UK Depressions Flashcards
How many storms arrived in the UK in February 2020?
- 3
How much rainfall was received in Feb 2020?
- 209mm
- over twice the expected amount
What were the antecedent conditions like prior to flooding in 2020?
- High soil moisture
- so high that soil moisture deficit had been at 0% for preceding 5 months
- Overland flow
How many people were evacuated form Ironbridge?
- 40
What was in the river that could create additional problems?
- Sewage
- can clog infrastructure meant to drain water
- flood gets worse and takes longer to subside
What was the economic impact of the Severn flooding?
- Farm animals lost
- Farmers harvests ruined
- lost barley, wheat, oat
- avg. £15,000 loss
- limited what crops could be grown afterwards as well
- Shops were not insured
- had to cover loss of restocking and cleaning
- Factories were inundated
- some closed after the costs of repairing or replacing machinery was too higher
- results in increase in unemployment
What positives are there from flooding?
- Sediment carried by river is deposited on flooded areas
- acts as fertiliser
- eg. orchards near Severn have benefitted from this
- however, can only be capitalised when soil has dried out
What soft engineering techniques are being used to mitigate flood risk from the Severn?
- Floodplains south of Worcester are allowed to flood
- increased interception slows down river flow
- reduces risk of flood lower down
- Could plant trees to achieve greater interception
- results in more managed flow of water, reduce risk of extreme flooding
When did flooding occur along the Severn?
- February 2020
Why did the UK receive this much rainfall?
- Position of jet-stream changed
- was more south than usual
- brought low pressure storms to UK
- thus rainfall
What caused the antecedent conditions?
- Low pressure mid latitude depressions stalled over the UK in November
- thus resulting in rainfall occurring for a large period of time
How did human actions have a hand in the flooding of the Severn?
- Large areas of Severn floodplain are built over
- less interception
- flood becomes more flashy
- Climate change could possibly have led jet-stream to move more southerly than usual
- resulted in depressions lingering for longer
Why have dams not been used in Shrewsbury?
- River valleys can become flooded
- blocked as a result
- Volume of water within dam reservoir can exceed capacity
- can potentially make situations worse
What hard engineering has been done to the Severn to reduce flood risk?
- course straightening + channel deepening and widening
- allows water to move more quickly through areas
- Clywedog Dam
- regulate water flow, reduce risk of flooding downstream
- Flood walls (temporary)
- effectively raises river bank, contains river
- Artificial levees / embankments (Worcester)
- Raises river banks, increase water flow in built up areas
What is the problem with embankments and flood walls?
- Temporary flood walls may not be as robust as permanent ones
- may be overwhelmed
- Embankments increase water flow, which could result in flooding further downstream
- same for channel straightening/widening and dredging
