Come Monday, the Colorado River through Grand Canyon National Park will take on the appearance of "Big Muddy" as flood gates in the Glen Canyon Dam are cranked open to spawn a controlled flood down the river.
Right around 11 p.m. Sunday a switch will be thrown, a button pushed, or a dial turned to unleash the river that's been pent up behind the dam that restrains Lake Powell.
Slowly at first, but growing at a rate of 1,500 cubic feet per second per hour, flows out of the dam's four outlet tubes will grow over the course of some 22 hours. From a relatively pedestrian flow of about 9,000 cfs, the Colorado will seeth up to 42,000 cfs, a raging torrent expected to dredge up and redeposit massive volumes of sand, silt, and other debris that the Paria River has dumped into the Colorado River channel about 15 miles downstream of the dam.
For five days this "high-flow experimental release" will continue with hopes it will mimic natural floods that used to flow through the picturesque canyon and build and rebuild sand bars and beaches.
“The idea with the high flow is to actually pick them up (from the river bed) and deposit them on the sides of the channel," explained Jan Balsom, the park's deputy chief for science management.
This will mark the first high-flow release through the Grand Canyon since 2008. Prior to that one, there was a similar release in 2004, and another in 1996. The difference this time around, Ms. Balsom noted, was that next week's is the first gusher in what is expected to be a decade of year-after-year-after releases -- some years will have two releases, spring and fall.
It was back in May when top Interior Department officials, with an eye toward restoring some semblance of natural rhythms to the Colorado River and its surrounding national park, announced plans to resume the high-flow releases.
In years past such releases, designed to transfer heavy sediment loads from Lake Powell into the Colorado to help rebuild beaches and improve habitat for native fishes, have been a point of contention between the National Park Service and the U.S. Bureau of Reclamation. While the Park Service desires to see seasonal ebbs and flows to the Colorado restored, something the Glen Canyon Dam has blocked, Bureau of Reclamation officials have been more concerned about power generation from the dam.
Interior Secretary Ken Salazar, though, has voiced his belief that the high flows can occur without diminishing the flows of electricity.
The scientists, meanwhile, are keenly interested to see how a more regular succession of high flows will affect beaches, fisheries, and riparian areas along the river corridor.
“This is the first time that we’ve actually had a program that allows for multiple flows. In the past they’ve been independent, and the protocol establishes a full ten-year package that allows for multiple flows over these years, so we may very well be looking at two a year if indeed we have enough sediment in the system to warrant it," said Ms. Balsom.
“The 2004 flow, we actually had some pretty good sediment conditions," she went on. "And we had varying results. In 2008 we did another spring flow, sediment conditions were pretty enriched, but we had some steady flows afterwards that reversed some of the gains that we saw. So each time there’s been some variables that were not anticipated, and we had confounding results from the science that was done.
"So we’re looking at this new protocol to allow us to have multiple events. The original idea, the '95 EIS (environmental impact statement) and the '96 ROD (record of decision) was that you could build upon each one of these events so that you’d have a gain," the scientist said. "It’s an erosive system, we’d have some losses, but we’d be able to rebuild again before we see big losses in the sediment resource."
The years of lag between the earlier high-flow releases, in 1996, 2004, and 2008, really didn't provide any indication of what annual events would do to the river system, she said. “So this is the first time we’re being able to see them in succession, we hope."
For now the flows will only be stirring up the sediments the Paria River gives to the Colorado. Dredging the sediments piling up behind the Glen Canyon Dam and somehow dumping them into the Colorado to be pushed downstream at this point isn't feasible.
"There are pros and cons to doing a dredging system," said Ms. Balsom. "Part of it is how do you get the sediment that you’re dredging up below the dam? If you went overland, you have a lot of environmental concerns, you’d have to construct a pipeline, or somehow you’d have to engineer it down the lake and through the dam."
Following next week's release, another is expected next fall. A high-flow release in the spring likely won't occur until 2015, she said, explaining that sediment levels below the Paria River aren't expected to be significant enough to justify a high-flow run before then. Plus, scientists want to conduct more studies surrounding trout production and different flow levels before moving ahead with the twice-yearly high-flow releases, she said.
"The other part of it is the releases are really key to sediment inputs, and most of the sediments that we see that are going to affect the system as a whole come in through the Paria," said Ms. Balsom. "And the sediment inputs in the Paria are almost always monsoonal, so the likelihood of having flows in the late fall triggered by the monsoonal inputs is greatest this time of year.”
How might the high water affect river runners?
According to the Park Service, "(M)ost campsites will be smaller, and some particularly low lying campsites may not be usable."
That said, the park has reached out to those scheduled to be on the river next week and alerted them to the high-flow release.
“We have links on the (park) website to campsite photographs, so that anybody who’s going to be on the water or backpacking along the river can basically pull up the area -- we’ll have copies of those available at various places, including up at Lee’s Ferry and our backcountry office -- so that if folks are going to be adjacent to the river or on the river, they can look and see where the flow lines will be," said Ms. Balsom.
"Essentially the 45,000 cfs line is kind of the high tamarisk zone. It’s not all that high, it’s below the mesquite zone. There’s actually a video on our site that talks about recognizing the old high water zone, and sort of the durable surfaces and vegetation zones."
During next week's experimental release the U.S. Geological Survey will have two crews on the river to monitor results, while the Park Service will run its annual river monitoring trip later in the month and observe changes then.