Swale 2

Swale -2
Design Channel Section
Capacity:
9.89 cfs
Prop. Channel Grade:
2.00 %
Prop. Vegetation:
Tall Fescue
Soil:
Clayey (Plastic)
Permissible Velocity (Vp):
5.5 fps
Retardance Classes B & D
26.25
Ditch Geometry: Trapezoidal
Determine Channel Dimensions:
A = Q/V, 1.80 ft2
Side Slopes: 3 :1
b = bottom width 1 ft
Z= 3
A=bd+ZdA2
R = (bd + ZdA2) / (b + 2d*(�ZA2+1))
Retardance Class D:
d (ft) A (ft) R (ft) n Vt (fps) Q (cfs)
1.40 7.28 0.74 0.051 3.38 24.58
Retardance Class B:
d (ft) A (ft) R (ft) n Vt (fps) Q (cfs)
1.40 7.28 0.74 0.125 1.38 10.03
Vt < Vp; Velocity OK
Q > Q10; Capacity OK
Vt < Vp; Velocity OK
Q > Q10; Capacity OK
Minimum ditch dimensions: 0.77' Deep, 1.0' Bottom, Side Slopes 3:1
Determine Temp. Liner
Q2 = 7.32 cfs
Proposed Liner:
Anticipated depth (Q2): 1.2 ft
n for Straw w/ Net when depth is 0.5 - 2.0': 0.033 (Table 8.05e, NC Erosion)
Check depth estimate for adequate flow
Depth:
1.2
n:
0.033
A:
5.52
R:
0.64
V:
4.76
Q:
26.25
26.25 >Q2 ; Depth Estimate is adequate.
Check allowable Td
Straw w/ Net Td: 1.45 Ib/ft2
T = yds: T= 1.50 Ib/ft2
Where
Y: 62.4 Ib/ft3
d: 1.2 ft
s: 2.00 %
Straw w/ Net OK as temporary liner