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    Author(s): Marie Oliver; Gordon Grant
    Date: 2017
    Source: Science Findings 193. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 5 p.
    Publication Series: Science Findings
    Station: Pacific Northwest Research Station
    PDF: Download Publication  (4.0 MB)


    In recent decades, dam removal has emerged as a viable national and international strategy for river restoration. According to American Rivers, a river conservation organization, more than 1,100 dams have been removed in the United States in the past 40 years, and more than half of these were demolished in the past decade. This trend is likely to continue as dams age, no longer serve useful purposes, or limit ecological functions. Factors such as dam size, landscape and channel features, and reservoir sediment characteristics differ widely, so dam removal projects must be evaluated individually to determine the best approach. Stakeholders need trusted empirical findings to help them make critical decisions about removal methods, how to recognize and avoid potential problems, and what to expect in terms of geomorphic and ecological recovery.

    Gordon Grant, a research hydrologist with the Pacific Northwest Research Station, in partnership with a U.S. Geological Survey working group, extracted key lessons from studies of dam removals to help guide future removals and predict geomorphic and ecological outcomes. The combined findings provide evidence that rivers are remarkably resilient, and when dam removal is well planned and executed, recovery is swift and few long-term problems have occurred. Although geomorphic responses are reasonably predictable, biological responses are less so, and in both cases dam owners and project managers would do well to plan for the unexpected. Numeric and physical models are proving to be valuable decisionmaking tools.

    Publication Notes

    • Visit PNW's Publication Request Page to request a hard copy of this publication.
    • We recommend that you also print this page and attach it to the printout of the article, to retain the full citation information.
    • This article was written and prepared by U.S. Government employees on official time, and is therefore in the public domain.


    Oliver, Marie; Grant, Gordon. 2017. Liberated rivers: lessons from 40 years of dam removal. Science Findings 193. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 5 p.


    Dam removal, sediment, geomorphic response, stream restoration

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