Numerical Modeling of Unsteady Compound Channel Flow

by R. S. M. Mizanur Rashid, Washington State Univ, Pullman, United States,
M. Hanif Chaudhry, Washington State Univ, Pullman, United States,

Document Type: Proceeding Paper

Part of: Hydraulic Engineering


The unsteady open channel flow equations describing conservation of mass and momentum (St. Venant equations) are integrated numerically to determine the depth of flow and the rate of discharge along the length of a compound channel at different time. Preissmann four-point implicit finite difference scheme is used. The suitability of two different approximations for the channel cross section are investigated: (1) The flow velocity over the flood plains is negligible as compared to the velocity in the main channel, i.e. the flood plain acts as storage only and does not contribute to the momentum transfer; area in the continuity equation represents the entire cross-sectional area; the flood plains and the main channel are separated by a vertical line at their interface and the division line is not included in the wetted perimeter. (2) The entire channel section contributes to momentum flux, i.e., without neglecting the flow velocity over the flood plains; the flood plain and the main channel are considered as a single flow section and the momentum coefficient is used to take care of the non uniform velocity distribution. The computed results are compared with the experimental data obtained by the authors. Approximation (1) compares better with the experimental results than approximation (2).

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