Rivers Flashcards
(41 cards)
Four processes of Erosion?
Attrition, Corrasion, Corrosion, Hydraulic Action
Four processes of Transportation?
Traction, Saltation, Suspension, Solution
When does Deposition occur in a River?
When a river loses energy, it will drop or deposit some of the material it is carrying.
What is Hydraulic Action?
The force of the river against the banks can cause air to be trapped in cracks and crevices. The pressure weakens the banks and gradually wears it away.
What is Abrasion?
Rocks carried along by the river wear down the river bed and banks.
What is Attrition?
Rocks being carried by the river smash together and break into smaller, smoother and rounder particles.
What is Solution? (Erosion)
Soluble particles are dissolved into the river.
What is Solution? (Transportation)
Minerals are dissolved in the water and carried along in solution.
What is Suspension?
Fine light material is carried along in the water.
What is Saltation?
Small pebbles and stones are bounced along the river bed.
What is Traction?
Large boulders and rocks are rolled along the river bed.
Where are River Energy levels highest?
Energy levels are usually higher near a river’s source, when its course is steep and its valley narrow. Energy levels rise even higher in times of flood.
Where are River Energy levels lowest?
Energy levels are lowest when velocity drops as a river enters a lake or sea (at the mouth).
What is the River Channel?
The main part of the River that holds the water
What factors may encourage flooding?
1) A Steep-Sided channel. It may cause faster surface run-off. 2) A lack of vegetation or woodland 3) A drainage basin in an urban area
Why are Floodplains so excellent for agriculture?
Flooding deposits fine silt (alluvium) onto the floodplain, making it very fertile.
What is Hard Engineering?
Tends to be more expensive and have a greater impact on the river and the surrounding landscape.
What is Soft Engineering?
Soft options are more ecologically sensitive.
Two examples of Hard Engineering options?
Dam Construction and River Engineering
Advantages of Dams?
Water is held back by the dam and released in a controlled way. This controls flooding.
Water is usually stored in a reservoir behind the dam. This water can then be used to generate hydroelectric power or for recreation purposes.
Disadvantages of Dams?
Building a dam can be very expensive.
Sediment is often trapped behind the wall of the dam, leading to erosion further downstream.
Settlements and agricultural land may be lost when the river valley is flooded to form a reservoir.
What is River Engineering?
The river channel may be widened or deepened allowing it to carry more water. A river channel may be straightened so that water can travel faster along the course. The channel course of the river can also be altered, diverting floodwaters away from settlements.
What is a Disadvantage of River Engineering?
Altering the river channel may lead to a greater risk of flooding downstream, as the water is carried there faster.
Three examples of Soft Engineering options?
1) Afforestation 2) Managed flooding (also called ecological flooding) 3) Planning
