Dam Removal - Purposes and Effects of Dams

Purposes and Effects of Dams

Many of the dams in the eastern US were built for water diversion, agriculture, factory watermills, and other purposes that are no longer useful. Because of the age of these dams, over time the risk for catastrophic failure increases. In addition, many of these dams block anadromous fish runs, such as Atlantic salmon and American shad, and prevent important sediments from reaching estuaries.

Many dams in the western US were built for agricultural water diversion in the arid country, with hydroelectric power generation being a very significant side benefit. Among the largest of these water diversion projects is the Columbia Basin Project, which diverts water at the Grand Coulee Dam. The Bureau of Reclamation manages many of these water diversion projects.

Dams in the Pacific Northwest and California block passage for anadromous fish species such as Pacific Salmon and Steelhead. Fish ladders and other passage facilities have been largely ineffective in mitigating the negative effects on salmon populations. Bonneville Power Administration manages electricity on 11 dams on the Columbia River and 4 on the Snake River, which were built by the Army Corps of Engineers.

In the Desert Southwest, dams can change the nature of the river ecosystem. In the particular case of the Glen Canyon Dam, the originally warm, sediment-filled, muddy water, instead runs cold and clear through the Grand Canyon, which has significant impacts on the downstream ecosystems. Three native fish species have become extinct in the Grand Canyon and others are endangered since the dam was completed, including humpback chub and razorback sucker.

Some dam projects, such as those on the Salt River Project in Arizona, eliminate the flow of the river downstream, by diverting the flow into the Arizona Canal system for use in agriculture and urban usage, such that only a dry channel or arroyo heads out across the desert.

So much water is taken out of the Colorado River for agriculture, urban use, and evaporation behind the dams, that the river no longer flows into the Gulf of California.

While the need for clean, alternative energy sources are important, with so many considerations involved, sometimes it makes sense to evaluate whether the benefits of dams outweigh the costs of safety concerns, ecosystem functions, and management expenses.