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I have a large data set of points, all of which lie on a river network and have x, y co-ordinates. I want to calculate the slope of the river channel at each point from the underlying DEM by taking the elevation at each point and the elevation of a point on the network 1km upstream. The best way I can think of doing this is by creating a line upstream from each point that stops when it reaches 1km away (obviously the line will not be straight in most instances), then create a point at the end of that line. I guess the flow direction or accumulation layer could be used to draw the line in the correct direction (upstream) from each point but I don't know where to start!

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    You can use Extract multi values to points to get the elevation at certain points. Your method of getting the upstream point is not likely to work; one point downstream have many different points/routes upstream. Even if you select the steepest path your not guaranteed to end up with a point that lies within your river at 1 km upstream. Maybe you can create a line feature in the river to trace backwards and pick a point close to it? – Martin Feb 21 '14 at 14:13
  • Have a look at RivEX it has tools for generating u/s and d/s line segments based upon points snapped to a river network. – Hornbydd Jan 29 '15 at 20:28
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This is a little difficult because of the branching nature of stream networks. Over 1km you will likely need your solution to be able to make a choice of which branch/tributary to trace up. I suggest calculating Horton stream order for your stream lines and then dissolving features based on the Horton order field. Once that is done you can create a point 1km upstream in python by using the shapely library and the .interpolate() function.

To calculate Horton order you can use GRASS or I have a messy script to calculate Horton order.

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