Pragmatic Approach for Addressing Hydrologic Alteration in River Conservation

As human appropriation of water increases globally, anthropogenic change of streamflow becomes an increasingly important stressor to address in the restoration of river ecosystems. Unlike restoration efforts focused on structural changes in river channels, efforts to protect or manipulate flows for ecological outcomes offer potential system-scale impacts but must adapt to current constraints on flows, focus on protection or manipulation efforts that will lead to improved ecological outcomes, and manage flows on an ongoing basis in the context of changing needs (ecological and social) for and benefits from streamflow.  Restoring streamflow patterns for ecological objectives is rarely feasible in the short term because of competing needs for river flows. Moreover, hydrologic restoration may be neither appropriate nor feasible over the long-term because of multiple stressors and climate change. Targeted flow releases from dams can improve components - though by no means restore - river ecosystems. In this case, management objectives must be tempered by type and magnitude of feasible manipulations, the effects of connectivity and discontinuity, and the influences of regulated flows not intended for ecological outcomes. These concepts are illustrated by drawing on a global review of large-scale flow manipulations at dams.