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HomeMy WebLinkAboutStormwater Report - 225 BRIDLE PATH 7/31/2003 STORMWATER DRAINAGE COMPUTATIONS TO ACCOMPANY A PERMIT SITE PLAN APPLICATION FOR WATERSHED SPECIAL PERMIT IN NORTH ANDOVER, MA RECEIVED SITE: AUG U 8 2003 225 Bridle Path, North Andover, MA NORTH ANDOV'EPI PLANNING DEPARTMENT OWNERS: APPLICANT: Gregory and Jeanne M. Andrusin Howell Design & Build 225 Bridle Path 44 Beechwood Drive North Andover, MA 01845 North Andover, MA 01845 DATE: July 31, 2003 H.S.A. NO. 10072 � f I� OF MASS RICHARD F. 7't� o DOHERTY H K p CIVIL No.31433 Q EN G m G O TES A�0 01 DIVISIO F H COCK SS S,INC. `SS/0 T . 235 NEWBURY �{ VERS, MA 01923 PHONE: (978) 777-3050, : (978) 774-4205 �� TABLE OF CONTENTS PAGE INTRODUCTION AND METHODOLOGY 1 SITE DESCRIPTION 1 PROJECT DESCRIPTION 2 HYDROLOGIC AND HYDRAULIC COMPUTATION METHODOLOGY 2 SUMMARY OF RESULTS 2 Hydrology Summary for 100-year, 24-hr. storm APPENDIX: • WATERSHED MAP • DRAINAGE CALCULATIONS • INFILTRATION CALCULATIONS #10072 Drainage Report 225 Bridle Path,North Andover, MA INTRODUCTION AND METHODOLOGY This report is intended to accompany a Permit Site Plan Application for Watershed Special Permit for a proposed addition located at 225 Bridle Path, North Andover, Massachusetts. Included in this report are calculations that support final engineering design as required by Section 4.136 of the Zoning Bylaw. The final design intent seeks to meet the following interrelated goals: 1. Collect and infiltrate stormwater runoff from proposed new impervious areas for the 100 year storm event. 2. Comply with Best Management Practices by meeting or exceeding appropriate local Stormwater Management Standards. 3. Provide adequate pipe/overland drainage, capable of passing peak flows for the 100-year, 24-hour storm. 4. Provide a cost-effective engineering solution that addresses regulatory issues, as well as, real world constraints. 5. Meet the goal of section 4.136 of the zoning bylaws by producing no discharge from the proposed addition into the Watershed Protection District. SITE DESCRIPTION The project site covers approximately 1.026 acres and is located in the Watershed Protection Non-Disturbance zone on the westerly side of Bridle Path. There is a bordering vegetated wetland located in the northeasterly corner of the property at the intersection with Timber Lane; and a small wetland area offsite to the west of the property. This smaller wetland is non-jurisdictional under both the Massachusetts Wetlands Protection Act and the North Andover Wetlands Bylaw and therefore not subject to a buffer zone. There is also an existing single family dwelling, utilities and a paved driveway on the property. The front yard slopes toward the street, the rear yard toward the small offsite wetland. The soil on the site is classified by the USDA Soil Conservation Service as Sutton very stony fine sandy loam (SuB), which is in hydrologic group B. Soils within the substratum were determined to be Loamy Sand during soil testing performed by this office. #10072 Drainage Report 225 Bridle Path,North Andover, MA PROJECT DESCRIPTION Development will include the construction of adjacent 7'-0" by 12'-11", 12'-0" by 16'-6", and 1'-0" by 5'-2" additions, totaling 294 square feet in area. The proposed drainage system will consist of roof drains from these additions discharging into Cultec Contactor-100 subsurface infiltration units. The proposed subsurface infiltration units were designed to store and infiltrate flows from a 100- year, 24-hour storm event. HYDROLOGIC AND HYDRAULIC COMPUTATION METHODOLOGY Runoff rates and volumes were computed using the Soil Conservation Service TR-20 Method. Rainfall amounts were taken from the Cornell University Publication No. RR 93-5. The following 24-hour rainfall event was analyzed: Frequency Rainfall (Inches) ears 100 8.4 Runoff hydrographs were routed through the analysis route using HydroCADTM, a stormwater modeling system by Applied Microcomputer Systems, P.O.Box 350, Chocorua, NH 03817. The infiltration rate of the subsurface infiltration basins is based upon the percolation test performed on-site by this office. SUMMARY OF RESULTS The calculations show that the five (5) subsurface infiltration basins will store and infiltrate the entire runoff volume from the 100-year storm event. Therefore, there will not be any significant degradation of the quality or quantity of water downstream from this site, in or entering Lake Cochichewick. .� ;i - t � _ >' �3 ' WATERSHED MAP % BMA 1 J A ij 2 0) ce) o C) Ij AT C*4 J (e) C) AT f J _Y C) C) LLI DA P0Sr-DEkM0AW9Vr WA 7ERMM MAP 71131103 3i N rl_ C) 225 BRIDLE PA TH CVD_ "— ' NORTH ANDOVER, 1 720 & co SHEET 1 OF 1 Engineering Associates HAlrCOCK JOB NO 235 NEWBURY STREET, DANVERS. MA. 01923 VOICE (978) 777-3050. FAX (978) 774-4205 ca 10072 U- TV DRA G! �;' Cl 100 YEAR, 24 HOUR STORM is ip Subca Reach on Link Drainage Diagram for 10072-Howell Design-100 yr Prepared by Hancock Engineering Associates 07/31/2003 HydroCAD®6.00 s/n 000821 ©1986-2001 Applied Microcomputer Systems 10072-Howell Design - 100 yr Type 11124-hr Rainfall=8.40" Prepared by Hancock Engineering Associates Page 1 HydroCADO 6.00 s/n 000821 ©1986-2001 Applied Microcomputer Systems 07/31/2003 Time span=0.00-20.00 hrs, dt=0.01 hrs, 2001 points Runoff by SCS TR-20 method, UH=SCS, Type III 24-hr Rainfall=8.40° Reach routing by Stor-Ind+Trans method - Pond routing by Stor-Ind method Subcatchment 1S: Roof Addition Tc=0.0 min CN=98 Area=772 sf Runoff=0.18 cfs 0.012 of Pond 1 P: Infiltration Area Peak Storage=88 cf Inflow=0.18 cfs 0.012 of Discarded=0.04 cfs 0.012 of Outflow=0.04 cfs 0.012 of Runoff Area=0.018 ac Volume=0.012 of Average Depth=7.80" 10072-Howell Design - 100 yr Type 111 24-hr Rainfall=8.40" Prepared by Hancock Engineering Associates Page 2 HydroCAD®6.00 s/n 000821 ©1986-2001 Applied Microcomputer Systems 07/31/2003 Subcatchment 1S: Roof Addition Runoff = 0.18 cfs @ 12.00 hrs, Volume= 0.012 of Runoff by SCS TR-20 method, UH=SCS, Time Span= 0.00-20.00 hrs, dt= 0.01 hrs Type III 24-hr Rainfall=8.40" Area (so CN Description 772 98 Roof Tc Length Slope Velocity Capacity Description (min) (feet) (ft/ft) (ft/sec) (cfs) 0.0 Direct Entry, Subcatchment 1S: Roof Addition Hydrograph Plot 0.1 0 - -- _ 0.18 ---------- --- ----- ----- ------ ---- ----- - 18 cfs Runoff - - ---- ------ 0.16 - - - - --- ----- 0.14 -; - - - ----- -------- ----- -- ---- 0.13 ------ --------- --------- --- --- ----- ---- ---- --- ---- ----- --- - - ---- --- ---- H0.12 - ------------- --- --- -- ---- ------------ ---- ---- -------------------- --- -- -- - --- 0.11-- ------ -T------------- -------- -- ----- ---- ---- ----- ---------------- ---- - ----- - ---- 3 0.1 -------- --- ------ ------------------=-- ---------- --------- ° 0.0— - - - - - -- - --------------- -- -- 0.08 - - ----------- ------------- - ---- -- -- ------ --- --- --- 0.07 - .._ - ------- ----< ----- -- --- -- ----- ---- --- --- ---- - --- 0.06 - - - --------- - - ---- ---- ----- --------- ---- ---- - --------- 0.05 - --- ---- - 0.04 - -------- >----------------------- ---- ---- --- -------- ----- ---- ---- --- ----- 0.03 _.. ---- ----------------------------------------- --- ---- --- 0.02 ----- - -------- --- - ---- -------------------- - --- ----- --- --- 0.01 -------- ---- -----!-------- -- - - --------- - ----- ---- -------------------- 0 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Time (hours) 10072-Howell Design - 100 yr Type 111 24-hr Rainfall=8.40" Prepared by Hancock Engineering Associates Page 3 HydroCADO 6.00 s/n 000821 ©1986-2001 Applied Microcomputer Systems 07/31/2003 Pond 1P: Infiltration Area Inflow = 0.18 cfs @ 12.00 hrs, Volume= 0.012 of Outflow = 0.04 cfs @ 11.68 hrs, Volume= 0.012 af, Atten= 78%, Lag= 0.0 min Discarded = 0.04 cfs @ 11.68 hrs, Volume= 0.012 of Routing by Stor-Ind method, Time Span= 0.00-20.00 hrs, dt= 0.01 hrs/2 Peak Elev= 1.31' Storage= 88 cf Plug-Flow detention time= 9.6 min calculated for 0.012 of(100% of inflow) Elevation Inc.Store Cum.Store (feet) (cubic-feet) (cubic-feet) 0.00 0 0 0.50 17 17 0.90 35 52 1.20 29 81 1.50 19 100 Qiscarded OutFlow (Free Discharge) 1=Exfiltration # Routing Invert Outlet Devices 1 Discarded 0.00' 0.04 cfs Exfiltration at all elevations Pond 1P: Infiltration Area Hydrograph Plot 0.1 -... 0.18 cfs...................-- - - - - ----- --- ' - - inflow 0.18 --------;- -- ---- --- ------- -- --- --- --- -- --- -- ------------- --- ----- -- Discarded ----0.17 - - ----- 0.16. ------- -- -. - ----- -- - ------------------------ ----- 0.1 - -- - 0.14 ------ ---.. - ------ -- ---- -- -- - ----- -------------- ----- -------- --- - 0.13-:-----+-------- --------------------- ------ ------ - ---- -------- ----- ----- --- --------- -- - - --- ------ y0.12 - . - ----- ----- --- ------ ---- -... ---- -- 0.11 ------------------------- -- --- - -- ----- - - 3 0.1 - ----- ------- - ----' - --- -- -------- - -------- ----- -- ---- 0 0.0 0.08 - .:.--- -- .... -- ---- --- --- --- --- -- -- 0.07 -'-- - ----;----- -----<-------:----- -------------- - - -- --- --- --- -------- 0.06 ------->---- ------!---------'•------+--------------------------------- - ---- --- ----- 0.0 - ----'- -- ----------------------------- 0.04 cfs ! ---- --- ---- ----- ------------- 0.04 - - --- ---- --- ----- -- --- 0.03 - --------------- ---- ---- - 0.02-:-- - ---- --- - --- - --- ---- -------- - - ----- 0.01 - - ----..!,... -------- .. -- ----- -- - - 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Time (hours) I NFILTRATION CALCULARM INFILTRATION BASIN STORAGE CALCULATIONS Job No. 10072 For: Howell Design & Build Calculated by: CRO Date: 0710812003 Checked by: RFD BASIN 11 Unit Model• Cultec Contactor 100 (Design Unit= Unit+ Stone) Design Unit WIDTH. 3.00 ft Design Unit LENGTH: 7.50 ft Stone Void Percent 30% Number of ROWS. 5 Units per Row.• 1 TOTAL UNITS. 5 Total Width: 15 ft Total Length: 7.5 ft Total Linear Feet: 37.5 ft INCREMENTAL STORAGE. STONE UNIT INCREMENTAL INCREMENTAL ELEV VOIDS VOIDS VOLUME VOLUME (per LF) (per LF) (per LF) (CF) 1.5 0.21 0.29 0.50 19 1.2 0.08 0.70 0.78 29 0.9 0.07 0.87 0.94 35 0.5 0.45 0.00 0.45 17 0.0 0.00 0.00 0.00 0 1.86 2.67 100 Volume per Unit: 20.03 INFILTRATION: Bottom Area: 112.50 sf Perc Rate: 4 mpi Infiltration Rate: 0.00035 cf/sf Total Infiltration: 0.04 cfs Cultec Infiltration.XLS