水库下游分组沙冲淤特性分析

Analysis of group-sized sediment transport downstream a reservoir

水库修建前后下游河道分组沙冲淤实测资料表明:建库前特定河段粗沙淤积主要是由于水力因素沿程显著减弱;建库后近坝河段,泥沙补给不足,各组泥沙均发生较剧烈的冲刷,床沙粗化迅速;距坝较远的河段,只要上游河段有足够泥沙补给,能够基本达到饱和的各组泥沙的冲淤特性与建库前保持一致,但淤积量趋于减小;水库下游发生长距离冲刷的主要原因是床沙补给不足,尤其是细沙补给严重不足。

Analysis and comparison of the field data of group-sized sediment transport for the two cases before and after the dam construction show a great difference of coarse particle transport in different reaches. In the natural river case, deposition of coarse particles is often caused by a dramatic decrease of flow velocity in some reaches, while in the case of reservoir operation the erosion of nearly all sizes of sediment are a consequence of supply shortage from the bed. In the reach closer to the dam site the erosion is more serious than the reaches far from the dam. In a reach far enough, the transport of some size groups will be similar to that of a natural river if the supply from the upstream is sufficient, as these groups are easily saturated. Long-distance erosion downstream a reservoir is caused by shortage of the supply from riverbed, particularly shortage of fine particles.