Study on Deformation Process of Sand Bars at River Mouth

在河口处，由于水流输沙和波浪输沙的相互作用，经常形成沙坝，严重影响河流的通行能力。因此，需要从河流工程的角度对河口沙坝的变形过程进行适当的建模。在河流输沙过程中，水流的非稳态和非均匀性对输沙的影响尤为引人关注，因此建立了一个非平衡输沙定律来描述这种非稳态非均匀条件下输沙的瞬态过程。河网输沙过程较为复杂，但对河口河流形态变化过程的模拟需要进行一定程度的简化。在实验室研究的基础上，利用乌塞尔数预测输沙方向，并提出了与河区建立的输沙流量公式相似的盾盾数输沙流量公式。为了评估屏蔽参数与波的特性之间的关系，测试了线性滤波方法的适用性。提出了一种以河口平衡断面为参数，代替水流和波浪输运能力等复杂参数，全面描述河口沙坝变形过程的松弛模型。根据实际河流的现场资料，检验了该分析模型对沙坝变形过程的适用性。

At river mouth, sand bar is often formed due to interaction of sediment transport by river flow and that by waves, and it affects the flow capacity of the river severely. Hence, an appropiate modelling of deformation process of sand bar at river mouth is required from the view point of river engineering.As for sediment transport in rivers, effect of unsteadiness and non-uniformity of flow on sediment transport is in particular interesting, and thus a non-eguilibrium transport law has been established to describe transient process of sediment transport under such unsteady nonuniform conditions.Sediment transport by weves is more complicated, but somewhat simplified modelling is required for modelling variation process of river morphology at river mouth. Based on laboratory studies, Ursell number is used to predict the direction of sediment transport, and transport discharge formula using Shields number has been proposed, which is quite similar to that established in river region. In order to evaluate the relation between Shields parameter and the characteristics of waves, applicability of a linear filter method is tested.A relaxation model is proposed to descride deformation process of sand bars at river mouth totally, in which equilibrium section of river mouth is used as a parameter instead of complicated parameters related to transport capacity of flow and waves. Based on the field data of actual rivers, the applicability of the present analytical model for deformation process of sand hars has been inspected.