Author(s): J. Aaltonen; M. Huokuna; K. Severinkangas; M. Talvensaari
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Abstract: Frazil ice and hanging dam formation in rivers may cause harm for hydropower production and the environment. This is the case especially in regulated rivers in which winter discharges are higher than the natural discharges. Kemijoki River is the longest river in Finland and its basin covers a vast area of Northern Finland. The river is harnessed for hydropower production with 16 separate power plants, mostly owned by Kemijoki Oy company. This article focuses on Ossauskoski power plant. Its capacity is 93 MW and annual energy output on 2006 was 415 GWh. The present design flow is 750 m3/s and an increase of 330 m3/s is planned resulting 31 MW increase of capacity. The reach below the power plant has however encountered frazil ice problems because of open water areas and hanging dams. A greater discharge will probably change ice conditions downstream of the power plant. To study the river ice phenomena, an extensive data survey program downstream of the Ossauskoski power plant was conducted 2005-2007 by Kemijoki Oy. In addition to standard weather observations and hydrological statistics from the power plant, several survey flights were flown during the winter 2006-2007. This produced a series of aerial photographs pointing out some critical open water areas. A ground penetrating radar and manual survey were used to gather data on the thickness of solid ice cover, snow and frazil slush. The river geometry was obtained with AquaticSonar Swathe Surveyor equipment. The JJT-model was used by Finnish Environment Institute to study the effect of hanging dams on water levels. Also an effect of modified river geometry was studied in the calculations. A description of the ice observations and the model simulation results downstream of Ossauskoski power plant is given in this paper.
Year: 2008