River Restoration in the Context of Hydropower Impacts to Anadromous Fish in Large River Networks: Evidence From the Columbia River Basin With Implications for Future Research

ABSTRACT Rivers are essential to humans and ecosystems, and can generate renewable energy. Yet hydropower dams substantially alter water and sediment flows, affecting river ecosystems including keystone species such as salmonids. Mitigation can include modification of dams and their operation, hatchery production, predator and harvest management, water and temperature management, and habitat restoration. Yet challenges enhancing and even measuring salmonid populations, realization of the importance of large‐scale interventions, and concerns about acceleration of climate change effects create a need to reassess the future of science and practice. Here we consider the role of river restoration as a tool for mitigation of hydropower impacts to anadromous fish. We use the Columbia River Basin (CRB) in North America as a model system, and view mitigation strategies in terms of their ability to overcome limitations to salmonid population growth. We review the state of the science regarding the interaction of hydropower and river restoration, and their effects on salmonid populations in the CRB, and identify important areas for future research. A key challenge is measuring and modeling both environmental and biological conditions and processes at both small and large scales simultaneously, which is critical to prioritizing actions in the CRB. We also identify promising tools for monitoring and numerical modeling. Such research and development is best paired with robust coordination among researchers, government regulators, and practitioners. Such a multi‐scale approach amplified by broader coordination is ultimately relevant to a range of large‐scale environmental challenges beyond the CRB.