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Samantha West

Losing volume from the model

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I am running an old 2004 1D/2D model which runs fine. I am now attempting to run this model in the 2008 version of Tuflow. I have found that in one section of my 1D channel the output hydrograph shows some instabilities. The hydrograph within the next section of channel reaches the peak flow and then drops to zero. This is then carried through the rest of the channel.

I'm wondering what would cause the model to lose half the volume of water. I can't see anything unique about that particular section of channel. I did have a culvert there which I thought was the cause but when I deleted I still got the same problem.

Any help would be appreciated.

Cheers

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The problem may be due to a change in the defaults used by TUFLOW since 2004, especially regarding the invert levels in the 1D domain (refer to the TUFLOW Manual, page B-16 under "Apply All Inverts"). If you are running the 2008 version of TUFLOW, you may want to turn on the "Defaults == PRE 2006-06" command in your TCF file.

Cheers

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Hi Samantha

Yes, the most likely reason is that the new defaults will be causing the problem. As per the cardno post the most likely offender is the "Apply All Inverts ==" command (see extract from manual below). Suggestions/tips when upgrading an old model are:

1. Read through the Section "Why do I Get Different Results?" (Section 9.5 in the 2008 manual).

2. Use something like UltraCompare (from UltraEdit people) to compare the old and new files such as the .eof, .tlf and the various check files. This helps highlight any changes between the models. For 1D issues, the .eof file is particularly good for this.

3. Use the various "Defaults ==" options to reset back to the old default, however, if the opportunity exists to upgrade the model using the latest defaults it is usually worthwhile doing this.

Cheers

Bill

From 2008 manual for "Apply All Inverts ==" command:

Note: If upgrading a model used prior to Build 2006-03-AB, any inverts for B, Blank and W channels need to be set to –99999 to ensure the inverts remain unchanged. Otherwise, the inverts for these channels are likely to be set to zero, as this is the default value set by MapInfo for the invert attributes.

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Bill,

I have tried changing the "apply all Inverts" back to pre 2006 defaults however I still get the same problem. I deleted the weir that was seemingly causing the problem however this just changed the location where the hydrograph suddenly drops away. The problem is now occuring at a 1d/2d interface. The 1 and 3 hour event runs fine as the peak flow is only 80m3/s. However once the flow reaches 100m3/s the hydrograph drops to 0. This doesn't occur at any other location of the model. The output hydrograph has NaN where the error occurs. It seems like it is going unstable but continues to run anyway.

The main difference is I have a lateral channel section coming in. The two incoming channels go from 1d to 2d and then back to 1d for the downstream channel. I have attached a diagram illustrating this. The diagram also shows no flow in the 1d channel (probably to do with the NaN) however it is still spilling out into the 2d.

Do you have any ideas of what is causing this?

Model_diagram.pdf

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Hi Samantha

Can you please email the .eof and .tlf files from the old 2004 model and that using the 2008 build to support@tuflow.com and we'll have a look through.

Cheers

Bill

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Bill,

It seems that I'm having a similar problem with a new ESTRY-TUFLOW model I'm building. At 05:30 in the simulation, I get NaN in my results occuring at several nodes along a short stretch of my model. The model continues to run and several nodes downstream, the flows seem sensible.

Did you find a solution to this problem?

Thanks,

Dave

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Hi Dave

From memory it was solved but I can't recall off-hand what the issue or fix was. Can you please email support@tuflow.com your .tlf and .eof files (they'll zip up small if they're large).

Thanks

Bill

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