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Ramesh

HQ Boundary: Insensible inundation depth on/near a outlet boundary in a 2D riverine flood simulation.

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In a river flood modeling,  I have given a HQ boundary at the outlet of the domain.

The output Inundation depth raster, there would be a patch of raster (with approx width = 2-3 pixels) on/near the outlet boundary with extremely high depth of water.

I request for, What could be the reason for insensible water depth  in the inundation depth raster ?  and suggestions to overcome this??

Thank you.

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Hi Ramesh,

Yes, that does look unusual.  Are you able to provide some more information:

  • Are you running TUFLOW Classic or the TUFLOW HPC solver?  
  • Are you specify a height-flow attribute or are you specifying a boundary slope (i.e. the "B" attribute in the GIS layer?
  • Which version of TUFLOW are you using?

The reason i ask about HPC and classic is that the two schemes treat HQ boundaries differently, an extract from the manual is below: 

Significant differences may occur at 2D HQ boundaries.  Classic treats the 2D HQ boundary as one HQ boundary across the whole HQ line, setting a water level based on the total flow across the line.  Due to model splitting to parallelise the 2D domain across CPU or GPU cores, HPC applies the HQ boundary slope to each individual cell along the boundary.  As with all HQ boundaries, the effect of the boundary should be well away from the area of interest, and sensitivity testing carried out to demonstrate this.

 

Regards

Phil

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15 hours ago, par said:

 

Hi Phil,

Thank you for your kind reply.

Actually, I got the similar insensible results with TUFLOW classic and TUFLOW HPC.  PFA for the attribute table for the outlet boundary condition,the values are kept default from the tutorial.

Is this making the problem??

Ramesh

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I'll say the boundary attributes look fine.

I don't suppose your model is up in some hills/mountains somewhere? And have you perhaps trimmed your input DTM to just your modelled area? (This is relatively common practice, for all it has potential to cause problems for people!)

If 'yes' for to both of those, it may simply be that the row of cells which your boundary is selecting was not covered by your DTM, and has been set to some arbitrary elevation. The slope boundary is causing the water level to be up somewhere "sensible" in relation to the water that's sitting on the DTM, and so you end up with your insensible depths. In which case the solution would be to either get your DTM data again so it covers that row of cells, or moved your boundary (and code polygon) in a row of cells to where you currently have good data.

You could check and see if this was your problem by looking in your zpt_check file and examining the elevations in that area.

...

Alternatively, given this post is a month old at this point, you may have already solved the problem! In which case I'd be interested to hear what it was, just so we can all learn. ^_^

Good luck,

Peter.

PS. As a general comment (which may not even relate to this case if the problem was not as I described) I'd recommend either not trimming DTM data to a model domain, or if you really want to then trim it with a generous buffer. Otherwise, you end up with difficulties like this at boundaries on the perimeter of the model, or if you find yourself needing to tweak your model extent (perhaps some glasswalling turns up in your extreme flood events) then you'll have to re-generate your DTM. All of which could be avoided by just not going to the trouble of trimming the data in the first place.

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