Interactions between migrating salmonids and low-head hydropower schemes

Field: Environmental Science (Physical Sciences)

The redevelopment of existing riverine barriers with modern hydropower turbines is becoming increasingly prevalent on main stem rivers with valuable stocks of migratory salmonids. This is a concern because these fish rely on longitudinal connectivity to complete their lifecycles, and modifications for hydropower could jeopardize that connectivity by obstructing or injuring migrating fish. In order to exploit very low head hydropower potential, novel turbine types are emerging. The Archimedean screw hydropower turbine is one such technology which is becoming increasingly popular for low-head applications. However the impact of these turbines on fish movements remains largely untested. This thesis aims to provide much needed evidence on the effects that these turbines and schemes may have on migrating salmonids.
Fixed radio and passive integrated transponder receivers were used to track the downstream movements of wild migrating juvenile salmonids through a low-head Archimedean screw hydropower scheme. Atlantic salmon smolts were found to pass through the alternative routes of the turbine and main river channel in proportion to flow through these channels. Passage times were generally fast through both routes (median = 17.6, range = 5.1-905.6 minutes over the 350m scheme extent, for radio tagged fish), and longer passage times were associated with daytime presence in both routes. The majority of PIT tagged Atlantic salmon and sea trout smolts that passed through the 100 m long turbine channel, did so in under 27 minutes (median = 6.8 minutes), whilst a few fish had much longer passage times, associated with daytime presence. There were no differences in onward survival (measured as distance survived downstream) between turbine passed and non-turbine passed migrants.
Atlantic salmon smolts were passed through an Archimedean screw turbine to test for harmful effects from the turbine, with comparison to equivalently handled non-turbine passed smolts. There was no evidence of visible damage aside from low to moderate scale loss, which was not significantly associated with turbine passage. Blood chemistry parameters were used to test for subtle turbine-induced damage. This novel application of these techniques did not yield conclusive results, but serves as a useful precedent for future studies.
Radio and PIT telemetry equipment were used to investigate the movements of upstream migrating adult salmonids at three separate low-head hydropower schemes which may act as obstacles to migration. These schemes each had distinct configurations and flow management regimes. Movements within, and progression beyond these schemes varied substantially between sites, and in some cases were related to flow management parameters. Whilst not conclusive, the results suggest that scheme configuration and the management of flows influence the time that fish spend at such schemes, and the proportion of fish that ascend beyond them.
With the global shift towards renewable energy generation, the exploitation of running water for hydropower is likely to become increasingly pervasive. The results of these studies provide valuable information for the informed and ecologically sustainable development of low-head hydropower schemes.