Evaluating technical improvements for downstream migrating diadromous fish at a hydroelectric plant

Published source details Calles O., Karlsson S., Hebrand M. & Comoglio C. (2012) Evaluating technical improvements for downstream migrating diadromous fish at a hydroelectric plant. Ecological Engineering, 48, 30-37.
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This study is summarised as evidence for the following.

	Action	Category
	Install exclusion devices at water intake and discharge points Action Link
	Install siphon fish passes Action Link
	Install bypass systems alongside exclusion devices Action Link

Install exclusion devices at water intake and discharge points

A study in 2007 in a river in southwestern Sweden (Calles et al. 2012) reported that an angled bar rack at a hydropower station did not prevent migrating European eels Anguilla anguilla from entering a turbine intake, and over one-third of tagged eels died passing through the bar rack and turbine. All 22 tagged eels passed through a bar rack across a turbine intake, eight of which died (36%). A bar rack (22 mm bar spacing in spring and 40 mm during rest of year, angled 77° from vertical) was installed across an intake leading to a turbine at a powerhouse. No downstream fish passages were present at the powerhouse (eels could only travel downstream via an upstream ‘Denil’ fish pass or when spill gates were open). In October 2007, forty-two silver eels were caught in the river, radio-tagged, and released 24 km upstream of the hydropower station. Sixteen radio-tagged eels were tracked as they passed one of two powerhouses at the hydropower station.

(Summarised by: Anna Berthinussen)
Install siphon fish passes

A study in 2007 in a river in southwestern Sweden (Calles et al. 2012) reported that a siphon fish pass at a hydropower station was used by low numbers of migrating European silver eels Anguilla anguilla to travel downstream. In total, three untagged eels and none of 16 tagged eels passed through the siphon pass. All 16 tagged eels passed through a bar rack across a turbine intake, four of which died (23%). In 2006, a siphon fish pass (200-mm diameter pipe) was installed at the bottom corner of a bar rack (90 mm bar spacing, angled 60° from vertical) across a turbine intake. In October 2007, forty-two silver eels were caught in the river, radio-tagged, and released 24 km upstream of the hydropower station. Sixteen radio-tagged eels were tracked as they passed one of two powerhouses at the hydropower station. Eels were captured in a trap on the siphon fish pass in October–November 2007.

(Summarised by: Anna Berthinussen)
Install bypass systems alongside exclusion devices

A study in 2007 in a river in southwestern Sweden (Calles et al. 2012) reported that a bypass system alongside a bar rack at a hydropower station was used by some European eels Anguilla anguilla migrating downstream but almost a quarter of tagged eels died passing through the bar rack and turbine. In total, 43 untagged eels and none of 16 tagged eels passed through the bypass system. All 16 tagged eels passed through a turbine intake covered by a bar rack, four of which died (23%). In 2006, a surface gate (3.3 m wide) connecting to a bypass system was installed adjacent to a turbine intake covered by a bar rack (90 mm bar spacing, angled 60° from vertical). In October 2007, forty-two silver eels were caught in the river, radio-tagged, and released 24 km upstream of the hydropower station. Sixteen radio-tagged eels were tracked as they passed one of two powerhouses at the hydropower station. Eels were captured in a trap on the bypass in October–November 2007. 

(Summarised by: Anna Berthinussen)