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Climate concern

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'We're getting the wrong sort of rain,' declares Severn Trent's director of engineering, Ian Elliott. He is perfectly serious. Looking at the effect of climate change on the trends in raw water, Elliott says that the shift to more intense rainfall will cause a problem because 'it's difficult to catch'.

From a water supply point of view drizzle is the ideal because it soaks down into an aquifer, or runs off into water courses at a steady rate so that it can be diverted into a water works and stored. Drought interspersed with storms causes difficulties with limits on abstraction during the dry period and severe problems capturing and treating the short term floodwater.

Elliott says that the company is 'currently well placed' in terms of supply. But it is not self-sufficient.

Geographically Severn Trent lies at the headwaters of two of England's most substantial rivers, but it also has a very large population to serve. Water is brought in to the West Midlands from Wales and the Eland Valley dams via an old aqueduct. But there is a long term problem in the East Midlands. Much of the water there comes from boreholes in the Nottinghamshire sandstone which is unsustainable. Lifting of some 25M litres/d will soon have to stop.

'Now we are very proactive, all the time looking over the horizon,' says Elliott. 'Water has always got to be there and it has got to be fresh and potable. Hence we need to research climate change and try and predict what is going to happen.'

Responsibility for this falls to water resources planning manager Will Bradford: 'The East Midlands has 3M people,' he says. 'The supply and demand balance is very tight and in the next three years we have to find other resources.'

The plan is to abstract water from the Triassic Limestone in the Birmingham area via new boreholes and feed it into the headwaters of the Trent during the period of 50 to 100 days a year when the river level is low. This will allow abstraction downstream near Derby to be continuous. Up to 10 boreholes producing 5M litres/d each will be needed and each will involve acquiring a site 'the size of a tennis court'.

'In trying to abstract water in an urban area there are a lot of issues,' says Bradford. For instance: 'Do you have to treat it before discharging it to a river?'

Head of technical development John Upton has an R&D team working out how to treat the water to be taken out of the Trent using membrane technology. 'It's a big project that has been going on for three years. In UK terms it is like treating the Rhine.' The plan is to have bankside storage in worked out gravel pits which will be filled when the Trent is running at a high level.

A pilot plant is running at Long Eaton in a joint venture with Anglian Water. The plant uses a combination of ultrafiltration and reverse osmosis membranes which is being compared with conventional treatment of the same river water. 'The idea is that if it's wet we can treat it,' summarises Upton.

Other schemes being planned are reinforcements of existing pipelines and strategic links from the Severn and Derwent. Part of the long-term plan is to find a new resource in Wales and extend the Eland Valley aqueduct.

'The Environment Agency is keener on leakage control but we feel the issue is that there are such long lead times that we need to start developing new resources,' says Bradford. 'We can't just hope that people will use less water and that climate change can't happen.'

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