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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Can morphologic restoration of hydropower outlet channels create hydraulically suitable spawning and larvae habitats for grayling? : Modelling the effects of environmental measures with HEC-RAS.

Ahonen, Jani January 2018 (has links)
The aim of this study was to model if hydraulically suitable habitats for juvenile and spawning grayling could be created by morphological restoration alone in the Bjurfors Övre hydropower outlet channel in the Ume River Basin. The study was done by 2D modelling with HEC-RAS using hourly water flow and level data collected during the period 20160521-20161029. Suitable water depth and velocity values for larvae and spawning grayling were collected from literature. Environmental measures for the Bjurfors Övre outlet channel were designed based on the morphology in outlet channels with documented reproducing grayling populations and large habitat diversities. The outlet channel at present morphology and after morphological modifications were modelled at different flow scenarios (0-369m3/s) and areas of suitable water velocities and depths before and after proposed measures were compared. Results show that suitable velocity areas would increase with a factor of between 1,03-1,81 and the suitable depth areas with a factor of 2,34-19,09 and that suitable depths may be the major limiting factor in current conditions. Results also show that zero-flow events at Bjurfors Övre hydropower plant create unsuitable velocities for larvae and spawning grayling and that the frequency and duration of such events could be more limiting than the mere occurrence of such events. The study indicates that the morphological restoration in hydropeaking outlet channels could improve the availability of habitats with suitability water depth and velocity not only for larvae and spawning grayling, but for other lotic organisms. The study also showed that HEC-RAS modelling is a potential resource effective way to assess to what extent certain proposed environmental measures may create suitable water depths and velocities in hydropeaking outlet channels.

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