Environmental Engineering Reference
In-Depth Information
A
10
1
10
0
10
-1
10
-2
10
6
B
10
5
10
4
10
3
10
2
C
10
4
10
3
10
2
01234567
Stream order
FIGURE 5.5
Relationships between stream order, average lengths of each order (A), num-
ber of streams of each order (B), and total length of streams of each order (C) for several wa-
tersheds in the southwestern United States. On average, streams of lower order are shorter,
but they can also be more numerous; individual watersheds can have a greater total length
of low-order streams [data from Allen (1995) and Leopold
et al.
(1964)].
Stream drainage systems may also be classified by the pattern of the
stream channels (Fig. 5.4). Various patterns develop in response to geo-
logical factors and can give rise to very different segment lengths of each
order. Patterns range from highly reticulated to almost linear in shape.
Another useful way to characterize stream hydrology is by discharge
and water velocity. Discharge is distinctly different from water velocity.
Discharge
is a volume of water passing through a channel per unit time,
whereas
water velocity
is the speed of water in any small region of the
channel (also referred to as current). Flow is a general term for movement
that can mean discharge, water velocity, or both. In later chapters, I dis-
cuss the strong biological effects of both discharge and water velocity in
streams.
A plot of discharge against time is called a
hydrograph
. Discharge can
vary from fairly constant in rivers fed primarily with groundwater (Figs.
5.6A and 5.6B) to intermittent in headwater streams of drier regions (Figs.
Search WWH ::
Custom Search