Help for fish in regulated rivers

The problem of young fish being stranded during hydro-peaking periods can be significantly -reduced.

By Christina B. Claussen

If electricity generating companies can avoid lowering the water level of their rivers by more than 13 cm in the course of an hour, the problem of fish stranding can be reduced significantly. This is one of the conclusions of the research report “Consequences of hydro peaking on ecosystems in running water”, by SINTEF Energy Research. In this project, the scientists looked at what could be done to improve the conditions that affect fish living in regulated rivers.
Hydro peaking means that electricity generators run their turbines at full power when electricity prices are highest, i.e. when we get up in the morning and during the early evening.
– When power production is at a peak, river levels are also high. When generating rates fall, the water level sinks and small fish may find themselves on dry land, says research scientist Atle Harby at SINTEF Energy Research.

The project has also revealed that small fish rapidly adapt to wide daily variations in river flow rates, as long as the river does not dry up completely. Life under water is not completely safe for small animals, however. During the winter, young fish suffer a much higher risk of being stranded during the day than in the dark. This is because the fish are most active at night, hiding in sand and gravel during the day. Electricity generators are therefore warned not to lower water levels in their rivers during the day in winter. However, if young fish do end up on dry land the low winter temperatures mean that thay are more likely to survive stranding during the cold season than in summer. This finding will be good news for Norwegian electricity generating companies. At present, the industry invests large amounts of money in setting out fry to compensate for the lethal side-effects of hydro-peaking operations

The field studies were carried out in the River Nidelva near Trondheim and the River Dalelva in Hordaland by SINTEF, in collaboration with LFI, the Norwegian Institute for Nature Research, the Norwegian Institute of Water Research and NTNU.