Table 5.8. Channel Response to Changes in Watershed and River Condition
(after Keefer et al. 1980).
Observed
Channel Response
Condition
Stable
Unstable
Degrading
Aggrading
Alluvial Fan
Upstream
X
X
Downstream
X
X
Dam and Reservoir
Upstream
X
X
Downstream
X
X
River Form
Meandering
X
X
Unknown
Unknown
Straight
X
Unknown
Unknown
Braided
X
Unknown
Unknown
Bank Erosion
Unknown
Unknown
Vegetated Banks
X
Unknown
Unknown
Headcuts
X
X
Diversion
Clear Water Diversion
X
X
Overloaded with Sediment
X
Channel Straightened
X
X
Deforested Watershed
X
X
Drought Period
X
X
Wet Period
X
X
Bed Material Size
Increase
X
X
Decrease
X
Unknown
X
5.8 STREAM STABILITY PROBLEMS AT HIGHWAY CROSSINGS
In the United States, the annual damage related to hydraulic problems at bridges and highways
has been estimated as high as million during years of extreme floods. Damages by
streams can be reduced by considering channel stability in site selection, bridge design, and
countermeasure placement. Ideally, a stable channel is one that does not change in size,
form, or position through time. However, all alluvial channels change to some degree and
therefore have some degree of instability. For engineering purposes, an unstable channel is
one whose rate or magnitude of change is great enough to be a significant factor in the
5.52
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