Model builder - area to define stream does not translate into cells to define stream

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03-24-2014 05:07 AM
StefanieSteinbach
New Contributor III
Dear all,
At the moment I am building a model containing a sequence to derive a stream network from a DEM.
I created the variable 'Area sqkm to define stream', but somehow the area doesn't translate into the number of cells to define stream automatically; not even when I insert the area directly into the tool window. Thus, the model doesn't work and since I have to run it several times with different values, I don't want to calculate the number of cells every time I change the area.
Has anyone encountered and solved this problem before?
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MalcolmNunn
New Contributor II
Hi Stefanie

Something related I just posted about the Stream Definition tool. I would be curious if it is actually honouring the input values or just defaulting to 1% FAC, as having any Area SqKm value causes the tool to do this when it actually runs for me (running Arc Hydro 10.2).

If this is happening for you as well, the only workaround I can see is to specify the number of cells and manually set the Area SqKm field to blank.

As for your particular problem:

I have a model currently (just the Stream Definition tool) that has Number of Cells and Area SqKm as model parameters. When I run the model, if I enter a value for Area, the Number of Cells parameter is automatically calculated (although not vice versa). Have you created Number of Cells as a model parameter too or just Area SqKm? Yours should be able to do this as well.

Given the problem I first mentioned - you could then delete the Area value so the field is blank, and it runs correctly for the number of cells/area desired (since Number of Cells was generated from your inital Area entry).

Cheers
Malcolm
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MalcolmNunn
New Contributor II
Having said that - it could be that the FAC input grid must be specified as an input parameter and loaded as a layer in the current MXD for the tool dialogue to be able to automatically populate Number of Cells from Area SqKm.

Depending on how many times you have to run your model with different inputs, I would suggest the simplest thing to do would have a list set up of your desired areas (eg Excel spreadsheet) and their corresponding Number of Cells, and just enter the values manually.

(assuming your input raster CELLSIZE is in meters):
NUMBER OF CELLS = (AREA SQKM * 1 000 000) / (CELLSIZE^2)

Then for your model, have input parameters for Number of Cells and Area SqKm, make sure that Area SqKm is set to blank (assuming the same issue I previously mentioned) and specify the number of cells according to your conversion sheet.

Cheers
Mal
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