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2019-12-18 Pine Grove Stormwater Management Report Supplement 4 Allen Place, Northampton, MA 01060 (413) 582-7000 bdg@berkshiredesign.com Berkshire Design Group December 18, 2019 Doug McDonald Northampton DPW RE: Pine Grove Golf Course – 254 Old Wilson Road, Northampton, MA Analysis of 5-lot subdivision Dear Doug: In response to our phone conversation on December 13, 2019 on the Stormwater Management Report for Pine Grove golf course, Berkshire Design has put together an additional hydraulic analysis focusing on the 5-lot subdivision area and runoff. The model includes the 5-lot area and an additional upstream tributary area which comprises approximately 7 acres of impervious, lawn/open space and wooded area. Table 1 summarizes the inputs to the model. It was assumed that the demolition areas (clubhouse, upper parking lot etc.) will become open space/lawn. Additional area was provided for each home to have an open space/lawn around the home. The analysis point is the boundary line between the proposed lots and the existing golf course. Table 2 provides the peak flow generated by the proposed subdivision. The hydraulic model is attached. Groundcover Breakdown Impervious (ac.) Gravel/Dirt (sq. ft.) Open Space (sq. ft.) Woods (sq. ft.) Existing 2.60 0.48 3.83 13.01 Proposed 2.01 0.03 5.43 12.45 Condition & Point of Analysis 2-Year Storm 3.07” 10-Year Storm 4.47” 100-Year Storm 7.68” Peak Flow Rate (cfs) Peak Flow Rate (cfs) Peak Flow Rate (cfs) Existing 33.55 61.59 128.90 Proposed 31.79 59.40 126.31 LOT 1FLAG LOTLOT 2LOT 3LOT 4Old Wilson Road Checked By:Drawn By:RevisionsScale:Date:Sheet NumberThis drawing is not intended nor shall it be used forconstruction purposes unless the signed professional seal of aregistered landscape architect, civil engineer or land surveyoremployed by The Berkshire Design Group, Inc. is affixed above.Do not scale drawing for quantity take-offs or construction. Usewritten dimensions only. If dimensions are incomplete, contactThe Berkshire Design Group Inc. for clarification.Copyright The Berkshire Design Group, Inc.This drawing and all of its contents are the express property ofThe Berkshire Design Group, Inc., and shall not be copied orused in any way without the written consent of The BerkshireDesign Group, Inc.cPINE GROVE GOLF COURSE254 OLD WILSON ROADNORTHAMPTON, MAWeb: http://www.berkshiredesign.comEmail: bdg@berkshiredesign.com (413) 582-70004 Allen Place, Northampton, Massachusetts 01060FAX (413) 582-7005Landscape ArchitectureCivil EngineeringPlanningBerkshireGroupDesignLand SurveyingFIG 6DECEMBER 18, 20191"=150'LC5-LOT DRAINAGE030015075450CC E1 EX DA P1 PR DA Routing Diagram for 5-LOT EX_PROP Prepared by Berkshire Design Group, Printed 12/18/2019 HydroCAD® 10.00-24 s/n 10759 © 2018 HydroCAD Software Solutions LLC Subcat Reach Pond Link NRCC 24-hr C 2-Year Rainfall=3.07"5-LOT EX_PROP Printed 12/18/2019Prepared by Berkshire Design Group Page 2HydroCAD® 10.00-24 s/n 10759 © 2018 HydroCAD Software Solutions LLC Summary for Subcatchment E1: EX DA Runoff = 33.55 cfs @ 12.13 hrs, Volume= 2.060 af, Depth> 1.24" Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 5.00-20.00 hrs, dt= 0.05 hrs NRCC 24-hr C 2-Year Rainfall=3.07" Area (sf) CN Description * 113,276 98 impervious 175,000 73 Woods, Fair, HSG C 391,858 79 Woods, Fair, HSG D 33,440 74 >75% Grass cover, Good, HSG C 20,926 96 Gravel surface, HSG D 133,540 80 >75% Grass cover, Good, HSG D 868,040 81 Weighted Average 754,764 86.95% Pervious Area 113,276 13.05% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 5.9 800 0.1938 2.28 Lag/CN Method, Contour Length= 33,648' Interval= 5' Subcatchment E1: EX DA Runoff Hydrograph Time (hours) 201918171615141312111098765Flow (cfs)36 34 32 30 28 26 24 22 20 18 16 14 12 10 8 6 4 2 0 NRCC 24-hr C 2-Year Rainfall=3.07" Runoff Area=868,040 sf Runoff Volume=2.060 af Runoff Depth>1.24" Flow Length=800' Slope=0.1938 '/' Tc=5.9 min CN=81 33.55 cfs NRCC 24-hr C 2-Year Rainfall=3.07"5-LOT EX_PROP Printed 12/18/2019Prepared by Berkshire Design Group Page 3HydroCAD® 10.00-24 s/n 10759 © 2018 HydroCAD Software Solutions LLC Summary for Subcatchment P1: PR DA Runoff = 31.79 cfs @ 12.13 hrs, Volume= 1.958 af, Depth> 1.18" Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 5.00-20.00 hrs, dt= 0.05 hrs NRCC 24-hr C 2-Year Rainfall=3.07" Area (sf) CN Description * 87,502 98 impervious 160,450 73 Woods, Fair, HSG C 382,070 79 Woods, Fair, HSG D * 1,500 96 Gravel surface, HSG D 43,480 74 >75% Grass cover, Good, HSG C 193,038 80 >75% Grass cover, Good, HSG D 868,040 80 Weighted Average 780,538 89.92% Pervious Area 87,502 10.08% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 6.0 800 0.1938 2.21 Lag/CN Method, Contour Length= 33,648' Interval= 5' Subcatchment P1: PR DA Runoff Hydrograph Time (hours) 201918171615141312111098765Flow (cfs)34 32 30 28 26 24 22 20 18 16 14 12 10 8 6 4 2 0 NRCC 24-hr C 2-Year Rainfall=3.07" Runoff Area=868,040 sf Runoff Volume=1.958 af Runoff Depth>1.18" Flow Length=800' Slope=0.1938 '/' Tc=6.0 min CN=80 31.79 cfs NRCC 24-hr C 10-Year Rainfall=4.47"5-LOT EX_PROP Printed 12/18/2019Prepared by Berkshire Design Group Page 4HydroCAD® 10.00-24 s/n 10759 © 2018 HydroCAD Software Solutions LLC Summary for Subcatchment E1: EX DA Runoff = 61.59 cfs @ 12.13 hrs, Volume= 3.845 af, Depth> 2.32" Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 5.00-20.00 hrs, dt= 0.05 hrs NRCC 24-hr C 10-Year Rainfall=4.47" Area (sf) CN Description * 113,276 98 impervious 175,000 73 Woods, Fair, HSG C 391,858 79 Woods, Fair, HSG D 33,440 74 >75% Grass cover, Good, HSG C 20,926 96 Gravel surface, HSG D 133,540 80 >75% Grass cover, Good, HSG D 868,040 81 Weighted Average 754,764 86.95% Pervious Area 113,276 13.05% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 5.9 800 0.1938 2.28 Lag/CN Method, Contour Length= 33,648' Interval= 5' Subcatchment E1: EX DA Runoff Hydrograph Time (hours) 201918171615141312111098765Flow (cfs)65 60 55 50 45 40 35 30 25 20 15 10 5 0 NRCC 24-hr C 10-Year Rainfall=4.47" Runoff Area=868,040 sf Runoff Volume=3.845 af Runoff Depth>2.32" Flow Length=800' Slope=0.1938 '/' Tc=5.9 min CN=81 61.59 cfs NRCC 24-hr C 10-Year Rainfall=4.47"5-LOT EX_PROP Printed 12/18/2019Prepared by Berkshire Design Group Page 5HydroCAD® 10.00-24 s/n 10759 © 2018 HydroCAD Software Solutions LLC Summary for Subcatchment P1: PR DA Runoff = 59.40 cfs @ 12.13 hrs, Volume= 3.707 af, Depth> 2.23" Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 5.00-20.00 hrs, dt= 0.05 hrs NRCC 24-hr C 10-Year Rainfall=4.47" Area (sf) CN Description * 87,502 98 impervious 160,450 73 Woods, Fair, HSG C 382,070 79 Woods, Fair, HSG D * 1,500 96 Gravel surface, HSG D 43,480 74 >75% Grass cover, Good, HSG C 193,038 80 >75% Grass cover, Good, HSG D 868,040 80 Weighted Average 780,538 89.92% Pervious Area 87,502 10.08% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 6.0 800 0.1938 2.21 Lag/CN Method, Contour Length= 33,648' Interval= 5' Subcatchment P1: PR DA Runoff Hydrograph Time (hours) 201918171615141312111098765Flow (cfs)65 60 55 50 45 40 35 30 25 20 15 10 5 0 NRCC 24-hr C 10-Year Rainfall=4.47" Runoff Area=868,040 sf Runoff Volume=3.707 af Runoff Depth>2.23" Flow Length=800' Slope=0.1938 '/' Tc=6.0 min CN=80 59.40 cfs NRCC 24-hr C 100-Year Rainfall=7.68"5-LOT EX_PROP Printed 12/18/2019Prepared by Berkshire Design Group Page 6HydroCAD® 10.00-24 s/n 10759 © 2018 HydroCAD Software Solutions LLC Summary for Subcatchment E1: EX DA Runoff = 128.90 cfs @ 12.13 hrs, Volume= 8.390 af, Depth> 5.05" Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 5.00-20.00 hrs, dt= 0.05 hrs NRCC 24-hr C 100-Year Rainfall=7.68" Area (sf) CN Description * 113,276 98 impervious 175,000 73 Woods, Fair, HSG C 391,858 79 Woods, Fair, HSG D 33,440 74 >75% Grass cover, Good, HSG C 20,926 96 Gravel surface, HSG D 133,540 80 >75% Grass cover, Good, HSG D 868,040 81 Weighted Average 754,764 86.95% Pervious Area 113,276 13.05% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 5.9 800 0.1938 2.28 Lag/CN Method, Contour Length= 33,648' Interval= 5' Subcatchment E1: EX DA Runoff Hydrograph Time (hours) 201918171615141312111098765Flow (cfs)140 130 120 110 100 90 80 70 60 50 40 30 20 10 0 NRCC 24-hr C 100-Year Rainfall=7.68" Runoff Area=868,040 sf Runoff Volume=8.390 af Runoff Depth>5.05" Flow Length=800' Slope=0.1938 '/' Tc=5.9 min CN=81 128.90 cfs NRCC 24-hr C 100-Year Rainfall=7.68"5-LOT EX_PROP Printed 12/18/2019Prepared by Berkshire Design Group Page 7HydroCAD® 10.00-24 s/n 10759 © 2018 HydroCAD Software Solutions LLC Summary for Subcatchment P1: PR DA Runoff = 126.31 cfs @ 12.13 hrs, Volume= 8.204 af, Depth> 4.94" Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 5.00-20.00 hrs, dt= 0.05 hrs NRCC 24-hr C 100-Year Rainfall=7.68" Area (sf) CN Description * 87,502 98 impervious 160,450 73 Woods, Fair, HSG C 382,070 79 Woods, Fair, HSG D * 1,500 96 Gravel surface, HSG D 43,480 74 >75% Grass cover, Good, HSG C 193,038 80 >75% Grass cover, Good, HSG D 868,040 80 Weighted Average 780,538 89.92% Pervious Area 87,502 10.08% Impervious Area Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 6.0 800 0.1938 2.21 Lag/CN Method, Contour Length= 33,648' Interval= 5' Subcatchment P1: PR DA Runoff Hydrograph Time (hours) 201918171615141312111098765Flow (cfs)140 130 120 110 100 90 80 70 60 50 40 30 20 10 0 NRCC 24-hr C 100-Year Rainfall=7.68" Runoff Area=868,040 sf Runoff Volume=8.204 af Runoff Depth>4.94" Flow Length=800' Slope=0.1938 '/' Tc=6.0 min CN=80 126.31 cfs