Feds start 3-day flood experiment of the Grand Canyon to improve Colorado River conditions
The Bureau of Reclamation opened the bypass tubes at Glen Canyon Dam early Monday and began three days of high water flows from Lake Powell to help improve environmental conditions on the Colorado River through the Grand Canyon.
It's the first such high-flow experiment at the dam since 2018 and the first during spring runoff season. The goal is to move accumulated sediment downstream and begin to rebuild beaches on the river that have eroded in recent years.
The engineered flood mimics some of the river's pre-dam flows, when snowmelt runoff from the mountains far upstream would raise water levels and redistribute sediment. Since Glen Canyon Dam's completion in 1963, the water flowing into the Grand Canyon has carried less sediment, much of the river's sand and other materials trapped behind the dam.
Releasing more water from Lake Powell won't change the total amount of water that flows through the system this year, bureau officials said. The water will arrive at Lake Mead earlier than it would have otherwise and remain there until it's needed downstream.
Dam operators began raising water flows early Monday, first through the power plant turbines and then through bypass tubes on the side of the dam. By mid-morning, water gushed from the tubes into the river at the dam's base, the start of a journey downstream through the Grand Canyon toward Lake Mead.
The amount of water released will fluctuate over the three days, but the bureau said the high flows will peak at about 39,500 cubic feet per second, or as much as quadruple the average output from the dam. The water releases will return to normal operations by Thursday.
The National Park Service is alerting river rafters, hikers and others who might be in the Canyon this week that Colorado River flows will ramp up sharply during the experiment.
"At higher flows, some normally difficult rapids might decrease in their technical difficulty, and other rapids might become more technically challenging," the park service said in a statement. "River runners are advised to scout rapids to check for new features, and ensure rapids are clear of boats or swimmers."
The high flows began just days after the bureau released new figures that projected improving conditions for water storage on the Colorado River, which is currently operating under shortage guidelines. Forecasters now say runoff into Lake Powell from April through July could total as much as 177 percent of the long-term average.
Earlier this year, Lake Powell and Lake Mead, the two largest reservoirs on the river, sat at barely one-quarter full, drained by more than two decades of drought and continued high use by more than 40 million people in seven states.
The new projections estimate Oct. 1 water levels at Lake Powell will be almost 50 feet higher than Oct. 1 of last year. This October, Lake Mead levels are projected to start about 22 feet higher than last fall, though that's still about 160 feet below what's considered capacity.
“This winter’s snowpack is promising and provides us the opportunity to help replenish Lakes Mead and Powell in the near-term — but the reality is that drought conditions in the Colorado River Basin have been more than two decades in the making,” said Reclamation Commissioner Camille Calimlim Touton.
“Despite this year’s welcomed snow, the Colorado River system remains at risk from the ongoing impacts of the climate crisis. We will continue to pursue a collaborative, consensus-based approach to conserve water, increase the efficiency of water use, and protect the system’s reservoirs from falling to critically low elevations that would threaten water deliveries and power production.”
The high-flow experiment, if successful, should help rebuild beaches along the river and create natural backwaters for fish. Eroded beaches have left hikers and river rafters with fewer options to camp.
An active monsoon last year moved tons of sand and sediment toward the river through tributaries like the Paria River, but runoff from the storms also gouged deeper cuts into the beaches downstream. The higher flows this week are intended to move some of the sediment downstream and deposit it along the way.
“It’s a happy day,” said Lynn Hamilton, executive director of Grand Canyon River Guides, a river recreation advocacy group. “I’m sure the river-running community will be happy to have beaches to camp on this season.”
The effects on fish and other wildlife are less certain since past experiments have occurred later in the year. Jim Strogen, president of Trout Unlimited’s Gila Trout Chapter, said the high flows could help reduce populations of the invasive brown trout around Lees Ferry. Brown trout spawn in fall and winter, and forcing the eggs or young out from spawning areas could help limit their numbers.
But environmental advocates say the flood could draw more smallmouth bass from Lake Powell into the Colorado River, threatening imperiled native species like the humpback chub. Taylor McKinnon, southwest director for the Center for Biological Diversity, said releasing water too early in the season — and before nets or other barriers are put in place near the dam — could create conditions favoring the invasive bass.
A dangerous move for humpback chub: BOR’s April floods in Grand Canyon—before the lake has risen or intakes screened—will draw more predatory smallmouth bass from the lake’s surface into the CO River, further threatening the chub’s last largest population. https://t.co/81RuGYAWQE
— Taylor McKinnon (@publiccarbon) April 18, 2023
Researchers discovered bass near Lees Ferry last year, downstream from Glen Canyon Dam near the top of the Grand Canyon. Scientists say low water levels in Powell enabled the bass to slip past the turbines and warmer water temperatures allowed the invaders to survive in the river.
Environmental coverage on azcentral.com and in The Arizona Republic is supported by a grant from the Nina Mason Pulliam Charitable Trust. Follow The Republic environmental reporting team at environment.azcentral.com and @azcenvironment on Facebook, Twitter and Instagram.
You can support environmental journalism in Arizona by subscribing to azcentral today.
This article originally appeared on Arizona Republic: Feds start 3-day flood of the Grand Canyon to help the Colorado River