Inflow into a Storate Area

[kevin]

Dear All,

I was running an unsteady analysis for a river channel with storage area on both sides, and I get the net inflow to one of the storage areas like this:

My concerns are:

— First, how bad is the oscillation? I get some warning message during the simulation, reporting the error after the max number of iterations. But the water level and flow hydrograph at my cross sections look fine.
— Second, as the oscillation mainly occurs at the trough of the inflow time series (where inflow is negative), why is the oscillation always happens when netflow is from the storage area to the river channel but not the opposite flow direction?

Help for any of the above questions is very appreciated.
Thank you in advance!

[Anonymous]

Kevin,

My first thought is that this could be related to the time step being too large and/or the lateral weir being extremely long. I would start by reducing the time step to see if that fixes the problem.

If not, I have found that breaking long weirs into multiple smaller weirs can help with addressing stability problems at storage area connections. This only works, however, when there are multiple cross-sections across the connection.

See link below for further discussion.

http://hecrasmodel.blogspot.com/2015/05/my-unsteady-hec-ras-model-is-unstablewhy.html

Hope this helps,
Keith

[Anonymous]

Hi, Keith,

Thank you indeed for your suggestion! I break the long weir into sections, and then it works like magic.

[Author]

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