Guardians of hydropower
Norway’s rockfill dams hold billions of cubic metres of valuable water in place high in the mountains. Behind every dam stands an extensive safety system and decades of engineering expertise that have been critical to Norwegian energy production.
Storvassdammen in Bykle, Agder, is Norway’s largest rockfill dam and a key component of Statkraft’s hydropower system. It is one of many Norwegian facilities where NGI experts have contributed to dam safety, design, and risk assessments over several decades. ( Photo: Martin NH / Wikimedia Commons.)
When Norwegians think about their electricity supply, many picture power lines and wall sockets. Few think about the dams themselves: massive structures of rock and earth that hold back enormous volumes of water. They form the foundation of the country’s energy security – but many of them are now ageing.
“Most of Norway’s large rockfill dams were built from the 1950s onwards, especially during the 1960s, 70s, and 80s. That creates a significant need for renewed safety assessments, maintenance, and rehabilitation,” says Arnkjell Løkke, Head of Section Dam Safety at NGI.
A collaboration that shaped Norway
Statkraft is by far Norway’s largest dam owner, operating around 500 dams in the country alone, in addition to a substantial international portfolio. The company manages roughly half of Norway’s total reservoir capacity.
NGI’s role in this story reaches back to the institute’s early years. During the 1960s and 70s, dam-related work accounted for the majority of the institute’s revenue. Many of NGI’s most prominent researchers built their reputations through this work.
“NGI has designed and supervised construction for roughly two-thirds of all large rockfill dams in Norway. That is a legacy we manage with both pride and a strong sense of responsibility,” says Løkke.
Norwegian nature enables unique solutions
While many countries traditionally built concrete dams or earthfill dams, Norway developed its own approach. Many dams sit high in the mountains, where roads and logistics pose major challenges. Engineers, therefore, relied on materials already available in the landscape: glacial moraine deposits.
“When the glaciers retreated after the last Ice Age, they left behind well‑graded deposits – mixtures of rock, gravel, sand, and silt. When you compact this material, it becomes highly watertight. That makes it ideal as the sealing core in rockfill dams,” Løkke explains.
Norway also has strong bedrock and high‑quality stone, and tunnel excavation for hydropower plants often produces large volumes of surplus rock. The result is rockfill dams with a central moraine core – a dam type that has become a Norwegian hallmark and delivered robust, cost‑effective solutions.
Norwegian rockfill dams are often built with an impermeable moraine core surrounded by rockfill made from locally sourced materials. For several decades, NGI has contributed to the design, analysis and safety assessment of such dam structures in Norway’s demanding mountain terrain.
From safety factors to risk analysis
Norway’s dam safety regulations are largely deterministic, based on detailed requirements for safety factors, material sizes, and structural design. But reality is more complex than what regulations alone can capture.
“The regulations do not sufficiently account for variations between dams and site‑specific conditions. How a dam has behaved over time, local hydrology, the geology at the dam site – all of this influences its actual safety,” says Løkke.
Internationally, a more risk‑based approach has therefore emerged, known as risk‑informed decision‑making. Instead of only asking whether a dam meets a specific safety factor, engineers ask: what is the actual probability of failure, and what would the consequences be?
NGI uses analytical tools such as event‑tree analysis and probabilistic Monte Carlo simulations to map the risks associated with a range of possible failure mechanisms. What happens during extreme floods? During earthquakes? Or during slow internal erosion over decades?
“When we complete these analyses, we are much better equipped to identify concrete risk‑reducing measures. You gain a comprehensive picture that allows you to prioritise actions where each invested krone delivers the greatest risk reduction,” says Løkke.
Statkraft has adopted NGI’s risk‑based methodology more extensively than any other Norwegian dam owner. In recent years, NGI has carried out risk analyses for more than a dozen dams for the company.
“We always learn something new about the dams. These analyses go beyond standardised assessments and systematically examine the entire picture of what can go wrong, how it might happen, and which factors influence the probability,” says Løkke.
Climate change raises the stakes
Future challenges do not only involve ageing infrastructure. Climate change is bringing more intense rainfall and new flood patterns. Storms such as “Dagmar” in 2011 and “Hans” in 2023 have revealed vulnerabilities in Norway’s river systems.
Statkraft plans to invest NOK 27 billion in more than 200 hydropower projects before 2030. A significant share of this investment will go toward rehabilitating dams such as Kjela, Nesjødammen, and Bjølsegrø to meet both present and future requirements.
The overarching goal is simple: it should be just as safe to live downstream from an old dam as from a new one.
“For NGI, this means continuing the work that began more than 60 years ago: ensuring that the foundation of Norwegian hydropower remains secure for generations to come,” Løkke concludes.
Arnkjell Løkke
Head of Section Dam Safety Dam Safety and Hydrodynamics arnkjell.lokke@ngi.no+47 480 48 843