Water and power: Test of Roosevelt Dam gates demonstrates flood control plan for Salt River

ROOSEVELT ― Salt River Project cranked open the floodgates at Theodore Roosevelt Dam on Wednesday, testing the structure's ability to protect metro Phoenix from disaster should rain and snowmelt overfill the reservoir behind it.

It’s an annual routine inspection, but one that this year carried extra weight ― and extra water. The spring's unusually strong snowmelt filled Roosevelt Lake’s storage capacity and inched into 77 vertical feet of safety buffer.

SRP, a water and power provider to much of the region, timed this year’s spillway test to the end of a federally mandated 20-day period in which it had to drain several feet of water out of the 357-foot dam's safety buffer. Most of the water passed before the test and ran through power-producing turbines.

By Wednesday, just about an inch of excess water remained to be drained, but that inch meant the difference between a test that usually would run at full throttle for only 10 minutes and one that lasted more than two hours.

It was the third time that water has encroached into the space reserved for flood control since the U.S. Bureau of Reclamation raised the dam in 1996, and the first that the spillway gates have been called on to aid in actually reducing flood risk below the Salt River Canyon northeast of Mesa.

It also was a sight to behold. At 9 a.m., some 40 people watched from a downstream overlook as gates on either end of the dam lifted 5 feet to produce gushes that curled off of concrete rims and dropped roaring waterfalls on the river below.

The water, at first black with the silt and organic muck deposited in the spillway tunnels over the past year, startled swimming cormorants into flight and soon turned the placid green river into a churn of white and brown foam. Mist filled the canyon.

“Very refreshing!” said Tayler Vencill, one of about a dozen children who came with their parents ― many of them SRP employees ― to witness the torrent. “And very relaxing to watch.”

Floodgates open to accommodate snowmelt

Some 650 million gallons, or 2,000 acre-feet in the language of water managers, was destined for capture and retention by smaller dams downstream. But the release was the last of some 300,000 acre-feet that SRP has released to make room for this year’s snowmelt, water supply manager Charlie Ester said, and much of that has washed past the dams and through the normally dry Salt River bed.

Together with water from the Verde River, SRP has released more than 700,000 acre-feet down the river, nearly as much as the 750,000 acre-feet or so that it delivers to users in a year.

The water isn’t wasted. Some of it replenishes the aquifer that SRP and others will later pump and use. And this year, for the first time in more than a decade, there’s so much flowing from the Salt to the Gila River that the water is temporarily reaching clear across the Sonoran Desert to its confluence with the Colorado River, near Yuma.

There, Ester said, it could help the U.S. meet its water treaty obligations to Mexico while easing demands on Lake Mead.

It also should aid some desert wildlife and lingering migratory birds in the short term, said Tyler Williford, an Arizona Game and Fish Department biologist in Yuma. He had not yet heard any reports of people fishing in the normally dry channel, he said, but the flows could continue for a couple of weeks.

How to save more water? SRP working on plans

SRP is working on three plans that would help it keep more water in storage or transfer some to other water providers in future wet years. The first is a permitting change that would allow it more time ― 120 days ― to drain up to 5 feet from Roosevelt Dam’s safety buffer.

Officials with the Bureau of Reclamation and the Army Corps of Engineers are reviewing that plan, and if they agree it’s safe, it could save up to 108,000 acre-feet in a wet year, or enough to supply a few hundred thousand households.

Another plan under review is the proposal to raise Bartlett Dam, adding about 115,000 acre-feet of storage on the Verde River.

Power plans: New reservoir proposed near Apache Lake, but SRP wouldn't use it to boost Arizona's water supply

Finally, over the next few years, SRP hopes to reach agreement with the Central Arizona Project and start construction on a pump connection allowing SRP water to flow into the CAP canal that supplies Colorado River water to the Phoenix and Tucson areas.

If that happens, CAP-linked water suppliers that invest in SRP’s improvements could get access to some of the resulting water. At present, water can flow by gravity out of the CAP canal and into the SRP system, but not in the other direction. The pump connection would help CAP weather water cutbacks that are likely to worsen.

“It’s unfortunate it’s not available right now,” Ester said, “because of the severe drought conditions on the Colorado.”

Impressive as Wednesday’s flush of water was, such releases could be much larger in a bigger flood year, said Ivan Insua, SRP’s director of hydropower generation. The test maxed out at 12,000 cubic feet per second, he said, but the gates are designed to pass 150,000 cubic feet per second when raised to their 30-foot limits.

How did the test go? All of the data not yet in

The equipment appeared to perform as expected during the test, Insua said, though the agency and its partners at the Bureau of Reclamation had yet to collect and study data on the motors, gears and concrete spillways.

For a week or so, he said, recreational tube floaters on the Salt River may notice the test's effects. It's not that the water will rise a lot, as Stewart Mountain Dam will intercept it. But the water flowing past that dam could be colder, having recently chilled in the depths of Roosevelt and poured through the spill gates instead of from the warming surface and into the hydropower turbines.

Brandon Loomis covers environmental and climate issues for The Arizona Republic and azcentral.com. Reach him at brandon.loomis@arizonarepublic.com or follow him on Twitter @brandonloomis.

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This article originally appeared on Arizona Republic: Salt River Project opens spillway gates for Roosevelt Dam release