Comprehension

ABOUT BRITISH DAMS SAFETY

At the end of January two dams in Brazil collapsed after weeks of torrential rain, leaving thousands homeless and causing millions of pounds' worth of destruction. A week earlier, a report about the American Teton dam failure, in which 11 people were drowned, was published. Such events raise again the question of dam safety in Britain, with the Reservoirs Act, 1975, still to be implemented. We can be sure that none of Britain's dams is completely safe. There is an accepted factor of uncertainty in any engineering project, and where nuclear engineers have their 'least credible accident', dam engineers have their 1,000 or 10,000 year flood.

A dam designed to stand up to a flood statistically expected only once every, say, 5,000 years, could conceivably fail a year after it was built if it experienced a 15,000 year flood.
Yet there is still a wide range of factors which might cause a dam to collapse, even without considering the likelihood of an event which occurs at intervals of 1,000 years or so. In Britain, the element that seems to pose the most risk is age. This problem is probably unique, or at most shared by only one or two countries. According to A. I. B. Moffat of the University of Newcastle, speaking at a recent conference on the evaluation of dam safety, held in California, the average age of dams in Britain is about 108 years. There are no records of the construction or subsequent behaviour of many of these and some are below present standards of safety.
Figures collated by Mr Moffat, and supported by general experience, tend to show that most dam failures occur either within the first few years of construction, or after a long uneventful period of operation. It appears that Britain's dams are now approaching this stage. There is a steady upward trend of incidents which may or may not lead to a major collapse, but which call for immediate remedial action. If the trend continues, then we may expect an increasing number of such events and, sooner or later, a failure.
Legislation can never be perfect, and the relatively good safety record of British dams, which no doubt follows from sound engineering practice and administration, might also owe a little to luck and an equable climate.
Until now, failure to remedy a defective dam has rarely been the cause of prosecution — and the penalties are very mild. Also, as Mr Moffat pointed out, some dams have never been inspected, despite the statutory obligation to do so. The new act places enforcement of its legislation in the hands of 66 local authorities. While it overcomes certain deficiencies in the Act it replaces, splitting responsibility between so many small bodies could result in a standard of safety that varies widely throughout the country. Local authorities do not always fulfil the dictates of Parliament. So while the legislation can go a long way towards preventing the kind of disaster that occurred in Brazil, its ultimate effectiveness lies in the hands of local government.