LOWER THAMES FLOOD RISK MANAGEMENT STRATEGY
from the Environment Agency. See www.environment-agency.gov.uk/lts for more detail.
March 2010
After several years of identifying costs and benefits of various options, the strategy is almost complete. The business case and strategic environmental assessment will be submitted to the national review group in 2010, and then go to DEFRA.
The strategy covers the Thames from Datchet to Teddington, and its partner the Thames Estuary 2100 project deals with the tidal section from Teddington to the sea.
Reach 3, Datchet to Walton, has a flat broad flood plain with 12,200 properties in the 1 in 100 year flood risk zone, compared to 2,750 properties in the much narrower valley of Reach 4, Walton to Teddington. Runnymede has the highest flood risk of all Surrey boroughs, and Spelthorne the second.
If the strategy is approved and funded, and the Environment Agency say the cost/benefit analysis puts it in the top 10 schemes nationally, construction could start in 2017. Work must begin at the downriver end and consists of
1) improvements to weirs at Teddington, Molesey and Sunbury
2) widening the Desborough Channel
3) diversion channel on the Middlesex side from above Chertsey weir to below Shepperton ferry
4) diversion channel on the Surrey side from opposite the end of Wheatsheaf Lane to below Chertsey weir
5) diversion channel on the Middlesex side from Datchet to the Glanty roundabout.
The diversion channels use existing lakes and rivers as far as possible, and go some distance from the Thames. The work will take 5-6 years, so there will be no relief for Staines until about 2023. The plans include various options depending on the speed of climate change. Some points are not yet decided, e.g. possible use of the Thorpe Park lakes, reducing flood risk from the Bourne, and the impact on the ecology of mixing lake and river waters with different nutrient levels.
5,000 homes will be taken out of the 1 in 20 year flood risk zone, making them safer and easier to insure. New housing land may become available because the flood risk has diminished. The scheme should also improve the character, biodiversity and recreational potential of the river corridor. Surrey CC, Spelthorne BC and other local councils will be expected to contribute to the cost.
There will also be bunds and other measures to safeguard areas particularly at risk and their escape routes, plus information, awareness raising etc. The Thames will not be ‘reprofiled’, which means dredged, because dredging is ecologically damaging and expensive, at current costs of disposing of the dredged material.
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