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General information


General facts of the Kymijoki drainage system

The drainage basin of the Kymijoki covers 37 107 square kilometres which is 11 percent of the whole area of Finland and the lake depth percentage is 19,7.

The Northern parts of the basin are located in Kinnula and Pihtipudas in Central Finland and Keitele and Pielavesi in the province of Savo.

In the north the annual rainfall average is 570 mm and in the southern parts around  610 mm.

The highest points of the catchment area are situated over 200 metres above the sea level (Laajavuori, Jyväskylä, 228 m). Lake Ylä Kintaudenjärvi in Petäjävesi lies 154 metres above the sea level. The average height of the area is 120 metres above the sea level.

The Kymijoki has its origin in Kalkkinen, lake Päijänne. The distance from there to the sea is 203 kilometres and the drop is 78,5 metres.

From Kalkkinen to lake Pyhäjärvi in Iitti the river flows in many branches. The waters from Mäntyharju route flow to the northeastern end of lake Pyhäjärvi. The catchment area of this route is 5470 km2 and the lake depth percentage 22,4%. The waters from lake Kivijärvi, drainage basin 1205 km2, lake depth 12,10%, make the so-called Valkeala route which flows into the Kymijoki near Voikkaa. From there to the Baltic Sea the river flows almost without any lakes and significant branches. Before reaching the sea the river is divided into two main branches near Pernoo. The eastern Pernoo branch descends to the sea in Kotka and the western Hirvikoski branch flows between Pyhtää and Ruotsinpyhtää into Ahvenkoski bay.

The eastern branch splits into Korkeakoski and Langinkoski branches. These two main branches still divide into altogether five branches before descending to the sea. The automatic sluice at Hirvivuolle controls the water distribution between the main streams.

At Pernoo the water flow in the Kymijoki is approximately 238 m3/s. The extreme values: maximum 816 m3/s (1899) and minimum 65 m3/s (1942).


Hydroelectric power

Excluding the minor branches of the river there are totally 13 hydroelectric power plants in the Kymijoki. The first of them were built at the end of the 19th century. The Ahvionkoski rapids, some 4,5 km before the branching spot, are the most powerful free-flowing waters in the Kymijoki. The fall there is 1,90 m after the river clearing made in 1933. In the Pernoo rapids of the eastern branch the fall is normally 4,0 m.


Water regulation

The flow of the Kymijoki is regulated from Lake Päijänne. The aim is to increase the economic benefits of the power plants and on the other hand to prevent floods. The flow does not change during one day because Kymijoki is not short-term regulated like many other big rivers.


Clearing the river Kymijoki

In 1820-1832 a lot of clearing work was done in the upper parts of the Kymijoki to prevent floods. The water level of lake Pyhäjärvi was then lowered by 1,5 metres and large land areas became arable. The farmers living along the river made an initiative to clear the rapids at Susikoski in 1826. Some plans were made but they never lead anywhere. In 1925 professor P. Kokkonen was given the task to evaluate the benefits of clearing the river. The clearing was started in Laajakoski in 1929 and was later continued in the main branch at Susikoski, Ahvionkoski and Kultaankoski.

The western branch was also cleared here and there. This meant approximately 6840 hectares of new soil for farming and other purposes.

The river clearing caused some problems for fishing industry. Therefore parts of the cleared rapids are planned to be reconstructed to spawning waters for salmon.


Log driving in the Kymijoki

Logs were floated along the river Kymijoki for more than two hundred years. The sawmill of Korkeakoski on the eastern branch of Kymijoki was in use before the Great Northern War and was renovated in the 1720's. At the end of the 18th century there were many sawmills by the river Kymijoki and log driving was very active. The government tightened the rules of log driving at the end of 19th century. In 1880 they confirmed the first regulation for log driving and the floating equipment owned by the government was alienated to Kymi floating company established in 1873. The company was closed down in 1907. The timber owners established a new association called Kymijoki floating association. The rules of the association were confirmed in 1945. The association is still working. In 2002 the log driving came to an end on the upper waters of the river in Kuusankoski and below Kuusankoski in 1966.


The quality of water

The quality of water of the lower parts of the Kymijoki is monitored by the follow-up program of national authorities. During the last decades the quality of water has improved a lot due to the decrease of industrial waste. From the late 1980's the biologically oxygen consuming waste has gone down to one hundredth of what it was. The amount of solid waste has reduced to one tenth and chemical oxygen consumption to one fifth. The water of the Kymijoki is slightly coloured by humus but the quality is high.