Drainage basins of the UK Flashcards
Define drainage basin
Area of land drained by a river and it’s tributaries
Define flow
Movement of water
Define store
Place where water is stationary within the water cycle
Define interception
When rainfall does not reach the ground as it is blocked by trees, buildings and so on
Define Infiltration
Movement of water into the soil
Define throughflow
Flow of water through the soil
Define overland flow
Flow of water across the ground surface
Define Groundwater flow
Flow of water through rocks
Define transpiration
Water given off by plants
Define stem flow
Movement of water hat has been intercepted down the stem or trunk of a plant
Define Percolation
Movement of water from soil into the bedrock
Explain why the speed varies due to the type and quantity of rainfall (3)
- Rain moves quicker in heavy rainstorms
- Raindrops are larger and fall in a shorter time period
- This means less infiltration and more surface run off
Explain why the speed varies due to the type and quantity of vegetation cover
more interception occurs in a woodland compared to a meadow
Explain why the speed varies due to the size and shape of the drainage basin (2)
- Round drainage basins lead to faster water movement compared to elongated ones
- Larger basins have larger discharge
Explain why the speed varies due to steepness of slopes
Greater surface run off and less infiltration
Explain why the speed varies due to the geology and soil type within the drainage basin
Impermeable soil and rocks mean less infiltration or ground water flow and more surface run off
Name 4 reasons why rivers flood
- Climate
- Vegetation
- Geology
- Urbanisation
Why may climate increase the chance of a river flooding? (2)
- Seasonal rainfall = saturated ground, more overland flow and higher river levels
- Strom event = storm, high volume of rainfall in short time period, causes sudden rise in river levels, flash floods
Why may vegetation increase the chance of a river flooding? (3)
- Different vegetation intercepts different amounts of rainfall
- This influences the speed the water reaches the drainage basins
- Removal of vegetation = trees removed, water reach river channel quicker due to quicker saturation of soil
Why may geology increase the chance of a river flooding? (3)
- Porous rocks have large spaces which allows water through, reducing flood risk due to increased groundwater flow
- Impermeable rocks have few spaces, little water passes through, creates more overland flow, higher flood risk
- Rock may be well jointed, allows water to pass through lines of weakness
Why may urbanisation increase the chance of a river flooding?
- Expansion of towns/cities = ground covered by impermeable surface (tarmac), reduces amount of infiltrated water, causes more overland flow, high risk of flooding
Define hydrograph
A line graph used to display discharge of a river over a period of time
Define lag time
Time between the peak rainfall and peak discharge in a river
Define rising limb
Part of hydrograph where the discharge of a river is increasing after a rainfall event
What impact does urbanisation have on a hydrograph? (3)
- Decreases lag time
- Steep rising limb
- High peak
What impact does Porous rocks have on a hydrograph? (3)
- Increases lag time
- Gentle rising limb
- Lower peak
What impact does Impermeable rocks have on a hydrograph? (3)
- Decreases lag time
- Steep rising limb
- High peak
What impact does Broad-leaved trees have on a hydrograph? (3)
- Increased lag time
- Gentle rising limb
- Lower peak
Name an example of a flood
Somerset Levels 2013-14
Name 5 physical causes of the Somerset Levels
- Large area of flat land
- 2 major rivers run through the area - Tone and Parrett
- Prolonged heavy rainfall causing saturated ground
- Silting up of the river channel therefore reducing capacity
- High tidal range
Name 2 human causes of the Somerset Levels
- Reduction in frequency at which the rivers were dredged
2. Building on the floodplain
Name 7 effects of the Somerset Levels
- Over 80 roads blocked
- Children couldn’t get to school, adults couldn’t get to work
- Villages were cut off
- 600 homes were affected and people evacuated
- Due to lack of grazing land farmers lost around £10m
- Half of the business’ in Somerset lost money
- Cost of £19m to local government and emergency services
Describe and name hard engineering strategies for river channel and drainage basin management (3)
- Involve constructing defences to control natural processes
- Often large scale, expensive and relatively effective
- Examples = dams, gabions, dredging, flood relief channel and embankments
Describe and name soft engineering strategies for a river channel and drainage basin management (5)
- Work with environment rather than trying to control it
- Often cheaper than hard engineering
- Less impact on the environment
- Can be less effective once river has flooded
- Examples = restrict building on floodplains, afforestation, ecological flooding, warning systems
Describe and name land-use zoning strategies for a river channel and drainage basin management (3)
- Planning what the land is used for within river basin so less valuable land closer to a river
- Housing put on higher ground away from river to lessen chance of being flooded
- Method not always straightforward to carry out as many years ago housing were built close to rivers many years ago
Name 2 conflicting views when considering the best way to manage the floodplains at Somerset Levels
- Somerset Wildlife Trust ‘We must allow the rivers to flood naturally. Some of the wetlands habitats are unique’
- Royal Society for the Protection of Birds ‘ Dredging has an impact on the habitat in and around the river’
Name 2 points of view in floodplain development conflict
- Insurance Broker ‘Over 80 new developments to be built on floodplains is a ridiculous amount, there should be non. If people don’t want their homes to be flooded, don’t build on floodplains’
- Young family on low income ‘We need more homes to be built so that the price of houses falls low enough for us to be able to afford them’
