冲积性河流河床冲淤调整对洪水泥沙过程的响应——以黄河游荡型河段为例

为研究冲积性河流造床机理，基于能量耗散原理分析河床调整与水沙过程（变异特性）间的关系十分必要。以黄河游荡型河段为例，利用实测资料分析和平面二维水沙数值模拟方法，进行了各种洪水泥沙条件下河流冲淤规律的探讨。研究发现平滩面积、河相系数与径流泥沙特征值间存在的关联性映射出冲积性河流能量关系中的制约机制；不同洪水泥沙过程的河床冲刷强度变化具有阶段性，主槽累积刷槽效应与洪水泥沙过程有密切响应关系；高效输沙的洪水过程通过塑造最适宜的河床断面形态，能实现最佳输沙效率与主槽的最大冲刷。在不同漫滩洪水条件中，综合系数Φ最大时的洪水过程具有最大累积刷槽效应，因此对应流量可作为黄河下游漫滩洪水的调控指标。

Alluvial river adjusting response to the flood-sediment process: For the wandering reach of Yellow River as an example

It is necessary to analyse the relationship between channel evolution and variation in sediment-laden floods based on the energy dissipation principle, in order to investigate the bed-forming mechanisms of an alluvial river. As an example of the braided reach in the Lower Yellow River, the characteristics of channel scouring and silting in the reach under various sediment-laden floods were presented, using a two-dimensional numerical model and the analysis of observed data. It is founded from this investigation that the relevance among bankfull area, geomorphic coefficient and characteristic values of a sediment-laden flood can reflect the restricting mechanisms in relation of the river energy; the channel scouring intensity changes periodically with various sediment-laden floods, and the accumulative scouring effect for the main channel can correlate strongly with the process of water and sediment transport; and only a flood process that can shape the most appropriate cross-sectional geometry of an alluvial river can attain both the best efficiency for sediment transport and the maximum efficiency of the main channel scouring. These results also indicate that a flood process with the maximum comprehensive factor Φ_max can obtain the best accumulative channel scouring efficiency, and therefore, the discharge corresponding to Φ_max can be considered as a control indicator for overbank floods in Lower Yellow River.