The Changing Role of Dams in Water Resources Management

The river system of the United States is a once-natural system dramatically transformedthrough the application of technology. The construction of river control works, dams, diversions, levees, pilot channels, water treatment plants, hydropower generators, and navigation structures has resulted in a national river system that is partly natural and partly artificial. Among the most important artificialities introduced by technology have been the fragmentation of watersheds and segmentation of rivers by dams (Figure 1). There are about 80,000 dams in the United States that are either 6 ft (2m) or greater in height with storage capacities of 50 ac ft (61,000m3) or more, or 25 ft (7.5m) or greater in height with storage capacities of 15 ac ft (18,500m3) or more (USACE, 1996 and subsequent unpublished revisions by the Nationa