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lo Complete Table B by entering the infiltration rate, drawdown time, and drainage area to the BMP. The spreadsheet <br />will then calculate the maximum depth to be retained/infiltrated. That depth can then be used to calculate the <br />appropriate area of the BMPs in Tables D and /or the rock depth below outlet in Table E. <br />Table B. Volume Reduction BMPs <br />Volume Reduction BMP ID <br />Infiltration <br />Rate (in/hr) <br />( ) <br />Drawdown <br />Time* br <br />( ) <br />Max Water <br />Depth to be <br />Retained/ <br />Infiltrated ** <br />(ft) <br />Drainage <br />Area <br />(acres) <br />Example: Rain Garden <br />0.6 <br />48 <br />2.4 <br />0.3 <br />Example: Subsurface Trench <br />0.8 <br />48 <br />3.2 <br />1.5 <br />1. Dry Basin <br />0.8 <br />48; <br />3, <br />1.59 <br />2.'friton <br />0.8 <br />48 <br />Y <br />1A7 <br />3. Tree Trench <br />0.8 <br />48 <br />,r, <br />m, a v <br />0.45 <br />4 <br />n= porosity (83/83) of media W <br />=width of BMP (n) 11 = <br />height of LIMP (8) t.= <br />length of BMP (R) <br />48 <br />-. <br />5 <br />48 <br />s?l . <br />332 <br />** Maximum Depth = ((Infiltration rate /12) x Drawdown time) <br />Table C. Storage Volume Calculation Formulas for Various Volume Reduction Practices <br />Category <br />Method <br />Accepted Storage Volume Credit Formulas (cu. Ft.) (Below <br />outlet of practice) <br />Nomenclature <br />Rain I3arrel /Cistem <br />Storage &Slow <br />Release, <br />Evaporation <br />V= 0.785 x 02 x 11 <br />or <br />V = Gallons per Barrel x 0.1337 <br />D =bane] diameter (R) it <br />=barrel height (8) <br />Green hoof /Roof Gardens <br />Storage & Slow <br />Release, is I' <br />V - L x W x [(Ds x Pe) + IX] <br />L = length of soil area (ft) W <br />= width of soil arca (8) Ds = <br />depth of soil (8) Dt = <br />depth of storage between soil surface & <br />overflow of practice (8) Pe = <br />effective porosity of the soil (typically <br />0.3-0.5) <br />Subsurface Infiltration <br />Storage & <br />Infiltration <br />V = (pipe volume + rock void volume) <br />Pipe Vol. = Pipe [A x L] <br />Rock Void Vol. _ ([ W x 11 x14 - Pipe[A x 14) x n <br />n = porosity (113/83) of rock media W <br />= width of Trench (11) 11= <br />height of trench (e) <br />length of trench and pipe (8) A = <br />area of pipe (82) <br />Rain Gardens/Surface Infiltration <br />Storage & <br />infiltration <br />, <br />V = BMI Area x I x 4 <br />BMP area using max depth from Table <br />13 (112) 1 <br />=infiltration rate (in /hr) 4 <br />= conversion for 48 hr drawdown <br />Filtration /Rain Garden w/ <br />Underdrain <br />Storage, Moisture <br />Retention & E1, <br />V = (BMP Area x I x 4) x 70% <br />BMP area using max depth from 'fable <br />13 (82) I <br />= infiltration rate (in/hr) 4 <br />= conversion for 48 hr drawdown <br />Sand Filter <br />Moisture Retention <br />& Slow Release, <br />Evaporation <br />Evaporation <br />V =(W x11 x L) x <br />n a porosity (83/113) of media W <br />=width of' (11) II= <br />height of1MP(8) L= <br />length of 13M1' (e) <br />Pervious Paveme n <br />ge & <br />Storage <br />Infiltration <br />V = (W x 11 x L) x n <br />n= porosity (83/83) of media W <br />=width of BMP (n) 11 = <br />height of LIMP (8) t.= <br />length of BMP (R) <br />â–ºTable C on the previous page can be used to determine the calculation of volume reduction provided with various <br />38 <br />