NUMERICAL SIMULATION OF HYDROLOGICAL AND HYDRODYNAMIC RESPONSES TO CHANNEL EROSION IN CHINA'S LARGEST FRESHWATER LAKE

Topography determines the nature of hydrodynamic processes and its changes potentially affect the water quantity and quality. This study assessed the spatiotemporal impacts of topography changes on hydrological and hydrodynamic characteristics of China's largest freshwater lake, Poyang Lake. Results from simulation of different channel erosion intensities indicated that topography changes induced hydrological and hydrodynamic variations with spatiotemporal heterogeneity. Water levels in the lake decreased and the effect was enhanced with stronger erosion intensities. The decrease in water level was significant during the dry period, but negligible during the wet period. Water levels decreased by an average of 0.90-1.1 m in the northern channel during the dry period, and 0.27 m and 0.20 m in the central and eastern lakes during the rising and recession periods. The changing water level further affected the distribution of water with the effect of gathering water to the channel from nearby areas. Moreover, channel erosion altered the lake-river interactions. During the dry period, outflow discharges increased as the channel conveyance capacity increased by 25-136%. In contrast, during the wet period, outflow discharges decreased as the inflow regulation volume increased by 3.8-8.2 x 10(8) m(3). Particularly, backflow frequency and volume increased during the flooding period of the Yangtze River. In addition, the dry period in Poyang Lake was extended, and the frequency of low-water events increased significantly. This study demonstrated the spatiotemporal impacts of topographical changes on hydrodynamic processes in Poyang Lake, therefore providing a better understanding of variations in water regimes and lake-river interactions.