Impacts of Streamflow and Topographic Changes on Water Level during the Dry Season of Poyang Lake, China

Abstract

Poyang Lake is the largest freshwater lake in China and is internationally recognized as an important lacustrine and wetland ecosystem with abundant biodiversity. Since 2003, the average lake water level has significantly declined by 1.35 m during the dry season. Quantifying the contribution of different factors to water level decline is necessary for lake management. The impact factors mainly include hydrological and topographic changes in terms of the decreased inflow from the five tributaries, lower water level in the Yangtze River, the decline of the lakebed, and the increased discharge ability of the lake. Back-propagation neural networks have been constructed to simulate the lake water level, considering preimpact and postimpact streamflow and topographic scenarios. The simulations verified the robustness and applicability of the networks and indicated that the streamflow and topographic changes contributed approximately 34% and 66% to the decline in the water level, respectively. The Three Gorges Reservoir exerts various impacts on the water level of Poyang Lake. The reservoir sedimentation causes riverbed erosion and lowers the downstream water level. The water release increases the downstream flow and is conducive to elevating the lake water level. But the impact is marginal because it is diluted by the topographic changes and the decreased runoff of the subbasins along the middle and lower Yangtze River. These results provide useful information to guide strategies for wetland and lacustrine ecological protection associated with water level fluctuations.