Potential Effects of Run-of-River Hydropower Projects on Salmonid Populations

Anthropogenic activities have the potential to change the natural patterns of flow and disturbances in lotic systems, altering conditions to which fish are adapted. Run-of-River (RoR) hydropower projects temporarily divert flows from rivers (without storing the water) to produce electricity, and have increased dramatically in number and importance in the last two decades in British Columbia and worldwide. Most research on flow alteration from hydropower operations concentrates on rivers impounded by large dams that store and release water out of phase and magnitude with natural flow conditions. Little research is available to understand how specific impacts of RoR dams on fish populations differ from those relatively well-understood impacts by traditional dams. I will discuss three main expected pathways of impact for salmonids: flow diversion, entrainment or loss of connectivity, and flow fluctuations. Such impacts can change habitat quality and quantity, increase mortality, and alter competition and resource availability, which have the potential to affect recruitment, growth and productivity of fish populations at different life history stages. The global emergence of renewable energy, and RoR projects specifically, emphasizes the importance of understanding their local and cumulative effects for salmonid populations.