Streams: ordering metrics
A stream network is a hierarchy: small headwater channels join to form larger ones, which join in turn. Ordering puts a number on that hierarchy, so you can style a river network sensibly, compare catchments, and pick out the main stem from the tributaries.
These tools take the stream raster from network extraction and the D8 pointer from flow routing.
Start here
Section titled “Start here”Strahler Stream Order
Section titled “Strahler Stream Order”The standard scheme, and the one to use unless you have a reason not to. Headwater channels are order 1. Where two channels of the same order meet, the result is one order higher. Where different orders meet, the higher one continues unchanged.
The practical consequence is that order grows slowly and stays readable: a large river basin rarely goes beyond order 7 or 8. It is the natural field to set line width on when styling a river network.
Shreve Stream Magnitude
Section titled “Shreve Stream Magnitude”The alternative arithmetic: each link carries the sum of the magnitudes upstream, so the value counts how many headwater sources feed it. Where Strahler tells you the rank of a channel, Shreve tells you the size of its contributing network.
Use Strahler for a readable classification, Shreve when you want a quantity proportional to the network feeding each point.
Stream Link Identifier and the link metrics
Section titled “Stream Link Identifier and the link metrics”A link is one segment of the network between two junctions. Stream Link Identifier gives each of them a unique number, which turns the raster network into something you can summarise per segment.
With those identifiers in place, Stream Link Length and Stream Link Slope give the length and the mean gradient of each segment, and Stream Link Class labels each as a source, an interior or an exterior link.
Horton Ratios
Section titled “Horton Ratios”Produces the classic morphometric ratios of a basin: bifurcation, length, area and slope. Those four numbers summarise the structure of a drainage network in a form comparable between catchments, which is why they appear in every hydrological characterisation.
Clean the network before computing them. Spurious short branches inflate the count of first order streams and distort every ratio.
All the tools
Section titled “All the tools”| Tool | What it does |
|---|---|
| Strahler Stream Order | The standard ordering: order rises only where two equal orders meet. |
| Shreve Stream Magnitude | Sums the upstream magnitudes, counting the headwater sources feeding each link. |
| Horton Stream Order | Horton’s ordering, which carries the higher order down the main stem. |
| Hack Stream Order | Hack’s ordering, numbered from the mouth upstream along the longest path. |
| Topological Stream Order | Order derived from the count of upstream links. |
| Horton Ratios | Bifurcation, length, drainage area and slope ratios for the basin. |
| Strahler Order Basins | Delineates the basins draining each link, labelled by its Strahler order. |
| Stream Link Identifier | A unique identifier per link, between two junctions. |
| Stream Link Class | Labels each link as source, interior or exterior. |
| Stream Link Length | Total length of each link. |
| Stream Link Slope | Mean slope of each link. |
| Stream Slope Continuous | Slope at every stream cell, rather than averaged per link. |
| Tributary Identifier | A unique identifier per tributary. |
| Vector Stream Network Analysis | A combined analysis of a vector stream network, producing its main topological and morphometric attributes. |
Order is not width. A stream order is a position in a hierarchy, not a discharge or a channel width. Two order 4 streams in different climates carry very different amounts of water.
Style by order. The point of running these tools is usually cartographic. Once the order raster is vectorised, set line width from the order field in Style and the network reads like a proper river map.