The Calculation Of Scour For Contracted Channel

Firstly, the present paper has established one-dimensional steadily saturated flow-sediment numerical model for contracted channel; then the discrete differential equations has been derived by a finite-difference method. The paper has applied Wspro software and the formulas 64-1 and 64-2 of general scour in china to calculate the general scour of contracted channel. According to the results, the paper has analyzed the reason of producing the difference among them.The reason is here: In the grade of the different flux the result that calculated by one-dimensional steadily saturated flow-sediment numerical model is relevant to the history and time of scour. In the contrary, the software and the formulas have no relationship with the time and the history. Secondly, in the facet of selecting the model, the fomula 64-2 has the difference with one-dimensional steadily saturated flow-sediment numerical model. The model has the progress changed gradually during channel getting to shrink so that it amplifies the length of the changing district in the river and the result is affected by the neighborhood section. The shrink of channel is a sudden progress in model based the fomula 64-2 and the part of section contracted is rather short. So the application of one-dimensional steadily saturated flow-sediment numerical model makes the rate of velocity less, and then the value of scour becomes less. Moreover, the model involves the problem on sedimentation velocity and granule diameter of sediment. Wspro software only introduces(adopts) the medium particle size of the grade of sediment, ignoring the influence from fine and coarse sediments. The formula 64-2 considers the sediment effect by a relative motion parameter of flow and sediment. And the formula 64-1 relates to the average particle of sediment and its units is not harmonious. The larger particle can bring the result less.