problem of river flow simulation

Liu

I just finish the code of simulation river flow with operator split method, that is: 1. predicting the velocity by a implicit scheme with considering the pressure gradient term. 2. calculating the water evaluation with the predicted velocity. 3. correcting the velocity with the calculated water evaluation.

My program runs well in equal depth river flow, But when it is apply in the simulating the real flow in Three Gorge Reservoir, some vortex well appear near the bank and the program will run out. I need any advise for the problem, thanks a lot.