Friction Modeling of Flood Flow Simulations

A new, three-parameter friction model at the boundaries of free surface flow is proposed. The model is valid for all flow and roughness characteristics and it is proposed to replace the widely used Manning equation in the flood simulation models. In the gauged flow domains, the parameters of the model can be calibrated directly using the appropriate field data. For the ungauged flow domains, the parameters are estimated following a four-step procedure: (1)selection of roughness zones; (2)generation of synthetic data from water depthflow velocityroughness height combinations; (3)calculation of shear stresses using a physically based equation; and (4)estimation of the model parameters through regression toward the results of this equation. The proposed friction model is used in the case study of the Tous dam break in Spain in 1982, as it was simulated by the two-dimensional hydrodynamic model FLOW-R2D. The results of this application show that the proposed friction model performs slightly better than the commonly used Manning equation.