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Modifications to landscapes and flow regimes of rivers have altered the function, biodiversity, and productivity of freshwater ecosystems globally. Reestablishing geomorphological and hydrological conditions necessary to sustain ecosystems is a central challenge for restoration within highly altered systems. Meeting this challenge requires simultaneously addressing multiple and interacting stressors within the context of irreversible changes and socio-economic constraints. Traditionally, river restoration approaches either physically change the landscape or channel (channel-floodplain manipulation) or adjust hydrology (environmental flows), and such actions are often independent. We juxtapose these two subfields of river restoration, which have undergone parallel transformations, from goals of reproducing static representations of form and flow regime to goals of reestablishing processes. The parallel transformations have generated shared ideas, which point to benefits of coupling channel-floodplain manipulation and environmental flow actions to achieve process-based goals. Such coupling supports comprehensive river restoration efforts aimed at supporting resilient ecosystems within human dominated landscapes in a nonstationary climate. We identify four elements of coupled approaches for restoring highly modified rivers: (1) identify physical and ecological process potential given interactive effects of altered landscapes and flows; (2) consider capacity for sustaining identified processes under potential future change; (3) model alternatives for coupled restoration actions to support identified processes; and (4) evaluate alternatives using metrics representing integrative effects of coupled actions. We suggest these emergent elements contribute to the development of standard practices for restoring highly modified rivers and encourage an increasing number and quality of coupled applications.

Plain Language Summary Freshwater ecosystems globally have been fundamentally altered and degraded by multiple human modifications of rivers, which have affected the amount and timing of water availability as well as the riverine landscape with which river flows interact. Knowing that it is often impossible or infeasible to completely reverse these impacts, a central challenge for restoring freshwater ecosystems of highly modified rivers is to determine what water management changes and physical habitat restoration actions can be taken to reestablish processes necessary to support ecosystems. These different river restoration approaches have traditionally been considered independently of one another. However, both river restoration subfields have shifted in recent decades from goals of reproducing static representations of channel forms or reference flow regimes to those of reestablishing processes driven by flow-landscape interaction. This shared understanding points to the benefits of coupling channel-floodplain manipulation and water management for a combined added positive impact to ecosystems. Four elements of coupled approaches are identified: (1) identify process potential; (2) consider capacity under potential future change; (3) model alternatives; and (4) evaluate metrics of integrative effects. This commentary supports the development of standard practices for coupled approaches for restoring highly modified rivers.