Rivers and Streams, Characteristics - Hydro-Environmental Analysis: Freshwater Environments - page 19

and be inluenced by, tributary inlows along its path to its outlet. The physical, chemical, and bio-
logical characteristics of the river would be expected to vary longitudinally as the channel and the
loodplain vary from their origin to the outlet. For example, the channel width and depth would be
expected to increase downstream as the drainage area and discharge increase.
A simpliied longitudinal model captures these observed changes by disaggregating the river into
three zones (Figure 2.5):

• Headwaters zone

• Transfer zone

• Depositional zone

The headwaters zone generally has the steepest slope, and the relatively high current velocities
often cut deep channels resulting in V-shaped valleys with rapids and waterfalls being common
(Miller 1990). The bed material is usually rocks, boulders, or particles of a relatively large size.
The river slope generally decreases as the river moves into the transition zone and eroded
material from the headwaters zone moves into this zone. Typically, the river will become
broader and the low will increase as the rivers merge. The river may begin to meander within
its loodplain.

Headwaters Transfer Deposition

Chann el depth
Mean flow velocity

FIGURE 2.5 Changes in the channel in the three zones. (From FISRWG, Stream Corridor Restoration:
Principles, Processes, and Practices , Federal Interagency Stream Restoration Working Group, 1998.)