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Title: Engineering and ecological aspects of dam removal - an overview
Authors: Conyngham, Jock, 1956-
Fischenich, J. Craig, 1962-
White, Kathleen D.
Keywords: Stream conservation
Dam retirement
Ecosystem Management and Restoration Research Program (U.S.)
Publisher: Engineer Research and Development Center (U.S.)
Series/Report no.: Technical Note (Ecosystem Management and Restoration Research Program (U.S.)) ; no. ERDC TN-EMRRP-SR-80
Abstract: Decommissioning and removing dams has emerged as one of the central foci of the new millennium for infrastructure management, river conservation, and the restoration of fisheries populations (American Institute of Biological Sciences (AIBS) 2002; Heinz Center 2002). Anadromous, catadromous, and adfluvial species (Figure 1) are especially impacted by dam decommissioning and removal. It represents arguably the most powerful tool and largest opportunity for restoration of aquatic ecosystems and communities that currently exists. Several phenomena underlie this development: • High dam densities and the aging of dam infrastructure. Of large dams, 85 percent will have exceeded their design lifespans by 2020 or soon thereafter (Federal Emergency Management Agency (FEMA) 2001). Though inventories are poor, dams exist at much higher densities than many realize (Figure 2). • Threats or occurrences of dam failures (Figures 3, 4, 5). In 2000 and 2001, 520 dam incidents and 61 dam failures occurred; the American Society of Civil Engineers (ASCE) gave dam management and safety a grade of “D” in the last two editions of its “Report Card for America’s Infrastructure” (ASCE 2002). Although inventories are incomplete (with 11 states having no inventory at all), 2,100 dams are categorized as unsafe and almost 10,000 as high hazard potential, and both categories show significant growth in recent years (ASCE 2002). • Failure of traditional restoration.The mixed success or outright failure of expensive efforts to protect and recover various threatened and endangered species as well as critical prey populations, e.g. the herrings, has received much attention in recent years. The effect of dams on both upstream and downstream migration success is usually cited as a central factor. • Improved knowledge of aquatic ecosystems and processes. Recent advances in knowledge and/or awareness of geomorphology and the ecology of regulated rivers have increased attention on the effects dams have on sediment budgets, hydrology, water chemistry, and life history needs. • Economics. Dam removal often costs far less than the restoration of deteriorating or sub-standard structures. One review of 30 case studies in Wisconsin indicated that removal cost about one third the price of dam repair (Born et al. 1998). In addition, many of the values that dams have historically provided, such as hydropower, have been superceded by the direct or opportunity costs of values now considered important (liability, recreational values, large populations of important recreational or commercial fish, etc.). Despite current enthusiasm, the process of dam decommissioning and removal cannot be viewed as a simple environmental panacea but, rather, as a set of analyses, decisions, and trade-offs with both beneficial and adverse impacts across the spectrum of ecological, social, and economic concerns. Dam removal can require considerable technical expertise and carries potential risk of physical instability, ecological or economic impacts, and local backlash. Recent dam removals have caused occasional but significant occurrences of released toxins or nutrients, channel instability, downstream sediment impacts, invasive populations, and increased risk of ice damming, often despite demanding regulatory overview. Scientists and regulators have expressed concern about current removal practices and requested technical guidance to delineate determination of dam fate, the suite of relevant issues, and the appropriate selection and sequencing of tools for dam removal and associated restoration where indicated. Due to the poor condition of many dams as well as restoration mandates and goals, guidance on efficient and cost effective project implementation stands out as a critical further need.
Description: Technical Note
Gov't Doc #: ERDC TN-EMRRP-SR-80
Rights: Approved for public release; distribution is unlimited
Appears in Collections:Technical Note

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