Semi-Implicit Numerical Models of Flood Hydraulic Routing (A Case Study: Lighvan-Hervi Reach of Lighvan-Chai, Tabriz)

River flow routing has been a significant issue in hydraulic engineering. The main goal of this research work was solving Saint-Venant equations by using the semi-implicit finite difference scheme and considering energy conservation principle at the discontinuous points of flow field. In this model, with the first order accuracy, the flux limiter scheme and Upwind for the scheme are used for the satisfaction of TVD condition and discretization of the advection phrase in the momentum equation, respectively. By using three assessment functions including Nash-.Sutcliffe, sum square error and correlation coefficient, the performance of the model was evaluated for flood routing through Lighvan-Chai River between Lighvan and Hervi hydrometric stations with the application of twenty cross-sections. Manning roughness coefficient as a parameter for calibration and verification processes was determined to be 0.028. Finally, a comparison was made between nonlinear Muskingham hydrological method and the presented model through the same river reach. The amount of assessment functions for the semi-implicit model was calculated to be more than the hydrological one. The results showed that the presented model not only had high calculative efficiency and no limitation in time step calculation, but also displayed more accuracy for the hydrodynamic characteristics of flow.