I am trying to create a polygon (and eventually a raster) surface of river deposits that have since been eroded away. We know that at maximum, deposits got up to 600 ft above the present river. Given that a river slopes as it goes down hill, the answer is not as easy as a raster calculation, or determining X ft above sea level + 600 ft. How does one make a sloping surface as constant elevation above certain points in the river to determine the previous geographic extent of these deposits?

Using ArcGIS 10.5.

closed as unclear what you're asking by ahmadhanb, PolyGeo Jun 26 '18 at 1:26

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    What software you are using? – Moh Jun 25 '18 at 23:12
  • Welcome to GIS SE! As a new user be sure to take the Tour to learn about our focussed Q&A format. I recommend not thinking about GIS SE as being some sort of online GIS tutor. For your questions to be answered here they should as much as possible describe not just what you want to do, but precisely what you have tried and where you are stuck trying that. – PolyGeo Jun 25 '18 at 23:20
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    What data do you have? – user2856 Jun 25 '18 at 23:47

You need to create a HAND (Height Above Nearest Drainage) raster. See this paper. You can use ArcHydro tools or TauDEM to create the D-infinity Down and intermediate layers.

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