Author(s): Randi Pytte Asvall
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Abstract: The construction of the Alta power station has influenced water temperature and ice conditions downstream of the power plant, and thus imposed changes on the fish in the river. The work presented here focuses on a ca 5 km stretch of the river from the power plant outlet to the Savco Lake. This stretch was covered with ice before the regulation, but only in very severe winter periods some ice may form here after the regulation. This is claimed to be the cause for a reduction in the fish population. There is an upper and a lower intake in the reservoir. By using the colder upper intake, ice formation will increase and an ice cover form in certain areas when the air temperature is sufficiently low. The upper intake can, however, only be used a limited time, depending on the discharge. When changing to the lower intake the temperature will increase and the ice cover melt. In order to utilise the reservoir in an optimum way the discharge should be increased in late winter. If this can be done will depend on its influence on ice conditions further downstream, which at this time means a heavy ice cover. The study will continue this coming winter to establish how the downstream ice cover will react to an increased discharge late in the winter. This will also require a modification of the rules of regulation. The results from this study will, combined with the results of the fish studies, be very important for the determining of the future management regime of the power plant.
Year: 2002