The Evolution of Annual Runoff and Sediment in the Dongting Lake and Their Driving Forces
洞庭湖年径流泥沙的演变特征及其动因

Some conclusions drawn from multianalysis of the evolution process of annual runoff & sediment and the driving forces in the Dongting Lake from 1951 t o 1998 are as follows: Runoff and sediment connect with each other closely and t he related modulus is 0.9013. Annual runoff volume and annual sediment discharge as a whole take on a synchronously-decreasing trend, and the evolution process is characterized by obvious stages. Because the major catchments of Xiangshui, Z ishui, Yuanshui and Lishui drainage basins and the high forest-covering-rate abo ve 52%, the newly built water conservance projects in recent years and the incre ase of industrial, agricultural and domestic water consumption cannot exert fund amental influence on the hydrological characteristics of the four rivers and the runoff and sediment flowing into the lake are basically stable, so they do not have profound effect on the runoff and sediment in the lake. The three-time adju stment of of water-sand relations of the rivers and the lake resulting from the pluging up of Tiaoxian bayou on the midlle reaches of the Yangtze River, the cur ve-cuttings in the lower Jingjiang River system and the flow-cutting at Gezhouba dam, however, become the main factor leading to the deceleration of the runoff and sediment in the Dongting Lake.