黄河下游河道萎缩致灾机理探讨

本文基于水力学原理，结合实体模型试验及原型实测资料分析，探讨了黄河下游河道萎缩的概念、致灾效应和致灾机理。分析表明，河道萎缩是造床过程中河道排洪输沙功能衰退的一种演变现象，其致灾效应是使洪水涨率增大，同流量下洪水水位不断抬升。致灾的现象主要表现在畸型河势增加、工程险情增多、直接造成工程损失及滩区经济损失等。试验研究揭示，主河槽宽度缩窄造成洪水水位涨幅增大，河底平均高程抬升和过水断面面积减小造成洪水水位起涨的基准面抬升是河道萎缩致灾的主要原因。河道萎缩致灾效应的大小与萎缩模式有关，其中以“集中淤槽”模式所形成的致灾效应尤为明显。

Channel shrinkage and its disaster-causing mechanism in the Lower Yellow River

The disaster-causing effect and mechanism of channel shrinkage in the Lower Yellow River are analyzed according to the physical model experiment and field data. The results show that the channel shrinkage is a evolution phenomenon of the decline of flood carrying capacity and sediment transport in the fluvial process of river channel, which leads to the increase of flood frequency and higher flood water level during the same flow discharge. The disaster-causing phenomena include the increase of distorted flow pattern, engineering damage and economic losses in shoal areas, and so on. The increase of the amplitude of the flood water level rising caused by the narrowing of main channel, the raise of mean elevation of the river bed and the elevated datum level at young flood caused by wetted area reduction are the main causes affecting the disaster-causing effect. The disaster-causing effect is dependent on the modes of channel shrinkage, among them the mode with heavy deposition happened to the main channel is the most.