The drainage area of the Jämsänjoki river is about 1,470 km². The river is 14 km long and its average depth is 2 metres. The river flow rate is very variable. In 1920, the water quantity was estimated to vary between 3 - 90 cubic metres per second. In 1962 - 1990, the mean discharge was 13.60 cubic metres per second. The height difference between the surfaces of lake Kankarisvesi and lake Päijänne is about 20 metres today. Most of the height of fall, about 14 metres, is in Patalankoski rapids. The fall of Rekolankoski rapids is about 5.5 metres. In 1911 - before the power plant was built - the length of Rekolankoski rapids was 90 m and the height differential 6.04 m.


Mills were the first to use the water power provided by the rapids. The earliest mill type was a Norse wheel mill, where a stream of water from the rapids was directed through a tube onto wings at the foot of a vertical axle. A more developed mill type was the wheel mill, of which there were several at Jämsänkoski. A wheel mill had a water wheel made wholly of wood or with iron reinforcements, with power transmitted from the water wheel via a horizontal axle to the millstones. Up to the 1800s, the water wheel was the most important source of mechanical energy. It remained in use for a long time, not only in mills but also at water-powered sawmills and ironworks.

The Jämsänkoski sawmill also obtained its power from a water wheel. Because the sawmill was only used in springtime when there was plentiful water, there was usually sufficient water available. The water was directed along a wooden sluice to the water wheel. A crank at the end of the water wheel axle moved, via a driving rod, frames into which the saw blades were inserted.


The first water turbines were adopted in Finland in the 1840s. Along with turbines, outputs improved, and through power axles energy could be transferred up to a distance of 100 metres from the power engine. The heyday of mechanical power transmission lasted until the turn of the century, and only began to wane when electric power became common in the first few decades of the 1900s.

When the Jämsänkoski pulp mill started up in 1888, the factory power source was a 150 horsepower turbine which was located next to the updated sawmill in a separate turbine room. The motive power was directed with the aid of a main shaft to the machinery in the sawmill and the factory. An alarm cord ran from the largest machines into the turbine room. In cases of emergency, the machine operator pulled the cord, making a bell ring in the turbine room, and the turbine operator shut down the turbine. Then all the other machines in the factory stopped, too.

At the turn of the 1900s, the Jämsänkoski mills still relied on water for their power supplies. After fire destroyed the old mill, the new pulp mill started up in 1898. The turbine room was placed at the end with the bleaching section cooking room. The bleaching, sifting and pulp container sections each had their own turbines. The fourth turbine worked a direct-current generator, which produced the power required outside the factory. A fifth turbine powered the acid-making and chipping sections via a long power transmission shaft.

The chemical pulp mill, two paper mills and two groundwood plants had 12 turbines in all at the end of the 1910s. They were positioned around the factory premises and had a combined output of about 2,000 horsepower. Regulation of water power was difficult, as the flow of the river Jämsänjoki fluctuated a great deal. Lack of water was a recurring problem, and sometimes the pulp mill had to pause several times during a shift in order to wait for the water to rise.

For the purpose of regulating the water, a dam had been built at the top of Hovilanhaara tributary at the time of the old factory. From the Verstas pond formed by the dam, water was first led into a wooden sluice and thence along a pipe made from the old factory boilers to the pulp mill turbines. The structure was in use until 1936, when the last pulp mill turbine was stopped.


Finnish groundwood plants worked on water turbines from the 1860s. Alongside pulp grinders developed the turbines that powered them; both were often manufactured in Finland. Usually, each pulp grinder was worked by its own turbine, but the same turbine could also have several grinders connected to it.

Ab Jämsänkoski built two grinding mills in 1898 -1899. The Rekolankoski groundwood plant was equipped with four 100 - 300 horsepower turbines. The 350 hp Francis turbines and grinding machine at Patalankoski grinding mill was replaced with 600 hp machines in 1926. The groundwood plants ceased operation in the years 1928 and 1936. Electricity-generating hydropower plants were built at both rapids.

Link:  Koskesta Voimaa