Case study:Restoration of dry riverbeds in Røssåga in conjunction with relocation of power plant outlets

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Location: 66° 4' 18.62" N, 13° 49' 40.10" E

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Project overview

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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

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Project summary

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The regulations in the Rossåga watercourse (Rossågavassdraget) at the end of the 1950s resulted, among other things, that an approximately 650 m long stretch of the river ("Sjøforsløpet") in the upper salmon-bearing part of Rossåga was drastically reduced. Low water velocities and large areas of stagnant water have characterized the riverbank, and the siltation and overgrowth have been considerable. Young fish registrations 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 a rehabilitation of Nedre Røssåga kraftverk (the lower Rossåga power plant) came to plan, 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. During 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, and the framework for this to work was given by the planned operating water supply of 30-85 m3/s.

Monitoring surveys and results

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The new Lower Rossåga power plant was commissioned on July 26, 2016, and the first fish biological studies in the river (juvenile fish registration by electrofishing from a boat) were carried out after about two months of operating the water supply in the "Sjøforsløpet". 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

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The measures ensure water-covered areas when the power plant is “hydro peaking”, and the combination of current indicators, thalweg and groups of boulders contributes to a large part of the river basin having water velocities within the salmonid's preference areas. "Sjøforsløpet" has the potential to supply significant areas with good spawning and breeding areas for salmonids to Rossåga, but it is premature to conclude. According to the water management regulation, the ecological potential for fish has changed from poor to good.

Image gallery

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Catchment and subcatchment Select a catchment/subcatchment Site Edit site Name Røssåga WFD water body codes 155-254-R (EU-ID: NO155-254-R) WFD (national) typology RML4311 WFD water body name Pre-project morphology Reference morphology Desired post project morphology Heavily modified water body No National/international site designation Local/regional site designations Protected species present Yes Invasive species present No Species of interest Salmon and Sea-trout Dominant hydrology Dominant substrate River corridor land use Average bankfull channel width category Average bankfull channel width (m) Average bankfull channel depth category Average bankfull channel depth (m) Mean discharge category 10 - 100 m³/s Mean annual discharge (m3/s) Average channel gradient category Average channel gradient Average unit stream power (W/m2) Project background Edit project background Reach length directly affected (m) 650650 m <br />0.65 km <br />65,000 cm <br /> Project started 2013/01/01 Works started Works completed Project completed 2016/07/26 Total cost category Total cost (k€) 456456 k€ <br />456,000 € <br /> Benefit to cost ratio Funding sources Statkraft AS Cost for project phases Phase cost category cost exact (k€) Lead organisation Contact forename Contact surname Investigation and design Stakeholder engagement and communication Works and works supervision Post-project management and maintenance Monitoring Reasons for river restoration Edit reasons for restoration Mitigation of a pressure Hydropower Hydromorphology Biology Fish: Abundance, Fish: Age structure Physico-chemical Other reasons for the project Measures Edit Measures Structural measures Bank/bed modifications Deflectors Floodplain / River corridor Planform / Channel pattern In-channel placement of boulders to provide flow diversity Other Non-structural measures Management interventions Habitat improvement through water and vegetation management Social measures (incl. engagement) Other Monitoring Hydromorphological quality elements Edit Hydromorphological quality elements Element When monitored Type of monitoring Control site used Result Before measures After measures Qualitative Quantitative Biological quality elements Edit biological quality elements Element When monitored Type of monitoring Control site used Result Before measures After measures Qualitative Quantitative Fish Yes Yes No No No Improvement Physico-chemical quality elements Edit Physico-chemical quality elements Element When monitored Type of monitoring Control site used Result Before measures After measures Qualitative Quantitative Any other monitoring, e.g. social, economic Edit Other responses Element When monitored Type of monitoring Control site used Result Before measures After measures Qualitative Quantitative Monitoring documents Upload monitoring documents Additional documents and videos Upload additional documents Additional links and references Edit links and references Link Description http://uni.no/media/manual upload/LFI 296 4opplag.pdf Measures Handbook for better physical aquatic environment Supplementary Information Edit Supplementary Information