River landscape processes (WJEC Eduqas GCSE Geography B): Revision Note

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The notes on this page cover part 2.2. 1 of the WJEC Eduqas GCSE B Geography.

2.2.1 How do people and processes contribute to the development of distinctive river landscapes in the UK?

• How fluvial processes, combined with weathering, mass movement and human activities, create distinctive river landscapes in the UK.

• At a local scale, fluvial erosional processes to include hydraulic action, abrasion, attrition and solution. Processes of transportation and deposition include traction, saltation, suspension and solutions.

Weathering and rivers

• Weathering is the breakdown of rock in the landscape around the river

• There are three types of weathering

• These happen in-situ

Physical

• Rock is broken down into smaller pieces

• This occurs due to changes in temperature, such as freeze-thaw and exfoliation

Chemical

• Rocks disintegrate and dissolve in slightly acidic rainwater 

Biological weathering

• Rocks are broken apart by the roots of plants 

Mass movement and rivers

• There are several types of mass movement where large-scale movement of material occurs

• In river valleys, there are two main types of mass movement:

  • Slumping occurs when the slope is eroded by the river.

    • This undercuts the slope, causing large-scale movement of material down the slope

    • Slumping often occurs when a softer, less resistant material overlies a harder, more resistant material

• Soil creep happens when the influence of gravity causes weathered material to slowly move down the slope towards the river

Factors affecting weathering and mass movement

• There are a range of factors that affect weathering and mass movement, including:

  • Climate: in hot, wet climates, chemical and biological weathering are dominant

  • Weather: heavy rainfall increases mass movement

  • Slope: any slope over 5° experiences mass movement

    • The steeper the gradient of the slope, the more mass movement there will be

  • Geology: different rocks have different levels of resistance to weathering

  • Altitude: at higher altitudes, freeze-thaw weathering occurs frequently due to the low temperatures

  • Aspect: physical weathering is more common on a colder, north-facing slope due to a higher likelihood of freeze-thaw

  • Vegetation: roots bind the soil together, which limits mass movement

Fluvial processes

• Most (about 95%) of a river's energy is used to overcome friction

  • There is more friction in the upper course of the river

    • It is shallow and narrow so more water is in contact with the bed and banks

    • The rocks in the river are larger so more energy is used to overcome the friction to move over and around them

• The rest of the river's energy is used in erosion and transportation

• Energy in the river depends on the river's:

  • Discharge

  • Velocity

• The greater the discharge and velocity, the more energy a river has for erosion and transportation

Erosion

• Erosion is the wearing away and movement of material

• There are four erosion processes that change the shape of the river channel:

  • Hydraulic action is when the force of the water removes material from the banks and bed of the river

  • Abrasion (corrasion) occurs when materials carried by the river scrape away at the banks and bed 

  • Attrition is when the material being carried by the river hits each other; as a result, the pieces become rounder and smoother

  • Corrosion (solution) occurs when some rocks are dissolved by the slightly acidic water

• Erosion can be mainly vertical or lateral: 

  • Vertical erosion is dominant in the upper course of rivers

    • It increases the depth of the river and valley as the river erodes downwards

  • Lateral erosion is dominant in the middle and lower course of rivers

    • It increases the width of the river and valley as it erodes sideways

Transportation processes

• There are four processes of transportation:

  • Traction occurs when larger rocks and materials are rolled along the riverbed 

  • Saltation is when smaller material is lifted by the water and bounces along the riverbed

  • Suspension occurs when lighter material is carried within the river flow

  • Solution is when materials are dissolved in the water

Deposition

• When a river does not have enough energy to carry materials, it drops them

• This is deposition

• The causes of reduced energy include:

  • Reduced discharge due to a lack of precipitation or abstraction upstream

  • Decreased gradient

  • Slower flow on the inside of a river bend

  • When the river enters a sea/ocean or lake

• The heaviest material is deposited first; this is known as the bedload

• The lighter materials, gravel, sand and silt, are known as alluvium and they are carried further downstream

• The dissolved materials are carried out to sea