黄河下游河槽治理方法分析

本文对已有的河槽形态与水流狭沙力关系的研究成果进行了探讨。进一步在考虑米沙组成变化、河槽综合阻力变化的条件下．计算得到了黄河下游典型断面流量分级平均水沙条件下河槽平衡输沙横剖面。平衡横断面与实际断面比较．下游无论游荡段与弯曲段，实际断面都显得过于宽浅。分析认为，尽管河槽缩窄可加大水挟沙能力．但受河型发育机制的制约．在现有水沙和边界条件下黄河下游河槽的横剖面是无法自动调整形成输沙平衡形态的。文中还利用黄河下游来水来沙和河道冲淤实测资料证明了黄河下游水流不冲狭沙量小于不淤沙量．河道从淤积转向冲刷时．水流含沙量明显降低，固此减少同流量下台沙量的变化有利于减轻下游河遭淤积。从理论分析结果看：缩窄中、小流量“下的河槽．以多级河槽方式重点整治花园口以下河段．使横断面总体形态呈上凸形．能显著减小黄柯河槽中的淤积；同时，应配合河道整治，利用水库调节水沙和进行必要的挖沙疏浚措施。具体实施方法还需要进一步研究；

Study on direction of channel training of the Lower Yellow River

The paper deals with a method of alleviating the severe sediment accumulation in the Lower Yellow River. Through analyzing the characteristics of the oncoming sediment and water of the river, and considering the variation of oncoming suspended sediment composition and in synthetic channel's hydraulic roughness, the shapes of some cross sections of the river demanded by sediment transport in equilibrium for the discharge carrying 97% of the sediment transported in the river is figured out. Comparing the calculated and measured shapes of the cross sections, it is obvious that the present channel in nearly all the reaches, from braided down to meandering, of the river is too shallow and wide. Although the river's sediment transport capacity can be enlarged by narrowing the present channel, the river channel cannot be narrowed further naturally to reach equilibrium of sediment transport under the existing boundary and oncoming water and sediment conditions due to the effect of mechanism ruling the evolution of channel pattern. Using the measured data of oncoming water and sediment, and sediment deposition in the river channel, it is demonstrated that the sediment concentration drops down obviously when the sedimentation in the river channel turns from accumulation to erosion; therefore, reducing the variation in the sediment concentration of same discharges is favorable to alleviate sediment accumulation in the river. In the light of theoretical analysis in the paper, it is reasonable that the sediment accumulation can be reduced markedly by narrowing the channel for the medium and low discharge to a compound one with two steps of berm following generally a convex upward curve in the relation of relative height H against width B of the channel, and other alleviating sediment accumulation measures such as regulation of water and sediment discharges, channel dredging etc., are also necessary to cooperate with channel training.