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Short Version BMP Computations For Worksheets 2 - 6
Albemarle County Water Protection Ordinance: Modified Simple Method
Plan: Preddy Creek Park, Phase -1 Water Resources Area:Rural Area
Preparer: David Anhold Date: March 4, 2009
Project Drainage Area Designation DA# 1 - Biofileter #1
L storm pollutant export in pounds, L = [P(Pj)Rv/121[ C(A)2.721
Rv mean runoff coefficient, Rv = 0.05 + 0.009(1)
Pj small storm correction factor, 0.9
1 percent imperviousness
P annual precipitation, 43" in Albemarle
A project area in acres in subject drainage area,A =5.47
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
Roads Length Width subtotal Length Width subtotal
1110 19 21090 1110 19 21090
0 0 0 1635 1 1635
0 0 0 0
0 21090 0 22725
Driveways Length Width no.subtotal Length Width no.subtotal
and walks 280 12 1 3360 280 12 1 3360
0 0 0 0 0 0
0 3360 0 3360
Parking Lots 1 2 3 4 1 2 3 4
0 0 0 0 0
Gravel areas Area Area 11636
x 0.70 =0 0 x 0.70 =8145.2
Structures Area no.subtotal Area no.subtotal
0 0 0 0
0 0 0 1 0
0 0 0 0 0 0
Actively - grazed pasture &Area Area
yards and cultivated turf 71457 x 0.08 =5716.56 87400 x 0.08 =6992
Active crop land Area Area
x0.25=0 x0.25=0
Other Impervious Areas
86 86
Impervious Cover 13%17%
l(pre)l(post)
Rv(post) V
0.21 63.7
New Development (For Development Areas, existing impervious cover <= 20 %)
C f I (pre) * Rv(pre) L(pre) L(post) RR RR Area Type
0.70 1.00 20% 0.23 7.72 6.92 0.80 12% Development Area
0.35 1.00 0% 0.16 2.76 3.46 0.70 20% Drinking Water Watersheds
0.40 1.00 1% 0.16 3.15 3.95 0.80 20% Other Rural Land
min. values
Redevelopment (For Development Areas, existing impervious cover > 20 %)
C f 1 (pre)* Rv(pre) L(pre) L(post) RR RR Area Type
0.70 0.90 20% 0.23 7.72 6.92 0.03 0% Development Area
0.35 0.85 0% 0.16 2.76 3.46 1.11 32% Drinking Water Watersheds
0.40 0.85 1% 0.16 3.15 3.95 1.27 32% Other Rural Land
Interim Manual, Page 70 rev. 16 Feb 1998 GEB
Short Version BMP Computations For Worksheets 2 - 6
Albemarle County Water Protection Ordinance: Modified Simple Method
Plan: Preddy Creek Park, Phase -1 Water Resources Area:Rural Area
Preparer: David Anhold Date: March 23, 2009
Project Drainage Area Designation DA# 2 - Biofilter #2
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 =1.74
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
Roads Length Width subtotal Length Width subtotal
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
0 0 0 0
Parking Lots 1 2 3 4 1 2 3 4
0 0 0 0 0
Gravel areas Area Area 24950
x 0.70 =0 0 x 0.70 =17465
Structures Area no.subtotal Area no.subtotal
0 0 0 138 1 138
0 0 0 48 1 48
0 0 0 0 0 186
Actively - grazed pasture &Area Area
yards and cultivated turf 75756 x 0.08 =6060.48 53929 x 0.08 =4314.32
Active crop land Area Area
x0.25=0 x0.25=0
Other Impervious Areas
86 86
Impervious Cover 8%29%
l(pre)post)
Rv(post) V
0.31 34.0
New Development (For Development Areas, existing impervious cover <= 20 %)
C f I (pre) * Rv(pre) L(pre) L(post) RR RR Area Type
0.70 1.00 20% 0.23 2.46 3.33 0.87 26% Development Area
0.35 1.00 0% 0.12 0.66 1.67 1.01 61% Drinking Water Watersheds
0.40 1.00 1% 0.12 0.75 1.90 1.15 61% 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% 0.23 2.46 3.33 1.12 34% Development Area
0.35 0.85 0% 0.12 0.66 1.67 1.11 66% Drinking Water Watersheds
0.40 0.85 1% 0.12 0.75 1.90 1.27 66% Other Rural Land
Interim Manual, Page 70 rev. 16 Feb 1998 GEB