ASPEN – The city of Aspen is poised to enter into an agreement with the Colorado Water Trust to forego some diversions from the Roaring Fork River into the Wheeler Ditch for up to five out of the next 10 years to boost low flows in the river.
The agreement with the nonprofit water trust is on the Aspen City Council’s consent agenda Monday evening.
The city is working with the water trust to add water to a “critical reach” of the river “downstream of the Salvation Ditch headgate to the confluence of the Roaring Fork River and Castle Creek,” according to the draft agreement.
Under the agreement the city will “feather back” its diversions into the Wheeler Ditch in increments of 1 cfs when the Fork drops below 32 cubic feet per second.
The city, in theory, could forego diverting as much 9 cfs into the Wheeler Ditch, as the city’s water right is for 10 cfs and the agreement says the city will continue to divert at least 1 cfs into the ditch.
In 2014, on the eve of the second year of a pilot program, city and Colorado Water Trust officials acknowledged the potential to forgo diverting up to 9 cfs, but said they expected to leave about 2 to 3 cfs in the river.
The city holds a senior water right from 1882 to divert 10 cfs into the Wheeler Ditch for municipal use. The diversion structures are on the edge of Ute Park, below the Aspen Club. They are “river left” when looking downstream.
Water from the ditch is used by the city to send water through the Hyman and Cooper Avenue malls to produce the fountain across from the Wheeler Opera House, and as base flows in the city’s storm water system. Any non-consumed water is returned to the river near Rio Grande Park.
The city estimates that at times less then 10 percent of the Roaring Fork’s native flow reaches central Aspen.
Flows in the Roaring Fork are initially diminished by the Independence Pass Transmountain Diversion System, which can divert up to 625 cfs from the headwaters of the Fork under the Continental Divide.
And the Salvation Ditch, which diverts at Stillwater Road east of Aspen upstream of the Wheeler Ditch, has water rights from 1902 for 58 cfs.
The Colorado Water Conservation Board holds a junior instream flow right of 32 cfs on the Roaring Fork between Difficult Creek and Maroon Creek, which includes the city’s identified “critical reach.” The level of 32 cfs is what the state found is needed to protect the river’s environment “to a reasonable degree.”
Two test years
The city diverted less water than it might otherwise have done in both 2013 and 2014 under one-year agreements with the water trust.
On July 9, 2013, the Fork below the Salvation Ditch dropped under 32 cfs and the city lowered its diversion levels into the Wheeler Ditch from 3.3 cfs to 0.9 cfs and then down to 0.6 cfs, according to public diversion records.
That meant the river between Ute Park and Rio Grande Park enjoyed another 2.4 to 2.7 cfs of flow, although it was still often below the threshold level of 32 cfs.
”Even with the city’s Wheeler Ditch water being left in the river, streamflow near Rio Grande Park averaged about 25 cfs during 2013, and fell to a recorded low of 14 cfs for three days,” states background material prepared by the city.
In 2014, the Roaring Fork dropped to 30 cfs in late August and the city lowered its diversions into the Wheeler Ditch by about 1 cfs.
Records show the city began diverting 1.5 cfs of water into the Wheeler Ditch on May 23. On Aug. 21 it was diverting less water, 0.5 cfs. And on Sept. 3 it was diverting 0.6 cfs and did so until mid-October.
“As a result of the (2014) Wheeler Ditch non-diversion agreement, it is estimated that the Roaring Fork River streamflow increased by approximately 1 cfs from Aug. 18 through Oct. 14,” the city material said.
In 2015, a high water year on the Fork, the city diverted between 5.2 and 8.2 cfs in the Wheeler Ditch, according to records, and did not need to leave water in the river to boost low flows.
If approved by city council, the agreement with the water trust would next require approval from the Colorado River Water Conservation District, under the terms of a state law from 2013, Senate Bill 19.
The law provides “safe harbor” to Western Slope water rights owners “when they decrease their consumptive use of water by participating in a variety of government-sponsored water conservation programs.”
Editor’s note: Aspen Journalism and the Aspen Daily News are collaborating on coverage of water and rivers. The Daily News published this story on Monday, May 9, 2016.