Modeling Note: The Computational Efficiency of Small Time Steps
It seems intuitive that smaller time steps generate larger run times. However, HEC-RAS will iterate on each solution until it reaches an acceptable tolerance. Iteration is computationally expensive and smaller time steps often iterate less. Therefore, selecting a smaller time step will often reduce the number of iterations, leading to less additional run time than users often expect. In rare cases, a smaller run time can actually speed the model up by more-than-compensating for the additional time steps by neutralizing iterations.