河口形状对河口环流和盐水入侵的影响

Impact of the Estuarine Funnel Shape on the Estuarine Circulation and Saltwater Intrusion

作者应用改进的ECOM模式,通过设计一个平直和喇叭形理想河口,研究河口形状对环流和盐水入侵影响。盐水入侵产生盐度锋面,在锋面处底层存在着向陆的密度流,为保持断面上质量连续,上层的流速明显增大;表层流有偏北的分量,底层流有向南分量,表明有横向环流存在。盐水入侵产生的盐度锋面在水平面上向西北倾斜,北岸盐水入侵比南岸大,在垂向上向上游倾斜,底层盐水入侵比表层大,高盐水位于北岸的下层。涨潮流、向陆的密度流和混合是产生盐水入侵的动力因子。科氏力使涨潮流向北岸偏转,向陆的密度流存在于底层,这种动力机制导致了盐度分布的不对称。盐度横向分布产生的斜压压强梯度力指向南岸,并随水深增加,导致底层流向南岸流动;因要满足质量守衡,在北岸因底层流的辐散产生下降流、水位下降,而在南岸因底层流的福合产生上升流、水位抬升,水位的横向分布又导致表层流向北,形成一垂向横向环流。喇叭形河口因口门内河口变宽,造成流的辐散,向海的流速减少和产生上升流,底层向陆的密度流向西流动的距离减少,口门处盐度增加,但盐水向西入侵的距离减少;河口喇叭口南岸下层也出现明显的高盐水;垂直混合增强,盐度垂向趋于均匀。

Using an improved ECOM model, designing an idealized strait and funnel - shape estuary, the impact of the estuarine funnel shape on the estuarine circulation and saltwater intrusion is studied. The saltwater intrusion produces salinity front, there exists a land - ward density induced current under the salinity front, and the current speed at the upper layer obviously enhances due to mass continuity through the transverse section. There is a northward component of current at upper layer and a southward component of current at lower layer, this indicates that there exists transverse circulation. The salinity front induced by saltwater intrusion inclines northwestward horizontally that means the saltwater intrusion at the north coast of the estuary is stronger than at the south coast, and inclines toward upstream vertically that means the saltwater intrusion at the lower layer is stronger than at upper layer. The higher salt water locates at the lower layer and near the north coast. The dynamic factors of saltwater intrusion are the tidal flood current, land - ward density current and mixing. The Coriolis force makes the flood current deflect to the north coast, and the land - ward density current exists at the lower layer, those dynamic mechanism result in asymmetry distribution of salinity. The baroclinic pressure gradient force induced by the salinity distribution in transverse section directs the south coast and increases with the water depth, this results in the current at bottom layer flows to the south coast. In order to keeping mass conservation, the divergence at bottom layer and north coast produces downwelling and drop of water level, and the convergence at bottom layer and south coast produces upwelling and rise of water level. This transverse distribution of water level makes the surface current flows northward, the above dynamic process induces a transverse circulation. The current divergence induced by the spreading width of funnel - shape estuary inner the mouth makes the current weaken and produces upwelling, the distance of land - ward flow of density current at bottom layer reduces, the salinity near the mouth increase, but the saltwater intrusion weakens; There exists obvious higher saltwater at the bottom layer and south coast of the funnel - shape estuary; The vertical mixing enhances, and salinity tends to uniform vertically.