Hallingdalselva Habitat Enhancement

In 2014, cbec was contracted by E-CO to undertake an options appraisal on a ~ 7 km reach of the River Hallingdalselva, nr. Gol, Norway.

The study reach is impacted by pressures associated with river regulation for hydropower, including the absence of the natural flow conditions that drive the creation of optimum salmonid habitat. Habitat within the study reach is also affected by the presence of nine weirs, which have been installed for aesthetic purposes. Parts of the River Hallingdaselva are classified as a Heavily Modified Water Body (HMWB) owing to its use for hydropower production.

The potential effects of these anthropogenic pressures included a detrimental impact on the quantity and dynamics of water flow, changes to the structure and substrate of the river bed and an adjustment to channel morphology (and the associated assemblage of habitat units). In addition, these pressures were potentially associated with a lack of extreme low flows controlling the distribution of instream macrophyte growth in summer. All these impacts were having potentially serious implications for in-channel populations through the degradation of habitat, and therefore required assessment and potential mitigation under the Water Framework Directive (WFD).

The project involved a robust evaluation process to produce a review of the available habitats and related geomorphic processes in the river as well as an appraisal of potential mitigation measures. Given the importance of hydropower operations on the Hallingdalselva, the feasibility study assessed the degree to which natural processes could be restored without compromising the function of the river for this purpose. A comprehensive final report was produced detailing all potential options and associated considerations.