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Flooding (Flooding Problems (Land use changes (small-->catchment…
Flooding
Flooding Problems
Groundwater flooding
Water cannot recede into groundwater fast enough
Urbanisation
--> greater impermeable surfaces
Land use changes
(small-->catchment-scale)
deforestation/agricultural practises
moorland
has very poor infiltration capacity so water simply runs off
bare fallow
poor infiltration
compaction
of earth by animals
exacerbates runoff as reduces pore space for infiltration
Streams / rivers
= too peaky
respond v quickly to rainfall events
Climate Change
Predicted increase in extreme events
Wetter conditions
2015-16 influence El Nino
Biodiversity
traditional flooding solutions reduce biodiversity
Population
increase
greater demand for land
poor planning decisions made to accomodate
UK River
Flooding
Boscastle 2004
intense rainfall vent channelled water there
Boscastle village inundated by raging torrent
FLASH FLOOD - very sudden
hundreds had to be rescued from roofs
steep sided valley
Carlisle 2005
more gradual / gentle flood onset
large effects
Central
England
2007
Sheffield & Hull & Tewskesbury
Tewkesbury church built on higher ground was unaffected
Cockermouth
LD 2009
Bridge collapsed, killing policeman
England &
Scotland
2015-16
York & Lancashire
Mill of 200 years collapsed
(water washed away bridge it sat on)
River Dee, Ballater
River washed away road
Alyth 2015
Imbercated cars
Stacked one over other
Akin to stacking of boulders/pebbles at river bed
River flow inundates its banks - land normally dry
Drainage Problems
Defenses fail & make problems worse (i.e. drains blocked)
Coastal & groundwater flooding
Too efficient
drainage system moves water away too quickly
Rivers rise too quickly
drainage insufficient
Rivers
straightened
/ canalised
to increase efficiency of water removal
moves water downstream really quickly
Inability to deal w/extreme events
drainage system overwhelmed
poor management
drains clogged w/leaves etc
Extreme UK Weather 2015-16
Large rainfall anomalies esp N/W Scotland
Record river level/discharge for many rivers
Some Q > 1000 cumecs ! (half of Rhine Q)
Normal Situation
Interception of precipitation by veg etc
Rainfall reaches ground at lower intensity/rate
Aids infiltration
Travel over leaves / down stems
Natural temporary basin storage
water travels through ground/soil (slower vs overland flow)
may recharge groundwater
Aim
replicate this in urban
improve this in rural
Importance
Extreme weather events on rise
El Nino
Climate change
Require sustainable prevention / mitigation developments
Drains
vital in impermeable urban areas for directing water away
Individual measures
people need to make own effort to protect property