The Environment Agency is studying flood prevention options for the Lower Thames area, a region that contains the biggest single group of residents in England and Wales at risk of flooding.

This is phase two of a strategy that offers a range of options for flood prevention in an area containing nearly 12,000 properties at risk.

The Lower Thames Strategy was initiated in response to the flooding of January 2003, and aims to establish the most appropriate flood risk management approach for the Lower Thames area, between Datchet in the Royal Borough of Windsor and Maidenhead, and Teddington in London.

Phase one of the study involved a review of the Datchet, Wraysbury, Staines and Chertsey flood alleviation scheme feasibility study, which was originally undertaken in 1992. This review was completed in January 2004 and found that the study was still relevant. It was then presented to the Regional Flood Defence Committee (RFDC) who gave approval for the Environment Agency to move to on to phase two.

Since then the Environment Agency has been working hard to complete phase two of the Lower Thames Strategy, and presented their findings to the FRAG last Wednesday. The objective of this phase was to identify all the possible options that could potentially reduce flood risk in the Lower Thames area. These options have been combined to form a number of different approaches.

Because of the significant landscape differences along the Lower Thames, the Environment Agency divided the area into four reaches . This strategy is looking at the most appropriate approach for reaches three and four. Reach three covers the area from Datchet to Walton Bridge and reach four the area from Walton Bridge to Teddington.

Reach three is made up of a large, flat and wide floodplain, with many open areas. The floodplain within reach four is significantly narrower and more confined by development and the topography of the land.

This landscape means that during a 1 in 100 year event (a 1% chance of a flood occurring in any given year) 30sq km and 9,800 properties would be affected in reach three – with approximately 25,000 people at risk. This is the largest number of properties and people in a single location (of equivalent size) at risk from river flooding in England and Wales. In reach four 5.4sq km and 1,900 properties would be affected, equating to approximately 4,800 people.

These significant differences in size, shape and physical characteristics mean that it is unlikely that a uniform approach will work for both reaches three and four. As a result, each of the approaches for flood risk management in the Lower Thames is made up of a combination of different options for each reach. Major engineering works, catchment wide storage, local defence schemes for groups of properties, flood–proofing of individual properties and the Environment Agency’s flood warning service are just some of the options being considered.

Phase two of the Lower Thames Strategy, which was presented to and approved by RFDC on the Tuesday 19 April, has identified five alternative approaches, as outlined below:

1) Major approach: Would involve large-scale engineering works in reach three and four and may result in diversion channels and/or riverbed re-profiling. Due to the topography of the land a diversion channel is not viable for reach four.

2) Minimalist approach: Would focus on existing non-structural options, such as community flood protection plans and the Environment Agency’s flood warning service.

3) Community/Local based approach: Reliance on community based options, such as temporary defences, local defences for groups of houses and individual property protection, but would also involve some engineering works including river bed re-profiling.

4) Medium integrated approach: A complementary package of options, including diversions channels or river bed re-profiling in reach three, and community based options in reach four. Improved non-structural options, such as land use planning and heightened public awareness could be applied to both reaches.

5) Major integrated approach: As with medium integrated, but including an additional diversion channel in Wraysbury (reach three).

Environment Agency flood defence manager Ian Tomes said: "With 11,700 properties and approximately 29,800 people at risk of a 1 in 100 year flood in the Lower Thames region, finding the most suitable approach for this area is a big priority for us. This does take time, but we are now one step closer to this goal."

The results of phase two will form the basis of phase three of the strategy – during which the Environment Agency will undertake a more detailed evaluation of each of the approaches. This work will involve assessing which prove to be technically sound and viable, and environmentally acceptable – resulting in the optimal approach for the Lower Thames