I'm using ArcGIS 3D Analyst 10.5.0.

I used a groundwater potentiometric surface raster to calculate flow direction in a "springshed" (the groundwater version of a watershed). Now I want to use this flow direction to create a shapefile of "contributing zones" for a set of groundwater wells using this direction.

I have some average groundwater velocities that I will use to roughly estimate a 1-year capture zone size, e.g. a darcy velocity of 10 cm d-1 would lead to 1-year capture zones that extend 36.5 m in the direction opposite of groundwater flow.

Now I want to use my rough estimates of distances of my 1-year capture zone along with my flow direction to create a capture zone for each well. My idea was to create buffers "upstream" from groundwater wells, then somehow angle them in the direction opposite of groundwater flow. I've read through threads explaining how to create square buffers, but I can't find any information for creating buffers that do not center on the attribute or how to angle the buffer using my direction values.

Is buffer the way to do this?

  • 1
    The Watershed tool in the Spatial Analyst toolbox will return the total contributing area from the well point and a flow direction surface. Then create the 36.5 meter buffer for the well and and use the buffer to define the one-year capture zone. – GBG Jul 10 '17 at 17:32
  • Okay, so I just tried this and the total contributing area is just a small line extending back from the points. A very thin line of variable length. Not sure if this is supposed to do this... – Man Jul 10 '17 at 20:19
  • 1
    Try running Snap To Pour Point before running the watershed tool to ensure that the point is over the best spot. – GBG Jul 10 '17 at 20:33
  • I will try that tomorrow when I get back to my desktop! I just wanted to show you a picture of what I'm working with: imgur.com/a/76eeu. I'm wondering if part of my issue is that the flow direction layer came out looking really weird, with a bunch of lines through it where water is flowing in a different direction than the bulk of the surrounding water. – Man Jul 11 '17 at 2:48
  • I used an updated potentiometric surface map to generate a new flow direction layer and also used fill to smooth out the flow direction layer... this really helped! However, now I need to essentially create polygons with an edge of the polygon centered over the well points and angled in the direction opposite of groundwater flow. I realized buffer isn't the way I need to do this, as I can't make a buffer on the edge of a point. Unless I create NEW points that are half of the distance of my total contributing area distance away and buffer those... but how to angle the points... – Man Jul 11 '17 at 17:39

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