Backwater effect in HEC-RAS 2D simulation

[Ahmad]

I am trying to simulate a flood event scenario in small reach of a large river. When I run the simulation It gives the backwater effect on the downstream discharge station. I am assuming It is considering my 2D Flow Area boundary as a barrier and giving me backwater effect in the downstream station. Any ideas how to resolve this issue?

[Anonymous]

I mean….thats not really an issue, thats a direct output from your direct input of a boundary condition.

If you are using a stage i highly suggest you change that because i personally do not believe they work as intended.

If you are using normal depth, that would be an incorrect DS BC for a reach ending in a junction with another reach. If you are intending on not showing the impacts of the main river you can change your normal depth to something abnormally high and the backwater effect will be removed, but this would be an incorrect simulation (or one that neglects the main reach)

[Vimal Sharma]

Dear Luis Partida,

Hope you are doing well

I am also trying to model the backwater effect due to a dam in the downstream of main river and a river junction where tributary is joining to main river. When I run the simulation, I run by using full momentum equation and diffusion wave equation for 2D mesh. I did see the WSE more in the case when full momentum equation was used than diffusion wave. I concluded or assumed that full momentum equation is giving accurate. I have few questions regarding this;

1. Is it correct if I consider the results from the above explanation for the model calibration?
2. What do you suggest as ds BC i) stage hydrograph ii) rating curve?
3. I am doing this only with HEC-RAS 2D? Is it necessary to go for combined 1D/2D ?
4. How can I show the prevailing of backwater effect quantitatively and qualitatively?

Please clarify above things so that I can run the model quickly

[Author]

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