Features
of Streams and Their Valleys
Steep Gradients: vertical
erosion predominates over lateral erosion. Narrow, V-shaped valleys occur
and longitudinal profiles are irregular (waterfalls and rapids are present).
Gentle Gradients: lateral erosion becomes
more important, broad valleys develop. The actual stream channel is much
narrower than the valley, most of which is occupied by the floodplain (the
area that could be submerged during a flood). A number of distinctive features
are present:
Natural Levees: immediately
adjacent to the channel. Low ridges formed by sandy sediments rapidly deposited
by flood waters.
Backswamps: develop
in low areas on the floodplain behind natural levees.
Meander: a bend in the
river channel as it meanders about the floodplain. Erosion on the outside
of a meander forms a cutbank, and deposition on the inside of a meander forms
a point bar. This erosion-deposition relationship causes the meander to move
across the floodplain.
During flood, the channel may break across a meander loop
to form a cutoff, or abandon the loop to form an ox-bow
lake.
Yazoo Streams: tributary
streams that flow across the floodplain before joining the main channel.
Stream Terraces: step-like
benches above the level of the present-day floodplain, representing remnants
of pre-existing floodplains or valley floors.