Geology Reference
In-Depth Information
Channel Type
suspended load
mixed load
bedload
1
Channel
Character
2
3a
3b
legend
channel boundary
flow
bars
4
5
high
relative stability
low
(<3 %) low
bed load / total load ratio
high (>11%)
small
sediment size
sediment load
flow velocity
stream power
large
small
large
high
low
low
high
Fig. 8.15
Classification of fluvial channels.
Channel patterns and the persistence of channel shapes are conceptualized as a function of nature of the sediment
load, velocity, and stream power. Modified after Schumm (1986).
armchair exploration of tectonic environments
across the globe. Viewing such imagery with
programs such as Google Earth brings the
added advantage of perspective views of the
landscape - you can check whether visible
landforms are consistent with inferences about
deformation. Simple observations of downstream
changes in planform patterns, correlation of
planform changes with topographic and
geomorphic forms along the margins of a river,
and quantification of the channel position with
respect to valley margins, all serve to delineate
potential deformation regimes.
Numerous previous studies of channel
patterns (Fig. 8.15) indicate that they respond to
several competing controls, including sediment
size and load, flow velocity, and stream power
(Schumm, 1986). In general, braided rivers are
favored by high sediment fluxes, coarse bedload,
weak bank material, and high variability in
water discharge, whereas meandering rivers are
typified by lower sediment fluxes, finer bedload,
more cohesive bank material, lower flow
velocity, less variable discharge, and lower
stream power. Braided rivers quite commonly
change downstream into meandering rivers as
slope and mean grain size diminish (Fig. 8.13).
Each of the variables affecting channel patterns
can clearly be independent of tectonic activity.
On the other hand, for a given grain size, specific
stream power (Eqn 8.2) during bankfull discharge
appears to distinguish between braided and
meandering rivers (Fig. 8.16) (Van den Berg,
1995). Given the sensitivity of stream power to
channel slope, subtle tilting due to tectonic pro-
cesses could certainly affect whether a river was
braided or meandering.
Stream-table experiments
Stream-table experiments designed to investigate
possible responses of channel patterns to chang-
ing slopes commonly take one of two approaches:
tilting of the entire stream table, or creating
