| The barrier lagoon coasts are the important part of the world sedimentary coasts,thus they are key areas to study the interaction of land and ocean.Xincun lagoon is located in the southeastern coast of Lingshui County in Hainan Province and belongs to the typical barrier-lagoon coast systems,which has unique natural landscapes,rich landform types,and functions such as flood control,harbor navigation,aquaculture,tourist viewing.In November 2011,Hainan International Tourism Island pilot area settled in the Li'an area of Lingshui.In April 2018,Hainan Free Trade Port was announced.Xincun lagoon has attracted attention from all walks of life because of its excellent geographical location and unique landscape resources.In the past 40 years,the ecological environment and landscape of Xincun Lagoon have been greatly affected by the continuous interference of human activities.Therefore,it is important to study the evolution of erosion and deposition of Xincun lagoon,it also has great guiding significance to the sustainable exploitation,scientific management and ecological environment protection of the future lagoon coastal resources.The remote sensing sounding method uses remote sensing(RS)image to measure the depth of water,which can obtain the depth information with quickly,large area and quasi synchronization.The remote sensing image has the advantages of wide coverage,strong effect and convenient access,and can supplement the historical terrain data.Geographic Information System(GIS)has powerful data processing and spatio-temporal analysis capability.So,RS and GIS techniques are suitable for the study on spatial-temporal topography evolution of the barrier-lagoon coast in long time series.This study took the Xincun lagoon as the study area.Based on remote sensing water depth inversion method,a water depth inversion model suitable for this research area was established by analyzing the correlation between the measured depth value and the spectral reflectance of remote sensing image.In addition,The spatial-temporal topography evolution characteristics and driving causes of the Xincun Lagoon in the recent 30 years were analyzed.by using multi-source data such as inversion depth,measured water depth,historical chart,sediment flow field and so on.The main results are as follows:1.Based on the statistical correlation model,the single-band,dual-band,and multi-band combination water depth inversion models were established.Multi-band combination models have better fitting effect than single-band and dual-band models,and complex correlation coefficient(R2)is above 0.96.The average relative error(RE)and root mean square error(RMSE)of the optimal depth inversion model were 23.95%and 0.48m respectively.The optimal model has the best inversion effect on 5?12m wa-ters,RE and RMSE are 6.75%and 0.59m respectively,which reach the better level of remote sensing water depth research.Using the remote sensing inversion method to obtain water depth can supplement the historical underwater terrain data,which is advantageous to the study of hydrodynamic geomorphology evolution in long period.2.During the 1981-2011 years,the underwater topography of the Xincun lagoon was in a deposition state.(1)The tidal main waterway swings roughly 400m to the southeast direction and gradually deepens.(2)In most areas of Xincun lagoon,the deposition thickness is less than 0.6m,and the local area deposition thickness is above 3m.(3)After 1996,the sediments of Xincun lagoons showed the development of the film,the deposition amount and the deposition thickness increased,and the deposition slightly accelerated.3.The underwater terrain evolution of Xincun Lagoon is the result of the combined effects of tides,waves,creatures and storm surges.,which are highly sensitive to the effects of extreme weather(storm surges,waves)and human activities.The storm surge events around 1995 caused the barrier break of the east edge,the offset diversion of tidal main waterway,and the accelerated siltation of local coastal.So,The strong storm circulation caused by typhoon weather is a powerful force for the suspended sediment diffusion and transport,which plays an important role in the topography evolution of the near-shore shallow water area.4.During the 1981-2011,the area of the fishing platoons.culture ponds and salt pans increased 0.57km2 and 3.95km2 respectively.However,the water area of the Xincun lagoon has reduced from 11.49km2 to 10.78km2.With the increase of the population,the expansion of the fishing rafts,aquaculture ponds,and salt fields,the original hydrodynamic conditions of the lagoon have changed,resulting in a decrease in the water area of the lagoon and silting in some areas.The dramatic human life style has a great influence on the topography,which has become the primary driving factor for the underwater topography evolution of Xincun lagroon. |
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