Factors affecting water in river landscapes (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.

At a wider scale, ways in which climate, geology and human activity influence flows and stores of water within river landscapes.

Coverage to include:

• The processes of interception, transpiration, infiltration, surface run-off and throughflow.

• How these may be affected by human activity through changes to vegetation and urbanisation.

• How climate creates seasonal variation in discharge.

• The concept of an annual regime.

• The use of hydrographs to show the relationship between climate and discharge

Drainage basin processes

A drainage basin is the area of land drained by a river and its tributaries

• This is also known as the catchment area of the river

• Drainage basins are open systems

• As well as stores and transfers, drainage basins have inputs and outputs

  • Inputs include any water entering the system (precipitation)

  • Outputs are where water is lost from the drainage basin (evaporation, transpiration and into the sea/lake)

• When precipitation falls into the drainage basin, it will take different paths. These include:

  • Direct channel precipitation, which occurs when the water falls directly into a river

  • Surface run-off when the water cannot infiltrate the surface, soil or rock due to the impermeable surface

  • Throughflow when the water flows through the soil

  • Groundwater flow when the water flows through the rocks

• Every drainage basin is unique, as they all have different shapes and sizes and contain different:

  • Rock types (permeable or impermeable)

  • Relief

  • Land uses (urban or rural)

  • Types and amount of vegetation

Geology and drainage basins

• Permeable rocks increase infiltration and percolation, which reduces surface run-off

• Impermeable rock decreases infiltration and percolation; this increases surface run-off

The impact of human activity on flows and stores of water

• Human activity within the drainage basin can have a significant impact on the flows and stores of water

• Human activities include:

  • Deforestation

  • Afforestation

  • River management

  • Urbanisation

  • Agriculture

• All of these impact on the natural processes and regime of rivers

Deforestation

• Lack of trees and other vegetation reduces interception and infiltration, increasing surface run-off

Afforestation

• An increased amount of trees increases interception and infiltration, reducing surface run-off

River management

• Dams can be used to control the level of discharge downstream; this affects the river regime as it becomes more consistent with fewer peaks and troughs

  • This reduces the flood risk downstream

• There may also be a reduction in the amount of erosion downstream due to more consistent discharge

• Reservoirs are human-made water stores which cause the water velocity to slow in the reservoir, leading to increased deposition

  • The dams also trap sediment which can impact on the amount of deposition downstream

Abstraction

• Abstraction is when water is taken from a store within the drainage basin

• Humans abstract water from surface stores and groundwater stores

• Groundwater stores are also known as aquifers

  • These are areas of porous rock such as chalk or sandstone

• When water is taken from the stores more quickly than it is replaced (recharged), it is known as over-abstraction

  • This reduces the level of water stores

Urbanisation

• Impermeable concrete and tarmac increase surface run-off

Agriculture

• Bare soil and ploughing increase surface run-off, especially where ploughing is downslope

• Replacement of pasture (grassland) with arable crops also increases surface run-off

Climate change

• Rising global temperatures may increase storm frequency and intensity, increasing precipitation, which increases surface run-off

• Increasing drought, which leads to baked soil and periods of extreme cold which freeze the soil which means that water cannot infiltrate and there is increased surface run-off

Influence of climate on river discharge

• The UK has a temperate climate, but there is wide variation across the country, which means:

  • Some areas, such as the north and west, experience more rainfall

  • The south and east have lower rainfall than average

  • Scotland and the north experience colder temperatures

  • The south experiences higher temperatures

Precipitation

• In areas where precipitation levels are higher, there will be:

  • Higher discharge levels

• Areas of the UK that experience lower than average precipitation will have:

  • Lower discharge levels

• The type of precipitation is also important

• In areas with higher levels of snowfall, then the higher discharge will be in spring when the snow and ice melts

Temperature

• Higher temperatures lead to increased evaporation and transpiration

• This reduces the amount of water entering the river and so discharge is lower

River regime and hydrographs

What is a river regime?

• The discharge of a river is defined as the amount of water passing a specific point on the river at a given time 

• Discharge changes over time

  • The river regime is a record of these changes over a year

• The regime of a river is affected by all the characteristics of drainage basins outlined above

• Any factor which increases surface run-off increases discharge in the river

• Any factor which increases interception, infiltration or abstraction will lead to a slower increase in discharge or a reduction in discharge

What is a hydrograph?

• A hydrograph shows the changes in river discharge after a storm event

• The graph shows a short period, usually 24 hours

• The storm hydrograph has several features:

  • Base flow, which is the 'normal' level of river discharge

    • The water mainly comes from groundwater flow

  • Peak rainfall is the highest rainfall level during the storm

    • The time of the peak rainfall is taken from the centre of the bar

  • The rising limb shows the increase in the river discharge

    • The steeper the limb the faster the river discharge has increased

  • Peak discharge or peak flow, is the highest level of discharge

  • Lag time is the time difference between the peak rainfall and the peak discharge

    • The shorter the lag time the higher the risk of flooding because the river may not have the capacity to contain the increase in discharge

    • Where there is more overland flow (surface runoff), the lag time will be shorter

  • The recessional limb shows the river discharge returning to normal flow

    • The steeper the recessional limb is, the faster the river returns to normal flow