Transcript PowerPoint presentation

INCREASING FLOOD RISK
IN THE CITY OF LONDON
An overview of the
human and physical
processes driving
hydrological change
THE HYDROLOGICAL CYCLE
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Natural surfaces
promote infiltration,
throughflow and a
lower flood risk
Urbanisation brings
impermeable
surfaces, overland
flow and a higher
flood risk for rivers
DECREASING URBAN PERMEABILITY
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In cities like London, homeowners are paving over their
gardens or adding decking
They are following fashion
trends or creating parking space
In London, an area of gardens
22 times larger than Hyde Park
has been lost
This makes the response of the
Thames flashier and increases
the fluvial flood risk; it also
creates pluvial flooding
problems
Source: www.cmhc-schl.ga.ca
THE HYDROLOGICAL IMPACT
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Urbanisation reduces
the storm hydrograph
lag time
It also increases the
peak discharge
Rivers are more likely
to reach bankfull
discharge
This increases the
fluvial flood risk
THE INCREASED PLUVIAL RISK
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Pluvial flooding causes
places to become
submerged in water,
even when they are not
near a river or coastline
High-intensity rainfall
and impermeable
surfaces combine to
create temporary lakes
in areas where the local
topography allows for
depression storage
CLIMATE CHANGE & STORM SURGES
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London is at risk from a
further type of flooding:
storm surges can push
unusually high levels of sea
water up the Thames estuary
Climate change is bringing
increased storm activity &
higher sea-levels
London is sinking at 1mm a
year due to isostatic change
The Thames Flood Barrier
is “holding the line” – for now
CLIMATE CHANGE & RIVER FLOODS
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Elsewhere in the UK,
there is evidence of
increased extreme
weather events
causing different types
of flooding
The village of Boscastle
suffered a major flash
flood in 2004
Pluvial flooding caused
£3 billion losses in the
UK in 2007
LONDON AT RISK
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The River Thames
brings many site
advantages for London
However, it brings
multiple flood risks
These risks are set to
increase over time,
while the value of
assets and population
numbers keep rising –
meaning disaster
potential is rising
LONDON AT RISK
LONDON AT RISK
Photograph & image credits: CGIS, www.cmhcschl.ga.ca, www.bae.ncsu.edu, Flickr user
gluemoon, D Ashton, Mark Saltern, Flickr user
Foshie, Environment Agency, Geography in the
News.