How do Rivers erode?
The pressure of the water being pushed against banks and beds of rivers.
Corrasion/Abrasionn
Compression of air in cracks by the power of the water puts pressure on the
cracks which may break away.
Particle carried along in the river (bedload) are thrown against the river banks
Attrition
and bed with considerable force.
A chemical reaction between certain rock types and water. The river bed is
Solution/Corrosion
dissolved. Particularly common on limestone river beds.
Wearing away of rocks which are in the river. Particles and rocks roll around and
collide with each other. They chip away at each other breaking into smaller,
Hydraulic Action
rounder and smoother pebbles.
EROSION
HAPPENS IN THE
RIVER!
What are the main types of Weathering?
Rainwater contains weak acids that can react with certain rock types. The
Physical Weathering
carbonates in limestone can be dissolved by weak acids for example. This causes
the rocks to break up or disintegrate.
Chemical Weathering
Freeze-Thaw weathering is when water gets into cracks in rocks. When
temperatures fall below freeing, the water turns to ice and expands (by9%).
This puts pressure on the rock and weakens it. The repetition of this cycle day
Biological Weathering
and night weakens it to the point where it may break apart.
The action of plants and animals can breakup rocks. Roots may grow through
cracks in rocks, further weakening them. Or burrowing animals may break up
rocks.
WEATHERING DOES NOT HAPPEN IN THE RIVER!
IT TAKES PLACE ON THE SURROUNDING LAND.
What is a Drainage Basin?
Confluence
Drainage Basin
Tributary
Source
Watershed
Mouth
Confluence
Imaginary line/boundary separating two Drainage Basins. Usually the high land surrounding a river.
Where the river meets the sea.
The point where two rivers meet/join.
Where the river starts, normally in the hills.
Smaller rivers/streams which feed into a bigger river.
The area of land drained by a river. Any precipitation that falls within this area, will eventually
end up in the river.
Stretch: What factors might affect how quickly rainwater reaches the river? Explain your ideas.