Geoscience Reference
In-Depth Information
Figure 16.26 Floodplain features of
a graded stream.
A graded stream
has well developed meanders, natu-
ral levees, oxbow lakes, and back-
swamps.
Meandering
stream
Uplands
River floodplain
Uplands
Bluffs
Bluffs
Oxbow
lake
Natural
levee
Meander scar
Meander
scar
Bedrock
Alluvium
Backswamp
active floodplain,
, which is the low, frequently flooded surface
that results mostly from point-bar formation on the inside of
meander bends.
KEY CONCEPTS TO REMEMBER
ABOUT GRADED STREAMS AND THE
EVOLUTION OF STREAM VALLEYS
Entrenched Meanders
As previously discussed, a mean-
dering stream develops when a stream reaches a graded condi-
tion. These conditions do not last forever, however, as streams
periodically adjust to new environmental conditions such as
tectonic uplift, a drop in base level, or climate change. The
landscape response to these changes is usually preserved in
stream valleys as distinct landforms.
1.
When a landscape is recently uplifted, the resulting
ungraded streams degrade by cutting V-shaped valleys
that probably contain numerous knickpoints.
2.
Waterfalls occur in places where rock is resistant to
erosion and progressively erode headward until the
gradient is smoothed.
VISUAL CONCEPT CHECK
16.2
This image shows a stream in an alpine setting. Given
what you see here, which one of the following statements
accurately reflects the stream in this landscape?
a)
The stream has a wide valley.
b)
The stream is actively meandering.
c)
The stream has high discharge.
d)
The stream is not graded.
e)
The stream is a high-order stream.
