Study Of Water Particle Motion And Water Exchange Simulation In Xiamen Bay

The primary problem on development and environmental protection of Waters in Xiamen Bay is the environmental capacity. Hydrodynamic conditions and water exchange capacity of the waters are main factors on environmental capacity. This article aims to discuss about these two factors.In this paper, a three-dimensional hydrodynamic model is established. The target area is devided into several blocks. With the Lagrange method to tracking water particles, the motion of water in each block is discussed during the process of the tide. The dynamic changes of the water particles which were input on high or low tide are also collected, including the quantitative change after several tidal cycles and the circumstance of exchange in different blocks. Method of box model is used to calculate the exchange time in different blocks and then analyze their self-purification capacity. This research starts from neap tide. It aims to track the movement of water particles in30tidal periods. These periods include two times of spring and neap tide. The results from this method can present the average self-purification capacity and water exchange time of target sea area.Hydrodynamic numerical model of the actual flow field shows that the velocity of flow in the moment of the spring tide is significantly larger than that in the moment of the neap tide, the deepwater channels which are belonged to the strong-current zone have remarkable velocities of flow. Weak-current zones exist at bayhead of the basin and the shallow-water regions near the shore. Water particles are tracked from spring or neap tide and characteristic of motion in30tidal periods is discussed base on the Numerical Simulation. The remnant water particles after several tidal periods in blocks are counted to calculate the net exchange rate and exchange time with the open sea. The west sea area of Xiamen has the longest exchange time in inner bays. The exchange time is13.7,203.1tidal periods in the case of high and low tide tracking respectively. The wide sea area has stronger self-purification capacity and less exchange time compared with narrow ones. For instance, the exchange time in south sea area of Xiamen is5.7,9.5tidal periods in the case of high and low tide tracking respectively, the exchange time in east sea area of Xiamen is3.5,12.9tidal periods in the case of high and low tide tracking respectively.This research also collect the data about the situation of water particles exchange between blocks to reflect the interaction of water contamination in different areas. for instance:pollutant from Jiulong river and south sea area of Xiamen is easy to affect the west sea area of Xiamen in flood tide; the self-purification capacity is poor if pollution happens in low tide in west sea area of Xiamen; the pollution from Tong’an Bay will affect bayhead area for long time, especially in flood tide when the pollution is much more difficult to decontaminate; pollution happens in north sea area of Jinmen island may have effect in Tong’an bay; pollution which is happened during the progress of flood tide can spread into Tong’an Bay.