Ground (water) zero
The Colorado River rightfully gets attention – so should aquifer depletion

Woes of the Colorado River have justifiably commanded broad attention. The slipping water levels in Lake Powell and other reservoirs provide a compelling argument for change. How close to the cliff’s edge are we? Very close, says a new report by the Center for Colorado River Studies.

But another cogent – and somewhat related – story lies underfoot in northeastern Colorado. That’s the story of groundwater depletion. There, groundwater in the Republican River Basin has been mined, by farmers and the few small towns in the region, at a furious pace for the last 50 to 60 years.

Much of this water in the Ogallala aquifer, which was deposited during several million years, will be gone within several generations. In some places it already is. Farmers once supplied by water from underground must now rely on what falls from the sky.

In the San Luis Valley, unlike the Republican River Basin, aquifers can be replenished somewhat by water that originates from mountain snow via canals from the Rio Grande. The river has been delivering less water, though. It has problems paralleling those of the Colorado River. Changes in the valley’s farming practices have been made, but more will be needed. 

In a story commissioned by Headwaters magazine (and republished in serial form at BigPivots.com), I also probed mining of Denver Basin aquifers by Parker, Castle Rock and other south-suburban communities.

Those Denver Basin aquifers, like the Ogallala, get little replenishment from mountain snow. Instead of growing corn or potatoes, the water goes to urban needs in one of America’s wealthier areas.

Parker and Castle Rock believe they can tap groundwater far into the future, but to diversify their sources, they have joined hands with farmers in the Sterling area with plans to pump water from the South Platte River before it flows into Nebraska. This pumping will require 2,000 feet of vertical lift across 125 miles, an extraordinary statement of need in its own way.

Like greenhouse gases accumulating in the atmosphere, these underground depletions occur out of sight. Gauges at wellheads tell the local stories, just like the carbon dioxide detector atop Hawaii’s Mauna Loa has told the global story since 1958.

Colorado’s declining groundwater also can be seen within a global context. Using data from satellites collected during the last two decades, researchers from Arizona, California and elsewhere recently used satellites data to track water held in glaciers, lakes and aquifers across the globe. In their study, published recently in Science Advances, they report that water originating from groundwater mining now causes more sea level rise than the melting of ice.

“In many places where groundwater is being depleted, it will not be replenished on human timescales,” they wrote. “It is an intergenerational resource that is being poorly managed, if managed at all, by recent generations, at tremendous and exceptionally undervalued cost to future generations. Protecting the world’s groundwater supply is paramount in a warming world and on continents that we now know are drying.”

This global perspective cited several areas of the United States, most prominently California’s Central Valley but also the Ogallala of the Great Plains.

In Colorado, the Ogallala underlies the state’s southeastern corner as well, but the main component lies north, in the Republican River Basin. The river was named by French fur trappers in the 1700s, long before the Republican Party was organized. The area within Colorado, which contains the towns of Wray, Yuma and Burlington and is likely unknown to most of Colorado’s mountain-gawking residents, is only slightly smaller than New Jersey. Approximately 600,000 acres are irrigated here annually using groundwater from approximately 4,000 high-capacity wells. There is minimal surface water irrigation.

A 1943 compact with Nebraska and Kansas has driven Colorado’s recent efforts to slow groundwater mining. The aquifer feeds the Republican River and its tributaries. As such, the depletions reduce flows into down-river states.

Farmers are being paid to remove land from irrigation with a goal of 25,000 acres by 2030 to keep Colorado in compliance. So far, it’s all carrots, no sticks. Colorado is also deliberately mining water north of Wray to send to Nebraska during winter months. This helps keep Colorado in compact compliance. So far, these efforts have cost more than $100 million, some of the money coming from self-assessments and others from state and federal grants and programs.

In recent years, more than 700,000 acre-feet of water have been drafted from the Ogallala in the Republican River Basin. In one hot and dry year, 2012, they pumped 940,000 acre-feet. As a point of reference, Blue Mesa Reservoir, the largest body of water in the state, can hold 947,435 acre-feet. Annually, Denver Water distributes an average of 232,000 acre-feet to a population of 1.5 million. 

Hard conversations are under way in the Republican River Basin and in the San Luis Valley, too. They will get harder yet. Sixteen percent of all of Colorado’s water comes from underground.

The Colorado River has big troubles. It’s not alone.

Allen Best chronicles water and energy changes in Colorado at BigPivots.com.