Hydropower-related pulsed-flow impacts on stream fishes: a brief review, conceptual model, knowledge gaps, and research needs

Abstract

The societal benefits of hydropower systems (e.g., relatively clean electrical power, water supply, flood control, and recreation) come with a cost to native stream fishes. We reviewed and synthesized the literature on hydropower-related pulsed flows to guide resource managers in addressing significant impacts while avoiding unnecessary curtailment of hydropower operations. Dams may release pulsed flows in response to needs for peaking power, recreational flows, reservoir storage adjustment for flood control, or to mimic natural peaks in the hydrograph. Depending on timing, frequency, duration, and magnitude, pulsed flows can have adverse or beneficial short and long-term effects on resident or migratory stream fishes. Adverse effects include direct impacts to fish populations due to (1) stranding of fishes along the changing channel margins, (2) downstream displacement of fishes, and (3) reduced spawning and rearing success due to redd/nest dewatering and untimely or obstructed migration. Beneficial effects include: (1) maintenance of habitat for spawning and rearing, and (2) biological cues to trigger spawning, hatching, and migration. We developed a basic conceptual model to predict the effects of different types of pulsed flow, identified gaps in knowledge, and identified research activities to address these gaps. There is a clear need for a quantitative framework incorporating mathematical representations of field and laboratory results on flow, temperature, habitat structure, fish life stages by season, fish population dynamics, and multiple fish species, which can be used to predict outcomes and design mitigation strategies in other regulated streams experiencing pulsed flows.

Run-of-River hydropower and salmonids: potential effects and perspective on future research

“…Other reviews have highlighted important knowledge gaps about how the magnitude, frequency, and timing of anthropogenic flow fluctuations downstream of reservoir-storage hydropower systems affect the growth, survival, and reproductive success of fish (Young et al 2011;Nagrodski et al 2012). These knowledge gaps are also relevant to rivers regulated by RoR hydropower, although we argue that the gaps are even larger.…”

“…Data from an unregulated montane stream in the US Pacific Northwest show that natural fluctuations in stage rarely exceeded 5 cm·h −1 (Hunter 1992, cited in Bell et al 2008, while frequent declines in river stage of 80-90 cm over 10 min were reported downstream of a reservoir-storage dam in Norway (Hvidsten 1985). Fish stranding or isolation in side channels may in turn lead to negative effects on survival, biomass, density, or fitness, as reported in studies from reservoir-storage systems (Young et al 2011;Nagrodski et al 2012;Senay et al 2016). Given the limited research that has specifically sought to understand the consequences of anthropogenic flow fluctuations in RoR hydropower systems, large uncertainties remain about how their effects differ from those documented downstream of reservoir-storage systems where most peer-reviewed research has occurred.…”

“…Besides their timing, the frequency and magnitude of anthropogenic flow fluctuations from RoR operations have the potential to generate impacts to salmonids. For example, even small, but repeated, flow fluctuations were found to decrease the feeding time, growth, and survival of fish (Young et al 2011). In addition, small but frequent anthropogenic fluctuations in flow have also been found to reduce fish density and biomass when compared to infrequent but large fluctuations generated by storage-reservoir hydropower in Canada (Senay et al 2016).…”

Narratives about Energy, Megaprojects, and the Ecology of Tropical Rivers: The Baram River Dam Project

“…In fact, the results of experiments to lift fish above high dams had already been published (Cobb 1925). By the 1950s, researchers have noted how velocities based on water releases can influence community assemblages (Young et al 2011). Species diversity can also depend on the amount of flows, where in some examples high species diversity was associated with high flow conditions (Brown and Ford 2002).…”

Displacement, velocity preference, and substrate use of three native California stream fishes in simulated pulsed flows

“…Human-controlled flow pulses from reservoirs are common in rivers around the world (Young et al 2007). In California, river flows may be pulsed for electrical power generation (daily) or for recreational, white-water rafting (daily to monthly).…”