Necessity of new reservoirs debated

Some say climate trends argue against building

Source: Noaa By Deborah Frazier, Rocky Mountain News

Published February 22, 2007 at midnight

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Climate change may mean less water in Colorado rivers and streams, but experts can't agree on whether building more reservoirs is a wise investment or a waste of billions.

A series of recently released studies on climate change in the West predict more drought, warmer weather and greater water loss because of evaporation.

"The future doesn't portend a new abundance of nature's water. Rather, nature will be taking more water than it's now delivering," said Martin Hoerling, of the National Center for Atmospheric Research in Boulder.

Hoerling's research focused on the Southwest and the Colorado River, which originates in the Rocky Mountain snowfields.

Denver, Aurora, Colorado Springs, Fort Collins and other cities tap the Colorado River in western Colorado and move about 500,000 acre-feet to reservoirs that serve the Front Range.

An acre-foot, 325,800 gallons, supplies one to four families for a year depending on lawn size and landscaping.

Hoerling and other weather researchers said that climate trends argue against building more reservoirs that rely on the Colorado River.

"If you add reservoirs, you are not going to fill them," he said.

The Colorado River serves seven states - Colorado, Wyoming, New Mexico and Utah in the upper basin and Arizona, California and Nevada in the lower basin.

When the 1922 Colorado River Compact divided the water among the states, the annual flow was estimated at 15 million acre-feet.

Hoerling said that the recent annual flows are about 13 million acre-feet, but by 2050, climate change may drop that to about 10 million acre-feet - less than what is currently used by all of the states. That could mean there would be no extra water to store in Colorado, which hasn't claimed it's full share of the river, he said.

"You can build all the reservoirs you want, but there are no existing surplus flows to fill them," he said.

That's not the conclusion that Chips Barry, manager of Denver Water, draws from the studies. Denver Water supplies 1.2 million homes in Denver and the suburbs. "It's a powerful argument for building more storage," Barry said. "More storage is one of the ways to adapt to climate change."

Barry said the climate studies also found a trend toward episodic periods of heavy precipitation with earlier and heavier runoff seasons.

"When you have a highly variable precipitation pattern, you store as much water as possible in times of plenty," he said. "That's the lesson of the West. You need more storage for the swings."

That doesn't mean a revival of the big dam building era that started in the 1960s after the devastating droughts of the 1950s.

Barry said that the best dam sites - mountain canyons - already have reservoirs. Environmental issues, political conflicts and costs make new reservoir construction difficult, he said.

That includes a reservoir that Denver Water wants to build near Wolcott in Eagle County. Denver Water owns enough water rights to fill a new reservoir, but a federal mediator is trying to resolve conflicts with western Colorado interests who want to keep the water there.

Despite the opposition, Barry said that Denver Water will pursue the project. The reservoir's size hasn't been determined, he said. "I can't afford to wait to fix global warming," Barry said. "And, you can't conserve your way out of global warming."

Neil Grigg, a civil engineering professor at Colorado State University and a water resources consultant, said that smaller projects may be the future.

Blue Mesa Reservoir near Gunnison is the state's largest storage project, at 940,000 acre-feet. Denver's Dillon Reservoir holds 252,000 acre-feet.

"If you built a large project and climate change diminished the water supply, it would never fill," Grigg said. "You'd have a failure."

Smaller reservoirs store up to 200,000 acre-feet, he said.

Large reservoirs at lower and warmer elevations also lose more water to evaporation - up to 30 percent of the stored supply in the southwest, officials said.

Grigg and others said that projects with smaller reservoirs that capture water from several river systems will be the most effective.

The Northern Colorado Water Conservancy District, which serves Fort Collins, Greeley and other towns in Larimer, Weld and Boulder counties, is studying several new storage projects.

"As we look at the forecasts for less runoff and most of it coming down all at once, we think we need to grab it as fast as we can," said Brian Werner, the district's spokesman.

The district is studying a 500,000 acre-feet reservoir near Maybell in northwestern Colorado to capture the Yampa River flows, he said. The Yampa River flows into the Colorado River, so the project would claim part of the state's share of the river.

The project could bring water to the South Platte, where farmers have had irrigation wells shut off, and to the south metro suburbs, Werner said.

The climate change projections make the project, estimated at up to $4 billion, more attractive, Werner said. "While the drier years will get drier, those few wet years will be wetter. In those high years, you need the largest vessel possible," he said.

Chuck Howe, an economics professor at the University of Colorado who specializes in water supply, agreed. "The runoff will come earlier and faster and you'll want to catch it," he said.

But Howe added a warning. "There are places where additional storage ought to be considered, but one has to consider whether they will fill."

Nolan Doesken, the state's climatologist, said that the recent studies have shifted the discussion from whether there was climate change to "what do we do about climate change?"

"We know we are grateful for the water-storage projects we have now, but will new ones be cost effective? I have no idea," he said. "That decision is the greatest challenge for the combination of science and policy that our part of the country has seen in a long time."

frazierd@RockyMountainNews.com or 303-954-5308

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