Running Water:
Stream Erosion and Transportation
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Running water includes all the water that falls on Earth as
rain,snow,or other precipitation and then moves downhill
under the pull of gravity.
Running water gets its energy from the sun.
Running water breaks up the bedrock over which it flows
primarily by mechanical means.
Sand, pebbles, and boulders cause abrasion.
Running water can chemically dissolve the soluble minerals of
the bedrock.
Water Removes Weathered Rock
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Once sediment is washed into the main river, it is carried by
the river in three ways.
Some mineral matter is carried in solution. This material is
dissolved from the bedrock (Ca, Mg).
Material that is carried by suspension looks muddy, including
silt, clay, fine sand. These materials are kept suspended by
the turbulence.
Sand, pebbles, and boulders that are too heavy to be
suspended may be moved along the stream bed, called bed
load.
Carrying Power and Load
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The carrying power of a stream is indicated by both the total
amount of sediment and by the size of the particles being
moved by the stream.
Stream discharge is the volume of water flowing past a given
point in the stream at a given time.(Ex:cubic metres/second)
Streams at high speeds with high discharge carry more and
larger sediments. This can also depend upon steepness.
During floods the discharge increases tremendously and its
carrying power greatly increases, causing the majority of the
river's erosion.
River Valleys
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V-Shaped valleys occur in mountain regions and high
plateaus, because youthful streams tend to flow at high
speeds, easily scouring the streambed.
Valleys with very steep, almost vertical walls (canyons,
gorges, chasms) can take a very long time to form.
Canyon
Base Level: Widening the Valley
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A stream cannot cut its bed any lower that the level of the
stream, river, or body of water into which it flows; called the
base level
As the stream approaches base level, the slope of the
streambed and the speed of the stream decreases.
The stream cuts into its bed more slowly, and the valley walls
continue to be attacked by weathering and erosion, creating a
wider valley.
Lengthening the Valley
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A gully is a small valley formed by
rain, they grow in length, width and
depth every time it rains.
Headward erosion is the wearing
away of land at the head of the gully
or stream valley.
If the stream cuts below the water
table, it becomes permanent.