Physiography of Flowing Water - Freshwater Ecology: Concepts and Environmental Applications - page 72

1

1 1 1

A

1

1

1

1

1

2 2 2 2

1

3

3

1

3 2

2

4 2

1

3

2

2

1

1

B

1

C

FIGURE 5.4 The Strahler method of stream ordering on a dendritic stream system (A). Or-
der increases only when two streams of equal order meet. Other types of drainage patterns
include rectangular, which may be found in Karst systems (B), and parallel, which occur
mainly in deeply eroded areas (C) (modified from Strahler and Strahler, 1979).

problems with determining and using stream order: (i) It is often
difficult to determine the smallest permanent stream; (ii) maps cannot al-
ways be relied on for accurate hydrological information because blue line
and dashed blue line features (permanent and impermanent flowing waters)
are not determined consistently; and (iii) stream order does not always cor-
relate closely with discharge, water chemistry, or other important abiotic
factors. However, low-order streams have some predictable differences from
those with higher orders. Stream order will continue to be used as a pri-
mary method to characterize streams at hierarchical levels of organization.
In general, a greater number of low-order streams occur in a water-
shed. Although streams of higher order have a greater length per stream,
the total length of low-order streams may be greater (Fig. 5.5). The rela-
tive abundance of small streams suggests that processes that occur at the
interface of land or groundwater with small streams dominate interactions
between aquatic and terrestrial systems.