Reservoirs full; La Niña likely again this winter

Bill Bradshaw / Farm & Ranch
At 43 percent of capacity, Ririe Reservoir was one of the lower reservoirs in the Upper Snake River system Tuesday, but still held more than last year thanks to last year's healthy snowpack, an early start on this winter's snowpack and lower-than-usual irrigation requirements by eastern Idaho farmers.

Bill Bradshaw / Farm & Ranch
Many eastern Idaho canals, such as this one just south of Ririe, are still running full, despite the end of the irrigation season. Many of the region's reservoirs are much fuller than normal for this time of year.

The new irrigation water year is shaping up to be excellent.

The Upper Snake River Region Reservoir System is about 74 percent full. Currently, it contains about 3.075 million acre-feet of water. An acre-foot is the amount of water it takes to cover an acre of ground 1 foot deep.

The system holds about 4.1 million acre feet of water, said Lyle Swank, Idaho Department of Water Resources District 1 water master, in Idaho Falls. The irrigation year began Wednesday, and continues through Oct. 31.

The system includes Jackson Lake and the Palisades, Island Park, Ririe, American Falls, Milner and Little Wood reservoirs.

“It’s already shaped up to be a great outlook for 2018,” Swank said.

In the past century, just one year surpassed 2017 in the amount of water flowing through, and measured, at the Heise Gauge on the Snake River; only 1997 was higher,” Swank said.

“The water flow at Heise was the second highest in the over 100 years that records have been kept there,” he said. “Considering that we had that much water coming at us, the water managers did pretty well this year to fill the reservoirs and not have much flooding.”

That, coupled with less late-season irrigation demand due to mid-September’s precipitation and a considerable drop in temperatures, has helped boost the amount of water held over in the system, Swank said.

“We went from having pretty warm temperatures to some very cold temperatures, and with the precipitation, the demand is below average,” Swank said. “Irrigators have not needed that much water to get through the end of the growing season for the past six weeks.”

In addition, the latest storms blanketed area mountains with snow.

“We have snow in the mountains, and that’s also helping us get off to a good start for water supplies in 2018,” Swank said.

The conditions also have lent themselves to recharge of the Upper Snake Plain Aquifer.

“With the high amount of storage water carried over and the precipitation, work is going on this fall to take advantage of recharging the Snake River aquifer in places where we can’t store water,” Swank said. “That’s how big the 2017 water year was.”

Right now, the forecast for the next three months looks similar to last year, according to Kurt Buffalo, a meteorologist with the National Weather Service in Pocatello.

“La Niña conditions are forecast to develop again this winter. La Niña conditions were in place last winter, and contributed to the well-above-average snowfall that fell across the area,” Buffalo said. “The outlook for this winter is again favoring above average precipitation based on the expected influence of La Niña.”

Farmers such as Louis Thiel are pleased with this year’s conditions. Thiel is a third-generation farmer in the New Sweden area west of Idaho Falls. Although he’s retired, he continues to serve on the New Sweden Irrigation District Board, and is currently the board’s chairman. Thiel’s sons, Marc and Ryan, raise potatoes, alfalfa, wheat, malt barley and seed barley on about 1,000 acres. They also have about 130 head of heifers.

“We’re going into this next year with one of the biggest reservoir reserves. Our whole reservoir system is in better shape than it’s been in years,” Thiel said.

In addition to helping out on the farm, and being chairman of the New Sweden Irrigation District, Louis Thiel keeps up on the latest weather forecasts and information about irrigation water supplies.

“For us in the farming business, weather is always an unknown, and that’s the scary part,” he said.

Often, two things determine how good the water supply will be: the weather during the spring runoff and spring precipitation, he said.

“If we have an early warm spell around March or April, and the water runs off too quick, we can still come out short. Once the runoff quits and we start using storage water, it doesn’t take long to drain the reservoirs,” he said. “Spring rains have a tremendous impact on our water supply. There’s a lot of things you have to watch, and keep an eye on. We’re really blessed that the people who came before us had enough outlook to get a lot of water in the water districts here.”