HomeMy WebLinkAboutSDP200900017 Calculations 2009-02-26Short Version BMP Computations For Worksheets 2 - 6
Albemarle County Water Protection Ordinance: Modified Simple Method
Plan: Humagen Fertility Diagnostics- Phase3 Water Resources Area:Rural Area
Preparer:Brian P. Smith, PE Date:2/26/2009
Project Drainage Area Designation DA #1
L storm pollutant export in pounds, L = [P(Pj)Rv /12 ] [ C(A)2.72 ]
Rv mean runoff coefficient, Rv = 0.05 + 0.009(1)
Pj small storm correction factor, 0.9
I percent imperviousness
P annual precipitation, 43" in Albemarle
A project area in acres in subject drainage area,A =0.47
C pollutant concentration, mg /I or ppm target phosphorus
f factor applied to RR
required treatment volume in cy, 0.5" over imperv. area = A(I)43560(0.5/12)/27
RR required removal , L(post) - f x L(pre)
RR removal efficiency , RR100 /L(post)
Impervious Cover Computation (values in feet & square feet)
Item
pre - development Area post - development Area
Length Width subtotal Length Width subtotal
0 0 0 0 0 0
0 0 0 0 0 0
0 0 0 0
0 0 0 0
Driveways Length Width no.subtotal Length Width no.subtotal
and walks 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0
371 1 371 371 371 1 371 371
Parking Lots 1 2 3 4 1 2 3 4
and road 5,528 5528 5,528 3,359 0 0 8887
Structures Area no.subtotal Area no.subtotal
1,489 1 1489 1,489 1 1489
0 0 0 0 0 0
0 0 0 1489 0 1489
Actively - grazed pasture &Area Area
yards and cultivated turf 13,194 x 0.08 =1056 9,835 x 0.08 =787
Active crop land Area Area
x0.25=0 x0.25=0
Other Impervious Areas
0 0
Impervious Cover 41%56%
l(pre)post)
Rv(post) V
0.56 17.8
New Development (For Development Areas, existing impervious cover <= 20 %)
C f 1 (pre) * Rv(pre) L(pre) L(post) RR RR Area Type
0.70 1.00 20% 0.42 1.22 1.61 0.39 24% Development Area
0.35 1.00 0% 0.42 0.61 0.80 0.20 24% Drinking Water Watersheds
0.40 1.00 1% 0.42 0.69 0.92 0.22 24% Other Rural Land
min. values
Redevelopment (For Development Areas, existing impervious cover > 20 %)
C f I (pre) * Rv(pre) L(pre) L(post) RR RR Area Type
0.70 0.90 20% 0.42 1.22 1.61 0.51 32% Development Area
0.35 0.85 0% 0.42 0.61 0.80 0.29 36% Drinking Water Watersheds
0.40 0.85 1% 0.42 0.69 0.92 0.33 36% Other Rural Land
Interim Manual, Page 70 rev. 31 March 1998 GEB
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