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

在正常泄流期，具有池、沟序的低洼水道具有鱼类和植物栖息地的功能。因此，研究低航道随水沙供应条件变化的变化特征具有重要意义。这与调查如何控制水和沉积物供应对河流中的鱼类和植物栖息地更好的信息相对应。本文采用水槽试验的方法，研究了水沙供应条件的变化对交替沙坝形成的低洼河道的影响。结果总结如下：1。在供沙期，低水道随河床淤积而积极波动，在无供沙期，低水道随河床淤积而统一稳定。输沙率的温和变化制约了低洼水道的稳定，并影响了池、沟序的适度变化。在高流量期，低水位河道随着出坝的冲刷而变成交替沙洲；在低潮期，随着出坝的发育，交替坝变成低潮水道。前者随床层退化而发生，后者随床层退化而发生。由于泥沙分选作用导致泥沙粗化，限制了河床的侵蚀作用，非均匀沉积层的低水道深度变化幅度小于均匀沉积层。

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.