The Numerical Simulation Of The Transport Of The Fluvial Water And Sediment To The Jiaozhou Bay

There are a lot of rivers around Jiaozhou Bay, and they bring a great deal of sediment and diluted water to the bay every year. The mixing process of the river and seawater would result in some important physical phenomenon, and the sediment brought by river also has significant effect on the geology and physiognomy offshore. Furthermore, it is necessary to address to the sediment research when studying contamination in estuary. So, the sediment problem in estuary and offshore is important in many research fields.In this dissertation, a three-dimensional hydrodynamic and sediment transport numerical model called ECOMSED is applied to Jiaozhou Bay. First, the model results (current, elevation and sediment concentration) are compared to the real data to testify its creditability. Then, simulation is carried out under two different circumstances: one is with flood input and considering wave effect (A), the other is with averaged discharge input and without considering wave effect (B).Study is addressed to the diluted water and sediment brought by twelve rivers around the bay, the especial physical phenomena during mixing process of the two different kinds of water and seeking to explain the cause underlying.Under circumstance A, the salinity and sediment concentration of water column are more closely related to the flood process, and under circumstance B, they are more influenced by tide. The salinity of both circumstances is increased with depth and distance from upstream. With situation A, the sediment concentration in the estuary would increase abruptly when low tide, this phenomenon is attributed to the retreat of the salt-wedge. And because of the existence of the halocline in the middle level and the small shear induced by tidal current, the sediment concentration there is greater than surface and bottom.Both of them have similar Eulerian residual current patterns, but the eddy in the inner mouth is weaker under B. And the water entering the inner mouth is no longer flowing north together, but to three different directions. The bottom residual current of B is less apparent than that of A, but its magnitude is greater than the latter.When simulated with condition B, the low salinity water is confined to the river mouth, diffusing at low tide, retreating at high tide. With condition A, the low salinity water is still around river mouth before flood peak, but occupies the whole inner bay at flood peak. When the flood ends, the surface water of the bay nearly becomes regular, but the salinity is still lower than before.Tidal current can't resuspend the bed sediment at most time, so under circumstance B, the sediment concentration at surface is greater than that at bottom, and the high concentration sediment is localized around the river mouth. The sediment concentration is larger at ebbing time than at flooding time, and there is high concentration at cape around the inner mouth of the bay. Under circumstance B, the concentration is low before the peak of the flood and it is larger at surface than at bottom. At the peak of the flood, most of the regions in the bay has semimetal concentration greater than 100mg/L, and the concentration at bottom is large too, but would only influence the areas ground the estuaries. When the flood ends, both of the two layers have low concentration.With the view from the distribution of deposition and erosion, under flood and wave condition, the erosion region is localized at inner bay mouth-outer bay mouth, bay head, and northeast of inner bay. Areas with thickness of deposition greater than 1cm mainly distribute at the Dagu river, some estuaries and northwest of inner bay.If wave effect is neglected (condition B), the areas of erosion would mainly localize at inner bay mouth-outer bay mouth, with smaller erosion areas around Baisha River, and the strength of deposition decreases. Under both circumstances, the river sediment would exert little influence to the sea near Huangdao and Xuejiadao.Comparing the two simulation results, it will be found that wave is the main cause to the erosion offshore and sudden siltation of estuaries, the strength of flood is the dominating factor to the areas of deposition and the tidal current is the main dynamic mechanism to the transport of the sediment. The sediment from river around Jiaozhou Bay would have some influence to Jiaozhou Bay, but the influence is so small that would do no serious harm to the bay.