Posted by: waterworks | July 9, 2008

35. When flood management becomes rocket science

As I write, highly civilized human beings are flying overhead, trying to save me. 


Mindful of a yawning data gap currently found in the flood risk analysis for Great Britain, the Environment Agency (EA) has swiftly set about mapping areas where a significant probability of repeated pluvial flooding can be identified – using new hi-tech laser measurements of local topography and land use.  £3 billion of flood damages last year were mostly caused by heavy rainfall exceeding the capacity of local hydrological systems to transmit the water quickly towards a river.  In urban districts such as Hull, precipitation intensity exceeded infiltration and percolation capacities of local drainage basin surfaces.  As a result, ephemeral lakes grew at localities where concavities in the relief collected water.  In populated areas, the rising waters seeped under doorways, initiating a series of unfortunate events for home-owners.  “Over half the property was flooded by water on its way to the rivers, not coming from the rivers.  It’s flash flooding, urban flooding” explains the head of the EA. 


Now, a highly detailed series of three-dimensional topographical maps is being generated to alert unsuspecting surface-hollow-dwellers to the potential risk they face from pluvial flooding.  EA scientists are currently hovering above the UK in aircraft carrying LIDAR units. These fire a laser beam downwards 100,000 times every second, scanning a transect of land up to 600m wide.  56% of England and Wales has been surveyed so far, with an early focus on urban areas most at risk from torrential flows of surface water during heavy storms – more of which can be expected in the future, according to many climate change models.  The results for Hull can be viewed here.  LIDAR can be read about here.



Right: It’s all very Tracy Island – Environment Agency boffins use lasers to save Britain from floods


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