Ämmä Hydropower Plant
Utanen was the last power plant built in River Oulujoki. It is located in Utajärvi municipality and was constructed by Oulujoki Power Company. The plant was designed by architect Aarne Ervi.
The specialty of Utanen was its 12 kilometres long tailrace that was excavated through Lake Utajärvi all the way to Lake Sotkajärvi that was located ten kilometres downstream. Earthworks for the tailrace started in the spring of 1954. Excavations for the canal were extensive. Over 7 million cubic metres of rock and earth had to be removed. Nine diggers, more than ten bulldozers and 30 heavy dump trucks were assigned to the task. It turned out to be the largest earthmoving job in Finnish history by that time. When finished, the channel altered the landscape substantially.
The power house was built with an in-situ concrete frame. Façades were constructed out of precast panels and sheet metal. Tailrace was finished by the end of the 1956 and the first set of machinery was connected to the power grid on 19 November. Because of the long tailrace, landscaping went on for decades. Electricity production started in fall 1957. Utanen has a maximum capacity of 58 megawatts, which makes it the third largest power plant in the Oulujoki.
Utanen was the last power plant built in River Oulujoki, thus completing the power plant chain in the river. Utanen, again, represents a new phase in Ervi’s design with evermore streamlined and “machine-like” aesthetics. The weighty monumentality and firm brickworks of his early power plants seem rather old-fashioned when compared to the curtain walls and aerial horizontality of Utanen.
In Utanen Ervi fitted only what was imperative inside the actual frame and, for example, placed the control gates on a platform outside the building’s envelope.
The power house of Utanen is a hall-like structure and its light envelope encloses all the spaces needed in the production process. The architecture of the building is easy to read. The diameters of the reinforced concrete frame, the measured structural details, the high-quality fair-faced raw concrete, that elegantly carries the lattice where the façade panels and the steel grid-supported roof are attached.
The architecture of the building is underlined by a tension between the simple but sturdy frame and the gentle details and materials. The mass of the power house consists of four monoliths casted in the riverbed, one for each turbine and one for the maintenance area of the machine hall.
Natural light occupies the machine hall while the glass surface constantly reflects its surroundings. A large steel door stands as a continuum to the glass curtain.
After Utanen was finished in 1957, the main channel of River Oulujoki was completely harnessed to electricity production.
Text: Samuli Paitsola