A two dimensional hydrodynamic-diffusion model based on MIKE21 software is established to predict the hydrodynamic environment and the water exchange characteristics of Haihua island and its surrounding sea area. The diffusion exchange process of pollutants is predicted under different discharge modes. The results show that for the same amount of pollution, when the water level is controled to be above 0m and the gates of 1#~4#culvert bridges are opened the pollutants in the island will oscillate between the artificial island and the shore under the action of ebb and flood tide and the exchange time is 25.5 days. After the optimization of the opening mode of the gate the migration and diffusion speed of pollutants is obviously accelerated and the exchange time is shortened to about 10.1 days.
Haihua island is located in the southern shore of Yangpu Bay, Hainan (Fig. 1). It is composed of three artificial islands formed by reclamation from the sea. Between the artificial islands and between the artificial islands and the shore there are four culvert Bridges with box culverts and gates. The water body inside the island can exchange with the water body outside the island by opening the box culvert door, so that the pollutants can be discharged outside the island so as to enhance the self-purification capacity of the water body inside the island. The main functions of Haihua island are living, tourism and recreation. With the increase of population density on the island especially the intensification of human activities in tourist season, the pollutants produced will increase accordingly. The efficiency of water exchange will directly affect the water quality of the sea and the main function of Haihua island. Therefore, the study on the water exchange capacity of Haihua island sea area and the optimization of pollutant discharge are of positive significance for improving the self-purification capacity of the sea area and protecting the Marine environment.
