A Dynamic Bidirectional Coupling Model for Watershed Water Environment Simulation

A dynamic bidirectional coupled model for watershed environment (E-DBCM), consisting of upland watershed module (UWSM) and 2D downstream waterbody module (DWBM), was developed. The computational domain was divided into upland watershed and downstream waterbody according to the water depth. The UWSM was used to describe pollutant transport process and determine the amount of non-point source (NPS) pollutant load to downstream waterbody, while the DWBM was used to simulate the 2D hydrodynamic and pollutant convection diffusion processes in downstream waterbody. The UWSM and DWBM were coupled by an interface, also called moving boundary, which can realize the simultaneous computations of both two modules and ensure the conservation of mass and momentum. The proposed E-DBCM was validated via four well-studied cases, and the results show that the E-DBCM can effectively reproduce the transport of the pollutants, and the position of pollutants discharged into the waterbody was defined compared with external coupling model, which has satisfactory numerical accuracy. The water environment in Yanqi River Basin was evaluated by the proposed model. The percent bias was lower than 25%, which proves that the proposed model was reliable, and the simulation accuracy can satisfy the engineering demand. The results show that the water pollutants in the basin were serious, and both the TP and TN concentration exceeded the standard, especially during flood season. The proposed E-DBCM is a new model with potential development, which is a useful tool for ensuing protection of water resources and environmental sustainability