Coastal erosion along the Changjiang Deltaic shoreline, China: History and prospective

Abstract

There are three large engineering works that are now under construction or to be constructed in the coming decade in the Changjiang (Yangtze) River catchment and its estuary, i.e. the Three-gorge Dam, the south-to-north water diversion schemes and the deepwater navigation channel. These engineering works are expected to reduce significantly the sediment supply into the deltaic coastal system, slow or reverse the development of the Changjiang River delta and enhance coastal erosion processes. Consequently, these changes will reduce land resources for reclamation and threaten the coastal defence, which are of primary importance for the protection of Shanghai's socio-economic development. In order to understand further the mechanism of the Changjiang delta development, especially of coastal erosion, this paper examines historical responses of the Changjiang delta growth and its shoreline movement to the sediment supply from the fiver basin in a millennium to decade time scale. This study shows that the deltaic growth rate has been very sensitive to the changes in sediment supply to the deltaic coastal system, though the mechanism that induced such changes may be different. Based on an estimate of 10-20% decrease in sediment discharge caused by the three engineering works, not to mention an additional impact of future global sea-level rise, it is believed that coastal erosion along the deltaic shoreline will become inevitable, resulting in a great stress on the land resource and coastal protection for Shanghai in the coming decades.