"A 13-year-old experiment aimed at improving ecological conditions in the Colorado River watershed below Glen Canyon Dam is failing and needs a management overhaul, according to a draft report by a group of scientists that monitors the dam's environmental effects. Since 1991, Glen Canyon Dam has operated under "modified low fluctuating flows" (MLFF), intended to help recover the endangered humpback chub and other species downstream in Grand Canyon National Park without scaling back power production or recreational activities such as rafting.
MLFF involves daily variations in flow. For example, on weekdays in July, daily fluctuations vary from 10,500 cubic feet per second (cfs) during the late evening and early morning off-peak hours to 18,500 cfs during peak times in the late afternoon and early evening. Still, the MLFF is a highly regulated version of the river's historic flows, which seasonally ranged from as little as 500 cfs to as much as 100,000 cfs.
Under the current flow regime, the endangered humpback chub, which once thrived throughout the Colorado River Basin but now occupies only the lower basin in the Little Colorado River, continues to spiral toward extinction, declining by an average of 14 percent each year, according to the draft report. "One of the justifications for the MLFF policy was apparently an assumption or prediction that MLFF would have beneficial ecological effects relative to the more violent diurnal flow variations that preceded it," the report says. "We show that no such beneficial effects are evident in the ecological system (except to abundance of exotic trout), and in fact the move to MLFF is correlated with a relatively sharp decline in humpback chub recruitment."
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In fact, the only beneficiaries of the modified low fluctuating flow regime have been exotic trout that eat endangered chub and the rafting industry, the report concludes. "At present, power utilities and their ratepayers are essentially subsidizing, at considerable cost, improvement in the quality of Grand Canyon for some recreational uses," the report reads. "It is one thing to impose such costs to deal with some broad public interest such as protecting an endangered species, but quite another one to impose it for the benefit of particular stakeholders." The issue of flows from the dam needs to be addressed "openly and quickly" before it "leads to a breakdown in the collaboration among stakeholders that has made adaptive management possible in Grand Canyon in the first place," the authors warn."
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