Project: Statkraft ripping to enhance fish habitat in River Suldalslågen
Location: Rogaland County, Norway
Cost: N/A, but was low-range and included surveillance, administration, machine costs, and monitoring
Dates: 2021-2024
Objectives: Enhance the habitat conditions and improve the natural reproduction levels of Atlantic salmon (Salmo salar) in a river designated as of national importance for salmon. Two large hydropower production schemes upstream have led to reduced flow during summer and less peak floods, causing fouling of the riverbed, in particular affecting shelter and breeding areas for fry. Lack of such habitats is regarded the main bottleneck to the natural reproduction of salmon in the river. One way to improve this is through ripping, which is a mechanical removal of fouling and sediments clogging the riverbed done by excavators. By ripping and improving natural reproduction of salmon it is also a goal to phase out stockings and prevent possible epigenetic effects while at the same time strengthening the salmon population.
Measures undertaken: Conducting a pilot ripping project to garner knowledge and experience. Acquiring the necessary permits, regarding which period to execute the work, gaining permission to reduce water flow to operate the excavators safely, and accessing the suitable river areas. Mapping suitable areas and reaching agreements with landowners on where heavy machinery could access the river. Undertaking a large-scale ripping project along the entire river.
Results: Follow-up investigations of the pilot project in 2019 and ripping performed in 2021 have shown 2-3 times greater densities of fry in the ripped areas as compared to reference stations. No negative effects from the work were observed downstream. Given the general low nutrient content and low temperatures in the river, fouling processes are relatively slow and the positive effects of ripping are expected to last for many years before a need to repeat.
Success factors:
- Performing a pilot project and building upon research and design knowledge;
- Thorough mapping of suitable areas for ripping, avoiding areas with clay and silt which can cause harm downstream and pose security risks to operators, and paying particular attention to spawning areas, cultural heritage sites, and infrastructure;
- Dialogue with landowners, the fishing community, and the municipality;
- Seeking clarity from authorities regarding all necessary permits;
- Timing works to avoid crucial periods to biodiversity, to minimise conflict with stakeholders, and to adapt to variations in unregulated waterflow;
- Utilising local the services of providers; and
- Long-term monitoring.
Images copyright: Statkraft
