HomeMy WebLinkAboutWPO200400093 Calculations 2004-08-26 STORMWATER BMP CALCULATIONS
FOR
ADVANCE MILLS FARM SUBDIVISION
PHASE 1
July 6, 2002
REV: August 26, 2004
LOCATION:
Tax Map 20 Parcel 6A1
Whitehall District, Albemarle County, Virginia
OWNER: oN
Advance Mills Land Trust, LLC �gpLTH
P.O. Box 8147 f.,:e0 ,
Charlottesville, VA 22911 2 v
'► T Y RAY MILLER
DEVELOPER: • 0402030542
•
C. W. Hurt •
195 Riverbend Road
‘12gio_t L6..0 ' /
41
Charlottesville, VA 22906 nvioNAL 04G`
PREPARED BY:
Rivanna Engineering & Surveying, PLC
P. O. Box 7603
Charlottesville, VA 22906
434.984.1599
F: 434.984.8863
RESI@CSTONE.NET
The Stormwater Quality BMP's for this subdivision shall be a 200' Riparian Buffer
Easement along the North Fork Rivanna River.
Short Version BMP Computations For Worksheets 2-6
Albemarle County Water Protection Ordinance: Modified Simple Method
Plan: Advance Mills Farm-Phase II Water Resources Area:
Preparer TRM Date: 25-Aug-04
Project Drainage Area Designation Rural Subdivision
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= 198,00
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 260018 46800
0 0 0 p 0 0
O 0 0 0
O 0 0 46800
Driveways Length Width no. subtotal Length Width no. subtotal
and walks 1500 10 1 15000 20010 1 2000
O 0 0 0 0 0 0 0
O 15000 0 2000
Parking Lots 1 2 3 4
1.._, 2__ 3 4
O 0 16786 0 16786
Gravel areas Area Area
x0.70= 0 x0.70= 0
Structures Area no. subtotal Area no. subtotal
800 1 800 800 1 800
0 0 0 1500 10 15000
0 0 0 800 0 15800
Actively-grazed pasture& Area Area
yards and cultivated turf 8,609,080 x 0.08= 688726.4 8,543,494 x 0.08= 683479.52
Active crop land Area Area
x0.25= 0 x0.25= 0
Other Impervious Areas
0 0
Impervious Cover 896 9%
Rv(post) V I(pre) l(post) . ,.
0.13 1180.3
New Development(For Development Areas,existing impervious cover<=20%)
C f I(pre)* Rv(pre) L(pre) L(post) RR % RR Area Type
G.70 1.00 20% 0.23 279.57 157.79 -121.78 -77% Development Area
0.35 t.b0 0% 0.12 75.07 78.90 3.83 5% Drinking Water Watersheds
o.4o, 1. ;_. 114 0.12 85.79 90.17 4.37 �`. 5% 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% 0.23 279.57 157.79 -93.82 -59% Development Area
0.3$ 0.85 0% 0.12 75.07 78.90 15.09 19% Drinking Water Watersheds
1% 0.12 85.79 90.17 17.24
0*" ���'�•� ' 19% Other Rural Land
Interim Manual, Page 70 rev. 16 Feb 1998 GEB