Dear Stephen :

In your particular model the channel is extremely steep. As such, you are dealing with very high velocities as the water leaves the reservoir structure and travels down the river. In these situations, it is often necessary to "smooth" the channel geometry so that the flow can transition as it expands and contracts. If the flow attempts to expand or contract too rapidly, the model can sometimes have difficulty in converging.

BTW, I am in Albuquerque teaching at URS :).

Sincerely,

Chris E. Maeder, M.S., P.E.
Senior Technical Engineer
chris.maeder@bossintl.com