Eco-Morphological Evaluation of a Residual Flow Reach Restoration Measure

It is a complex and challenging task to evaluate the effects of a river restoration measure on the riverscape’s habitat mosaic. This study investigated the medium term effects of a restoration measure in a residual flow reach downstream of a hydroelectric dam. The restoration measure consisted of a sediment replenishment that was coupled with an artificial flood in the Sarine river in 2016. It was evaluated using the indicator set habitat diversity of FOEN’s recently published guideline for the evaluation of revitalization projects. Although dedicated to a different category of restoration projects, the guideline’s indicator set proved to be a transferable and effective assessment tool kit for the studied sediment replenishment. To quantify the observed impairment of streambed habitat by substrate degradation, a proposal for an indicator was developed, which can extend the indicator set. The assessment workflow was significantly enhanced by a digital, GNSS-supported surveying solution, which was estimated to provide time savings of up to 50% and improve data accuracy. The study’s results suggest that neither the single artificial flood nor its coupling with the 2016 sediment replenishment are sufficient to restore a functional habitat mosaic in the medium or long term.