Author(s): Alex Balzarini; Mathias Hochschwazer; Walter Gostner
Linked Author(s): Alex Balzarini, Walter Gostner
Keywords: Ecohydraulics; Fish passage; Small hydropower; Alpine rivers; Upstream migration; Downstream migration
Abstract: Longitudinal connectivity is a fundamental prerequisite for sustaining aquatic ecosystems in rivers. Fish passage structures have therefore become a central mitigation measure at hydropower plants across Europe. While extensive research and guidance exist for large hydropower schemes, many river barriers in Alpine regions are associated with small hydropower plants. These installations are typically characterized by limited space, high hydraulic variability, data scarcity, and strict economic constraints, which significantly affect the feasibility and effectiveness of fish passage solutions. This paper presents a practice-based comparative assessment of upstream and downstream fish passage design at small hydropower plants in Alpine and Central European regions, focusing on regions in Austria, Germany, Switzerland, France, and Italy, where small hydropower plants are widely distributed across mountainous catchments and subject to differing regulatory and design philosophies. Drawing on the authors' experience in the design and construction of fish passage structures across multiple regulatory frameworks, the paper examines how legislation, design guidelines, and financing mechanisms influence ecohydraulic design choices, modelling depth, and final implementation. Key challenges related to geometric constraints, flow variability, data limitations, and cost pressure are discussed for both upstream and downstream passage. Based on cross-border project experience, transferable lessons and practice-oriented recommendations are derived, aiming to improve ecohydraulic performance while maintaining overall feasibility for small hydropower plants that are more and more recognized as an essential contributor for decarbonization.
DOI: https://doi.org/10.64697/iahr.proc.ise2026.abs.335
Year: 2026