Liquid Assets

A new breed of bankers is helping communities save for un-rainy days

Before last fall’s hurricane season deluged the southeastern United States with water, water, and more water, meteorological news had focused on the paucity of rain. Persistent droughts had been parching most of the eastern half of the country, racking up huge economic and environmental impacts.

Water from streams, rivers, and lakes seldom is sufficient to supply a city’s needs. Groundwater fills the gap. Dennis Wentz/USGS

The snow-bank savings plan: Water droplets from sprayer freeze into snow, which falls onto a mound. An insulating blanket could control melting. Sampson & Associates

During the 1999 drought, water levels in the reservoir in Calvin’s Cove, Va., dropped 29 feet. Rick Griffith/Virginia Issues & Answers

For instance, farmers in Maryland, which had its second-driest year in recorded history, suffered losses valued at $100 million. Despite an Indiana ban on open burning, almost 1,000 uncontrolled fires ravaged that drought-stricken state. In portions of Vermont, up to 90 percent of the frogs succumbed to the dry spell. Roots on tens of thousands of New York trees lost their anchoring grip, causing them to topple over during autumn storms.

The National Drought Mitigation Center in Lincoln, Neb., issued a drought watch in July 1998 for parts of Maryland, West Virginia, and Pennsylvania. Over the ensuing year, the affected areas expanded and coalesced with other desiccated pockets to encompass a huge swath of land from south-central Texas through northern New England.

“Unfortunately,” maintains Don Wilhite, the center’s director, “this country—and most others—have not done a very good job of preparing for droughts. We tend to react to them in some emergency mode” during crises, then become lulled back into complacency as each crisis subsides.

“Drought is a normal part of climate,” points out Wilhite. Droughts’ impacts, however, have intensified. The problem, he suspects, is that “people still view water as an essentially unlimited resource—one [that’s] basically free.” Yet with a growing population and increased consumption of water, mushrooming development of arid and desert landscapes, and widespread pollution of the aquatic environment, such an attitude can be dangerous, he says.

Increasingly, water managers are recognizing that even in times of bounty, the water supply must be considered precarious. Reluctant to rely solely on precipitation for the replenishment of their water, many are seeking ways to squirrel away their liquid assets during years of plenty.

Some communities are moving surplus water to replenish underground reservoirs, where water naturally accumulates. Meanwhile, scientists are exploring new technologies to optimize such stores. Other researchers are coming up with more creative ways to bank water. Schemes range from making huge snow piles to creating commercial markets for water rights.

Refilling aquifers

Public utilities dispense about 40 billion gallons of water to U.S. customers daily. Nearly 40 percent of it is pumped from subterranean aquifers—usually beds of water-saturated gravel and sand. Though utilities take the larger portion of their water directly from lakes, rivers, and streams, a large share of even this resource traces back to groundwater aquifers upstream.

Particularly in the arid western United States, many communities have been withdrawing groundwater faster than nature replaces it. To improve the balance sheet, water managers are exploring artificial ways to refill those aquifers.

Methods for occasionally recharging groundwater systems have been around since before the time of Christ, observes Wayne A. Pettyjohn, a consulting hydrologist in Stillwater, Okla. Back then, communities would divert river water or snowmelt into a pond and allow its contents to seep into the ground.

Around 35 years ago, Pettyjohn designed such a system for Minot, N.D., a town whose wells had all but run dry. Within 6 months, he says, the groundwater recharge “brought the [underground aquifer’s] water level up 22 feet.”

Lately, utilities have turned to more aggressive recharge methods that inject water underground. While the technology for such active banking of water has been around for nearly half a century, “it was no more than sporadically used until about 10 years ago,” notes Daniel J. Acquaviva, a groundwater-recharge consultant in Cape Coral, Fla.

Hydrologists in Las Vegas initiated one of the first systems in 1989. That city gets most of its drinking water from surface sources, tapping into groundwater only to make up the residual demand.

The aquifer below Las Vegas naturally collects 35,000 to 55,000 acre-feet of water per year. “For quite some time, we were pumping out a lot more than that, about 70,000 acre-feet per year,” notes Erin Cole, senior hydrologist for the Southern Nevada Water Authority in Las Vegas.

An acre-foot is 325,851 gallons, or the volume of one acre flooded 12 inches deep. Not only was the city’s rate of pumping unsustainable, but it also risked collapsing the aquifer. Without enough water to support the earth above it, the aquifer might subside and compact. Water managers couldn’t rely on refilling the aquifer with seepage from surface ponds, Cole notes, because the city’s underground reservoir was confined beneath an impermeable layer of clay. So, Las Vegas has initiated an active banking program. Nevada residents have rights to water from the Colorado River, which touches the southern tip of the state. Las Vegas now runs a portion of this water through municipal treatment plants and injects it into the aquifer via some 60 wells spaced over a 16-square-mile area that includes the city. Notes Cole, “We now recharge [the aquifer] with about 30,000 acre-feet per year.”

Slime build-up

There’s a problem with injection wells, however. “They generally screw up,” Pettyjohn notes. “If you don’t use practically distilled water, a slime can build up and the infiltration rate diminishes to practically zero.” Ten years into water banking by water injection, Cole acknowledges that the Nevada wells are exhibiting signs of obstruction. “We think what’s happening is a biological and particulate clogging,” Cole says. The high oxygen content of the injected water, for instance, may feed bacteria in the aquifer, encouraging them to congregate in a slimy biofilm at or near the well. Injected water may also carry particulates or stir up silts in the gravel bed, leading to blockages in the well or in pores of the aquifer.

Clearly, injection-well aquifer recharge is not a mature technology, she says, but a continuing challenge. That’s something John M. Stomp appreciates. Water resources manager for Albuquerque, he’s in charge of developing an injection-well water-banking system there. “We face a ton of research challenges,” he says, because no such system is available off-the-shelf.

Though Albuquerque purchased water rights to the Colorado River from the federal Bureau of Reclamation 30 years ago, it has to date relied solely on groundwater. Last year, this city of 450,000 people pumped out almost 120,000 acre-feet.

Stomp’s job over the next 5 years will be to guide the city in a transition to total reliance on river water for routine use. The city has just implemented a series of rate hikes to pay for a new pipeline to access that water and a new water-treatment plant.

Once the pipeline is in place, the city will bank any excess water underground. “It’s our intent to transform our groundwater into a drought reserve,” notes Stomp, “something we desperately need here in the desert.”

“A huge challenge” in the project will be matching the chemistry of the river water to that of the pristine groundwater, Stomp says. That step will be essential, he says, because it will limit well clogging and prevent chemical reactions that could unleash minerals now lying undisturbed in the water system. These minerals could make the water unappealing, a problem that has plagued Tucson, he notes.

Water savings bank

Arid regions aren’t the only ones banking water. Right now, “it’s being looked at on a very large scale in Florida,” notes William M. Alley of the U.S. Geological Survey in Reston, Va. Though Florida experiences plenty of rain, it falls at the wrong time. “We get two-thirds of it in about one-third of the year—and that one-third includes summer, when demand is lowest,” explains Jack McCoy of Lee County’s Division of Natural Resources in Fort Myers. Unlike other states, Florida’s peak water demands occur in winter, when more people populate the state.

In response, he notes, some Florida water utilities have begun capturing summer rains and banking them underground. “When snowbirds and tourists arrive in the winter,” he explains, “we just reverse the wells’ pumps, chlorinate the water, and then send it to customers.”

Even New England states face the need to bank water. It’s there, in fact, that researchers are exploring one of the more unusual engineering approaches.

Hydrologists across the country have begun eyeing sites other than natural aquifers as potential reservoirs, including abandoned underground mines. Moshe Alamaro of the Massachusetts Institute of Technology has a flakier idea. His simple scheme is to make a big mound of snow in winter and then melt it as needed the next summer.

Alamaro says he started thinking about the possibility of banking water in Massachusetts a few years back. That’s when he heard a news report about a coastal suburb of Boston considering a costly water-desalinization plant as a means to deal with summer water shortages.

“This is crazy,” Alamaro recalls thinking. “Desalinization might be appropriate in arid regions like Egypt or Saudi Arabia but not Massachusetts.” As an Israeli native, Alamaro had been dazzled by the Boston area’s precipitation. Its heavy winter snowfalls set him brainstorming about how towns might bank their snow.

The trick to making this affordable, Alamaro’s calculations indicate, would be to pump water from a local river and spray it from high above the ground—perhaps 350 feet up—on cold, dry, windy days.

Water would turn to snow. For every 20 grams of water sprayed during this snowmaking, 1 g would evaporate, he says. That small amount of lost water would take heat with it, forcing what’s left to freeze.

“When I spray water droplets from high altitudes,” Alamaro notes, “their extra-long flight path gives them contact with lots of air,” fostering heat exchange. Wind helps, he adds, by continuously whisking moisture-saturated air from the evaporative zone.

At 0ºC, a wind speed of 1 meter per second, and 50 percent humidity, this technology can generate 180 kilograms of snow per square meter of land per day, Alamaro’s calculations show.

In Quebec City during midwinter, he crows with enthusiasm, “temperatures get low enough that we could freeze all its yearly water needs in just 1 day.” Commercial snowmakers could then fold up their water-spraying scaffolds, relocate to some other drought-prone community, and begin 1 or more days of banking winter moisture there.

To limit melting, Alamaro would jacket these snow banks with a sandwich of thin layers of silvery plastic separated by air. Because it should lose no more than a few percent of its mass to melting during each of the early months of storage, a well-insulated municipal mound could last more than a year. Communities could use the steady trickle of water throughout most of their normal dry season and peel off the insulating blanket to quickly thaw more snow during droughts.

Alamaro has been fielding calls from municipalities in the United States and Canada, and even as far away as New Zealand, inquiring about his snow-banking technology.

Trading water rights

California is experimenting with market-based approaches to its water shortages. Deborah Braver, a Sacramento-based consultant, explains that the idea isn’t to bank water per se. Rather, communities have begun trading water rights in novel ways.

In one type of contractual arrangement, farmers who normally irrigate their land have begun entering agreements with communities or industries. During a drought, farmers will temporarily turn over their water rights for a steep price. Affected growers could live on this income while they temporarily fallow fields or grow less thirsty, but less lucrative, crops.

In another form of water-rights banking, communities with diminishing groundwater buy long-term rights to surface water from communities with a surplus. While the purchasing community uses the procured water from canals and rivers, it foregoes use of its groundwater so that rains and snowmelt can replenish the aquifers.

To discourage depletion of water supplies, several utilities have raised water prices during periods of high demand, low availability, or when consumers exceed an allowance.

The most impressive example of such an approach, Braver says, is the Irvine Ranch Water District in Orange County, which 9 years ago issued every customer an individualized water budget.

After surveying the size, landscaping, and microclimate of each customer’s property, the utility assigned a monthly allotment of water. Explains Dale Lessick, the utility’s water-efficiency manager, any consumption over the budget is billed at up to eight times the base rate—a price intended to trigger sticker shock and conservation.

These budgets have proved enormously effective, Lessick notes. Almost overnight, the utility registered a 19 percent reduction in water use. To date, it has saved the community around 65,000 acre-feet of water. It’s now investing the extra revenues from budget-busting consumers in water-reclamation and novel conservation efforts. The advantage, she notes, is that only those who exceed their budget must finance these additional measures.

Dry spell or drought?

Most people don’t realize that drought can ravage any state, in any month, in any year, observes climatologist Mark Svoboda of the National Drought Mitigation Center.

Though communities expect to see dry spells, they’ve been loath to spend money preparing for them. When does a dry spell become a drought? No objective definition exists today, observes Cody Knutson of the drought center. Nor is any one body coordinating emergency responses to drought, which can involve up to some 70 different federal agencies, notes Wilhite.

At least as important, he says, no clearinghouse exists to collect and disseminate information on strategies—such as water banking—that could help communities prepare.

That could change.

Eighteen months ago, the President signed into law an act setting up the National Drought Policy Commission. This spring, the panel will issue a report to Congress addressing “what’s broke and needs to be fixed” in drought policy and government responses to water shortages, explains George Cross, a member of the commission’s staff in Washington, D.C. Wilhite and others hope the commission will not focus merely on responding to drought damage. If the commission and, in turn, government agencies would stress prevention of water shortages, he argues, fewer people will suffer from drought.

“In the long run,” he adds, “it’s also cheaper.”

Janet Raloff

Janet Raloff is the editor of Science News for Students, a daily online magazine for middle school students. She started at Science News in 1977 as the environment and policy writer.

More Stories from Science News on Earth

From the Nature Index

Paid Content