SUPPLIED BY MANUFACTURER. (SEE INSTALLATION DETAIL) 9. INSTALLATION INSTRUCTIONS SHALL BE FURNISHED WITH MANUFACTURER SUPPLIED INSTALLATION KIT. INSTALLATION KIT SHALL INCLUDE: A. INSTALLATION INSTRUCTIONS B. PVC ANTI-SIPHON VENT PIPE AND ADAPTER C. OIL-RESISTANT CRUSHED CELL FOAM GASKET WITH PSA BACKING D. 3/8" STAINLESS STEEL BOLTS E. ANCHOR SHIELDS DRILLED HOLE ANCHOR SHIELD EXPANSION CONE (NARROW END OUT) STAINLESS BOLT PROJECT NUMBER FILE DRAWN BY CHECKED BY SCALE DRAINAGE DETAILS????? R. Hansen J.Nate Reeve, P.E. As indicated

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