河口形状对最大浑浊带形成的影响

Impact of the Estuarine Shape on the Formation of Turbidity Maxima

利用改进的ECOM模式和耦合三维的悬沙输运方程,通过设计一个平直和喇叭形理想河口,研究河口形状对最大浑浊带的影响.在滞流点处存在着最大浑浊带,中心位于南岸,从动力机制上揭示了最大浑浊带形成的原因.与平直河口相比,喇叭形河口因口门内河口变宽,使得表层向海的流辐散而流速减小,从而造成喇叭形河口段盐水入侵加剧,进而造成底层向陆的密度流及其向西流动的距离增加,盐水在平直河道内向西入侵的距离增加.喇叭形河口悬沙浓度减少,但存在着两个最大浑浊带.一个在平直河道段,因滞流点上移,而相应向上游移动,另一个在喇叭形河口段南岸,主要是由挟带悬沙的径流受科氏力的作用向南岸偏转以及底层横向环流向南岸输送高浓度悬沙造成的.河口形状对河口环流、盐水入侵和最大浑浊带的影响明显.

Using the improved ECOM model and suspended sediment transportation equation, the impact of the estuarine shape on the formation of estuarine turbidity maximum zone is studied with an idealized strait and funnel-shape estuary designed in this paper. There exists turbidity maximum zone at stagnation point, and its center locates at south side of the river coast. The reason of formation of estuarine turbidity maximum zone was revealed in terms of dynamic mechanism. Compared with the case of the strait estuary, the current divergence induced by the spreading width of funnel-shape estuary inner the mouth makes the current weaken, the distance of landward flow of density current at bottom layer induces, and the saltwater intrusion strengthens in the funnel-shape estuarine area. In addition the landward density induced current at bottom layer and its westward flowing distance increases. The westward intrusion distance of saltwater in the strait river channel region increases. The concentration of suspended sediment in the funnel-shape estuary decreases, but there are two turbidity maximum zones in it. One lies in the strait river way. Because the stagnant point moves toward upstream, its position relevantly moves toward upstream. However, the other lies in the south coast of the funnel-shape estuary area. It is mainly induced by the river flow, which turns toward the south coast under the effect of Coriolis force, and the bottom transverse circulation which transport high concentration suspended sediment to the south coast. The variation of the river mouth shape has obvious impact on the estuarine circulation, the salinity intrusion and the turbidity maximum zone.