As people across the nation suffer through one of the worst droughts in a century, Treasure Valley farmers look forward to a bumper crop and homeowners are free to water their lawns.

Part of the reason is Idaho had a heavy winter snowpack and a wet spring that filled the three Boise River reservoirs and Lake Lowell to the brim.

And part of it is the deep aquifer beneath the Valley that provides water security for now — and the near future.

But a new comprehensive plan for the Treasure Valley aquifer urges such actions as studying new reservoirs, recharging the groundwater and implementing new water-conservation measures to ensure that Valley water supplies are sufficient for the next 50 years.

In a half century, the Valley’s population is expected to triple to more than 1.6 million people. Climate change already is bringing earlier runoffs, but in 50 years much of the snowpack that provides the core of the Valley’s seasonal water storage may be gone, said Brian Patton, chief of the Idaho Department of Water Resources planning bureau.

Experts expect that even with changes in the climate, Idaho precipitation will average out — less snow, more rain — to about the same amount as it is today. But the state will see more extreme swings in drought and wet years, Patton said.

And in years with lots and lots of water?

“Our reservoir system is not designed to store those wet years,” he said.

That’s why Paul Deveau, manager of the Boise Board of Control that runs the New York Canal, wants to build a new dam on the Boise River to serve future development and growth.

“They keep adding stuff and they keep adding stuff,” Deveau said. “I worry about where the water is going to come from.”

FUTURE SUPPLIES

The U.S. Army Corps of Engineers did a broad look from 2009 to 2011 at possible new reservoir sites at the request of the Idaho Water Resources Board, the eight-member board that oversees water management in the state. It looked at 12 sites in Boise County, sparking controversy and sending environmentalists and irrigators to their respective corners to prepare for a fight.

But when the Corps came back with its recommendations, it determined that the best option was to increase the capacity of Arrowrock Dam by raising it 72 feet, a far less polarizing alternative than building a new dam.

“There may be storage options we can live with, but we want them to look at all the options,” said Peter Anderson, an attorney for Trout Unlimited.

Now the Corps and the state are working with the Bureau of Reclamation, which owns Arrowrock and Anderson Ranch dams, on a formal feasibility study. This step would lay the groundwork for asking Congress to authorize major construction.

But water supply is only part of the question for the federal agencies. Protecting against flooding is as important to consider as protecting against drought, said Ellen Berggren, project manager for the Army Corps of Engineers in Boise.

With an estimated $10 billion worth of homes, buildings and other structures in the Boise River flood plain, flood protection is a high priority. But there are alternatives to dam-building for flood control, like new levees, more wetland protection and measures to lift buildings above flood level.

“It can’t just be a study about a dam, because we’re required to look at alternatives,” she said.

EXAMINING THE AQUIFER

The Comprehensive Aquifer Management Plan for the Treasure Valley, which is out for review and will be the subject of community meetings in September, also looks beyond dam-building.

While the region’s network of canals supplies farmers and, increasingly, subdivisions with irrigation water, the vast majority of the water for residential and industrial use comes from groundwater supplies. United Water, the private company that supplies most of Boise’s water, has 85 wells that provide 70 percent of its supply.

While some areas have more than enough well water, in other places, including Southeast Boise, the aquifer can’t meet the demand for drinking water, lawns and industrial use. For those areas, United Water uses Boise River water to provide 30 percent of its supply.

But experts know that the aquifer is finite and want to plan ahead to keep it healthy. The new comprehensive plan calls for promoting conservation of groundwater uses, to put off the day when the Valley faces the kinds of conflicts that divided groundwater and surface water users in the Hagerman area and points east.

The plan also promotes continued groundwater recharging as United Water does in Boise — where surface water is pumped into the aquifer at times of abundance. Groundwater also gets recharged, incidentally, by canal companies by simply running water down their porous ditches and canals.

Anderson said he sees aquifer recharge as more effective for staving off the effects of future drought than a new dam would, and prefers that option to the irrigator’s choice of a new dam.

“The best form of storage for climate change is aquifer recharge,” he said.

Despite many different viewpoints, the Comprehensive Aquifer Management Plan reached a consensus of support among the groups that have been working on it since 2010.

But there will be conflicts in the future.

An effort by cities to put in the plan a process for them to designate water to supply their future needs — which irrigators see as a challenge to their water rights — was rebuffed by the water board. “That’s a wholly separate issue,” said Vern Case of the Wilder Irrigation District, who led the fight against including the city proposal.

In the Magic Valley, the bitter Eastern Snake Plain controversy pitted farmers who pump water from the aquifer against farmers and fish companies who depend on flows from springs for their water. At one point, the state threatened to force farmers to turn off pumps to thousands of acres of cropland and to force cities there to strictly limit water use.

Only after groundwater users taxed themselves to pay for alternative water supplies for farmers and fish farms who depend on springs and had senior water rights — and in some cases to buy the fish farms — was the dispute settled.

FUTURE WATER WAR?

How soon supplies could force such a standoff in the Treasure Valley is among the debates. Some, like Case and Deveau, think a legal water war could be just one long drought away.

But Patton said such a fight is less likely here. Irrigation makes up just 6 percent of aquifer use while 94 percent of the water goes to domestic, commercial, municipal and industrial users.

Because the deep aquifer that United Water and most cities depend on is relatively stable, such a dispute seems far off. But all sides agree that monitoring groundwater and improving the understanding of the connections between groundwater and surface water are critical to the region’s future.

Scott Rhead, an engineer with United Water, has watched water supply issues change dramatically over the past decade. No one was talking about climate change then, and scientists better understand how the system works today than 20 years ago.

“Certainly this Valley watched the Eastern Snake Plain play out and we certainly don’t want to go down that route,” he said.

Rocky Barker: 377-6484