Modellering och utvärdering av omlöp vid Näktens regleringsdamm : En icke-stationär flödesanalys av en kombinerad teknisk och naturlik fiskpassage i Jämtland, Sverige

Sammanfattning: Dams and power plants in watercourses pose a serious threat to diversity and aquatic species as they fragment habitats and create barriers. New legislation aims to facilitate the restoration of watercourses and in many places, various fish passages have been built. Evaluations of these are important in order to ensure that the desired function has been achieved. At Näkten regulation dam in Jämtland, Sweden, a combined technical and natural fishway has been built to enable migration for trout and grayling. The purpose of the study is to find out whether the technical solution has had suitable flows and gate settings for the fish that one wanted to enable migration for. To investigate this, unsteady flow analyzes were performedin HEC-RAS and then compared to field measurements as well as information from the dam owner. The results show that the gate during the study period has not been set according to recommended settings and that the flows at times have been too high to be suitable for migration. However, comparison with field measurements and previous calculations suggest that the modeled flows do not match reality but are too high in the model. The conclusion is therefore that further modeling and a more thorough comparison with field measurements is recommended to create reliable results and that one then possibly can adjust the settings on the gates.