Soil and Water Conservation Engineering · Soil and Water Erosion · 2 marks · Multiple choice
Design a parabolic grass waterway for 2.85 m³/s on3% slope. Permissible velocity1.78 m/s and Manning n=.04. Excluding freeboard, select top width and depth in metres.
Required area is $Q/V=2.85/1.78=1.6011$ m². For a parabola $A=2Td/3$, so T d≈2.4017. A and B both give area 1.6; roughness resolves them. Required $R=(Vn/\sqrt{.03})^{3/2}=.2636$ m. For B, $P\approx T+8d^2/(3T)=6.0711$, R=.2635, matching Manning; A gives R≈.377. Thus **6 m and .4 m, B**.
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