Overcoming hydraulic barriers : Design, construction, and hydraulic evaluation of a tube fishway for juvenile eel trap and transport

Sammanfattning

There are more than 2000 hydropower plants in Sweden, and hydropower accounts for 45 percent of the country’s total electricity production. To fulfill the European Union’s Water directive, Sweden has developed a national plan to ensure good ecological status in all its waterways, and this plan includes reevaluating the environmental permit of most hydropower stations in the country. Hydropower contributes to habitat fragmentation, an important environmental problem, and the resulting loss of connectivity between ecosystems particularly affects migration species. One of those migratory species is the European eel, which migrates from the Sargasso Sea to rearing grounds in Europe, including Swedish inland waters. To support the migration of juvenile European eels, known as elvers, specific fishways over barriers such as hydropower dams are needed. This master thesis evaluated a novel type of fishway, called the tube fishway, a closed conduit system that uses an unsteady surge to lift and transfer fish past barriers. This was done by designing and evaluating a physical model of a tube fishway in a laboratory environment. Volume delivered for three different head differences between reservoir and delivery tank was measured, showing that water could be successfully delivered to all head differences, even for delivery up to 2.31 m above the reservoir tank. Soft plastic elvers together with a Lagrangian sensor elver were used to estimate delivery efficiency and experienced acceleration and pressure in the system. The results indicate that a tube fishway might be a viable option to delivery elvers past barriers, but further design modifications will be needed to ensure successful and sufficient elver delivery for head heights greater than the reservoir tank height.