Unsteady Flow HEC-RAS Model Troubleshooting

1. Model stability can be very sensitive to the computational time step. Lowering the

computation time step may r educe computational instabilities and make the model more

stable.

2.

3.

some of the cross sections, causing the model to become unstable.

4. Too small of a computational time step can cause the model to become unstable. For

unstable. In addition, the computational run times can get overly long.

5.

6. However, for dam failure models a much shorter time step is required to account for the steep

change in discharge.

7. A trial and error method can be used to test various computational time steps to see which of

the largest time steps works while providing accurate results and minimal convergence errors.

Time Step Issues

Chapter 2 Time Step Issues