Ämmä Hydropower Plant
Pälli was the third power plant built by Oulujoki Power Company in River Oulujoki. This facility, designed by Aarne Ervi, is located in the municipality of Muhos. Pälli hydropower plant is built in a section of River Oulujoki where the serene Paskonkoski turns into an effervescent, 300 metres long, Pälli rapids. Pälli showcased new architectural features and construction techniques and was important for the development of the construction industry throughout the country.
Construction started early in 1950, when the work at Pyhäkoski was ending. In addition to the power plant, a small number of administrative and service buildings were built on the site. An average of 500 men worked on the site and 500,000 square metres of earth was excavated and removed. Work progressed rapidly because the biggest shortages were over, and more machines were available. Also, the workforce was more experienced, and they could utilize the practices and teachings of past efforts.
The power house was built in the southern river bank and the 300 metres long tailrace was excavated in the river flowing downstream. Upstream, the river banks were elevated with embankments, so that when the water was impounded to the reservoir, the total head of the power plant was 14 metres. The water discharging from the penstocks was directed into the new channel and the spillway gates open up to the old river bed. The two channels were separated by a concrete wall. Pälli was fully operational in 1954 and had a capacity of 51 megawatts.
Pälli signifies an evolution in Ervi’s power plant design. After certain static monumentality and classicist undertones of Pyhäkoski and Jylhämä, in Pälli, Ervi took a step towards the principles, construction methods and aesthetic aspirations of Modernism. The biggest shift was that Ervi moved away from brick façades and started to use precast, insulated panels, that were assembled on-site. Modernism is also the distinctive feature in the overall appearance of Pälli’s power house. This can be seen in the disposition of the masses, the butterfly roof, the large window surfaces and the curtain-like façades.
Today forests cover any sign of the construction work, and the river runs quietly through the facility. The riverbanks are shallow, and the wide reservoir dominates the scenery upstream from the power house. It is noteworthy, that the whole Oulujoki project was a significant testing ground for Finnish concrete construction. The concrete laboratory in Pyhäkoski produced results that benefited the whole country. With the use of precast panels in these power plants, Ervi quickly became the frontrunner in the use of prefabricated concrete in Finland.
Text: Samuli Paitsola