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Stormwater Analysis Report r STORMWATER ANALYSIS REPORT For a Proposed Single Family Residence Prepared for: Scott & Jackie Wheeler State Rt. 9L Tax Map # 239.18-1-27 Town of Queensbury Warren County New York Prepared by: G. Thomas Hutchins, P.E. Hutchins Engineering 169 Haviland Road Queensbury, NY 12804 January 8, 2008 Revision 1 — March 28, 2008 Project Description This project consists of the construction of a new asphalt driveway with associated slope stabilization and stormwater management and erosion controls on a 1.59 acre parcel owned by Scott and Jackie Wheeler on Rt. 9L on Lake George in the Town of Queensbury. The existing driveway is short and extremely steep and will be removed and partially re-vegetated. Site Conditions The parcel presently contains a main house, garage, guest house, guest cabin, patios and a short and very steep (+30% max slope) asphalt driveway. In order to achieve a reasonable grade for the new driveway, its length must be considerably longer than the existing drive. The new entrance is proposed to be located 120' to the east of the existing entrance. The first 30' of the driveway will come off perpendicular to Rt. 9N at a 6% grade then will make nearly a 90 degree turn and will traverse the side hill at a maximum grade of 15%. Finally, the driveway will flatten and will merge into the lower portion of the existing driveway. In order to create a parking area near the garage, the steep portion of the existing driveway which is on the Wheeler's property will be excavated and a boulder retaining wall will be installed to retain the bank. Fill slopes on the sides of the driveway will be stabilized erosion control blankets to allow vegetative plantings to establish and stabilize the slope naturally. The remaining asphalt from the existing drive will be removed and the area re-vegetated. Vegetation on the lot is a mixture of evergreen and hardwoods in fair condition with moderate density and size. The site slopes northerly towards the lake at an average grade of 12-18%. Site soils are mapped as Bice very bouldery fine sandy loam which are deep, well drained soils in wooded areas on hillsides. Drainage Methodology For major projects in the Lake George drainage basin, the Town of Queensbury requires that there will be no increase in runoff volume from a 10-year design storm and no increase in runoff rate from a 25-year design storm in predeveloped vs. developed site conditions. Presently there are no significant stormwater control measures on the site, runoff generally flows to Lake George. In the central portion of the lot, there is a 28" culvert which receives discharge from a 24" culvert under Rt. 9N and discharges to a channel which flows to the lake. Similarly, there is an intermittent drainage channel on the easterly property which also discharges to the lake. The proposed project amounts to a 2300 SF increase in impervious area due to the length of the new driveway that is required to minimize its slope while it traverses the side slope. Areas for stormwater retention areas are severely limited on the site due to the slopes and existing site features. A 100' setback from stormwater management devices to the lake for major projects also restricts the areas available for stormwater management. For this project, two vegetated retention areas are proposed, to be located on the south side of the driveway, on each side of the intermittent drainage channel in the middle of the parcel. The retention area west of the drainage channel will receive runoff from the existing driveway area which will become the new parking area. This retention area is sized to have 620 CF of storage with a rip-rap lined outlet channel which will outlet to the existing drainage channel. The retention area east of the drainage channel will receive runoff from the upper portion of the new driveway. This retention area is sized to have 450 CF of storage with a rip-rap lined outlet channel which will also outlet to the existing drainage channel. A 3% cross slope towards the south side of the new driveway is proposed, which will allow the runoff to sheet flow to the retention areas. A soils test pit was performed 100' east of the retention areas and revealed fine sandy loam and fine sands, with the seasonal high groundwater table at approximately 4 feet below existing grade. The westerly retention area is excavated approximately 4 feet into existing grade, therefore it is modeled as a wet retention area. For this retention area no infiltration credit is taken in the stormwater model. The easterly retention area is excavated approximately 2 feet into existing grade and will provide the required 2 feet of separation to seasonal high ground water. For this retention area, an infiltration rate of 1 inch per hour is taken in the stormwater model, and an infiltration trench constructed to frost depth in the bottom of bottom. Runoff calculations have been prepared utilizing SCS TR-20 methodology and HydroCAD analysis software for 10-year and 25-year Type II simulated rainfall distributions. Criteria utilized in the analysis are summarized as follows: Design Storm Events: 10 year, 24hr, Type II distribution, 3.9" 25 year, 24hr, Type II distribution, 4.4" Total Lot Area: 1.59 Acres Existing Buildings & Driveway: 6840 SF Proposed Driveway: 4215 SF Total Existing Impervious: 6840 SF Proposed Impervious: 9140 SF Total Disturbed Area: 10,300 SF Runoff computations for undeveloped, existing and proposed conditions have been completed for 10-year and 25-year recurrence interval 24 hr storm events over the entire parcel area. Calculations are attached and are summarized as follows: 101R1 RUNOFF EXISTING — 10-YR 1.61 CFS/0.145 AF PROPOSED— 10-YR 1.43 CFS/0.133 AF EXISTING - 25-YR 2.23 CFS / 0.187 AF PROPOSED - 25-YR 2.02 CFS /0.173 CF Full results of stormwater runoff computations are attached to this report. Operation and Maintenance Issues During construction, the contractor shall inspect the sediment control fence daily and after every rain event and remove trapped sediment and maintain the devices such that they are in good working order. Periodic maintenance is needed in order to ensure continuous and effective operation of the stormwater control practices. Maintenance includes debris removal in stormwater basins and culvert inlets and vegetation trimming of the stormwater basins. Sediment removal and inspection of the detention basin should be performed annually or as needed due to surrounding and contributing site conditions. Results The analyses show that the system of proposed retention basins are of adequate capacity to manage calculated runoff from the proposed construction without increasing peak calculated runoff rate or calculated runoff volume from the current conditions for 10-and 25-year design storms. Attachments Pre and Post Construction Subcatchment Maps HydroCAD Analysis for Type II 24 hr Rainfall = 3.9" (10 year) & 4.4" (25 year) - Existing & Proposed 10-Year - Existing & Proposed 25-Year EXISTING i z � i 2 I / . n oil PIl I1 I uuu ' 4 v I e d 9 � I 9 ! I ' I I �, l�l • CFI@ �i i i 1S 2S BUILDINGS & RIVE REM DER OF LOT 1L j LAKE GEORGE SUl7Cat iReachl on Link. Drainage Diagram for WHEELER CURRENT Prepared by HUTCHINS ENGINEERING 3/28/2008 HydroCA06 7.10 s/n 002373 0 2005 HydroCAD Software Solutions LLC WHEELER CURRENT Type 1124-hr 10-YEAR Rainfall=3.90" Prepared by HUTCHINS ENGINEERING Page 2 HydroCAD®7.10 s/n 002373 ©2005 HydroCAD Software Solutions LLC 3/28/2008 Time span=0.00-24.00 hrs, dt=0.05 hrs, 481 points Runoff by SCS TR-20 method, UH=SCS Reach routing by Stor-Ind+Trans method - Pond routing by Stor-Ind method Subcatchment 1S: BUILDINGS & DRIVE Runoff Area=6,840 sf Runoff Depth>3.66" Flow Length=50' Tc=6.2 min CN=98 Runoff=0.84 cfs 0.048 of Subcatchment 2S: REMAINDER OF LOT Runoff Area=71,865 sf Runoff Depth>0.71" Flow Length=150' Tc=14.9 min CN=60 Runoff=1.23 cfs 0.098 of Link 1L: LAKE GEORGE Inflow=1.61 cfs 0.145 of Primary=1.61 cfs 0.145 of Total Runoff Area = 1.807 ac Runoff Volume= 0.145 of Average Runoff Depth = 0.97" WHEELER CURRENT Type/1 24-hr 10-YEAR Rainfall=3.90" Prepared by HUTCHINS ENGINEERING Page 3 HydroCADO 7.10 s/n 002373 ©2005 HydroCAD Software Solutions LLC 3/28/2008 Subcatchment 1S: BUILDINGS & DRIVE Runoff = 0.84 cfs @ 11.96 hrs, Volume= 0.048 af, Depth> 3.66" Runoff by SCS TR-20 method, UH=SCS, Time Span= 0.00-24.00 hrs, dt= 0.05 hrs Type II 24-hr 10-YEAR Rainfall=3.90" Area (sf) CN Description 5,390 98 MAIN HOUSE & DRIVE 1,450 98 GUEST COTTAGE 6,840 98 Weighted Average Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 6.2 50 0.1800 0.1 Sheet Flow, Woods: Light underbrush n= 0.400 P2= 2.20" Subcatchment 2S: REMAINDER OF LOT Runoff = 1.23 cfs @ 12.10 hrs, Volume= 0.098 af, Depth> 0.71" Runoff by SCS TR-20 method, UH=SCS, Time Span= 0.00-24.00 hrs, dt= 0.05 hrs Type II 24-hr 10-YEAR Rainfall=3.90" Area (sf) CN Description 71,865 60 Woods, Fair, HSG B Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 14.9 150 0.1800 0.2 Sheet Flow, Woods: Light underbrush n= 0.400 P2= 2.20" Link 1L: LAKE GEORGE Inflow Area = 1.807 ac, Inflow Depth > 0.97" for 10-YEAR event Inflow = 1.61 cfs @ 12.04 hrs, Volume= 0.145 of Primary = 1.61 cfs @ 12.04 hrs, Volume= 0.145 af, Atten= 0%, Lag= 0.0 min Primary outflow = Inflow, Time Span=0.00-24.00 hrs, dt= 0.05 hrs WHEELER CURRENT Type/1 24-hr 25-YEAR Rainfall=4.40" Prepared by HUTCHINS ENGINEERING Page 4 HydroCADG 7.10 s/n 002373 ©2005 HydroCAD Software Solutions LLC 3/28/2008 Time span=0.00-24.00 hrs, dt=0.05 hrs, 481 points Runoff by SCS TR-20 method, UH=SCS Reach routing by Stor-Ind+Trans method - Pond routing by Stor-Ind method Subcatchment 1S: BUILDINGS& DRIVE Runoff Area=6,840 sf Runoff Depth>4.16" Flow Length=50' Tc=6.2 min CN=98 Runoff=0.95 cfs 0.054 of Subcatchment 2S: REMAINDER OF LOT Runoff Area=71,865 sf Runoff Depth>0.96" Flow Length=150' Tc=14.9 min CN=60 Runoff=1.79 cfs 0.132 of Link 1L: LAKE GEORGE Inflow=2.23 cfs 0.187 of Primary=2.23 cfs 0.187 of Total Runoff Area = 1.807 ac Runoff Volume = 0.187 of Average Runoff Depth = 1.24" WHEELER CURRENT Type 1124-hr 25-YEAR Rainfall=4.40" Prepared by HUTCHINS ENGINEERING Page 5 HydroCADO 7.10 s/n 002373 ©2005 HydroCAD Software Solutions LLC 3/28/2008 Subcatchment 1S: BUILDINGS & DRIVE Runoff = 0.95 cfs @ 11.96 hrs, Volume= 0.054 af, Depth> 4.16" Runoff by SCS TR-20 method, UH=SCS, Time Span= 0.00-24.00 hrs, dt= 0.05 hrs Type II 24-hr 25-YEAR Rainfall=4.40" Area (sf) CN Description 5,390 98 MAIN HOUSE & DRIVE 1,450 98 GUEST COTTAGE 6,840 98 Weighted Average Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 6.2 50 0.1800 0.1 Sheet Flow, Woods: Light underbrush n= 0.400 P2= 2.20" Subcatchment 2S: REMAINDER OF LOT Runoff = 1.79 cfs @ 12.09 hrs, Volume= 0.132 af, Depth> 0.96" Runoff by SCS TR-20 method, UH=SCS, Time Span= 0.00-24.00 hrs, dt= 0.05 hrs Type 11 24-hr 25-YEAR Rainfall=4.40" Area (sf) CN Description 71,865 60 Woods, Fair, HSG B Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 14.9 150 0.1800 0.2 Sheet Flow, Woods: Light underbrush n= 0.400 P2= 2.20" Link 1L: LAKE GEORGE Inflow Area = 1.807 ac, Inflow Depth > 1.24" for 25-YEAR event Inflow = 2.23 cfs @ 12.05 hrs, Volume= 0.187 of Primary = 2.23 cfs @ 12.05 hrs, Volume= 0.187 af, Atten= 0%, Lag= 0.0 min Primary outflow = Inflow, Time Span= 0.00-24.00 hrs, dt= 0.05 hrs PROPOSED a 4 0 ri 4 SF .M W l J ! p 1 ! p 9gi $ e I r e i 1S 2S 3S BUILDI S REMAI ER OF LOT UPPER JIVEWAY 4S LOWER RIVEWAY 1P 1,L� P D 2P �. LAKE GEORGE POND 1R L __J 28" CPP li Subcat 'Reachi on Link- Drainage Diagram for WHEELER PROPOSED REV 1 Prepared by HUTCHINS ENGINEERING 3/28/2008 HydroCAD®7.10 s/n 002373 0 2005 HydroCAD Software Solutlons LLC WHEELER PROPOSED REV 1 Type 11 24-hr 10-YEAR Rainfall=3.90" Prepared by HUTCHINS ENGINEERING Page 2 HydroCAD®7.10 sin 002373 ©2005 HydroCAD Software Solutions LLC 3/28/2008 Time span=0.00-24.00 hrs, dt=0.05 hrs, 481 points Runoff by SCS TR-20 method, UH=SCS Reach routing by Stor-Ind+Trans method - Pond routing by Stor-Ind method Subcatchment 1 S: BUILDINGS Runoff Area=4,850 sf Runoff Depth>3.66" Flow Length=50' Tc=6.2 min CN=98 Runoff=0.59 cfs 0.034 of Subcatchment 2S: REMAINDER OF LOT Runoff Area=69,640 sf Runoff Depth>0.71" Flow Length=150' Tc=14.9 min CN=60 Runoff=1.19 cfs 0.094 of Subcatchment 3S: UPPER DRIVEWAY Runoff Area=1,720 sf Runoff Depth>3.67" Flow Length=100' Tc=0.7 min CN=98 Runoff=0.24 cfs 0.012 of Subcatchment 4S: LOWER DRIVEWAY Runoff Area=2,495 sf Runoff Depth>3.67" Flow Length=100' Tc=0.7 min CN=98 Runoff=0.35 cfs 0.017 of Reach 1 R: 28" CPP Peak Depth=0.02' Max Vel=2.8 fps Inflow=0.01 cfs 0.004 of D=28.0" n=0.013 L=60.0' S=0.1500'P Capacity=132.16 cfs Outflow=0.01 cfs 0.004 of Pond 1P: POND Peak Elev=348.54' Storage=296 cf Inflow=0.24 cfs 0.012 of Discarded=0.01 cfs 0.008 of Primary=0.00 cfs 0.000 of Outflow=0.01 cfs 0.008 of Pond 2P: POND Peak Elev=345.81' Storage=570 cf Inflow=0.35 cfs 0.017 of Outflow=0.01 cfs 0.004 of Link 1 L: LAKE GEORGE Inflow=1.43 cfs 0.133 of Primary=1.43 cfs 0.133 of Total Runoff Area = 1.807 ac Runoff Volume = 0.158 of Average Runoff Depth = 1.05" WHEELER PROPOSED REV 1 Type 1124-hr 10-YEAR Rainfall=3.90" Prepared by HUTCHINS ENGINEERING Page 3 HydroCADO 7.10 s/n 002373 ©2005 HydroCAD Software Solutions LLC 3/28/2008 Subcatchment 1S: BUILDINGS Runoff = 0.59 cfs @ 11.96 hrs, Volume= 0.034 af, Depth> 3.66" Runoff by SCS TR-20 method, UH=SCS, Time Span= 0.00-24.00 hrs, dt= 0.05 hrs Type II 24-hr 10-YEAR Rainfall=3.90" Area (sf) CN Description 3,470 98 MAIN HOUSE & DRIVE 1,380 98 GUEST COTTAGE 4,850 98 Weighted Average Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 6.2 50 0.1800 0.1 Sheet Flow, Woods: Light underbrush n= 0.400 P2= 2.20" Subcatchment 2S: REMAINDER OF LOT Runoff = 1.19 cfs @ 12.10 hrs, Volume= 0.094 af, Depth> 0.71" Runoff by SCS TR-20 method, UH=SCS, Time Span= 0.00-24.00 hrs, dt= 0.05 hrs Type II 24-hr 10-YEAR Rainfall=3.90" Area (sf) CN Description 69,640 60 Woods, Fair, HSG B Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 14.9 150 0.1800 0.2 Sheet Flow, Woods: Light underbrush n= 0.400 P2= 2.20" Subcatchment 3S: UPPER DRIVEWAY Runoff = 0.24 cfs @ 11.89 hrs, Volume= 0.012 af, Depth> 3.67" Runoff by SCS TR-20 method, UH=SCS, Time Span= 0.00-24.00 hrs, dt= 0.05 hrs Type II 24-hr 10-YEAR Rainfall=3.90" _ Area (sf) CN Description 1,720 98 NEW DRIVEWAY Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 0.7 100 0.1200 2.3 Sheet Flow, Smooth surfaces n= 0.011 P2= 2.20" WHEELER PROPOSED REV 1 Type 1124-hr 10-YEAR Rainfall=3.90" Prepared by HUTCHINS ENGINEERING Page 4 HydroCADO 7.10 s/n 002373 ©2005 HydroCAD Software Solutions LLC 3/28/2008 Subcatchment 4S: LOWER DRIVEWAY Runoff = 0.35 cfs @ 11.89 hrs, Volume= 0.017 af, Depth> 3.67" Runoff by SCS TR-20 method, UH=SCS, Time Span= 0.00-24.00 hrs, dt= 0.05 hrs Type II 24-hr 10-YEAR Rainfall=3.90" Area (sf) CN Description 2,495 98 NEW DRIVEWAY Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 0.7 100 0.1200 2.3 Sheet Flow, Smooth surfaces n= 0.011 P2= 2.20" Reach 1R: 28" CPP Inflow Area = 0.097 ac, Inflow Depth > 0.55" for 10-YEAR event Inflow = 0.01 cfs @ 12.97 hrs, Volume= 0.004 of Outflow = 0.01 cfs @ 13.00 hrs, Volume= 0.004 af, Atten= 2%, Lag= 2.0 min Routing by Stor-Ind+Trans method, Time Span= 0.00-24.00 hrs, dt= 0.05 hrs 12 Max. Velocity= 2.8 fps, Min. Travel Time= 0.4 min Avg. Velocity= 2.8 fps, Avg. Travel Time= 0.4 min Peak Depth= 0.02' @ 12.99 hrs Capacity at bank full= 132.16 cfs Inlet Invert= 343.00', Outlet Invert= 334.00' 28.0" Diameter Pipe, n= 0.013 Corrugated PE, smooth interior Length= 60.0' Slope= 0.1500 'P Pond 1 P: POND Inflow Area = 0.039 ac, Inflow Depth > 3.67" for 10-YEAR event Inflow = 0.24 cfs @ 11.89 hrs, Volume= 0.012 of Outflow = 0.01 cfs @ 13.64 hrs, Volume= 0.008 af, Atten= 97%, Lag= 104.6 min Discarded = 0.01 cfs @ 13.64 hrs, Volume= 0.008 of Primary = 0.00 cfs @ 0.00 hrs, Volume= 0.000 of Routing by Stor-Ind method, Time Span= 0.00-24.00 hrs, dt= 0.05 hrs Peak Elev= 348.54' @ 13.64 hrs Surf.Area= 297 sf Storage= 296 cf Plug-Flow detention time= 286.1 min calculated for 0.008 of(67% of inflow) Center-of-Mass det. time= 185.7 min ( 929.2 - 743.5 ) Volume Invert Avail.Storage Storage Description #1 347.00' 448 cf Custom Stage Data (Prismatic)Listed below (Recalc) WHEELER PROPOSED REV 1 Type 1/24-hr 10-YEAR Rainfall=3.90" Prepared by HUTCHINS ENGINEERING Page 5 HydroCAD®7.10 s/n 002373 ©2005 HydroCAD Software Solutions LLC 3/28/2008 Elevation Surf.Area Inc.Store Cum.Store (feet) (sq-ft) (cubic-feet) (cubic-feet) 347.00 105 0 0 348.00 210 158 158 349.00 370 290 448 Device _Routing Invert Outlet Devices #1 Primary 348.70' 4.0' long x 8.0' breadth Broad-Crested Rectangular Weir Head (feet) 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60 1.80 2.00 2.50 3.00 3.50 4.00 4.50 5.00 5.50 Coef. (English) 2.43 2.54 2.70 2.69 2.68 2.68 2.66 2.64 2.64 2.64 2.65 2.65 2.66 2.66 2.68 2.70 2.74 #2 Discarded 0.00' 1.000 in/hr Exfiltration over Surface area Discarded OutFlow Max=0.01 cfs @ 13.64 hrs HW=348.54' (Free Discharge) 2=Exfiltration (Exfiltration Controls 0.01 cfs) Primary OutFlow Max=0.00 cfs @ 0.00 hrs HW=347.00' (Free Discharge) t-1=Broad-Crested Rectangular Weir (Controls 0.00 cfs) Pond 2P: POND Inflow Area = 0.057 ac, Inflow Depth > 3.67" for 10-YEAR event Inflow = 0.35 cfs @ 11.89 hrs, Volume= 0.017 of Outflow = 0.01 cfs @ 12.97 hrs, Volume= 0.004 af, Atten= 96%, Lag= 64.6 min Primary = 0.01 cfs @ 12.97 hrs, Volume= 0.004 of Routing by Stor-Ind method, Time Span= 0.00-24.00 hrs, dt= 0.05 hrs 12 Peak Elev= 345.81' @ 12.97 hrs Surf.Area= 247 sf Storage= 570 cf Plug-Flow detention time= 479.3 min calculated for 0.004 of(25% of inflow) Center-of-Mass det. time= 267.4 min ( 1,010.9- 743.5 ) Volume Invert Avail.Storage Storage Description #1 342.00' 619 cf Custom Stage Data (Prismatic)Listed below (Recalc) Elevation Surf.Area Inc.Store Cum.Store (feet) (sq-ft) (cubic-feet) (cubic-feet) 342.00 70 0 0 343.00 105 88 88 344.00 150 128 215 345.00 200 175 390 346.00 258 229 619 Device Routing Invert Outlet Devices #1 Primary 345.80' 4.0' long x 8.0' breadth Broad-Crested Rectangular Weir Head (feet) 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60 1.80 2.00 2.50 3.00 3.50 4.00 4.50 5.00 5.50 Coef. (English) 2.43 2.54 2.70 2.69 2.68 2.68 2.66 2.64 2.64 2.64 2.65 2.65 2.66 2.66 2.68 2.70 2.74 WHEELER PROPOSED REV 1 Type //24-hr 10-YEAR Rainfall=3.90" Prepared by HUTCHINS ENGINEERING Page 6 HydroCADO 7.10 s/n 002373 ©2005 HydroCAD Software Solutions LLC 3/28/2008 Primary OutFlow Max=0.01 cfs @ 12.97 hrs HW=345.81' (Free Discharge) t1=Broad-Crested Rectangular Weir (Weir Controls 0.01 cfs @ 0.2 fps) Link 1L: LAKE GEORGE Inflow Area = 1.807 ac, Inflow Depth > 0.88" for 10-YEAR event Inflow = 1.43 cfs @ 12.06 hrs, Volume= 0.133 of Primary = 1.43 cfs @ 12.06 hrs, Volume= 0.133 af, Atten= 0%, Lag= 0.0 min Primary outflow = Inflow, Time Span= 0.00-24.00 hrs, dt= 0.05 hrs WHEELER PROPOSED REV 1 Type 1124-hr 25-YEAR Rainfall=4.40" Prepared by HUTCHINS ENGINEERING Page 7 HydroCADO 7.10 s/n 002373 ©2005 HydroCAD Software Solutions LLC 3/28/2008 Time span=0.00-24.00 hrs, dt=0.05 hrs, 481 points Runoff by SCS TR-20 method, UH=SCS Reach routing by Stor-Ind+Trans method - Pond routing by Stor-Ind method Subcatchment 1S: BUILDINGS Runoff Area=4,850 sf Runoff Depth>4.16" Flow Length=50' Tc=6.2 min CN=98 Runoff=0.67 cfs 0.039 of Subcatchment 2S: REMAINDER OF LOT Runoff Area=69,640 sf Runoff Depth>0.96" Flow Length=150' Tc=14.9 min CN=60 Runoff=1.73 cfs 0.128 of Subcatchment 3S: UPPER DRIVEWAY Runoff Area=1,720 sf Runoff Depth>4.16" Flow Length=100' Tc=0.7 min CN=98 Runoff=0.28 cfs 0.014 of Subcatchment 4S: LOWER DRIVEWAY Runoff Area=2,495 sf Runoff Depth>4.16" Flow Length=100' Tc=0.7 min CN=98 Runoff=0.40 cfs 0.020 of Reach 1 R: 28" CPP Peak Depth=0.03' Max Vet=3.6 fps Inflow=0.04 cfs 0.007 of D=28.0" n=0.013 L=60.0' S=0.1500 7 Capacity=132.16 cfs Outflow=0.04 cfs 0.007 of Pond 1P: POND Peak EIev=348.70' Storage=343 cf Inflow=0.28 cfs 0.014 of Discarded=0.01 cfs 0.009 of Primary=0.00 cfs 0.000 of Outflow=0.01 cfs 0.009 of Pond 2P: POND Peak EIev=345.82' Storage=574 cf Inflow=0.40 cfs 0.020 of Outflow=0.04 cfs 0,007 of Link 1L: LAKE GEORGE Inflow=2.02 cfs 0.173 of Primary=2.02 cfs 0.173 of Total Runoff Area = 1.807 ac Runoff Volume = 0.200 of Average Runoff Depth = 1.33" WHEELER PROPOSED REV 1 Type/1 24-hr25-YEAR Rainfall=4.40" Prepared by HUTCHINS ENGINEERING Page 8 HydroCAD®7 10 s/n 002373 ©2005 HydroCAD Software Solutions LLC 3/28/2008 Subcatchment 1S: BUILDINGS Runoff = 0.67 cfs @ 11.96 hrs, Volume= 0.039 af, Depth> 4.16" Runoff by SCS TR-20 method, UH=SCS, Time Span= 0.00-24.00 hrs, dt= 0.05 hrs Type II 24-hr 25-YEAR Rainfall=4.40" Area (sf) CN Description 3,470 98 MAIN HOUSE & DRIVE 1,380 98 GUEST COTTAGE 4,850 98 Weighted Average Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 6.2 50 0.1800 0.1 Sheet Flow, Woods: Light underbrush n= 0.400 P2= 2.20" Subcatchment 2S: REMAINDER OF LOT Runoff = 1.73 cfs @ 12.09 hrs, Volume= 0.128 af, Depth> 0.96" Runoff by SCS TR-20 method, UH=SCS, Time Span= 0.00-24.00 hrs, dt= 0.05 hrs Type II 24-hr 25-YEAR Rainfall=4.40" Area (sf) CN Description 69,640 60 Woods, Fair, HSG B Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft1sec) (cfs) 14.9 150 0.1800 0.2 Sheet Flow, Woods: Light underbrush n= 0.400 P2= 2.20" Subcatchment 3S: UPPER DRIVEWAY Runoff = 0.28 cfs @ 11.89 hrs, Volume= 0.014 af, Depth> 4.16" Runoff by SCS TR-20 method, UH=SCS, Time Span= 0.00-24.00 hrs, dt= 0.05 hrs Type II 24-hr 25-YEAR Rainfall=4.40" Area (sf) CN Description 1,720 98 NEW DRIVEWAY Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 0.7 100 0.1200 2.3 Sheet Flow, Smooth surfaces n= 0.011 P2= 2.20" WHEELER PROPOSED REV 1 Type 1/ 24-hr 25-YEAR Rainfall=4.40" Prepared by HUTCHINS ENGINEERING Page 9 HydroCAD07 10 s/n 002373 02005 HydroCAD Software Solutions LLC 3/28/2008 Subcatchment 4S: LOWER DRIVEWAY Runoff = 0.40 cfs @ 11.89 hrs, Volume= 0.020 af, Depth> 4.16" Runoff by SCS TR-20 method, UH=SCS, Time Span= 0.00-24.00 hrs, dt= 0.05 hrs Type it 24-hr 25-YEAR Rainfall=4.40" _ Area (sf) CN Description 2,495 98 NEW DRIVEWAY Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 0.7 100 0.1200 2.3 Sheet Flow, Smooth surfaces n= 0.011 P2= 2.20" Reach 1R: 28" CPP Inflow Area = 0.097 ac, Inflow Depth > 0.85" for 25-YEAR event Inflow = 0.04 cfs @ 12.19 hrs, Volume= 0.007 of Outflow = 0.04 cfs @ 12.21 hrs, Volume= 0.007 af, Atten= 2%, Lag= 1.2 min Routing by Stor-Ind+Trans method, Time Span= 0.00-24.00 hrs, dt= 0.05 hrs/2 Max. Velocity= 3.6 fps, Min. Travel Time= 0.3 min Avg. Velocity = 2.8 fps, Avg. Travel Time= 0.4 min Peak Depth= 0.03' @ 12.20 hrs Capacity at bank full= 132.16 cfs Inlet Invert= 343.00', Outlet Invert= 334.00' 28.0" Diameter Pipe, n= 0.013 Corrugated PE, smooth interior Length= 60.0' Slope= 0.1500 T Pond 1P: POND Inflow Area = 0.039 ac, Inflow Depth > 4.16" for 25-YEAR event Inflow = 0.28 cfs @ 11.89 hrs, Volume= 0.014 of Outflow = 0.01 cfs @ 13.73 hrs, Volume= 0.009 af, Atten= 97%, Lag= 110.2 min Discarded = 0.01 cfs @ 13.73 hrs, Volume= 0.009 of Primary = 0.00 cfs @ 0.00 hrs, Volume= 0.000 of Routing by Stor-Ind method, Time Span= 0.00-24.00 hrs, dt= 0.05 hrs Peak Elev= 348.70' @ 13.73 hrs Surf.Area= 322 sf Storage= 343 cf Plug-Flow detention time= 292.2 min calculated for 0.009 of(64% of inflow) Center-of-Mass det. time= 188.0 min ( 929.3 - 741.3 ) Volume Invert Avail.Storage Storage Description #1 347.00' 448 cf Custom Stage Data (Prismatic)Listed below (Recalc) ♦ WHEELER PROPOSED REV 1 Type 1124-hr 25-YEAR Rainfall=4.40" Prepared by HUTCHINS ENGINEERING Page 10 HydroCAD®7 10 s/n 002373 ©2005 HydroCAD Software Solutions LLC 3/28/2008 Elevation Surf.Area Inc.Store Cum.Store (feet) (sq-ft) (cubic-feet) (cubic-feet) 347.00 105 0 0 348.00 210 158 158 349.00 370 290 448 Device Routing Invert Outlet Devices #1 Primary 348.70' 4.0' long x 8.0' breadth Broad-Crested Rectangular Weir Head (feet) 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60 1.80 2.00 2.50 3.00 3.50 4.00 4.50 5.00 5.50 Coef. (English) 2.43 2.54 2.70 2.69 2.68 2.68 2.66 2.64 2.64 2.64 2.65 2.65 2.66 2.66 2.68 2.70 2.74 #2 Discarded 0,00' 1.000 in/hr Exfiltration over Surface area Discarded OutFlow Max=0.01 cfs @ 13.73 hrs HW=348.70' (Free Discharge) t2=Exfiltration (Exfiltration Controls 0.01 cfs) Primary OutFlow Max=0.00 cfs @ 0.00 hrs HW=347.00' (Free Discharge) t1=Broad-Crested Rectangular Weir ( Controls 0.00 cfs) Pond 2P: POND Inflow Area = 0.057 ac, Inflow Depth > 4.16" for 25-YEAR event Inflow = 0.40 cfs @ 11.89 hrs, Volume= 0.020 of Outflow = 0.04 cfs @ 12.19 hrs, Volume= 0.007 af, Atten= 90%, Lag= 17.6 min Primary = 0.04 cfs @ 12.19 hrs, Volume= 0.007 of Routing by Stor-Ind method, Time Span= 0.00-24.00 hrs, dt= 0.05 hrs/ 2 Peak Elev= 345.82' @ 12.19 hrs Surf.Area= 248 sf Storage= 574 cf Plug-Flow detention time= 369.8 min calculated for 0.007 of (34% of inflow) Center-of-Mass det. time= 198.9 min ( 940.1 - 741.3 ) Volume Invert Avail.Storage Storage Description #1 342.00' 619 cf Custom Stage Data (Prismatic)Listed below (Recalc) Elevation Surf.Area Inc.Store Cum.Store (feet) (sq-ft) (cubic-feet) (cubic-feet) 342.00 70 0 0 343.00 105 88 88 344.00 150 128 215 345.00 200 175 390 346.00 258 229 619 Device Routing Invert Outlet Devices #1 Primary 345.80' 4.0' long x 8.0' breadth Broad-Crested Rectangular Weir Head (feet) 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60 1.80 2.00 2.50 3.00 3.50 4.00 4.50 5.00 5.50 Coef. (English) 2.43 2.54 2.70 2.69 2.68 2.68 2.66 2.64 2.64 2.64 2.65 2.65 2.66 2.66 2.68 2.70 2.74 40 WHEELER PROPOSED REV 1 Type // 24-hr 25-YEAR Rainfall=4.40" Prepared by HUTCHINS ENGINEERING Page 11 HydroCADO 7.10 s/n 002373 ©2005 HydroCAD Software Solutions LLC 3/28/2008 Primary OutFlow Max=0.03 cis @ 12.19 hrs HW=345.82' (Free Discharge) L1=Broad-Crested Rectangular Weir (Weir Controls 0.03 cfs @ 0.4 fps) Link 1L: LAKE GEORGE Inflow Area = 1.807 ac, Inflow Depth > 1.15" for 25-YEAR event Inflow = 2.02 cfs @ 12.06 hrs, Volume= 0.173 of Primary = 2.02 cfs @ 12.06 hrs, Volume= 0.173 af, Atten= 0%, Lag= 0.0 min Primary outflow = Inflow, Time Span= 0.00-24.00 hrs, dt= 0.05 hrs