The most significant environmental impacts of hydropower are caused by construction of power plants and dams, and the dredging of riverbeds. Hydropower and the related regulation of water levels can alter river systems and shorelines as well as the routes and natural flow rates of rivers. Regulating the level of water in lakes and discharges of rivers can affect the aquatic habitat, other uses of the water systems and, above all, fish populations. The migration of fish to spawning areas can be hindered, making reproduction difficult. The impacts on fish populations can be reduced and
offset by restocking fish and through projects that improve the natural reproduction of fish as well as through catch-and-transport systems.
Regulation of water systems
Because of hydropower production, the flow rate of water in water systems is regulated both on an annual level and in the short term. With annual regulation, flood waters are stored and the bigger releases of water are done in the winter season, when more electricity is consumed. In short-term regulation, the releases are adjusted during the day or week to correspond with electricity demand.
The permit conditions for our hydropower plants and lake regulation define the limits for surface water levels and flow-rate variations in the water systems. The permits also define our obligations to prevent and to compensate for environmental impacts. As a result of careful operation, there were no permit non-compliances at our hydropower plants in Finland in 2014. In Sweden, we reported one
non-compliance. A production disruption at our Åsen hydropower plant resulted in the rapid rise of the water level downstream from the power plant. After the incident, we decided to start the control system renewal project in 2015, a couple of years earlier than initially planned.
In Finland, we worked with environmental authorities to study the possibilities to develop the regulation of the Oulujoki water system to mitigate future flood situations. As a result of the study, we took into use a maximum water level recommendation in the regulating of the Oulujärvi lake; the recommendation will benefit recreational use of the lake and improve flood protection in summers with heavy rainfall.