Impact of dams on Yangtze River sediment supply to the sea and delta intertidal wetland response

Abstract

On the basis of estimates of sediment accumulation in reservoirs, the impact of 50,000 dams on sediment supply and intertidal wetland response in the Yangtze River catchment is examined. The total storage capacity of reservoirs is 200 × 10 9 m 3, or 22% of the Yangtze annual runoff. The sediment accumulation rate in reservoirs has increased from ∼0 in 1950 to >850 × 10 6 t/yr in 2003. Although sediment yield has increased with broader soil erosion in the river basin, the total riverine sediment discharge rate shows a strong decreasing trend from the late 1960s to 2003, likely due to dam construction. Consequently, the total growth rate of intertidal wetlands at the delta front has decreased dramatically. A significant relationship exists between intertidal wetland growth rate and riverine sediment supply that suggests riverine sediment supply is a governing factor in the interannual to interdecadal evolution of delta wetlands. Regression analysis of intertidal wetland growth rate and sediment supply shows that intertidal wetlands at the delta front degrades when the riverine sediment discharge rate reaches a threshold level of <263 × 10 6 t/yr. Owing to the construction of the Three Gorges Dam and other new dams, the sediment discharge rate of the Yangtze River will most likely decrease to below 150 × 10 6 t/yr in the coming decades. Therefore unless current management policies are adjusted, drastic recession of Yangtze River delta intertidal wetlands can be expected to occur.