Anundsjö test case
| Fact box: Anundsjö | |
|---|---|
| Country | Sweden |
| River | Mo (Moälven) |
| Operator | Statkraft |
| Capacity | 5 MW |
| Head | 61 m |
| Inter-annual discharge | 10 m3/s |
| Turbine(s) | 1 Francis turbine |
| Detailed report | Click for pdf |
Contents
Introduction
The Test Case is located on the small river Mo (Moälven) in the northern part of Sweden. The hydrology of the river Mo is typical for north of Sweden, with a lot of snow in the winter, a spring flood when the snow melts, low flows during the summer and often some higher flows and an autumn flood before the next winter starts with snow accumulation.
The catchment area is 820 km2. Mean annual precipitation for the whole catchment area is approx. 727 mm per year, with a mean flow at the outlet into the Baltic Sea of 27.9 m3/s, and 10.2 m3/s at the HPP Anundsjø.
About the hydropower plant
The HPP is impounding a small reservoir, releasing the water through the turbines and a tunnel back into the river about 4km further downstream. It has an installed capacity of 5 MW. The mean annual discharge is 10 m3/s with a low flow of 2.21 m3/s.
Layout
A small reservoir of 0.5 ha is located upstream of the HPP Anundsjø. Further upstream are important areas of spawning for salmon and trout, which are not directly affected by the HPP. During the winter, a larger reservoir further upstream provides water to the HPP. The bypassed river reach between the dam and the outlet of the power plant is 4 km. This river reach receives an environmental flow release.
The Operator: Statkraft
Statkraft is a leading company in hydropower internationally and Europe’s largest generator of renewable energy. The Group produces hydropower, wind power, solar power, gas-fired power and supplies district heating. Statkraft is a global company in energy market operations. It is Norway's largest and the Nordic region's second largest power producer. Read more.
Pressures on the water body's ecosystem
Due to two dams downstream of the HPP, for which the fish passage efficiency is unknown, the continuity is moderate. Most parts of the rapids further downstream have been modified for timber floating, with only a few being restored. Furthermore, the hydrology directly downstream of the power plant outlet is affected by short-time regulation. The water level in the small reservoir may fluctuate by up to 0.5 m. A recurring problem in Sweden is pollution through Mercury, which is released from the ground through logging activities, causing a moderate pollution of the water body.
Test case topics
Fish population
The fish species that can be found in the Mo are: salmon, sea trout, grayling, pike, perch, brown trout and crayfish. During the summer from July to October, the power plant is shut down twice a week for one hour, releasing the discharge through the gates in order attract salmon into the residual area. However, after one hour this flow has still not reached downstream to the outlet of the power plant.
Downstream migration
To facilitate better downstream fish migration, a floating guidance device is attached right next to the intake, leading the fish into a smolt trap and then out to the downstream side of the dam. The license of 2012 states that this device shall be placed out 1 May every year and water released in the smolt trap shall be 0.25 m3/s. This solution was evaluated together with the authorities after the first year, 2016, and the conclusion was that it did not work as intended. In 2017 a new solution with fishing nets was tested, leading the smolts to the fishway instead. The water released to the smolt trap was then instead released to go through the fishway. The starting time for the installation fot he guidance device is moved to a flexible time due to when the reservoir is ice-free.
Upstream migration
The upstream migrating fish encounter the outlet of the power plant, located 4 km downstream the fishway. The attraction flow is represented by the minimum flow, 0.8 m3/s between the 15th of July and the 5th of October; 0.25 m3/s the rest of the year. At the end of the 4 km long residual area the upstream migration continues in the nature-like fishway. At the end of the nature-like fishway, there is a short concrete fish ladder for the final ascent into the reservoir.
E-flow
In the new license from 2012, the requirements are release of water in the fishway between the 15th of July and the 5th of October of 0.8 m3/s and the rest of the year 0.25 m3/s. During the same period one hour every Tuesday and Thursday, the power plant must shut down and release the full discharge through the gates in order to attract salmon up in the residual area.
Research objectives and tasks
The overall question at the HPP Anundsjø is how FIThydro can improve the situation for fish by different measures and means around the HPP. This includes the situation for the salmon smolt, which are mainly arriving at the HPP after being released in the upstream area. It also includes the situation of juvenile fish of different species as well as the possibility for salmon to pass on the way to spawn and back (influenced also by the HPP located downstream of Anundsjø and influencing especially the number of migrating fish).
Research tasks
The research tasks and field studies conducted at Anundsjö are:
- Bathymetry and velocity in reservoir
- Bathymetry of the fishway and the entrance with GPS and drone flights for Structure for Motion (SfM)
- Bathymetry, flow velocity data and drone flights for SfM and habitat in bypassed river reach
Results
Gallery
Reservoir at the Anundsjö hydropower plant.
Aerial view of the Anundsjö upstream migration fishway.
Downstream view of the Anundsjö dam spillway
Intake to the Anundsjö fishway.
Layout of the Anundsjö hydropower plant and surrounding area.
Floating downstream fish migration device at Anundsjö hydropower plant.
