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INCREASING FLOOD RISK IN THE CITY OF LONDON

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

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INCREASING FLOOD RISK IN THE CITY OF LONDON

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  1. INCREASING FLOOD RISK IN THE CITY OF LONDON An overview of the human and physical processes driving hydrological change

  2. 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

  3. 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

  4. 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

  5. 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

  6. 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

  7. CLIMATE CHANGE & RIVER FLOODS • Elsewhere in the UK, there is evidence of increased extremeweatherevents 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

  8. 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 disasterpotential is rising

  9. LONDON AT RISK

  10. 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.

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