Under pressure23 September 2008
The southeast of England is suffering from serious water stress. To help secure future water supplies one water company is proposing the development of new reservoirs. Jon Holland gives more details
UK water company, South East Water is preparing its plans for supplying water to customers over the next 25 years. With significant population growth anticipated in the southeast of England, this presents a real challenge. Although climate change is expected to increase water consumption by individuals, it will also potentially reduce the availability of water from some existing sources. In addition, changing lifestyles with smaller households is leading to an increase in average consumption.
South East Water is committed to reducing leakage to ensure economic operation, but the company is still predicting that it will need to supply up to 150M l/day more water during periods of peak demand by 2035.
As part of its planning process South East Water has investigated over 600 possible new resource options. These include upgrades to existing and some new groundwater sources, plus improved connectivity with new strategic mains between resource zones. Of particular importance are the proposals for two new winter storage reservoir schemes at Clay Hill near Lewes in Sussex, and Broad Oak near Canterbury in Kent. These plans are currently being put out for consultation. Clay Hill is programmed for completion and supplying water by 2017, whilst Broad Oak is due to be on line by 2024.
Broad Oak reservoir
The Broad Oak scheme would be able to supply up to 28M l/day (average) and 55M l/day (peak) via a new water treatment works and booster pumping station. Located north of Canterbury in Kent, between the villages of Tyler Hill and Broad Oak, the reservoir will have a surface area of 250ha. It will store up to 15,000M l behind a 650m long and 25m high earthfill/clay core embankment.
The scheme will operate by abstracting surplus water from the River Stour during times of high flows, primarily in the winter. This water will be stored in the reservoir for supply throughout the year, with the major benefit of giving a robust resource for meeting summer peaks. Project costs are in the region of £125M (US$247M), with a further £50M (US$99M) anticipated to be required for new strategic mains, in conjunction with other schemes for the future.
Whilst much of the water will support growth in the towns of Canterbury and Ashford, the full capacity will be used via existing strategic mains to serve the Weald of Kent and as far afield as East Sussex. This will free up existing resources to supply into the north of Kent, Maidstone and elsewhere in West Kent and East Sussex.
The Broad Oak scheme has been proposed as a technically viable scheme since the 1940s and subsequent studies, including the most recent ones, have clearly confirmed this. South East Water has owned the land for the project since the 1970s, when it prepared a detailed scheme and made a planning application. This was refused on that occasion since the need for the size of the proposed scheme could not be demonstrated at the time. There were also significant impacts on the community at Tyler Hill.
The current proposals put forward a slightly smaller scheme which deals with the local community issues, and includes clear proposals for more acceptable construction and permanent access. The need for the scale of the current proposal is more easily understood with housing growth now so tangible across the southeast region.
There are still issues, not least the potential environmental impact. However, South East Water is working hard with organisations such as Natural England and the Environment Agency, to ensure it establishes a full understanding, and puts in place a comprehensive package of mitigation and enhancement. South East Water is setting up a series of exhibitions and workshops during the latter part of 2008 and into 2009 to ensure that all those with an interest can have a say in what the final scheme will look like.
Clay Hill reservoir
Northeast of Lewes in East Sussex, the Clay Hill reservoir is proposed to operate in conjunction with the existing River Ouse scheme, with Ardingly at the head of this scheme. The existing Barcombe works, with bankside storage, already provides a substantial water supply. Clay Hill will effectively increase the capacity of the Barcombe site by approximately 17M l/day on average and up to 22M l/day under peak demand conditions. The water will be treated in an extension of the existing Barcombe works.
Although further investigations and consultations with the Environment Agency are ongoing, in essence the scheme makes use of existing abstraction licence conditions, storing surplus water from the River Ouse abstracted during high flows. Abstraction will be primarily during the winter.
The scheme would inundate approximately 160ha of arable land, behind a low clay core embankment, with an impounded volume of 4700M l. The embankment, constructed to protect adjacent woodland, would be a curved structure, some 1300m long and 11m high. The scheme will cost approx £90M (US$178M), and primarily use existing mains for distribution.
Key issues include the need to purchase the land required for the reservoir and associated works, and also various ecological impacts. In consultation with the Environment Agency and Natural England, Lewes District Council and other organisations, a package of mitigation and enhancement measures will be developed to minimise or offset impacts, and to provide some tangible benefits.
The Clay Hill and Broad Oak schemes were introduced at recent public exhibitions. In both cases a level of opposition was encountered, quite understandably, although the two schemes have been possible options for many years. South East Water is committed to work with statutory bodies and all others with an interest, to ensure it fully understands the issues, and as far as possible deals with these within cost effective scheme proposals.
The water resource management planning process is ongoing, with the public consultation having concluded on 1 August 2008, following which a decision will be given by the Department for Environment, Food and Rural Affairs during the autumn. Assuming DEFRA directs for the two reservoir schemes to go ahead, the final plan would be prepared for publication during summer 2009. In the meantime, further investigations continue in relation to the various issues with the schemes to ensure they can be dealt with as part of cost effective proposals. A decision will be made during 2009 to proceed with one or both of the schemes.
Jon Holland is the engineering manager for major resources at South East Water, Rocfort Road, Snodland, Kent ME6 5AH, England. Email: [email protected]