Revised C22007- Sand Filter_Calcs

Project: Huber Technology Date: 08.19.2022 Revision:
Project No:C22007 By:MD Location:
Input values in red
Drainage Area 8.33 ac
Impervious Area 5.98 ac
Percent Impervious 71.81 %
Design Rainfall 1.0 in
"Schueler's Method" Formula Rv = 0.05 + 0.009(I)
where
Rv = 0.70 in/in
Water Quality Volume Calculation WQv = (Design Rainfall) (Rv) (Drainage Area)
WQv = 0.48 ac-ft
21048 ft3 15786 Discounted Design Volume
Modified Curve Number:
Modified Curve Number CNm = 1000 / [10 + 5P + 10WQv - 10(WQv 2 + 1.25WQvP)
CNm = 97
From HydroCAD:
WQv Peak 13.72 cfs
Sand Filter Sizing
Rv = Runoff Coefficient = stormwater runoff (inches)
/ stormwater rainfall (inches)
I = Percent Impervious = drainage area (acres) /
impervious portion of the drainage area (acres)
101 N Tryon St., Suite 1400, Charlotte, NC 28202 Tel [phone] www.stewartinc.com
Release Rates:
WQv release = 0.115 cfs over 51 hrs
Sand Filter Sizing:
Filter bed depth (df) 2.50 ft
Coeff. of permeability (k) 3.50 ft/day
Filter bed drain time (t) 2.125 days
hmax filter 4.00 ft (height from top of sand to spillway)
hf 2.00 ft
Required volume of Sediment Chamber (Vs) = 7893.0 cf
Required surface area of Sed. Chamber (As) = 1973.3 sf
Required surface area of Sand Filter (Af) = 1973.3 sf
Total Surface Area of Pond =3946.5 sf
2700 sf OK
16200 cf OK
2700 sf OK
Elevation Area
(sq ft)
Area
(ac)Avg Area Inc Height
(ft)
Inc Vol
(ac-ft)
Acc Vol
(ac-ft)
Ht
(ft)
769.00 5400 0.1240 0.1240 0 0.000 0.000 0.00
770.00 6426 0.1475 0.1357 1.00 0.136 0.136 1.00
771.00 7524 0.1727 0.1601 1.00 0.160 0.296 2.00
772.00 8694 0.1996 0.1862 1.00 0.186 0.482 3.00
Underdrain System Design:
Minimum drawdown discharge:
WQv = 21048 ft3
Drawdown = 0.1146 cfs
Perforation Capacity:
Total pipe length 180 ft pipes spaced 10' o.c. maximum
Number of perforations 2880 holes (3/8" holes spaced 3" o.c., along 4 rows spaced at 90°)
50% of perforations 1440 holes
h 2.00 ft
Capacity per hole 0.008 cfs
Total capacity 11.891 cfs
Perforation capacity > filter capacity?YES
Underdrain Pipe Capacity:
Pipe size 6 inch
Pipe slope 0.005 ft/ft
Capacity of pipe 0.395 cfs
50% assuming clogging 0.198 cfs
Capacity of pipe half clogged > filter capcity?YES
Provided Af =
Af =(WQv) (df)
(k) (t) (hf + df)
Provided Vs =
Provided As =
101 N Tryon St., Suite 1400, Charlotte, NC 28202 Tel [phone] www.stewartinc.com
Denver, NC
+ 1.25WQvP)0.5 ]
101 N Tryon St., Suite 1400, Charlotte, NC 28202 Tel [phone] www.stewartinc.com
Qo
(cfs)
0.0000
0.1531
0.1969
0.2406
(3/8" holes spaced 3" o.c., along 4 rows spaced at 90°)
(WQv) (df)
(k) (t) (hf + df)
101 N Tryon St., Suite 1400, Charlotte, NC 28202 Tel [phone] www.stewartinc.com