August 18, 2004
Shaun McKinnon
The Arizona Republic

Arizona's two largest water providers spilled billions of gallons of water onto dry riverbeds and flat, undeveloped desert over the past decade, enough since 1994 to fill Tempe Town Lake 600 times.

And they did it on purpose.

In the middle of a drought.

What Salt River Project and the Central Arizona Project did, and continue to do, is called water recharge or water banking. It helps shore up long-term water supplies, allowing Arizona to collect its full share of the Colorado River, even when it doesn't use it, and shields the water from the pressures of growth or a long dry spell.

Think of a water-recharge project as an underground storage reservoir at a time when the above-ground kind, like Roosevelt Lake or Lake Powell, are too expensive and too environmentally unpopular to build.

Interior Secretary Gale Norton held up the recharge program as an example of good water management and urged other Western states to consider it. But some of Arizona's drought-stricken neighbors grumble about the practice, suggesting it's little more than water hoarding.

"We're just storing water here instead of Lake Mead, where Nevada or California could have access to it," said Bruce Hallin, manager of water business development for SRP, which opened the first water bank 10 years ago this month. "It lets Arizona use its allocation, and by storing it underground, we don't have all the evaporation."

How it works

SRP has recharged about 770,000 acre-feet of mostly Colorado River water in the Granite Reef Underground Storage Project northeast of Mesa. The CAP has stored more than 400,000 acre-feet of water in five projects between Peoria and Tucson. In all, including several smaller projects, the state's water banking program has put away more then 1.8 million acre-feet. An acre-foot is 325,851 gallons, enough to serve a five-person household for one year.

The technology behind water recharging is deceptively simple: Pour water on the ground and let it seep into the aquifer, where it can be retrieved later.

The Persians were doing it in the fifth century. California adopted it as a water management strategy in the 1930s. Heck, even though your mother scolded you for wasting water when you left the hose running, you were actually running your own little recharge project, and you're still doing it when you water your lawn now.

Arizona's water banks are just bigger. Much bigger. And the bankers - SRP, the CAP, the state Water Banking Authority - don't pour the water just anywhere.

"We invest a lot of time and effort up front in finding sites for the recharge projects," said Tom Harbour, supervisor for the CAP's water planning department. "We try to get these things as efficient as we can because water is valuable, and it's getting more valuable every day."

SRP's Granite Reef project sits on about 200 acres in the dry Salt River. A riverbed can be an ideal location for a recharge basin, said Mario Lluria, SRP's senior geohydrologist. The soil and the layer of sand and gravel above the aquifer allow the water to percolate quickly. In the fastest of Granite Reef's seven recharge basins, water seeps downward at a rate of 5 feet per day.

That's important because it reduces the water lost to evaporation - Lluria said Granite Reef loses less than 2 percent a year - and keeps the site from attracting mosquitoes and other pests.

Water banks operate much like the bank where you keep your money. Some of the deposits are meant to be saved for the long term, a non-rainy day when water supplies run short. Some of the water stored is withdrawn soon after and, like your bank, this one allows withdrawals at other locations, a sort of ATM for water.

Chandler, for example, puts some of its SRP and CAP allocations into the Granite Reef project. The city is given a "credit" for the deposit. It can then pump water from one of its municipal wells without running afoul of the state's strict groundwater regulations.

"It's an economical way of utilizing all of our resources," said Doug Toy, senior engineer for Chandler's water-resources department. "It also allows us to meet our peak demands in the summertime."

If Chandler took all of its SRP allocation directly from the canal, it would have to build bigger and costlier water-treatment plants and distribution lines. By using wells, Toy said, the city can serve neighborhoods from wells, treating the water on-site.

Tucson uses a water-recharge project to filter its CAP allocations, complying with voter-approved rules that water from the 336-mile CAP Canal can't be delivered directly to residents. Other cities are storing water as a hedge against shortages. Arizona even stores a small amount of water for Nevada, as part of an interstate banking program.

Glendale has signed on with SRP to use part of a new recharge project set to open in 2005 near the confluence of the Agua Fria and New rivers. But instead of storing SRP or CAP allocations, the city plans to recharge effluent from its treatment plant not far from the new recharge project.

"Storing water is like putting money in the bank, and we're fortunate to be able to put water in this bank," said Doug Kukino, Glendale's environmental resources director. "This is a way to take another source and not use groundwater."

Other Western states

Some Western water leaders aren't convinced that recharging is a truly beneficial use of water, especially during a drought. Colorado officials hinted that if the Colorado River can't meet demands in future years, they might challenge the water bank and try to force Arizona to leave the water in the river.

Arizona officials doubt such a challenge would stand. Other states are studying Arizona's blueprint, and both SRP and the CAP see a need for water banking to help the state manage its growth and to handle future water surpluses.

Environmentalists even see the technology as an alternative to huge reservoirs, but water managers say it's unlikely such projects would replace an existing above-ground project.

"You need them both," the CAP's Harbour said. "You can't recharge the volume of water stored in Lake Powell. But it's good to see people connecting the dots."

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