Current status and formational mechanisms of coastal erosion on typical islands in China

A geological hazard survey of 82 islands in coastal China from 2010 to 2012, and subsequent periodic monitoring of coastal erosion on 10 representative islands from 2012 to 2014, found 138 coastal erosion points on 39 islands. Coastal erosion was a typical pattern of the coastal geological hazards, with the most serious impacts occurring on the southeastern coast of Chongming Island, the maximum erosion rate was 18.3 m/a under the conditions of sediment reduction and drastic hydrodynamic changes of the Yangtze river. The primary causes were changes in river dynamics, the marine hydrodynamic environment, and human activities, the specific factors included sea-level rise, river diversion, river-borne sediment reduction, wind-driven waves, storm tides, construction, coastal degradation, beach drainage, and sand mining. Natural and human factors accounted for 57 and 43 % of coastal erosion effects, respectively. Sea-level rise operated on a long-time scale, causing an annual mean shoreline retreat of 0.15 - 0.30 m, although such changes were not obvious over short time scales, they were significant at the decennial and centennial scale. Storm tides were among the most important factors operating over shorter time scales, although increasing human development of islands is rapidly becoming a significant cause of coastal erosion.