Author(s): Khalid Essyad; Irene Samora; Celine Delaloye; C. T. Meile

Linked Author(s): Irene Samora, Khalid Essyad

Keywords: Bedload regime; river restoration; hydropeaking

Abstract: Following the Swiss Law on Water Protection, hydropower plant owners must adopt measures to reduce the ecological impact of dam exploitation. This law also compels the Swiss cantons to plan the revitalization of their watercourses. Higher restoration objectives are enforced in alluvial areas which are subject to specific regulations. Switzerland has implemented sectoral approaches with the creation of relevant, pragmatic, and context-specific guidelines for remediation measures. In this sectoral context, the key objective of the remediation of the bedload regime is to restore the alluvial style of the river; the remediation of hydropeaking aims to reasonably reduce the impact on aquatic fauna; the remediation of migration restores the continuity for fish as far as these can be achieved with proportionate measures; and the revitalization of watercourses focuses on the diversity of bedforms and habitats. The resulting measures for each type of dam-impact are constrained by external components (finances, land use, flood vulnerability, etc.) but are also internally limited in their interconnection between the different target sectors. For example, bedload restoration can have an impact on the bed material which will decrease the sensibility to hydropeaking regimes but will also have an impact on the morphology which will increase the areas that can be potentially affected by hydropeaking. The approach that is proposed in this study is an overall vision based on a pragmatic diagnosis of the state of the river. Firstly, the factors limiting its ecological state are identified simultaneously according to the different sectoral approaches. These factors are specific to each river and may vary from one reach to another. Secondly, for each dam-induced stress or factor, the stakeholders and their mobilizable resources are identified. An action plan is then conceived based on the principle that all limiting factors need to be addressed together, according to their impact, the possibilities of action, their synergy, and the financial means. To conceive such a plan, a prognosis of the benefits of the action plan must be evaluated considering all synergies between actions. This can be achieved by numerical modelling or by experimental approaches (artificial floods) and expert knowledge. The result is a set of measures that address all stressing-factors in a homogeneous and proportionate way. The application of this approach is presented with two examples in the Sarine River. The first is the downstream of the Lessoc Dam, where the river is under a hydropeaking regime. The second is the downstream of the Rossens Dam, where the river is under an ecological flow regime.

DOI: https://doi.org/10.3929/ethz-b-000675921

Year: 2024