SW4200501_17-116 - Wetland Sizing Calculation_5/28/2020

DATE
5/28/20 Q
PROJECT NAME PROJECT NO �n
Lewisville MS 17-116 �J
LOCATION BY
Forsvth Countv. NC KAL 000
Drainage Area, (DA) = 2.05 ac
Impervious Area c= 0.95 0.75 ac Includes 0.06 AC Future
Pervious Area c= 0.30 1.30 ac
Cc = 0.54
Wetland Surface Area & Volume
% Impervious = 37 %
Design Storm Rainfall 1.00 in
Runoff Coeff. (Rv = 0.05 + 0.009 (% Imperv.)) = 0.38 in/in
Required Volume (design rainfall)(Rv)(DA) = 2,822 cf
Depth of Temporary Pool (Dplants) = 12 in (I5-inmax)
Approx. Ave. Surface Area for Design = 2,822 sf
Surface Area at Permanent Pool= ( 812.00 ) 2,593 sf @ 0.0 in. ponding
Surface Area at 1/2 Depth= ( 812.50 ) 3,922 sf @ 6.0 in. ponding
Surface Area at Temporary Pool= ( 813.00 ) 4,670 sf @ 12.0 in. ponding
Temporary Ponding Volume Provided= 3,777 cf > 2,822 cf OK
Required Design Volume= 2,822 cf
Interpolation From Stage -Storage Table (Hydraflow Hydrographs)=
Elevation Depth Storage
812.60 ft 0.60 ft 2390 cf Depth at Req'd Desion
812.80 ft 0.80 ft 3187 cf Volume (ft) _
0.71
Surface Area at Design Volume Depth (sf) 4274 sf
Temp. Storage Depth above Dewatering Hole =
0.71 ft
Diameter of Dewatering Hole =
1.00 in
Detention (Draw -Down) Time =
2.6 days
T days=(Req. Temp. Storage Vol / (0.6 ' A ' (2'g'(h))Al
/2) ' 86400
(where h = one third temp. storage depth measured to centroid of orifice)
Wetland Zones Required
Forebay Surface Area (10-15%) =
427 641 sf
Non-Forebay Deep Pools (5-15%) =
214 641 sf
Shallow Water Zone (35-45%) =
1496 1923 sf
Temp. Inundation Zone (30-45%) =
1282 1923 sf
Wetland Zones Provided
Forebay Surface Area =
494 sf
12%
OK
Non-Forebay Deep Pools =
475 sf
11 %
OK
Shallow Water Zone =
1,624 sf
38%
OK
Temporary Inundation Zone =
1,681 sf
39%
OK
s:\1319\0001\calcs\17-116 - PondSize-Wetland-2017-MDCYLS printed: 5/28/2020 2:04 PM Page 1 of 1