Dams, Classification
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DAM FAILURES: IMPACT ON RESERVOIR SAFETY LEGISLATION IN GREAT BRITAIN J. Andrew Charles Formerly, Building Research Establishment, Watford, Hertfordshire, UK
Introduction “Every dam, regardless of its size, is in some degree a potential menace to everything below it. There is nothing so relentless in its immediate destructiveness, so uncontrollable and deadly as a huge volume of water suddenly released.” This warning, which was given at a symposium in New York on the public supervision of dams (Hinderlider, 1932), forms a necessary reminder that although reservoirs have provided immense benefits to mankind, as with all human progress, there is a price to be paid. Part of that price is the potential hazard of a dam breach when the uncontrolled release of the impounded water can cause enormous property damage, injury, and death. In 1930, the year that the New York symposium was held, comprehensive reservoir safety legislation was introduced into Great Britain in the form of the Reservoirs (Safety Provisions) Act. British reservoir safety legislation applies to “raised reservoirs,” that is to say it applies where artificially created bodies of water are impounded above the level of the surrounding ground. The legislation does not apply to naturally formed bodies of water such as lakes and lochs, nor does it apply where fluids other than water are impounded. The scope of the legislation is restricted to “raised” reservoirs since reservoirs formed by digging a basin in the ground rather than by building a dam are not normally a threat to public safety. Before considering dam failures and their impact on the development of
safety legislation, the history of dam construction in Great Britain and the current population of dams are briefly reviewed.
Reservoir construction in Great Britain Reservoir construction has a long history in Britain, and the 70-m-long, 6-m-high earth embankment which forms the “Great Weir” near Alresford in Hampshire was built in about 1200 AD. It has been suggested that the reservoir, which originally covered 80 ha but is now much reduced in extent, formed part of navigation works on the River Itchen, but it is more likely that it was just a fish pond. During the Middle Ages, power to drive water wheels for mills was one of the principal objectives of constructing dams and weirs, and in the seventeenth century, many weirs were built to improve inland navigation. From the middle of the eighteenth century, it became fashionable for the owners of country estates to have their grounds landscaped, sometimes involving earth moving on a large scale. Capability Brown, the best known of the landscape gardeners of that time, built many small embankment dams, typically 6 m high, to form “lakes” in the grounds of these country estates. In contrast to the earlier mill dams, these lakes were not utilitarian and were formed solely to improve the environment. This has a certain irony in the light of modern environmental opposition to dam construction. By the end of the eighteenth century, reservoirs were needed
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