Sea-level changes, human impacts and coastal responses in China

The rate of sea-level rise during the past hundred years has been 2-3 mm/year along China's coasts; sea level will probably continue to rise in the future. The process has decreased wave winnowing of submerged coastal sediment but enhanced erosion by waves breaking on the upper beaches. Following the rise of sea level, river-channel slopes have been reduced, decreasing fluvial sediment discharges to the ocean. Human impacts through diverting river discharge and constructing dams in the lower reaches of rivers for fresh water supplies have also upset coastal processes. Paucity of coastal sediment supply is a world-wide phenomenon which, when combined with the frequency of storm surges and El Nino events to strengthen hydrodynamics, invariably results in beach erosion and the landward retreat of sand barriers along the coastal zone. Overpumping of groundwater and overloading by constructions on the delta plain and lowland coast have had serious effects: the average rate of relative sea-level rise is 24.5-50.0 mm/year in TianJing, the old Yellow River delta area along the Bohai Sea, 4.5-5.5 mm/year in the modern Yellow River delta, and 6.5-11.0 mm/year in the Shanghai area of the Changjiang River mouth. These rates are much higher than the mean annual rate of 1.4 mm/year. Under the circumstances saltwater intrusion has been changing river water salinity and fresh water quality. Storm surges often cause the lowland coast to be inundated and flooded. All such effects are ultimately the result of human activities.