The characteristics of flood responses to the restoration of polders on Dongting Lake, China

The serious shrinkage of Dongting Lake in China has led to the deterioration of its flood diversion and storage capacity, and now flood disasters have become more frequent. A lake restoration strategy is proposed in order to relieve flood-prone areas. However, flood movement is a dynamic process, so that approaches neglecting the hydrodynamics cannot accurately represent flood responses to restoring polders to a lake in a complex river basin. Here, a coupled one-dimensional and two-dimensional hydrodynamic model was applied to investigate flood responses to restoring polders to Dongting Lake under the conditions of the 1998 flood event. Quantified flood reduction effects show that the characteristics of flood responses vary significantly with the management option chosen. Appropriate strategies of lake restoration are suggested according to different flood responses. Polders of type II, which favour flood discharge, should be restored in order to streamline flood conveyance. Considering the ecological requirements of the lakes and wetlands, type I polders far from main flows can be partially restored, resulting in evacuation of residents to safe areas but keeping the cultivation.