Many rivers to cross

Using reservoirs to supplement rivers is now a necessity. But what is the environmental impact of water that has travelled in several river systems? Martyn Kelly reports

Last summer, the people of north-east England saw a whiteelephantfinally change into a useful beast of burden. While their neighbours to the south and west - not to mention most of central and southern England - suffered drought orders, the lawns of Northumbria remained lush and green. The reason? Kielder Water, the largest reservoir in Europe, plus a pipeline that enables water from Kielder to be pumped to rivers in the region.

"At the time it was completed it was seen as a white elephant because the industrial expansion of Teesside, whose demand it was built to meet, never materialised," explains Andrew Panting of Northumbria Water. "I think it is fair to say that for the first eight years, through to about 1990, it wasn't used a great deal. Since then it has really come into its own, being used more each year than the previous one, to the point at which last year it was playing a vital role in keeping the rivers Tyne, Derwent and Wear topped up. If we hadn't had Kielder Water then, the situation in the North-east would have been potentially worse than that in Yorkshire."

Even at the end of the summer, Kielder Water, with a capacity of 200 billion litres, was still almost 80 per cent full. This compared with only 11 per cent in some of the worst affected reservoirs of West Yorkshire.

Not surprisingly, then, Yorkshire Water spent much of last summer casting wistful glances towards their friends in the North. They spent pounds 27m bringing in tankerloads of water - 300 a day at the peak - from Teesside. This year they plan to go one step further by building a permanent pipeline to take water from the River Tees, near Darlington, 13km to the river Wiske, a tributary of the Swale. From there it will flow down the rivers Swale, Ure and Ouse and through another 23km of new pipes to a water treatment centre near York before arriving in the Yorkshire water mains.

By the time the water arrives in York it will have travelled in three separate river systems: the North Tyne, Tees and Swale-Ouse. Working out exactly what impact this will have on each river is not easy. "There has been remarkably little written on water transfers," comments Chris Gibbons of the University of Northumbria, who recently completed a PhD on the ecological effects of the Kielder scheme. "There seem to be a lot of hurried proposals for transfers now and next to no pre-impact studies at all."

Generalisations about the effect of transfers are difficult. "It all depends upon the differences between the donor system and the receiving system," Gibbon explains. His own studies showed that the effects of releases of Kielder water on the River Wear were slight because the two rivers are, chemically, very similar. "The water quality issues are more related to the sorts of changes that occur within the transfer tunnel," he explains. "Quite often water stands for a long period of time in the transfer tunnel and, when it is released, it is relatively low in dissolved oxygen."

Deoxygenated water can be fatal for fish and other animals in the river, so it is important that weirs, and other means to re-aerate the water are provided before it enters the river. However, Gibbons goes on to explain that these changes were relatively short-lived in the Wear and had disappeared a few hundred metres downstream of the discharge.

Other problems that need to be taken into account are the transfer of new pests and diseases. Zander, an aggressive, alien fish, loathed by coarse fishermen, was able to spread through an earlier scheme that linked rivers in East Anglia. And, in 1989, a chemical spill in the River Tyne was accidentally transferred, thanks to the Kielder Scheme, to other rivers - and water-treatment works - in the region and about 100,000 households were supplied with drinking water that had a distinct odour of TCP.

Yorkshire Water and the Environment Agency are both quick to point out that plans to transfer water between the Tees and the Wiske (and, consequently, for the Tees to be supplemented by Kielder) are only likely to be used in an emergency. However, the greater distance between the Tyne and Tees will mean that water spends more time in the pipes and will, potentially, be more severely deoxygenated than is the case for discharges to the Wear. Add to this the potential need for larger volumes of water to be transferred and the impact on the otherwise pristine upper reaches of the Tees could be more serious than Gibbons observed on the Wear.

The next stage of the journey, however, might even have a positive environmental impact. Yorkshire Water will abstract high-quality water from the Tees from a stretch just upstream of Darlington and pump it into a river which, an Environmental Agency spokeswoman commented wryly, leaves a lot to be desired in water-quality terms. The net effect might be an overall improvement in chemical terms, due to dilution of river Wiske water by river Tees water. The ability of a small North Yorkshire stream to cope with such an increase in flow is a question that Environment Agency staff will be asking Yorkshire Water to answer before giving the final go-ahead.

A closing irony is that plans to extend the Kielder transfer scheme to the Swale were first proposed in the Seventies, but were blocked by Parliament on the grounds that the then water authorities should get their water from within their own regions. Had it gone ahead at the time, many of the changes that Yorkshire Water have had to make in the past few months would already have been in place. It is probably small comfort to Yorkshire Water to know that it is not the only one to blame for its current misfortunes.