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Home My WebLink AboutSDP200700104 Calculations 2007-09-18f Albemarle County r - r r Ponds Timberwood Boulevard Erosion Control Narrative and Detention Pond Calculations First Submittal: April 23, 2007 Second Submittal: September 18, 2007 wp 0 U EDMUND H. U/ 31.A.C'k R-'J*I . Lic. ,.02 = 31 S AI- Blackwell EnLyineerint! PLC 566 East Market Street Harrisonburg, VA 22801 Ph. (540) 432 -9555 Fax (540) 434 -7604LvBlackwellengineering.com BE # 1853 Albemarle County Regional SWM -BMP Ponds Timberwood Boulevard Erosion Control Narrative and Detention Pond Calculations First Submittal: April 23, 2007 Second Submittal: September 18, 2007 I'D N ION 1) 11. u PLACK`VFI_I. 4 Lip, No,023S I Blackwell Engineering PLC 566 East Market Street Harrisonburg, VA 22801 Ph. (540) 432 -9555 Fax (540) 434 -7604 Blackwellengineering.com BE # 1853 Tebbe o Contents FT18 Erosion Control Narrative .............................................. ............................1 - 6 Soiland USES Maps ........................................................ ............................7 - 8 Pond #1 Short Version BMP Computations ....................................... ......................... 9 -10 Runoff Calculations, Existing and Proposed ....................... ..........................11 -12 Preliminary Detention Pond Sizing Calculations ................ ..........................13 -14 2 -year and 10 -year Critical Duration Storm ........................ ..........................15 -16 Sediment Forebay and Pond Volume Calculations .......... .............................17 Hydrographs, Inflow and Routing: 2, 10, 25, 100 -year ....... ..........................18 -27 Outlet Protection Chart ..................................................... .............................28 Sediment Basin Calculations .................... . .................................................... 29 -33 BL_4CK1f"ELL ENGIAEERINC, PLC HARRISONBURG, VIRGINIA 540 -432 -9555 9/17/2007 Regional SWM -BMP Detention Pond Timberwood Boulevard North of Airport Road Project # 1853 EROSION & SEDIMENT CONTROL NARRATIVE PROJECT DESCRIPTION The purpose of this project is the construction of a regional storm water management SWM) and best management practices (BMP) detention pond to serve the several properties tributary to them. Pond #1 will also meet the sediment control and water quality requirements for the LDS Church shown on the plans for reference purposes. The site is located in Albemarle County, Virginia, north of Airport Road toward the end of the proposed Timberwood Boulevard. The site consists vacant and wooded land. The design of the detention pond assumes a significant portion of the tributary area will be developed with impervious surfaces. A total of 2.2 acres will be disturbed during the construction of the pond and will be built by the United Land Corporation of America. EXISTING SITE CONDITIONS The site is currently forested and is considered rolling terrain sloping to the north at about an 8% slope with steeper portions in ravines of 2'/2:1 slopes. ADJACENT PROPERTY The site is bounded by Industrial lots along its western border by industrial lots on Dobleann Drive, vacant land to the north and east, and Airport Road and the recently approved LDS Church to the south. OFF -SITE AREA If any onsite material needs to be exported from the site it shall be taken to a permitted disposal site. If any material needs to be imported to the site it shall come from a permitted borrow site. SOILS (See Soil Map) 47C): Louisburg sandy loam, 7 to 15% slopes. Louisburg is a strongly sloping to moderately steep, deep or very deep, well drained soil. Typically the surface layer is sandy loam about 5 inches thick. The surface layer has a moderately low content of organic matter. The slowest permeability is rapid. It has a moderate available water capacity and a low shrink swell potential. This soil is not flooded and is not ponded. The seasonal high water table is at a depth of more than 6 feet. This soil is not hydric. Erosion factors Kw and Kf are both 0.24. 1 1 BL.4 CW H "ELL F_ AI IAWERING, PLC HARRISONBURG, VIRGINIA 540- 432 -9555 9/17/2007 9413): Wedowee sandy loam, 2 to 7% slopes. Wedowee is a gently sloping to moderately sloping, very deep, well drained soil. Typically the surface layer is sandy loam about 7 inches thick. The surface layer has a moderately low content of organic matter. The slowest permeability is moderate. It has a moderate available water capacity and a low shrink swell potential. This soil is not flooded and is not ponded. The seasonal high water table is at a depth of more than 6 feet. This soil is not hydric. Erosion factor Kw ranges between 0.24 and 0.28. Erosion factor Kf ranges between 0.24 and 0.28. CRITICAL EROSION AREAS There are no critical erosion areas. EROSION & SEDIMENT CONTROL MEASURES Unless otherwise indicated, all vegetative and structural erosion and sediment control practices shall be constructed and maintained according to the minimum standards and specifications of the Virginia Erosion and Sediment Control Regulations, latest edition. The minimum standards of the handbook shall be adhered to unless otherwise waived or approved by a variance. STRUCTURAL PRACTICES 1. Temporary Construction Entrance — 3.02 A temporary construction entrance shall be installed as shown on the plans. During muddy conditions, drivers of construction vehicles shall be required to clean off their wheels before entering the highway. Runoff created during this procedure shall pass through an approved sediment removing process. 2. Silt Fence — 3.05 A temporary sediment barrier constructed of posts, welded wire fabric, and filter fabric shall be installed downslope form the toe of the pond embankments.. 3. Culvert Inlet Protection — 3.08 Modified dewatering devices are proposed for the pond and will act as culvert inlet protection until the upslope land area disturbed by future construction is stabilized. 4. Temporary Sediment Basin — 3.14 The pennanent SWM -BMP detention pond will serve as temporary sediment basins while upslope land disturbing activities are in progress. Because the volume of the pennanent pond is based on 4xWQV of the tributary area which may be developed with up to 80% impervious surfaces, it exceeds the combined wet and dry storage requirements of a standard sediment basin. The riser and dewatering provisions of a typical sediment basin are not applicable and a modified dewatering device is proposed. The basin shape of Pond #1 produces a 2 2 BL.1 C IUVT LL ENGINEEIUAI ,I'LL' HARRISO NBURG, VIRGINIA 540-432-9555 9/17/2007 length -to -width ratio of L /We 2. n plywood baffle is proposed to increase the flow path of the pond. 5. Outlet Protection — 3.18 The installation of riprap channel sections shall be installed at the downstream end of storm drain outlets to reduce erosion and under - cutting from scouring at outlets and to reduce flow velocities before ston enters receiving channels below these outlets. 6. Permanent Seeding— 3.32 Permanent seeding shall be applied to denuded areas within seven days after final grade is reached on any portion of the site. 7. Soil Stabilization Blankets and Matting — 3.36 A soil stabilization mat on a prepared planting area shall be installed on the slopes leading from the sediment forebay to the permanent deep pool of the SWM -BMP pond and is shown in the construction drawings. 8. Dust Control — 3.39 Dust control measures shall be applied to disturbed areas of the site to reduce the presence of airborne dust. 9. Permanent Ditch A permanent ditch shall be constructed where shown on the plans to channel stormwater to the SWM -BMP detention pond. 10. Other practices shall be provided if determined by the Engineer or County E &SC Administrator. VEGETATIVE PRACTICES 1. Top soiling (stockpile) Topsoil shall be stripped from the area to be graded and stockpiled for later use and shall be stabilized by seeding with seed mix appropriate for the time of year. 2. Permanent Seeding Permanent seeding shall be installed (appropriate to the time of year) according to Seeding and Mulching Table detail on the plan. 3 3 PL,4 C fs 1rr ELL EA PLC HARRISONI3URG, VIRGINIA 540- 432-9555 Q/17/2007 MANAGEMENT STRATEGIES 1. Perimeter sediment trapping measures to be installed prior to any excavation on site. 2. Construction shall be conducted so that existing cover will not be disturbed anymore than necessary. 3. Construction shall be sequenced so that grading operations can begin and end as quickly as possible. 4. Permanent seeding and other stabilization shall follow immediately after grading. 5. Areas that will be disturbed shall be clearly marked by flags, signs, etc. 6. The job superintendent shall be responsible for the installation and maintenance of all erosion and sediment control practices. 7. After achieving adequate stabilization to the satisfaction of the E &SC Administrator, the temporary E &S controls shall be removed. PERMANENT STABILIZATION All areas disturbed by construction and not otherwise stabilized, shall be stabilized with permanent seeding within 7 days following finish grading. Seeding shall be done according to standard & specification 3.32, PERMANENT SEEDING, of the handbook Seeding shall be applied depending on time of the year according to E &SC handbook specifications. In all seeding operations, seed, fertilizer, and lime shall be applied prior to mulching. Erosion control blankets shall be installed over fill slopes which have been brought to final grade and have been seeded to protect the slopes from rill and gully erosion and to allow seed to germinate properly. Mulch (straw or fiber) shall be used on relatively flat areas. In all seeding operations, seed, fertilizer, and lime shall be applied prior to mulching. STORMWATER MANAGEMENT Pond #1 has been designed to accommodate the critical storm events of the 2, 10, and 100 -year return periods from developed properties with an average 80% of the tributary area developed with impervious surfaces, i.e., buildings and pavement. The pond will serve as a sediment basin while until upslope disturbing activities are in progress. The critical 25 -year storm event from post- developed tributary area was routed through the pond instead of the undeveloped flow rates produced with the standard Rational Method. 4 4 r 17/2007 When upslope denuded land is permanently stabilized the accun sedimeni will be removed from the pond and disposed of in an approved manner and location to be determined at that time. EXISTING DOWNSTREAM CHANNEL The existing downstream channel is an intermittent stream as shown on the USGS 7.5' Series Earlysville Quadrangle and is assumed to be adequate receiving channel. The developed flow from the pond will not exceed the pre - development runoff rates. MAINTENANCE In general, all erosion and sediment control measures shall be checked daily and after each significant rainfall. The following items shall be checked in particular: 1. The seeded area shall be checked regularly to ensure that a good stand is maintained. Areas shall be fertilized and reseeded as needed. 2. The gravel Construction Entrance shall be maintained in a condition, which will prevent tracking or flow of mud onto public right -of -ways. Periodic top dressing with additional stone or the washing and reworking of existing stone shall be required when the stone is covered or has been pushed into the soil. It shall be returned to its original depth of 6" (min.). 3. The Silt Fence barrier shall be checked regularly for undermining of deterioration of the fabric. Sediment shall be removed when the level of sediment deposition reaches half way to the top of the barrier. 4. The outlet protection shall be checked regularly for sediment buildup that will prevent drainage. If the stone is clogged by sediment, it shall be removed and cleaned or replaced. Riprap shall be inspected periodically to determine if high flows have caused scour beneath the riprap or filter fabric and dislodged any of the stone. Care must be taken to properly control sediment -laden construction runoff, which may drain to the point of the new installation. 5. The inlet protection measures shall be inspected after each rain and repairs made as needed. Sediment shall be removed and the trap restored to its original dimensions when the sediment has accumulated to the cleanout elevations specified in the plans. 4. Maintenance of the SWM -BMP pond shall include mowing and repair of the detention basin berm, drainage structure, and grass area; cleaning out sediment buildup; clearing of debris and trash from the outlet pipe system, as well as the removing of sediment when it reaches the cleanout level. 5 5 Q/17/2007 5. The pefinanent ditch shall lie Inspccted a Tier eves)/ stori and repairs made If necessary. Once every two weeks whether a storm has occurred od not, the measure shall be inspected and repairs made if' needed. Damages made by construction traffic or other activity shall be repaired before the end of the working day. 6. The inlet protection filter system shall be checked regularly for sediment buildup which will prevent drainage. if the filter medium is clogged by sediment, it shall be removed and cleaned or replaced. 6 6 SOIL MAP Source: soildatamart.nres.usda.gov J 1 *00 NI,el Ili 1.7 MirIA4 Li f USGS MAP 1.1 KorMw, Uhenxde (oun|yVVaksPonheoUor/ 0/dnanca k4/J|ad Sim| 6XnUmd Mon REGK)NALSVVlfi pDqwwT VVntarResour(_-eaAroa:Dne|opm:nixi ea YUABERVVOCmB( Prepnrer: Basil Finnegan Date: September 14, 200, Project Drainage Area Des Pond #1 L mmnn pollutant export in »nvms. L = [P(Pj)Rv/12 | |C(A)2.72 | R" mean runoff coefficient, Rv~0,0o+0.0V9(l) pj small storm correction factor, 0.9 percent imperviousness P annual precipitation, 43''inAlbemarle 4 project area in acres in subject drainage area, A= 12.0 C pollutant concentration, mgAn target phosphorus f factor applied mRR V required trea volume mc9.0.5^ over impcmarea A(1)43500(0.5/12)/27RRrequiredremoval .L(nvst) fxL(Pn;) RR removal efficiency, RR100/11(post) Impervious Cover Computation (values in feet u square feet) mm pre-development Area post-development AreaRoadsLengthWidthsubtotalno» Width subtotal o O o O 0 n 0 0 0 U o U 0 0 O o o o Driveways Length Width no. subtotal Length Width no subtotal 0 o and walks O O O 0 O 0 O 0 O U 0 0 0 0 0 O O 0 Parking Lots Area 1 Area Area Area Area 1 Area Area Area O U 12034 2080 0 14714 12034 Gravel areas Area Area subtotal Area 2080 O 14714 Area subtotal 0 O O xo7O= U O Structures Area no subtotal O 0 x0rO=0 Areaa no nuumtu( 4420 1 4420 4420 1 *420 3030 1 3030 3030 1 3030 Actively-grazed pasture & Area 0 O O 7450 O O O 7450 yards and cultivated turf 0 x0.08= O Area 0 x008=Active crop land Area Area O Other Impervious Ama» Ao1 O»25= Area O 0x«25=0 Area Area Area Impervious Cover » » » » 397319 »0 3e7319 4%eO% I(pre) mvnos v I(post) 0.77 647.4 New Development (For Development Areas, existing impervious cover <=2uY6)C ' |(pm)^ mv(pm) L(pre) L(post) mn % RR Area xpo0701.00 20% 0.23 10.84 50.89 39.85 70%Development Area0.35 1.00 0% 0.09 325 28.45 25.20 88Y6 Drinking Water Watersheds0.40 1.00 1% 0.09 3.71 32.51 28.80 88%Other Rural Landmin. values Redevelopment (For oev*|opmen, Areas, existing impervious cover 2o%)C f |(pe)° Rv(pm) L(pm) L(post) RR %Rm Area Type0.70 090 20% 023 1694 50.89 41.04 73%Development Area0.35 U5 0Y6 0.09 325 28.45 2560 90%Drinking Water Watersheds0.40 0.85 1% 0.09 3.71 3251 2935 90%Other Rural Land Notes: ' Existing sites onDob|nannRoad included, LDS Chmrhvmmiuodfrom pre-development computations, included in post-development computations.rev. on May zoVzJMx Q W01 Nberfiark, County! Water PvnteGabon Ordinclnce: fV oditied' Sirrq)k. Me-tho d iarl; I`eEWONAL S@ft,VA POND AT Water ReSOUrces Avea HITBEERWOOD BOULEVARD Preparer: Basil Finnegan Date Project Drainage Area Designation Pond #1 Drainage area (A)12.0 acres Percent impervious cover 80% Impervious cover 418,176 sf WQV (' /Z" on impervious surfaces)17,424 cf 4 x WQV 69,696 cf Sediment Forebay Runoff depth from impervious surfaces 0.25" Target Volume 8,712 cf Deep Pool Depth 6 ft Target Volume 60,984 cf March 14, 2007 Development Area 10 File 'i5:1 C)EEf!l)IJ F'UID i.;;l f'rini d. f/I i120U% Existing Flow Through Site 1.) Area = 11 .69 ac Project Name: Regional SWM Pond #1 Project # : 1853 2.) C = 0.32 11.23 ac @ 0.30 vegetated 0.46 ac @ 0.90 impervious 0.00 ac 6 0.00 3.) Time of Concentration a. Overland: L = 200 ft. Height =8 ft. 4.0% VDOT Drainage Manual Appendix 6D -1: T, =13.0 min. b. Shallow: L = 0 ft. Height =0 ft. Average velocity =0.0 fps (paved) VDOT Drainage Manual Appendix 6D -6: T =0.0 min. L = 520 ft. Height =36 ft. 6.9% Average velocity =4.2 fps (unpaved) VDOT Drainage Manual Appendix 6D -6: T, =2.0 min. T = L /60V Subtotal T =2.0 min. c. Channel: L = 0 ft. Height =0 ft.(paved) VDOT Drainage Manual Appendix 6D -5: T, =0.0 min. L = 560 ft. Height =42 ft.(unpaved) 7.5% VDOT Drainage Manual Appendix 6D -5: T =2.9 min. Subtotal T, =2.9 min. d. Total Tc: Tc = 18.0 min 4.) Rainfall Intensities: For Tc= 18 min.: 12 =3.14 iph 125 =4.70 iph 110=4.18 iph 150 =5.07 iph 1100 =5.54 iph 5.) Peak Flows: Q = ACI 02 =11.89 cfs Q25 =17.78 cfs Q10 =15.80 cfs Q50 =19.18 cfs Q100=20.97 cfs Blackwell Engineering, PLC 566 East Market Street Harrisonburg, VA 22801 540 - 432 -9555 11 File 1 9uuec.. I''/ i 1/1007 Rati Method Proposed Flow Through Developed Site 1.) Area = 12.0 Project Name: Regional SWM Pond # 1_ Project # : 1853 2.) C = 0.78 2.40 ac @ 0.30 vegetated 9.60 ac @ 0.90 impervious 0.00 ac (a) 3.) Time of Concentration 4.69 iph a. Overland: L = 200 ft. Height =10 ft. 5.0% VDOT Drainage Manual Appendix 6D -1: T, =6.0 min. b. Shallow: L = 0 ft. Height =0 ft. Average velocity =0.0 fps (paved) VDOT Drainage Manual Appendix 6D -6: T, =0.0 min. L = 0 ft. Height =0 ft. Average velocity =0.0 fps (unpaved) VDOT Drainage Manual Appendix 6D -6: T =0.0 min. T, = L /60V Subtotal T, =0.0 min. c. Channel: L = 905 ft. Height =74 ft.(paved) 8.2% VDOT Drainage Manual Appendix 6D -5: T, =0.8 min. L = 0 ft. Height =0 ft.(unpaved) VDOT Drainage Manual Appendix 6D -5: T, =0.0 min. Subtotal T =0.8 min. d. Total Tc: Tc = 6.8 min 4.) Rainfall Intensities: For Tc= 7 min.: 12 =4.69 iph 125 =6.79 iph 110 =6.07 iph 150 =7.29 iph 1100 =7.93 iph 5.) Peak Flows: Q = ACI Q2 =43.89 cfs Q25 =63.55 cfs Q10 =56.77 cfs Q50 =68.26 cfs Q100=74.19 cfs Blackwell Engineering, PLC 566 East Market Street Harrisonburg, VA 22801 540 - 432 -9555 12 t=ile. 1853 -DE1 EI`JTIC)N PCIJU 'I As i - 'i irried. W 171200 i Blackwell Engineering, PLC 566 East Market Street Harrisonburg, VA 22801 540 - 432 -9555 13 Regional SVVM Pond #1 Equations used:Tc =sgrt[2 x C x A x a x (b - tc / 4) / Qe] - b Vp =0.5 x tc x 2.67 x (Qp- Qe +Qu) x 60 Vc =OcxT +{Qcxtc /4)- {QexT /2)- {3xQextc /4 }]x60 Q =AxCxI Where:I =rainfall intensity for storm duration T. tc =time of concentrantion, minutes Tc =critical storm duration, minutes tc =watershed time of concentration, minutes Vp =peak storm storage volume required, cubic feet Vc =critical storm storage volume required, cubic feet Qe =existing peak flow for storm duration tc, cfs Qp =proposed peak flow for storm duration tc, cfs Qc =proposed critical flow for storm duration Tc, cfs Qa =allowable peak outflow, cfs 2 Year 10 Year a =106.02 161.60 b =15.51 18.73 Existing Conditions:A =11.69 ac tc = 18.0 min C =0.3236 Proposed Conditions:A =12.00 ac tc = 7.0 min C =0.78 Design procedure: 1.)Existing rainfall intensities: 12 =3.14 iph 110 =4.18 iph 2.)Existing peak discharge Qe: Qe2 =11.89 cfs Qe10 =15.80 cfs 3.)Proposed peak rainfall intensities: 12 =4.69 iph 110 =6.07 iph 4.)Proposed peak discharge Qp (for tc): Qp2 =43.89 cfs Qp10 =56.77 cfs Blackwell Engineering, PLC 566 East Market Street Harrisonburg, VA 22801 540 - 432 -9555 13 hIr 10"53 -DE_ f E_N71UIN 1'01\11.) 1.xls 5.) Dete0 mine VDILlIne for tc (Peak storrn volume). VP2 = 11921 cf VP10 = 22946 c 6.) Uncontrolled Flow: Area = 0 ac Qu2 = 0.00 cfs Qu10 = 0.00 cfs 7.) Offsite Flow: Area = 0 ac tc= 0 min C = 0 12= 0.0 Qi2 = 0.00 cfs 110= 0.0 Qi10 = 0.00 cfs 8.) Allowable Release Rate: Qa2 = 11.89 cfs Qa10 = 15.80 cfs Blackwell Engineering, PLC 566 East Market Street Harrisonburg, VA 22801 540 - 432 -9555 I'rili lC , ci: 901102001 14 Fib-: '2)53 -14 TFN1101\1 FOND I .rl, 2, Il €=;AR It R1 TG--A RA 9IO 1 4' II SAD T USIN a AND b COEF -RCI T6 2 YEAR CRITICAL DURATION STORM PROJECT NAME: Regional SWM Pond #9 ALBEMARLE COUNTY a =106.02 A =12.00 Acres b=15.51 C=0.78 t, =6.81 minutes qo =11.89 cfs Where Tc = critical storm duration in minutes C = Rational coefficient for developed area A = drainage area in acres (post development) t, = Time of Concentration after development in minutes allowable peak outflow in cfs T =2CAa (b- t, /4)/g _ b T =32.49 minutes (critical duration) I =Rainfall Intensity (inches /hour) I =a /(b +Tc) I =2.21 inches /hour for critical duration Critical Duration =32.49 minutes Critical Duration Rainfall =2.21 inches /hour Peak inflow (Qo) =20.67 cfs for Critical Duration V =QoTc) +(Qot (g /2)- (3g /4))60 Approx. Basin Vol. =27,179 cubic feet CRITICAL DURATION HYDROGRAPH 25.0 20.0 15.0 EnLLU Cy 10.0 5.0 0.0 0 5 10 15 20 25 30 35 40 45 MINUTES Blackwell Engineering, PLC 566 East Market Street Harrisonburg, VA 22801 540 - 432 -9555 Pnni^ai. 9/i71' W - / 15 Fil• 1853 -UE.1 EI! i I0I\! POI 1D 'i.xls Pi inie0: 911 %/2007 10 Y R CRITICAL DMA_TION T ®RM F RA [WETHOLT USING a AND b COEFFICIENTS 10 YEAR CRITICAL DURATION STORM PROJECT NAME: Regional SWM Pond #k1 ALBEMARLE COUNTY a = 161.60 A = 12.00 Acres b = 18.73 C = 0.78 t = 7.00 minutes q = 15.80 cfs Where Tc = critical storm duration in minutes C = Rational coefficient for developed area A = drainage area in acres (post development) t = Time of Concentration after development in minutes q = allowable peak outflow in cfs T = (2CAa (b- t /q /2- b T = 38.28 minutes (critical duration) I = Rainfall Intensity (inches /hour) I = a /(b +Tc) I = 2.83 inches /hour for critical duration Critical Duration = 38.28 minutes Critical Duration Rainfall = 2.83 inches /hour Peak inflow (Qo) = 26.53 cfs for Critical Duration V = ((QoTc) +(Qot (q.Tc /2)- (3g Approx. Basin Vol. = 40,597 cubic feet CRITICAL DURATION HYDROGRAPH 30.0 25.0 - - - -- -- - -- - - 20.0 - — - - -- - - - y v 15.0 - - -- - -- - — -- G7 10.0 - -- - -- — - -- 5.0 - -- -- -- -- - 0.0 0 5 10 15 20 25 30 35 40 45 50 MINUTES Blackwell Engineering, PLC 566 East Market Street Harrisonburg, VA 22801 540 - 432 -9555 16 1014 [ 101 ) 1.x15 SEDIMENT FO EBAY ELEVATION ft APEA INC. VOLUME ft2 ft3 TOTAL VOL. ft3 542 1,539 0 9,066 546 2,994 9,066 PERMANENT DEEP POOL ELEVATION ft AREA ft2 INC. VOLUME ft3 TOTAL VOL. ft3 524 7,693 0 64,947 530 13,956 1 64,947 Combined Volumes (4 x WQV) = 74,013 DETENTION POND ABOVE PERMANENT DEEP POOL WATER SURFACE ELEVATION ft AREA ft2 INC. VOLUME ft3 TOTAL VOL. ft3 530 13,965 0 86,433 535 20,608 86,433 21,350 536 22,092 107,783 Blackwell Engineering, PLC 566 East Market Street Harrisonburg, VA 22801 540 - 432 -9555 h inied: 9/1 8200 / 17 Q (Cfs) 50.00 0.00 30.00 20.00 10.00 40.00 30.00 20.00 10.00 0.00 J- i--- I I I I I I I I I I I v- 1 0.00 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Hyd No. 1 Time (min) Pond #1 - Inflow Hyd. No. 1 -- 2 Year Q (Cfs) 50.00 Monday, Sop 17, 21007 Peak discharge = 43.89 cfs; Time to peak Hyd. volume Runoff coeff. Tc by User Storm duration Est. Req'd Storage 7 min 18,433 GA 0.78 7.00 min 1.0 x Tc 0 cuft ff.] Hydtaflow Hydiogiaphs by In[elisolve v9.2 HeHyd. Fftv I Pond #1 - Inflow Hydrograph type =Mod. Rational Storm frequency =2 yrs; Time interval =1 min Drainage area =12.000 ac Intensity =4.689 in/hr OF Curve =Albemarle.IDF Target Q =0.000 cfs Q (Cfs) 50.00 0.00 30.00 20.00 10.00 40.00 30.00 20.00 10.00 0.00 J- i--- I I I I I I I I I I I v- 1 0.00 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Hyd No. 1 Time (min) Pond #1 - Inflow Hyd. No. 1 -- 2 Year Q (Cfs) 50.00 Monday, Sop 17, 21007 Peak discharge = 43.89 cfs; Time to peak Hyd. volume Runoff coeff. Tc by User Storm duration Est. Req'd Storage 7 min 18,433 GA 0.78 7.00 min 1.0 x Tc 0 cuft ff.] Hydiafiow Flydrogmphs Icy hitalisolve vc) 2 HYCL Nc ? Pond #1 - Routing Hydrograph type = Reservoir Storm frequency = 2 yrs Time interval = 1 min Inflow hyd. No. = 1 - Pond #1 - Inflow Reservoir name = Pond #1 - Above Deep Pool Storage Indication method used Q (Cfs) 50.00 40.00 30.00 i1 11 10.00 000 0 60 Hyd No. 2 Monday, Sep '17, 2007 Peak discharge 4.632 cfs Time to peak 13 min Hyd. volume 18,427 cuft Max. Elevation 530.97 ft Max. Storage 16,761 cuft Pond #1 - Routing Hyd. No. 2 -- 2 Year 120 180 Hyd No. 1 240 300 360 420 Total storage used = 16,761 cuft Q (Cfs) 50.00 40.00 30.00 20.00 10.00 000 480 Time (min) 19 Flydrallow Nydiogiaphs by Intelisoh e v92 Monday, Sep 17, 2007 Pond No. i Pond 41 . -, Above Deep Po0 Ponce Data Contours - User defined contour areas.Average end area method used for volume calculation. Begining Elevation 530.00 ft Stage / Storage Table Stage (ft)Elevation (ft)Contour area (sqft)Incr. Storage (tuft)Total storage (tuft) 0.00 530.00 13,965 0 0 5.00 535.00 20,608 86,433 86,433 6.00 536.00 22,092 21,350 107,783 Culvert I Orifice Structures Weir Structures A] [Rl C] [PrfRSr]A] [B]C]D] Rise (in)21.00 0.00 0.00 0.00 Crest Len (ft)0.00 0.00 0.00 0.00 Span (in)21.00 0.00 0.00 0.00 Crest El. (ft)0.00 0.00 0.00 0.00 No. Barrels 1 0 0 0 Weir Coeff.0.00 0.00 0.00 0.00 Invert El. (ft)530.00 0.00 0.00 0.00 Weir Type Length (ft)61.00 0.00 0.00 0.00 Multi -Stage No No No No Slope ( %)14.75 0.00 0.00 n/a N -Value 014 .000 000 n/a Orifice Coeff.0.60 0.00 0.00 0.00 Exfil.(in /hr)0.000 (by Contour) Multi -Stage n/a No No No TW Elev. (ft)0.00 Note Culvert /Orifice outflows are analyzed under inlet (ic) and outlet (oc) control Weir risers checked for orifice conditions ic) and submergence (s) tage (ft) 6.00 5.00 1191I17 3.00 2.00 11 0.00 _L_ 0.00 3.00 Total Q Stage / Discharge 6.00 9.00 12.00 15.00 18.00 21.00 24.00 Elev (ft) 536.00 16=10 534.00 533.00 532.00 11116110,91111 1 530.00 27.00 Discharge (cfs) 20 Q (cfs) 60.00 0.00 40.00 30.00 20.00 10.00 50.00 40.00 30.00 20.00 10.00 0.00 -)-'- I I I I i i I I I `s 0.00 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Hyd No. 1 Time (min) Pond #1 - Inflow Hyd. No. 1 -- 10 Year Q (cfs) 60.00 Monday, Sep 17, 2007 Peak discharge = 56.77 cfs Time to peak Hyd. volume Runoff coeff. Tc by User Storm duration Est. Req'd Storage= 7 min 23,845 cuft 0.78 7.00 min 1.0 x Tc 0 cult 21 Hydiadow Hydrographs by hitelisolve v9.2 lAyd, NO. i Pond #1 - In Hydrograph type =Mod. Rational Storm frequency =10 yrs Time interval =1 min Drainage area =12.000 ac Intensity =6.066 in/hr OF Curve =Albemarle.IDF Target Q =0.000 cfs Q (cfs) 60.00 0.00 40.00 30.00 20.00 10.00 50.00 40.00 30.00 20.00 10.00 0.00 -)-'- I I I I i i I I I `s 0.00 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Hyd No. 1 Time (min) Pond #1 - Inflow Hyd. No. 1 -- 10 Year Q (cfs) 60.00 Monday, Sep 17, 2007 Peak discharge = 56.77 cfs Time to peak Hyd. volume Runoff coeff. Tc by User Storm duration Est. Req'd Storage= 7 min 23,845 cuft 0.78 7.00 min 1.0 x Tc 0 cult 21 ta Hydra low Hydiogiaphs by Inklisolve v9.2 No@ 2 Pond #1 - Routing Monday, Sep '17, 2007 Hydrograph type Reservoir Storm frequency 10 yrs Time interval 1 min Inflow hyd. No.1 - Pond #1 - Inflow Reservoir name Pond #1 - Above Deep Pool Storage Indication method used Pond #1 - Routing Peak discharge = 6.894 cfs Time to peak = 13 min Hyd. volume = 23,839 cuft Max. Elevation = 531.24 ft Max. Storage = 21,400 cuft Q (Cfs) Hyd. No. 2 10 Year Q (Cfs) 60.00 - 60.00 0.00 - 50.00 40.00 - 40.00 30.00 - 30.00 f. 20.00 20.00 10.00 10.00 0. 00 .0 0.00 0 60 120 180 240 300 360 420 Time (min) Hyd No. 2 --- Hyd No. 1 Total storage used = 21,400 cuft 22 Hychaflow Hydiogmphs by Intelisolve v9.2 Pond #1 - Inflow Hydrograph type Mod. Rational Storm frequency 25 yrs Time interval 1 min Drainage area 12.000 ac Intensity 6.790 in/hr OF Curve Albemarle.IDF Target 0 0.000 cfs Q (cfs) 70.00 Pond #1 - Inflow Hyd. No. 1 -- 25 Year 90.00 50.00 40.00 Monday, Sep '17, 2007 Peak discharge = 63.55 cfs Time to peak Hyd. volume Runoff coeff. Tc by User Storm duration Est. Req'd Storage 7 min 26,692 CUft 0.78 7.00 min 1.0 x Tc 0 cult 20.00 10.00 Q (cfs) 70.00 50.00 40.00 30.00 20.00 10.00 0.00 V -L ------ I I I I I I I I I 0.00 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Hyd No. 1 Time (min) 23 Flydiaflovv Hydrogi by hitelisolve v9.2 IIWO- No. 2 Pond #1 - Routing Hydrograph type Reservoir Storm frequency 25 yrs Time interval 1 min Inflow hyd. No.1 - Pond #1 - Inflow Reservoir name Pond #1 - Above Deep Pool Storage Indication method used Pond #1 - Routing Vbnday, Sop '0, 2007 Peak discharge 8.094 cfs Time to peak 13 min Hyd. volume 26,685 cuft Max. Elevation 531.38 ft Max. Storage 23,805 cuft Q (Cfs) Hyd. No. 2 25 Year Q (Cfs) 70.0070.00 - 60.0090.00 50.00 -50.00 40.0040.00 - 30.00 30.00 20.00 20.00 10.0010.00 0.00 0.00 0 60 120 180 240 300 360 420 Hyd No. 2 — Hyd No. 1 - Total storage used = 23,805 cuft Time (min) 24 o-- lydraflow Hydrogiaphs by Intelisolve \/9.2 lyd. klo 1 Pond #1 - Inflow Hydrograph type Mod. Rational Storm frequency 100 yrs Time interval 1 min Drainage area 12.000 ac Intensity 7,926 in/hr OF Curve Albemarle.IDF Target Q 0.000 cfs Q (cfs) 80.00 70.00 60.00 50.00 40.00 30.00 20.00 10.00 70.00 11 50.00 40.00 30.00 20.00 10.00 I — I I I --L I I I I I "0.00 ------ I— 1 0.00 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Hyd No. 1 Time (min) Pond #1 - Inflow Hyd. No. 1 -- 100 Year Q (cfs) 80.00 Monday, Sep '17, 2007 Peak discharge = 74.1 cfs Time to peak Hyd. volume Runoff coeff. Tc by User Storm duration Est. Req'd Storage 7 min 31,160 tuft 0.78 7.00 min 1.0 x Tc 0 cult 25 Flydraflovv Hydrographs by Intelisolve v9.2 ydi. Nye 2 Pond #1 - Routing Hydrograph type = Reservoir Storm frequency = 100 yrs Time interval = 1 min Inflow hyd. No. = 1 - Pond #1 - Inflow Reservoir name = Pond #1 - Above Deep Pool Storage Indication method used Q (cfs) 80.00 70.00 60.00 50.00 40.00 30.00 20.00 10.00 1WITi7 Monday, Sets 17, 9007 Peak discharge = 9.753 cfs Time to peak = 13 min Hyd. volume = 31,154 cult Max. Elevation = 531.60 ft Max. Storage = 27,587 cuft Pond #1 - Routing Hyd. No. 2 -- 100 Year Q (cfs) 80.00 70.00 60.00 50.00 9,F 40.00 30.00 r 20.00 10.00 n nn 0 60 Hyd No. 2 120 180 Hyd No. 1 240 300 360 Total storage used = 27,587 cuft 420 Time (min) 26 Hydrailow Hydrographs by Intelisolve v9.2 Return -- Period Yrs) 1 2 3 5 10 25 50 100 File name Intensity - I 0.0000 49.0200 0.0000 55.7100 46.9500 40.1100 35.6800 31.0900 4lbemarle.IDF juration- Frequenc D 0.0000 10.5000 0.0000 11.5000 9.5000 7.7500 6.5000 5.0000 Intensity = B / (Tc + D) "E V Equation Coefficients- (FHA) E (N /A) 0.0000 -- - - - - -- 0.8200 -- - - - - -- 0.0000 -- - - - - -- 0.8000 -- - - - - -- 0.7300 -- - - - - -- 0.6600 -- - - - - -- 0.6100 -- - - - - -- 0.5500 -- - - - - -- Monday. Sep 1%, 200/ Return Period Intensity Values (in /hr) Yrs)5 min 10 15 20 25 30 35 40 45 50 55 60 1 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 2 5.18 4.12 3.44 2.97 2.63 2.36 2.14 1.97 1.82 1.70 1.59 1.50 3 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 5 5.91 4.79 4.05 3.53 3.13 2.83 2.58 2.38 2.21 2.06 1.94 1.83 10 6.67 5.37 4.55 3.97 3.54 3.21 2.94 2.72 2.54 2.38 2.24 2.12 25 7.48 6.01 5.10 4.47 4.01 3.65 3.36 3.13 2.93 2.76 2.61 2.48 50 8.04 6.45 5.49 4.83 4.35 3.98 3.68 3.43 3.22 3.05 2.89 2.76 100 8.76 7.01 5.98 5.29 4.79 4.40 4.09 3.83 3.62 3.43 3.27 3.13 Tc = time in minutes. Values may exceed 60. Precio. file name: Alhemarle.nr Storm Rainfall Precipitation Table (in) Distribution 1 -yr 2 -yr 3 -yr 5 -yr 10 -yr 25 -yr 50 -yr 100 -yr SCS 24 -hour 3.30 3.70 0.00 4.70 5.60 6.80 7.90 9.10 SCS 6 -Hr 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Huff -1st 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Huff -2nd 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Huff -3rd 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Huff -4th 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Huff -Indy 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Custom 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 27 kw C"Worksheet : Pond #1 - Outlet Barrel SO[Ve FOU Full Flow Capacity Manning's Formula A Mannings Coefficient: I 0-014 1 Flow Area Channel Slope: 14. 75 1 Wetted Perimeter: i 5 It Top Width:0-00 It Depth 21 in Critical Depth 1-75 It Diameter:in Percent Full:100-00 b , -j42558CriticalSlope:It/ft Discharge: 156-50 CIS Velocity:23-49 It/s Velocity Head:It Specific Energy:FULL It Fioude Number: Maximum Discharge 60-70 cts 1 Full Flow Capacity:56.50 cfs Full Flow Slope:76& ftfit Output Pa O tis Rs LISIW, OF NTLET PROTECTION FROM A ROUND PIPE FIOWIfir. FLU M N't IMUM TAILWATER COWTTION (I. - 0.5 DIAMETER) 4 11 = 21' W = 32 ' Ootlet W -Ty L. Pipe 2 w Diameter. D t water 4 i 4 L 30' min 3 5 1.9 ONAX = 56.5 ds 21" CMP -d. 14.75*•) Flowing Full OUTLET PROTECTION AT POND #1 Class 11 jrDepth - 4.8 jUW W hhvlor, Erse ah It; liCFn, , i Rational Methofl Existing Flow to Pond I (after permanent ditches are constructed) 1.) Area= 12.00 ac Project Name: Regional SWM -BMP Ponds mT =TJ Project # : 1853 2.) C = 0.3 11.58 ac @ 0.30 0.46 ac @ 0.90 0.00 ac @ 0.00 3.) Time of Concentration a. Overland: (200' ( L = 200 ft. Height =8 ft. 4.0% Using Plate 5 -1 of VESCH: Tc=13.0 min. b. Shallow: (1000' r L = 0 ft. Height =0 ft. 12.0 Average velocity =0.0 fps (paved) VDOT Drainage Manual Appendix 6D -6: T, =0.0 min. L = 520 ft. Height =36 ft. 6.9% Average velocity =4.2 fps (unpaved) VDOT Drainage Manual Appendix 6D -6: T, =2.0 min. T = L /60V Subtotal T, =2.0 min. c. Channel: L = ft. Height =0 ft.(paved) VDOT Drainage Manual Appendix 6D -5: T, =0.0 min. L = 560 ft. Height =42 ft.(unpaved) 7.5% VDOT Drainage Manual Appendix 6D -5: T, =2.9 min. Subtotal T, =2.9 min. d. Total T,: T, = 18.0 min. 4.) Rainfall Intensities: For Tc= 18 5.) Peak Flows: min.: 12 = 3.1 iph 110 = 4.2 iph Q = ACI Q2 = 12.2 cfs Q10 = 16.2 cfs 125 =4.7 iph 150 =5.1 iph 1100 =5.5 iph Q25 =18.2 cfs Q50 =19.6 cfs Q100=21.5 cfs W 19 )2 With or without an emergency spillway) Project Regional SWM -BMP Pond Basin # 1 Location NW Corner of Property Total area draining to basin: 12.0 acres after permanent ditches are constructed. Basin Volume Desi_pn Wet Storage: 1- Minimum required volume = 67 cu. Yds. x total Drainage Area (acres). 67 cu.yds. 12.0 acres = 804 cu.yds. ( 21,708 cf) 2- Available basin volume = 804 cu.yds. at elevation 524.33 From Elevation - Volume Table) 3- Excavate cu.yds. To obtain required volume *. Elevation corresponding to required volume = invert of the dewatering orifice. 4- Available volume before cleanout required 33 cu.yds. 12.0 acres = 396 cu.yds. ( 10,692 cf) 5- Elevation corresponding to cleanout level = 524.16 From Elevation - Volume Table) 6- Distance from inv of the dewatering orifice to c.o. level = 5.84 ft. Min. = 1.0 ft.) Dry Storage: 7- Minimum required volume = 67 cu. yds. x Total Drainage Area (acres). 67 cu.yds. 12.0 acres = 804 cu.yds. ( 21,708 cf) 8- Total available basin vol. at crest of riser* = 1608 cu.yds. ( 43,416 cf) At elev. 524.67 (From Elevation - Volume Table) Minimum = 134 cu.yds. /acre of total drainage area. 9- Diameter of dewatering orifice = N/A in. 10- Dia of flexible tubing = N/A in. (Dia. of Dewatering orifice + 2 in.) 30 1 t!' 92 Pi WWjk Ary kE d-QsI El0- 11- Crest of Riser = Top of Dam = Design High Water = Upstream Toe of Dam = N/A 536.00 532.59 from hydrograph routing report 524.00 Basin Shape A = 13,965 L = 102 12- Length of Flow We = 137 (A /L) Effective Width L / We = 0.7 (A= Suf. Normal Pool) L = Length of flow path) If > 2, baffles are not required If < 2, baffles are required Develop 167' flow path with baffle Runoff 13- Q2 = 12.2 cfs. (From Chapter 5) 14- Q25 = 18.2 cfs. (From Chapter 5) Principal Spillway Design 15- With emerg. spillway, req. spillway capacity Qp = Q2 = riser and barrel) W /out emerg. Spill., req. spillway capacity Qp = Q25 = riser and barrel) 16- With emergency spillway 12.2 cfs 18.2 cfs Assumed available head (h) = ft. (Using Q2) h = Crest of Emergency Spillway Elevation - Crest of Riser Elevation Without emergency spillway: Assumed available head (h) = ft. (Using Q25) h = Design High Water Elevation - Crest of Riser Elevation 17- Riser diameter (Dr) = N/A in. Actual head (h) = N/A ft. From Plate 3.14 -8) Note: Avoid orifice flow conditions. 31 9 e)_ 18- [,arrel length ('i ) 61 It. I - lead (H) on barrel through embankment = From Plate 3.14 -7) 19- Barrel Diameter = 21 in. 20- Trash rack and anti - vortex device Dia. = N/A in. Height = N/A in. From table 3.14 -D). Emeraencv Saillwav Desian 11.59 rt. 21- Required spillway capacity Qe = Q25 - Qp = N/A cfs. 22- Bottom with (b) = ft.; the slope of the existing channel (s) _ ft. /foot; and the minimum length of the existing channel (x) _ ft. From Table 3.14 -C) Anti -Seep Collar Design 23- Depth of water at principal spillway crest (Y) = 2.59 ft. Slope of upstream face of embankment (Z)= 2.5 :1. Slope of principal spillway barrel (Sb) = 14.75 % Length of barrel in saturated zone (Ls) = 0 ft. 24- Number of collars required = 0 dimensions = 54 "x54" From Plate 3.14 -12) 1 collar provided Final Desian Elevations 25- Top of Dam = Design High Water = Emergency Spillway Crest = Principal Spillway Crest = Dewatering Orifice Invert = Cleanout Elevation = 536.00 532.59 Q25 Developed N/A 530.00 Weir invert 530.00 See modified dewatering detail on plans. 524.16 Elevation of Upstream Toe of Dam of Excavated Bottom of Wet Storage Area" (if excavation was performed) = 524.00 32 File: '1853 — `eel= .bllVV[ i i R:_p /a; Y3E,G <I rs 11(3cl: ,i i SEDIMENT BASIN VOLWWES IN PERMANENT DEEP POOL OF POND #1 ELEVATION AREA INC. VOLUME TO AL VOL..ELEVATION VOLUME FUNCTION ft ft'ft ft ft ft 524 7 ,693 0 64,947 524.16 10,692 Cleanout 530 13_,956 64,947 524.33 21,708 Wet 86,410 524.67 43,416 Wet + Dry 535 20,608 151,357 21,350 536 22,092 172,707 33 Modified Simple Method Worksheets Divide the Site into Drainage Areas — Worksheet I Calculate the area in acres for each drainage area, and label each drainage area on the plan. It will be necessary to fill out the following series of worksheets for each drainage area. Drainage Area 1:C' acres (on-site);acres (off-site)-total acres Drainage Area 2:acres (on-site); Y1 acres (off-site);total acres Drainage Area 3:acres (on-site);acres (off -site);S total acres Drainage Area 4:acres (on-site);acres (off -site);total acres Drainage Area 5:acres (on-site);acres (off-site):total acres Drainage Area 6:acres (on-site);acres (off -site).total acres Drainage Area 7:acres (on-site);acres (off site);total acres Total (On-site) Area — acres 05 February 2003 WR-8 Calculate Pre - Development Impervious Cover (I pre) - Worksheet 2 Calculate I(pre) using actual site information for each drainage area (on -site acres only) as identified in Worksheet 1. if the project is phased, include only the active phase(s). DRAINAGE AREA # I ON -SITE AREA = _ -_ ACRES (on -site drainage area size) Roads: length (ft) x width (ft) for all roads = Driveways: average length (ft) x average width (ft) x number of driveways = Parking Lots: square footage — Gravel Areas: square footage x 0.70 Structures (including houses): sum of actual square footage for all structures, OR average house square footage x number of houses = Actively - grazed pasture (livestock present), Yards & areas of cultivated turf: actual square footage of areas x 0.08, OR average yard area x number of yards x 0.08 — Active crop land: square footage x 0.25 — Other Impervious Areas = square feet square feet square feet square feet square feet square feet square feet square feet Total Equivalent Impervious Area square feet (sum of all the above values) I(pre) = Total Equivalent Impervious Cover (sq ft) x 100 — 'y 43560 sq ft per acre/on-site drainage area (acs.) DRAINAGE AREA P -' ON -SITE AREA = _ > >- ______ ACRES (on -site drainage area size) Roads: length (ft) x width (ft) for all roads — Driveways: average length (ft) x average width (ft) x number of driveways = Parking Lots: square footage = Gravel Areas: square footage x 0.70 Stru4tureS (including houses): rf' Ictual square footage for all structures. OR x r unber ofhouses — ti. <, 4 :- ves"O ': present)_ Yards & areas of cultivated furl: square feet square feet square feet square feet square feet 1k Calculate Pre- Development Impervious Cover (I pre ) - Worksheet 2 Calculate I(pre) using actual site information for each drainage area (on -site acres only) as identified in Worksheet 1. if the project is phased, include only the active phase(s). DRAINAGE AREA # 3 ON -SITE AREA = 1_o___. ACRES (on -site drainage area size) Roads: length (ft) x width (R) for all roads Driveways: average length (ft) x average width (ft) x number of driveways = Parking Lots: square footage Gravel Areas: square footage x 0.70 Structures (including houses): sum of actual square footage for all structures, OR average house square footage x number of houses = Actively - grazed pasture (livestock present), Yards & areas of cultivated turf. actual square footage of areas x 0.08, OR average yard area x number of yards x 0.08 Active crop land: square footage x 0.25 _ Other Impervious Areas square feet square feet square feet square feet square feet square feet square feet square feet Total Equivalent Impervious Area = c> square feet (sum of all the above values) I(pre) = Total Equivalent Impervious Cover (sq ft) x I00 — ._ _ % 43560 sq ft per acre /on -site drainage area (acs -) DRAINAGE AREA # ON-SITE AREA = __ ACRES (on -site drainage area size) Roads: length (ft) x width (ft) for all roads square feet Driveways: average length (ft) x average width (ft) x number of driveways =square feet Parking Lots: square footage =square feet Gravel Areas: square footage x 0.70 —square feet Structures (including houses): sum of actual square footage for all structures, OR average house square footage x number of houses =square feet Actively - grazed pasture (livestock present), Yards & areas of cultivated turf actual square footage of areas x 0.08, OR average yard area x number of yards x 0.08 _ -square feet Active crop land: square footage x 0.25 square feet Other .Impervious Areas square feet Total Equivalent Impervious Area = square feet (sum of all the above values) I(pre) = Total Equivalent Impervious Cover (sq ft) x I00 — % 43560 sq ft per acre /on -site drainage area (acs.) 05 February 2003 WR ^8 Calculate PreDevelopment Phosphorus Load (Lpre) — Worksheet 3 Use the following table to calculate L(pre) based on the water resources area in which the project is located. Water Resources Area L(pre) _ Development Area, where I(pre) is less than 1.41 x A or equal to 20% Development Area, where I(pre) is greater 6.14 x [0.05 + (0.009)(Ipre)] x A than 20% Water Supply Protection Area, no existing 0.15 x A impervious cover (do not count existing equivalent impervious cover from pasture or crop land) Water Supply Protection Area, site with 3.07 x [0.05 + (0.009)(Ipre)] x A existing impervious cover Other Rural Land, no existing impervious 0.21 x A cover (do not count existing equivalent impervious cover from pasture or crop land) Other Rural Land, site with existing 3.51 x [0.05 + (0.009)(Ipre)] x A impervious cover L(pre) = Pre - Development Phosphorus Load (pounds/year) I (pre) = Pre - Development Equivalent Impervious Cover expressed in whole numbers from Worksheet 2) A — On -Site Drainage Area (acres) DRAINAGE AREA # I ON -SITE AREA = ACRES (on -site drainage area size) L (pre) = j i ,f pounds per year (annual loading) 05 February 2003 WR -R Worksheet 3 — Continued) DRAINAGE AREA # 2- ON-SITE AREA = __- -d — ACRES (on-site drainage area size) L (pre) = _ -3 - - __ pounds per year (annual loading) DRAINAGE AREA # , ON-SITE AREA = 1, C2 ------- - ACRES (on-site drainage area size) L (pre) /- W pounds per year (annual loading) DRAINAGE AREA ON-SITE AREA = ACRES (on-site drainage area size) L (pre) = ____ pounds per year (annual loading) DRAINAGE AREA # ON-SITE AREA = ACRES (on-site drainage area size) L (pre) = pounds per year (annual loading) DRAINAGE AREA # ON-SITE AREA = ACRES (on-site drainage area size) L (pre) pounds per year (annual loading) DRAINAGE AREA # ON-SITE AREA = i ACRES (on-site drainage area size) L (pre) = pounds per year (annual loading) 05 Fetwuary 2003 WR-8 Calculate Post - Development Ultimate Impervious Cover (I post) - Workslieet 4 Use the following worksheet to calculate I(post) using assumed figures for build -out of the project, including roads, houses, driveways, yards, etc. DRAINAGE AREA # _'l ON -SITE AREA = J1___,. ACRES (on -site drainage area size) Roads: length (ft) x width (ft) for all roads . -_ 79, square Feet Driveways: average length (ft) x average width (8) x number of driveways = square feet Parking Lots: square footage = 2 <4zquare feet Gravel Areas: square footage x 0.70 =' -1> square feet Structures (including houses): sum of actual square footage for all structures, OR average house square footage x number of houses = square feet Actively- grazed pasture (livestock present), Yards & areas of cultivated turf- actual square footage of areas x 0.08, OR average yard area x number of yards x 0.08 = square feet Active crop land: square footage x 0.25 - square feet Other Impervious Areas - square feet Total Equivalent Impervious Area = square feet (sum of all the above values) I(post) = Total Equivalent Impervious Cover (sq M x 100 = t5 j % 43560 sq ft per acre/on -site drainage area (acs.) DRAINAGE AREA # Zr ON -SITE AREA = 2_- t3 ACRES (on -site drainage area size) Roads: length (ft) x width (ft) for all roads = Driveways: average length (ft) x average width (ft) x number of driveways = Parking Lots: square footage Gravel Areas: square footage x 0.70 - Structures (including houses). sum of actual square footage for all structures, OR average house square footage x number of houses - Actively- grazed pasture (livestock present), Yards & areas of cultivated turf. actual square footage of areas x 0,08, OR average yard area x number of yards x 0.08 - Active crop land: square footage x 0.25 Other Impervious Areas - Total Equivalent Impervious Area = ' square feet I(post) = Total Equivalent Impervious Cover (sq 4) x 100 43560 sq ft per acre /on -site drainage area (acs.) square feet square feet square feet square feet square feet square feet square feet square feet sum of all the above values) 05 February 2003 W R -8 Calculate Post - Development Ultimate Impervious Cover (I post) - Worksheet 4 Use the following worksheet to calculate I(post) using assumed figures for build -out of the project, including roads, houses, driveways, yards, etc. DRAINAGE AREA # ON -SITE AREA —_ ACRES (on -site drainage area size) Roads: length (11) x width (ft) for all roads = Driveways: average length (ft) x average width (ft) x number of driveways = Parking Lots: square footage — Gravel Areas: square footage x 0.70 = Structures (including houses): sum of actual square footage for all structures, OR average house square footage x number of houses — Actively- grazed pasture (livestock present), Yards & areas of cultivated turf- actual square footage of areas x 0.08, OR average yard area x number of yards x 0.08 _ Active crop land: square footage x 0.25 = Other Impervious Areas = square feet square feet square feet square feet square feet square feet square feet square feet Total Equivalent Impervious Area square feet (sum of all the above values) I(post) = Total Equivalent Impervious Cover (sq ft) x 100 = % 43560 sq ft per acre /on -site drainage area (acs.) DRAINAGE AREA # ON -SITE AREA = _ _ ACRES (on -site drainage area size) Roads: length (ft) x width (ft) for all roads . =square feet Driveways: average length (ft) x average width (ft) x number of driveways =square feet Parking Lots: square footage =square feet Gravel Areas: square footage x 0.70 =square feet Structures (including houses): sum of actual square footage for all structures, OR average house square footage x number of houses =square feet Actively - grazed pasture (livestock present), Yards & areas of cultivated turf: actual square footage of areas x 0.08, OR average yard area x number of yards x 0.08 —square feet Active crop land: square footage x 0.25 —square feet Other Impervious Areas = _square feet Total Equivalent Impervious Area = square feet (sum of all the above values) I(post) = Total Equivalent Impervious Cover (sq ft) x 100 = 43560 sq ft per acre /on -site drainage area (acs.) 05 February 2003 W R -8 Calculate Post - Development Phosphorus Load (L post) — Worksheet 5 Use the following table to calculate L(post) based on the water resources area in which the project is located. Water Resources Area L(post) _ Development Ar i 6.14 x [0.05 + (0.009)(Ipost)] x A Water Supply Protection Area i 3.07 x {0.05 + (0.009)(Ipost)] x A Other Rural Land 3.51 x [0.05 + (0.009)(Ipost)] x A L(post) = Post - Development Phosphorus Load (pounds /year) I (post) = Post- Development Equivalent Impervious Cover expressed in whole numbers from Worksheet 4) A = On -Site Drainage Area (acres) DRAINAGE AREA # ! ON -SITE AREA = // — ACRES (on -site drainage area size) L (post) = S3 pounds per year (annual loading) DRAINAGE AREA #' ON -SITE AREA = ACRES (on -site drainage area size) L (post) _ ( t`%5 pounds per year (annual loading) DRAINAGE AREA # - 3 ON -SITE AREA = — J'_t? ACRES (on -site drainage area size) L (post) _ _ pounds per year (annual loading) 05 Fetmtary 2003 i pvYR —A Calculate Pollutant Removal Requirement — Worksheet 6 RR = (Pollutant) Removal Requirement = L post — ( L pre x f ) (pounds per year) Where "f' is a factor applied to the Removal Requirement based upon the Conditions described below. RR = Overall BMP Pollutant Removal Efficiency = ( RR x 100 ) / L post (percent) Condition Ii — "No Existing Impervious Cover" ; f= 1.0 This condition does not include equivalent impervious cover from pasture /crop land. It includes "new development" in all water resources areas and "adding impervious cover to existing sites" when existing impervious cover is within: Development Area and is less than or equal to 20% Water Supply Protection Area and is 0% Other Rural Land and is less than or equal to 1% Condition 2 — "Adding Impervious Cover To Sites With Existing Impervious Cover" in the Development Areas ; f= 0.90 This condition includes "adding impervious cover to existing sites" when existing impervious cover is greater than 20% or is designated as "infill and redevelopment ". Condition 3 — "Adding Impervious Cover To Sites With Existing Impervious Cover" in the Water Supply Protection Area or Other Rural Land ; f = 0.85 This condition includes "adding impervious cover to existing sites" when existing impervious cover is within: Water Supply Protection Area and is greater than 0% Other Rural Land and is greater than I% Designated as "infill and redevelopment" DRAINAGE AREA # ,' - Condition: I 2 L post = L pre RR = %RR % 05 February 2003 WR -8