Abstract

The suspended load at Datong comes mainly from the Changjiang (Yangtze) upper reach and constitutes almost all sediment discharge flowing into the sea. Based upon the data obtained by hundreds of investigation sections on middle and lower reaches, the sediment discharge at Datong in 100 years after the Three-Gorges-Dam (TGD) completion has been mathematically projected, which is 384 X 10⁶ tons/yr. on average. Considering factors reducing sediment discharge, such as water diversion from the Changjiang Basin to the Yellow River Basin (South-to-North Water Diversion Project), building reservoirs on the river and its tributaries, close hillsides to facilitate afforestation and converting cultivated land back to forest and grassland in Changjiang upper basin, decreasing population in 21^th century and some technical problems in prediction etc. the suspended sediment load at Datong might be estimated to be about 200-250 X 10⁶ t/yr after TGD completion. The sediment discharge at Datong, calculated by drillcores in the Changjiang Delta, was 1.84-228 X 10⁶ t/yr. during the postglacial period, which is close to that predicted in 100 years after the dam completion, and is deviated from that measured at Datong during the last five decades. Examination of the environmental change in the Changjiang basin, triggered by population growth, deforestation, soil erosion etc. in Chinese historical time leads to conclude that the predicted suspended discharge in 100 years after damming may be more representative for the Changjiang during the postglacial period. The suspended load at Datong, measured during the last five decades, is only a record of a short period with highest suspended load in the history of the Changjiang development, resulted from abrupt population growth, serious deforestation and severe soil erosion. The Changjiang Delta should not be seriously changed and would not subject to serious erosion in 100 years after the TGD completion. However, accelerated tidal flat reclamation project in the Changjiang Delta might likely trigger a serious coastal erosion of adjacent provinces, where the sediments of coastal zone are mainly transported from the Changjiang Delta.

Keywords:Sediment discharge, Potential impact, Chinese population, Deforestation and afforestation, Soil erosion, Delta formation