Since the conception of this amb

Since the conception of this ambitious engineering project, the specification of the Maidenhead Windsor and Eton Flood Alleviation Scheme (MWEFAS) was revised continuously so it could meet its flood alleviation and environmental objectives within the existing financial constraints. The level of its success will depend entirely upon how well it has met those objectives.

When the Maidenhead Windsor and Eton Flood Alleviation Scheme (MWEFAS) faced its first major test in the January 2003 floods, the Flood Risk Action Group’s (FRAG) Mechanism of Flooding (MOF) report revealed that the MWEFAS eventually passed only 144 m³/s of flow in the Jubilee River, 5m³/s of flow in the Maidenhead Ditch and 244m³/s of flow in the River Thames. This means there was a total of only 393m³/s of water flowing through the scheme in comparison to the objective of 515m³/s (only 76% of its intended maximum capacity), therefore it has been unsuccessful in reaching its objective. The reason for this was finally revealed in the Atkins hydraulic and technical reviews through a catalogue of errors in the design of the major structures that control the flow throughout the Jubilee River.

The question must be asked, are the taxpayers now expected to pay for the repairs or could the people who designed and constructed the Jubilee River pay for it instead? This would be a difficult question to answer because of the legal and political implications. Firstly, there were a great number of consultants and sub-consultants that worked on the design and construction of the scheme (NRA 1992h) and the Environment Agency would have trouble identifying those directly responsible. If the Environment Agency were to try and recover costs from the designers and contractors, it is likely that they would opt for a settlement instead of risking damage to their reputations and brand image. Besides this, the Environment Agency was fully informed of all of the decisions made with regards to design. Also they didn’t follow the recommended operating procedures for the Jubilee River so it may be difficult to take the case to court.

Accessing the success of the defences at Cookham is difficult because the flood banks around Cookham were not scheduled for completion until after the 2003 floods. During the floods, emergency works were used to lessen the effect of the flooding. However, to the local residents, this is understandably seen as another failure of the scheme. The flood banks were completed in spring 2003 (FRAGS, 2004) within the original budget of the scheme. This has not, however, solved the problem. Owing to the higher than expected water levels at Strand Lane in Cookham, remedial works are currently underway to raise the standard of protection in the area to pre-MWEFAS levels. Also, the existing dip in Strand Lane is to be filled in to facilitate the raising of the road level and maintain access. The Environment Agency has forecast an additional expenditure for this as 3.5million pounds over three years (Environment Agency, 2004c). This represents a significant failing in the design objective with substantial extra costs to correct it.

The analysis of the available information illustrates that the design of the scheme exacerbated the flooding downstream of the Jubilee River for a number of reasons. The fundamental reason is due to the errors in the design and construction of the Jubilee River that has reduced its capacity to just 67% of its design objective. As a result of this, the Environment Agency operated the MWEFAS differently from the operating procedures throughout the January 2003 flooding to alleviate the flooding. This, in turn, led to the Environment Agency failing to react to the fact that the speed of the River Thames flood peak from Maidenhead to Windsor took an additional 12 hours, when in the past the use of the flood plain slowed the speed of the flood peak from 2 to 2½ days. This meant that the Environment Agency then failed to divert the rising flood peak into the Jubilee River at an early stage of the flood event in line with the original operating intent. An additional failure was that the Environment Agency failed to understand the importance of closing down the Jubilee River as the peak commenced to drop at Maidenhead, with the result that the Jubilee River was continuously flowing at maximum channel volume when the natural peak of the flow through the MWEFAS passed through the confluence above Datchet.

Although it did not play a part in the 1992 Public Inquiry the issue of dredging of the Thames has been emphasised in light of the problems downstream of the MWEFAS. There was a continuous dredging programme from 1947 to 1995 (Flood Risk Action Group, 2004). This was terminated in 1995 and failure to continue a dredging programme has meant the loss of water volume capacity particularly in Wraysbury, Ham Island and Old Windsor. There is the possibility that with the addition of the Jubilee River, the overall flow in the Thames has decreased in areas and there is the potential that siltation may have increased thus reducing the capacity of the Thames further. This review cannot make any firm judgments on this as there is no data available.

While the MWEFAS is operating below its intended design objectives, it creates a development planning problem for the Borough Councils located within the schemes boundaries. This is because they have based their planning decisions upon information in the 2001 flood maps but because of the reduced level of flood protection, the Environment Agency will now object to applications based on these maps in the future. This leaves the local Borough Councils to operate using pre-MWEFAS flood maps, resulting in a very confusing situation for the councils and the public.

Also, thousands of householders downstream from the Jubilee River now face the prospect of being flooded again by the scheme. However this is not their only worry. There are insurance problems such as many residents dare not claim for damages caused by the flood because of the fear of becoming uninsurable. Also the loss of property values is conservatively estimated in excess of £30 million in Wraysbury and Old Windsor (Thamesweb, 2003).

The success of the environmental enhancement of the scheme is almost equal in value to the scheme’s flood alleviation success. The analysis of available ecological monitoring shows that in comparison to the management objectives, the Jubilee River is developing into a precious wildlife and recreational resource for the area. Most of the mosaics planted for grassland and woodland areas have been successful and are developing on course with the aid of minor management techniques. The marginal and in-stream flora has faired less well with a noticeable domination of filamentous algae due to high nutrient levels. This is the only result of concern as the correct management of the situation will be vital if the scheme is to meet its water quality objectives in the long term. In terms of the fauna in the area there are already a number of notable examples of success. These can be seen in the discovery of many ground beetles, successful breeding of the little ringed plover and the mandarin duck. Less successful points have been the instability of the islands and gravel banks, also the Bat boxes and hotel. Hopefully with the continued monitoring and careful management, the water course will mature and the habitats develop in time. This will hopefully create a greater diversity and bring the colonisation of many of the desirable species in the management objectives.

The Future

The Environment Agency has already completed a lot of the remedial works necessary to restore the scheme to its capacity set out in the design objectives but it will not be completely finished until 2006/7. This has caused understandable concern for residents who fear flooding in the intervening periods and put the topic of future flood defence options for the Lower Thames region, to the top of the agenda. Local residents could not understand why the scheme was not extended all the way to Teddington Lock (where the Thames becomes tidal) so the problem isn’t passed from one town to the next. This was actually considered as part of the original feasibility study for the MWEFAS but ruled out on cost benefit analysis.

In terms of flood alleviation, this review has shown the MWEFAS as very unsuccessful in meeting its objectives. The cost of the scheme over time has risen from estimated costs of £48.6m in 1991 (NRA, 1992a) to £73.4m and then £110m. It now has the addition of approximately £5m (Environment Agency, 2004c) for repair but when completed, the Environment Agency say the floodplain will be defended and the original financial benefits will stand. Although proof of this will have to be found in the future.

Overall, the environmental enhancement of the scheme is a great success and is on its way to becoming a unique wildlife corridor that will attract species to the area that have previously been lost through development on the River Thames. The true value of a non-market good, such as the Jubilee River, is very hard to assess but such an asset to the community should never be undervalued.

In the long term the scheme will be successful because the environmental value of the scheme will offset the expense caused by the temporary flood alleviation failures. However, because of the cost of the scheme to the taxpayer and the vast number of people that rely on it to protect them, the success of the scheme will be debated for years to come.