Reservoir safety

Although failure is often portrayed as a catastrophic failure of the dam wall to contain the mass of water held up behind the dam, there a number of significant other causes of failure. These include: • Inadequate spillway capacity resulting in water overtopping the dam wall and cascading down the unprotected wall causing erosion and eventually collapse • The dam inadequately bonded to the underlying rock allowing seepage under the dam wall resulting in erosion and undercutting of the dam. • Insufficient geological surveying pre-construction allowing water to seep out at a location away from the dam and erode a new discharge channel. • Spillway of inadequate construction allowing erosion and degradation of the face of the dam from routine discharges. • Geological subsidence because of poor geology, mining or oil extraction. • Inadequate capacity of discharge pipework because of blocking or corrosion. • Inadequate design for actual rainfall events ==Status by country==

Not all countries have specific legislative control over the safety of dams and reservoirs, and a number of those that do have legislation have it at State or province level only. Some such as the US have both Federal and State legislation. In some, such as Australia legislation is at State level but only some states have relevant legislation. Australia Australia issued "Guidelines on Dam Safety Management in 1994" but specific safety legislation is enacted at State level. New South Wales, Queensland and Victoria have all enacted legislation. In Queensland a concept of a "referable dam" is used to determine whether the legislation applies. A referable dam is defined by a number of criteria including a height exceeding and a volume of . A number of other conditions and caveats apply. The consultation include proposed definitions of "classifiable" dams which would be either "at or above 4 metres in height and 20,000 cubic metres in volume; or less than 4 metres in height, but at or above 30,000 cubic metres in volume". The document acknowledges the special issues facing New Zealand because of the frequency of potentially damaging earthquakes. Reservoirs (Safety Provisions) Act 1930 The Reservoirs (Safety Provisions) Act 1930 (20 & 21 Geo. 5. c. 51) entered the statute book following the coupled failure of two reservoirs in North Wales. Llyn Eigiau and the Coedty Reservoir were two relatively small reservoirs. On a wet November night, Eigiau failed and the out-wash overwhelmed Coedty 2.5 miles downstream. Sixteen villagers in Dolgarrog were killed. The new act applied to reservoirs holding more than and mandated that construction had to be supervised by a qualified engineer and the filling of the reservoir also had to be supervised and certified. It also set out for the first time an inspection requirement that every qualifying reservoir had to be inspected every ten years by an engineer included on a published list or panel of engineers. These panels were compiled by the relevant Secretary of State in liaison with the president of the Institution of Civil Engineers. As a result, Congress enacted Public Law 92–367 in November 1977 which authorized the U.S. Army Corps of Engineers to inventory and inspect non-Federal dams. The Water Resources Act 1986 established a National Dam Safety Review Board although there was not a National Dam Safety Program until 1986. Western Europe The legislation varies on a country by county basis across Europe. Italy and Spain both have a minimum reservoir capacity of . France sets a minimum height of while Spain and Portugal and Austria all set a minimum height of but each with different volume minima. == Notes ==