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If you're already familiar with the upstream trace tools, you should be able to apply the following steps: Create a constant raster. A constant value of zero is a convenient number. Subtract the elevation raster from the constant raster, leaving you with an inverse of the elevation raster. If you used a constant value of zero, your inverse raster is now a ...


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There is a tool in the free and open-source (GNU GPL licensed) GIS Whitebox Geospatial Analysis Tools that can identify the flowpath from any point or collection of points specified either as a ShapeFile or as a categorical raster. The tool is called Trace Downslope Flowpaths: The tool takes a D8 flow pointer (flow directions) grid as an input, which ...


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Martin is correct that while your workflow will do well for a specific user case, it doesn't account for many of the issues that road embankments create for flowpath modelling using fine-resolution LiDAR data, such as the problems with discontinuous flow in roadside ditches and the effects of minor unmapped culverts (which can alter flowpaths considerably). ...


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This is a good question, and one that I tend to get asked from time to time. First, as you've pointed out, the equation for TWI = ln(a / tan(B)), where a is the 'specific' catchment area (i.e. the upslope inflowing area normalized for a measure of contour length) and B is the slope gradient, in radians, at the grid cell. As you correctly pointed out TWI will ...


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I would like to defend RivEX and what its capable of. I have to admit I have a vested interest as I'm the developer behind it. Some very clever people (not me!) developed an algorithm that could compute Strahler order and RivEX uses this algorithm for assigning Strahler order. It's very fast and can handle highly threaded networks. I've thrown networks in ...


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You are correct that Arc Hydro only uses elevation information to delinieate streams, catchment, etc. There is not a tool built in to do exactly what you're asking. Arc Hydro does provide other tools such as calculating drainage area centroid, and longest flow path. These tools may be helpful to you in finding catchment properties in a more traditional ...


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Out of curiosity I downloaded the NVS stream tool and ran it on a vector river network that has loops and compared the Strahler order generated by this tool with the Strahler order computed by RivEX. The algorithm used by the NVS tool is slower (not really a big problem) but more importantly it is not robust when it is dealing with river networks that have ...



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