Quantifying the Influence of Water Impoundment Phases I and II of the Three Gorges Reservoir on Downstream Suspended Sediment Flux

To estimate the alteration of downstream sediment flux affected by dam construction is an international scientific problem. In this paper, we estimate the water and sediment supplies from ungauged area next to the main river that the gauging stations of tributaries failed to cover. In combination of the estimated data with the geodesic datum collected at Cuntan, Yichang, Hankou and Datong stations and the tributaries gauge stations between Cuntan and Datong, we build a suspended sediment budget to quantify the influence of water impoundment phases I and II of the Three Gorges Reservoir on downstream (to estuary) suspended sediment flux. The results indicated: (1) During the Three Gorges Reservoir phases I (2003-2005) and II (2006-2007) impoundment period, the settlement rates of SSC in the Three Gorges Reservoir was 64% and 83% respectively. (2) Due to the dam downstream river bed erosion and sediments from tributaries, water impoundment phases I and II of Three Gorges Reach induces the suspend sediment of Yichang station decreased by 62% and 82%, Hankou station decreased by 37% and 54%, Datong station decreased by 28% and 40%. (3) Compared with the former five years (1998-2002), the five years (2003-2007) after The Three Gorges Dam put into operation, the suspended sediment load of three stations mentioned above was decreased by 354, 172 and 163×109 kg/a respectively. The decrease rates attributed to water impoundment of the Three Gorges Reservoir were 41%, 55% and 45%, respectively.