Wetland inundation modeling of Dongting Lake using two-dimensional hydrodynamic model on unstructured grids

Abstract

Abstract To understand the inundation process (wetting and drying) in the bottomlands of Dongting Lake, a two-dimensional hydrodynamic model based on shallow water equations has been developed to model complex flow regime controlled by both the Yangtze River and its own basins. The governing equations are discretized using the finite volume method with the combination of quadrilateral and triangular grids and the mass and momentum fluxes are solved using the approximate Riemann solver, HLLC scheme with high spatial resolution. The processes of wetting and drying are specially treated to simulate the flow routing over dry bed. Verification shows that the proposed method can accurately capture flow propagation over dry bed resulting from suddenly breach of the dam. This performance is preferred for inundation modeling. After theoretical test, we applied the model to simulate the inundation process in Dongting Lake. Setting the calibrated roughness parameters, we successfully simulated flow processes in the lake from 2006 to 2010. The water extent changes rapidly along with the stage fluctuation in the lake. In dry season, water is mainly limited in channels, large parts of bottomlands are exposed and water extent reaches the yearly minimum. The whole lake is inundated in the flood season and the maximum of water extent reaches. After the flood season, the bottomlands expose again along with the gradual decrease of water. Particular hydrological regimes cause the regular zonal distribution of vegetation in Dongting Lake Wetland. Hydrology in the middle Yangtze River Basin is undergoing great changes. This model can be applied to assess possible responses of lake wetland for the changing environment.