Rivers and Streams, Characteristics - Hydro-Environmental Analysis: Freshwater Environments - page 22

2.2.1.3 Planform Classiication
Perhaps one of the more common classiication systems of channels is the planform classiication of
Leopold and Wolman (1957). This classiication system relects changes in the shape or pattern of
the river or stream in a plan view (as seen from above) as it moves through the three zones (headwa-
ter, transition, and deposition; Figure 2.5).
One characteristic on which the classiication is based is whether the river has one ( single thread )
or multiple channels ( multithread ) (see Figure 2.9). While single-channel rivers are more com-
mon (Figure 2.9a), multichannel rivers often occur in areas with erodible banks, an abundance
of course sediments, and highly variable lows (Interagency Stream Restoration Working Group
1998). Multithread braided streams, as illustrated in Figure 2.9b, typically have wide and shallow
channels, and the channel structure may rapidly change in response to lows, impacting vegetation.
Hydraulic analyses of these braided systems are often dificult. Less common than the multithread
braided systems are anastomosed streams, which commonly have narrow, deep channels and result
from rising downstream water levels resulting in sediment deposition.
Another planform characteristic of streams is sinuosity , or how crooked or meandering the stream
is. Sinuosity is a measure of the amount of curvature in a river, as relected, for example, by the length
of the river versus the length of the river valley or by other metrics such as the channel wavelength or
the meander radius or curvature. The length of the river is measured along the river channel, or thal-
weg . Sinuosity generally increases in rivers from the headwater to the depositional zones (Figure 2.10).

(a) (b)

FIGURE 2.9 Single (a) versus multithread (b) streams. (From FISRWG, Stream Corridor Restoration:
Principles, Processes, and Practices , Federal Interagency Stream Restoration Working Group, 1998.)

(a) (b)

FIGURE 2.10 Sinuosity of rivers: (a) high and (b) low. (From FISRWG, Stream Corridor Restoration:
Principles, Processes, and Practices , Federal Interagency Stream Restoration Working Group, 1998.)