Thames Basin Flashcards
Where is the River Thames?
England
How long is the River Thames?
346km
What is the course of the river?
- The Thames rises in Cotswold Hills (made out of Jurassic limestone)
- Then it flows Eastwards through a gap between the Chilterns and Berkshire Downs (made out of permeable chalk)
- For the rest it flows over impermeable London clay into the North sea
Where is the driest region in the country?
- The South-East region
- The Thames flows here
What is the effect of the driest region?
- Puts pressure on water resources as the area already struggles to meet the demands
- Growing population doesnt help
What is the average rainfall a year in the driest region?
690mm
Where does London get 40% of its water supply from?
Groundwater in the chalk that lies beneath the city
How does London get water from the groundwater?
- Boreholes are drilled through the clay
- To get groundwater from the chalk aquifer
- Aquifer: underground layer of water bearing rock
What type of river is the Thames?
A lowland river
Why does the Thames not have waterfalls or gorges?
- Its source in Cotswolds is 108 metres above sea level
- It has less force from gravity
- So it lacks in the energy of an upland river that has a source in the mountains
How was the Thames meander formed?
- Thames has a gentle gradient and little downward erosion
- The river does have energy for lateral erosion
- Because it carries large volumes of water
- It flows side to side across its valley
- This forms a meander
What is the effect on the River Thames when sea levels rise?
- The river gained energy
- Because it had to drop further to seal level
- It eroded downwards into its old floodplain
What is the effect on the River Thames when sea levels fall?
- The river lost its energy
- Began depositing more material on its floodplain
Rejuvenation
A river that has eroded down into its old floodplain due to a fall in sea level
What happened each time the river was rejuvenated?
- Formed a new floodplain at a lower level
- Leaving an old floodplain as a river terrace at a higher level
Where are river terraces found?
- Along the Thames valley
- West and East of London
River Terrace
An old floodplain of a rejuvenated river
When was the Thames flood?
February 2014
What places were affected by the flood?
- Village of Wraysbury
- Nearby town of Staines
How many homes and businesses were flooded?
More than 5000
How many people were evacuated?
Thousands
What was the estimated cost of cleaning up the flood?
Over £500 million
Reduced risks of flooding
- Precipitation
- Interception
- Transpiration
- Drip and stem flow
- Water absorbed by roots
Increased risk of flooding
- Precipitation
- Run off from roof
- Impermeable surface
- Water flows into underground drains
Causes of flooding
- The ground is impermeable rock
- The ground is frozen
- The soil is saturated with water after weeks/months of rain
- Rainfall is so intense it cant soak into the ground
Human activities that increase the risk of flooding
- Deforestation: increases the rate at which water reaches the ground
- Urbanisation: increases the rate at which water flows over the ground
- River straightening: this speeds the flow of water in the river
Winter 2013/14
The winter of 2013/14 was the wettest on record in Southern England
How much rainfall was there between December 1st 2013 to 19th February 2014?
487mm
What did the Winter of 2013/14 cause?
A series of Atlantic storms that lashed the UK with heavy rain throughout the winter
What happened on the 9th February?
- The ground was saturated
- Water levels in Thames were very high
- The environment agency issued 14 severe flood alerts across the Thames
What made the flooding worse in Wraysbury?
A new artificial channel on the Thames called the Jubilee river
Why did they make the Jubilee River?
- Built for the Queens golden jubilee in 2002
- Designed to take overflow from the River Thames to reduce flooding in Maidenhead, Windsor and Eton
How much did the Jubilee river cost?
£110 million
How did the Jubilee river contribute to the flood?
- Takes a shorter route so water reaches its destination faster
- In 2014 it carried water quickly downstream to Wraysbury and Staines increasing flooding
What are they planning on doing to reduce floods?
- Flood relief channel to Teddington
- Part of a £500 million project
- To reduce flood risk in Thames West London
When was the last major flood that affected central London?
1928
How many people died due to the 1928 flood?
14
What happened in 1953?
- A storm surge in the North Sea drove water up the river
How many people became homeless due to the 1928 flood?
Thousands
What prevented the flood in 1953?
The man made embankments along the river
How many people drowned due to the 1953 flood?
Over 300
When and why was the Thames barrier built?
- Built in 1984 in East of London
- In response to previous events to make sure it didnt happen again
How does the Thames barrier work?
- When there are high tides
- The gates on the barrier are raised
- To prevent water from reaching London
During the stormy winter of 2013/14 how many times was the Thames barrier shut?
More than 50 times
What is the problem with South East England?
Severe shortage of housing
What is the solution to the housing shortage?
A major new residential development at Barking Riverside is being built to the East of London
How are they going to transform the flood risk into a feature of the landscape?
- Rather than barriers water will be allowed to spread naturally over the floodplain to fill creaks
- Green corridors within the development with water as a feature
- Trees/parkland will help to slow the rate of infiltration and increase water absorption
- Residential areas within the site will be raised land to protect from flooding
