Case study:Restoration of dry riverbeds in Røssåga in conjunction with relocation of power plant outlets
Project overview
| Status | Complete |
|---|---|
| Project web site | |
| Themes | Environmental flows and water resources, Fisheries, Habitat and biodiversity, Hydropower, Hydromorphology, Monitoring |
| Country | Norway |
| Main contact forename | Bjørn |
| Main contact surname | Grane |
| Main contact user ID | |
| Contact organisation | Statkraft AS |
| Contact organisation web site | http://www.statkraft.no |
| Partner organisations | Ferskvannsbiologen AS, The Norwegian Water Resources and Energy Directorate (NVE), The Norwegian Environmental Agency (Miljødirektoratet) |
| Parent multi-site project | |
| This is a parent project encompassing the following projects |
No |
Project summary
Flow regulation in the Rossåga watercourse (Rossågavassdraget) at the end of the 1950s resulted in, among other things, drastically reduced flow levels in an approximately 650 m long stretch of the river ("Sjøforsløpet") in the upper salmon-bearing part of Røssåga. There were low water velocities and large areas of stagnant water, while siltation and macrophyte overgrowth were considerable. Juvenile and spawning fish counts showed that the river stretch was of no significance for fish production in the river (O. Kanstad-Hanssen, pers. Medd. Lamberg et al. 2010).
When the need for rehabilitation of Nedre Røssåga kraftverk (the lower Rossåga power plant) came about, Statkraft decided to build a new power plant (Nye Nedre Rossåga kraftverk). This power plant was planned with an outlet under "Sjøforsen", i.e. at the upper part of the 650 m long, partially dry stretch of the river. A test of discharge water from the intake reservoir further up the watercourse showed that the planned maximum operating water supply from the new power plant (85-105 m3/s) would put large forest areas under water. It was therefore decided that these forest areas should be cleared and that a plan for the restoration of the riverbed be drawn up. The aim of the restoration was to optimize conditions for juvenile fish, given the planned operating discharge of 30-85 m3/s.
Monitoring surveys and results
The new Lower Rossåga power plant was commissioned on July 26, 2016, and the first fish studies in the river (juvenile fish recording by electrofishing from a boat) were carried out after about two months of operating the new water supply in the "Sjøforsløpet". A spawning fish count was carried out in mid-October. The juvenile fish records showed that juvenile salmon had already taken up the new river stretch, and the relative density was almost as high as in the best production areas further down the river. The spawning fish count showed that well over 50 salmon, or approx. 30% of all salmon observed in Rossåga stayed in the "Sjøforsløpet" during the spawning season.
Lessons learnt
The measures ensure water-covered areas when the power plant is “hydro peaking”, and the combination of the thalweg enhancement and the placing of groups of boulders, contributes to a large part of the river basin having water velocities within the salmonid's preferences. "Sjøforsløpet" has the potential to add significant areas of good salmonid spawning and breeding areas to Rossåga, but time is needed to judge the success of the measures. According to the water management regulations, the ecological potential for fish has changed from poor to good.
Image gallery
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Catchment and subcatchment
Site
Project background
Cost for project phases
Reasons for river restoration
Measures
MonitoringHydromorphological quality elements
Biological quality elements
Physico-chemical quality elements
Any other monitoring, e.g. social, economic
Monitoring documents
Additional documents and videos
Additional links and references
Supplementary InformationEdit Supplementary Information
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