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scott

Flow from 2D Cells

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Hi,

Attached is a screen shot showing a models 2D grid check and zpt check with a results layer overlayed (depth less than 50mm eliminated, and colour grading in 50mm intervals). I'm wondering why the model is calculating ponding in the middle of the page (darker blue with depth greater than 200mm)? Water is escaping the 1d_pit (green node at bottom right of the page). When looking at the heights in the zpt check file it is surprising to see that depth of ponding. I'm a bit rusty with how TUFLOW transfers water from cell to cell, so if someone could help explain this and why the ponding is occurring that would be great.

Thanks

post-2457-0-77862000-1333409763_thumb.jp

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Hi Scott,

If I am interpreting the image correctly, the elevation in the cell with the 1d_pit is 79.923 and the elevations in the centre of the image where water is ponding are ~78.4? If this is the case, I would expect to see water ponding in the depression.

How are the inflows being applied to the TUFLOW model?

Water levels are calculated at the cell centres and the flows calculated at the cell sides. It might be worth a read of Section 4.4.4 of the 2010 TUFLOW manual, this section describes the computational points around the cell.

Regards

Phillip

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Thanks Phillip, your interpretations are correct. I'm applying inflows as a 1d_bc layer with the hydrograph being split evenly across each of the 1d_pit and applied at the bottom of the pit. In this instance the pipe capacity is exceeded and overland flow results. I'm surprised to see the ponding given that there is no defined low point, there is a slight change in grade but still there is grade parallel and perpendicular to the alignment of the cells.

Thanks

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Hi Both,

I have to say, from elevations alone I'm surprised to see that measure of build up there, as the cells to the left and down (as viewed in the picture) are of lower elevations. However if there are any high roughnesses going on (buildings for example) then they might hold up the water as it passed down the slope. Could that be what's happening here Scott?

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Hi Scott,

Are you able to export the the peak water levels as points (I assume that it is a maximum depth in the earlier figure?). If you export these are points (TUFLOW_to_gis.exe -mif -t99999 results_h.dat) and label these, in the figure, that would make it easier to understand what might be happening.

Cheers

Phillip

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Hi Phillip,

Sorry for late reply. The model has since changed and as a result that flooding area is not of concern. However, I have attached the peak water levels points for you to have a look at, I'm still puzzled as to why that ponding would have occurred?

Cheers

Scott

post-2457-0-36328400-1334125866_thumb.jp

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