I’m encountering a problem that I’ve not seen prior: a very simple model is unstable when the number of vertical cells is greater than 1. The model is comprised of a 100m X 100m X 1m grid with 2m cell resolution, a single adjacent 4 four cell inflow boundary on the left, a single adjacent 4 cell outflow boundary on the right, and a single impulse dye time series applied to the inflow BC. When only one vertical cell is specified the model runs fine. If more than one vertical cell is specified the model crashes after one time-step. The time-step used is 0.1 sec. which is less than what is required by the CFL DetlaT. Any suggestions?
Most likely you might need to lower your time step. The time step for single layer model and multi-layer model would change significantly. Have you tried changing the different smaller time step ? However, some other parameters might also need some adjustment. Would you send your single layer model and multi layer model so that we can take a look ? I think you should be able to upload it here. If not send me a Private message and will send you my email address.