HomeMy WebLinkAboutSDP200600059 Calculations Minor Amendment 2006-06-06 Mill Creek Offices
Drainage and Stormwater Management Computations
June 6, 2006
Revised:
Prepared For:
Ronald D. Carter 3093 Darby Road Keswick VA 22947
By:
C `)
henliree design
LANDSCAPE ARCHITECTURE, ENGINEERING a PLANNING
908 East High Street Charlottesville VA 22902
434-220-2551 434-220-2553 fax
Mill Creek Offices •
Storm Drains
Bent Tree Design, PLC Revised:
June 6, 2006 Struct Struct Area Area Area E I Q Inv Inv Length Slope Diam. Cap'y Vel Flow t
ID Type 1 ID 2 ID 3 ID CA Tc 10 yi 10 yr Top Upper Lower ft ft/ft in. n cfs fps min. Remarks
B-3 DI-3C 1 0.27 9.5 5.5 1.48 479.77 475.77 465.74 81.06 0.1237 15 0.012 24.61 11.04 0.1
B-2 DI-1 2 0.32 9.6 5.5 1.74 469.00 462.69 461.51 49.12 0.0240 15 0.012 10.84 6.48 0.1
A-3 DI-1 3 0.79 10.8 5.2 4.12 460.64 457.30 457.10 10.79 0.0185 15 0.012 9.52 7.48 0.0 BMP discharge
A-2 DI-1 4 0.86 10.8 5.2 4.48 459.66 457.00 453.00 104.96 0.0381 15 0.013 13.66 9.97 0.2 pipe under entrance
A-1 MH-1 5 0.86 11.0 5.2 4.45 456.00 451.00 450.63 13.26 0.0279 15 0.013 11.69 9.42 0.0 Connect to existing DI
Short Version BMP Computations For Worksheets 2 -6
Albemarle County Water Protection Ordinance: Modified Simple Method
Plan: Mill Creek Offices Site Plan Amendment Water Resources Area: Development Area
Preparer: Bent Tree Design Date: 6/1/2006
Project Drainage Area Designation Site
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
1 percent imperviousness
P annual precipitation,43"in Albemarle
A project area in acres in subject drainage area, A= 2 31
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
O 0 0 0 0 0
O 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 16020 16020
Parking Lots 1 2 3 4 1 2 3 4
0 0 0
Gravel Areas 1 2 subtotal 1 2 subtotal
0 x0.70 0 0 x070 0
Structures Area no subtotal Area no subtotal
O 0 0 4000 1 4000
0 0 0 0 0 0
0 0 0 0 0 4000
Actively-grazed pasture& Area Area
yards and cultivated turf 0 x 0.08= 0 5000 x 0.08= 400
Active crop land Area Area
0 x0.25= 0 x0.25= 0
Other Impervious Areas
0 0
Impervious Cover 0% 20%
I(pre) l(post)
Rv(post) V
0.23 31.5
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 3.26 3.30 0.04 1% Development Area
0.35 1.00 0% 0.05 0.35 1.65 1.30 79% Drinking Water Watersheds
0.40 1.00 1% 0.06 0 48 1 89 1.41 75% 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 3.26 3.30 0.36 11% Development Area
0.35 0.85 0% 0.05 0.35 1.65 1.35 82% Drinking Water Watersheds
0.40 0.85 1% 0 06 0.48 1.89 1.48 78% Other Rural Land
rev.30 May 2002 JMK