冲积河流混合活动层内床沙级配变化的动力学基本方程

Basic equation for variation of bed material composition in active layer of alluvial river

本文将冲积河流混合活动层内床沙的交换、掺混概括为表层床沙与水中运动泥沙在床面附近湍流作用下的掺混交换和混合活动层中泥沙在沙波运动作用下的掺混交换过程,建立了冲积河流混合活动层内床沙级配变化的基本方程。该方程定量地反映了水流强度、床面沙波运动及河床冲淤变化与床沙级配变化的关系,描述了河床冲淤过程中床沙级配时空变化的动力学特性。文中还应用该方程,分析了河床冲刷粗化现象。

The infulence of sediment-laden flow on bed material composition of the active layer in the process of degradation and aggreagtion are considered to be composed of two parts with different sacle and mechanism. One is the turbulence burst taken place on the bed surface inducing the exchange between the sediment carried by flow and those setting on the bed surface. The other is the periodical deformation of the bed forms, especially the sand waves, which causes the mixing of bed material within the active layer. The equation describing these two processes is derived on the basis of mass conservation in the active layer.The variables of the equation are decomposed into two parts, one is corresponding to the average movement of sediment in active layer and the other one is corresponding to the disturbance due to bed form deformation.This partical difference equation appears to be a diffusion equation with source term.The application of the proposed equation to a simplified case of bed degradation is presented.The result shows it is reasonable.