| Coastal zones are the areas where land and sea interact,and are also the main areas for human life and production activities.The beach is an important part of the sandy coast,and has disaster protection,tourism and leisure,ecosystem services and other great functions.The continuous effects of wind,wave and tide reshape the beach dynamically,while the changes of these natural conditions and human activities will have an impact on the trend of morphological evolution of beach.In the context of promoting the construction and development of Hainan International Tourism Island,the monitoring and research on this natural tourism resource,the beach,is not only of great practical significance to the planning and management of the tourism resources of Hainan Island,but also a scientific basis for the disaster prevention of the coastal zone and the sustainable development of the international tourism island.Based on the observation data of beach profiles around Hainan Island in recent years,using wavelet transform and EOF analysis,the overall patterns and regional characteristics of morphological changes of beach around the island are analyzed.The main factors and mechanisms affecting the changes of beach are discussed by using the multivariate regression model.Based on the fractal theory and power spectrum analysis,the spatial scales of the shoreline changes on eastern and southern coasts under the influence of typhoon are studied.For the two major external factors that affect Hainan Island in recent years,typhoon and construction of artificial islands,the hydrodynamic process of typhoon RAMMASUN landing in Hainan Island and the alongshore variation as well as the mechanisms of beach changes affected by typhoon are analyzed combined with the numerical model TELEMAC,and the influences of artificial island on the beach around Hainan Island are discussed with the interpretation of historical remote sensing images.(1)Around the Hainan Island,the hydrodynamic conditions with bathymetry under-5 m along the eastern coast between Hainanjiao and Yinggezui are fairly similar,with small tidal range and significant seasonal changes of wave height and direction;the tidal range along the northwestern coast is relatively large,and the significant wave height is small.Correspondingly,the western and northern coast are relatively stable,the shoreline changes are quite small,and the variations of the beach profiles show typical seasonal features;due to the influence of typhoon,the eastern and southern coasts of Hainan Island are unstable,while the coast between the Wanquan Estuary and Luhuitou is the most unstable coast on the island,where the submerged slopes are 0.5°higher than the rest coasts;(2)It can be found that under different dynamic environments with different investigated time intervals,each of the shoreline change,beach volume change and beach slope change has a significant relationship with the variations of maximum tidal range,submerged slope,profile azimuth,average wave period and average wave height as a group.Amongst them,the wave height and period have direct impact on beach volume and slope;coastline contour(shoreline azimuth and capes)make alongshore differences of shoreline changes and beach slope changes by redistributing the wave height and period in alongshore direction;changes in wave direction can not only influence the magnitude and trend of the alongshore differences,but also change the direction of sediment transportation and then cause different shoreline changes in alongshore direction;tidal range and submerged slope mainly enhance or reduce these mechanisms,but if there is significant alongshore variation of tidal range or submerged slope,they can also make alongshore differences of beach changes.(3)The variations of shoreline around Hainan Island have temporal and spatial rhythmic characteristics,which mainly occured in relatively fixed space units as bays with length around 30 km,and the directions of the changes between the adjacent units are different,while within the same unit the beach shows seasonal variation;and the changes of shoreline on eastern and southern coasts show obvious fractal features,the fractal features of the shoreline changes can be extended to the alongshore scale of 30 km,which indicates a relationship between the patterns of shoreline changes and the orderly variations of their intensities under the scale of 30 km.The typhoon mainly affects the shoreline change patterns with alongshore scales about 15?25 km.(4)The storm waves were distributed along the coast of Hainan Island in spatial scale over 520 km(most coastlines except the section from Linshuijiao to Yinggezui)during RAMMASUN,and the storm surge occurred along the coastline with the length of about 110 km(from Haikou Bay to Tongguling),the coast which was dramatically reshaped by RAMMASUN is the coast section suffered storm surge.Affected by the coastline shape such as Hainanjiao and Jingxinjiao,the storm waves and surge varied in alongshore direction.Because the backshore erosion caused by storm surge and storm wave can hardly be recovered by nature,the parameter of beach volume change could preserve the storm erosion.While the shoreline change is relate to the realtime hydrodynamic condition,the deposited sediment could be moved back to beach surface,in the meantime,the submerged slope and storm surge decided the position of movable sediment and then have an impact on the progress of shoreline recovery(5)In recent years,there are 12 artificial island projects constructed around Hainan Island,of which artificial island projects in the Dongjiao Coconut Forest Bay,the Tanmen Fishing Port and the Riyue Bay reshaped the beach morphology and the shoreline dramatically.The short distances between artificial islands and the land coasts,the impermeable embankments connecting the islands,and improper protection methods exacerbate the impact and damage of artificial islands on the adjacent land coasts.In summary,this study investigate the Hainan Island as a whole for the morphological change and influencing factors,creatively utilized the fractal theory to evaluate the differences in the scale features of shoreline changes between fair weather and storm weather,and the fractal scale discovered breaks the upper limit in other study This study found rythemic patterns of shoreline change in time and space,which will be strengthen during storm.This study investigated the hydrodynamic process during storm and it's alongshore variation,discussed the effects of artificial islands built since 2010 on coasts around Hainan Island.This study offers the complementary information for the fractal and self-organised coastal morphology,which is not only useful for better understanding of the large-scale morphodynamic processes under the control of wave,tide and geological conditions,but also for the research of multi-scale morphodynamic machnisms.This study also gives some references for the planning and management of the tourism resources of Hainan Island. |
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