| Barrier-lagoon coast is one of the important components in deposition coasts, which has been the focus of land-ocean interactions in the coast zone ressearch. Based on data including remote sensing images, historical sea charts in different times, and historical sediment records, morphodynamic processes of barrier-lagoon coast in Shuidong bay, Yuexi was studied, and its different driving forces of anthropogenic actions and nature were also furtherly discriminated.(1) Barrier-lagoon coast in Shuidong is a typical arc-shaped coast with the fractal dimension of the shoreline of 1.202. The state of coast has been in a negative-dynamic equilibrium status in the last three decades. During this period, coastal siltation that affected by both wave and tidal flow was moved into the lagoon, which resulted in shallow water depth of lagoon than ever. Moreover, sediment transportation alongshore from west to east was controlled by wave diffraction, which made the reverse spit formation and extension at the west of inlet. In addition, the grain size in sediment of the lagoon has been finer than that in 1982. Because of insufficient supply in sediment from continental shelf, the west of the barrier is in eroded status, and the reverse spit becomes slender.(2) Here, threshold segmentation was used to extract waterline information based on ARCGIS and ENVI platforms. By comparisons of different waterlines extracted from sensing images with similar tidal level value, and sea charts data simultaneously, the related results shows that siltation in tidal flat of the lagoon has been dominant evidence with the accreted rate of 0.12 km2/a since 1967. The accumulation parts are in the east of the lagoon, and corresponding erosion regions are in west of the lagoon channel from Shang Dahai to Yan Jinling. Isobaths of 2 m and 5 m are receded landward to some degree. The landscape of the bar-lagoon coast has changed, which is obvious change in building land with area of 36.71km2 in 1987 and 51.94 km2 in 2004. However, the water area in lagoon has been obviously reduced. (3) During the period of evolution processes in barrier-lagoon coast, Shuidong bay, anthropogenic activities are dominant impacts on the morphodynamic change of barrier-lagoon coast in Shuidong. The depth of ebb channel has been dredged from 1.1～1.9 m to 9.8m,5m depth of channel has been completed. From 1967 to 2000, the area of tidal flat has been decreased with 7.47 km by reclamation, and the area changed by erosion/deposition is only 7.47 km2. A large-scale tidal flat area was reclaimed into residential areas, salts and fishponds, which directly made the area of tidal flat decreased to 27.44 km2.Because highly extensive anthropogenic activities had the area of the lagoon decreased, the tidal prism is reduced, and hydrodynamics is weakened. Therefore, the evolution process of barrier-lagoon is indirectly affected, which could exacerbate lagoon environment. So, the function of barierr-lagoon coast in Shuidong is degenerated, which could be silted and fromed into land in the end. Thereafter, barrier-lagoon coast in Shuidong bay should be utilized by rational and scientific methods, with the sustainable developed.
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