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Future-proofing Sweden's dams

Green advisor

Hydropower currently constitutes the primary source of renewable energy in Sweden.

As Swedish dams begin to show signs of age and climate change leads to rising water levels, Sweden's large hydropower companies are investing billions to improve dam safety. ÅF is working on one major such initiative at the Ajaure hydropower plant, where dam failure could precipitate a national crisis.

One of Sweden's oldest dams

Water has been used to generate electricity in Sweden for more than 100 years. Today, with around 45 percent of the country's electricity coming from hydro-power stations, water is the nation's most important source of renewable electricity.

There are an estimated 1,800 hydropower plants in Sweden and 10,000 dams of varying size and age; 190 of these are large enough for dam failure to lead to serious local, regional or even national consequences. One such dam is at the Ajaure power station on the River Ume in northern Sweden. The dam, owned by Swedish state utility Vattenfall, was commissioned in 1967 and is now one of the oldest in operation in Sweden.

ÅF improves dam safety

At the request of Vattenfall Vattenkraft AB, ÅF has proposed and project engineered measures to improve dam safety at Ajaure. The dam is one of 25 in Sweden with the highest consequence classification. The failure of these dams could have a dramatic impact on their surroundings and society in general, posing the risk of damage to roads, other infrastructure, land and property, disruptions in the electricity grids and, in the worst case scenario, endangering human health and lives. It has been suggested that a dam failure at Ajaure could necessitate the evacuation or relocation of more than 100,000 people. To avert a catastrophe of these dimensions and minimise the risks, dam owners must work constantly on dam safety measures.

Dam safety top of the agenda

Dam safety has slowly but surely moved up the agenda. Many of Sweden's dams date from the 1950s and 60s, and large numbers are in need of renovation and refurbishment. To compound the situation climate change is causing a rise in water levels, increasing the risk of extremely high flows in the rivers. Against this background dam safety expertise would appear to be crucial to secure the long-term production of safe, sustainable energy in Sweden.

Three-phase project

The Ajaure project tasked ÅF not only with improving safety through measures to strengthen and stabilise the embankment dams and the adjacent steep sandbanks that are a typical feature of dams in this part of Sweden, but also with improving drainage. Work commenced in September 2014 and consisted of three phases: initial investigation, production of documentation for the invitation to tender for general contracting services and construction documentation.

As ÅF was commissioned to carry out all three phases of the project, it was necessary to put together a team with a broad spectrum of skills and experience: project engineers and others with a track record of expertise in embankment dams, rock reinforcement, land development, concrete construction and electrical engineering. Their skills were complemented by those of administrators, field engineers in geotechnology and geophysics, instrumentation engineers to work on scanning and surveying, and project leaders – all playing a key role in the project.

Stabilising measures

The first phase focused on geotechnical and geophysical investigations, together with measures to scan and accurately survey the plant. This paved the way for preparing and evaluating various proposals for rebuilding the dam and measures designed to safeguard the drainage and stability of the embankment dams.

Once questions of how best to improve the dam's stability had been resolved, the ÅF team drew up documentation for the invitation to tender and construction documentation: drawings, bills of quantities and technical specifications for how the contracting work should be carried out.

Enduring design

As it has become fairly rare to build new hydropower plants in Sweden, work on modernising and improving the efficiency of existing plants has increased in importance. "Our approach was to design a solution that will work far into the future. Although many power plants are already more than 50 years old, they will be needed for many years to come. Measures to improve dam safety are therefore key to safeguarding the function and physical integrity of a plant if it is to be utilised to its full capacity," says ÅF project leader Johanna Sipola.

The work helps increase safety so that the dam's capacity can continue to be fully utilised for the production of renewable energy. The project has led to solutions for maintaining sustainable energy use and has improved the plant's resource efficiency.