Rivers and fluvial systems

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Characteristics of the upland areas of river valleys
Steep slopes with streams. Flows can be quite turbulent due to uneven rocks and interlocking spurs, especially after seasonal melt-water is added in the Spring.
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What is the watershed?
The 3D catchment zone area for a river.
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What determines the route of a river?
Climate, geology, human activities in the area.
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What are the inputs and outputs of water for a drainage basin?
Inputs= Precipitation, meltwater. Outputs=River flow out to sea, Evaporation, groundwater flow.
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Define: gullying.
Erosion of deep channels by accelerated source of water.
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When does overland flow occur?
When precipitation> infiltration of the rainwater into the ground.
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What is sheet erosion?
Erosion by laminar flow
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Define: rill erosion.
Where turbulence in the flow produces small channels-these may eventually form tributaries.
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Compare the two types of river flow.
Laminar- Straight/gently curving streamlines. Turbulent-Crossing/mixing streamlines, swirls and eddies.
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What happens to the suspended material load of a river as the current velocity increases.
The load can also increase. Larger material may be picked up.
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What is saltation?
Where small particles are bounced along the riverbed.
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What material can be carried as a solute in the water?
Ions- dissolved
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What makes up the bed load?
Sand and gravel
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Why is clay not in the bedload?
Finer particles are suspended in the river unless the water becomes stagnant- then they would settle to the riverbed.
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What is the maximum load?
The stream's capacity for material.
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What can increase soil erosion into a river?
Steeper slopes, earth movements-decrease stability, human activity i.e. development, deforestation.
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What is sediment yield?
Amount of sediment removed by overland flow from a unit area of ground over a unit time.
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What is colluvium?
Where sediment comes to rest at the bottom of a slope before it reaches water.
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What is alluvium?
Where sediment carried downstream by a river is deposited and accumulates as layers on the valley floor.
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What influences the depths of river channels?
Balance between erosion of the river bed and the sedimentation.
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What processes occur in fluvial systems?
Erosion, transportation, deposition.
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Which rock types are more susceptible to corrosion?
Chalk, limestone
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What is mechanical wearing of the rocks?
Abrasion
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What is hydraulic action?
Plucking of material from the channel.
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Describe the profile of the upper part of a river catchment.
Deep v-shaped valleys and gorges. Steep sections marked by waterfalls and potholes.
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Describe the characteristics of the lower catchment area.
Large volumes of sediment are deposited as alluvium. Rivers start to meander.
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Define: anabranching
Where streams split around bars and become braided channels
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How do bars develop?
As rivers lose momentum, they deposit material.
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Describe floodplains
Flat valley floors that may periodically flood. Terraces may form as rivers erode the valley.
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What are alluvial terraces?
When old valley floors are covered with alluvium and then eroded again.
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How are alluvial fans formed?
When a stream flows from a mountain onto a plain.
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What is a playa?
Monsoon rains deposit large quantities of alluvial sediment but when hot, dry weather follows the surface hardens and cracks into a crusty layer of sand, silt and clay. No vegetation. Flat and smooth with polygonal cracking.
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What are river terraces?
Old valley floors that remain after river down-cutting. These show the past floodplain levels.
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Other cards in this set

Card 2

Front

The 3D catchment zone area for a river.

Back

What is the watershed?

Card 3

Front

Climate, geology, human activities in the area.

Back

Preview of the back of card 3

Card 4

Front

Inputs= Precipitation, meltwater. Outputs=River flow out to sea, Evaporation, groundwater flow.

Back

Preview of the back of card 4

Card 5

Front

Erosion of deep channels by accelerated source of water.

Back

Preview of the back of card 5
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