径流量和海平面变化对河口最大浑浊带的影响

应用改进的ECOM模式,耦合泥沙输运方程,研究径流量和海平面变化对河口最大浑浊带的影响.河口最大浑浊带位于滞流点处,底层上下游余流均向该处输运泥沙,造成该处泥沙汇合,而由流场辐合产生的上升流又使该处的泥沙不易落淤.由于盐水入侵带来的高盐水位于北岸的底层,其斜压效应使底层的横向环流由北向南流动,把底层高浓度的泥沙向南岸平流,使得最大浑浊带位于南岸.研究河口最大浑浊带现象必须使用三维泥沙输运模式.在径流量增大的情况下,与控制试验相比底层向陆的密度流减弱,滞流点下移,导致最大浑浊带也下移;因上游来沙量增加,在最大浑浊带中心和河口拦门沙处悬浮泥沙浓度趋于增加.在径流量减少的情况下,最大浑浊带的变化趋势与径流量增大情况的结果相反.在海平面上升的情况下,拦门沙区域底层向陆的密度流趋于增强,滞流点上移,最大浑浊带也相应向上游移动;最大浑浊带中心处泥沙浓度趋于增大,但口门拦门沙处泥沙浓度趋于减小.径流量和海平面变化对最大浑浊带影响明显.

Impacts of change of river discharge and sea level on estuarine turbidity maximum zone

Using the improved ECOM model and coupling the sediment transport equation, the impacts of change of river discharge and sea level on estuarine turbidity maximum zone are studied. The estuarine turbidity maximum zone locates at the stagnation point. Both the upper-stream and lower-stream residual currents at low layers convey sediments to the stagnation point that induces the convergence of sediments, and the upwelling current induced by the convergence of flow field makes sediment difficult to settle down near the stagnation point. Because higher salt water brought by the saltwater intrusion lies in the bottom layer of the north coast, its baroclinic effect induces the transverse current at bottom layer flows from north to south which advects horizontally the high concentration sediments from north to south coast, it makes the turbidity maximum zone lie in the bottom of south coast. It is necessary for using a three dimension sediment transport model to study estuarine turbidity maximum zone. In the case of river discharge increase, compared with the case of control experiment, the land-ward density induced current at bottom layer reduces, the stagnation point moves downstream that makes the turbidity maximum zone move downstream. The suspended sediment concentration at the center of the turbidity maximum zone and near the sand bar tends to increase because of the sediment addition from upstream. In the case of river discharge decrease, the variation tendencies of estuarine circulation, saltwater intrusion and turbidity maximum zone are in contrast with the results of river discharge increase. In the case of rise of sea level, the land-ward density induced current near sand bar enhances, the stagnation point moves upstream that makes the turbidity maximum zone move upstream. The sediment concentrations of turbidity maximum zone tends to be higher, but the sediment concentration at sand bar tends to be lower. The variations of change of river discharge and sea level have obvious impact on the turbidity maximum zone.