In September, Front Range water providers released some water downstream — which they were storing in Homestake Reservoir — to test how they could get it to the state line in the event of a Colorado River Compact call.
But accurately tracking and measuring that water — from the high mountain reservoir in the Eagle River watershed all the way through the Colorado River at the end of the Grand Valley — turned out to be tricky, according to a recently released report from the Colorado Division of Water Resources.
From Sept. 23 through Sept. 29, Colorado Springs Utilities, Aurora Water and Pueblo Board of Water Works released a total of 1,667 acre-feet of water, which would have otherwise been diverted to the Front Range, from the reservoir into Homestake Creek, a tributary of the Eagle River. The release gradually ramped up from about 25 cubic feet per second to 175 cfs and then gradually back down over the seven days.
But officials were unable to put a number on how much of that water made it to the state line.
In their attempt to quantify the actual amount of reservoir release delivered to the state line, state engineers ran into challenges that caused uncertainty, they said in an email.
Although they couldn’t measure how many acre-feet officially made it, State Engineer Kevin Rein said that the exercise was still a success and that all the water, minus transit losses, crossed into Utah.
“We have heard this is a failure because not everything worked perfectly, but in my mind, this was an opportunity under non-stress conditions to find out what we need to do to ensure that things will work,” Rein said.
A goal of this project, known as the State Line Delivery Pilot Reservoir Release, was to see if the water could be “shepherded” downstream without senior water-rights holders diverting the extra water. This required Division 5 water commissioners to actively administer some headgates, especially on Homestake Creek and the Eagle River.
According to the report, the water took about 2½ days to make the journey from the reservoir to the gage on the Colorado River near Cameo — about 16 hours longer than predicted by the Colorado Basin River Forecast Center. Along the way, about 10% of the water either evaporated or was soaked up by thirsty streamside soils and vegetation — processes known collectively as transit loss.
Making sure water could get to the state line would be essential in the case of a compact call.
This scenario, the chances of which increase as climate change continues to reduce river flows, could occur if the upper-basin states (Colorado, Wyoming, Utah and New Mexico) can’t deliver the 7.5 million acre-feet of water per year to the lower-basin states (Arizona, California and Nevada), as required by a nearly century-old binding agreement.
A compact call could be especially problematic for Front Range water providers since most of their rights that let them divert water over the Continental Divide from the Western Slope date to after the 1922 Colorado River Compact. That means mandatory cutbacks in water use could fall more heavily on the post-compact water rights of Front Range water providers.
Colorado Springs Utilities and Aurora Water, operating together as Homestake Partners, said the problem was that the rate of release was too low. It was more a matter of flow volume than administration. Even in a dry year, a release of 175 cfs was not high enough to reliably track the water, especially when it reaches the Colorado River, which has a much higher volume of water than Homestake Creek or the Eagle River, and the reservoir release is a smaller fraction of its overall flow.
In an email to Aspen Journalism, Homestake Partners said: “A bigger pulse of water would overcome some of the issues that DWR had in tracking the release. This sort of result is exactly what we wanted to explore — it tells us that if we, or anyone else in the state, chooses to make a state line release in the future, a higher volume of water will probably need to be released to be reliably tracked.”
State engineers also had to deal with a river that was constantly in flux. Upstream reservoir releases and changes to irrigation diversions made for additional challenges.
State officials said it was hard to separate the reservoir release from the rest of the Colorado River’s flow at the state line because of numerous ungaged streams and return flows from irrigation that enter the river between Palisade and the state line.
“The ungaged inflows could not be subtracted from the total flow in the river, therefore the separated flows were too large and did not allow for the initial waves of the reservoir release to be identified,” officials said in an email.
The total flows at the state line at the time of the reservoir release’s arrival were around 2,500 cfs, according to DWR.
River District concerns
The Glenwood Springs-based Colorado River Water Conservation District, which protects Western Slope water interests, had several concerns about the reservoir release.
“I think it’s important that the public and the state recognize that they released 1,600 acre-feet of water during an incredibly dry period and they couldn’t actually track it to the state line,” said River District general manager Andy Mueller.
But Mueller’s concerns go beyond the trouble with tracking. He said the state engineer did not reach out to Western Slope water users who had the potential to be injured by the release. He also doesn’t trust that the cities won’t just refill the hole created by the release with more Western Slope water.
The River District’s main concern is that in a water-collection system as complex as Homestake Partners — with several different transmountain diversions bringing water from the Western Slope to the Front Range — it’s hard for the state to make sure they won’t take more water to replace the pool they released.
“From our perspective, it’s very difficult for the state to verify that they haven’t just brought the water over from a different part of their diversion system,” Mueller said. “So it leaves us with a lot of skepticism, and we voiced that in several discussions.”
To address some of these concerns, the cities are required to submit a verification plan to the state to prove three things: that they had enough space available in reservoirs on the east side of the divide to store the water, and they weren’t just releasing water downstream they couldn’t use anyway; that they actually decreased water taken through the Homestake Tunnel by the same amount as the pilot release; and that they didn’t create additional space in Homestake Reservoir to allow for greater storage this year.
“In essence, we brought the ‘hole’ we created in our storage in Homestake Reservoir through to the East Slope when we operated the tunnel in February and March,” the Homestake Partners’ email reads. “This was accomplished by not drawing down Homestake Reservoir quite as much as we otherwise could have this winter in preparation for spring runoff.”
The reservoir release also could have implications for a potential demand-management program, the feasibility of which the state is currently investigating. At the heart of a demand- management program is a reduction in water use on a temporary, voluntary and compensated basis in an effort to send as much as 500,000 acre-feet of water downstream to Lake Powell to bolster water levels in the giant reservoir — which spans Utah and Arizona — and, indirectly, to meet Colorado River Compact obligations.
Under such a program, agricultural water users could get paid to temporarily fallow fields and leave more water in the river. Front Range water providers could participate by releasing water stored in Western Slope reservoirs.
Rein was careful to say that the Homestake pilot release was in no way connected to demand management. Still, the experiment may have revealed potential problem areas should a demand-management program become reality.
“The ability to track water that is conserved consumptive use all the way to the state line is really critical for the success of that program,” Mueller said. “And if you can’t track a slug of 1,600 acre-feet of water to the state line, how are you going to track the voluntary reduction in use of a small ditch on the West Slope that maybe they are saving 15 acre-feet?”