Survival of fish passing downstream at a small hydropower facility

Abstract

Hydropower dams can negatively affect upstream and downstream migratory fish populations in many ways, such as blocking access to upstream habitats and causing injuries or mortality during downstream passage. For downstream passage at projects in the USA, federal regulators and agencies responsible for oversight of hydropower facilities typically require assessment studies and mitigation to address negative effects, with a primary goal of minimising fish impingement and turbine entrainment and mortality. So as to assess the effects of downstream passage of fish populations at a unique, small hydro project on the Mississippi River, impingement and entrainment rates, Oberymeyer gate passage, spillway gate passage, turbine survival, and total downstream passage survival were estimated. It was determined that 85% of fish passing downstream at the project would be small enough to pass through the bar spacing of the trash racks and 15% would be physically excluded. When 55% of river flow enters the turbine intake channel, the total project survival rates were estimated to be 77.3% with an Obermeyer gate bypass rate of 10 and 96.6% with a gate bypass rate of 90%. Therefore, any effects on local fish populations resulting from the operation of the project are expected to be negligible and inconsequential on the basis of expected survival rates for the range and probability of river flows occurring at the project.

Downstream fish passage at small-scale hydropower plants: Turbine or bypass?

“…As a result, behavior-influencing effects that could also keep smaller individuals from passing the screen or guide them towards bypasses no longer apply. Moreover, fish can be injured or killed if the current velocities at the screen are too high, as they can no longer actively avoid the screen, but are pressed against or between the bars (Deng et al, 2010;Brown et al, 2014;Amaral et al, 2018).…”

Dispersal of fish eggs and larvae in a cascade of small hydropower plants with fish ladders

“…Many fish protection and safe downstream passage techniques have been developed, such as screens or diversion pipes (Geiger et al, 2018). These technologies can be used by companies that operate those powerplants as mitigation measures, either alone or in combination, to provide safe egress downstream (Amaral et al, 2018). However, before suggesting such technologies for Retiro and Palmeiras Dams, there is a need to understand the actual proportion and the fate of eggs and larvae moving through each one of the available routes during downstream drift as well as determine passage routes based on injuries that can potentially be identified in sampled larvae.…”

Impacts and Risks of Hydropower

“…Turbine entrainment can cause damages and mortalities, and thus, be a significant population impact factor not only for juveniles with weaker swimming abilities or migratory species (i.e., salmonid smolts) (Mathur et al 2000;Thorne and Johnson 1993) but also for potamodromous (Harrison et al 2019) and even resident adult fishes, mainly in fall and winter (Martins et al 2013). However, survival for smaller (i.e., juvenile) fishes at turbine passage is often higher than for adults, and turbine entrainment may therefore contribute to the persistence of downstream populations, albeit at the expense of populations upstream (Amaral et al 2018;Harrison et al 2019). Entrainment and mortality of drifting fish larvae are severely understudied and have not been quantified so far.…”