Sediment transport in supercritical flow

[Anonymous]

Hi!

I’m doing some sediment transport simulation (HEC RAS 4.1.0) in a steep river (S = 0.02-0.04), where flow is sub- and supercritical according to steady state simulations. Now I noticed that the flow is always subcritical (with the flow depth always at critical level) in case of the quasi-unsteady flow which has to be used for sediment transport simulations.
Does anyone know, if a mixed flow option exist like in the steady flow calculation? I could not find any remark on the flow conditions neither in the User Manual nor the Reference Manual.
Thank you very much for your help!

[Anonymous]

I am struggling with the same problem even in HEC-RAS 5.0.4 . Tried to do it inunsteady also, and although my model runs fine with no error messages without sediments, it produces embankment at about 00:00:30 hours (starting from 00:00:00) in the simulation, which is just not possible. Tried changing a lot of the sediment data, max depth, bank limits for moving bed, etc, however at most I’ve been able to get to 00:01:30 hours of simulation.

How can one model sediment transport in supercritical flow?

[Zoran]

According to this paper from 2018 (Quasi-unsteady flow calculation), p. 32-33:

“However HEC-RAS does not allow for a mixed flow regime simulation to occur within sediment transport modelling, so solutions that have supercritical values are not valid solutions. If the solution is supercritical, the model will display an error message and set the water surface to the critical depth(Brunner & CEIWR-HEC, 2016).”

[Author]

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