STRAHLER STREAM ORDER

The 'Strahler Stream Order' is a simple hydrology algorithm used to define stream size based on a hierarchy of its tributaries.
The streams range from one at the headwaters (which is a "1") to the most powerful which is the Amazon River which is a "12." The Ohio River is an "8" and the Mississippi River is a "10." 80 percent of the streams and rivers on the planet are first or second order.
To qualify as a stream it must be perennial. When two 'first-order' streams come together, they form a 'second-order' stream. When two second-order streams come together, they form a 'third-order' stream. Streams of lower order joining a higher order stream do not change the order of the higher stream. Thus, if a first-order stream joins a second-order stream, it remains a second-order stream. It is not until a second-order stream combines with another second-order stream that it becomes a third-order stream.
It is important to appreciate that stream order is dependent upon map scale. As scale decreases and more detail is added to the river network (i.e. new tributaries) then a river may increase its stream order.
Arthur Newell Strahler first proposed the hierarchy in 1952 in an article “Dynamic basis of geomorphology,” in the Geological Society of America Bulletin. It is often referenced in professional descriptions of rivers as ''Strahler 1952''.

Contents

GIS Algorithms

See also

External links

References

GIS Algorithms

Gleyzer ''et al.'' (2004) developed a recursive algorithm which would process vector river networks for Strahler stream order values. This algorithm is implemented by RivEX, an ArcGIS 9.1 tool. The algorithm requires the vector network to be topologically correct to successfully process. The network must be a centre-lined network where each arc (sometimes referred to as an edge) must be joined at their node (sometime referred to as a junction). No left and right banks or lake side shores should be present. The image below demonstrates a map representation of a river network, an invalid network where lake and river bank sides have been digitally captured and a valid, topologically correct, centre-lined river network which the algorithm can process.

If the network is "broken" (arcs not connecting) then the output will be incorrect. The algorithm would treat the disconnected catchment as a separate river system, so it is important to check the connectivity of your river network before attempting to compute Strahler order values.

See also

★ Mainstem (hydrology)

External links

★ CET article

★ RivEX is an ArcGIS 9.1 compatible GIS tool capable of computing Strahler stream order

References

# Gleyzer, A. , Denisyuk, M. ,Rimmer, A. and Salingar, Y. (2004). A Fast Recursive GIS Algorithm for Computing Strahler Stream Order in Braided and Nonbraided Networks. Journal of the American Water Resources Association, 40(4), 937 - 946.
# Lanfear, K. J. (1990). A fast algorithm for automatically computing Strahler stream order. Water Resources Bulletin, 26(6), 977 - 981.
# Strahler, A. N. (1952). Dynamic basis of geomorphology. Geological Society of America Bulletin, 63, 923 - 938.