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ArcGIS 10.3 provides a hydrology tool "flow length" which calculates the length of flow paths within a basin to the outlet of the basin. I am trying to calculate flow path length and flow path gradient from a given pixel of interest to where it enters the stream network. Using TauDEM (which I do not have access to), they define this as the 'distance from a pixel of interest to the stream channel using the D8 flowpath direction'.

I have a 30m DEM, flow direction raster and river network. From these flow path values I need to calculate mean flowpath length and mean flowpath gradient for a catchment for use in a catchment classification study.

Using ArcGIS 10.3 for Desktop.

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    Convert cells under stream into NO DATA value, recalculate flow length Commented Feb 23, 2016 at 22:10
  • How would I convert the cells under the stream layer to NO DATA? I can't just reclassify the flow direction layer because the stream network isn't consistently represented by one direction. Commented Feb 24, 2016 at 16:51

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I solved this problem by converting the cells under the stream network to 'NO DATA' as per FelixIP's comment and recalculating the flow length.

I set the stream network cells to NO DATA using the Raster Calc equation: SetNull(~(IsNull("Stream Raster")), "Original Flow Direction Raster")

Also of note, when calculating flow length, must set as DOWNSTREAM flow length.

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  • @FelixIP I have 15 catchments and I want to do the same as what Brun has done for each catchment. Is it possible to do that for all 15 catchments at the same time? Commented Oct 16, 2017 at 7:15
  • Yes it is. What stops you? Commented Oct 16, 2017 at 8:24

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