Effects of water discharge and sediment supply on deformation of riverbed with sand bars

研究了水沙条件对沙坝河床变形的影响。研究了晶粒分选对变形不良的影响。主要研究结果如下：1.流量变化对交错沙生长和转化的影响（1）变化率对波浪周期长的交错沙转化影响较小，对波浪周期短的交错沙转化影响较大。(2)在洪水期，非均匀沙床中单个交错沙坝的波高低于均匀沙床中的波高。(3)波浪周期较长时，波高、水深和输沙率对流量变化的响应滞后较小，而波浪周期较短时，波高、水深和输沙率对流量变化的响应滞后较大。非均匀沙床中交错沙坝对流量变化的响应滞后小于均匀沙床中.泥沙供给对交错沙坝改造和曲流河形成的影响（1）由于流量减少，水流在交错沙坝池中集中，出现了露出的沙坝，形成曲流河。有输沙量时曲流浅，变化活跃，无输沙量时曲流深，稳定。(2)非均匀沙床中出现的沙坝是由颗粒分选形成的，比均匀沙床中的沙坝稳定.流量对曲流变形和交错沙坝改造的影响（1）非均匀沙床中的交错沙坝比均匀沙床中的易受冲刷，易形成交错沙坝。(2)由于河床淤积和枯水流量的作用，曲流河转化为更大的交错沙坝。

Effects of water discharge and sediment supply on deformation of sandbar beds are investigated. The effect of grain sorting on the bad deformation is also investigated. The summary of results is as follows :1. Effects of change in water discharge on growth and transformation of alternate bars(1) Effect of change rate on the transformation is relatively small in case of a long wave period, whereas it is large in case of a short one.(2) Wave height of an individual alternate bar in the non-uniform sediment bed is lower than that in the uniform one during the flood period.(3) Response-lag of the wavelength and height, flow depth and sediment transport rate to discharge change are small when the wave period is long, whereas they are large when the wave period is short. And, response-lag of alternate bars to discharge change in the non-uniform sediment bed is smaller than that in the uniform one.2. Effects of sediment supply on alternate bar transformation and meandering stream formation(1) The centralization of flow at pools of alternate bars due to decrease of water discharge makes emerged bars appear, and forms meandering streams. The meandering streams in case with sediment supply are shallow and vary actively, whereas those in case without sediment supply are deep and stable.(2) The emerged bars in the non-uniform sediment bed are formed with grain sorting, and are more stable than those in the uniform one.3. Effects of water discharge on meandering stream deformation and alternate bar reformation(1) Alternate bars are formed easily in the non-uniform sediment bed because the emerged bars in that bed are eroded easily than those in the uniform one.(2) The meandering streams are transformed into more large alternate bars by the riverbed aggradation and the low water discharge.