Drastic decrease in sediment supply from Yantze River and coastal crisis

The periodicity and trends of 1951-2004 time series of water and sediment discharges at Datong Station and precipitation in the catchment were analyzed using wavelet method. Bathymetric data were processed for coastal area and profile using Arc-GIS software. A typical intertidal flat was daily measured from May 2002 to August 2005 for comparison of bed level between pre- and post-impoundment of the Three Gorges Reservoir. The results indicate that the sediment discharge shows a decreasing trend from the late 1960s (P < 0.001) while it varies in periods of 2-3 years and 8-9 years together with water discharge and precipitation. The decreasing trend is attributed mainly to dam construction while the periodicity is attributed to climate variability. After the impoundment of the Three Gorges Reservoir, the sediment discharge was reduced to the lowest level in the history. As a result of the drastic decrease in riverine sediment supply, the delta is transforming from progradation to recession. The sediment supply from the Yangtze is forecasted to decrease from 1.5 × 10⁸-2 × 10⁸ t/a at the present to -1 × 10⁸ t/ a in the coming decades, which will result in crisis of coastal resources.