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Environmental flows describe the quantity, timing, and quality of water flows required to sustain freshwater and estuarine ecosystems and the human livelihoods and well being that depend on these ecosystems.〔http://www.eflownet.org/viewinfo.cfm?linkcategoryid=4&linkid=64&siteid=1&FuseAction=display〕 Through implementation of environmental flows, water managers strive to achieve a flow regime, or pattern, that provides for human uses and maintains the essential processes required to support healthy river ecosystems. Environmental flows do not necessarily require restoring the natural, pristine flow patterns that would occur absent human development, use, and diversion but, instead, are intended to produce a broader set of values and benefits from rivers than from management focused strictly on water supply, energy, recreation, or flood control. Rivers are parts of integrated systems that include floodplains and riparian corridors. Collectively these systems provide a large suite of benefits. However, the world's rivers are increasingly being altered through the construction of dams, diversions, and levees. More than half of the world's large rivers are dammed,〔Nilsson, C., Reidy, C. A., Dynesius, M., and Revenga, C. 2005. Fragmentation and flow regulation of the world's large river systems. Science 308:405-408.〕 a figure that continues to increase. Almost 1,000 dams are planned or under construction in South America and 50 new dams are planned on China's Yangtze River alone.〔 (Rivers and Lakes: Reducing the Ecological Impact of Dams )〕 Dams and other river structures change the downstream flow patterns and consequently affect water quality, temperature, sediment movement and deposition, fish and wildlife, and the livelihoods of people who depend on healthy river ecosystems.〔Postel, S., and Richter, B. 2003. Rivers for Life: Managing Water for People and Nature. Island Press, Washington, D.C.〕 Environmental flows seek to maintain these river functions while at the same time providing for traditional offstream benefits. ==Evolution of environmental flow concepts and recognition== From the turn of the 20th century through the 1960s, water management in developed nations focused largely on maximizing flood protection, water supplies, and hydropower generation. During the 1970s, the ecological and economic effects of these projects prompted scientists to seek ways to modify dam operations to maintain certain fish species. The initial focus was on determining the minimum flow necessary to preserve an individual species, such as trout, in a river. Environmental flows evolved from this concept of "minimum flows" and, later, "instream flows," which emphasized the need to keep water within waterways. By the 1990s, scientists came to realize that the biological and social systems supported by rivers are too complicated to be summarized by a single minimum flow requirement.〔Bunn, S. E., and Arthington, A. H. 2002. Basic principles and ecological consequences of altered flow regimes for aquatic biodiversity. Environmental Management 30:492-507.〕〔Richter, B., and Thomas, G. A. 2008. () Dam Good Operations. International Water Power and Dam Construction July 2008:14-17.〕 Since the 1990s, restoring and maintaining more comprehensive environmental flows has gained increasing support, as has the capability of scientists and engineers to define these flows to maintain the full spectrum of riverine species, processes and services. Furthermore, implementation has evolved from dam reoperation〔Richter, B., and Thomas, G. A. 2008. () Dam Good Operations. International Water Power and Dam Construction July 2008:14-17.〕 to an integration of all aspects of water management,〔Dyson, M., Bergkamp, G. J. J., and Scanlon, J., eds. 2003. Flow: The Essentials of Environmental Flows. International Union for Conservation of Nature and Natural Resources (IUCN), Gland, Switzerland, and Cambridge, UK .〕 including groundwater and surface water diversions and return flows, as well as land use and storm water management. The science to support regional-scale environmental flow determination and management has likewise advanced.〔Arthington, A. H., Bunn, S. E., Poff, N. L., and Naiman, R. J. 2006. The challenge of providing environmental flow rules to sustain river ecosystems. Ecological Applications 16(4):1311-1318.〕 In a global survey of water specialists undertaken in 2003 to gauge perceptions of environmental flow, 88% of the 272 respondents agreed that the concept is essential for sustainably managing water resources and meeting the long-term needs of people.〔Moore, M. 2004. Perceptions and interpretations of environmental flows and implications for future water resource management: A survey study. Masters Thesis, Department of Water and Environmental Studies, Linköping University, Sweden.〕 In 2007, the Brisbane Declaration on Environmental Flows was endorsed by more than 750 practitioners from more than 50 countries.〔(The Brisbane Declaration )〕 The declaration announced an official pledge to work together to protect and restore the world's rivers and lakes. By 2010, many countries throughout the world had adopted environmental flow policies, although their implementation remains a challenge.〔Le Quesne, T., Kendy, E., and Weston, D. 2010. (The Implementation Challenge: Taking stock of government policies to protect and restore environmental flows. ) WWF and The Nature Conservancy.〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「environmental flow」の詳細全文を読む スポンサード リンク
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