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‘It’s tough’: Drought could lead to Treasure Valley irrigation ending a month early

Treasure Valley farmers and other water users are likely staring down a shortened irrigation season as high temperatures continue to bake the region.

In a normal year, water runs across southwestern Idaho from a network of three reservoirs in the hills above Boise through a vast network of irrigation canals to water crops through October. But, this year, the brutal one-two punch of a dry spring and record-breaking summer temperatures took the Boise River Basin to near record lows. This means irrigation could stop flowing sometime in September, roughly a month earlier than normal.

[The Boise River: nature, development, and water quality shape its future]

Boise Watermaster Rex Barrie, who manages the Boise River irrigation system, recently warned irrigators and other water users, like water company Suez, to conserve water so the supply can stretch as long as possible. He said this year’s low numbers are on track with 1977, the lowest runoff year on record for the Boise River Basin.

He said some irrigation districts instruct their users to alternate watering on odd and even days, and residential users should slow down watering their lawns.

“The more water we can conserve, the further we can stretch our season,” Barrie said. “In agriculture, there are crops that have to be watered. If they don’t get the water, the guys lose their yield and a loss of yield results in a loss of income, and it’s tough. As far as the urban folks watering your yard, the grass is extremely resilient. It can go brown, but when you start to water it again, it will start to go green again.”

Lower than average reservoir levels

This drought started unusually, with a typical snowpack that normally marks the start of a good water year. But, without the typical spring rains and multiple days over one hundred degrees in June and July’s heatwave evaporating the water, the network of reservoirs powering the Boise River network didn’t fill. Numbers from the Bureau of Reclamation show 2021 volumes at the Arrowrock, Anderson, and Lucky Peak reservoirs far below average.

A graph from the Idaho Bureau of Reclamation showing average water volumes in the Arrowrock, Anderson, and Lucky Peak reservoirs over time.

Typically, the three reservoirs would have 704,000-acre-feet of water in them at this point in the season, according to Bureau of Reclamation Hydrologist Ryan Hedrick. This year there are only 478,000-acre-feet in the system at the end of July. 

The way water is distributed to users is based on a complex legal system of water rights. At the beginning of the season, as long as there is enough water, all users who have water rights can divert their full amount of allotted water into the canals. As the water supply depletes, water users are allotted a smaller and smaller percentage. Eventually, the Watermaster starts curtailing their rights to divert from the river based on priority date. The newest water rights are shut off first, and the order goes back in time, all the way to the earliest rights in 1864.

[Water woes: Canyon County turns down 35-home subdivision south of Nampa over groundwater concerns]

Right now, Barrie is releasing water only to customers with water rights given in 1871 or earlier. However, customers with storage rights are still entitled to water being held in the reservoirs. Barrie is responsible for releasing the proper amount of water from Lucky Peak to meet the orders from the various irrigation districts and other customers every day.

Irrigators pulling the highest volumes off of the River

One of the largest customers on the Boise River is the New York Canal, which is diverting 2,000 cubic feet per second of water every day. This water feeds five different irrigation districts, including one across the Oregon border. Bob Carter, project manager for the New York Canal Boise Project, told BoiseDev the heat had been an “unknown factor” in 2021, driving high demand since the floodgates first opened.

Idaho fishing
An angler along the Boise River. Photo: Don Day/BoiseDev file

“We’ve been at capacity now since day one, and demand has been high just because of the heat and the dry spring,” Carter said. “The customers are concerned because of how certain crops are towards the end, so they like to have that extra water. Sugar beets and corn use a lot of water. Some people say they’ll be fine and get by, but other ones will be more concerned because of the crop choice.”

Suez also diverts water from the Boise River to fuel its drinking water distribution system for the Treasure Valley, but not nearly as much as irrigators do. On July 19th, Suez diverted 14 cubic feet per second from the Boise River, far less than the New York Canal. When their storage capacity is exhausted, the system will have to completely rely on pumping groundwater to meet the valley’s drinking water needs.

Suez usage up a billion gallons

With less water in the canals comes less water recharging the aquifers for residents to drink from. And in turn, there is more pumping of groundwater to meet demand. Last month, Idaho Depart of Water Resources staff told BoiseDev that the valley has plenty of groundwater to meet current demand, but it raises long-term questions about how water moves through the valley.

“That feedback loop troubles me,” Hedrick said. “You have to look at the growth of the value in how many more people are drilling wells and depleting that aquifer than before.”

Suez recently urged customers to cut down on water use by only watering lawns two or three times per week, avoiding watering during the heat of the day, and aiming sprinklers on the grass instead of sidewalks. The company has used a billion more gallons of water than expected in 2021 so far, with usage up 15% in July, according to company spokesperson Katie Birkenstein.

“It has been an unusually hot, dry summer, and using water wisely has never been more important in the Treasure Valley,” Birkenstein wrote in a press release. “As the water provider to nearly a quarter of a million people, SUEZ carefully tracks water use in order to ensure there is enough supply for everyone.”

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Margaret Carmel - BoiseDev Sr. Reporter
Margaret Carmel is a BoiseDev reporter focused on the City of Boise, housing, homelessness and growth. Contact her at [email protected] or by phone at (757)705-8066.

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