Idaho irrigation

Demand for water from canals like this one outside Kuna, Idaho, dropped substantially as rain persisted during the second half of May.

Irrigation demand dropped substantially in the second half of May in southwestern Idaho and southeastern Oregon as heavy rain persisted, leaving canal operators managing extra water and preparing for a surge in usage as soils dry.

“With the precipitation and how cold it is, irrigators are pulling back on the amount taken from New York Canal,” said Joel Fenolio, water management team supervisor at the U.S. Bureau of Reclamation Snake River Area Office in Boise. The canal is just below Lucky Peak, the closest of the three Boise River reservoirs to the city.

Irrigators as of May 19 were taking about 2,100 cubic feet per second worth of Boise River flow, he said. They took about 1,500 as of May 22, or 28.5% less, when soils were saturated and the river’s flow through the city totaled around 4,000 cfs — down from about 9,300 earlier in the month following irrigation and other diversions.

Nampa & Meridian Irrigation District Water Superintendent Greg Curtis said May 22 that flows from the district’s main canal are down from a year ago, “but the other thing to that is we are spilling water to drains this week because demand is down.”

About 5% of the current lower total is going into drains, in part “so when demand picks back up, it’s right there in the system,” he said. Current flood-control releases from the dams — which the Treasure Valley Water Users Association say occur in the Boise system seven of 10 years historically — make the strategy viable in that it uses streamflow rather than reservoir-stored water.

The three Boise River reservoirs are on track to fill on schedule, in middle to late June, Fenolio said.

Lake Lowell, an off-river storage reservoir fed by New York Canal, as of May 22 contained about 155,000 acre-feet of water compared to an active capacity of 160,000, he said.

Long periods of consistent rainfall bookended a dry period in the region from about mid-April to mid-May.

After April’s wet start delayed some planting, “we were starting to ramp up to make deliveries,” Curtis said. “Then with this last couple of weeks we’ve had, it put a damper on everything.”

Crop fields in the second half of May received 1 to 2 inches of rain depending on location within the region, slowing demand for irrigation water and postponing some first cuttings of hay, he said. The district is preparing for demand to jump as the weather warms.

At Caldwell-based Pioneer Irrigation District, Superintendent Mark Zirschky on May 22 said diversions were down by about 20% from a year earlier, when a storm slowed demand.

“There have been tractors sitting in the field in the last week not moving,” he said.

Wet weather prompted Pioneer to reduce diversions, and run some groundwater wells to help lower the water table and reduce risk of surface-water flooding. Managing groundwater levels in this way “is largely because the drain ditches are running so high because of all the rain we are getting,” Zirschky said.

Reducing diversions, and using supplemental sources like wells, ultimately reduces Pioneer’s need to spill water later and helps save reservoir-stored water, he said.

District crews will make some ditch, bank and access-road repairs when conditions dry, Zirschky said.

“As soon as this rain stops, we know (demand) is going to go in the other direction,” he said. “I look forward to it ramping up fairly quickly as soon as the weather passes.”

In Nyssa, Ore., Owyhee Irrigation District General Manager Jay Chamberlin said demand traditionally rises by late May to around three-quarters of system capacity.

But there was little or no demand May 22 as rain continued, he said. Flows were essentially stopped except for amounts needed to maintain system operations.

“We expect demand ramping up fairly quickly,” Chamberlin said. “We have to prepare and be ready for when that demand occurs.”

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