Study On Characteristic And Influence Factors Of Erosion And Deposition In Sanshan Island-diaolongzui Area, Laizhou

The Sanshan Island-Diaolongzui area is located in the east of Laizhou Bay, the coastlineof which is composed of sandy coast and artificial coast, spreading flat along E-W. Because ofthe impact of Laizhou Shoal, the hydrodynamic environment is relatively stable and thevariation of erosion and deposition is not obvious. In recent years, the frequent humanactivities, such as the construction of marine engineering and sea sand mining in LaizhouShoal, have influenced the original hydrodynamic force in the sea area, and then changed theenvironment of erosion and deposition, which causes shoreline retreating, larger slope ofbeach and near-shore sediments coarsening and affects the stability of the beach. Based on themeasured data, sediment distribution and the current situation of erosion and deposition aresystematically analyzed in a variety of research methods and formulas. Many factors thatresult in changes of erosion and deposition are discussed in this paper. The major results andconclusions are presented as follows.（1）Distribution of surface sediment are systematically analyzed on the basis ofmeasured data and previous research results. Results show that there are4types of surfacesediment in the study area, including sand, silty sand, sandy silt, clayey silt; dominatedsurface sediments of in the near-shore area is sand and the grain size become gradually thinfrom near-shore to offshore area; in the Laizhou shoal, distribution of surface sediment issymmetrical the grain size become finer from center to both sides. The distributionalcharacteristics of grain size parameters are almost same as the distribution of sediment type.There are sand bars and trenches on the seafloor in some parts of study area, where thecharacteristics of grain size correspond with the hydrodynamic environment.（2）Shoreline changes during2003-2012are analyzed using the collected remotesensing images, which are processed by ENVI, Arcgis, AutoCad. The result shows that thesandy coast in the east of study area, trended to retreat, and the erosion is relatively serious.Because of the construction of the breeding pond, the west shoreline, which is artificial, goesforward to the sea.（3）Based on measured depth data and the collected sea chart data, the changes oferosion and deposition during2003-2012are represented in the study area. The result showsthat the whole study area is in an erosion state. In the near-shore area, erosion is between0.5 ~1m and from east to west, it increases gradually, which is consistent with the compareresults of profile. The sea area beyond5m isobath is in a deposit state and the deposit is morethan0.5m.（4）In the study sea area, the changes of erosion and deposition and shoreline aresimulated in numerical simulation method. The results show that the change of erosion anddeposition in study sea area is in a state of dynamic balance as a whole. Coastal sea area isslightly erosion and the amount of erosion is small; Laizhou shoal is in an erosion state, withmicro-silting on both sides of shoal. Beyond2m isobaths, the sea area is in the micro-siltingstate. Under the long-term effects of hydrodynamic, the coastline in the study area is basicallystable. Under the effect of the northwest and north wind, the entire sandy coastline, which ison the east of the study area, is in equilibrium with shoreline changing a little. Some parts ofthe west artificial shoreline go forward to the sea and in the northwest direction and theamount of silting is larger.（5）The factors influencing the recent variation of erosion and siltation in research seaarea are systematically analyzed using formulas of incipient velocity, CERC and offshoretransport of sediment. The results show that the main factors include sediment source,hydrodynamic environment and human activities, among which, the small river sedimentdischarge, the interruption of littoral sediment and the sediment transport capacity decrease oftide and wave lead to the insufficient sediment supply in research sea area and the disturbingof previous sediment balance, and then affect the variation of erosion and siltation in sea area.It is demonstrated by the comparison result of sediment incipient velocity and tide velocity inresearch offshore area and the calculations of littoral sediment transport and transversesediment transport, that both of tide and wave can influence the variation of erosion andsiltation in research area and hydrodynamic environment is the direct factor. Marineengineering construction, sand excavation activities and some other human activities candestroy the original hydrodynamic environment in sea areas, which result in the variation oferosion and siltation in certain areas. Therefore, human activities are the essential factorsaffecting the variation of erosion and siltation in research offshore area.