Study On Accuracy Improvement Of 1-D Numerical Model In Mountain Stream

Numerical models have been widely applied in hydraulic engineering research, planning, and so on. 1-D unsteady flow numerical model is still the main method to solve problems for its efficiency and reliability. It included water discharge, the flow motion or wave movement of flood, water movement after gate opened or closed.The mountain streams are characterized with complexity. The processes and main parameters will affect the accuracy and the result. This paper studies on the accuracy improvement of 1-D unsteady flow numerical model by numerical model experiments and water channel experiments.Firstly, this paper offers an expression of the velocity water ratio of flood plain to main channel in a compound channel. This expression based on the experiments in a 6m water channel and other experiments data. It focused on the water depth in main channel and flood plain and corresponding roughness. It reveals that the velocity ratio will increase while water depth ratio increases and vice versa.Secondly, this study puts forward and verifies formula that determines roughness in compound channels considering momentum exchange.It makes use of the expression of the velocity water ratio, the resistance superposition principle and continuity equation. After calculating, it shows that the results fit practical values well. Besides, the formula also reveals the momentum exchanges and the water depth effects on comprehensive roughness in unsteady flows.Thirdly, this paper also analyzes some other parameters in 1-D unsteady flow numerical model of mountain streams. These parameters include momentum correction coefficients, flow patterns, river bends and artificial buildings. In order to apply the transcritical flows, the reduction of convective acceleration term has been improved. After that, momentum correction coefficient formula has been derived from the expression of velocity ratio. According to the comparison, linear SCS method is regarded as the best choice for determining bend river resistances.Lastly, applying these improved methods to 1-D unsteady flow numerical model. The result agrees with practical values well, and it should predict the unsteady flow propagation characteristics of the river of Xiangjiaba to Chongqing.