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Dam removal: Panacea or Pandora for rivers?

Correspondence to: Gordan Grant, Corvallis Forestry Sciences Laboratory, 3200 SW Jefferson Way, Corvallis, OR 97331, USA. E-mail: gordan.grant@orst.edu We stand at a curious juncture with respect to the increasingly passionate debate about what to do with aging dams in the US—numbering more than 75 000 by one recent count (Graf, 1999). This debate is playing out against a backdrop of power crises, cycles of flood and drought, endangered ecosystems, and changing societal expectations and demands for water. Within this larger debate, the idea that dams are not necessarily permanent features of the landscape, but can and—by some views—should be removed, has emerged as a rallying cry, political lightning rod, and unparalleled scientific opportunity for understanding the behaviour of rivers. As evidence of interest in this issue, all of the major American geoscience and ecological societies (i.e. AGU, GSA, AAG, NABS, ESA) hosted special sessions on dam removal in the past year, two national panels (at the Aspen Institute and Heinz Center) are examining dam decommissioning, and the topic surfaced in last fall’s US presidential debates. Clearly, something is going on. Why is dam removal emerging as an issue? A convergence of science, management, and policy concerns is driving it forward, centred on the increasing hazards to human and ecological communities posed by aging dams that have, in many cases, outlived either their design lives or original purposes. An open ‘policy window’ due to the large cohort of non-Federal hydropower dams up for relicencing by the Federal Energy Regulatory Commission (FERC) in the next decade, is prompting scrutiny of past dam effects and discussions of dam removal in some cases. Dam removal is also being proposed in response to concerns about threatened and endangered fish species, physical fragmentation of river systems, and calls for a return to a more ‘natural’ hydrologic regime to restore ecological and geomorphic functions to rivers (Poff et al., 1997; Richter et al., 1997). Finally, dam removal has great symbolic value in terms of representing our good intentions towards the environment, as embodied by former Secretary of the Interior Bruce Babbitt’s sledgehammer, or a recently published comment that ‘Dam breaching is America’s own exercise in truth and reconciliation’ (Moore, 2001). For most, the topic of dam removal conjures the image of large dams being removed from large rivers, such as the ongoing debate over the fate of the lower four dams on the Snake River in Idaho (Kareiva et al., 2000). Most dams are small, low-head, and run-ofriver, however, and most dam removals in the past and foreseeable future will likely involve these more modest structures. Their greater number, smaller size, and lower hydraulic and political profiles