Abstract: The water exchange capacity of the encircled harbor has an important influence on the water quality of the harbor basin, adding water exchange channel is an effective measure to improve it. Taking the seawall reconstruction project of Zhapo fishing port as an example, the irregular triangular mesh and finite volume method were employed, based on the research results of tidal current numerical simulation, a two-dimensional convection-diffusion model was established. The numerical simulation research of water exchange capacity before and after the expansion of Zhapo fishing port was carried out, and the half exchange period and water exchange rate of the harbor before and after the project were evaluated. The results show that the water exchange capacity of Zhapo fishing port is strong, the half-life time of water body is 129 hours before the engineering, and 104 hours after the project. After the project, the Zhouzaixia breakwater is changed into a culvert-type bridge, so that the water body exchange channel is formed between the fishing port and the offshore, the water body interaction and water body exchange capacity inside and outside the harbor basin are increased, and the corresponding water body exchange capacity is enhanced. As a comparison, two aquaculture areas outside the harbor basin have strong water exchange capacity as they are well connected with the sea, so the limit change in water exchange capacity caused by the project is reasonable.

Key words: water exchange, half-life time, numerical simulation, Zhapo fishing port