River Hydraulics

River hydraulics is the study of water flow in natural channels, focusing on velocity distribution, discharge, sediment transport, and channel morphology. Flow behavior is influenced by channel geometry, slope, roughness, and boundary conditions. Regime theory relates stable channel dimensions to discharge, while Manning’s equation is widely used for estimating flow in open channels. Sediment transport occurs through suspension, saltation, and bedload, with initiation of motion determined by the Shields criterion (critical shear stress). Meandering rivers evolve through erosion on outer banks and deposition on inner banks, creating sinuous channels. Flood routing predicts the movement of flood waves downstream, accounting for attenuation and translation. Engineers apply river hydraulics in flood control, navigation, sediment management, and ecological restoration.

Governing FormulaManning’s equation: Q = (1/n) × A × R^(2/3) × S^(1/2) Shields criterion: τ_c = θ_c (ρ_s - ρ) g d Where: A = cross-sectional area (m²) R = hydraulic radius (m) S = slope of energy grade line n = Manning’s roughness coefficient τ_c = critical shear stress θ_c = Shields parameter (~0.03–0.06) ρ_s = sediment density ρ = water density d = particle diameter

Knowledge Check

10 Questions

1.A river has a width of 50 m, average depth of 3 m, and velocity of 1.5 m/s. What is the discharge?

2.What is a meandering river?

3.The Shields criterion is used to determine:

4.A river reach has a length of 5 km and the water surface elevation drops by 2.5 m. What is the slope?

5.Flood routing is used to:

6.In regime theory, the width of a river is related to discharge by:

7.What is the main agent of sediment transport in a river?

8.A river has Manning’s n = 0.035, hydraulic radius R = 2.5 m, slope S = 0.0008, and cross-sectional area A = 100 m². What is the discharge?

9.The Manning’s roughness coefficient (n) for a natural river is typically:

10.What causes sediment deposition in a river?