EXPERIMENTAL WATER RELEASES from Glen Canyon dam on the Colorado river above Grand Canyon National Park in the US have received environmental clearances and were set to begin on 1 January 2003.
The flows were analysed in an environmental assessment in accordance with the National Environmental Policy Act and were found to pose no significant environmental effects.
Three federal agencies including the US Bureau of Reclamation (USBR), the National Park Service (NPS), and the US Geological Survey (USGS) jointly prepared the study and have signed the implementing document called a Finding of No Significant Impact. The proposed flows are the result of ongoing studies by scientists from USGS and were recommended by the Adaptive Management Work Group, a federal advisory committee. The experiment is intended to test methods for protecting the ecosystem downstream of the dam.
There are two aspects to the proposed experiment. The first relates to sediment conservation in Grand Canyon. Scientists propose using high flow tests to move sediment to rebuild beaches and sand bars. Unlike the experiment of March and April 1996, these flows would be timed to make use of sand and sediment that enters the Colorado river from tributary flows of the Paria river. Seasonal monsoon storms provide an average of one million tons of sediment a year to the Colorado river from the Paria river.
The 1996 test flows were designed to attempt to mobilise sediment in deep pools in the river bottom to achieve the same result. Studies by USGS scientists over the past six years demonstrated that while high flows work to rebuild beaches and sand bars, the 1996 experiment scoured the upper reaches of the canyon to rebuild beaches further downstream. By timing the high flow test to correlate with sediment inputs from the Paria river, which is about 25.7km downstream of Glen Canyon dam, the sediment supply for rebuilding beaches would be increased.
The past drought year failed to produce sufficiently sized monsoon storms to enable a high flow test in 2003. That portion of the experimental programme will carry over into 2004.
The second aspect of the experiment relates to endangered fish species. Scientists have recognised that the humpback chub population has been in a general decline since highly fluctuating flows were curtailed in November 1991. Those flows helped keep the non-native fish – especially the rainbow and brown trout – in check. The trout are thought to prey upon, and compete with, native fish such as the endangered humpback chub.
To address those concerns, the experimental flow proposal includes high fluctuating flows starting in January 2003 and continuing through March to disrupt the spawning and survival to adulthood of the non-native trout. In addition to benefiting the native fish, a secondary purpose of the experiment is also to improve the quality of the Lee’s Ferry trout fishery by reducing the density of rainbow trout immediately below the dam.
Finally, the experiment includes mechanical removal of non-native fish, primarily rainbow and brown trout, near the confluence of the Little Colorado river and the mainstem Colorado river. The effort will involve using electro-fishing techniques on the non-native fish and then removing them to reduce their population.
One item of special sensitivity involved the removal and death of the trout. This was of concern to the Native American tribes. The confluence of the Little Colorado and Colorado rivers is an area that is spiritually significant to the tribes, as are the lives of the fish themselves. Through government-to-government consultations with the tribes, USBR, the Park Service and USGS were able to address those concerns. The Haulapai Tribe will return the trout to the earth as fertiliser in garden areas.