Abstract: To deeply understand the hydrodynamic characteristics of large-scale river-lake system, two-dimensional(2D) mathematical model instead of traditional one-dimensional(1D) model is required for simulation and research when calculation accuracy is given higher priority than calculation efficiency. With high-resolution grid as the premise, the contradiction between accuracy and efficiency of 2D hydrodynamic model turns into a bottleneck of calculation efficiency. With the Jingjiang-Dongting (JDT) system (divided into 328 000 quadrilateral cells with the minimum grid scale about 50 m) as research background, the performances of both explicit and implicit hydrodynamic models for large-scale river-lake system were compared using MIKE21 model and a semi-implicit Eulerian-Lagrangian model. The practicability of high-resolution 2D models of large-scale river-lake systems was also discussed. Results illustrated that explicit model is less stable (maximum allowable time step 0.8 s) than implicit model (time step reaching over 60 s). The efficiency test results on a conventional 16-core workstation revealed sound parallelism of explicit model, with the speedup ratio varying linearly with the number of cores. Implicit model (using the prediction-correction block parallel computing method) can also achieve a very large speedup ratio, amounting to 11.1 under 16-core parallel conditions. The explicit and implicit models took 411 and 10.76 hours (16 cores), respectively, to simulate the one-year unsteady flow in JDT system. The calculation efficiency of the latter is 38.2 times higher than that of the former. In conclusion, implicit model meets the practical requirements of high-resolution 2D hydrodynamic simulation for large-scale river-lake system.

Key words: large-scale river and lake system, high-resolution hydrodynamic model, explicit model, implicit model, comparison of calculation efficiency