This study report provides background information to support a recommendation by the American Fisheries Society’s (AFS) Resource Policy Committee to develop a Dam Removal Policy Statement for consideration by the Governing Board and the full membership. The report is neither a comprehensive nor global review of the ecological, economic, and social costs and benefits of dams. Instead, the report provides the reader with a comprehensive literature review related to dam removal in the United States, with some application to Canada. For this document, a dam is defined as “a bank or mound of earth, or any wall or framework, raised to obstruct a current of water” (Webster’s Dictionary 1979) that changes physical or biological conditions of a lotic ecosystem above or below the dam, or obstructs the passage of fish. A dam is considered to be “removed” when the physical blockage is removed from the waterway and stream flow approaches pre-dam conditions. Although this study report and the policy focus on dam removal, some of the following discussion may also apply to dam breaching, which is a partial removal with a different mix of benefits and impacts.
Dams are dominant elements on many rivers and streams in the United States (Graf 1999). While the largest dams are among the few construction projects that can be identified from space, it is the more than 75,000 dams that exceed six feet in height (USACE 1999a in Appendix 3) that expand this issue to all 50 states. Collectively these dams have the capacity to store nearly 60 percent of the annual U.S. runoff (Graf 1999; Hirsch et al. 1990). In the arid southwest United States, dams on the Colorado River can store four years of typical flow (Andrews 1991). Many smaller dams (estimates range from hundreds of thousands to two million (Naiman and Turner 2000)) influence watersheds and natural resources across the national landscape. As recommended by the Aspen Institute (2002), the U.S. Department of the Interior’s Fish and Wildlife Service and Department of Commerce’s NOAA Fisheries started in late 2002 a state-by-state inventory of all dams, aiming toward a data base of all listings. Canadian provinces, with the exception of Prince Edward Island, had 455 dams producing hydropower in 2000, including 221 with capacity exceeding 10 MW (Canadian Hydropower Association,
While this document and the associated policy statement focus on dam removal, the Society recognizes that improved fish passage is often a viable alternative to full removal.
When removal is too contentious, costly, or otherwise prohibitive, a successful passage design may achieve some of the goals. This report does not address fish passage.
Dams have been constructed for many reasons, including electricity generation, mechanical power, irrigation, flood control, drought management, public water supply, navigation, fire protection, industrial cooling, recreation, fishing, wetlands creation (e.g., wildlife flooding in the mid-west in the 1960-70s), non-native species management, and native species protection. These structures have contributed to the economic development of the nation and to the social welfare of its citizens (Schuman 1995; Graf 1999; Heinz Center 2002), but have had ecological impacts on river and riparian ecosystem structure and function. Dam removal is a viable option to restore native or self-sustaining aquatic and riparian ecosystems (cf. Poff et al. 1997; Anonymous 1999), although other options exist and dam removal does not guarantee any particular result.
Amidst this debate, societies continue to construct new dams and operate aging facilities. While dams may provide fewer benefits and more impacts than predicted (Reisner 1986; Pringle 2000; Lemly et al. 2000.), some impacts can be mitigated through dam modification, operating rules, or outright dam removal (cf. Wunderlich et al. 1994; Schuman 1995; NRC 1996; Born et al. 1998; Doyle 1998; American Rivers et al. 1999 in Section 9.3.1 of Appendix 3; Postel 2000). However, each of these “remedial” activities has ecological, economic, and social impacts that also must be considered. Each dam and
each removal option represent complex issues that transcend ecology and economics.
An additional consideration in dam removal is the growing number of dams that are obsolete, aging, or dilapidated to the point that they pose significant societal risks (Schuman 1995; Born et al. 1998; Buckley et al. 1998). All dams have a finite life span and eventually will have to be rehabilitated, replaced, or removed.
Water and aquatic resource management in the United States experienced a major shift during the 1990s with implications to public perceptions about dams. Concerns about decreasing biodiversity (Cairns and Lackey 1992; Hughes and Noss 1992; Winter and Hughs 1997; Postel 2000; Naiman and Turner 2000), inability to meet the water quality goals of the Clean Water Act (CWA) (NRC 1996), and general failure to sustain fish populations and fisheries harvests (Williams et al. 1989; Nehlsen et al. 1991; Williams 1997) contributed to developing strategies for ecosystem management. Watershed protection and restoration now complement the historical approaches of point source-, chemical-, and species-specific management (Naiman 1992; Doppelt et al. 1993; Kauffman et al. 1997; Lehman 1997; Roper et al. 1997; Williams et al. 1997; Doyle 1998; Leathery 1998; Pajak 2000).
Dam removal as an option to support watershed restoration focuses on recovery needs for anadromous, catadromous, and potadromous fish passage, spawning and rearing habitat, and ecosystem processes such as sediment and nutrient transport (Wunderlich et al. 1994; NRC 1996; Nemeth and Kiefer 1999). Debate on dam removal has increased since the late 20th century (e.g., Devine 1995; Joseph 1998; Booth 2000; Levy 2000; Aspen Institute 2002).