The Roaring Fork River, a headwater tributary in the Colorado Basin, adds to the beauty and economic vitality of Aspen, Colorado. Photo credit: Grand River Consulting for the Colorado Water Trust.

When residents in Denver, Colorado Springs and other cities on the Front Range of the Rocky Mountains turn on their sprinklers to irrigate lawns, they rarely think about the fate of fish in the headwaters of the Colorado River on the other side of the Continental Divide.

But, in fact, competition for water between Front Range lawns and high-mountain fish is growing keen, especially as droughts combine with mounting water demand to increase stress on regional supplies.

Some 89% of Coloradans live east of the Rocky Mountains, a region that naturally gets just 16% of the state’s freshwater.  Most of Colorado’s supply begins as winter snowpack.  When the mountain snow melts in the spring, it fills the Fraser, Roaring Fork, Yampa and other tributaries of the Colorado River, sustaining cold-water trout fisheries and diverse freshwater habitats.

But as Colorado’s population swelled 8-fold over the 20th century, with most newcomers settling east of the Rocky Mountains, planners turned to massive engineering projects to solve the dilemma of too many people and not enough water: they built an elaborate system of canals, reservoirs, and tunnels that transport water from one side of the Continental Divide to the other.

A map of the state’s “trans-mountain” diversions makes the spine of the Rocky Mountains look like arrows in a quiver.  Today, 29 separate diversions grab water from Colorado River tributaries on the west slope and transport it to the east. Water once destined to flow southwest toward the Grand Canyon and the Sea of Cortez instead gets siphoned east to supply cities and farms situated in the South Platte, Arkansas and Rio Grande basins.

More than 180 billion gallons of water are annually moved from one side of the Colorado Rockies to the other – a volume that would fill a string of Olympic swimming pools laid end-to-end from California to Australia.

Rivers Pay the Price

This elaborate system of tunnels and diversions has allowed cities and farms to flourish along the Front Range, but has come with a high and largely hidden cost for many of the rivers and streams that form the lifeblood of the upper Colorado River and its local communities.

For example, the Fraser River – an iconic headwater tributary that boasts a popular trout fishery, and decades ago provided a favorite fishing spot for President Dwight D. Eisenhower – suffers from the transfer of as much as 60% of its flow to the Denver area.  Most of that flow is captured before the Fraser even emerges from the high mountains.

Similarly, a bit further south, the Roaring Fork can see up to 80% of its flow diverted and piped across the mountains before it reaches the town of Aspen.

Not surprisingly, when demand for water is high, the Roaring Fork and Fraser—and many other rivers like them—don’t carry enough water to meet the needs of both people and the river.  At times, some stretches go dry, or fail to support trout through the summer months.  The low-flows can also cause hardship for local ranchers and recreation businesses, such as fly-fishing and kayaking.

During the 2012 drought, the Roaring Fork’s flow dropped low during mid-summer (L); the following year, summer flows got a boost when Aspen chose to leave water in the river (R). Photo credit: Brent Gardner-Smith/Aspen Journalism

There has long been finger pointing in both directions across the Continental Divide.

Historically most of this trans-mountain water was used to support agriculture on the plains, but today Colorado’s Front Range cities use up to half of their residential water to maintain outdoor landscaping .  It’s no surprise that west-slope mountain communities accuse eastern cities of depleting their rivers to keep thirsty lawns green.

For their part, the urbanites are quick to point out that economic vitality in the cities is critical to sustaining the state’s economy.  They note that west-slope rural communities also play a part in depleting flows since they too divert water from those same rivers to meet their local needs.

A Search for Solutions

In 2013, when severe drought was projected for the Colorado Rockies, several groups rose above the finger pointing and began working together to create homegrown solutions for headwater streams in the Colorado Basin.

Working closely with the Colorado Water Trust (CWT), the City of Aspen developed a plan to reduce outdoor water use and substitute alternative water supplies so that the town could temporarily dedicate a portion of its water rights to keep the Roaring Fork flowing during critical low flow periods.

The previous year, severe drought conditions combined with water diversions had left the Roaring Fork nearly dry during parts of June, July, August and October. With so much of Aspen’s beauty and economy dependent on a healthy flowing river, the city was highly motivated to avoid a similar situation in 2013.

The “non-diversion” agreement Aspen signed with the CWT allowed the town to use one of its senior water rights to keep the Roaring Fork flowing through a critical 2.5-mile stretch of the river.

St. Louis Creek meanders through ranch country on the western slope of the Rockies before joining the Fraser River. The restoration of flow to the lower portion of St. Louis Creek kept it connected to the Fraser and improved the health of both. Photo credit: Edalin Koziol/Colorado Water Trust

Similarly, Winter Park Ranch Water and Sanitation District saw an opportunity to work with the Colorado Water Trust to test a similar solution for the Fraser River.  Concerned about looming drought and diminished flows, the district agreed to work with the CWT to test a new approach to boost flows at a time when a significant portion of the Fraser’s water is either diverted to Denver or used for irrigation in the Fraser valley.  Partners agreed to pilot a water-leasing project to boost flows in the river during select years over a ten-year period.

(A similar water-lease, also orchestrated by the CWT, helped prevent the Yampa River, another Colorado headwater tributary, from crashing ecologically during the drought of 2012.  That lease had been the first use of a 2003 state law allowing water users to temporarily loan water to rivers and streams in times of need.)

The initial results of these projects are promising.  Together they restored to the Fraser and Roaring Fork more than 150 million gallons in a pilot year that was predicted to bring very low flows to Colorado’s rivers and streams.  Although this amount of restored flow is just a fraction of the total water diverted, these projects offer new hope that local innovation and collaborative solutions can keep rivers flowing at healthier levels when conditions get tough.

As stakeholders throughout Colorado weigh in on ideas for a new state water plan, droughts, diversions and depleted rivers will no doubt figure prominently in the discussions.  Constructive solutions like these offer promise of finding a better balance between human uses of water and a river’s need for flow.

Now, about those lawns…

Originally posted at National Geographic Newswatch.