Compute open-channel uniform-flow discharge Q = (1/n)*A*R^(2/3)*sqrt(S) from roughness n, cross-sectional area A, hydraulic radius R and bed slope S.
由糙率 n、过水断面 A、水力半径 R 与底坡 S，按 Q=(1/n)A·R^(2/3)·√S 计算明渠均匀流流量。
Constants and standards used on this page with their authoritative sources, for verification and citation.
| Quantity | Value | Unit | Source |
|---|---|---|---|
| SI coefficient | 1.0 | m^(1/3)/s | Manning R. (1890); the coefficient is exactly 1 in SI units |
| US customary coefficient | 1.486 (often written 1.49) | ft^(1/3)/s | Chow V.T. (1959), Open-Channel Hydraulics |
| Roughness n (concrete) | 0.012–0.017 | s/m^(1/3) | Chow (1959) Table 5-6; common values in Chinese hydraulics texts |
| Roughness n (earth canal / natural channel) | 0.018–0.030 / 0.030–0.050 | s/m^(1/3) | Chow (1959); GB 50286-2013 levee design code |
| Chezy coefficient relation | C = R^(1/6)/n | m^(1/2)/s | Chezy-Manning relation (Chow 1959) |
Note: the Manning equation applies to uniform turbulent open-channel flow. n is empirical and depends on bed material, vegetation, irregularity and stage; select it from site survey and design codes. The coefficient 1.0 applies only in SI units.
| Item | Formula / Note | Source / Standard |
|---|---|---|
| Manning formula | v = (1/n) × R^(2/3) × i^(1/2), Q = A × v | Manning 1889 |
| Roughness n values | Concrete 0.012–0.017, earth canals 0.022–0.030, natural rivers 0.030–0.060 | Chow 1959 Open-Channel Hydraulics Table 5-5 |
| Hydraulic radius | R = A ÷ χ (wetted perimeter); full circular pipe R = D/4 | Section hydraulic elements |
| Most efficient section | Rectangular most efficient at b=2h giving R=h/2 | Classic open-channel result |