Einsatz des Leitrechen-Bypass-Systems nach Ebel, Gluch & Kehl an Wasserkraftanlagen — Grundlagen, Erfahrungen und Perspektiven

Impacts and Risks of Hydropower

“…Bypasses are dedicated downstream migration routes for fishes and most often used in combination with deflection screens or behavioural guidance facilities (Ebel et al 2015). Their set-up is usually relatively simple, comprising concrete or metal chutes, slides or pipes that flush entering fishes downstream.…”

“…Their set-up is usually relatively simple, comprising concrete or metal chutes, slides or pipes that flush entering fishes downstream. Operational and efficient bypasses must be easily accessible, sufficiently dimensioned and supplied with enough water (commonly measured as a proportion of the turbine flow rate), and the entering water should have a slightly higher flow velocity than the recommended approaching flow of deflection screens (Ebel et al 2015;Larinier and Travade 2002). Studies quantifying bypass mortalities are comparably scarce (Algera et al 2020), but documented bypass-related damages and mortalities are mainly caused by sheer forces, rapid pressure changes, collisions, disorientation and subsequent predation in the tailrace (Williams et al 2001); however, mortalities remained generally lower compared to other downstream routes (Algera et al 2020).…”

“…Deflection screens with much smaller bar spacing installed at HPP behind or instead of trash racks are mechanical and behavioural barriers that prevent fishes from entering the turbines. Fish deflection screens come in a wide variety of designs e.g., vertically inclined with vertical bars and horizontally angled screens with horizontal bars that mostly deflect fishes mechanically, or horizontally angled screens with vertical bars inducing an additional behavioural change that increases the deflection performance up to 95% (Albayrak et al 2020;Amaral 2003;Beck 2019;Calles et al 2013;Ebel 2013a;Ebel et al 2015;Nyqvist et al 2018). The purely mechanical deflection rate can be approximated using empirical length-width-regressions by (Ebel 2013b): for example, 18 mm bar spacing would deflect fusiform fish of approximately ≥16 cm and eel of approximately ≥55 cm length; 15 mm bar spacing would lower these values to 13.6 and 48 cm.…”

“…In contrast, a common trash rack with 80-100 mm bar spacing is consequently passable for almost all native species. When the approaching flow exceeds the recommended value of approximately 0.5 m/s (Calles et al 2013;DWA 2014;Ebel et al 2015;Larinier and Travade 2002), fish may be impinged in the screen and get damaged (Calles et al 2013;Larinier 2001). Typically, physical/behavioural deflection screens and downstream bypasses form a functional unit (Ebel et al 2015;Gosset et al 2005;Larinier and Travade 2002;Nyqvist et al 2018;Økland et al 2019) and are not considered operational in absence of each other.…”

A Physical and Behavioral Barrier for Enhancing Fish Downstream Migration at Hydropower Dams: The Flexible FishProtector

“…Hence, fish protection measures for downstream migration at hydropower plants have to be effective for various species and sizes. Besides efficiently protecting fish from injuries, guidance is required to a safe downstream migration corridor without any appreciable delay [15][16][17][18][19].…”