黄河龙门—三门峡段河漫滩组成物质的粒度特征

GRAIN SIZE CHARACTERISTICS OF FLOOD PLAIN SUBSTANCE COMPOSITION ALONG LONGMEN SANMENXIA SECTION OF THE YELLOW RIVER

本文分析了河漫滩组成物质的粒度组成特征，并与河床质粒径级配与悬移质粒径级配进行了比较，研究了河漫滩宽度及物质组成对河槽几何形态的影响。结果表明：使黄河产生游荡的首要条件是河道的强烈堆积以及要有能够满足其大幅度游荡的宽广的河漫滩，如果河漫滩组成物质中细颗粒物质含量低，抗冲性能小，则更能进一步促使河道变得宽浅，游荡程度加剧。

This paper analyzes grain size characteristics based on samples of flood plain substance composition collected systematically from Longmen Sanmenxia section of the Yellow River. In terms of spatial changes, the longitudinal distribution of alongshore flood plain substances is characterized by coarseness at upstreams and fineness at downstreams. In terms of horizontal changes, grain size of flood plain substances changes from coarse at forward fringe to fine at backward fringe. Comparisons of grain size graduation of flood plain substances with that of river bed substances indicated that substances of flood plain facies are finer than that of river bed facies. They differ distinctively from each other. Comparisons of flood plain substances with suspended particles showed that sediments deposited on flood plains are mainly the portion of coarser particles in incoming suspended load from upstreams. The paper also studies the impact of flood plain width and substance composition on river bed geometric morphologies. It is found out that river bed width depth ratio is very closely related with flood plain width as well as percentage of silt and clay content in flood plain substances. The results of the above studies indicated that the first important condition accountable for Yellow River wandering is intense channel accumulation, and then a broad flood plain wider enough to satisfy the great amplitude in wandering. In case finer particles in flood plain substances is low in concentraction with weak anti scouring capability, the river channel will become even shallower and wider, so aggravating the extent of wandering.