Effects of unsteady supply conditions of water and sediment and sediment sorting on variations in low-waterway morphology

有水池和冲刷序列的枯水航道在正常泄洪期起到鱼和植物的栖息地的作用。因此，研究枯水航道因供水、输沙条件变化而变化的特征具有重要意义。这与调查控制水和沉积物供应如何更有利于河流中的鱼类和植物栖息地的信息相对应。通过水槽试验，研究了输水输沙条件的变化对沙洲交替发育的枯水航道的影响。主要研究结果如下：1.枯水航道在来沙期随着河床淤积而剧烈波动，在无来沙期随着河床退化而统一稳定。输沙速率的平缓变化制约了枯水航道的稳定，影响了水池和冲刷序列的适度变化。枯水期间，随着出沙坝的冲刷，枯水河道演变为交替坝；枯水期，随着出沙坝的发育，交替坝变为枯水河道。前者随着床层的退化而发生，后者随着床层的淤积而发生。非均匀泥沙床面的枯水航道水深变化幅度小于均匀泥沙床面，这是由于泥沙颗粒分选导致泥沙粗化，限制了底泥的冲刷。

Low-waterways with pool and riffle sequence functions as fish and plant habitat in ordinary discharge period. Therefore, it is important to investigate characteristics of low-waterway variation due to change of water and sediment supply conditions. This corresponds to information in order to investigate how controls of water and sediment supply are better for fish and plant habitat in rivers. In this study, effects of the change of water and sediment supply conditions on low-waterway, which developed from alternate bars, variation were investigated by means of flume tests. Results are summarized as follows :1. The low-waterways fluctuate actively along with bed aggradation during the periods of sediment supply, and they unify and stabilize along with bed degradation during the periods of no-sediment supply.2. Gentle change of sediment supply rate restricts stabilization of low-waterway, and it effects moderate variations of pool and riffle sequence.3. The low-waterway changes into alternate bars with erosion of emerged bars during the high-water discharge period ; and the alternate bars change into low-waterways with development of emerged bars during the low-water discharge period. The former occurs along with the bed degradation and the latter occurs along with the bed aggradation.4. The variation range of the depth of low-waterway in the non-uniform sediment bed is smaller than that in the uniform sediment bed because the erosion of bed sediments is restricted by means of sediment coarsening due to grain sorting.