Study on Deformation Process of Sand Bars at River Mouth

在河口处，水流输沙与波浪输沙相互作用，常形成拦门沙，严重影响河流的过流能力。因此，从河流工程的角度，需要对河口拦门沙的变形过程进行适当的模拟，而在河流输沙方面，水流的不稳定性和不均匀性对泥沙输移的影响尤为重要。因此，建立了描述这种非恒定非均匀条件下泥沙输移瞬态过程的平衡输移定律，河口地貌变化过程的模拟需要较复杂但又较为简化的模拟。本文在室内试验的基础上，利用乌塞尔数预测泥沙的输移方向，提出了与河流地区相似的利用希尔兹数的输沙流量公式。为了评价Shields参数与波浪特性之间的关系，对线性滤波方法的适用性进行了检验，提出了一种以河口平衡断面为参数的松弛模型来全面描述河口拦门沙的变形过程。根据实测资料，检验了本文提出的沙坝变形过程分析模型的适用性。

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.