The effects of regulation on fluctuations in waterlevel downstream of Viforsen's powerplant in Ljungan

Hydropower production has advantages but also negative ecological consequences. Thisstudy analyzes the degree of flow variations downstream Viforsen's power plant to investigate how well the regulated flow is re-regulated towards a more natural flow pattern. The studyalso examine effects of the regulation on valuable salmon habitats in the section from Viforsen's power plant down to the sea and whether there is a downstream gradient in the presence of different fish species. Data on water level changes was obtained by installingthree pressure loggers in a gradient downstream of the Viforsen power plant. Collection of hourly flow-data in Viforsen and Vindelälven have been part of the data in the survey. The presence of different species of fish was determined by examination of the Swedish electrofishing registry. Results showed a strong correlation between flow and water level at all three sites in Ljungan and there is no ecologically significant dampening of water level fluctuations downstream Viforsen. The current requirement for a minimum discharge of 30 m3/s is too low as important salmon habitats risk being drained. The strong correlation between water levels and flow that this study shows make it possible to map in more detail the risks of valuable salmon habitats drying up. The results also showed that typically marine species” of fish are much more common in Viforsen than in Vindelälven. This study emphasizes that ecologically sustainable flows are complex and relevant field investigations at each watercourse are necessary when reconsidering and designing the new environmental conditions