Study On The Influence Of Three Types Of Typical Coastal Structures To The Adjacent Beach In China

Coastal zone of China is one of the fastest growing and most economically vibrant regions in the world.With the development of the economy,various coastal projects have sprung up in order to meet the needs of the development and utilization of largescale offshore resources.In China,beaches are widely distributed,and coastal structures have had a negative impact on the beach over time.Because there is a lack of argumentation and analysis on the influence of adjacent beaches in the early stage of coastal construction in China,so the investigation and research on the adjacent beaches of typical coastal projects and the analysis and summary of the impact characteristics of different types of coastal projects on adjacent beaches are of great significance to China's beach protection and coastal structures construction management.According to the location relationship between the structures and the shoreline,coastal structures can be divided into three types,longshore structures,structures perpendicular to the shoreline and offshore structures.Among the many coastal structures types in China,the three types of coastal structures,such as hard revetment,fishing port structures and offshore artificial island have a large number and a wide distribution.In this paper,hard revetment represent the longshore project and the vertical bank breakwater in the fishing port project is the representative of the project perpendicular to the shoreline and the offshore artificial island represents the offshore project.This paper is based on the field investigation data of the Qingshan Bay revetment,the Chongwu center fishing port breakwater and the Nanhaimingzhu artificial Island,using research methods of geological and geomorphological survey,beach shoreline and profile measurement and comparative analysis of satellite imagery to explore the mechanism and causes of the impact of the three types of coastal structures on the shoreline and profile of adjacent beaches,and the conclusions are as follows:1)Hard revetment mainly produces two types of impacts on adjacent beaches.One type is revetment impact on the beach front of it.Revetment obstruct sediment supply perpendicular to the coast,while the sediment is moving to the sea,causing the beach front of the revetment show an overall downward erosion.And The bottom of the revetment is particularly serious.The other type is the construction of the revetment,which will cause the erosion of downstream along the coast.Upstream erosion is often the material source of beach development along the coast.The construction of the revetment hinders the recharge of sediment downstream along the coast,causing erosion of this section.The profile morphology shows that the gradient of the middle tide zone is steeper and generally erode downwards.2)The fishing port breakwater project has two effects on adjacent beaches.One is the construction of the breakwater weakened the power environment and sediment is silted up in this area.Another is the construction of the breakwater damaged the balance of sediment transport along the coast,and the shoreline moves inland.On eroded shoreline,the profile shows that the gradient of the middle tide zone is steeper and generally erode downwards.On silted shoreline,the profile shows that the slope of the middle tidal zone is reduced and the whole area is deposited into the sea.3)Due to the difference of island size,offshore distance and relative position,the adjacent beach of artificial island is mainly affected by the difference of two types of protrusions,namely the promontory and the island bar.The degree of erosion regression is more serious in the case of island bar formation than in the case of cape formation.4)Hard revetment replaces natural systems with solidified artificial structures.For the negative impact of hard revetment on the beach,the natural system integrity of beach can be maintained through beach restoration,planting shelter forests,and building suitable hard-coast projects.In the early stage of construction of fishing port breakwaters and offshore artificial islands,a series of means such as numerical simulation and field investigation should be used to predict the impact of the project on the stability of the beach,and the natural properties of the beach should be gradually restored in combination with artificial sand-fixing to maintain the stability of the beach.