Water pollution is a critical issue of global importance. Water environment modeling is an important tool for studying water pollution in basins. Based on a review of existing water environment models, a dynamic bidirectional coupling model for the water environment (E-DBCM), consisting of an upland watershed module (UWSM) and a 2D downstream waterbody module (DWBM), was developed using the multi-grid technique. The computational domain was discretized with grids of different sizes, and different time steps were adopted in regions with different grid sizes. The UWSM was applied to describe the generation and transport of pollutants on coarse grids to improve the computational efficiency, while the DWBM was capable of simulating the hydrodynamic and pollutant transport processes on fine grids to obtain a high accuracy. These two modules were spatially connected by a moving coupling boundary. Two test cases were used to validate the performance of the proposed model, and the results indicated that the E-DBCM had satisfactory computing efficiency while maintaining acceptable numerical accuracy. The water environment of the Yanqi River Basin was evaluated using the proposed E-DBCM. The maximum percent bias was 10.31 %, which indicates that the E-DBCM is reliable and that the numerical accuracy satisfies the engineering demand. The computational efficiency dramatically increased by 90 % when the watershed was discretized using the multi-grid technique. It was found that water pollution problems in this basin were serious, especially during the flood season. Various measures should be taken to improve the water environment treatment and strengthen protection measures in the Yanqi River Basin.
Keywords: Dynamic bidirectional coupling; E-DBCM; Multi-grid technique; Watershed water environment model.
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