Drainage basins of the UK Flashcards
What 5 factors influence the rate of which water moves through a drainage basin?
Type + quantity of rainfall Type + quantity of vegetation cover Size + shape of drainage basin Steepness of slopes Geology + soil type within the drainage basin
Define drainage basin
The area of land drained by a river.
Define interception
When rainfall does not reach the ground as it is blocked by trees, buildings etc.
Define infiltration
The movement of water into the soil.
Define throughflow
The downhill flow of water through soil.
Define overland flow
The flow of water over the surface of the land.
Define groundwater flow
The flow of water through rocks.
Define transpiration.
Water given off by plants.
Define stem flow.
Movement of water that has been intercepted down the stem or trunk of a plant.
Define percolation
Movement of water from the soil into the bedrock.
List the flows in a drainage basin.
Infiltration Percolation Overland flow Through flow Groundwater flow Evaporation Precipitation Transpiration Stem flow
List the stores in a drainage basin.
Atmosphere Vegetation Ground surface Soil Rocks Rivers and lakes Oceans
What physical and human factors cause rivers to flood?
Climate (physical)
Geology (physical)
Urbanisation (human)
Vegetation (physical)
How does seasonal rainfall cause rivers to flood?
Continuous rainfall causes ground to become saturated, leading to more overland flow - therefore higher river levels.
How does a storm event cause rivers to flood?
Brings high volume of rainfall in short period of time, causes sudden rise in river levels that can lead to flash floods.
How does heavy rainfall cause rivers to flood?
Lower chance of heavy rainfall being infiltrated, so runs off into river. The faster the water reaches river, more likely it is for it to flood.
How does prolonged rainfall cause rivers to flood?
If rains a lot, land around river can become saturated. If more rainfall, can’t be infiltrated, so runs along the surface - surface runoff.
How does geology cause rivers to flood?
Impermeable rocks don’t allow water to pass through them, so little water passes through, more overland flow so higher flood risk.
If valley made up of impermeable rocks, higher chance of flooding as increase in surface runoff.
How does steep relief cause rivers to flood?
Steeper valleys are more likely to flood than a flatter valley as the rainfall will run-off into the river quicker.
How does vegetation/deforestation cause rivers to flood?
Trees + plants absorb water (interception), so reduces flood risks. Deforestation increases risks of floods, as water isn’t intercepted, so quicker saturation + water will flow into the river quickly.
How does urbanisation cause rivers to flood?
Area surrounding river is built on, ground is covered with impermeable surfaces (tarmac and concrete) - reduces amount of water infiltrated.
So more overland flow + increases chances of flooding.
Drains + sewers take water directly and quickly to river which increases the flood risk.
How do tributaries cause rivers to flood?
If river has lots of tributaries, the river’s flow will be much higher as lots of water is entering from tributaries.
After heavy precipitation, water will rise more, making floods more likely to happen - especially at confluences as this is where the water flow is at its highest.
How does climate change/global warming cause rivers to flood?
Could be both human and physical factors.
Change in climate means that certain areas experience more frequent + intense storms, leading to large floods.
What is a hydrograph?
A line graph used to display the discharge of a river over a period of time.
What is lag time?
The time between the peak rainfall + peak discharge in a river.
What is rising limb?
Part of a hydrograph where the discharge of a river is increasing after a rainfall event.
How does urbanisation affect the shape of a hydrograph?
Decreases lag time
Steep rising limb
High peak
How do porous rocks affect the shape of a hydrograph?
Increases lag time
Gentle rising limb
Lower peak
How do impermeable rocks affect the shape of a hydrograph?
Decreases lag time
Steep rising limb
High peak
How do broad-leaved trees affect the shape of a hydrograph?
Increases lag time
Gentle rising limb
Lower peak
What are hard engineering strategies?
Involve constructing defences to control natural processes:
Dams
Artificial levees/embankments
Artificial river channels (channelisation)
Gabions
Dredging the river channel
Creating a flood relief channel
What are soft engineering strategies?
Work with the environment rather than trying to control it:
Land use zoning
Afforestation
Washlands
What is land-use zoning?
Planning what land is used for within river basin so less valuable land is closer to river.
Housing + key services usually put on higher ground away from river to lessen chance of them being flooded.
Method not always straightforward to carry out as in many towns/cities, housing + key services have been built close to river (years ago).
Define catchment area
The area within the drainage basin.
Define watershed
The edge of highland surrounding a drainage basin. It marks the boundary between two drainage basins.
Define source
The beginning or start of a river.
Define confluence
The point at which two rivers or streams join.
Define tributary
A stream or smaller river which joins a larger stream or river.
Define mouth
The point where the river comes to an end, usually when entering a sea.
Describe/draw what a drainage basin looks like.
The mouth of the river with a river flowing the opposite direction - including features like tributaries, confluence, main river channel and a watershed around it (like an incomplete circle around the whole thing).
Define estuary
Estuaries are where freshwater (rivers) and saltwater (sea) interact.
Define porosity
The ability of rocks to store water in tiny air spaces.
Define groundwater store
Water in the ground below the water table.
Define surface stores
Places where water is found on the surface, such as lakes and rivers.
What are the 5 key features of a drainage basin?
Tributary Confluence Source Mouth Watershed
What are the 4 natural causes of flooding?
Prolonged rainfall (raining for a long time) Heavy rainfall Steep relief (steep slopes) Impermeable geology (rocks that don’t allow water to sink through it.
What are 2 manmade causes of flooding?
Urbanisation
Deforestation
What are the + and - of soft engineering techniques?
+ Often cheaper than HE
+ Less impact on environment
- Can be less effective once river has flooded
What are the + and - of hard engineering techniques?
- Often large scale
- Expensive
+ Relatively effective
What were the causes of the Boscastle flooding?
High tide
Steep valley sides - overland flow
Impermeable surfaces - surface runoff
Ground saturated due to storms in the days before
Confluence of the River Valency and River Jordan
Give effects of the Boscastle flooding.
Roads blocked - Helicopter Property destroyed Emergency accommodation Vehicles carried out to sea Insurance costs increased for homeowners Tourism industry seriously affected
Give an example of river flooding that you studied (apart from Boscastle).
Somerset Levels 2014
What were the causes of the Somerset Levels flooding?
Flat landscape
Levels only 8m above sea level
Lots of rainfall in the days before therefore ground was saturated
No dredging
