Research On The Spatial-temporal Morphodynamic Evolution Of The Sand Barrier Lgaoon In Linshui County,Hainan Province

The barrier lagoon coasts are the important part of world coasts,thus they are ideal areas to study the interaction of land and ocean.The barrier of lagoon can block the waves and storm,wind and waves calm in lagoon.The nutrient content is rich in lagoon,so it's suitable for aquaculture,port and the development of tourism.However,because of the disturbance of human activities,some of barrier-lagoon coasts have been destroyed seriously.Therefore,it would be of interest to learn how to grasp the development status of barrier-lagoon coast,investigate the evolution,affection process and dynamics mechanism of the typical lagoon.It also has significance to rational development and utilization of natural resources in coastal lagoons.The remote sensing(RS)technology has advantage to get materials in earth observation speed,short cycle,informative and not subject to any terrain conditions.Geographic information system(GIS)can perform precise and accurate analysis of spatial-temporal data.So the RS/GIS are very suitable for the spatial-temporal geomorphic evolution research of barrier-lagoon coast in decadal scale.Xincun and li'an lagoon are located in the southeast coast of Hainan island and there are typical barrier-lagoon coast systems and geomorphic type,which have rich and natural landscape unique.Therefore,this paper took the lagoons of Xincun and li'an as the studied area and based on the multi-temporal satellite remote sensing images,sea chart,topographic maps,measurement water depth and tide level,a geodatabase of coastlines,subaqueous reliefs and geomorphic patterns was established by using remote sensing interpretation and geographic modeling technology.In addition,the quantitative information of coastline,subaqueous relief and the geomorphic pattern changes was calculated by using the superposition of different period data.Some results are shown below.1.Using the remote sensing image of the lagoon mean high tide line position and the surface elevation data,we obtained the mean value of the high tide line position after the K-T transform.We further calculated the mean value of the high tide line for other years.This method makes up the flaw of traditional methods of the lack of the tidal observations for lagoon shoreline in the corresponding year.2.By using multi-time phase and long period remote sensing image,we analyzed the variation of lagoon shoreline during the past 30 years.The length of artificial shoreline has reached a half of the total length in Xincun and li'an and the total length of shoreline occurred promoting to the middle of the lake large scale.The average propulsive distances were 94.04 and 102.56 m respectively.Xincun lagoon area reduced from 21.17 km2 to 19.43 km2 and li'an lagoon area decreased from 9.94 km2 to 7.92 km2.The decrease in lagoon is 8.2%and 20.3%respectively.Along the shoreline,the spatial-temporal evolution geomorphology of barrier-lagoon coast have greatly influenced by the reclamation and aquaculture development.3.We analyzed the evolution of erosion and deposition of the underwater terrain model in two periods(1981 and 2011 of Xincun lagoon and 1985,2011 of Li'an lagoon)and measured sediments deposition rate of bottom column.The results showed that,two lagoons in the central basin of water occurred large area deposition and the average siltation thickness is 1.72 cm of Xincun and 1.56 cm of Li'an from 1980 to 2011.The analysis of the spatial and temporal changes in the lagoon bathymetric showed that the main ebb tidal channel of Xincun is constantly scouring the south while the swinging of the river is constantly washed.4.Through field survey in the study area of coastal landform types,we established professional criteria for classification of coastal geomorphic types.Using this standard,we extracted and classified the remote sensing image of the coastal geomorphic types of information landform types by the transfer matrix.The original geomorphic patterns around lagoons have profoundly changed by human activities from 1987 to 2011.Mutual transition for natural landform is very limited.A large area of tidal flat and marine deposition plain has been developed as artificial ponds between marine deposition plain and underwater bank.The original material exchange mode was changed.These results indicated that the evolution of lagoon landform has changed obviously by continuously strengthen human activities over the past 30 years.The lagoon area decreased continuously and deposition rates were relatively high.All these phenomena led to the change of hydrodynamic action way,extension of the lake water exchange cycle and reduction of the tidal volume.These bring negative effect on barrier lagoon landscape and ecological environment.Thus this research can provide scientific basis and technical support for the management of coastal zone resources and the development of starting pilot zone sustainable exploitation and utilization policy.