| Nowadays,global warming is causing serious sea level rise,and the widespread construction of dams in uprivers lead to the shortage of sediment resources in the estuary,the coastal erosion problem has become more serious.Under this circumstance,beach nourishment has become a common approach in coastal protection and tourism management.At present,the negative impact caused by the construction of artificial islands in China has gradually emerged.Some coasts have been unevenly eroded due to the increasing alongshore sediment transport caused by artificial islands,beach nourishment is urgently needed in such area.Classical method of beach nourishment is difficult to solve the problem of alongshore sand transport.Sediment recycling nourishment technology as one of the methods of sediment management,can effectively solve the alongshore sediment transport problem caused by the construction of near shore structures.The research objects in this paper are Haikou Bay and the seacoast on Xihaian.At first,this paper analyzed the changes of grain size parameter and beach morphology,based on surface sediment samples and topography survey data.And discussed the impact of artificial island on Haikou Bay and Xihaian combining with the geographic background.Then discussed the methodology and technology of beach sediment recycling nourishment with the cases of sediment backpassing.At last,the suitable sediment recycling measures for Xihaian were proposed according to the situation of Haikou Bay.In the end,this article provide basis theory for the development and protection of the eroded coast of Haikou Bay.The research results show that the surface sediments of Haikou Bay are mainly composed of sand,silt and clay before the construction of the Nanhaimingzhu(NHMZ)artificial island.After the construction of NHMZ,the fine-grained ingredients of surface sediments in Haikou Bay were increased,the average grain size becomes smaller and the sorting coefficient getting worsen.NHMZ island has weakened the tidal current and wave strength in Haikou Bay,which mainly caused the changes in sediment characteristics and the coastline of Haikou Bay and Xihaian.After the construction,the coastline of Xihaian is silting-up behind the wave shadow zone of the NHMZ island.The beach profile of Xihaian shows the erosion at both ends of the coast and deposition in the middle,eroded in winter and partly recovered in summer.The beach width and sediment volume increased in Wuyuanhekou inlet and wave shadow zone of NHMZ island,decreased at the edge of shadow zone.The sediment average grain size remains stable along Xihanan.Changes on the beach in Xihanan are directly related to the impact of the NHMZ island.The beach sediment recycling is a nourishment method based on sediment management.It reasonably allocates sediments in coastal zone according to the conditions of coastal cell,which can solve the problem effective of coastal alongshore transport under the effect of artificial islands.Beach sediment recycling systems can be divided into three types: mobile,semi-fixed,and fixed system,which are suitable for different sediment transport volumes,traffic and topography in the study area.According to the topography and sediment transport process of Xihaian,it could divide into a large coastal cell and three subcells.Due to the change of nearshore wave conditions caused by NHMZ islands,sediments are transported from the subcells at both ends to the middle subcell in wave shadow zone.According to the different conditions,three sediment recycling routes are settled.The traffic around the nourishment area is convenient,and is suitable for the mobilized sediment recycling system.There is little difference in grain size between the sand nourishment area and borrow area,the recycling will not adversely affect the ecological environment.The annual erosion volume on Xihaian is small,it can be renourishment at intervals of 5-7 years according to the situation of beach erosion.The best time of nourishment of Xihaian is from April to July in each year. |
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