Numerical Modeling of the Water Exchange in Jiaozhou Bay
|School||Ocean University of China|
|Keywords||water exchange water quality model FVCOM Jiaozhou Bay|
The research of water exchange in the offshore area is a basic proposition in the marine environmental science, and is also an important index and method in studying the physical self purification capability of waters, evaluating and predicting the marine environment quality. The waters with weak exchange ability always have many environmental problems such as eutrophication, the frequently occurring red tides in Jiaozhou Bay is a good example. This thesis simply introduces the background of this kind of study, and summarizes the hydrodynamic model and water quality model developing at home and abroad in details, then sets up a water quality model based on the 3D current model to study the water exchange regularity, so as to provide scientific basis and technological support for the full implementation of the "Central Bay protection, owned Bay" strategic plan, accelerating the Central Bay watershed pollution comprehensive treatment, and overall improvement in the quality of the ecological environment in Jiaozhou Bay. Specific works are listed as follows:1. In order to provide a dynamic field to the water exchange research, the barotropic tidal current is calculated by FVCOM tidal numerical model which takes the tidal zone in consideration, and verified by comparing with the measured data from three current stations and one tidal station.2. On basis of correct calculation of tide current, this thesis sets up a three-dimensional conservative substance transport model, and simulates the concentration of CODMn in 2007 in Jiaozhou Bay, verified by comparing with the measured data and previous studies. The result shows that the distribution of CODMn in Jiaozhou Bay is banded diminishing from the bay head to the bay mouth, in most area the averaged concentration is about 2mg/1; Most rivers are located on the top of Jiaozhou Bay, far from the bay mouth, and the tidal current near these areas are small, so the concentration of COD near these estuaries is between 2mg/l and 5mg/l, which is more larger than any other areas.3. Based on the correct three-dimensional water quality model of Jiaozhou Bay, PDCM is used as the tracer to calculate the "average residence time". The modeled average residence time is about 62 days. The spatial difference of average residence time is controlled by the tidal currents, the distance to the bay mouth, and the distribution of the tidal residual current. The modeling result is unrelated to the origin density of PDCM or the starting modeling time.4. Compared with the previous research results, it is found that to take the tidal zone into consideration during modeling is the main reason of causing differences between the results of this thesis and others’, and the influence of the tidal zone is operated primarily through the tidal pirsm. In order to study the function of the tidal zone, several numerical experiments are designed and the results show that:(1) the average residence time of Jiaozhou Bay becomes to 76 days if the tidal zone is ignored during the numerical modeling, which is increased by 24.6% than the actual value. This result is quite close to Lv’s in 2010.(2) the tidal prism of Jiaozhou Bay is about 9.02×108m3, this result will be induced by 24.6%, to 7.24×108m3 if the tidal zone is ignored.(3) actually, the tidal zone has effects both on the tidal currents and the tidal prism, but the effect on the tidal current can be neglected by changing modeling conditions during the actual research, and the tidal prism is closely related to the area of the bay, which cannot be neglected by human factor during the numerical modeling. So the influence of the tidal zone to the water exchange time is primarily displayed by the tidal prism, and this is the reason why the thesis has a different result of the average residence time in Jiaozhou Bay with the previous research. It can also be seen that the tidal zone plays a crucial role in the water environment of Jiaozhou Bay, which needs us to be more concerned of the tidal zone in the process of the environment management of Jiaozhou Bay.