Full-Flow Sewer Capacity by Manning
MediumManning's equationsewer capacity
A 300 mm concrete sewer (n = 0.013) is laid at a slope of 0.005 and flows full. Using Manning's equation, its capacity is most nearly:
- A0.068 m³/s
- B0.034 m³/s
- C0.172 m³/s
- D0.967 m³/s
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Answer: A. 0.068 m³/s
Equations: Manning (SI) V = (1/n)R^(2/3)S^(1/2); for a circular pipe flowing full R = D/4; Q = VA. Values: n = 0.013, D = 0.300 m, S = 0.005. Step 1: R = 0.300/4 = 0.075 m and R^(2/3) = 0.1778. Step 2: V = (1/0.013) × 0.1778 × 0.0707 = 0.967 m/s. Step 3: A = π(0.3)²/4 = 0.0707 m², Q = 0.967 × 0.0707 = 0.068 m³/s. 0.172 uses R = D; 0.967 reports velocity as flow; 0.034 is half-full flow.
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