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----pjanning Issues/Background' C:~ c) i'\) to N '"'" If it is the aesthetic aspect of this landscape that stirs human imagination, it was the economic potential of the Colorado in an arid region that interested developers. In 1935 Hoover Dam was completed at the lower end of Grand Canyon and 28 years later, in 1963, Glen Canyon Dam controlled the river's flow at the head of the canyon. Both of these projects were to have an impact on river running through the Grand Canyon. Lake Mead, formed by Hoover Dam, extended into the lower section of the canyon, producing slack water that marked the end of the free-flowing Colorado. Glen Canyon Dam's effects have been more dynamic. The amount of sediment and driftwood that was formerly carried naturally along the river's course through the canyon has been significantly reduced. Water releases from Glen Canyon Dam (its primary I function is to generate hydroelectric power) have created more predictable seasonal water levels but have resulted ia extreme daily fluctuations. Canyon beaches, which provide campsites for river runners, no longer receive sediment and are being eroded. Previoos heavy spring runoffs no longer scour the Colorado's banks, and a new ecosystem has grown up in the pre-dam flood zone. There are other influences that could affect river management in the future that are outside the scope of this plauning effort. For example, the Water and power Resources Service is presently studying the possibility of converting Glen Canyon Dam to a peaking power facility. This conversion would result in even greater fluctuations in daily water flow than now occur. The sharp fluctuations, particularly periods of very low flows, would make river running with large rafts or wooden boats ex- tremely difficult, if not impossible. The desire of the American public to exper- ience this unique part of their natural heritage has dramatically increased. In 1967, 2,100 people made the river trip. The number had jumped to 16,500 in 1972. This :sudden rise in use was noticeably impacting the vulnerable inner canyon ecosystem. Trash, charcoal, and human waste were accumu- lating, multiple trails were developing to points of interest, and the numerous prehistoric and historic sites near the river were being damaged. In 1973, the National Park Service (NPS) initiated a research program and planning process leading to the development of the Colorado River Management Plan in 1979. One major feature of this 1979 plan was the phasing out of motorized craft over a five year period. 2 . .