DENVER — Colorado officials are planning to build multiple large reservoirs on the prairie northeast of Denver to capture more of the South Platte River's Nebraska-bound water, then pump it back westward to booming metro suburbs struggling to wean themselves off dwindling underground aquifers.
They're trying to prevent urban "buy-and-dry" of irrigated farmland and preserve rural communities across the South Platte Basin, which covers Colorado's northeastern quadrant and ranks among the nation's productive agricultural regions.
Booming growth along Colorado's semi-arid Front Range has led to cities buying farms to take control of rights to withdraw scarce water from the river, a relatively feeble source given the magnitude of urban, industrial and agricultural development.
This new push to trap an additional 150,000 acre-feet of water, above what is held in an existing chain of reservoirs built by farmers, surfaced in Denver Post interviews with lawmakers and other officials this summer. The effort would cost hundreds of millions of dollars and affect natural habitat for wildlife, including endangered sandhill cranes. It reflects a growing willingness in a nature-oriented state to re-shape river landscapes for meeting human needs.
"If nothing is done, up to 50% of the irrigated agriculture in the South Platte River Basin is projected to be dried up by 2050 because there's no other place for cities to get bigger water supplies other than from irrigated agriculture," said Joe Frank, manager of the Colorado's Lower South Platte Water Conservancy District, who is helping to coordinate planning.
"We owe it to our state, to our water users and our farmers to capture as much water as we can" out of the South Platte, Frank said, "because otherwise we see what is going to happen."
In the decades since the U.S. Environmental Protection Agency in 1990 vetoed the Two Forks Dam proposed for the foothills 25 miles southwest of Denver, metro suburbs have relied heavily on pumping up groundwater as the foundation for housing and commercial expansion. The South Metro Water Supply Authority — which represents 13 municipalities, including Parker, Highlands Ranch and Castle Rock, that pump about 25,000 acre-feet a year (about a fourth of their supply) — has prioritized securing new surface sources.
The latest state data from well monitoring reveal south metro Denver groundwater tables are falling. While the groundwater depletion since 2008 varies across the suburbs, the data show, decreases around Castle Rock exceeded 16 feet. State officials don't intervene as long as municipalities determine that the sponge-like aquifers they tap wouldn't be totally exhausted for 100 years.
"We need to get our house in order, to better manage our water supplies," South Metro director Lisa Darling said. "A number of us have water rights on the South Platte."
Costs of piping water back from new reservoirs are "significant" and would be paid by "participants," including those suburbs, where the current 350,000 households will increase to 500,000 "at buildout" in 2065, Darling said. Daily water use per person has decreased from utilities' pre-2002 planning estimate of 165 gallons to 120 gallons, she noted.
Colorado's new reservoirs would capture water that otherwise flows in the South Platte to Nebraska. A 1923 South Platte River Compact requires Colorado to leave a mean flow of 120 cubic feet per second from April through October.
Colorado lawmakers pointed to gauging-station records showing annual surplus flows from 10,000 acre-feet to 1.9 million acre-feet — an average of 300,000 acre-feet of water each year that Colorado could claim. (An acre-foot equals 325,851 gallons, enough to sustain two families for a year.)
State engineer Kevin Rein confirmed that "in many years more water is passing that gauging station at the state line than needs to. … Conceptually I agree with what they are saying."
Impact on sandhill cranes
Nebraska officials contemplated what this could mean. Nebraska monitors "the potential effects of new water-related activities on the states' apportionment" and "will look at the proposed projects and communicate directly with Colorado on issues of concern relating to the compact," along with efforts to recover endangered birds, Jeff Fassett, the state's director of natural resources, said in an emailed response to queries from the Denver Post.
South Platte flows nourish a diversity of species, including the imperiled sandhill cranes in Nebraska. Colorado and other states legally must prevent extinction. The birds need flows that form sandy beach habitat.
Reservoir proponents said impacts would be mitigated. They contend off-channel reservoirs could help cranes because reservoir operators, by trapping high flows during wet years, would be able to release water strategically, simulating nature, just when birds and habitat need more.
But less water and distortion of natural surges would be devastating, and reservoirs themselves would destroy habitat, Audubon Society vice president Brian Rutledge said.
"We have living systems that depend on this water. New reservoirs are not the answer," Rutledge said. "We are overpopulating our western deserts. We need to get this under control. We need cities to use some reason."
The reservoirs would be built at three or more sites northeast of Denver, near the river but not directly blocking the main stem, and hold up to 70,000 acre-feet of water apiece, according to a consultant's report.
It's not yet clear how many separate reservoirs would be built under the plan.
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Sites and pipeline routes haven't been set. Planners identified more than 20 potential locations for reservoirs but are focusing on areas north and south of Fort Morgan and near Sedgewick. Two or more pipelines, which cost more than $1 million a mile to install, would move captured river water back west to the Front Range, ending near Brighton, Aurora and possibly elsewhere.
Meeting future needs
Colorado lawmakers strongly supported building new reservoirs and pipelines.
"We should do our best to manage our water, and still meet our compact obligations. If that means less above the compact is going to cross out of our state, we should do that," said state Sen. Jerry Sonnenberg, R-Sterling, who represents 11 counties across northeastern Colorado and serves on the legislature's water resources review committee. He and eight other lawmakers, including key committee members, recently toured the South Platte Basin with Water Education Colorado.
"We're fortunate in Colorado to live in the greatest state in the country. People want to come here for a vast variety of reasons. Whether or not we need those expensive homes and more water, I don't think you stop that. I don't know how you would stop it. ... We need to manage our resources in Colorado to meet our future needs," Sonnenberg said.
"We can control the flow in the river if we have those new storage structures available," he said. "If we can have more storage, then farms can stay in production."
Lawmakers from across the Continental Divide in western Colorado, where rivers are depleted by diversions through tunnels to the Front Range, embraced the push for bigger storage as preferable to siphoning more water out of the Colorado River Basin and to boost resilience amid global warming.
"I would prefer that they find their own water," said Rep. Dylan Roberts, D-Avon, vice chair of the lawmakers' water resources review committee.
Sen. Don Coram, R-Montrose, said Coloradans on the Western Slope sense "that a lot of the water we're sending over isn't being utilized fully. ... We want to keep as much of it as we can."
And lawmakers representing south Denver suburbs saw increased storage as essential to enable continued Front Range population and economic growth, which they accept as inevitable, without destroying agriculture.
"This is one of those rare solutions that really is good for both rural Colorado and folks who live in the Denver metro area," said Sen. Jeff Bridges, D-Greenwood Village.
"We're paying an enormous amount of money right now to continue to grow, to make sure we have the water that we need to continue to grow in the Denver metro area. What you see, oftentimes, is that this leads to drying up land in rural Colorado," he said.
Water follows money
The push for new reservoirs has gained momentum after Colorado's 2015 State Water Plan enshrined the notion of boosting storage along the South Platte, though the plan doesn't specify projects.
Colorado Water Conservation Board director Rebecca Mitchell, an architect of that plan, this summer indicated a favorable state posture toward what she called the South Platte Regional Opportunities Working Group project.
"The South Platte River Basin is the most populous basin in the state, and in planning for Colorado's water future... we need to bridge Colorado's future water supply-demand gap," Mitchell said in a statement. "Combined with conservation and a focus on environmental health, project concepts like SPROWG create an opportunity ..."
Back in the 1970s, Aurora and Colorado Springs purchased farmland along the Arkansas River in southeastern Colorado to obtain rights to water. This led to the loss of more than 100,000 acres of irrigated farmland and hurt rural communities.
Metro Denver suburbs, including Parker, along with independent water brokers, have bought thousands of acres in the South Platte Basin that could be dried up in the future.
"Water does, definitely, follow money," said Jim Yahn, manager of the existing North Sterling (74,590 acre-feet) and Prewitt (32,000 acre-feet) reservoirs along the South Platte, which store and distribute water to 350 farms across 70,000 acres. Yahn is a farmer and cattle rancher who serves as one of 10 voting members of the Colorado Water Conservation Board, which helps set state water policy.
Cities buying rural land and diverting irrigation water threaten northeastern rural communities and create economic uncertainty, Yahn said.
"We're talking about several municipalities working together with farmers and making big storage" so that food production survives, he said.
"And we want people to know we are very efficient with our water. We're trying to use every drop to its fullest capacity for the most beneficial use."