Posted: Feb. 15, 2013
Thar’ she blows Colorado River flexes might during Glen Canyon Dam experiment
by Lisa Meiman
Water runs through Glen Canyon Dam’s four bypass tubes into the Colorado River
For five days in November 2012 more than 200,000 gallons of water per second roared through Glen Canyon Dam’s eight-generation turbines and four bypass tubes. The mighty water sent sediment down the Colorado River in hopes of rebuilding sandbars, beaches and backwaters.
“It was truly breathtaking to hear and see the power of the water being unleashed through the bypass tubes,” said Acting Administrator Anita Decker. “Although the experiment is a release of water that might otherwise be used for generation, we also appreciate the environmental and recreational value that this experiment is expected to deliver.”
|Water runs through Glen Canyon Dam’s four bypass tubes into the Colorado River at teh height of the high-flow experiment from Nov. 18 to 23, 2012. (Photo courtesty of Bureau of Reclamation)|
At its peak, this high-flow experiment, or HFE, demonstrated the Colorado River’s mighty power with water releases between double and triple normal operations.
The Secretary of the Interior, Assistant Secretary for Water and Science, National Park Service director and Bureau of Reclamation commissioner along with Western’s acting administrator and acting Colorado River Storage Project manager were all present to witness the first HFE release at Glen Canyon Dam under a new Department of the Interior initiative announced in December 2009.
“The experiment went well thanks to the coordination efforts between DOI and Western,” said Acting CRSP Management Center Manger Darren Buck.
This HFE is part of an experimental protocol, expected to continue through 2020, for more frequent Glen Canyon Dam “floods” that simulate the natural flooding that occurred in the Colorado River before Glen Canyon Dam was constructed. Before the dam, seasonal flooding moved sand, silt and other sediment from the riverbed to the shoreline, which:
- created sandbars that provide habitat for wildlife
- served as camping beaches for recreationists
- helped preserve vegetation and archaeological sites
- provided low-velocity backwaters needed as habitat for endangered fish
The goal is to find how to better conserve and sustain the ecosystem below the Glen Canyon Dam and through the Grand Canyon National Park. Using a strategy called adaptive management, scientists, government agencies and Native American tribes hope to discover a more permanent, long-term protocol that helps protect sandbars and beaches, native fish and flora and also hydropower production.
Past HFEs represent trial, learning, adjustment cycle
The 2012 high-flow release was the fourth such release to occur since 1996. The first three were conducted during different seasons, for different durations and with different amounts of release to test whether HFEs would preserve the ecosystem. They now provide the basis for the new HFEs through 2020.
“We’ve gained tremendous knowledge about the unique resources of the Grand Canyon in the Colorado River downstream of Glen Canyon Dam over the past sixteen years,” said Secretary of Interior Ken Salazar.
Scientists learned much from the various experiments about how the Colorado River reacted to different releases over several years. “Research and long-term monitoring of the effects of three high-flow experiments have allowed scientists to unravel some of the many uncertainties about how these Glen Canyon Dam releases affect downstream river resources,” said Dr. Ted Melis, deputy chief of the U.S. Geological Survey Grand Canyon Monitoring and Research Center.
1. The first HFE took place from March 26 to April 7, 1996 and was the largest experiment with the greatest water flow at 45,000 cfs for seven days.
Results: Sand on the lower portion of the sandbar was redistributed higher on the same sandbar, making sandbars higher but not wider.
- More closely follow tributary seasonal floods, which provide “new” sand to the river to build wider sandbars.
- HFEs should be shorter in duration with less water released.
- Sandbars can be built quickly, but also erode quickly so smaller, more frequent artificial floods are needed.
2. The next HFE was a 60-hour release from Nov. 21 to 23, 2004 at a steady 41,000 cfs.
Results: Since timed with “new” sand arriving from tributaries, sandbars received more sand in a wider distribution than in 1996.
- Follow tributary seasonal floods, leading to two-thirds of HFEs occurring in fall and the other one-third over various times of the year when enough sand is available for maximum sandbar building.
- Specially design and plan for each HFE in response to the volume and location of new sand in the river.
Between 1996 and 2004, there were three habitat maintenance flows that remained within powerplant capacity and therefore are not considered “true” HFEs for the study.
3. The third HFE took place from March 5 to 7, 2008 at a steady 41,500 cfs and revealed a startling undesired impact despite timing the experiment with the highest sediment inputs in a decade.
Results: Again, sandbars experienced growth—75 percent had experienced net increases in volume since 1996—but so did non-native rainbow trout populations, by a whopping 800 percent. Rainbow trout then moved downstream, competed with the endangered humpback chub for food and snacked on their young.
- Spring high flows benefit rainbow trout populations with little discernible benefit to the humpback chub.
- Spring or late-winter HFEs benefit native vegetation over nonnative vegetation.
So more study and work needs to be done to find that sweet spot of environmental conservation and hydropower production, but those involved are optimistic about the study.
“This new protocol developed by Reclamation will protect both the Grand Canyon and the delivery of water for communities, agriculture and industry,” Salazar said. “We are taking a practical approach. If, for any reason, the new high-flow experiments do not yield the positive results we anticipate, we have the ability to change and adjust future flows.”