By HANNA HOLM

Grand Junction’s new Las Colonias River Park, carved into a slough off the main channel of the Colorado River near downtown, is providing new opportunities to safely and conveniently escape the relentless heat of summer.

It’s also providing more opportunities to experience the way the river’s flows change through the season: deep and fast in late May and early June; lower and slower now, to the point where the inlet for the river park had to be dammed off to protect fish habitat in the main channel.

This seasonal variability is driven by the fact that most of the flow in our rivers comes from snow, which piles up (to greater or lesser degrees) in the winter, and then melts off in a rush when temperatures heat up. But there are a lot of other factors that contribute to how much water is in the river, too.

Irrigation takes water out — but also keeps it coming downstream

On July 2, the Colorado River near Cameo, just upstream from the Roller Dam in De Beque Canyon, was flowing at 3,850 cubic feet/ second (cfs). In Palisade, below the last major diversion from the river, it was flowing at 2,010 cfs. Close to half its volume had left the river channel to flow into irrigation canals. That’s why our valley is green.

If that water didn’t flow into the canals, it wouldn’t necessarily be in the river channel, though. The way Colorado water law works, older claims on the river have priority over new ones. The Grand Valley’s irrigation canals secured their rights to use the river’s water before tunnels were built that take hundreds of thousands of acre feet of water each year from the Colorado River’s headwaters to farms and cities on the Front Range. The senior water rights in the Grand Valley limit how much water can be taken to the other side of the mountains, pulling water downstream that contributes to the flows rafters enjoy in Gore and Glenwood canyons.

If you like to float, thank a pikeminnow!

The river park is on the 15-mile reach below the irrigation diversions and above the confluence with the Gunnison River. This reach is critical habitat for the endangered Colorado pikeminnow and razorback sucker, and flows can get really low in the summer. Colorado pikeminnows are the largest minnows in North America, can live as long as 40 years, and historically grew up to 6 feet long. Razorback suckers can live even longer and grow up to 3 feet long. They are both pretty good-looking fish, and you can learn more about them at www.coloradoriverrecovery.org.

Over the years, the Upper Colorado River Endangered Fish Recovery Program has worked with irrigation providers and other stakeholders to find ways to keep more water in this section of river to help the fish. These include upgrades to Grand Valley Water Users and Orchard Mesa Irrigation District canals that significantly reduce the amount of water they have to take out of the river in order to deliver irrigation shares all the way to the end of their systems; Ute Water leases of stored water out of Ruedi Reservoir; and work by the Colorado Water Trust to help put more water through the hydropower plant on the Orchard Mesa ditch and then back into the river at the top of the reach. The river park itself was carefully engineered to avoid pulling too much water off the main river channel.

Flows in the river reflect our natural hydrologic conditions, but also the sum-total of many different decisions made collectively and individually up and down the river. How we choose to use limited water resources reflects what our society values, and how those values are implemented in laws, agreements and financial investments. This summer, kids of all ages in Grand Junction have been enjoying the fact that those values include providing a new way to play in the river.

Hannah Holm coordinates the Hutchins Water Center at Colorado Mesa University, which promotes research, education and dialogue to address the water issues facing the Upper Colorado River Basin. Support for Hutchins Water Center articles is provided by a grant from the Walton Family Foundation. You can learn more about the center at http://www.coloradomesa.edu/water-center.