Success of a low‐sloping rack for improving downstream passage of silver eels at a hydroelectric plant

Abstract

Summary The European eel (Anguilla anguilla) is a critically endangered species, and one major threat is the survival of silver eels migrating downstream towards the sea from lake and river rearing areas. During this migration, many eels are impinged and die on intake racks, or are injured or killed when passing through turbines. Intake racks at a hydroelectric plant were modified to avoid impingement and to collect eels without injury; high mortality on both racks and in turbines was previously documented. Modifications consisted of reducing the rack gap width from 20 to 18 mm, decreasing the rack slope from 63 to 35 degrees, increasing the rack surface area by 58% and installing six openings in the rack leading to traps. Downstream passage conditions for silver eels at the hydroelectric plant were significantly improved, reducing mortality from >70% at the old steep 20 mm racks to <10% at the modified 18 mm rack collection facility. No tagged eels were impinged and killed on the racks, and 80% entered the collection facility. Survival can probably be improved even more, as the individuals that passed the facility most likely escaped through holes in the traps. Moreover, injured untagged eels were still encountered at the modified racks, illustrating the need for rehabilitative measures to be implemented at all obstacles between the main eel rearing areas and the sea.

Silver eel downstream migration in fragmented rivers: use of a Bayesian model to track movements triggering and duration★

“…Many have focused on the behaviour of silver eels passing downstream through hydroelectric power stations to estimate mortality (Boubée and Williams, 2006;Carr and Whoriskey, 2008;Travade et al, 2010;Pedersen et al, 2012) or to improve mitigation solutions (Gosset et al, 2005;Russon and Kemp, 2011;Calles et al, 2013). Some studies have tracked silver eels along fragmented watercourses to estimate escapement (Haraldstad et al, 1985;Jansen et al, 2007;Acou et al, 2008;Breukelaar et al, 2009;Verbiest et al, 2012;Piper et al, 2013;Marohn et al, 2014;Mccarthy et al, 2014;Reckordt et al, 2014).…”

Mortality of silver eel (Anguilla anguilla) migrating downstream through a small hydroelectric plant on the Drawa River in northern Poland

“…Half of the fish in our experiment exhibited this behavior. Silver eel usually stop migrating when confronted with a barrier often swimming back and along dams, or they search for a path downstream (Haro et al 2000, Behrmann-Godel and Eckmann 2003, Winter et al 2006, Brown et al 2007, Jansen et al 2007, Acou et al 2008, Travade et al 2010, Pedersen et al 2011, Piper et al 2013, Calles et al 2013, Stein et al 2015. The eel in our experiment behaved similarly.…”

Numerical Investigation of Turbulent Flow through Rectangular and Biconvex Shaped Trash Racks

“…To avoid damaging of the water turbines from large floating trash in the waterways, the turbine intakes are protected by grids of racks, so called trash racks as exemplified in Figure 1 being a sketch of one of the turbine intakes in Bruksfors a Power-station in Rickleån, Västerbotten, Sweden own by Skellefteå Kraft. This trash rack is placed in a horizontal plane but the rack can be at any angle to the ground (Calles et al 2013 [11]). …”