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

许多关于交替沙洲的研究都是在平衡供沙条件下进行的，并讨论了平衡状态下的现象。然而，河流中的坝形并不总是在这种条件下形成的。因此，研究某些水沙排放条件对沙坝形态的影响具有重要意义。在本研究中，研究了均匀和非均匀沉积层中由水沙输送能力不平衡引起的旋转退化/沉积对交替沙洲形态变化的影响。还讨论了分选对变异的影响。结果总结如下：1。在双低沙洲形成区附近的小流量条件下，随着退化的进行，交替沙洲的波长逐渐增大，因为泥沙输运较少的区域发育。随着离子的进一步深入，波长和高度都随着低水道的形成而增加。在无砂坝形成区附近的大流量下进行降解时，由于交替砂坝的发育受到限制，其波长和高度下降。特别是，在不均匀的沉积层中，交替沙洲的发育是不稳定的。3 .在无砂坝形成区附近大流量淤积时，由于促进了交替砂坝的发育，其波长逐渐增大。在非均匀沉积层中，交替沙洲的波长和高度随退化而显著增加和减少。影响沙洲形态变化的不仅是河床坡度，还有坡度变化率。棒材的迁移速度随退化而减小，随加重而增大。迁移速度的降低与水塘的固定化和低水位河道的形成有关。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