Study on the influence of coastline evolution on water exchange in Zhifu bay

The Zhifu bay of Yantai, a typical semi-closed bay, was taken as our research object.Firstly, based on multi-temporal remote sensing images and topographic data, data of coastline was extracted in 4 time phases from 1976 to 2016.Then a 2D advection-diffusion model of Zhifu bay was established by water exchange rate to study the evolution of its water exchange ability under the influence of coastline changes.The western Zhifu bay, whose coastline had changed significantly, was divided into 5 sub-regions to analyze heterogeneity of regional water exchange ability elaborately.The results showed that the coastline of Zhifu bay has been growing seaward tortuously, in which the western part has greatly changed and increased by 58.17% in the past 40 years.Construction of ports and jetties was the main cause of coastline variation.The water exchange ability of Zhifu bay firstly strengthened from 1976 to 1991, and then weakened during 1991~2016.The average half-life time showed an overall growth trend, and the time of 2016 was 127 h, increasing by 35 h compared with that of 1976 (92 h).The regional disparity of water exchange ability varied widely in the west of Zhifu bay, and the formation of 3 harbors, the North Harbor, the Harbor Ⅲ and the Harbor I, was the major contributor which weakened the water exchange ability of Zhifu bay.