The impact of human activities on lake level changes in a large floodplain lake: Dongting Lake, China

Abstract:

The Dongting Lake is the second largest freshwater lake in China with a natural water area of 2,623 km². It is the first large lake in the lower reaches of the Three Gorges Reservoir and is of great significance for buffering the floods in the middle and lower reaches of the Yangtze River. Few studies have focused on the influence of bathymetric changes on the hydrological regime in such a complex river-lake floodplain system. In this study, we simulate the water level, discharge, and sediment transport of the major rivers in the middle reaches of the Yangtze River and the Dongting Lake based on the one-dimensional numerical model of water and sediment in the river network. The following conclusions can be drawn from the results of this study: (1)The pattern of lake inundation has altered, primarily manifested by the changes under TGD’s seasonal water dispatches.Combining both impacts of flow regulation and reduction of the Yangtze level, the TGD-regulated flow slightly reduces the stage of the outlet of the Dongting Lake by 0.2-0.7m. (2)The flood-channel undercutting by sand mining makes the water level in the lake area drop significantly during the low-level season by 1.5-3m, especially in winter and spring. The rapid increase in vegetation has increased the roughness of the over-flow section of the floodplain and raised the water level by 0.4-1.5m. (3)The water level changes are mainly concentrated in the East and South Dongting Lake, especially during the low water level period. This study quantified the impact of the bathymetric changes on the lake water levels, thereby providing a better understanding of the potential effects of continued sand mining operations and providing scientific explanations for the considerable variations in the hydrological regimes of the Dongting Lake. Moreover, this study attempts to provide a reference for the assessment of similarly dramatic bathymetric changes in complex floodplain lakes.