Rivers: Erosion, Transportation and Deposition

AS Geography Rivers notes covering erosion, deposition, transportation, the hjulstrom curve, fluvial processes and velocity.

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THE RIVER PROFILE KEY WORDS
THE UPPER COURSE
Rapids Vshaped valley Vertical erosion
Abrasion Friction High wetted perimeter
Low velocity Potholes Large bedload
Angular boulders Active hillslopes Interlocking spurs
Steep gradient Low levels of discharge Narrow, shallow channel
THE MIDDLE COURSE
Bluff line Lateral erosion Higher velocity
Less friction Spurs cutback Increased sinuosity
Gentle slopes Attrition Wider valley bottom
THE LOWER COURSE
Oxbow lake Meanders High levels of discharge
Fine sediment Laminar flow Deep, wide channel
Gentle gradientWide floodplain Low wetted perimeter
Slipoff slope High hydraulic radius Highest velocity
FLUVIAL PROCESSES KEY DEFINITIONS
Erosion: The wearing away of naturallyoccurring materials such as rock due to the effects
of wind, water or ice. This also includes the movement of the brokendown material.
Hydraulic action: The way in which a river's bed and banks are worn away by the sheer
force of the water.
Abrasion (corrasion): The scraping, scouring and rubbing action of material against the river
bed and banks.
Attrition: The process by which particles in the river are made smoother and rounder. The
particles collide, breaking them into smaller pieces.
Transportation: The way in which material moves in a river.
Load: The material carried by a river.
Traction: The way in which larger material eg. boulders are moved in a river using a rolling
motion along the river bed.
Saltation: When material such as small pebbles and stones are bounced along the river bed.
Suspended load: Fine silt is suspended in the water.
THE HJULSTROM CURVE

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Particles are transported when the velocity drops below the level needed for
entrainment.
Erosion of the particle will occur when the velocity reaches a level higher than that
required for entrainment.
Deposition occurs when velocity drops below the level needed for transport.
DON'T FORGET: Clay particles require the same velocity for entrainment as larger
particles such as pebbles and boulders. This is because clay particles clump together,
making it hard to entrain. Clay particles cannot be deposited in the river channel.…read more

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