The scraping/scouring/rubbing of materials carried by the river. It wears down the bed and banks.
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What is hydraulic action?
The power of water moving loose material. Turbulent flow lifts a large number of grains from the river bed, eroding it.
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What is corrosion?
Most effective on rocks that contain carbonates (e.g. limestone, chalk). Minerals in the bed & banks are dissolved by weak acids in the river water.
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What is attrition?
The reduction in size of fragments/particles within a river. They strike one another and the river bed/banks and become smoother, smaller and rounded.
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What is vertical erosion?
When a river tries to cut down to base level, mainly caused by abrasion and hydraulic action - which happens when the river level & velocity are high. Produces steep sided valleys.
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What is lateral erosion?
The river valley widens as the river meanders. Occurs in the middle and lower courses.
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What is traction?
When large stones and boulders are rolled along the river bed by water moving downstream - only occurs at times of high discharge.
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What is saltation?
When small stones bounce along the channel bed, dislodging other particles upwards in relatively high conditions.
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What is suspension?
Very small particles such as sand and silt carried by the river flow.
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What is solution?
Dissolved minerals deposited within a mass of moving water.
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What is deposition?
When a river loses energy, it drops its sediment, with the largest particles first.
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What is rejuvenation?
When the river revives its erosion activity in a vertical direction when the sea level falls or when land surface rises, giving the river more energy.
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What are the characteristics of the upper course's channel?
The channel is narrow and uneven due to boulders on the bed. A rectangular channel. Has a large wetted perimeter.
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What are the characteristics of the middle course's channel?
An asymmetrical channel on the river bends, smooth and asymmetrical on the straight stretches.
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What are the characteristics of the lower course's channel?
The channel widens and deepens further. Sometimes levees occur.
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What is the thalweg?
The main flow of the current.
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Why do rivers become more efficient at transportation downstream?
There is less irregular material to cause friction.
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What does the Bradshaw Model say increases downstream?
Discharge, occupied channel width, channel depth, average velocity, and load quality.
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What does the Bradshaw Model say decreases downstream?
Load particle size, channel bed roughness, gradient.
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Other cards in this set
Card 2
Front
What is abrasion?
Back
The scraping/scouring/rubbing of materials carried by the river. It wears down the bed and banks.
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