Welcome to the RAS Solution Forums HEC-RAS Help Modeling Ephemeral streams using HEC-RAS

Viewing 3 posts - 1 through 3 (of 3 total)
  • Author
    Posts
  • #5490
    Mohamed elgamal
    Participant

    Dear All,
    I am attempting to carry out a dynamic unsteady state simulation to model the dynamic response of a located mid-way pond in an ephemeral wadi stream that is subjected to a sporadic flooding hydrograph. What is requested is to identify the part of the flood water volume that will succeed to pass by the pond and to identify also the second part that would be trapped by the pond and would not succeed to cross the pond and to enter the downstream wadi reach located d/s of the pond.
    In order to do so, I have used the cross section approach to deal with the pond (not the storage, pool-level, approach) because I do need some more flow details to be calculated at the pond sections.
    I’ve started with a dry pond initial condition however I figured out that Hec-ras automatically disregard the initial dry condition and on purpose fill the pond initially and thus no part of the incomming flow is intercepted by the pond despite that the pond has a significant volume to intercept at least 50% of the coming water volume.
    Can some body guide me regarding how to deal with that issue.
    If hec-ras can not model the initially dry sections then how to use it to model the initially dry ephemeral wadies and how to deal with all its local ponds. does it work with the inundation mapping which basically means wetting the drying areas?
    Best Regards
    M. Elgamal

    #8771
    Anonymous
    Guest

    The unsteady flow equations (St. Venant Eqs.) require that there be a finite depth at all locations. The flow can be zero. So, you will need to provide a flow path thru the pond that always has some depth for the unsteady flow solver to work. You might consider using a pilot channel thru the pond to keep some depth in the model. If that does not work, you will probably have to model the pond as a RAS storage area.

    #8772
    Anonymous
    Guest

    Dear MichaelG
    Thank you for your reply and suggestion.
    I need to add that I have recently managed to solve the same problem using EPA-SWMM version 5.1 (the last released version). Both Hec-ras and epa-swmm solve the fully dynamic St. Vennant equation however EPA-SWMM solver seems to be much robust than hec-ras. In EPA-SWMM I can assume a dry element with no problems. It is now clear to me that the issue was in the numerical schemes adopted in hec-ras itself.

    Best Regards

    M. Elgamal

Viewing 3 posts - 1 through 3 (of 3 total)
  • You must be logged in to reply to this topic.