Strahler stream order

• RivEX implements a fast recursive algorithm to calculate Strahler stream order.  It is also capable of identifying stream segments.  The algorithm that RivEX implements was developed by Gleyzer et al., 2004 and is documented in the Journal of the American Water Resources Association.  Click here to visit the webpage for this paper.

• The output of a Strahler stream order are two new fields in the attribute table: Strahler and Segment.

• The difference between Strahler and segment is best described in the images below.

This network achieves 3rd Order

Here are the same polylines encoded as segments,

one segment for each Strahler reach

• RivEX is capable of dealing with multi-channelled networks.  The output of these sections may sometime be incorrect or just plain meaningless!  To apply stream ordering on artificial grid-like channels can produce some very strange results and should be interpreted with extreme caution.

• It is possible for RivEX to produce ZERO value stream orders, these are the results of polylines pointing from a mouth to source direction.  To deal with these you must:

• Flip the polyline.
• Rebuild from- and to- node fields
• Re-run the stream ordering

• Click here to be shown how to flip a single polyline.

• You may want to create the reverse of the Strahler stream order.  You can achieve this by creating a new field and running a calculation script, which you can download here.