三峡水库蓄水后荆江沙质河段冲淤分布特征及成因

Features and causes of sediment deposition and erosion in Jingjiang reach after impoundment of the Three Gorges Project

根据实测水沙、地形资料,分析了荆江沙质河段内洪枯河槽、宽窄河段等不同部位的冲淤幅度差异,并结合观测资料讨论了河道形态调整对水沙过程的响应关系。结果表明:荆江河道泥沙冲淤强度平面分布不均,泥沙冲刷主要集中于枯水河槽,断面形态趋向窄深;宽浅河段冲刷强度大于束窄河段,河道形态沿程趋于均一化。蓄水前河道形态与水沙过程相适应,河床在不同流量下以造床流量为界发生冲淤交替,长时期水沙过程作用下河道整体冲淤平衡。蓄水后含沙量大幅减小、大洪水消减而中洪水持续时间增长是荆江沙质河段冲淤分布特征形成的主要原因。

Using hydrologic and morphological observations from the Jingjiang reach of the Yangtze River, the differences of bed deformation among different channel types are examined and the response of channel form adjustment to regulated flow and sediment process has been investigated. It is revealed that the magni- tude of channel deformation is uneven in the whole reach, although the channel bed is totally covered with erosive sand. The erosion amounts mainly concentrate in the part of channel bed below the low flow stage, which causing the section geometry of channel becoming narrow and deep. Meanwhile, the erosion is more intensive in shallow and wide reaches than deep and narrow reaches, which tends to be uniform for the whole channel. Obviously, the relation between channel geometry and process of flow and sediment dis- charge has changed after the Three Georges Dam closure. In the pre-dam period, although erosion or depo- sition took place in the channel under different discharges, channel geometry adapted to the process of flow and sediment discharge and the sediment transport process had shown equilibrium in long term. In the post-dam period, the dramatic reduction of incoming sediment load, the elimination of large flood and the prolongation of medium flow duration are inducing an uneven erosion magnitude and unequal channel form- ing frequency in different part of the channel.