Normally you can have a maximum Courant number in your model of up to 5. The maximum value which you can use without having stability problems does, however, depend on your bathymetry:
· If you are modelling an estuary with tidal channels you should adhere to the rules given under Bathymetry (p. 77). Alternatively you can use a maximum Courant number of 1, in which case you should have no problems in resolving the flow in the channels. The CPU time requirements might, however, become very high.
· The MIKE 21 Flow Model is designed for Courant numbers up to about 20. You should, however, only allow these very high numbers in areas where the bathymetry is very smooth.