海岸沙丘形态对台风响应的初步观测

Preliminary observation of morphological responses to typhoon of coastal dunes

基于2014年第10号强台风"麦德姆"登陆前后福建平潭岛海岸前丘、爬坡沙丘、横向沙丘和沙席等海岸沙丘形态的高精度测量数据,分析了典型海岸沙丘在台风登陆前后的形态变化,初步总结了华南海岸风沙地貌形态的台风响应模式。结果表明:4类典型海岸沙丘在台风"麦德姆"登陆前后的形态变化较大且主要是以体积减小和沙丘高度降低为主,测点高程的平均变化值为0.22 m,样区海岸沙丘体积平均减小0.59%,测点高程变化的平均值为高度降低0.05 m,但不同类型海岸沙丘及其不同部位的响应变化并非一致且存在较大差异,此与台风"麦德姆"的强侵蚀力及不同海岸沙丘的形态及其下伏地形、表面植被分布等的差异有关。

Pingtan Island is located in the sea of eastern Fujian Province, which is one of the typical coastal aeolian landform regions in China, well known for its typical shape, volume and less human disturbance. On the Pingtan Island coast, which was taken as the research region for the observation of coastal dunes＇ morphological responses to typhoon, four areas were chosen as the field observation sample areas, separately representing the four types of coastal aeolian landforms such as coastal foredune, coastal transverse dune, coastal sand sheet and climbing dune. By using high-precision RTKGPS technology and surveying method, the elevation data before and after typhoon landed at 931 observation points and 15 transect belts in four sample areas were measured. Based on the high-precision surveying data over the four typical coastal dunes in Pingtan Island before and after the 10th typhoon （Matmo） in 2014, the morphological change of the four types of coastal dunes in response to the typhoon Matmo event is analyzed. The typical observation results suggest that the basic feature of the impact of typhoon Matmo on the morphological change of coastal dunes in Pingtan Island is the reduction of volume and height. The average elevation change of the 931 observation points in the four sample areas is 0.22 m, and the average elevation of all the observation points decreased by 0.05 m. The volume of four coastal dunes in the four sample areas reduced at an average of 0.59% after the typhoon Matmo landing, the biggest volume reduction is 2.20%, which was observed in the coastal foredune sample areas. However, the magnitudes of morphological responses are different in different types of coastal dunes and different sites over the coastal dunes. For example, the volume and height of coastal sand sheet was found to increase after the typhoon Matmo landing while other types of coastal dunes decreased. For the coastal climbing dunes the highest decrease in height was at the middle site of windward slope in front of coastal climbing dune and the smallest decrease in height was at the top site of windward slope in front of coastal climbing dune. The basic reasons for the impact of typhoon Matmo on the morphological change of coastal dunes are the strong wind erosion, the landform under the coastal dunes, the shape of coastal dunes and the differences of the distribution of coastal dunes＇ surface vegetation.