Swale 1

Swale -1
Design Channel Section
Capacity:
1.18 cfs
Prop. Channel Grade:
2.00 %
Prop. Vegetation:
Tall Fescue
Soil:
Clayey (Plastic)
Permissible Velocity (Vp):
5.5 fps
Retardance Classes B & D
1.13
Ditch Geometry: Trapezoidal
Determine Channel Dimensions:
A = Q/V, 0.21 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)
0.50 1.25 0.30 0.044 2.15 2.68
Retardance Class B:
d (ft) A (ft) R (ft) n Vt (fps) Q (cfs)
0.50 1.25 0.30 0.09 1.05 1.31
Vt < Vp; Velocity OK
Q > Qio; Capacity OK
Vt < Vp; Velocity OK
Q > Q10; Capacity OK
Minimum ditch dimensions: 1.0' Deep, 1.0' Bottom, Side Slopes 2:1
Determine Temp. Liner
Q2 = 0.87 cfs
Proposed Liner:
Anticipated depth (Q2): 0.4 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:
0.4
n:
0.065
A:
0.88
R:
0.25
V:
1.28
Q:
1.13
1.13 >Q2 ; Depth Estimate is adequate.
Check allowable Td
Straw w/ Net Td: 1.45 Ib/ft2
T = yds: T= 0.50 Ib/ft2
Where
Y: 62.4 Ib/ft3
d: 0.4 ft
s: 2.00 %
Straw w/ Net OK as temporary liner