Irrigation districts are beginning to divert water from the Boise River this week, filling the canals and ditches that irrigate the croplands, yards and parks that make our valley green and prosperous.
Cities and subdivisions from Boise to Caldwell won’t be in a hurry to turn on the pressured irrigation systems that allow homeowners to water lawns and gardens because moisture is usually high this time of year. We have a lot of snow in the mountains, so it doesn’t look like Idaho will be short of water in 2016.
But a new report compiled for the Idaho Water Resource Board, which oversees water planning and project financing for the state, suggests that demand for water is going to soar over the next 50 years as the Treasure Valley’s population more than doubles. The report, written by water engineer Christian Petrich, predicts that demand for domestic, commercial, municipal and industrial — also known as DCMI water — could rise from 110,000 acre-feet per year to 270,000 to 390,000 acre-feet per year.
That sounds ominous. But don’t forget, 95 percent of the water used in the Treasure Valley goes to irrigation. Some of the 485,000 acre-feet of irrigation water goes to lawns, parks and other DCMI uses, but most goes to crops.
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Idaho water supplies are far better off than in many places across the West. That’s one of the reasons I say Idaho will be better able to ride out climate change than much of the West.
But the rising population here, which Petrich estimates will grow 252 percent to 1.5 million people in 50 years, will place added pressures on our supply. That prospect should prompt state and local officials to begin planning now for how we will meet this need.
Most of the discussions have focused on building more dams or raising the levels of existing reservoirs, such as Lucky Peak. The Water Board has pressed this and put up funding for studies so that the U.S. Army Corps of Engineers will make sure this preference of the Treasure Valley’s farmers and irrigation companies is front and center.
But the state also is looking at managed aquifer recharge, upgraded irrigation headgates and piping water in from the Snake River. Petrich’s study shows that the Treasure Valley needs a lot more research before it can begin a large-scale aquifer-recharge program.
What doesn’t get discussed is the possibility of transferring water from irrigation to DCMI use.
Farmers and irrigation districts hate the idea and have the lawyers and lobbyists to make sure it doesn’t happen anytime soon. But marketing water to those willing to pay is a central part of the first-come, first-served, prior-appropriation doctrine that requires the full beneficial use of the water owned by the state and all its citizens. Resistance aside, it will eventually arrive here.
But that’s an argument for later.
Today, the Water Resources Board study suggests conservation and efficiency be considered as one option. Petrich said that as the price of water rises, people will naturally find ways to use it more efficiently. So he says the lower range of his 270,000 to 390,000 acre-feet future water demand prediction is more likely.
But cities, counties, developers and the state can take steps to tap into water that now flows through the canals and back into the Boise River, heading to Washington and Oregon. If we took such steps, we could leave more water in our storage reservoirs for farmers and everyone to use later in the year, even in drought years.
Here’s how it could work. About 30,000 acres of the Treasure Valley is now watered with pressurized irrigation systems. A lot of those acres have been converted over the past 25 years to houses, driveways, streets, parking lots, stores and factories.
The Department of Water Resources has noted in past reports that the area irrigated in a subdivision usually drops by 40 percent to 65 percent from the amount watered when that land was a farm. Yet irrigation districts report that water use in these areas actually rises.
Really? Well, yes. But that’s because few of these pressurized water systems rotate their watering the way a farmer does. A farmer would irrigate no more than nine acres of an 80-acre tract at any one time.
The Treasure Valley is blessed with a much better water supply than most cities in the arid West.
Christian Petrich, Boise water engineer
But the irrigation district has to keep the ditches full to serve residential water users, who can turn their lawn sprinklers on at any time. So to serve the 40 acres of irrigable land that remain, the district often diverts the same amount of water as it did when there were 80 acres in crops.
Changing the irrigation infrastructure to serve the real needs of residential users — and divert only the water that goes to beneficial use — will be expensive for existing systems. Residents will resist having to time their watering, even though it’s routine elsewhere in the West.
But the sooner we begin looking at these ideas and, perhaps, requiring new developments to include such things as storage ponds for lawn-irrigation water, the more water we can store in our existing reservoirs.
If you think your irrigation district should talk about these ideas, give them a call. They are governmental entities that collect taxes and have elected boards. It’s time for a wider discussion of our water future.