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
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
In cities like London, home owners 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
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
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
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
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
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.cmhc schl.ga.ca, www.bae.ncsu.edu, Flickr user gluemoon, D Ashton, Mark Saltern, Flickr user Foshie, Environment Agency, Geography in the News.