Water Lesson 7: Causes of Flooding Flashcards
Define a flood
When a river exceeds its bank full discharge
Describe storms and flash flooding
Intense, torrential storms are often associated with the UK during summer months. Storms cause the capacity of the river to be overwhelmed quickly
Example of storms and flash flooding
September 2016, flash flooding caused travel chaos as almost half a month’s worth of rain fell within hours in some places - UK
Describe monsoon rainfall
This occurs across South and southeast Asia between May and September
Example of monsoon rainfall
July 2016 the Philippines experienced heavy monsoon rains leading to flooding, landslides and evacuations in villages northwest of the capital Manila
Describe snowmelt
Flooding can occur when this happens as the ground becomes saturated quickly.
Example of snowmelt
Norfolk in 2013, very mild and wet weather caused rapid thawing, which combined at the same time as heavy rain, causing local floods
When was Storm Desmond, UK?
5-6th December 2015
Areas affected by Storm Desmond?
Cumbria, Northwest England
How much rain fell in Honister Pass in 24hrs?
341.4mm
When was the wettest 48hrs? How much rain fell?
Thirlmere
405mm
How many died from storm Desmond?
2
How many named storms in the UK in 2015/16?
4
Causes of Storm Desmond?
-Very mild, moist air from the tropics pushed across to the UK
-Air quickly forced to rise over mountainous terrain, producing lots of rain - orographic rainfall
-The position of the jet stream – which are the driving force of the direction of depressions and speed of movement – remained over the northwest longer than usual
Human causes of flooding in Cumbria from Desmond?
Changing land use
Mismanagement of rivers
Describe land use in Cumbria
-Agricultural landscape managed by farmers
-Overgrazing leads to bare slopes as vegetation is removed. This leads to a reduced amount of interception and an increase in overland flow which means that lag times are reduced and a higher discharge peaks.
Soil is also trampled, reducing infiltration
Describe mismanagement of rivers in Cumbria
Hard-engineering strategies have been common including raised riverbanks, pumping stations and diversion channels
Which river in Cumbria rose by how much breaching its riverbank? Why?
River Greta in Keswick
Rose by 5.9m
No dredging - raised river bed
Number of homes affected by Desmond?
5200
Number of schools closed by Desmond?
40
Insurance claims amounted to what?
£325 million
Estimated cost of Desmond flooding?
£500 million
Effect of Desmond on the environment?
Water pollution from debris and sewage
Destruction of habitats and increased erosion
Location of storm Eva?
West Yorkshire and Lancashire - hit Manchester, Leeds and York heavily
Number of properties flooded by Eva?
9000
Number of homes with power cuts by Eva?
7574 homes
What transport links were closed due to Eva?
Irish Ferries
M62
Rail services across the North
Estimated cost of Eva?
£800 million
Number of deaths from Eva?
1
Effect on environment from Eva?
Habitats severely destroyed and increased erosion
Increased saturation of soil reducing infiltration
Location of Storm Frank?
North-west Scotland and West of UK
Number of properties evacuated by Frank?
300+
What reduced the ability to rescue people by Frank?
Flooding combined with freezing temperatures and snow
Transport routes closed by Frank?
A93 between Ballater to Braemar partly washed away down river Dee
Transport routes closed by Frank?
A93 between Ballater to Braemar partly washed away down river Dee
Which river changed its route from Frank?
River Quoich
Number of wading birds around Braemar increased by what from Frank?
From 40 to 82 pairs
Effect to environment from Frank?
Trees knocked down provided more dead wood and new habitats
Increase in wading birds
Estimated cost of Frank?
£700-900 million
How much did the UK gov give to Cumbria and Lancashire for recovery from Desmond?
£50 million
Number of water pumps and length of flood barriers in response to Eva?
20 pumps and 2km of barriers
Number of families into temporary accommodation?
300
Average cost of domestic flood claims was?
£50 000
Amount gov gave out for flood recovery?
£200 million
Amount committed by gov for flood management projects over 6 years?
£2.3 billion
Estimated total cost of floods by KPMG?
£5 billion
