Project: Hafslund Hunderfossen hydropower plant – optimisation of minimum flow, gate manoeuvring and non-intrusive fish counting.
Location: Gudbrandsdalslågen River, Norway
Cost: 70 000 EUR per annum (estimated cost based on energy production lost due to minimal flow)
Objectives: Improve the migration of brown trout (Salmo trutta), a nationally valuable species, past the dam, as well as improving spawning and nursing conditions on the minimum water stretch downstream.
Measures undertaken: Implementing a voluntary new water manoeuvring regime with increased minimum water flows to improve spawning and growth conditions. Attraction floods to stimulate migration, by mimicking naturally occurring patterns. Optimized gate manoeuvring for improved migration, with minimal loss of energy generation. Replaced the fish ladder’s manual trap and handling with an automatic
fish counter, to improve data quality in a non-intrusive manner.
Results: A large increase in wild trout numbers passing the fish ladder. Between the 1960s and the 2000s, the five-year average rarely exceeded 250 trout per year. After implementing the measures, a new record for fish migration was set in 2023 with 1,561 trout passing the da. To compensate for reduced natural recruitment, the authorities imposed a requirement for 15,000 cultivated two-year-old trout to be
released upstream of the dam annually. Due to the success of the measures and increase in wild trout natural recruitment, the obligation to stock fish was removed in 2023.
Challenges:
- The hydropower plant was built in the 1960s and has had a significant, negative impact on the trout population, leading to, public demand for the improvement of conditions for the trout; and
- Retrofitting an old power plant reduces the number of available ZZZ i.e. cost effective solutions at hand.
Success factors:
- Long-term monitoring data and extensive research as a basis for assessment and implementation of the measures;
- Having detailed historic scientific data, knowledge of long-term conditions, and detailed, specific local knowledge and expertise;
- Good post-measure monitoring to reveal the impacts; and
- A holistic approach to habitat bottleneck by understanding of the interconnectedness of the individual challenges hindering fish migration.
Images copyright: Hafslund
