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Hydrologically Correct TIN for SFR2 Package?

Bruce Campbell

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Hi -- I'm using the TIN option in the SFR2 package (by the way - thanks for incorporating that into GMS) to get the ELEVUP and ELEVDN data but I'm getting lots of negative slope errors in the SFR2 MODFLOW input file created from the TIN. Started with USGS DEM data for the study area and did several manipulations in ARCMap to winnow the DEM point data down to a manageable size for GMS. This might be where I'm introducing errors? Also, tried adjusting the vertices spacing on the polygon when creating the TIN but that had very little effect on the number of negative slope errors. I'm using the "Linear" option to interpolate the DEM 2-D scatter points to the TIN. Is there a way in GMS to check the hydrological "correctness" (that water will flow downhill throughout the TIN)?

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Hi Bruce,

Did you know that version 10 will allow you to use a DEM to assign the ELEVUP and ELEVDN parameters? This may or may not resolve your issue.

There is an option to adjust the stream directions based on the stream properties (ELEVUP...) or based on the elevations of the nodes (you can interpolate to a coverage). From this you could see the places where the flow direction is incorrect based on your knowledge. I realize that this can be difficult with a large, complex stream network.

Defining hydrological "correctness" can become difficult because TINs or DEMs can have pits in them which makes tracing a flow path more complicated? We do have other software (WMS) that can take a DEM and define a stream network from it but we have not yet implemented the same functionality in GMS.

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Hi Alan -- Thanks for the quick response. I am using the a TIN to assign the ELEVUP and ELEVDN parameters. It's the same TIN as I'm using for the top of the upper layer in the model, so I was expecting the SFR2 altitudes would match the top of layer 1 pretty closely (knowing that some interpolation is going on). I had my GIS guy correct the DEM points I'm using in ARC that I'm using for the TIN, there's a command to do the hydrologic correction in ARC.

This fixed the negative slope errors but...

However, when I move the SFR2 data to MODFLOW, then attempt to run the model, I'm getting SFR2 errors (200+ cells) that the SFR2 segment is below the cell bottom. This is as much as 20 meters for some of the segments. I can lower the bottom of layer 1 by 21 meters and get past the error but it's important that I keep the original layer 1 bottom altitude and can't do this going forward.

I've put the files on your FTP site: NFRR_8.zip. This set has the layer 1 bottom lowered by 21 meters.

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