tailieunhanh - Encyclopedia of Global Resources part 127

Encyclopedia of Global Resources part 127 provides a wide variety of perspectives on both traditional and more recent views of Earth's resources. It serves as a bridge connecting the domains of resource exploitation, environmentalism, geology, and biology, and it explains their interrelationships in terms that students and other nonspecialists can understand. The articles in this set are extremely diverse, with articles covering soil, fisheries, forests, aluminum, the Industrial Revolution, the . Department of the Interior, the hydrologic cycle, glass, and placer mineral deposits. . | 1166 Streams and rivers Global Resources some irrigation water. Dams were built in Western Europe during the late Middle Ages to provide power for waterwheels. The Anasazi constructed small dams on the Mesa Verde in Colorado for irrigation some eight hundred years ago. The use of heavy machinery in the twentieth century led to an enormous expansion of dam construction especially in the United States and Russia. In recent years a growing recognition has developed in the United States that certain dams should be considered for demolition because of problems with salmon runs scouring of beds and banks below the dam as the released waters are relatively clear because the sediment load has been left behind and changes in the temperature of the water that may be undesirable for aquatic life. In stark contrast to the previous discussion of selected dam removal in the United States China began construction of the Three Gorges Dam on the Chang in 1994. This enormous structure is close to 200 meters high has a width of more than 2 kilometers and creates a reser voir with a length of 600 kilometers. The purported benefits include electricity generation without burning coal navigation improvements and a potential decrease in flooding events. On the negative side are the large-scale movement of several million people who were living in the river valley sediment reduction that could affect downstream areas including the East China Sea and a growth in the risk of new landslides and the possibility of increased geological instability in an area that is already seismically active. Robert M. Hordon Further Reading Abramovitz Janet N. Imperiled Waters Impoverished Future The Decline of Freshwater Ecosystems. Edited by Jane A. Peterson. Washington . Worldwatch Institute 1996. Allan J. David and María M. Castillo. Stream Ecology Structure and Function of Running Waters. 2d ed. Dordrecht the Netherlands Springer 2007. Arnell Nigel. Hydrology and Global Environmental Change. Harlow .