Reservoirs Full To The Brim, More Rain Due

Second wet winter soaks Rim Country, fills Roosevelt and replaces drought worries with flooding potential

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A second sopping wet winter has swapped fears of drought for potential flooding, as the Salt River Project opens the sluice gates and sends water rushing down to the Valley.

The Rim Country braced this week for another winter storm, with all of the Salt River Reservoirs like Roosevelt Lake already at record levels.

Payson has already received 2.3 inches of rain in February on top of 3.06 inches in January.

The wet bounty was reflected this week in creek levels across Rim Country.

Tonto Creek rushed down towards Roosevelt Lake at a flow of 387 cubic feet per second on Monday, compared to a normal flow for this time of year of 120 cubic feet per second.

Daily inflow into SRP’s reservoirs on Monday totaled 1,687 cubic feet per second, about 21 percent above normal.

A wet January and February throughout the area drained by the Salt and Verde Rivers came on top of a December that proved to be the 11th wettest month in more than a century of record keeping on the Salt and Verde river watersheds, with 4.3 inches.

Climate experts credit the two wet years to La Niña conditions in the Pacific during which water near the surface in the Eastern Pacific is a degree or so cooler than normal. Such periods occur every five to seven years and may last for several seasons — usually following a warm-water El Niño event. Even small changes in water temperature in the Pacific affect rainfall and storms worldwide.

In a normal year, the Salt and Verde watershed gets 6.2 inches between December and March, which means rainfall has totaled 70 percent of a whole season’s average with three months left to go.

Moreover, last week’s heavy snowfall had already left a healthy snow pack in the high country. Most of the high country still had 30 to 45 inches of snowpack, including 29 inches on the Sierra Anchas at Workman Creek, 27 inches at Happy Jack, 31 inches at Hannagan Meadows, 30 inches on Mount Baldy and 29 inches at Alpine.

A substantial snowpack generally keeps reservoir levels high through the spring and into the summer, while also postponing the fire season and easing the impact of drought on the world’s largest expanse of ponderosa pine forest, where the dehydration and bark beetles in the past few years have killed millions of trees.

The past two wet winters represent a solid break from the severe, decade-long drought that had drained the massive Roosevelt Lake to about 15 percent of its capacity.

The brimming Salt and Verde river reservoirs hold enough water to get the Valley through three to five years of drought.

Moreover, snowpack on the upper Colorado River basin is well above normal in most areas, providing an even more substantial hedge against the return of the drought. Although the giant Colorado River reservoirs like Lake Mead remain at about half capacity, spring runoff could provide a substantial recharge.

However, the brimming Salt River reservoirs could pose more of a downstream problem, if a warm spring causes a rapid melting of the snowpack the forest so desperately needed.

Already, the flood of water released from Roosevelt, Apache, Canyon and Saguaro lakes has cascaded down the often-dry Salt River bed in the Valley — washing out some vulnerable roads.

Roosevelt still sits at 100 percent capacity, which means lake levels are near the highest level ever because of a 77-foot-tall addition to the dam several years ago to provide more flood control.

The level on Monday was about 1 foot short of the record level set last spring and about 2 feet short of the level at which SRP would have to let virtually all incoming water pass through.

Roosevelt Lake holds 1.6 million acre feet, while the three other reservoirs on the Salt River hold a combined total of about 352,000 acre feet. All four of those reservoirs are full and spilling water to make room for anticipated runoff.

The two reservoirs on the Verde River hold about 167,000 acre feet. Horseshoe remains at 33 percent capacity and Bartlett at 74 percent capacity, mostly as a result of an agreement with the U.S. Fish and Wildlife Service to protect riparian habitat for an endangered songbird that would be flooded if the reservoirs filled up. The Verde River on Monday at Triangle was flowing at 530 cubic feet per second.

All told, SRP’s system of reservoirs on Monday stood at 94 percent of capacity, compared to 87 percent at the same time a year ago.

The recently completed addition to Roosevelt Dam gives the dam managers ample capacity to handle more water. However, lake levels have already submerged thousands of acres of desert and riparian habitat along the streams flowing into the lake. Additional level increases will submerge picnic areas, campgrounds and boat ramps — in addition to drowning vegetation on thousands of additional acres.

As a result, dam managers try to keep the water level from rising above the current elevation of 2,151 feet. That means big storms in the high country will now generate big flows all the way through Phoenix and on down to Painted Rock Reservoir near Gila Bend.

Those nuisance flows could become real floods if the weather warms in March and melts the snow in the high country quickly.

The federal Bureau of Reclamation has set the maximum elevation of the lake at 2,151, although SRP can let levels rise temporarily into the “flood control space” in an emergency.

“Our plan is to start releasing smaller amounts of water — just before Roosevelt Lake reaches elevation 2,151,” said Charlie Ester, SRP’s manager of water resources.

“That will allow us to see how much runoff we get from these next storms without having to take too much water into the flood control space that we would have to release after a 20-day period.”

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