EFDC model is quite a complex model and can be used for several applications. However, at the same time it is very difficult to debug the model.
In several instances, you may encounter the error messages such as “Negative depth in Cell Centers” and “Maximum Iterations Exceeded in External Solution”. These error mean that the model is not stable. So the things you need to go back and look are initial conditions, bathymetry. Another thing you may try to do is to decrease the time step. By decreasing the time step the model would be able to model for sudden increase in flows.
Another thing you may try is to increase the Smagorinsky coefficient to make the model stable. You may also disable the HMD and you may get the model working fairly.
I think this tip would be very handy to all the EFDC users since I have been a EFDC user for a while.
Do you know any other methods or parameters you can adjust so that you can make your model stable ? Please share your ideas in the comments.