Full 2D absence of initial flow

[AdrienV]

Hello everybody,

I try to modelize a river of 200 m width, with several arms during the flood and only one arm for usual flow.

For these usual flows (7 – 20 m3/s) wich are the initial flows, water appears evrywhere on my 2D area and i can’t get an initial arm. The flow and the depth acts like waves on my terrain..

I don’t know if the problem comes from my terrain or the initial conditions? Did i forget to specify something? It sounds so easy with Mr. Goodel : http://hecrasmodel.blogspot.fr/2015/01/hec-ras-model-with-2d-mesh-only.html (i wish to have same results!!)

Thanks for helping me!

Adrien

[Kyle Moynihan]

What value did you use for the EG Slope for distributing flow along the BC Line?

The smaller the value the more flow will spread out across your BC line and cause the flooding you see.

[AdrienV]

Hello Kyle,

thanks very much for your help, i had EG slope = 0.01, and i try with EG slope = 1 and the result seems to be very good (no waves effect)

thanks again

[Anonymous]

Hi. I have a same problem in hec2D as you had. but I could not solve it. A braided river by 200 m width and Q=22 m^3/s. What should I do?thank you

[Anonymous]

Waves are also caused by incorrect computational and mapping output time intervals. If waves are occurring in RAS mapper visually i can guarantee that in all cases the model is either unstable or the mass balance is completely off. Both of which are highly manipulated by dt.

As was mentioned above the EG slope used is very important as to how the flow distributes along each cell face. Ive notices for urbanized areas, values upwards of 1E-10 is best used when trying to distribute flow evenly.

[Author]

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