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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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

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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

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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 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 Røssåga mellom samløp Leirelva og Sjøforsen 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 Artificially regulated Dominant substrate Boulders, Cobble River corridor land use Coniferous woodland (semi natural), Urban 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 Quantity & dynamics of flow, Freshwater flow regime Biology Fish Physico-chemical Other reasons for the project Measures Edit Measures Structural measures Bank/bed modifications Deflectors, Creation of low flow channel, Creation of fish spawn nursing places, Introduction of spawning gravels Floodplain / River corridor Construction of flood wall 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, Flow 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 Yes Yes 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