Morphological Response of Coastal Sand Sheets to Typhoons

Abstract

Typhoons, as essential influential factors for the formation and evolution of coastal dunes, are one of the most important aspects of surf zone-beach-dune interaction research. Pingtan Island is located on the eastern coast of Fujian Province, China, and preserves a typical type of coastal dunes on China's coastline. These dunes are well-known for their typical shape, volume, and limited human disturbance. Pingtan Island suffers frequent, unavoidable damage from typhoons, and was therefore selected as the study site for this research. Field investigations were conducted on the island before and after typhoon events, by using high-precision RTK GPS technology and surveying methods. The field site was visited 16 times between 2014 and 2017. We analyzed the morphological responses of coastal sand sheets to typhoons, and the related morphological changes. Finally, we summarized the morphological response patterns of coastal sand sheets to typhoons. This study is of great importance for comprehensively understanding the morphological evolution of coastal dunes, which is fundamental for effective coastal planning and management. The following results were obtained: (1) The typhoon imposed significant morphological changes on coastal sand sheets, which can be summarized as a decrease in the height of the beach and frontal coastal sand sheets (maximum erosional depth of 0.92 m), minor variations in the height of coastal sand sheets at middle sites (≤ 0.15 m), and a slight increase in the height of coastal sand sheets at the trailing edge (maximum accumulation thickness of 0.75 m). (2) After the typhoon season, the morphological changes in coastal sand sheets are more consistent, and they mainly manifest as a decrease in volume and a slight increase in the height of the beach and frontal coastal sand sheets (maximum accumulation thickness of 0.78 m). There was a very slight decrease in the height of the middle coastal sand sheets (≤ 0.10 m), and a slight decrease in height at trailing edge of the coastal sand sheets (maximum erosion depth of 0.47 m). (3) Coastline direction is an important factor that affects the response of regional coastal dunes to typhoons. At sites that lack sand resources and experience dominantly offshore wind, typhoons play a prominent role in frontal coastal sand sheet erosion, and can result in a receding coastline (up to 4.0-5.0 m).

Keywords

• coastal sand sheet
• typhoon
• morphological change
• trend of the coastline
• pingtan island