Loading...
2021-03-15 Pine Grove SW report revision 4 Allen Place, Northampton, MA 01060 (413) 582-7000 bdg@berkshiredesign.com Berkshire Design Group March 15, 2021 Doug McDonald Northampton DPW RE: Pine Grove – 254 Old Wilson Road, Northampton, MA Stormwater revisions Dear Doug, This letter report presents stormwater design revisions since the original submittal of this Special Permit in November 2019. The revised plans include updated driveways, building locations, and footprints. New lot lines are also proposed. The major changes are as follows:  The existing house on Lot 1 will be demolished and a larger new home will be built further back from Wilson Road at the end of a 250’ driveway just north of the former golf course.  The Flag lot has been reconfigured with the larger new home at a lower elevation at the back of the lot.  The existing road which serves Lots 2, 3, and 4 will be reduced in width.  Plans for Lot 2 include a larger home than what was previously shown as well as a circular driveway.  The proposed homes on Lots 3 and 4 have been relocated away from the cell tower and at lower elevations. The driveway accessing the lot 3 and 4 homes has been reconfigured.  See plan for new lot lines. Groundcover and Impervious Calculations: Although there is an increase in impervious area from the 2019 submittal, proposed impervious area remains well below existing impervious area within the 5-lot subdivision. Table 1 provides an overall summary of the groundcovers for existing conditions, the 2019 plan and the current plan. Table 2 provides the change in impervious area data on a per lot basis. Note that the lot boundaries have been changed to accommodate new house locations in the 2021 plan. Table 1: Comparison of Existing and Proposed Groundcover for 5-Lot Drainage Area * The existing impervious areas consisting of asphalt pavement, roofs, gravel and dirt paths and parking areas have been estimated from aerial photos. Groundcover Breakdown For 5-lot drainage area Impervious (roof/pave) - ac. - Impervious (gravel/dirt) - ac. - Open Space - ac. - Woods - ac. - Existing* 1.77 1.30 3.94 12.92 Proposed (2019) 2.01 0.03 5.43 12.45 Proposed (current) 2.21 0.12 5.98 11.62 March 15, 2021 Pine Grove Golf Course – 254 Old Wilson Road, Northampton, MA Revised Stormwater Letter Report Page 2 of 4 4 Allen Place, Northampton, MA 01060 (413) 582-7000 bdg@berkshiredesign.com Table 2: Comparison of Existing and Proposed Impervious by Lot * Lot 2 includes cell tower and access (384 sq. ft. roof, 5,334 sq. ft. gravel/dirt). Phasing: Lot 2 will be constructed first resulting in a decrease in impervious area of more than 36,000 sf within the 5-lot drainage area. Given that that the bulk of the impervious area is within Lot 2, there is no construction sequence, with Lot 2 being constructed first, that would result in more impervious cover created than currently exists. This is illustrated in Table 3. Table 3: Phasing Impact on Impervious Area Peak Runoff: Table 4 provides the results of the hydraulic analysis for the 5-lot drainage area which encompasses the development and contributing upstream area. The modeling takes into account the existing and proposed Existing Impervious (roof and pave) - sq. ft. - Existing Impervious (gravel and dirt) - sq. ft. - Existing Impervious TOTAL - sq. ft. - Proposed Impervious (roof and pave) - sq. ft. - Proposed Impervious (gravel and dirt) - sq. ft. - Proposed Impervious TOTAL - sq. ft. - Lot 1 2,746 13,163 15,909 10,500 0 10,500 Lot 2 43,107 33,961 77,068 35,630* 5,334* 40,964 Lot 3 0 0 0 6,660 0 6,660 Lot 4 0 0 0 3,560 0 3,560 Flag Lot 826 9,531 10,357 9,600 0 9,600 Total 46,679 56,655 103,334 65,950 5,334 71,284 Impervious area removed - sq. ft. - Impervious area added - sq. ft. - Net impervious - sq. ft. - Cumulative Impervious - sq. ft. - Lot 2 77,068 40,964 -36,104 -36,104 Lot 3 0 6,660 6,600 -29,444 Lot 4 0 3,560 3,560 -25,884 Lot 1 15,909 10,500 -5,409 -31,293 Flag Lot 10,357 9,600 -757 -32,050 March 15, 2021 Pine Grove Golf Course – 254 Old Wilson Road, Northampton, MA Revised Stormwater Letter Report Page 3 of 4 4 Allen Place, Northampton, MA 01060 (413) 582-7000 bdg@berkshiredesign.com impervious areas as well as the conversion of wooded areas to open space resulting from the construction. The HydroCAD model is attached. Table 4: Comparison of Existing and Proposed Peak Flow The modeling shows a decrease in peak flow for all storm events. Water Quality: The redevelopment of the site results in a decrease in the water quality impact based on the decrease in impervious area. The design of the proposed drainage includes sheet flow to forested or future meadow areas, and dry wells for roof area runoff infiltration. The drainage system currently in place and discharging directly to the golf course pond will be eliminated. A new catch basin with a sump will be constructed and the formerly piped flow will be daylighted, discharged over a level spreader and allowed to sheet flow into the conservation land. Water quality will be enhanced by the up to date catch basin and the level spreader/sheet flow. Most of the proposed driveways include a cross slope to allow runoff to sheet flow off into forested or meadow areas. Although the vegetated areas are steeply sloped in many areas, the distance to the stream exceed 500 feet and runoff travels through wooded and open space meadow areas. On the driveway to Lot 3, the cross slope is reversed to flow to the cutoff swale to the west to protect the steep slope to the east. Seven-hundred-gallon dry wells are proposed for each dwelling to provide infiltration of roof runoff. The proposed dry well volume provides storage for approximately 1/2” of runoff from each proposed house roof. 700 gal (93.6 cf) dry well = 1/2” of rainfall over 2,250 sf roof. The larger dwellings will include two dry wells or one larger dry well to accommodate the larger roof area. Runoff Conveyance along driveways: The existing riprap swale conveyance for the main driveway to Lots 2-4 is re-used with new catch basin outlet and conveyance pipe to level spreader. Along the driveway to Lots 3 and 4 which is also access to the cell tower, three additional 12” culverts are proposed to convey the tributary runoff over several locations. All of the culvert outlets include level spreaders. 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 March 15, 2021 Pine Grove Golf Course – 254 Old Wilson Road, Northampton, MA Revised Stormwater Letter Report Page 4 of 4 4 Allen Place, Northampton, MA 01060 (413) 582-7000 bdg@berkshiredesign.com The driveway to the Flag lot includes a swale on the south side which conveys flows east and west. Flows to the east are conveyed under the driveway to a level spreader. Flows to the west are conveyed to a swale, a second culvert under the Lot 1 driveway and then into the City swale on Old Wilson Road. As is standard practice, the 25-year storm has been used as the design storm for conveyances. Figure 6 provides information on the drainage area size, 25-year flow and pipe capacity for all proposed culverts. Erosion and Sediment control: The revised project plans include provisions for erosion control during construction. Silt fence along with a straw wattle is proposed down gradient of all proposed construction. The silt fence could be replaced by an organic filter berm which could be constructed from cleared trees. Soil stockpiles will be located away from drainage conveyances. A silt fence shall be placed around the perimeter of stockpiles. The steep slopes created by the lots 3/4 driveway will be restored and stabilized with double net straw/coconut biodegradable matting (East Coast Erosion control ECSB-2B) and seeded with New England Erosion Control/Restoration mix. If you have any questions or comments on this analysis, please do not hesitate to contact me. Sincerely, Berkshire Design Group Christopher Chamberland, P.E. Principal 275280285275270265255260 250260265FFE 262260FFE 280 .5 310 305 300 295290 285 280275260255250255265270275280290300310320330340355350x HP350340330320310300290280270260340330320310300 290 280 270 260 250 240 x HP267.0X253252250246270. 00 269 .00269.55 270 .00 269 .65 261 .00FFE=271.00TW 260 .5BW 255 .0268. 00 TW 269 .5BW 266 .0261.0 0 268 .75261. 00DDD D DDDDDDD D D D D D D D D D D D DDDDDD DSSSSSSSSD D D 275 SSOHWOHWOHWOHWOHWOHWOHWOHWOHWOHWOHWOHWOHWOHWOHWOHWOHWOHWOHWE/TE/TE/TE/TE/TE/TE/TE/TE E E EEEEEE EE E E E E EE EEEOHWOHWOHW27 0 255270 260 265290291 255260260265265 255255289290288287286285280277 270280 285 290 295 300 275 270 260 265 265 270 LOWER 266FFE 276 270275 27 8 + 2 7 0 . 5 +FFE 280 .5 275 270 285 285290 295 285 280 290291265 260 254 253 FFE 255 .5247.0+260260265270OHW OHW OHW D DDOHWOHWOHWOHWOHWOHWOHWOHWOHWOHWOHWOHWOHWOHWOHW OHWOHWOHWOHWOHWOHWOHWOHWFLAG LOTLOT 2LOT 1LOT 3LOT 4Checked 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.cWeb: http://www.berkshiredesign.comEmail: bdg@berkshiredesign.com (413) 582-70004 Allen Place, Northampton, Massachusetts 01060FAX (413) 582-7005Landscape ArchitectureCivil EngineeringPlanningBerkshireGroupDesignLand SurveyingFIG 5NOVEMBER 16, 20191"=100'LCPROPOSED DRAINAGE030015075450CCMARCH 15, 2021 - REVISED SITE PLAN 275280285275270265255260 250260265FFE 262260FFE 280 .5 310 305 300 295290 285 280275260255250255265270275280290300310320330340355350x HP350340330320310300290280270260340330320310300 290 280 270 260 250 240 x HP267.0X253252250246270.0 0 269 . 00 269 .55 270 .00 269 . 65 261 . 00FFE=271.00TW 260 .5 BW 2 5 5. 0268.0 0 TW 269 .5 BW 2 6 6 . 0 261.00 268 .75261.0 0DDDD DDD D DD D D D D D D D D D D D D DDDDDD DSSSSSSSSD D D 275 SSOHWOHWOHWOHWOHWOHWOHWOHWOHWOHWOHWOHWOHWOHWOHWOHWOHWOHWOHWE/TE/TE/TE/TE/TE/TE/TE/TOHWOHWOHW27 0 255270 260 265290291 255260260265265 255255 289290288287286285280277 270280 285 290 295 300 275 270 260 265 265 270 LOWER 266FFE 276270275 27 8 + 2 70 . 5 +FFE 280 .5 275 270 285 285290 295 285 280 290291265 260 254 253 FFE 255.5247.0+260260265270D DD Old Wilson Road FLAG LOTLOT 2LOT 1LOT 3LOT 4Checked 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.cWeb: 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 DRAINAGEIMPERVIOUS SUMMARYAND PIPE SIZING030015075450CCMARCH 15, 2021 - REVISED SITE PLAN 275280285275270265255260 250260265FFE 262260FFE 280.5 310 305 300 295290 285 280275260255250255265270275280290300310320330340355350x HP350340330320310300290280270260340330320310300 290 280 270 260 x HP267.0X253252250246FFE=271.00DDD DDD D D DDD D D D D D D D D D D D DDDDDD DDD D 275 E E E EEEEEEEE E E E E E EEEE270 255270 260 265290291 255260260265265 255255 289290288287286285280277 270280 285 290 295 300 275 270 260 265 265 270 LOWE R 266 FFE 2 76 270275 27 8 + 2 7 0 . 5 +FFE 280.5 275 270 285 285290 295 285 280 290291265 260 254 253 FFE 255.5247.0+260260265270D DD FLAG LOTLOT 2LOT 1LOT 3LOT 4Checked 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.cWeb: http://www.berkshiredesign.comEmail: bdg@berkshiredesign.com (413) 582-70004 Allen Place, Northampton, Massachusetts 01060FAX (413) 582-7005Landscape ArchitectureCivil EngineeringPlanningBerkshireGroupDesignLand SurveyingFIG 7MARCH 15, 20211"=150'LC5-LOT IMPERVIOUSSUMMARY030015075450CC E1 EX DA P1 PR DA Routing Diagram for 5-LOT EX_PROP REV 20210315 Prepared by Berkshire Design Group, Printed 3/15/2021 HydroCAD® 10.00-24 s/n 10759 © 2018 HydroCAD Software Solutions LLC Subcat Reach Pond Link 5-LOT EX_PROP REV 20210315 Printed 3/15/2021Prepared by Berkshire Design Group Page 2HydroCAD® 10.00-24 s/n 10759 © 2018 HydroCAD Software Solutions LLC Project Notes Rainfall events imported from "NRCS-Rain.txt" for 4213 MA Northampton Hampshire County Rainfall events imported from "NRCS-Rain.txt" for 4213 MA Northampton Hampshire County 5-LOT EX_PROP REV 20210315 Printed 3/15/2021Prepared by Berkshire Design Group Page 3HydroCAD® 10.00-24 s/n 10759 © 2018 HydroCAD Software Solutions LLC Area Listing (all nodes) Area (acres) CN Description (subcatchment-numbers) 1.813 74 >75% Grass cover, Good, HSG C (E1, P1) 8.102 80 >75% Grass cover, Good, HSG D (E1, P1) 1.423 96 Gravel surface, HSG D (E1, P1) 7.926 73 Woods, Fair, HSG C (E1, P1) 16.615 79 Woods, Fair, HSG D (E1, P1) 1.391 98 off site impervious (E1, P1) 1.514 98 on site impervious (P1) 1.072 98 on stie impervious - roofs and pave (E1) 39.855 80 TOTAL AREA 5-LOT EX_PROP REV 20210315 Printed 3/15/2021Prepared by Berkshire Design Group Page 4HydroCAD® 10.00-24 s/n 10759 © 2018 HydroCAD Software Solutions LLC Soil Listing (all nodes) Area (acres) Soil Group Subcatchment Numbers 0.000 HSG A 0.000 HSG B 9.739 HSG C E1, P1 26.140 HSG D E1, P1 3.976 Other E1, P1 39.855 TOTAL AREA 5-LOT EX_PROP REV 20210315 Printed 3/15/2021Prepared by Berkshire Design Group Page 5HydroCAD® 10.00-24 s/n 10759 © 2018 HydroCAD Software Solutions LLC Ground Covers (all nodes) HSG-A (acres) HSG-B (acres) HSG-C (acres) HSG-D (acres) Other (acres) Total (acres) Ground Cover Subcatchment Numbers 0.000 0.000 1.813 8.102 0.000 9.915 >75% Grass cover, Good 0.000 0.000 0.000 1.423 0.000 1.423 Gravel surface 0.000 0.000 7.926 16.615 0.000 24.541 Woods, Fair 0.000 0.000 0.000 0.000 1.391 1.391 off site impervious 0.000 0.000 0.000 0.000 1.514 1.514 on site impervious 0.000 0.000 0.000 0.000 1.072 1.072 on stie impervious - roofs and pave 0.000 0.000 9.739 26.140 3.976 39.855 TOTAL AREA NRCC 24-hr C 2-Year Rainfall=3.07"5-LOT EX_PROP REV 20210315 Printed 3/15/2021Prepared by Berkshire Design Group Page 6HydroCAD® 10.00-24 s/n 10759 © 2018 HydroCAD Software Solutions LLC Time span=5.00-24.00 hrs, dt=0.05 hrs, 381 points Runoff by SCS TR-20 method, UH=SCS, Weighted-CN Reach routing by Stor-Ind method - Pond routing by Stor-Ind method Runoff Area=868,040 sf 8.87% Impervious Runoff Depth>1.37"Subcatchment E1: EX DA Flow Length=800' Slope=0.1938 '/' Tc=5.9 min CN=81 Runoff=33.55 cfs 2.268 af Runoff Area=868,040 sf 11.09% Impervious Runoff Depth>1.30"Subcatchment P1: PR DA Flow Length=800' Slope=0.1938 '/' Tc=6.0 min CN=80 Runoff=31.79 cfs 2.160 af Total Runoff Area = 39.855 ac Runoff Volume = 4.428 af Average Runoff Depth = 1.33" 90.02% Pervious = 35.879 ac 9.98% Impervious = 3.976 ac NRCC 24-hr C 2-Year Rainfall=3.07"5-LOT EX_PROP REV 20210315 Printed 3/15/2021Prepared by Berkshire Design Group Page 7HydroCAD® 10.00-24 s/n 10759 © 2018 HydroCAD Software Solutions LLC Summary for Subcatchment E1: EX DA [49] Hint: Tc<2dt may require smaller dt Runoff = 33.55 cfs @ 12.13 hrs, Volume= 2.268 af, Depth> 1.37" Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 5.00-24.00 hrs, dt= 0.05 hrs NRCC 24-hr C 2-Year Rainfall=3.07" Area (sf) CN Description * 46,680 98 on stie impervious - roofs and pave 180,566 73 Woods, Fair, HSG C 382,242 79 Woods, Fair, HSG D 32,343 74 >75% Grass cover, Good, HSG C 56,655 96 Gravel surface, HSG D 139,264 80 >75% Grass cover, Good, HSG D * 30,290 98 off site impervious 868,040 81 Weighted Average 791,070 91.13% Pervious Area 76,970 8.87% 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' Summary for Subcatchment P1: PR DA Runoff = 31.79 cfs @ 12.13 hrs, Volume= 2.160 af, Depth> 1.30" Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 5.00-24.00 hrs, dt= 0.05 hrs NRCC 24-hr C 2-Year Rainfall=3.07" Area (sf) CN Description * 65,948 98 on site impervious 164,688 73 Woods, Fair, HSG C 341,506 79 Woods, Fair, HSG D * 5,334 96 Gravel surface, HSG D 46,620 74 >75% Grass cover, Good, HSG C 213,654 80 >75% Grass cover, Good, HSG D * 30,290 98 off site impervious 868,040 80 Weighted Average 771,802 88.91% Pervious Area 96,238 11.09% 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' NRCC 24-hr C 10-Year Rainfall=4.47"5-LOT EX_PROP REV 20210315 Printed 3/15/2021Prepared by Berkshire Design Group Page 8HydroCAD® 10.00-24 s/n 10759 © 2018 HydroCAD Software Solutions LLC Time span=5.00-24.00 hrs, dt=0.05 hrs, 381 points Runoff by SCS TR-20 method, UH=SCS, Weighted-CN Reach routing by Stor-Ind method - Pond routing by Stor-Ind method Runoff Area=868,040 sf 8.87% Impervious Runoff Depth>2.52"Subcatchment E1: EX DA Flow Length=800' Slope=0.1938 '/' Tc=5.9 min CN=81 Runoff=61.59 cfs 4.184 af Runoff Area=868,040 sf 11.09% Impervious Runoff Depth>2.43"Subcatchment P1: PR DA Flow Length=800' Slope=0.1938 '/' Tc=6.0 min CN=80 Runoff=59.40 cfs 4.040 af Total Runoff Area = 39.855 ac Runoff Volume = 8.224 af Average Runoff Depth = 2.48" 90.02% Pervious = 35.879 ac 9.98% Impervious = 3.976 ac NRCC 24-hr C 10-Year Rainfall=4.47"5-LOT EX_PROP REV 20210315 Printed 3/15/2021Prepared by Berkshire Design Group Page 9HydroCAD® 10.00-24 s/n 10759 © 2018 HydroCAD Software Solutions LLC Summary for Subcatchment E1: EX DA [49] Hint: Tc<2dt may require smaller dt Runoff = 61.59 cfs @ 12.13 hrs, Volume= 4.184 af, Depth> 2.52" Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 5.00-24.00 hrs, dt= 0.05 hrs NRCC 24-hr C 10-Year Rainfall=4.47" Area (sf) CN Description * 46,680 98 on stie impervious - roofs and pave 180,566 73 Woods, Fair, HSG C 382,242 79 Woods, Fair, HSG D 32,343 74 >75% Grass cover, Good, HSG C 56,655 96 Gravel surface, HSG D 139,264 80 >75% Grass cover, Good, HSG D * 30,290 98 off site impervious 868,040 81 Weighted Average 791,070 91.13% Pervious Area 76,970 8.87% 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' Summary for Subcatchment P1: PR DA Runoff = 59.40 cfs @ 12.13 hrs, Volume= 4.040 af, Depth> 2.43" Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 5.00-24.00 hrs, dt= 0.05 hrs NRCC 24-hr C 10-Year Rainfall=4.47" Area (sf) CN Description * 65,948 98 on site impervious 164,688 73 Woods, Fair, HSG C 341,506 79 Woods, Fair, HSG D * 5,334 96 Gravel surface, HSG D 46,620 74 >75% Grass cover, Good, HSG C 213,654 80 >75% Grass cover, Good, HSG D * 30,290 98 off site impervious 868,040 80 Weighted Average 771,802 88.91% Pervious Area 96,238 11.09% 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' NRCC 24-hr C 100-Year Rainfall=7.68"5-LOT EX_PROP REV 20210315 Printed 3/15/2021Prepared by Berkshire Design Group Page 10HydroCAD® 10.00-24 s/n 10759 © 2018 HydroCAD Software Solutions LLC Time span=5.00-24.00 hrs, dt=0.05 hrs, 381 points Runoff by SCS TR-20 method, UH=SCS, Weighted-CN Reach routing by Stor-Ind method - Pond routing by Stor-Ind method Runoff Area=868,040 sf 8.87% Impervious Runoff Depth>5.43"Subcatchment E1: EX DA Flow Length=800' Slope=0.1938 '/' Tc=5.9 min CN=81 Runoff=128.90 cfs 9.025 af Runoff Area=868,040 sf 11.09% Impervious Runoff Depth>5.32"Subcatchment P1: PR DA Flow Length=800' Slope=0.1938 '/' Tc=6.0 min CN=80 Runoff=126.31 cfs 8.835 af Total Runoff Area = 39.855 ac Runoff Volume = 17.860 af Average Runoff Depth = 5.38" 90.02% Pervious = 35.879 ac 9.98% Impervious = 3.976 ac NRCC 24-hr C 100-Year Rainfall=7.68"5-LOT EX_PROP REV 20210315 Printed 3/15/2021Prepared by Berkshire Design Group Page 11HydroCAD® 10.00-24 s/n 10759 © 2018 HydroCAD Software Solutions LLC Summary for Subcatchment E1: EX DA [49] Hint: Tc<2dt may require smaller dt Runoff = 128.90 cfs @ 12.13 hrs, Volume= 9.025 af, Depth> 5.43" Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 5.00-24.00 hrs, dt= 0.05 hrs NRCC 24-hr C 100-Year Rainfall=7.68" Area (sf) CN Description * 46,680 98 on stie impervious - roofs and pave 180,566 73 Woods, Fair, HSG C 382,242 79 Woods, Fair, HSG D 32,343 74 >75% Grass cover, Good, HSG C 56,655 96 Gravel surface, HSG D 139,264 80 >75% Grass cover, Good, HSG D * 30,290 98 off site impervious 868,040 81 Weighted Average 791,070 91.13% Pervious Area 76,970 8.87% 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' Summary for Subcatchment P1: PR DA Runoff = 126.31 cfs @ 12.13 hrs, Volume= 8.835 af, Depth> 5.32" Runoff by SCS TR-20 method, UH=SCS, Weighted-CN, Time Span= 5.00-24.00 hrs, dt= 0.05 hrs NRCC 24-hr C 100-Year Rainfall=7.68" Area (sf) CN Description * 65,948 98 on site impervious 164,688 73 Woods, Fair, HSG C 341,506 79 Woods, Fair, HSG D * 5,334 96 Gravel surface, HSG D 46,620 74 >75% Grass cover, Good, HSG C 213,654 80 >75% Grass cover, Good, HSG D * 30,290 98 off site impervious 868,040 80 Weighted Average 771,802 88.91% Pervious Area 96,238 11.09% 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'