Sediment Concentrations Lag Times

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Sediment Concentrations Lag Times

Nayyar Minhaj Asif
Hello Everyone

Well, i downloaded HEC RAS version 5.0 as soon as i get to know that sediment concentrations could be called in using the rule based boundary conditions. I thought of using these concentrations in order to get an idea on lag times and control my lateral structures accordingly.

I used the unsteady module for sediment computations and gave "Sediment Load Series" as an upstream boundary condition. What i did is that i input short doses of sediments (washload) in the system i.e. for  1 hour and then no sediment. The idea is that as soon this sediment gets transported, i instruct my lateral structure to adjust its gate openings depending on the amount of concentration coming upstream.

Now comes the question. i was hoping that Sediment Concentrations vs Simulation Time graphs will give me a clear idea of the sediment travel times but the surprising fact is that in all of my cross sections, sediment concentrations rises up and falls down exactly at the same time which is not making sense to me. Technically, the cross section most upstream should have the most earliest rise in concentrations and so on. But in the model, the concentrations are rising at the same time in all the cross sections and same is the case with falling.

Could anyone please explain the above situation? Any suggestion or help will be appreicated.

Regards
Nayyar
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Re: Sediment Concentrations Lag Times

Nayyar Minhaj Asif
Well, figured it out. Needed to change the routing method from continuity to water velocity . Volla.
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