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Chiara

Recommended Downstream Boundary Type

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Is there a type of downstream boundary that SMS/RMA2 prefers in the following scenario:

-Floodplain area approximately 45kmx20km in size

-Very flat, no good channel definition

-Most of the downstream edge of the mesh will recieve floodwater (downstream edge approx 20km in length)

I have tried running the model with rating curves for the downstream sections, as well as a constant head boundary (at an elevation just above the highest elevation within the mesh).

Any suggestions would be appreciated :)

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Hi Chiara,

You should be able to use a constant head boundary condition or a rating curve, but it sounds like your model is going unstable. Rating curves add extra complexity to the model and so you are better off working from a constant boundary condition at first.

If your model is going unstable with a constant heady boundary just above the highest elevation within the mesh, you might try an even deeper model and/or a smaller flowrate. Once you get the model to run stably for this modified condition you can use hotstarts or the steering module to "guide" RMA2 into the correct solution. see http://xmswiki.com/wiki/index.php5?title=SMS:RMA2_Spindown

The RMA2 model isn't particularly well suited for this type of modeling project. It uses a finite element solver which isn't particularly stable for wetting and drying and is better utilized when representing true channel or estuarine areas. If changing the model is an option, this type of scenario would work better using TUFLOW since its finite difference solver is much more stable when dealing with wetting/drying, there isn't the need for everything to start out wet, dynamic runs work better, and you can specify rating curves.

Is there a type of downstream boundary that SMS/RMA2 prefers in the following scenario:

-Floodplain area approximately 45kmx20km in size

-Very flat, no good channel definition

-Most of the downstream edge of the mesh will recieve floodwater (downstream edge approx 20km in length)

I have tried running the model with rating curves for the downstream sections, as well as a constant head boundary (at an elevation just above the highest elevation within the mesh).

Any suggestions would be appreciated :)

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Rusty,

Unfortunately changing models is definately out of the question. I am trying a downstream constant water level with small inflows, and creating hotstart files from the runs. However whenever I input a hotstart file into the next run, RMA2 says that it does not recognise the file, or cannot find it. I thought a shorter path name might help matters, but this does not seem to help.

Any suggestions?

Thanks!

:blink:

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Chiara,

A few things to check:

* Is the run used to create the hotstart file completing successfully?

* Is the hotstart file read only?

- John

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Hi John

I am trying to use the same method by creating a hotstart file and use the created hostart file in my next simulation with bigger flowrate. I managed to run completely the first scenario where my flowrate is 60m3/s but then when i tried to use my hotstart file and modify the flowrate to 100m3/s, error comes up saying that "STOP depth convergence exceeds 25.0". How could this thing happen? What is the common reason causing this error?

Hope to hear from you soon, thanks!

Vera Kurniawan

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Hi Vera,

John isn't working with SMS anymore.

Anyway, as stated in earlier posts RMA2 isn't a very stable model. If it is an option, you would be much better off investigating alternative engines. It will save you lots of time and headaches.

In case this isn't an option, I'll try to explain where the error comes from and some ways to try to handle it.

This error indicates that the model went unstable. One way to try to keep the model stable is to try changing the flowrate more slowly. Rather than going from 60 m3/s to 100 m3/s, try going from 60 m3/s to 80 m3/s. If you look at the convergence reports, it will tell you which nodes had the biggest changes. If you use the Node | Find option in SMS, you can find where these nodes are. Sometimes this will lead to see places that have poorly shaped elements or very rapid geometry changes that can increase the instabilities of the model.

You may want to try using the steering module option in SMS. This tool runs the model over and over trying to get to a target boundary condition adjusting the model each run.

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