Drainage Morphometry: Stream Ordering

Morphometry is the study of shape or form of different landforms.

Stream Ordering

Stream order shows the hierarchical linkage between streams within a drainage basin. Two methods of stream ordering is the Shreve method and the Strahler method. The latter method is the most widely used.

Strahler’s Method

Strahler states that when first order streams i.e streams without any tributaries join they form second order streams. When second order streams meet a third order stream is formed and so on.

However, when two streams of different order meet the stream of higher order will take precedence eg when second and third order streams meet the higher third order stream will take precedence.

Shreve’s Method Shreve’s method takes into account stream magnitude. When two streams join they are added together eg third and second magnitude streams will add to give a fifth magnitude stream.

In the Shreve method magnitude increase at all junctions unlike the Strahler method where the stream with the highest order is taken when two streams of different order meet.

Bifurcation Ratio

Bifurcation ratio is the ratio of lower order streams to higher order streams. This means that we divide the total number of first order streams by the total number of second order streams, second order streams by the total of third order streams and so on.

N₁/N₂
N₂/N₃
N₃/N₄ and so on.
If we need to find the average bifurcation ratio we simply:
N₁/N₂ + N₂/N₃ + N₃/N₄ / 3.