topic Re: Upstream and downstream gradient? in Water Resources Questions

Upstream and downstream gradient?

TomKearns — Tue, 10 Dec 2013 20:29:37 GMT

Is there a way to calculate the gradient of only the streams? The D8 style of slope accounts for too much bank, I am interested in the slope of only the stream.

Thanks

Re: Upstream and downstream gradient?

MarkBoucher — Wed, 11 Dec 2013 16:50:46 GMT

You could create a raster using the stream polyline. Then use the Con() function to create a raster from the DEM that only includes that DEM grid cells that are "under" the stream grids. Then run the slope function.

Re: Upstream and downstream gradient?

TomKearns — Wed, 11 Dec 2013 17:42:40 GMT

I think that will work, thanks.

Re: Upstream and downstream gradient?

808707 — Wed, 18 Dec 2013 13:11:54 GMT

You could create a raster using the stream polyline. Then use the Con() function to create a raster from the DEM that only includes that DEM grid cells that are "under" the stream grids. Then run the slope function.

Hello MBoucher I would like to have a go at this myself but I'm not sure how to set up the Con function. Do I need to use the Con tool or the Con function in Raster calculator? If so how do I get it to select DEM grid cells that are under the stream grids? Thanks for any help

Re: Upstream and downstream gradient?

MarkBoucher — Wed, 18 Dec 2013 20:55:03 GMT

The Con() function can be tricky. There are helps online from ESRI. http://resources.arcgis.com/en/help/main/10.1/index.html#//009z00000005000000

I tend to migrate to the Raster Calculator in Spatial Analyst. If you double click on functions, operators, and layers and it make sure there are spaces in the right places in the syntax. I do this seldom enough that it is always a bit of trial and error for me. I have modified the SA tool bar to have the Raster Calculator icon on it for easy access instead of finding it in the toolbox, though I think it works the same either way.

Re: Upstream and downstream gradient?

808707 — Thu, 19 Dec 2013 07:47:27 GMT

Thanks MBoucher. I think I figured it out using the Con tool.

I put the Input Conditional Raster as the Stream Network.

Seeming as though streams in the Stream Network had a value of 1 I put it to equal this in the Expression.

I then put the Input True Raster as the DEM.

When I run the slope tool on the results it seems to give the results I was looking for.