Effects of water and sediment discharge conditions on variation in sand bar morphology

在与来水量相对应的平衡输沙条件下，对交替沙洲进行了大量的研究，并对平衡状态下的现象进行了讨论。然而，河流中的沙洲形态并不总是在这种条件下形成的。因此，研究某些来水来沙条件下形成的沙洲形态如何随其他条件的变化而变化是很重要的。在这项研究中，研究了均匀和非均匀泥沙床中由输沙能力不平衡引起的旋转冲淤对交替沙洲形态变化的影响。还讨论了颗粒分选对变化的影响。主要研究结果如下：1.在双低坝形成区附近小流量条件下，由于输沙量较小的区域发育，交替坝的波长逐渐增大。当…降级时更多的离子进一步发展，波长和高度都由于低水位的发展而增加。2.在靠近无坝形成区的大流量条件下，由于交替坝的发育受到限制，降解进行，波长和高度减小。尤其是在非均匀泥沙床中，交替沙坝的发育是不稳定的。3.在无沙洲形成区附近的大流量淤积过程中，由于促进了交替沙坝的发育，波长逐渐增大。4.在非均匀泥沙床中，由于泥沙的退化，交替沙坝的波长和高度的增加和降低是显著的。5.河床坡度及其变化率不仅影响沙坝形态的变化。6.沙坝的运移速度随泥沙的退化而减小，并随淤积而增加。运移速度的降低与水池的固定和枯水河道的形成有关。较少

Many studies on alternate bars have been conducted under an equilibrium sediment supply condition which corresponds to the water discharge, and discussed phenomena in an equilibrium state. However, bar morphology in rivers are not always formed under such condition. Therefore, it is important to investigate how the bar morphology formed by some water and sediment discharge condition varies by the other conditions. In this study, effects of rotational degradation/aggradation caused by an imbalance between water and sediment transport capacity on variation in alternate bar morphology are investigated in uniform and non-uniform sediment beds. Effect of grain sorting on the variation is also discussed. Results are summarized as follows :1.In case that the degradation progresses under the condition of small-water discharge near the double-low bar formation regime, the wavelength of alternate bars increases gradually because the areas with little sediment transport develop. When the degradat … More ion progresses further, both of the wavelength and height increase because low watercourse develops.2.In case that the degradation progresses under the large-water discharge near the no-bar formation regime, the wavelength and height decrease because the development of alternate bars is restricted. In particular, the alternate bar development is unstable in the non-uniform sediment bed.3.In case that the aggradation progresses under the large-water discharge near the no-bar formation regime, the wave length increases gradually because the development of alternate bars is promoted.4.The increase and the decrease of wavelength and height of alternate bars in consequence of the degradation are remarkable in the non-uniform sediment bed.5.Not only bed slope but also its changing rate affects variations in bar morphology.6.The migration velocity of bars decreases with degradation, and that increases with aggradation. The decrease of migration velocity relates to immobilization of pools and the formation of a low-watercourse. Less