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<br /> <br />Introduction <br /> <br />The halcyon days of building large dams in the United States have passed. Most of the <br />"good sites:' based purely on the engineering perspective of high canyon walls, solid <br />foundation, and a large basin upstream, have already been used. The price tag on a dam is <br />now orders of magnitude greater than for equivalent structures built during the 1930s. But <br />more importantly. the American public has grown to expect a full cost/benefit accounting <br />of a large project. not just in terms of construction cost versus immediate benefits. but also <br /> <br /> <br />The ratio of reservoir storage to annual water supply in parts of North America <br />(modified (rom Hirsch and others, i 990). The western United Stales and ,ooth. <br />western Canada have the most extensive reservoir development relative to avail- <br />able water supply. More darns have been construtted in the Columbia River basin <br />and in the Tennessee Valley (neither are shown), but these basins have higher water <br />yields. Many of the forgest problems with downstream effects of reservoirs are in <br />the basins with the highest ratio of reservoir storage to annual water supply <br />because dam operations are constrained more in those basins. <br /> <br />5 <br />