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HomeMy WebLinkAbout25 SUB 2 Stormwater Report 3-28-25 H+H Engineering Associates, LLC 232 Greenmanville Avenue, Suite 201 Mystic, Connecticut 06355 860-980-8008 www.hh-engineers.com 2024-0177 Via E-mail March 28, 2025 Planning & Zoning Commission Montville Town Hall 310 Norwich-New London Turnpike Uncasville, CT 06382 RE: Stormwater Narrative Subdivision Modification application East Lake Road 8-Lot Subdivision Previously Approved Drainage Improvements On July 26, 2022, the Town of Montville Planning & Zoning Commission approved subdivision application #22sub3 for a new 8-lot subdivision. The approved plans and stormwater management report were previously prepared by Boundaries, LLC. The approved subdivision included 8 new lots, each with frontage on East Lake Road and did not include any public improvements. Existing runoff generated along East Lake Road is collected in a series of catch basins which discharges onto approved Lot 7 (1121 East Lake Road). Previously, a 24” culvert was proposed divert the roadway runoff around the proposed improvements for Lot 7. The culvert was sized to pass flows through the 100-year storm event from the contributing 1.8-acre East Lake Road Drainage Watershed. To be conservative, the East Lake Road Drainage Watershed was evaluated as entirely impervious. Proposed Drainage Modifications Due to site constraints, the applicant is proposing to modify the previously approved drainage system by removing the 24” culvert, installing a new 24” HDPE pipe from the existing catch basin in East Lake Road to a new drainage manhole, which will direct runoff to the west via a 24” HDPE pipe under the proposed driveway to a flared end section and riprap apron. Runoff is then conveyed around the proposed Lot 7improvements via a new 6’(W) vegetated swale. The proposed improvements have been designed to convey flows through the 100-year storm event. Please refer to Attachment A – Proposed HydroCAD Report, Attachment B – Pipe Flow Velocity Calculations, and Attachment C – Riprap Sizing Calculations for modeling results. The proposed drainage modifications are shown on the plan entitled, “Lot 7 Drainage Modifications, Subdivision Modification, East Lake Road & Fire Street, Montville, CT 06370, Prepared for: Sunmar/RAF Builders, LLC, 285 Old Colchester Road, Uncasville, CT 06382,” scale: 1”=20’, dated 3/28/2025, prepared by H+H Engineering Associates, LLC. Attachment A – Proposed HydroCAD Report DA DA SW Grassed Swale CBCB EX-CB DMH CB PR-DMH Routing Diagram for SWALE CALCSPrepared by HH Engineering Assoc, Printed 3/27/2025 HydroCAD® 10.20-2h s/n 12772 © 2024 HydroCAD Software Solutions LLC Subcat Reach Pond Link SWALE CALCS Printed 3/27/2025Prepared by HH Engineering Assoc Page 2HydroCAD® 10.20-2h s/n 12772 © 2024 HydroCAD Software Solutions LLC Area Listing (selected nodes) Area (sq-ft) CN Description (subcatchment-numbers) 78,408 98 Paved parking, HSG B (DA) 78,408 98 TOTAL AREA Type III 24-hr WQV Rainfall=1.30"SWALE CALCS Printed 3/27/2025Prepared by HH Engineering Assoc Page 3HydroCAD® 10.20-2h s/n 12772 © 2024 HydroCAD Software Solutions LLC Time span=0.00-72.00 hrs, dt=0.02 hrs, 3601 points Runoff by SCS TR-20 method, UH=SCS, Weighted-CN Reach routing by Dyn-Stor-Ind method - Pond routing by Dyn-Stor-Ind method Runoff Area=1.800 ac 100.00% Impervious Runoff Depth=1.08"Subcatchment DA: DA Tc=5.0 min CN=98 Runoff=2.23 cfs 7,080 cf Avg. Flow Depth=0.15' Max Vel=2.24 fps Inflow=2.23 cfs 7,080 cfReach SW: Grassed Swale n=0.030 L=205.0' S=0.0283 '/' Capacity=60.81 cfs Outflow=2.18 cfs 7,080 cf Peak Elev=262.27' Inflow=2.23 cfs 7,080 cfPond CB: EX-CB Primary=2.23 cfs 7,080 cf Secondary=0.00 cfs 0 cf Outflow=2.23 cfs 7,080 cf Peak Elev=258.12' Inflow=2.23 cfs 7,080 cfPond DMH: PR-DMH Primary=2.23 cfs 7,080 cf Secondary=0.00 cfs 0 cf Outflow=2.23 cfs 7,080 cf Total Runoff Area = 78,408 sf Runoff Volume = 7,080 cf Average Runoff Depth = 1.08" 0.00% Pervious = 0 sf 100.00% Impervious = 78,408 sf Type III 24-hr WQV Rainfall=1.30"SWALE CALCS Printed 3/27/2025Prepared by HH Engineering Assoc Page 4HydroCAD® 10.20-2h s/n 12772 © 2024 HydroCAD Software Solutions LLC Summary for Subcatchment DA: DA Runoff = 2.23 cfs @ 12.07 hrs, Volume= 7,080 cf, Depth= 1.08" Routed to Pond CB : EX-CB Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Type III 24-hr WQV Rainfall=1.30" Area (ac) CN Description 1.800 98 Paved parking, HSG B 1.800 100.00% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 5.0 Direct Entry, Direct Subcatchment DA: DA Runoff Hydrograph Time (hours) 727068666462605856545250484644424038363432302826242220181614121086420Flow (cfs)2 1 0 Type III 24-hr WQV Rainfall=1.30" Runoff Area=1.800 ac Runoff Volume=7,080 cf Runoff Depth=1.08" Tc=5.0 min CN=98 2.23 cfs Type III 24-hr WQV Rainfall=1.30"SWALE CALCS Printed 3/27/2025Prepared by HH Engineering Assoc Page 5HydroCAD® 10.20-2h s/n 12772 © 2024 HydroCAD Software Solutions LLC Summary for Reach SW: Grassed Swale Inflow Area = 78,408 sf,100.00% Impervious, Inflow Depth = 1.08" for WQV event Inflow = 2.23 cfs @ 12.07 hrs, Volume= 7,080 cf Outflow = 2.18 cfs @ 12.09 hrs, Volume= 7,080 cf, Atten= 2%, Lag= 1.0 min Routing by Dyn-Stor-Ind method, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Max. Velocity= 2.24 fps, Min. Travel Time= 1.5 min Avg. Velocity = 0.56 fps, Avg. Travel Time= 6.1 min Peak Storage= 199 cf @ 12.09 hrs Average Depth at Peak Storage= 0.15' , Surface Width= 6.90' Bank-Full Depth= 1.00' Flow Area= 9.0 sf, Capacity= 60.81 cfs 6.00' x 1.00' deep channel, n= 0.030 Earth, grassed & winding Side Slope Z-value= 3.0 '/' Top Width= 12.00' Length= 205.0' Slope= 0.0283 '/' Inlet Invert= 255.80', Outlet Invert= 250.00' ‡ Reach SW: Grassed Swale InflowOutflow Hydrograph Time (hours) 727068666462605856545250484644424038363432302826242220181614121086420Flow (cfs)2 1 0 Inflow Area=78,408 sf Avg. Flow Depth=0.15' Max Vel=2.24 fps n=0.030 L=205.0' S=0.0283 '/' Capacity=60.81 cfs 2.23 cfs 2.18 cfs Type III 24-hr WQV Rainfall=1.30"SWALE CALCS Printed 3/27/2025Prepared by HH Engineering Assoc Page 6HydroCAD® 10.20-2h s/n 12772 © 2024 HydroCAD Software Solutions LLC Summary for Pond CB: EX-CB [57] Hint: Peaked at 262.27' (Flood elevation advised) Inflow Area = 78,408 sf,100.00% Impervious, Inflow Depth = 1.08" for WQV event Inflow = 2.23 cfs @ 12.07 hrs, Volume= 7,080 cf Outflow = 2.23 cfs @ 12.07 hrs, Volume= 7,080 cf, Atten= 0%, Lag= 0.0 min Primary = 2.23 cfs @ 12.07 hrs, Volume= 7,080 cf Routed to Pond DMH : PR-DMH Secondary = 0.00 cfs @ 0.00 hrs, Volume= 0 cf Routing by Dyn-Stor-Ind method, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Peak Elev= 262.27' @ 12.07 hrs Device Routing Invert Outlet Devices #1 Primary 261.65'24.0" Round 24" Outlet Pipe L= 9.0' CPP, end-section conforming to fill, Ke= 0.500 Inlet / Outlet Invert= 261.65' / 261.00' S= 0.0722 '/' Cc= 0.900 n= 0.013 Corrugated PE, smooth interior, Flow Area= 3.14 sf #2 Secondary 264.96'20.4" x 38.0" Horiz. Top of Grate C= 0.600 Limited to weir flow at low heads Primary OutFlow Max=2.21 cfs @ 12.07 hrs HW=262.27' TW=258.12' (Dynamic Tailwater) 1=24" Outlet Pipe (Inlet Controls 2.21 cfs @ 2.68 fps) Secondary OutFlow Max=0.00 cfs @ 0.00 hrs HW=261.65' (Free Discharge) 2=Top of Grate ( Controls 0.00 cfs) Pond CB: EX-CB InflowOutflowPrimarySecondary Hydrograph Time (hours)727068666462605856545250484644424038363432302826242220181614121086420Flow (cfs)2 1 0 Inflow Area=78,408 sf Peak Elev=262.27' 2.23 cfs 2.23 cfs 2.23 cfs 0.00 cfs Type III 24-hr WQV Rainfall=1.30"SWALE CALCS Printed 3/27/2025Prepared by HH Engineering Assoc Page 7HydroCAD® 10.20-2h s/n 12772 © 2024 HydroCAD Software Solutions LLC Summary for Pond DMH: PR-DMH [57] Hint: Peaked at 258.12' (Flood elevation advised) Inflow Area = 78,408 sf,100.00% Impervious, Inflow Depth = 1.08" for WQV event Inflow = 2.23 cfs @ 12.07 hrs, Volume= 7,080 cf Outflow = 2.23 cfs @ 12.07 hrs, Volume= 7,080 cf, Atten= 0%, Lag= 0.0 min Primary = 2.23 cfs @ 12.07 hrs, Volume= 7,080 cf Routed to Reach SW : Grassed Swale Secondary = 0.00 cfs @ 0.00 hrs, Volume= 0 cf Routing by Dyn-Stor-Ind method, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Peak Elev= 258.12' @ 12.07 hrs Device Routing Invert Outlet Devices #1 Primary 257.50'24.0" Round 24" Outlet Pipe L= 118.0' CPP, end-section conforming to fill, Ke= 0.500 Inlet / Outlet Invert= 257.50' / 255.80' S= 0.0144 '/' Cc= 0.900 n= 0.013 Corrugated PE, smooth interior, Flow Area= 3.14 sf #2 Secondary 265.50'3.0" Horiz. Top of Frame C= 0.600 Limited to weir flow at low heads Primary OutFlow Max=2.21 cfs @ 12.07 hrs HW=258.12' TW=255.95' (Dynamic Tailwater) 1=24" Outlet Pipe (Inlet Controls 2.21 cfs @ 2.68 fps) Secondary OutFlow Max=0.00 cfs @ 0.00 hrs HW=257.50' (Free Discharge) 2=Top of Frame ( Controls 0.00 cfs) Pond DMH: PR-DMH InflowOutflowPrimarySecondary Hydrograph Time (hours) 727068666462605856545250484644424038363432302826242220181614121086420Flow (cfs)2 1 0 Inflow Area=78,408 sf Peak Elev=258.12' 2.23 cfs 2.23 cfs 2.23 cfs 0.00 cfs Type III 24-hr 2-Year Rainfall=3.46"SWALE CALCS Printed 3/27/2025Prepared by HH Engineering Assoc Page 8HydroCAD® 10.20-2h s/n 12772 © 2024 HydroCAD Software Solutions LLC Time span=0.00-72.00 hrs, dt=0.02 hrs, 3601 points Runoff by SCS TR-20 method, UH=SCS, Weighted-CN Reach routing by Dyn-Stor-Ind method - Pond routing by Dyn-Stor-Ind method Runoff Area=1.800 ac 100.00% Impervious Runoff Depth=3.23"Subcatchment DA: DA Tc=5.0 min CN=98 Runoff=6.25 cfs 21,083 cf Avg. Flow Depth=0.28' Max Vel=3.26 fps Inflow=6.25 cfs 21,083 cfReach SW: Grassed Swale n=0.030 L=205.0' S=0.0283 '/' Capacity=60.81 cfs Outflow=6.19 cfs 21,083 cf Peak Elev=262.74' Inflow=6.25 cfs 21,083 cfPond CB: EX-CB Primary=6.25 cfs 21,083 cf Secondary=0.00 cfs 0 cf Outflow=6.25 cfs 21,083 cf Peak Elev=258.59' Inflow=6.25 cfs 21,083 cfPond DMH: PR-DMH Primary=6.25 cfs 21,083 cf Secondary=0.00 cfs 0 cf Outflow=6.25 cfs 21,083 cf Total Runoff Area = 78,408 sf Runoff Volume = 21,083 cf Average Runoff Depth = 3.23" 0.00% Pervious = 0 sf 100.00% Impervious = 78,408 sf Type III 24-hr 2-Year Rainfall=3.46"SWALE CALCS Printed 3/27/2025Prepared by HH Engineering Assoc Page 9HydroCAD® 10.20-2h s/n 12772 © 2024 HydroCAD Software Solutions LLC Summary for Subcatchment DA: DA Runoff = 6.25 cfs @ 12.07 hrs, Volume= 21,083 cf, Depth= 3.23" Routed to Pond CB : EX-CB Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Type III 24-hr 2-Year Rainfall=3.46" Area (ac) CN Description 1.800 98 Paved parking, HSG B 1.800 100.00% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 5.0 Direct Entry, Direct Subcatchment DA: DA Runoff Hydrograph Time (hours) 727068666462605856545250484644424038363432302826242220181614121086420Flow (cfs)7 6 5 4 3 2 1 0 Type III 24-hr 2-Year Rainfall=3.46" Runoff Area=1.800 ac Runoff Volume=21,083 cf Runoff Depth=3.23" Tc=5.0 min CN=98 6.25 cfs Type III 24-hr 2-Year Rainfall=3.46"SWALE CALCS Printed 3/27/2025Prepared by HH Engineering Assoc Page 10HydroCAD® 10.20-2h s/n 12772 © 2024 HydroCAD Software Solutions LLC Summary for Reach SW: Grassed Swale Inflow Area = 78,408 sf,100.00% Impervious, Inflow Depth = 3.23" for 2-Year event Inflow = 6.25 cfs @ 12.07 hrs, Volume= 21,083 cf Outflow = 6.19 cfs @ 12.08 hrs, Volume= 21,083 cf, Atten= 1%, Lag= 0.7 min Routing by Dyn-Stor-Ind method, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Max. Velocity= 3.26 fps, Min. Travel Time= 1.0 min Avg. Velocity = 0.80 fps, Avg. Travel Time= 4.3 min Peak Storage= 389 cf @ 12.08 hrs Average Depth at Peak Storage= 0.28' , Surface Width= 7.67' Bank-Full Depth= 1.00' Flow Area= 9.0 sf, Capacity= 60.81 cfs 6.00' x 1.00' deep channel, n= 0.030 Earth, grassed & winding Side Slope Z-value= 3.0 '/' Top Width= 12.00' Length= 205.0' Slope= 0.0283 '/' Inlet Invert= 255.80', Outlet Invert= 250.00' ‡ Reach SW: Grassed Swale InflowOutflow Hydrograph Time (hours) 727068666462605856545250484644424038363432302826242220181614121086420Flow (cfs)7 6 5 4 3 2 1 0 Inflow Area=78,408 sf Avg. Flow Depth=0.28' Max Vel=3.26 fps n=0.030 L=205.0' S=0.0283 '/' Capacity=60.81 cfs 6.25 cfs 6.19 cfs Type III 24-hr 2-Year Rainfall=3.46"SWALE CALCS Printed 3/27/2025Prepared by HH Engineering Assoc Page 11HydroCAD® 10.20-2h s/n 12772 © 2024 HydroCAD Software Solutions LLC Summary for Pond CB: EX-CB [57] Hint: Peaked at 262.74' (Flood elevation advised) Inflow Area = 78,408 sf,100.00% Impervious, Inflow Depth = 3.23" for 2-Year event Inflow = 6.25 cfs @ 12.07 hrs, Volume= 21,083 cf Outflow = 6.25 cfs @ 12.07 hrs, Volume= 21,083 cf, Atten= 0%, Lag= 0.0 min Primary = 6.25 cfs @ 12.07 hrs, Volume= 21,083 cf Routed to Pond DMH : PR-DMH Secondary = 0.00 cfs @ 0.00 hrs, Volume= 0 cf Routing by Dyn-Stor-Ind method, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Peak Elev= 262.74' @ 12.07 hrs Device Routing Invert Outlet Devices #1 Primary 261.65'24.0" Round 24" Outlet Pipe L= 9.0' CPP, end-section conforming to fill, Ke= 0.500 Inlet / Outlet Invert= 261.65' / 261.00' S= 0.0722 '/' Cc= 0.900 n= 0.013 Corrugated PE, smooth interior, Flow Area= 3.14 sf #2 Secondary 264.96'20.4" x 38.0" Horiz. Top of Grate C= 0.600 Limited to weir flow at low heads Primary OutFlow Max=6.20 cfs @ 12.07 hrs HW=262.74' TW=258.59' (Dynamic Tailwater) 1=24" Outlet Pipe (Inlet Controls 6.20 cfs @ 3.55 fps) Secondary OutFlow Max=0.00 cfs @ 0.00 hrs HW=261.65' (Free Discharge) 2=Top of Grate ( Controls 0.00 cfs) Pond CB: EX-CB InflowOutflowPrimarySecondary Hydrograph Time (hours)727068666462605856545250484644424038363432302826242220181614121086420Flow (cfs)7 6 5 4 3 2 1 0 Inflow Area=78,408 sf Peak Elev=262.74' 6.25 cfs 6.25 cfs 6.25 cfs 0.00 cfs Type III 24-hr 2-Year Rainfall=3.46"SWALE CALCS Printed 3/27/2025Prepared by HH Engineering Assoc Page 12HydroCAD® 10.20-2h s/n 12772 © 2024 HydroCAD Software Solutions LLC Summary for Pond DMH: PR-DMH [57] Hint: Peaked at 258.59' (Flood elevation advised) Inflow Area = 78,408 sf,100.00% Impervious, Inflow Depth = 3.23" for 2-Year event Inflow = 6.25 cfs @ 12.07 hrs, Volume= 21,083 cf Outflow = 6.25 cfs @ 12.07 hrs, Volume= 21,083 cf, Atten= 0%, Lag= 0.0 min Primary = 6.25 cfs @ 12.07 hrs, Volume= 21,083 cf Routed to Reach SW : Grassed Swale Secondary = 0.00 cfs @ 0.00 hrs, Volume= 0 cf Routing by Dyn-Stor-Ind method, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Peak Elev= 258.59' @ 12.07 hrs Device Routing Invert Outlet Devices #1 Primary 257.50'24.0" Round 24" Outlet Pipe L= 118.0' CPP, end-section conforming to fill, Ke= 0.500 Inlet / Outlet Invert= 257.50' / 255.80' S= 0.0144 '/' Cc= 0.900 n= 0.013 Corrugated PE, smooth interior, Flow Area= 3.14 sf #2 Secondary 265.50'3.0" Horiz. Top of Frame C= 0.600 Limited to weir flow at low heads Primary OutFlow Max=6.20 cfs @ 12.07 hrs HW=258.59' TW=256.07' (Dynamic Tailwater) 1=24" Outlet Pipe (Inlet Controls 6.20 cfs @ 3.55 fps) Secondary OutFlow Max=0.00 cfs @ 0.00 hrs HW=257.50' (Free Discharge) 2=Top of Frame ( Controls 0.00 cfs) Pond DMH: PR-DMH InflowOutflowPrimarySecondary Hydrograph Time (hours) 727068666462605856545250484644424038363432302826242220181614121086420Flow (cfs)7 6 5 4 3 2 1 0 Inflow Area=78,408 sf Peak Elev=258.59' 6.25 cfs 6.25 cfs 6.25 cfs 0.00 cfs Type III 24-hr 10-Year Rainfall=5.13"SWALE CALCS Printed 3/27/2025Prepared by HH Engineering Assoc Page 13HydroCAD® 10.20-2h s/n 12772 © 2024 HydroCAD Software Solutions LLC Time span=0.00-72.00 hrs, dt=0.02 hrs, 3601 points Runoff by SCS TR-20 method, UH=SCS, Weighted-CN Reach routing by Dyn-Stor-Ind method - Pond routing by Dyn-Stor-Ind method Runoff Area=1.800 ac 100.00% Impervious Runoff Depth=4.89"Subcatchment DA: DA Tc=5.0 min CN=98 Runoff=9.33 cfs 31,971 cf Avg. Flow Depth=0.35' Max Vel=3.74 fps Inflow=9.33 cfs 31,971 cfReach SW: Grassed Swale n=0.030 L=205.0' S=0.0283 '/' Capacity=60.81 cfs Outflow=9.25 cfs 31,971 cf Peak Elev=263.04' Inflow=9.33 cfs 31,971 cfPond CB: EX-CB Primary=9.33 cfs 31,971 cf Secondary=0.00 cfs 0 cf Outflow=9.33 cfs 31,971 cf Peak Elev=258.89' Inflow=9.33 cfs 31,971 cfPond DMH: PR-DMH Primary=9.33 cfs 31,971 cf Secondary=0.00 cfs 0 cf Outflow=9.33 cfs 31,971 cf Total Runoff Area = 78,408 sf Runoff Volume = 31,971 cf Average Runoff Depth = 4.89" 0.00% Pervious = 0 sf 100.00% Impervious = 78,408 sf Type III 24-hr 10-Year Rainfall=5.13"SWALE CALCS Printed 3/27/2025Prepared by HH Engineering Assoc Page 14HydroCAD® 10.20-2h s/n 12772 © 2024 HydroCAD Software Solutions LLC Summary for Subcatchment DA: DA Runoff = 9.33 cfs @ 12.07 hrs, Volume= 31,971 cf, Depth= 4.89" Routed to Pond CB : EX-CB Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Type III 24-hr 10-Year Rainfall=5.13" Area (ac) CN Description 1.800 98 Paved parking, HSG B 1.800 100.00% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 5.0 Direct Entry, Direct Subcatchment DA: DA Runoff Hydrograph Time (hours) 727068666462605856545250484644424038363432302826242220181614121086420Flow (cfs)10 9 8 7 6 5 4 3 2 1 0 Type III 24-hr 10-Year Rainfall=5.13" Runoff Area=1.800 ac Runoff Volume=31,971 cf Runoff Depth=4.89" Tc=5.0 min CN=98 9.33 cfs Type III 24-hr 10-Year Rainfall=5.13"SWALE CALCS Printed 3/27/2025Prepared by HH Engineering Assoc Page 15HydroCAD® 10.20-2h s/n 12772 © 2024 HydroCAD Software Solutions LLC Summary for Reach SW: Grassed Swale Inflow Area = 78,408 sf,100.00% Impervious, Inflow Depth = 4.89" for 10-Year event Inflow = 9.33 cfs @ 12.07 hrs, Volume= 31,971 cf Outflow = 9.25 cfs @ 12.08 hrs, Volume= 31,971 cf, Atten= 1%, Lag= 0.7 min Routing by Dyn-Stor-Ind method, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Max. Velocity= 3.74 fps, Min. Travel Time= 0.9 min Avg. Velocity = 0.93 fps, Avg. Travel Time= 3.7 min Peak Storage= 507 cf @ 12.08 hrs Average Depth at Peak Storage= 0.35' , Surface Width= 8.10' Bank-Full Depth= 1.00' Flow Area= 9.0 sf, Capacity= 60.81 cfs 6.00' x 1.00' deep channel, n= 0.030 Earth, grassed & winding Side Slope Z-value= 3.0 '/' Top Width= 12.00' Length= 205.0' Slope= 0.0283 '/' Inlet Invert= 255.80', Outlet Invert= 250.00' ‡ Reach SW: Grassed Swale InflowOutflow Hydrograph Time (hours) 727068666462605856545250484644424038363432302826242220181614121086420Flow (cfs)10 9 8 7 6 5 4 3 2 1 0 Inflow Area=78,408 sf Avg. Flow Depth=0.35' Max Vel=3.74 fps n=0.030 L=205.0' S=0.0283 '/' Capacity=60.81 cfs 9.33 cfs 9.25 cfs Type III 24-hr 10-Year Rainfall=5.13"SWALE CALCS Printed 3/27/2025Prepared by HH Engineering Assoc Page 16HydroCAD® 10.20-2h s/n 12772 © 2024 HydroCAD Software Solutions LLC Summary for Pond CB: EX-CB [57] Hint: Peaked at 263.04' (Flood elevation advised) Inflow Area = 78,408 sf,100.00% Impervious, Inflow Depth = 4.89" for 10-Year event Inflow = 9.33 cfs @ 12.07 hrs, Volume= 31,971 cf Outflow = 9.33 cfs @ 12.07 hrs, Volume= 31,971 cf, Atten= 0%, Lag= 0.0 min Primary = 9.33 cfs @ 12.07 hrs, Volume= 31,971 cf Routed to Pond DMH : PR-DMH Secondary = 0.00 cfs @ 0.00 hrs, Volume= 0 cf Routing by Dyn-Stor-Ind method, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Peak Elev= 263.04' @ 12.07 hrs Device Routing Invert Outlet Devices #1 Primary 261.65'24.0" Round 24" Outlet Pipe L= 9.0' CPP, end-section conforming to fill, Ke= 0.500 Inlet / Outlet Invert= 261.65' / 261.00' S= 0.0722 '/' Cc= 0.900 n= 0.013 Corrugated PE, smooth interior, Flow Area= 3.14 sf #2 Secondary 264.96'20.4" x 38.0" Horiz. Top of Grate C= 0.600 Limited to weir flow at low heads Primary OutFlow Max=9.26 cfs @ 12.07 hrs HW=263.03' TW=258.88' (Dynamic Tailwater) 1=24" Outlet Pipe (Inlet Controls 9.26 cfs @ 4.00 fps) Secondary OutFlow Max=0.00 cfs @ 0.00 hrs HW=261.65' (Free Discharge) 2=Top of Grate ( Controls 0.00 cfs) Pond CB: EX-CB InflowOutflowPrimarySecondary Hydrograph Time (hours)727068666462605856545250484644424038363432302826242220181614121086420Flow (cfs)10 9 8 7 6 5 4 3 2 1 0 Inflow Area=78,408 sf Peak Elev=263.04' 9.33 cfs 9.33 cfs 9.33 cfs 0.00 cfs Type III 24-hr 10-Year Rainfall=5.13"SWALE CALCS Printed 3/27/2025Prepared by HH Engineering Assoc Page 17HydroCAD® 10.20-2h s/n 12772 © 2024 HydroCAD Software Solutions LLC Summary for Pond DMH: PR-DMH [57] Hint: Peaked at 258.89' (Flood elevation advised) Inflow Area = 78,408 sf,100.00% Impervious, Inflow Depth = 4.89" for 10-Year event Inflow = 9.33 cfs @ 12.07 hrs, Volume= 31,971 cf Outflow = 9.33 cfs @ 12.07 hrs, Volume= 31,971 cf, Atten= 0%, Lag= 0.0 min Primary = 9.33 cfs @ 12.07 hrs, Volume= 31,971 cf Routed to Reach SW : Grassed Swale Secondary = 0.00 cfs @ 0.00 hrs, Volume= 0 cf Routing by Dyn-Stor-Ind method, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Peak Elev= 258.89' @ 12.07 hrs Device Routing Invert Outlet Devices #1 Primary 257.50'24.0" Round 24" Outlet Pipe L= 118.0' CPP, end-section conforming to fill, Ke= 0.500 Inlet / Outlet Invert= 257.50' / 255.80' S= 0.0144 '/' Cc= 0.900 n= 0.013 Corrugated PE, smooth interior, Flow Area= 3.14 sf #2 Secondary 265.50'3.0" Horiz. Top of Frame C= 0.600 Limited to weir flow at low heads Primary OutFlow Max=9.26 cfs @ 12.07 hrs HW=258.88' TW=256.15' (Dynamic Tailwater) 1=24" Outlet Pipe (Inlet Controls 9.26 cfs @ 4.00 fps) Secondary OutFlow Max=0.00 cfs @ 0.00 hrs HW=257.50' (Free Discharge) 2=Top of Frame ( Controls 0.00 cfs) Pond DMH: PR-DMH InflowOutflowPrimarySecondary Hydrograph Time (hours) 727068666462605856545250484644424038363432302826242220181614121086420Flow (cfs)10 9 8 7 6 5 4 3 2 1 0 Inflow Area=78,408 sf Peak Elev=258.89' 9.33 cfs 9.33 cfs 9.33 cfs 0.00 cfs Type III 24-hr 25-Year Rainfall=6.17"SWALE CALCS Printed 3/27/2025Prepared by HH Engineering Assoc Page 18HydroCAD® 10.20-2h s/n 12772 © 2024 HydroCAD Software Solutions LLC Time span=0.00-72.00 hrs, dt=0.02 hrs, 3601 points Runoff by SCS TR-20 method, UH=SCS, Weighted-CN Reach routing by Dyn-Stor-Ind method - Pond routing by Dyn-Stor-Ind method Runoff Area=1.800 ac 100.00% Impervious Runoff Depth=5.93"Subcatchment DA: DA Tc=5.0 min CN=98 Runoff=11.24 cfs 38,758 cf Avg. Flow Depth=0.39' Max Vel=3.98 fps Inflow=11.24 cfs 38,758 cfReach SW: Grassed Swale n=0.030 L=205.0' S=0.0283 '/' Capacity=60.81 cfs Outflow=11.16 cfs 38,758 cf Peak Elev=263.22' Inflow=11.24 cfs 38,758 cfPond CB: EX-CB Primary=11.24 cfs 38,758 cf Secondary=0.00 cfs 0 cf Outflow=11.24 cfs 38,758 cf Peak Elev=259.07' Inflow=11.24 cfs 38,758 cfPond DMH: PR-DMH Primary=11.24 cfs 38,758 cf Secondary=0.00 cfs 0 cf Outflow=11.24 cfs 38,758 cf Total Runoff Area = 78,408 sf Runoff Volume = 38,758 cf Average Runoff Depth = 5.93" 0.00% Pervious = 0 sf 100.00% Impervious = 78,408 sf Type III 24-hr 25-Year Rainfall=6.17"SWALE CALCS Printed 3/27/2025Prepared by HH Engineering Assoc Page 19HydroCAD® 10.20-2h s/n 12772 © 2024 HydroCAD Software Solutions LLC Summary for Subcatchment DA: DA Runoff = 11.24 cfs @ 12.07 hrs, Volume= 38,758 cf, Depth= 5.93" Routed to Pond CB : EX-CB Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Type III 24-hr 25-Year Rainfall=6.17" Area (ac) CN Description 1.800 98 Paved parking, HSG B 1.800 100.00% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 5.0 Direct Entry, Direct Subcatchment DA: DA Runoff Hydrograph Time (hours) 727068666462605856545250484644424038363432302826242220181614121086420Flow (cfs)12 11 10 9 8 7 6 5 4 3 2 1 0 Type III 24-hr 25-Year Rainfall=6.17" Runoff Area=1.800 ac Runoff Volume=38,758 cf Runoff Depth=5.93" Tc=5.0 min CN=98 11.24 cfs Type III 24-hr 25-Year Rainfall=6.17"SWALE CALCS Printed 3/27/2025Prepared by HH Engineering Assoc Page 20HydroCAD® 10.20-2h s/n 12772 © 2024 HydroCAD Software Solutions LLC Summary for Reach SW: Grassed Swale Inflow Area = 78,408 sf,100.00% Impervious, Inflow Depth = 5.93" for 25-Year event Inflow = 11.24 cfs @ 12.07 hrs, Volume= 38,758 cf Outflow = 11.16 cfs @ 12.08 hrs, Volume= 38,758 cf, Atten= 1%, Lag= 0.6 min Routing by Dyn-Stor-Ind method, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Max. Velocity= 3.98 fps, Min. Travel Time= 0.9 min Avg. Velocity = 1.00 fps, Avg. Travel Time= 3.4 min Peak Storage= 574 cf @ 12.08 hrs Average Depth at Peak Storage= 0.39' , Surface Width= 8.34' Bank-Full Depth= 1.00' Flow Area= 9.0 sf, Capacity= 60.81 cfs 6.00' x 1.00' deep channel, n= 0.030 Earth, grassed & winding Side Slope Z-value= 3.0 '/' Top Width= 12.00' Length= 205.0' Slope= 0.0283 '/' Inlet Invert= 255.80', Outlet Invert= 250.00' ‡ Reach SW: Grassed Swale InflowOutflow Hydrograph Time (hours) 727068666462605856545250484644424038363432302826242220181614121086420Flow (cfs)12 11 10 9 8 7 6 5 4 3 2 1 0 Inflow Area=78,408 sf Avg. Flow Depth=0.39' Max Vel=3.98 fps n=0.030 L=205.0' S=0.0283 '/' Capacity=60.81 cfs 11.24 cfs 11.16 cfs Type III 24-hr 25-Year Rainfall=6.17"SWALE CALCS Printed 3/27/2025Prepared by HH Engineering Assoc Page 21HydroCAD® 10.20-2h s/n 12772 © 2024 HydroCAD Software Solutions LLC Summary for Pond CB: EX-CB [57] Hint: Peaked at 263.22' (Flood elevation advised) Inflow Area = 78,408 sf,100.00% Impervious, Inflow Depth = 5.93" for 25-Year event Inflow = 11.24 cfs @ 12.07 hrs, Volume= 38,758 cf Outflow = 11.24 cfs @ 12.07 hrs, Volume= 38,758 cf, Atten= 0%, Lag= 0.0 min Primary = 11.24 cfs @ 12.07 hrs, Volume= 38,758 cf Routed to Pond DMH : PR-DMH Secondary = 0.00 cfs @ 0.00 hrs, Volume= 0 cf Routing by Dyn-Stor-Ind method, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Peak Elev= 263.22' @ 12.07 hrs Device Routing Invert Outlet Devices #1 Primary 261.65'24.0" Round 24" Outlet Pipe L= 9.0' CPP, end-section conforming to fill, Ke= 0.500 Inlet / Outlet Invert= 261.65' / 261.00' S= 0.0722 '/' Cc= 0.900 n= 0.013 Corrugated PE, smooth interior, Flow Area= 3.14 sf #2 Secondary 264.96'20.4" x 38.0" Horiz. Top of Grate C= 0.600 Limited to weir flow at low heads Primary OutFlow Max=11.15 cfs @ 12.07 hrs HW=263.21' TW=259.06' (Dynamic Tailwater) 1=24" Outlet Pipe (Inlet Controls 11.15 cfs @ 4.25 fps) Secondary OutFlow Max=0.00 cfs @ 0.00 hrs HW=261.65' (Free Discharge) 2=Top of Grate ( Controls 0.00 cfs) Pond CB: EX-CB InflowOutflowPrimarySecondary Hydrograph Time (hours)727068666462605856545250484644424038363432302826242220181614121086420Flow (cfs)12 11 10 9 8 7 6 5 4 3 2 1 0 Inflow Area=78,408 sf Peak Elev=263.22' 11.24 cfs 11.24 cfs 11.24 cfs 0.00 cfs Type III 24-hr 25-Year Rainfall=6.17"SWALE CALCS Printed 3/27/2025Prepared by HH Engineering Assoc Page 22HydroCAD® 10.20-2h s/n 12772 © 2024 HydroCAD Software Solutions LLC Summary for Pond DMH: PR-DMH [57] Hint: Peaked at 259.07' (Flood elevation advised) Inflow Area = 78,408 sf,100.00% Impervious, Inflow Depth = 5.93" for 25-Year event Inflow = 11.24 cfs @ 12.07 hrs, Volume= 38,758 cf Outflow = 11.24 cfs @ 12.07 hrs, Volume= 38,758 cf, Atten= 0%, Lag= 0.0 min Primary = 11.24 cfs @ 12.07 hrs, Volume= 38,758 cf Routed to Reach SW : Grassed Swale Secondary = 0.00 cfs @ 0.00 hrs, Volume= 0 cf Routing by Dyn-Stor-Ind method, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Peak Elev= 259.07' @ 12.07 hrs Device Routing Invert Outlet Devices #1 Primary 257.50'24.0" Round 24" Outlet Pipe L= 118.0' CPP, end-section conforming to fill, Ke= 0.500 Inlet / Outlet Invert= 257.50' / 255.80' S= 0.0144 '/' Cc= 0.900 n= 0.013 Corrugated PE, smooth interior, Flow Area= 3.14 sf #2 Secondary 265.50'3.0" Horiz. Top of Frame C= 0.600 Limited to weir flow at low heads Primary OutFlow Max=11.15 cfs @ 12.07 hrs HW=259.06' TW=256.19' (Dynamic Tailwater) 1=24" Outlet Pipe (Inlet Controls 11.15 cfs @ 4.25 fps) Secondary OutFlow Max=0.00 cfs @ 0.00 hrs HW=257.50' (Free Discharge) 2=Top of Frame ( Controls 0.00 cfs) Pond DMH: PR-DMH InflowOutflowPrimarySecondary Hydrograph Time (hours) 727068666462605856545250484644424038363432302826242220181614121086420Flow (cfs)12 11 10 9 8 7 6 5 4 3 2 1 0 Inflow Area=78,408 sf Peak Elev=259.07' 11.24 cfs 11.24 cfs 11.24 cfs 0.00 cfs Type III 24-hr 100-Year Rainfall=7.78"SWALE CALCS Printed 3/27/2025Prepared by HH Engineering Assoc Page 23HydroCAD® 10.20-2h s/n 12772 © 2024 HydroCAD Software Solutions LLC Time span=0.00-72.00 hrs, dt=0.02 hrs, 3601 points Runoff by SCS TR-20 method, UH=SCS, Weighted-CN Reach routing by Dyn-Stor-Ind method - Pond routing by Dyn-Stor-Ind method Runoff Area=1.800 ac 100.00% Impervious Runoff Depth=7.54"Subcatchment DA: DA Tc=5.0 min CN=98 Runoff=14.19 cfs 49,269 cf Avg. Flow Depth=0.45' Max Vel=4.30 fps Inflow=14.19 cfs 49,269 cfReach SW: Grassed Swale n=0.030 L=205.0' S=0.0283 '/' Capacity=60.81 cfs Outflow=14.11 cfs 49,269 cf Peak Elev=263.52' Inflow=14.19 cfs 49,269 cfPond CB: EX-CB Primary=14.19 cfs 49,269 cf Secondary=0.00 cfs 0 cf Outflow=14.19 cfs 49,269 cf Peak Elev=259.37' Inflow=14.19 cfs 49,269 cfPond DMH: PR-DMH Primary=14.19 cfs 49,269 cf Secondary=0.00 cfs 0 cf Outflow=14.19 cfs 49,269 cf Total Runoff Area = 78,408 sf Runoff Volume = 49,269 cf Average Runoff Depth = 7.54" 0.00% Pervious = 0 sf 100.00% Impervious = 78,408 sf Type III 24-hr 100-Year Rainfall=7.78"SWALE CALCS Printed 3/27/2025Prepared by HH Engineering Assoc Page 24HydroCAD® 10.20-2h s/n 12772 © 2024 HydroCAD Software Solutions LLC Summary for Subcatchment DA: DA Runoff = 14.19 cfs @ 12.07 hrs, Volume= 49,269 cf, Depth= 7.54" Routed to Pond CB : EX-CB Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Type III 24-hr 100-Year Rainfall=7.78" Area (ac) CN Description 1.800 98 Paved parking, HSG B 1.800 100.00% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 5.0 Direct Entry, Direct Subcatchment DA: DA Runoff Hydrograph Time (hours) 727068666462605856545250484644424038363432302826242220181614121086420Flow (cfs)15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 Type III 24-hr 100-Year Rainfall=7.78" Runoff Area=1.800 ac Runoff Volume=49,269 cf Runoff Depth=7.54" Tc=5.0 min CN=98 14.19 cfs Type III 24-hr 100-Year Rainfall=7.78"SWALE CALCS Printed 3/27/2025Prepared by HH Engineering Assoc Page 25HydroCAD® 10.20-2h s/n 12772 © 2024 HydroCAD Software Solutions LLC Summary for Reach SW: Grassed Swale Inflow Area = 78,408 sf,100.00% Impervious, Inflow Depth = 7.54" for 100-Year event Inflow = 14.19 cfs @ 12.07 hrs, Volume= 49,269 cf Outflow = 14.11 cfs @ 12.08 hrs, Volume= 49,269 cf, Atten= 1%, Lag= 0.6 min Routing by Dyn-Stor-Ind method, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Max. Velocity= 4.30 fps, Min. Travel Time= 0.8 min Avg. Velocity = 1.10 fps, Avg. Travel Time= 3.1 min Peak Storage= 672 cf @ 12.08 hrs Average Depth at Peak Storage= 0.45' , Surface Width= 8.68' Bank-Full Depth= 1.00' Flow Area= 9.0 sf, Capacity= 60.81 cfs 6.00' x 1.00' deep channel, n= 0.030 Earth, grassed & winding Side Slope Z-value= 3.0 '/' Top Width= 12.00' Length= 205.0' Slope= 0.0283 '/' Inlet Invert= 255.80', Outlet Invert= 250.00' ‡ Reach SW: Grassed Swale InflowOutflow Hydrograph Time (hours) 727068666462605856545250484644424038363432302826242220181614121086420Flow (cfs)15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 Inflow Area=78,408 sf Avg. Flow Depth=0.45' Max Vel=4.30 fps n=0.030 L=205.0' S=0.0283 '/' Capacity=60.81 cfs 14.19 cfs 14.11 cfs Type III 24-hr 100-Year Rainfall=7.78"SWALE CALCS Printed 3/27/2025Prepared by HH Engineering Assoc Page 26HydroCAD® 10.20-2h s/n 12772 © 2024 HydroCAD Software Solutions LLC Summary for Pond CB: EX-CB [57] Hint: Peaked at 263.52' (Flood elevation advised) Inflow Area = 78,408 sf,100.00% Impervious, Inflow Depth = 7.54" for 100-Year event Inflow = 14.19 cfs @ 12.07 hrs, Volume= 49,269 cf Outflow = 14.19 cfs @ 12.07 hrs, Volume= 49,269 cf, Atten= 0%, Lag= 0.0 min Primary = 14.19 cfs @ 12.07 hrs, Volume= 49,269 cf Routed to Pond DMH : PR-DMH Secondary = 0.00 cfs @ 0.00 hrs, Volume= 0 cf Routing by Dyn-Stor-Ind method, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Peak Elev= 263.52' @ 12.07 hrs Device Routing Invert Outlet Devices #1 Primary 261.65'24.0" Round 24" Outlet Pipe L= 9.0' CPP, end-section conforming to fill, Ke= 0.500 Inlet / Outlet Invert= 261.65' / 261.00' S= 0.0722 '/' Cc= 0.900 n= 0.013 Corrugated PE, smooth interior, Flow Area= 3.14 sf #2 Secondary 264.96'20.4" x 38.0" Horiz. Top of Grate C= 0.600 Limited to weir flow at low heads Primary OutFlow Max=14.08 cfs @ 12.07 hrs HW=263.50' TW=259.35' (Dynamic Tailwater) 1=24" Outlet Pipe (Inlet Controls 14.08 cfs @ 4.64 fps) Secondary OutFlow Max=0.00 cfs @ 0.00 hrs HW=261.65' (Free Discharge) 2=Top of Grate ( Controls 0.00 cfs) Pond CB: EX-CB InflowOutflowPrimarySecondary Hydrograph Time (hours)727068666462605856545250484644424038363432302826242220181614121086420Flow (cfs)15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 Inflow Area=78,408 sf Peak Elev=263.52' 14.19 cfs 14.19 cfs 14.19 cfs 0.00 cfs Type III 24-hr 100-Year Rainfall=7.78"SWALE CALCS Printed 3/27/2025Prepared by HH Engineering Assoc Page 27HydroCAD® 10.20-2h s/n 12772 © 2024 HydroCAD Software Solutions LLC Summary for Pond DMH: PR-DMH [57] Hint: Peaked at 259.37' (Flood elevation advised) Inflow Area = 78,408 sf,100.00% Impervious, Inflow Depth = 7.54" for 100-Year event Inflow = 14.19 cfs @ 12.07 hrs, Volume= 49,269 cf Outflow = 14.19 cfs @ 12.07 hrs, Volume= 49,269 cf, Atten= 0%, Lag= 0.0 min Primary = 14.19 cfs @ 12.07 hrs, Volume= 49,269 cf Routed to Reach SW : Grassed Swale Secondary = 0.00 cfs @ 0.00 hrs, Volume= 0 cf Routing by Dyn-Stor-Ind method, Time Span= 0.00-72.00 hrs, dt= 0.02 hrs Peak Elev= 259.37' @ 12.07 hrs Device Routing Invert Outlet Devices #1 Primary 257.50'24.0" Round 24" Outlet Pipe L= 118.0' CPP, end-section conforming to fill, Ke= 0.500 Inlet / Outlet Invert= 257.50' / 255.80' S= 0.0144 '/' Cc= 0.900 n= 0.013 Corrugated PE, smooth interior, Flow Area= 3.14 sf #2 Secondary 265.50'3.0" Horiz. Top of Frame C= 0.600 Limited to weir flow at low heads Primary OutFlow Max=14.08 cfs @ 12.07 hrs HW=259.35' TW=256.24' (Dynamic Tailwater) 1=24" Outlet Pipe (Inlet Controls 14.08 cfs @ 4.64 fps) Secondary OutFlow Max=0.00 cfs @ 0.00 hrs HW=257.50' (Free Discharge) 2=Top of Frame ( Controls 0.00 cfs) Pond DMH: PR-DMH InflowOutflowPrimarySecondary Hydrograph Time (hours) 727068666462605856545250484644424038363432302826242220181614121086420Flow (cfs)15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 Inflow Area=78,408 sf Peak Elev=259.37' 14.19 cfs 14.19 cfs 14.19 cfs 0.00 cfs Attachment B – Pipe Flow Velocity Calculations Inputs: Pipe Diameter, dₒ24.0000 in Manning Roughness, n 0.0130 Pressure slope (possibly equal to pipe slope), S₀ 1.4400 % slope Percent of (or ratio to) full depth (100% or 1 if flowing full)0.5134 fraction Results: Flow, Q 14.1923 ft^3/s Velocity, v 8.7370 ft/s Velocity head, hv 1.1864 ft Flow Area, A 1.6244 ft^2 Wetted Perimeter, P 3.1952 ft Hydraulic Radius 0.5084 ft Top Width, T 1.9993 ft Froude Number, F 1.71 Shear Stress (tractive force), τ 0.9230 psf Manning Formula Uniform Pipe Flow at Given Slope and Depth Version 2.0 (20 June 2017) HawsEDC Calculators Attachment C – Riprap Apron Sizing Calculations Outlet Protection Design Outlet FES-1 Reference: A.     Apron width at culvert end (W1) = 3 Sp where Sp = outlet pipe diameter B.     Apron length (La) = 1.8 (Q-5) + 10 (Sp)3/2 C.     Apron width at downstream end (W) = 3Sp + 0.7La where La = apron length Type A Riprap Apron (Tailwater Condition) : TW<0.5 dia of outlet Peak Q (25-yr) =14.19 cfs PIPE DIA=2 ft A. W1= 3(Sp ) = ft 6 ft B. La = 1.8 ( Q-5 ) + 10 = ft 16 ft (Sp) 1.5 C. W2 = 3(Sp ) + 0.7(La) = ft 18 ft V(25yr)=8.74 fps Therfore; Use Intermediate Riprap Connecticut Department of Transportation Drainage Manual, Dated October 2000