Flying the flag for safer dams15 June 2001
Hydrological upgrading, dam safety guidelines, and the establishment of a dam safety authority are three important steps towards complete dam safety in Sweden. Report by Olle Mill and Claes-Olof Brandesten
Hydro power is the primary function of Swedish dams, although the structures also play an important role in navigation (channels and locks) and the mining industry (tailings dams). In addition, an abundance of old, disused floating dams can be found in Swedish rivers.
Swedish dam owners hold full responsibility for their dams. A general set of rules and regulations for activities which may have environmental consequences are enshrined in the Swedish Environmental Code, which also governs water rights and dam safety. Nevertheless, the owners themselves, in collaboration with their trade organisation Swedenergy, provide their own guidelines.
The dam owner has a far-reaching responsibility for his actions. He must pursue the necessary knowledge and implement precautions to protect human health and the environment from damage. This may mean investing in the latest technology and involves meticulous planning and monitoring activities. The safety aspects of planned dams or modifications to existing dams are scrutinised in court.
There are 21 County Administrative Boards in Sweden, which are assigned to the supervisory authorities on dam safety. Their supervision focuses on controlling routines for self-regulation. The extent of this control should be relative to potential consequences should the dam breach. Another important objective of the authorities is to attain transparency for the public.
Svenska Kraftnät is a state-owned utility which operates the Swedish national grid. In 1998 Svenska Kraftnät was authorised to undertake key central assignments within the dam safety arena. The government has also authorised Svenska Kraftnät to develop and implement a protocol for Country Administrative Boards to follow for the supervision, follow-up and reporting of dam safety. For this reason, Svenska Kraftnät has appointed an advisory committee on dam safety. This comprises representatives from all the authorities and organisations concerned, and has 12 members and two deputies. The chairman is a lawyer who has gained experience in dam safety, with the members representing the power industry, the mining industry, the Country Administrative Boards, local authorities, the Swedish Meteorological and Hydrological Institute, the Swedish Rescue Services Agency, the judiciary and Svenska Kraftnät.
Over the past 15 years dam owners in the hydro power industry have taken several initiatives with regard to dam safety. An important step came in 1994 with the decision to work out general guidelines for dam safety. The Swedish Power Association, now Swedenergy, presented these guidelines in 1997, which were named RIDAS.
The main document of RIDAS contains general dam safety guidelines. Coupled to this are various standards which define minimum dam safety. The individual dam owner may apply additional requirements. The guidelines are not enforced by law but each dam project has to be scrutinised formally by the Water Rights Courts in the court approval process. RIDAS states that dam owners shall:
• Design, construct, operate and maintain their dams so that the risk of the serious consequences of dam breach will be eliminated as much as possible; and the risk of damage to dams and operations disturbances will be kept at the lowest reasonable level.
• Use action plans to minimise the consequences in case of breach or damage to a dam.
• Provide for good dam safety by means of quality assurance.
• Develop dam safety from a long term perspective.
RIDAS states that dams are to be categorised according to the potential consequences of dam failure. The classification presently involves classes 1, 2 and 3, where class 1 represents the worst consequences. The classification applies the concept of marginal damage, that is, the difference between the damages caused by the flood with and without a dam breach.
The Guidelines for Design Flood Determination have been incorporated into the RIDAS framework as a standards and requirements document. For high hazard dams, the guidelines propose a deterministic approach similar to the probable maximum flood (PMF) procedure, with the emphasis on critical timing of flood generating factors. The precipitation input is not based on estimates on probable maximum precipitation (PMP), but rather on an evaluation of observed maximum rainfalls. For a low hazard dam the 100-year flood is used as the design flood.