London's small but relentless dip

Their study – based on tide gauge, GPS, gravity, and satellite measurements – shows a general pattern of subsidence of 1-2mm a year.

With waters rising in the region by about 1mm a year, the combined effect is a 2-3mm a year rise in sea level with respect to the land.

The study has been conducted for the Environment Agency.

Monitoring of the estuary will give us a really good understanding of the likely trajectory in terms of risk. Owen Tarrant, Environment Agency

The information is critical to the planning of London’s sea defences in the face of climate-driven ocean rise. The region is home to 1.3 million people and has a property value put at more than £80bn.

These numbers are set to increase substantially as the capital, together with the estuary counties of Kent and Essex, look to expand development ahead of, and beyond, the 2012 Olympics.

The 300km of tidal defences including embankments, walls, gates and barriers will, at some stage, have to be adapted or moved, or new types of defences created that make better use of the natural floodplain.

London’s key defensive installation, the Thames Barrier at Woolwich, also faces upgrading.

The new housing and business developments in the tidal floodplain, behind those defences, are also challenged to be located, designed and built to manage the increasing risk of flooding.

Engineers would like to know where improvements should be prioritised and on what timescale. “Monitoring of the estuary will give us a really good understanding of the likely trajectory in terms of risk,” said Owen Tarrant, from the Environment Agency’s TE2100 Project.

“The way that risk evolves through the century will not only affect the timing of the implementation of the options, but it will also affect the identification of the preferred options,” he told BBC News.

More info at BBC

Jonathan.Amos-INTERNET@bbc.co.uk



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