Effect Of Waves And Tide-current On Pollutant Transport In The Local Artificial Shoreline Of Near-shore Area

Waste water soars due to increase of population and development of industries, so sewage ocean disposal becomes more important for its efficience and shortcut. Considered the cost of the project, the drain outlets are always being established near the shoreline. Due to the water depth is low, the effect of pollutant transport is not satisfied. As every littoral cities now speed up the development of ocean exploitation, such as establish industrial parks, coastal reclamation and so on, the land begins to expand to the ocean, which makes it possible that the waste water discharges in deeper water. In this paper, in order to acquire the rules of waste transport near shore area, the convection and diffusion of the waste exhausted to the sea will be studied in the condition of wave, tide and the combination of wave and tide, respectively.Firstly, the generalized conjugated gradient method is used to solve elliptic mild slope equation numerically. When compare the results with parabolic mild slope equation and experiments, it is found that the parabolic mild slope equation has a higher efficience with the same precision. So in this paper, the parabolic mild slope equation will be utilized to compute the wave field after being verified by experiments.Secondly, the coastal current model forced by radiation stress is used to solve coastal current field, then put the velocity into the convective and diffused equation to get the results. Because the radiation stress is caused by wave breaking, so convection and diffusion of the waste are studied under four breaking models put forward by Battjes et al.(1978)、Dally et al.(1985)、Chawla et al.(1998)、Baldock et al.(1998) respectively in order to find a better one by comparing with the experiments.Finally, the application of the coupled model to the convection and diffusion of the waste in Tianjin south coastal area of Bohai Bay is carried out. The drain outlets A1, A2, A3are set in sequence off the shoreline. Through comparing the computational results with the shoreline of2010and the designed, we can get the conclusion:at the outlet A1, the convection and diffusion of the waste in the shoreline of2010has an evident longshore and offshore trend under the combination of wave and tide; but the waste is hampered to transport and diffuse in the designed shoreline which breaks the continuity of longshore current in the nearshore, so the location of drain outlets should be selected far away from the shoreline. The locations of A2and A3in tide seldomly suffer from the influence of shoreline. Since A2is nearer to the break zone than A3, so it suffers more influence, leading the exchange of the waste along the shore to be more intense. Though A3suffers less influence of wave, its discharge speed by tide to the outer ocean is faster than A2.