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.