中文摘要：

黄河下游沿程出现的辫状河流（游荡型河流）、弯曲河流（弯曲型河流）、顺直河流（顺直微弯型河流）的转化现象引人关注,并有不同方面的专门研究。本研究针对以往研究的不足,通过对不同河型段的水沙演变、断面形态对流量的响应、河道断面演变、河床沉积速率及能耗率特征等方面,系统分析了不同河型段河道的水沙效应。认为黄河下游沿程出现的三类河型是由河道比降小、河床质细、洪枯水交替、粗泥沙输入少及大堤限制等因素起主导作用。其中顺直河流的出现是人工大堤的胁迫性产物。随着近年来水沙的阶段性减小,顺直河流在大堤的挟持下得以维持；弯曲河段河道的侧向摆动依然、宽度略微变窄,河床加积速率最大,但不会导致整个下游河道比降发生明显变化；辫状河段能耗率相对较大,冲淤强烈,滩槽更替频繁,但随着流量的减小,其能耗率明显减小,其比邻弯曲河流段的河道会逐渐曲流化,表现为弯曲河段的适度上延,但延伸有限。各类治理措施中,以中上游修建水库和淤地坝是最有效的,可拦截大量粗泥沙,从而降低下游河床的加积速率,以延缓悬河的发展。当然,针对决口险情的大堤建设是必要的,但要与不同河型段的河道稳定性相适应。

英文摘要：

It is an important science problem that braiding, meandering and straight channel patterns appeared in the lower Yellow River. Some researches have studied this problem in different aspects. However, some existent insufficiencies still need to study. In this work, it is mainly studied the water and sediment load effect to the different channel patterns in terms of discharge and sediment load evolution, cross-section form responding to discharge, channel cross-section evolution, depositional rate of channel bed, channel width evolution, and the channel gross power. The results show that the main dominant process of fornlation of the different channel patterns is gently channel gradient, fine materials of channel bed, alternation of low water and floodwater, a little of coarse sediment input to the channel, and restriction of the artificial levees. The formation of the straight channel pattern is induced by the artificial levee restriction. This channel pattern will be persistent with the decreasing suspended sediment load and mean discharge in recent decades and the restriction of the artificial levees. In the meandering reach the channel lateral migration is still evident, channel is narrowed gently, and the depositional rate on channel bed is the most among the three channel patterns. However, the higher depositional rate is unlikely to change the channel gradient of the lower Yellow River. The gross power of the braiding channel reach is higher than that of the other channel pattern reaches. Strong erosion and deposition occurred in braiding reach and lead to frequent change of the elevation and location of the channel bed and mid-channel bars. It is evident the gross power of the braiding channel decreased in rent decades which must lead to the end reach of the braiding channel tend to meandering, namely, the meandering channel may be outspread up-wards in limited length. In many management ways for the Yellow River basin the building of reservoirs and check dams in the upper and middle river basin is the effe