03.12.2008
Kollaja plan completed: Ecological values preserved
The final plan on how the Kollaja reservoir and hydropower plant would be implemented is ready. Realisation of the plan would mean improvement in the living conditions of stream fish, and the Natura areas in the catchment area would not be jeopardised.
The starting point of the plan has been that not all the water will be diverted to the reservoir. Instead, some of it will be left to flow through a natural channel. The solution is based on environmental assessments and on dialogue at the local level in particular.
“No rapids would be built and all of the power plant structures would be located far from the river channel. The largest flood peaks would be eliminated and there would no longer be detrimentally low levels of water in Lake Pudasjärvi. Moreover, methane emissions in the Kollaja region could even decrease,” says PVO-Vesivoima’s President Birger Ylisaukko-oja.
There are already five hydropower plants on the River Iijoki, which for most of the year operate at reduced capacity. During the flood season, though, their capacity is insufficient. Under the plan, most of the water would be diverted in the flood season from Lake Pudasjärvi via Lake Aittojrävi to the Kollaja reservoir. This would enable hydropower to be utilised by the Iijoki hydropower plants outside of the flood season. Improved efficiency of the power plant chain would provide Finland with 100 MW of fast regulating power, the need of which will grow with the increase in wind power.
More habitats favourable for fish
A suitable discharge for the rapids has been determined on the basis of a stream fish habitat model. The results of the modelling show that a less turbulent flow is better for the fry of all stream fish. The greatest number of habitats suitable for various age groups are established in rapids and currents when the discharge during the summer is 30 cubic metres per second.
“On account of landscape issues and recreational use, however, we intend to discharge water at a minimum rate of 50 cubic metres per second during the summer. In practice, the discharge during mid-summer will be close to the current rate,” says Ylisaukko-oja.
The prospects of preserving and improving fish stocks have been raised as highly important issues at the local level, and for this reason particular attention has been given to stream fish in the plan.
“Habitat assessments show that at appropriate flows there is an abundance of suitable habitats for grayling, trout and salmon fry of various ages in the rapids in the Kollaja area. There are relatively few spawning grounds, however. This is due to major flood discharges, which have washed away the spawning beds from the rapids. When the major floods are eliminated, spawning beds could be restored in the rapids by gravelling. Slowing flows would also improve the habitats of newly-hatched fry.”
Improved shore use potential
Thanks to the construction of Kollaja, the highest flood peaks in Lake Pudasjärvi would be lowered by nearly a metre and in the River Iijoki below the lake by over a metre.
“The spring floods cover extensive areas in Pudasjärvi and downstream of it along the River Iijoki. This is also reflected in the values of waterfront properties: prices in the built-up area downstream and above the Kollaja area are higher than in the area itself," says Birger Ylisaukko-oja.
During floods of average or greater magnitude, hundreds of cubic metres per second will be discharged in the natural channel because the reservoir will be unable to contain all the water. Floods, therefore, will not be entirely eliminated, but high floods will be eradicated.
After the construction of Kollaja, the lower water levels would rise in Lake Pudasjärvi by nearly a metre. In the natural channel of the River Iijoki and associated Lake Naisjärvi, detrimentally low water levels would be raised by low bottom elevations. It would still be possible to travel on the river. All structures in the river channels would be made in such a way as to enable travel by boat.
Preservation of Pudasjärvi’s Natura areas
There are three Natura areas in the project's catchment area. Of these, two will be excluded from the catchment area by means of a dam. Preservation of the third, the Pudasjärvi Natura area, will be protected by mimicking the processes of nature.
There are so-called flood meadows on the shores of Lake Pudasjärvi. Preservation of these requires that the shores both sometimes flood and dry out. In the Kollaja plan, this is ensured by regulating the water level of the lake in accordance with the processes of nature. The shores will flood and the flood meadows will be dry for nearly as long as they are currently," explains Birger Ylisaukko-oja.
Further information
Birger Ylisaukko-oja
President
PVO-Vesivoima Oy
tel. +358 50 3133 403
birger.ylisaukko-oja [at] pvo.fi