🏞️ Physical: Rivers Flashcards
What is the drainage basin of a river?
The area of land drained by a river and its tributaries.
What is a confluence of a river?
The point where a tributary joins a larger river.
What is the river watershed?
The edge of a river basin.
Define erosion.
The wearing away of material.
Why do rivers tend to erode vertically in the upper course?
Discharge is smaller and the river cuts down due to gravity and the larger size of sediment.
Why do rivers tend to erode laterally in the middle course?
Material carried by the river erode the banks.
What is attrition?
When rocks bang together to smoothen and break down.
What is hydraulic action?
When the force of the water flows into the cracks in the bank and causes them to break.
What is abrasion?
When rocks scrape the bed and banks.
What is the erosional process of solution?
When soluble materials as rocks get dissolved into the river.
What is the river’s load?
The materials that are carried by the river.
What is the river’s discharge?
The amount of water in a river at any given time.
What is traction?
When large rocks and boulders are rolled along the river bed by the force of the water at times of high discharge.
What is saltation?
When small rocks and sand particles are bounced along the river bed by the flow of water.
What is suspension?
When fine clay and sand particles are carried along within the water even at low discharges.
What is the transported process of solution?
When some minerals dissolve in water and get carried along by the flow of water.
What is a floodplain?
An area of low-lying land next to a river which is prone to flooding.
When does deposition normally occur.
When the velocity of the river slows.
What are the characteristics of the river channel and valley in the upper course of the River Severn?
Steep V-shaped valley sides, channel is very shallow and valley is small.
What are the characteristics of the river channel and valley in the middle course of the River Severn?
Valley is wider + deeper, flattening out by lateral erosion.
What are the characteristics of the river channel and valley in the lower course of the River Severn?
Very flat and wide.
What are the landforms in the upper course of the River Severn?
Interlocking spurs, waterfalls and gorges.
What are the landforms in the middle course of the River Severn?
Meanders + Ox-bow lakes
What are the landforms in the lower course of the River Severn?
Flood plains, meanders, levees, estuaries and mud flats
What processes and size of materials are in the upper course of the River Severn?
Large rocks. Lots of transportation and vertical erosion.
What processes and size of materials are in the middle course of the River Severn?
Lateral and vertical erosion all types of transportation and deposition. Rocks are smaller.
What processes and size of materials are in the lower course of the River Severn?
All of the processes, pretty much no vertical erosion. Sediment is tiny and deposition is very high.
What are erosional river landforms?
Interlocking spurs, waterfalls and gorges
How are interlocking spurs formed?
- The start of the river has lots of energy so it erodes vertically due to gravity and creates a steep V-shaped valley
- Overt time the valley sides become less steep due to freeze-thaw weathering
- The river then winds its way around the hard rock and creates interlocking spurs
How are waterfalls formed?
- Water runs over alternating bands of hard and soft rock and erosion will start to break down the rocks
- Hydraulic actions wears away the soft rock because it is less resistant than the hard rock
- Over time the soft rock starts to undercut the hard rock
- The hard rock is left unsupported and its weight collapses into the river
- Rocks that have fallen either get transported down the river or scrape away and abrade the base of the river bed, a plunge pool is then created with the waterfall
How are gorges formed?
- After a waterfall is formed it retreats backwards and leaves behind steep sided vertical walls called a gorge
What fluvial processes does a meander use to be formed?
Erosion and deposition
How are meanders formed?
- Water swings to the outside of the river where there is less friction
- As the river erodes the bank, the river will take the shortest route and take on a straight course
- On the inside of the bend, the flow is slower so it deposits sediment
How are ox-bow lakes formed?
- The neck of a meander grows narrower and when it breaks through the river flow will take the shortest path, straight
- The look becomes sealed off altogether as a result of deposition. This is known as an ox-bow lake
What is a levee?
A levee is a raised bank formed on the banks of a river in the lower course.
How is a levee formed?
- During a flood water passes over the banks and increased friction occurs resulting in slower flow
- The heaviest material is deposited first at the closest point to the river as the water doesn’t have enough energy to carry it
- The levee gradually gets higher after successive floods
How are floodplains formed?
- When a river floods, it deposits the heaviest sediment first and lightest last
- This build up of sand, silt and clays leads to the formation of a flat piece of land either side of a river
- Every time the river floods, deposition build up the floodplain
How can you work out the discharge of a river?
Area x Velocity = Discharge
What are some physical factors that affect flood risk?
- Relief
- Rainfall
- Soil Saturation
- Basin Size
- Rock Type
What are some human factors that affect flood risk?
- Urbanisation
- Deforestation
- Agriculture
What are some examples of hard engineering strategies?
- Dams and Reservoirs
- Dredging
- Embankments
- Concrete Channel
- Channel Straightening
What are some examples of soft engineering strategies?
- Land-use Zoning
- Afforestation
- Wetland Creation
- River Bank Conservation
- Flood Warnings + Preparation
How do dams and reservoirs work?
A dam is a large concrete barrier built across a river to hold back its flow. This causes the valley behind the dam to flood and creates a lake called a reservoir. This controls the amount of river downstream with the controlled gates.
What are the benefits of dams and reservoirs?
- Can create energy, HEP
- Can attract tourists
- Water is released in a controlled way
What are the disadvantages of dams and reservoirs?
- Super expensive
- Sediment can get trapped
- Can lead to rotting and methane production
