Difference between revisions of "Case study:Restoration of dry riverbeds in Røssåga in conjunction with relocation of power plant outlets"

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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.
 
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.
 
|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 learn=The measures ensure water-covered areas when the power plant is “hydro peaking”, and the combination of thalweg and groups of boulders, contribute 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.
+
|Lessons learn=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.
 
|Project title=Restoration of dry riverbeds in Røssåga in conjunction with relocation of power plant outlets
 
|Project title=Restoration of dry riverbeds in Røssåga in conjunction with relocation of power plant outlets
 
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Location: 66° 4' 19", 13° 49' 40"
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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
Project picture

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.


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Catchment and subcatchment



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

Reach length directly affected (m) 650
650 m
0.65 km
65,000 cm
Project started 2013/01/01
Works started
Works completed
Project completed 2016/07/26
Total cost category
Total cost (k€) 456
456 k€
456,000 €
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

Mitigation of a pressure Hydropower
Hydromorphology Quantity & dynamics of flow, Freshwater flow regime
Biology Fish
Physico-chemical
Other reasons for the project


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

Element When monitored Type of monitoring Control site used Result
Before measures After measures Qualitative Quantitative

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

Element When monitored Type of monitoring Control site used Result
Before measures After measures Qualitative Quantitative

Any other monitoring, e.g. social, economic

Element When monitored Type of monitoring Control site used Result
Before measures After measures Qualitative Quantitative


Monitoring documents



Additional documents and videos


Additional links and references

Link Description
http://uni.no/media/manual upload/LFI 296 4opplag.pdf Measures Handbook for better physical aquatic environment

Supplementary Information

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