7423 - Laserfiche WebLink

Home Browse Search

78 I I I I I I I I I I I I I I I I I I I Possible adverse consequences of such a modification would have to be evaluated prior to implementation. These include the cost of dam modification, the effect of temperature increase on the trout fishery, the change in water quality of both Lake Powell and Lake Mead, and the potential for increase in warm-water exotic species that could prey on or compete with hump- back chub or other native fishes. Loss of marshes. The flood flows of 1983 eliminated most well-established marshes in the Grand Canyon. These highly productive areas provide habitat for a variety of native fishes, aquatic mammals, and terrestrial birds and mammals. Marshes might be recreated by diverting flow into low-lying or protected terrestrial habitats adjacent to the river. However, objections might well be raised if such a diversion re- quired the building of structures or water control facilities that would detract from the naturalness of the canyon. Not much is known regarding the marsh ecology in Grand Canyon. Research would need to be completed prior to considering any structural fea- tures. White-water boatina. Fluctuating releases have many negative effects on white-water boating, such as the need for moving boats at night, waiting for better flows, the unnaturalness of fluctuations, and the difficulty of selecting campsites and mooring locations. Mitigating these impacts of fluctuations through non-operational means would be very difficult. The only non-operational method we are aware of is construction of a re-regulating dam downstream of Glen Canyon Dam to catch and dampen the fluctuating releases. Such structures have been proposed in the past and rejected because of their unacceptable impact on Grand Canyon National Park. The difficulty of rapids at high flows could be mitigated by using larger boats, but this would exacerbate problems with rapids at low flows. Also, it is unlikely that river runners would willingly change the type of boat they use. For example, it would be difficult for private boaters to obtain and use larger rigs (motor or oar-powered), and the use of motors would be resisted by most private boaters. The primary hazard associated with white-water boating is drowning after falling into the river. The water released from the dam is extremely cold, quickly ren- dering persons helpless. Since 1980, five individuals