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Stormwater Report Preliminary Stormwater Management Plan for Chanhassen Retail Prepared for: Kraus-Anderson Realty Company 501 South 8th St Minneapolis, MN 55404 Prepared by: Westwood Professional Services 12701 Whitewater Drive, Suite 300 Minnetonka, MN 55343 (952) 937-5150 Project Number: 0015032.00 Date:06/09/2021 Chanhassen Retail June 9, 2021 1 INTRODUCTION This report summarizes the stormwater management design for the proposed Chanhassen Retail project. Chanhassen Retail is part of the Crossroads of Chanhassen development located at Crossroads Boulevard and Lyman Boulevard. The proposed project is located on the northwest corner of Lot 2 and consists of a 6,652 SF building with associated parking. Attachment 1 shows the drainage areas for this project. The total drainage area of Phase 3 is 1.227 acres. REGULATIONS The proposed project site is located within the City of Chanhassen, Minnesota and Riley Purgatory Bluff Creek Watershed District. The following rules from the City and Watershed apply: • Limit peak runoff to existing conditions for the 2-, 10-, and 100-year 24-hour storm events. • Provide abstraction for 1.1 inches of runoff from impervious surfaces, or 0.55 inches for restricted sites; • Provide at least 60% TP removal and 90% TSS removal on an annual average basis. EXISTING CONDITIONS The existing property is partially developed with a retail building along the east side of the property, in addition to the eastern half of the parking lot and two site entrances to Crossroads Boulevard. Most of the existing site drains toward the center of the site to a catch basin. The entire site drains via site storm sewer and discharges to the MnDOT Brae Burn Pond. SOIL CONDITIONS A Geotechnical Evaluation Report was completed by American Engineering Testing, Inc. on October 7, 2005 for the overall Crossroads of Chanhassen development. Four of the borings were located in Lot 2. Soil boring profiles are included in Attachment 2. The site consists of silty sand and clayed sand topsoil. Underlying the topsoil, there exists alluvial deposits, mostly consisting of lean clay with some silty sand, and clayey sand, and sand with silt layers. The site soil classification varies throughout the site from Hydraulic Soil Group “A” to “D”, with the majority being type D soils. Groundwater was found in the borings ranging in elevation from 917.1 to 921.1. PROPOSED CONDITIONS The proposed project fills in the western pad site with a 6,652 SF retail building and parking lot. The proposed parking extends to the southern entrance drive and goes beyond the proposed lot to be created for the retail building. Existing storm sewer that Chanhassen Retail June 9, 2021 2 runs through the proposed site is rerouted to allow for proposed storm sewer and treatment facilities. While stormwater management was originally designed and included for the overall development, stormwater regulations have changed since 2008 and new facilities are proposed for this development. Runoff from the proposed project will be directed to three landscaped areas where storm sewer will route the runoff to an underground chamber system and treatment device prior to connecting to existing storm sewer. Stormwater management is proposed for the new and reconstructed impervious areas. Based on Table 2 below, the proposed project does not meet the thresholds to require stormwater management of the entire parcel. Table 2: Impervious Site Coverage of Lot 2 Total Existing Impervious 84,095 SF Total Proposed Impervious 111,333 SF 32% increase New/reconstructed impervious 35,902 SF 43% of existing RATE CONTROL Stormwater discharges for the proposed project have been reduced to the existing rates by utilizing the storage capacity in the underground chamber system. Pretreatment will be provided by the isolator rows in the system. Stormwater discharge rates were computed using HydroCAD stormwater modeling software which incorporates Atlas-14 rainfall distributions. See Attachment 3 for the existing and proposed HydroCAD models. The table below summarizes the existing and proposed peak runoff rates from the site discharge point. Table 2: Peak Runoff Rate Storm Event Existing Discharge Rate (cfs) Proposed Discharge Rate (cfs) 2-year (2.84”) 2.41 2.21 10-year (4.20”) 4.54 4.48 100-year (7.18”) 9.45 9.13 The 100-yr HWL of the underground system is 920.2. The lowest floor elevation of the proposed building is 924.2 which meets the 2’ freeboard requirement. Chanhassen Retail June 9, 2021 3 VOLUME ABSTRACTION The Watershed requires abstraction of 1.1 inches of runoff from all impervious surfaces. Based on the old soil borings, the appears to be some areas with soils conducive to infiltration; however, high groundwater was encountered in all the boring s on the lot. Additional soils investigation, including borings in the area of the proposed underground system, will be done to confirm groundwater in this area prior to finalizing the design . Based on current available information, the site is restricted for volume abstraction due to high groundwater. Options for infiltration basins and pervious pavement is limited by the high groundwater, reuse is limited by minimal irrigation area, and a green roof by the relatively small building footprint and cost considerations. Table 3 below summarizes the site impervious areas and required abstraction volumes. Table 3: Volume Abstraction Requirement Impervious Area (SF) Required Volume (1.1”) (CF) Volume Abstraction Provided (CF) Proposed project 35,902 3,291 0 WATER QUALITY The Watershed requires storm water facilities to be designed to provide 60% annual removal of total phosphorus (TP) and 90% annual removal of total suspended solids (TSS). A filter system is proposed to help meet the water quality standard in combination with the landscape islands and isolator row pretreatment of the underground chamber system. The proprietary filter system has been tested to demonstrate 80% TSS ad 55% TP removal. In addition, the MnDOT Brae Burn Pond was designed to provide treatment for this development, even though it was constructed prior to the watershed reenacting their permitting process. CONCLUSIONS The proposed Chanhassen Retail project and its storm water management facilities have been designed to meet the rate control and water quality requirements of the City of Chanhassen and the Riley Purgatory Bluff Creek Watershed District. No volume abstraction is proposed for the restricted site. ATTACHMENT 1: DRAINAGE AREA MAP 203 E E E ST TUGTUGTUG PUGPUGPUGPUGPUGPUGPUGPUGPUGPUGPUGPUGPUG PUG PUGFOFOFOFOFOFOFOFOFOFOFOFOFOFOFOGASGASGASGASGASGASGASGASGASGASGASGASGASGASGASGASSTOFOFOFOFOFOFOFOFOFOFOFOFOFOFOFOX STO STO STO STO STO STO STO STO STO STO STO STO STO STO STO STO STO STO STO STO STO STO STOSTOSTOSTOSTOSTOSTOSTOSTOSTOSTOSTOSTOSTOSTOSTOSTOSTOSTOSTOSTOSTOSTO STOSTOSTOSTOSTOSTOSTOSTOSTOSTOSTOSTOSTOSTOSTOSTOSTOSTOSTO STO STO STO PUG FOFOFOFOFOFOFOFOFOFOFOFOFOFOFOFOFOFOFOFOFOCTVCTVCTVCTVCTVCTVCTVCTVCTVCTVCTVCTVCTVCTVCTVCTVCTVCTVT E E TE E STO STO EXISTING BUILDINGEXISTING BUILDING MISC. STUB ABOVE GROUND TRAS H ENCL O S U R ESTO STO STO STO STO STO STO STO STO STO STO STOSTOSTOSTOSTOSTOST STO STO STO STO STO STO STO STO STO FUTURE BUILDING 15,000 SF 75 STALLS REQ'D (5/1000) PROPOSED BUILDING 6,652 SF FFE=924.20 69 STALLS X X X XXX X X XXXX925 923923924924921 922923924925924924 925 922 9231P 2P 2P 4P 923 923 9 2 3 923922 923 924 924 923922924923 SHEET NUMBER: DATE:DATE:LICENSE NO.PREPARED FOR:Phone(952) 937-515012701 Whitewater Drive, Suite #300Fax(952) 937-5822Minnetonka, MN 55343Toll Free(888) 937-5150VERTICAL SCALE:HORIZONTAL SCALE:DRAWN:CHECKED:DESIGNED:INITIAL ISSUE:REVISIONS:N:\0015032.00\DWG\0015032C-DRAN.DWG06/04/2021 CHANHASSEN RETAIL1 CHANHASSEN, MNCHANHASSENRETAILDRAINAGEAREA MAP501 SOUTH 8TH STMINNEAPOLIS, MN 55404KRAUS-ANDERSONREALTY COMPANY...06/04/2021NOT FOR CONSTRUCTION© 2021 Westwood Professional Services, Inc.Common Ground Alliance Call 48 Hours before digging: 811 or call811.com 0'20'40'60' 1" = 20'..........20'4' or 2'PROJECT NUMBER: 0015032.00 ATTACHMENT 2: SOIL BORINGS ATTACHMENT 3: HYDROCAD MODELS 1E Existing Routing Diagram for 21-06-04 Pre Post HydroCAD Prepared by Westwood Professional Services, Inc., Printed 6/10/2021 HydroCAD® 10.00-22 s/n 03363 © 2018 HydroCAD Software Solutions LLC Subcat Reach Pond Link 21-06-04 Pre Post HydroCAD Printed 6/10/2021Prepared by Westwood Professional Services, Inc. Page 2HydroCAD® 10.00-22 s/n 03363 © 2018 HydroCAD Software Solutions LLC Area Listing (selected nodes) Area (acres) CN Description (subcatchment-numbers) 1.047 80 >75% Grass cover, Good, HSG D (1E) 0.173 96 Gravel surface, HSG D (1E) 0.007 98 Paved parking, HSG D (1E) 1.227 82 TOTAL AREA MSE 24-hr 3 2-Year Rainfall=2.84"21-06-04 Pre Post HydroCAD Printed 6/10/2021Prepared by Westwood Professional Services, Inc. Page 3HydroCAD® 10.00-22 s/n 03363 © 2018 HydroCAD Software Solutions LLC Time span=1.00-72.00 hrs, dt=0.01 hrs, 7101 points Runoff by SCS TR-20 method, UH=SCS, Split Pervious/Imperv. Reach routing by Stor-Ind+Trans method - Pond routing by Stor-Ind method Runoff Area=53,458 sf 0.59% Impervious Runoff Depth=1.26"Subcatchment 1E: Existing Tc=10.0 min CN=82/98 Runoff=2.41 cfs 0.129 af Total Runoff Area = 1.227 ac Runoff Volume = 0.129 af Average Runoff Depth = 1.26" 99.41% Pervious = 1.220 ac 0.59% Impervious = 0.007 ac MSE 24-hr 3 2-Year Rainfall=2.84"21-06-04 Pre Post HydroCAD Printed 6/10/2021Prepared by Westwood Professional Services, Inc. Page 4HydroCAD® 10.00-22 s/n 03363 © 2018 HydroCAD Software Solutions LLC Summary for Subcatchment 1E: Existing Runoff =2.41 cfs @ 12.18 hrs, Volume=0.129 af, Depth= 1.26" Runoff by SCS TR-20 method, UH=SCS, Split Pervious/Imperv., Time Span= 1.00-72.00 hrs, dt= 0.01 hrs MSE 24-hr 3 2-Year Rainfall=2.84" Area (sf) CN Description 45,593 80 >75% Grass cover, Good, HSG D 7,552 96 Gravel surface, HSG D 313 98 Paved parking, HSG D 53,458 82 Weighted Average 53,145 82 99.41% Pervious Area 313 98 0.59% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet)(ft/ft) (ft/sec)(cfs) 10.0 Direct Entry, MSE 24-hr 3 10-Year Rainfall=4.20"21-06-04 Pre Post HydroCAD Printed 6/10/2021Prepared by Westwood Professional Services, Inc. Page 5HydroCAD® 10.00-22 s/n 03363 © 2018 HydroCAD Software Solutions LLC Time span=1.00-72.00 hrs, dt=0.01 hrs, 7101 points Runoff by SCS TR-20 method, UH=SCS, Split Pervious/Imperv. Reach routing by Stor-Ind+Trans method - Pond routing by Stor-Ind method Runoff Area=53,458 sf 0.59% Impervious Runoff Depth=2.38"Subcatchment 1E: Existing Tc=10.0 min CN=82/98 Runoff=4.54 cfs 0.244 af Total Runoff Area = 1.227 ac Runoff Volume = 0.244 af Average Runoff Depth = 2.38" 99.41% Pervious = 1.220 ac 0.59% Impervious = 0.007 ac MSE 24-hr 3 10-Year Rainfall=4.20"21-06-04 Pre Post HydroCAD Printed 6/10/2021Prepared by Westwood Professional Services, Inc. Page 6HydroCAD® 10.00-22 s/n 03363 © 2018 HydroCAD Software Solutions LLC Summary for Subcatchment 1E: Existing Runoff =4.54 cfs @ 12.18 hrs, Volume=0.244 af, Depth= 2.38" Runoff by SCS TR-20 method, UH=SCS, Split Pervious/Imperv., Time Span= 1.00-72.00 hrs, dt= 0.01 hrs MSE 24-hr 3 10-Year Rainfall=4.20" Area (sf) CN Description 45,593 80 >75% Grass cover, Good, HSG D 7,552 96 Gravel surface, HSG D 313 98 Paved parking, HSG D 53,458 82 Weighted Average 53,145 82 99.41% Pervious Area 313 98 0.59% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet)(ft/ft) (ft/sec)(cfs) 10.0 Direct Entry, MSE 24-hr 3 100-Year Rainfall=7.18"21-06-04 Pre Post HydroCAD Printed 6/10/2021Prepared by Westwood Professional Services, Inc. Page 7HydroCAD® 10.00-22 s/n 03363 © 2018 HydroCAD Software Solutions LLC Time span=1.00-72.00 hrs, dt=0.01 hrs, 7101 points Runoff by SCS TR-20 method, UH=SCS, Split Pervious/Imperv. Reach routing by Stor-Ind+Trans method - Pond routing by Stor-Ind method Runoff Area=53,458 sf 0.59% Impervious Runoff Depth=5.10"Subcatchment 1E: Existing Tc=10.0 min CN=82/98 Runoff=9.45 cfs 0.521 af Total Runoff Area = 1.227 ac Runoff Volume = 0.521 af Average Runoff Depth = 5.10" 99.41% Pervious = 1.220 ac 0.59% Impervious = 0.007 ac MSE 24-hr 3 100-Year Rainfall=7.18"21-06-04 Pre Post HydroCAD Printed 6/10/2021Prepared by Westwood Professional Services, Inc. Page 8HydroCAD® 10.00-22 s/n 03363 © 2018 HydroCAD Software Solutions LLC Summary for Subcatchment 1E: Existing Runoff =9.45 cfs @ 12.17 hrs, Volume=0.521 af, Depth= 5.10" Runoff by SCS TR-20 method, UH=SCS, Split Pervious/Imperv., Time Span= 1.00-72.00 hrs, dt= 0.01 hrs MSE 24-hr 3 100-Year Rainfall=7.18" Area (sf) CN Description 45,593 80 >75% Grass cover, Good, HSG D 7,552 96 Gravel surface, HSG D 313 98 Paved parking, HSG D 53,458 82 Weighted Average 53,145 82 99.41% Pervious Area 313 98 0.59% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet)(ft/ft) (ft/sec)(cfs) 10.0 Direct Entry, 1P To UG System 2P Direct off-site 3P Total Proposed 4P UG System Routing Diagram for 21-06-04 Pre Post HydroCAD Prepared by Westwood Professional Services, Inc., Printed 6/10/2021 HydroCAD® 10.00-22 s/n 03363 © 2018 HydroCAD Software Solutions LLC Subcat Reach Pond Link 21-06-04 Pre Post HydroCAD Printed 6/10/2021Prepared by Westwood Professional Services, Inc. Page 2HydroCAD® 10.00-22 s/n 03363 © 2018 HydroCAD Software Solutions LLC Area Listing (selected nodes) Area (acres) CN Description (subcatchment-numbers) 0.281 80 >75% Grass cover, Good, HSG D (1P, 2P) 0.947 98 Paved parking, HSG D (1P, 2P) 1.227 94 TOTAL AREA MSE 24-hr 3 2-Year Rainfall=2.84"21-06-04 Pre Post HydroCAD Printed 6/10/2021Prepared by Westwood Professional Services, Inc. Page 3HydroCAD® 10.00-22 s/n 03363 © 2018 HydroCAD Software Solutions LLC Time span=1.00-72.00 hrs, dt=0.01 hrs, 7101 points Runoff by SCS TR-20 method, UH=SCS, Split Pervious/Imperv. Reach routing by Stor-Ind+Trans method - Pond routing by Stor-Ind method Runoff Area=47,042 sf 85.72% Impervious Runoff Depth=2.40"Subcatchment 1P: To UG System Tc=10.0 min CN=80/98 Runoff=3.58 cfs 0.216 af Runoff Area=6,416 sf 14.18% Impervious Runoff Depth=1.34"Subcatchment 2P: Direct off-site Tc=5.0 min CN=80/98 Runoff=0.37 cfs 0.016 af Inflow=2.21 cfs 0.224 afReach 3P: Total Proposed Outflow=2.21 cfs 0.224 af Peak Elev=918.84' Storage=2,355 cf Inflow=3.58 cfs 0.216 afPond 4P: UG System Outflow=2.09 cfs 0.207 af Total Runoff Area = 1.227 ac Runoff Volume = 0.232 af Average Runoff Depth = 2.27" 22.87% Pervious = 0.281 ac 77.13% Impervious = 0.947 ac MSE 24-hr 3 2-Year Rainfall=2.84"21-06-04 Pre Post HydroCAD Printed 6/10/2021Prepared by Westwood Professional Services, Inc. Page 4HydroCAD® 10.00-22 s/n 03363 © 2018 HydroCAD Software Solutions LLC Summary for Subcatchment 1P: To UG System Runoff =3.58 cfs @ 12.17 hrs, Volume=0.216 af, Depth= 2.40" Runoff by SCS TR-20 method, UH=SCS, Split Pervious/Imperv., Time Span= 1.00-72.00 hrs, dt= 0.01 hrs MSE 24-hr 3 2-Year Rainfall=2.84" Area (sf) CN Description 40,324 98 Paved parking, HSG D 6,718 80 >75% Grass cover, Good, HSG D 47,042 95 Weighted Average 6,718 80 14.28% Pervious Area 40,324 98 85.72% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet)(ft/ft) (ft/sec)(cfs) 10.0 Direct Entry, MSE 24-hr 3 2-Year Rainfall=2.84"21-06-04 Pre Post HydroCAD Printed 6/10/2021Prepared by Westwood Professional Services, Inc. Page 5HydroCAD® 10.00-22 s/n 03363 © 2018 HydroCAD Software Solutions LLC Summary for Subcatchment 2P: Direct off-site Runoff =0.37 cfs @ 12.13 hrs, Volume=0.016 af, Depth= 1.34" Runoff by SCS TR-20 method, UH=SCS, Split Pervious/Imperv., Time Span= 1.00-72.00 hrs, dt= 0.01 hrs MSE 24-hr 3 2-Year Rainfall=2.84" Area (sf) CN Description 910 98 Paved parking, HSG D 5,506 80 >75% Grass cover, Good, HSG D 6,416 83 Weighted Average 5,506 80 85.82% Pervious Area 910 98 14.18% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet)(ft/ft) (ft/sec)(cfs) 5.0 Direct Entry, MSE 24-hr 3 2-Year Rainfall=2.84"21-06-04 Pre Post HydroCAD Printed 6/10/2021Prepared by Westwood Professional Services, Inc. Page 6HydroCAD® 10.00-22 s/n 03363 © 2018 HydroCAD Software Solutions LLC Summary for Reach 3P: Total Proposed Inflow Area =1.227 ac, 77.13% Impervious, Inflow Depth = 2.19" for 2-Year event Inflow =2.21 cfs @ 12.27 hrs, Volume=0.224 af Outflow =2.21 cfs @ 12.27 hrs, Volume=0.224 af, Atten= 0%, Lag= 0.0 min Routing by Stor-Ind+Trans method, Time Span= 1.00-72.00 hrs, dt= 0.01 hrs MSE 24-hr 3 2-Year Rainfall=2.84"21-06-04 Pre Post HydroCAD Printed 6/10/2021Prepared by Westwood Professional Services, Inc. Page 7HydroCAD® 10.00-22 s/n 03363 © 2018 HydroCAD Software Solutions LLC Summary for Pond 4P: UG System Inflow Area =1.080 ac, 85.72% Impervious, Inflow Depth = 2.40" for 2-Year event Inflow =3.58 cfs @ 12.17 hrs, Volume=0.216 af Outflow =2.09 cfs @ 12.28 hrs, Volume=0.207 af, Atten= 42%, Lag= 6.7 min Primary =2.09 cfs @ 12.28 hrs, Volume=0.207 af Routing by Stor-Ind method, Time Span= 1.00-72.00 hrs, dt= 0.01 hrs Peak Elev= 918.84' @ 12.28 hrs Surf.Area= 1,889 sf Storage= 2,355 cf Plug-Flow detention time= 66.2 min calculated for 0.207 af (96% of inflow) Center-of-Mass det. time= 44.7 min ( 806.6 - 762.0 ) Volume Invert Avail.Storage Storage Description #1A 917.00'1,726 cf 25.25'W x 74.82'L x 3.50'H Field A 6,612 cf Overall - 2,297 cf Embedded = 4,315 cf x 40.0% Voids #2A 917.50'2,297 cf ADS_StormTech SC-740 +Cap x 50 Inside #1 Effective Size= 44.6"W x 30.0"H => 6.45 sf x 7.12'L = 45.9 cf Overall Size= 51.0"W x 30.0"H x 7.56'L with 0.44' Overlap 5 Rows of 10 Chambers 4,023 cf Total Available Storage Storage Group A created with Chamber Wizard Device Routing Invert Outlet Devices #1 Primary 917.50'15.0" Round Culvert L= 5.0' RCP, square edge headwall, Ke= 0.500 Inlet / Outlet Invert= 917.50' / 917.40' S= 0.0200 '/' Cc= 0.900 n= 0.012 Concrete pipe, finished, Flow Area= 1.23 sf #2 Device 1 917.50'9.0" Vert. Orifice/Grate C= 0.600 #3 Device 1 919.25'4.0' long Sharp-Crested Rectangular Weir 2 End Contraction(s) Primary OutFlow Max=2.09 cfs @ 12.28 hrs HW=918.84' (Free Discharge) 1=Culvert (Passes 2.09 cfs of 4.46 cfs potential flow) 2=Orifice/Grate (Orifice Controls 2.09 cfs @ 4.73 fps) 3=Sharp-Crested Rectangular Weir ( Controls 0.00 cfs) MSE 24-hr 3 2-Year Rainfall=2.84"21-06-04 Pre Post HydroCAD Printed 6/10/2021Prepared by Westwood Professional Services, Inc. Page 8HydroCAD® 10.00-22 s/n 03363 © 2018 HydroCAD Software Solutions LLC Stage-Area-Storage for Pond 4P: UG System Elevation (feet) Storage (cubic-feet) 917.00 0 917.05 38 917.10 76 917.15 113 917.20 151 917.25 189 917.30 227 917.35 264 917.40 302 917.45 340 917.50 378 917.55 455 917.60 533 917.65 610 917.70 687 917.75 764 917.80 841 917.85 917 917.90 993 917.95 1,069 918.00 1,145 918.05 1,220 918.10 1,295 918.15 1,369 918.20 1,444 918.25 1,517 918.30 1,591 918.35 1,664 918.40 1,736 918.45 1,809 918.50 1,880 918.55 1,952 918.60 2,022 918.65 2,093 918.70 2,162 918.75 2,232 918.80 2,300 918.85 2,368 918.90 2,435 918.95 2,502 919.00 2,568 919.05 2,634 919.10 2,698 919.15 2,762 919.20 2,825 919.25 2,887 919.30 2,948 919.35 3,008 919.40 3,067 919.45 3,124 919.50 3,181 919.55 3,236 919.60 3,290 919.65 3,342 Elevation (feet) Storage (cubic-feet) 919.70 3,392 919.75 3,439 919.80 3,484 919.85 3,526 919.90 3,567 919.95 3,607 920.00 3,645 920.05 3,683 920.10 3,721 920.15 3,758 920.20 3,796 920.25 3,834 920.30 3,872 920.35 3,910 920.40 3,947 920.45 3,985 920.50 4,023 MSE 24-hr 3 10-Year Rainfall=4.20"21-06-04 Pre Post HydroCAD Printed 6/10/2021Prepared by Westwood Professional Services, Inc. Page 9HydroCAD® 10.00-22 s/n 03363 © 2018 HydroCAD Software Solutions LLC Time span=1.00-72.00 hrs, dt=0.01 hrs, 7101 points Runoff by SCS TR-20 method, UH=SCS, Split Pervious/Imperv. Reach routing by Stor-Ind+Trans method - Pond routing by Stor-Ind method Runoff Area=47,042 sf 85.72% Impervious Runoff Depth=3.71"Subcatchment 1P: To UG System Tc=10.0 min CN=80/98 Runoff=5.47 cfs 0.334 af Runoff Area=6,416 sf 14.18% Impervious Runoff Depth=2.46"Subcatchment 2P: Direct off-site Tc=5.0 min CN=80/98 Runoff=0.68 cfs 0.030 af Inflow=4.48 cfs 0.356 afReach 3P: Total Proposed Outflow=4.48 cfs 0.356 af Peak Elev=919.49' Storage=3,170 cf Inflow=5.47 cfs 0.334 afPond 4P: UG System Outflow=4.23 cfs 0.326 af Total Runoff Area = 1.227 ac Runoff Volume = 0.364 af Average Runoff Depth = 3.56" 22.87% Pervious = 0.281 ac 77.13% Impervious = 0.947 ac MSE 24-hr 3 10-Year Rainfall=4.20"21-06-04 Pre Post HydroCAD Printed 6/10/2021Prepared by Westwood Professional Services, Inc. Page 10HydroCAD® 10.00-22 s/n 03363 © 2018 HydroCAD Software Solutions LLC Summary for Subcatchment 1P: To UG System Runoff =5.47 cfs @ 12.17 hrs, Volume=0.334 af, Depth= 3.71" Runoff by SCS TR-20 method, UH=SCS, Split Pervious/Imperv., Time Span= 1.00-72.00 hrs, dt= 0.01 hrs MSE 24-hr 3 10-Year Rainfall=4.20" Area (sf) CN Description 40,324 98 Paved parking, HSG D 6,718 80 >75% Grass cover, Good, HSG D 47,042 95 Weighted Average 6,718 80 14.28% Pervious Area 40,324 98 85.72% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet)(ft/ft) (ft/sec)(cfs) 10.0 Direct Entry, MSE 24-hr 3 10-Year Rainfall=4.20"21-06-04 Pre Post HydroCAD Printed 6/10/2021Prepared by Westwood Professional Services, Inc. Page 11HydroCAD® 10.00-22 s/n 03363 © 2018 HydroCAD Software Solutions LLC Summary for Subcatchment 2P: Direct off-site Runoff =0.68 cfs @ 12.12 hrs, Volume=0.030 af, Depth= 2.46" Runoff by SCS TR-20 method, UH=SCS, Split Pervious/Imperv., Time Span= 1.00-72.00 hrs, dt= 0.01 hrs MSE 24-hr 3 10-Year Rainfall=4.20" Area (sf) CN Description 910 98 Paved parking, HSG D 5,506 80 >75% Grass cover, Good, HSG D 6,416 83 Weighted Average 5,506 80 85.82% Pervious Area 910 98 14.18% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet)(ft/ft) (ft/sec)(cfs) 5.0 Direct Entry, MSE 24-hr 3 10-Year Rainfall=4.20"21-06-04 Pre Post HydroCAD Printed 6/10/2021Prepared by Westwood Professional Services, Inc. Page 12HydroCAD® 10.00-22 s/n 03363 © 2018 HydroCAD Software Solutions LLC Summary for Reach 3P: Total Proposed Inflow Area =1.227 ac, 77.13% Impervious, Inflow Depth = 3.48" for 10-Year event Inflow =4.48 cfs @ 12.24 hrs, Volume=0.356 af Outflow =4.48 cfs @ 12.24 hrs, Volume=0.356 af, Atten= 0%, Lag= 0.0 min Routing by Stor-Ind+Trans method, Time Span= 1.00-72.00 hrs, dt= 0.01 hrs MSE 24-hr 3 10-Year Rainfall=4.20"21-06-04 Pre Post HydroCAD Printed 6/10/2021Prepared by Westwood Professional Services, Inc. Page 13HydroCAD® 10.00-22 s/n 03363 © 2018 HydroCAD Software Solutions LLC Summary for Pond 4P: UG System Inflow Area =1.080 ac, 85.72% Impervious, Inflow Depth = 3.71" for 10-Year event Inflow =5.47 cfs @ 12.17 hrs, Volume=0.334 af Outflow =4.23 cfs @ 12.24 hrs, Volume=0.326 af, Atten= 23%, Lag= 4.2 min Primary =4.23 cfs @ 12.24 hrs, Volume=0.326 af Routing by Stor-Ind method, Time Span= 1.00-72.00 hrs, dt= 0.01 hrs Peak Elev= 919.49' @ 12.24 hrs Surf.Area= 1,889 sf Storage= 3,170 cf Plug-Flow detention time= 52.4 min calculated for 0.326 af (97% of inflow) Center-of-Mass det. time= 37.4 min ( 793.6 - 756.2 ) Volume Invert Avail.Storage Storage Description #1A 917.00'1,726 cf 25.25'W x 74.82'L x 3.50'H Field A 6,612 cf Overall - 2,297 cf Embedded = 4,315 cf x 40.0% Voids #2A 917.50'2,297 cf ADS_StormTech SC-740 +Cap x 50 Inside #1 Effective Size= 44.6"W x 30.0"H => 6.45 sf x 7.12'L = 45.9 cf Overall Size= 51.0"W x 30.0"H x 7.56'L with 0.44' Overlap 5 Rows of 10 Chambers 4,023 cf Total Available Storage Storage Group A created with Chamber Wizard Device Routing Invert Outlet Devices #1 Primary 917.50'15.0" Round Culvert L= 5.0' RCP, square edge headwall, Ke= 0.500 Inlet / Outlet Invert= 917.50' / 917.40' S= 0.0200 '/' Cc= 0.900 n= 0.012 Concrete pipe, finished, Flow Area= 1.23 sf #2 Device 1 917.50'9.0" Vert. Orifice/Grate C= 0.600 #3 Device 1 919.25'4.0' long Sharp-Crested Rectangular Weir 2 End Contraction(s) Primary OutFlow Max=4.22 cfs @ 12.24 hrs HW=919.49' (Free Discharge) 1=Culvert (Passes 4.22 cfs of 6.90 cfs potential flow) 2=Orifice/Grate (Orifice Controls 2.70 cfs @ 6.12 fps) 3=Sharp-Crested Rectangular Weir (Weir Controls 1.52 cfs @ 1.60 fps) MSE 24-hr 3 10-Year Rainfall=4.20"21-06-04 Pre Post HydroCAD Printed 6/10/2021Prepared by Westwood Professional Services, Inc. Page 14HydroCAD® 10.00-22 s/n 03363 © 2018 HydroCAD Software Solutions LLC Stage-Area-Storage for Pond 4P: UG System Elevation (feet) Storage (cubic-feet) 917.00 0 917.05 38 917.10 76 917.15 113 917.20 151 917.25 189 917.30 227 917.35 264 917.40 302 917.45 340 917.50 378 917.55 455 917.60 533 917.65 610 917.70 687 917.75 764 917.80 841 917.85 917 917.90 993 917.95 1,069 918.00 1,145 918.05 1,220 918.10 1,295 918.15 1,369 918.20 1,444 918.25 1,517 918.30 1,591 918.35 1,664 918.40 1,736 918.45 1,809 918.50 1,880 918.55 1,952 918.60 2,022 918.65 2,093 918.70 2,162 918.75 2,232 918.80 2,300 918.85 2,368 918.90 2,435 918.95 2,502 919.00 2,568 919.05 2,634 919.10 2,698 919.15 2,762 919.20 2,825 919.25 2,887 919.30 2,948 919.35 3,008 919.40 3,067 919.45 3,124 919.50 3,181 919.55 3,236 919.60 3,290 919.65 3,342 Elevation (feet) Storage (cubic-feet) 919.70 3,392 919.75 3,439 919.80 3,484 919.85 3,526 919.90 3,567 919.95 3,607 920.00 3,645 920.05 3,683 920.10 3,721 920.15 3,758 920.20 3,796 920.25 3,834 920.30 3,872 920.35 3,910 920.40 3,947 920.45 3,985 920.50 4,023 MSE 24-hr 3 100-Year Rainfall=7.18"21-06-04 Pre Post HydroCAD Printed 6/10/2021Prepared by Westwood Professional Services, Inc. Page 15HydroCAD® 10.00-22 s/n 03363 © 2018 HydroCAD Software Solutions LLC Time span=1.00-72.00 hrs, dt=0.01 hrs, 7101 points Runoff by SCS TR-20 method, UH=SCS, Split Pervious/Imperv. Reach routing by Stor-Ind+Trans method - Pond routing by Stor-Ind method Runoff Area=47,042 sf 85.72% Impervious Runoff Depth=6.64"Subcatchment 1P: To UG System Tc=10.0 min CN=80/98 Runoff=9.63 cfs 0.598 af Runoff Area=6,416 sf 14.18% Impervious Runoff Depth=5.16"Subcatchment 2P: Direct off-site Tc=5.0 min CN=80/98 Runoff=1.39 cfs 0.063 af Inflow=9.13 cfs 0.653 afReach 3P: Total Proposed Outflow=9.13 cfs 0.653 af Peak Elev=920.20' Storage=3,796 cf Inflow=9.63 cfs 0.598 afPond 4P: UG System Outflow=8.51 cfs 0.589 af Total Runoff Area = 1.227 ac Runoff Volume = 0.661 af Average Runoff Depth = 6.47" 22.87% Pervious = 0.281 ac 77.13% Impervious = 0.947 ac MSE 24-hr 3 100-Year Rainfall=7.18"21-06-04 Pre Post HydroCAD Printed 6/10/2021Prepared by Westwood Professional Services, Inc. Page 16HydroCAD® 10.00-22 s/n 03363 © 2018 HydroCAD Software Solutions LLC Summary for Subcatchment 1P: To UG System Runoff =9.63 cfs @ 12.17 hrs, Volume=0.598 af, Depth= 6.64" Runoff by SCS TR-20 method, UH=SCS, Split Pervious/Imperv., Time Span= 1.00-72.00 hrs, dt= 0.01 hrs MSE 24-hr 3 100-Year Rainfall=7.18" Area (sf) CN Description 40,324 98 Paved parking, HSG D 6,718 80 >75% Grass cover, Good, HSG D 47,042 95 Weighted Average 6,718 80 14.28% Pervious Area 40,324 98 85.72% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet)(ft/ft) (ft/sec)(cfs) 10.0 Direct Entry, MSE 24-hr 3 100-Year Rainfall=7.18"21-06-04 Pre Post HydroCAD Printed 6/10/2021Prepared by Westwood Professional Services, Inc. Page 17HydroCAD® 10.00-22 s/n 03363 © 2018 HydroCAD Software Solutions LLC Summary for Subcatchment 2P: Direct off-site Runoff =1.39 cfs @ 12.12 hrs, Volume=0.063 af, Depth= 5.16" Runoff by SCS TR-20 method, UH=SCS, Split Pervious/Imperv., Time Span= 1.00-72.00 hrs, dt= 0.01 hrs MSE 24-hr 3 100-Year Rainfall=7.18" Area (sf) CN Description 910 98 Paved parking, HSG D 5,506 80 >75% Grass cover, Good, HSG D 6,416 83 Weighted Average 5,506 80 85.82% Pervious Area 910 98 14.18% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet)(ft/ft) (ft/sec)(cfs) 5.0 Direct Entry, MSE 24-hr 3 100-Year Rainfall=7.18"21-06-04 Pre Post HydroCAD Printed 6/10/2021Prepared by Westwood Professional Services, Inc. Page 18HydroCAD® 10.00-22 s/n 03363 © 2018 HydroCAD Software Solutions LLC Summary for Reach 3P: Total Proposed Inflow Area =1.227 ac, 77.13% Impervious, Inflow Depth = 6.38" for 100-Year event Inflow =9.13 cfs @ 12.20 hrs, Volume=0.653 af Outflow =9.13 cfs @ 12.20 hrs, Volume=0.653 af, Atten= 0%, Lag= 0.0 min Routing by Stor-Ind+Trans method, Time Span= 1.00-72.00 hrs, dt= 0.01 hrs MSE 24-hr 3 100-Year Rainfall=7.18"21-06-04 Pre Post HydroCAD Printed 6/10/2021Prepared by Westwood Professional Services, Inc. Page 19HydroCAD® 10.00-22 s/n 03363 © 2018 HydroCAD Software Solutions LLC Summary for Pond 4P: UG System Inflow Area =1.080 ac, 85.72% Impervious, Inflow Depth = 6.64" for 100-Year event Inflow =9.63 cfs @ 12.17 hrs, Volume=0.598 af Outflow =8.51 cfs @ 12.22 hrs, Volume=0.589 af, Atten= 12%, Lag= 2.7 min Primary =8.51 cfs @ 12.22 hrs, Volume=0.589 af Routing by Stor-Ind method, Time Span= 1.00-72.00 hrs, dt= 0.01 hrs Peak Elev= 920.20' @ 12.22 hrs Surf.Area= 1,889 sf Storage= 3,796 cf Plug-Flow detention time= 36.5 min calculated for 0.589 af (99% of inflow) Center-of-Mass det. time= 27.7 min ( 777.3 - 749.5 ) Volume Invert Avail.Storage Storage Description #1A 917.00'1,726 cf 25.25'W x 74.82'L x 3.50'H Field A 6,612 cf Overall - 2,297 cf Embedded = 4,315 cf x 40.0% Voids #2A 917.50'2,297 cf ADS_StormTech SC-740 +Cap x 50 Inside #1 Effective Size= 44.6"W x 30.0"H => 6.45 sf x 7.12'L = 45.9 cf Overall Size= 51.0"W x 30.0"H x 7.56'L with 0.44' Overlap 5 Rows of 10 Chambers 4,023 cf Total Available Storage Storage Group A created with Chamber Wizard Device Routing Invert Outlet Devices #1 Primary 917.50'15.0" Round Culvert L= 5.0' RCP, square edge headwall, Ke= 0.500 Inlet / Outlet Invert= 917.50' / 917.40' S= 0.0200 '/' Cc= 0.900 n= 0.012 Concrete pipe, finished, Flow Area= 1.23 sf #2 Device 1 917.50'9.0" Vert. Orifice/Grate C= 0.600 #3 Device 1 919.25'4.0' long Sharp-Crested Rectangular Weir 2 End Contraction(s) Primary OutFlow Max=8.51 cfs @ 12.22 hrs HW=920.20' (Free Discharge) 1=Culvert (Inlet Controls 8.51 cfs @ 6.93 fps) 2=Orifice/Grate (Passes < 3.24 cfs potential flow) 3=Sharp-Crested Rectangular Weir (Passes < 11.49 cfs potential flow) MSE 24-hr 3 100-Year Rainfall=7.18"21-06-04 Pre Post HydroCAD Printed 6/10/2021Prepared by Westwood Professional Services, Inc. Page 20HydroCAD® 10.00-22 s/n 03363 © 2018 HydroCAD Software Solutions LLC Stage-Area-Storage for Pond 4P: UG System Elevation (feet) Storage (cubic-feet) 917.00 0 917.05 38 917.10 76 917.15 113 917.20 151 917.25 189 917.30 227 917.35 264 917.40 302 917.45 340 917.50 378 917.55 455 917.60 533 917.65 610 917.70 687 917.75 764 917.80 841 917.85 917 917.90 993 917.95 1,069 918.00 1,145 918.05 1,220 918.10 1,295 918.15 1,369 918.20 1,444 918.25 1,517 918.30 1,591 918.35 1,664 918.40 1,736 918.45 1,809 918.50 1,880 918.55 1,952 918.60 2,022 918.65 2,093 918.70 2,162 918.75 2,232 918.80 2,300 918.85 2,368 918.90 2,435 918.95 2,502 919.00 2,568 919.05 2,634 919.10 2,698 919.15 2,762 919.20 2,825 919.25 2,887 919.30 2,948 919.35 3,008 919.40 3,067 919.45 3,124 919.50 3,181 919.55 3,236 919.60 3,290 919.65 3,342 Elevation (feet) Storage (cubic-feet) 919.70 3,392 919.75 3,439 919.80 3,484 919.85 3,526 919.90 3,567 919.95 3,607 920.00 3,645 920.05 3,683 920.10 3,721 920.15 3,758 920.20 3,796 920.25 3,834 920.30 3,872 920.35 3,910 920.40 3,947 920.45 3,985 920.50 4,023