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I'm attempting to calculate the relative height (values between 0 and 1 preferably) of waypoints on a slope along the path of least resistance. Ideally, points in creeks would have values of 0 and points on ridges would have values of 1 (or opposite values would also work). I have about 200 waypoints that I need to do this for and will need to do it manually otherwise. I'm using ArcMap version 10.1.

To clarify, I have waypoints in mountainous terrain and I need to know the change in elevation that water will likely flow from the top of the ridge. I would also like to know the change in height from the same waypoint to the point where it will intersect the nearest creek. I will manually calculate the ratio of the difference in height from the waypoint to the ridge vs. the overall change in height in order to get a ratio of the height of water flow to the overall height of the water path before intersecting a creek. It would be nice if there was a tool that already did this.

  • The "top of the ridge" is not well-defined, because water can arrive at some points from multiple locations along a ridge at different elevations. (Similarly, "creek" is not well-defined, but that problem can be overcome using a standard layer of permanent waterways.) In light of this, could you explain the purpose of this calculation? – whuber Dec 9 '13 at 19:16
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    I am trying to utilize GIS as a surrogate for Topographic Relative Moisture Index (TRMI) (Parker, 1982). One of his paramaeters is called topographic position "ranging from 0 on exposed, well-drained ridge-tops to 20 in valley bottoms). I have a pretty good idea where the continuously flowing water begins. The "flow length" tool seems like a valid surrogate which I'm going to try. – sdb348 Dec 9 '13 at 19:51
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Consider using Global Mapper as as your toolset instead, this type of geo-analysis relies on elevation terrains and flow networking within a watershed (of any scale). Global Mapper provides Watershed Delineation tools to run these calculations.

If you are planning to use ArcGIS tools, this analysis is run using the "hydrology toolset" within Spatial Analyst toolbox (Spatial Analyst extension required).

The following tools will be used in building this analysis.

  • build basin/watershed from terrain
  • burn in your streams
  • Build Flow Direction
  • Build Flow Length/Accumulation

IMHO - Global Mapper tools are inexpensive ($499US a license) and more direct in running the analysis, whereas esri tools are far more expensive and require more setup to get the output you desire.

  • A good reference for using the Hydrology toolset within Spatial Analyst can be found here: web.ics.purdue.edu/~vmerwade/education/hydrology.pdf – bjmarra Dec 10 '13 at 14:01
  • Thanks for the help. I ended up doing it manually since I didn't end up liking the results from the flow length tool. I might revisit this in the future. – sdb348 Dec 12 '13 at 19:44

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