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See Inside March 2007

Down Go the Dams

Many dams are being torn down these days, allowing rivers and the ecosystems they support to rebound. But ecological risks abound as well. Can they be averted?

At the start of the 20th century, Fossil Creek was a spring-fed waterway sustaining an oasis in the middle of the Arizona desert. The wild river and lush riparian ecosystem attracted fish and a host of animals and plants that could not survive in other environments. The river and its surrounds also attracted prospectors and settlers to the Southwest. By 1916 engineers had dammed Fossil Creek, redirecting water through flumes that wound along steep hillsides to two hydroelectric plants. Those plants powered the mining operations that fueled Arizona's economic growth and helped support the rapid expansion of the city of Phoenix. By 2001, however, the Fossil Creek generating stations were providing less than 0.1 percent of the state's power supply.

Nearly two years ago the plants were shut down, and an experiment began to unfold. In the summer of 2005 utility workers retired the dam and the flumes and in so doing restored most of the flow to the 22.5 kilometers of Fossil Creek riverbed that had not seen much water in nearly a century. Trickles became waterfalls, and stagnant shallows became deep turquoise pools. Scientists are now monitoring the ecosystem to see whether it can recover after being partially sere for so long, to see whether native fish and plants can again take hold. They are also on the lookout for unintended ecological consequences of the project.

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