Quantifying the drying during drought
Post Independent Contributor
Glenwood Springs, CO Colorado
BASALT, Colorado – Anyone who drove alongside the Roaring Fork or Crystal rivers last summer knows that stretches of those waterways were almost completely dry during the drought of 2012.
But it’s hard to pinpoint exactly where those parched sections were, when they dried up and how last year’s low stream flows affected the health of the rivers’ ecosystem.
A new study released recently by the nonprofit groups The Roaring Fork Conservancy and Public Counsel of the Rockies attempts to answer those questions.
The “Snapshot assessment of the Roaring Fork Watershed” finds that the Roaring Fork River was driest on July 25 near Aspen’s Mill Street Bridge, when flows were measured at a trickling 4.7 cubic feet per second (CFS).
The lowest flow on the Crystal River was measured near the Thomas Road Bridge south of Carbondale on Sept. 22, at a paltry 1 CFS.
“That creates real pinch points for the river, and compromises connectivity,” said Chelsea Brundich, water director for Public Counsel of the Rockies.
“Those stretches of the river really need help, and this work provides a perfect platform to start a conversation about how the river will be put back together.”
The study, which cost a total of $47,750, was partly funded by the Pitkin County Healthy Rivers and Streams Fund.
It states that in addition to impairing the ability of aquatic species to migrate in the river, low stream flows can also lead to higher water temperatures, endangering some fish species.
The Colorado Division of Parks and Wildlife defines 66 degrees Fahrenheit as the threshold above which the health of brown trout is stressed. Cutthroat and brook trout are even less heat tolerant.
Although the study team didn’t document temperatures above that threshold on the Roaring Fork River during the summer of 2012, they recorded them twice on the Crystal River in early September.
Aside from drought conditions, the main factor leading to low water levels last summer was diversion by water users for irrigation or other purposes.
The Crystal River is subject to several irrigation diversions, most of them between Avalanche Creek and the river’s confluence with the Roaring Fork River.
In addition to being used for irrigation, much of the water in the Roaring Fork River above Aspen is diverted in the early summer to users on Colorado’s Front Range, through the Independence Pass Tunnel and into the Arkansas River basin.
By mid-July or early August, a water right held by downstream agricultural users in the Grand Valley called the Cameo Call typically comes into effect, leading so-called “transbasin” diversions to cease and prompting water levels to rise in the river through much of the Roaring Fork Valley.
When it comes to keeping more water in the Roaring Fork and Crystal river basins, the new report doesn’t claim to have any silver bullet solutions.
“It is unclear to what extent low stream flow issues in the Crystal River and Roaring Fork River can be solved,” reads the report’s conclusion.
According to Brundich, that’s because the number of tools available to keep water in the river is so limited.
In fact, there may be only one – a short-term leasing program administered by the Denver-based nonprofit Colorado Water Trust.
Essentially, the trust pays the owners of unused water rights to keep them in the river, or “retire” them temporarily. First, however, the group must ensure that those with more senior water rights downstream won’t simply lap up the unused water for themselves.
Seth Mason, who owns the S.K. Mason environmental consulting firm and helped complete the “snapshot” report, said representatives from the Colorado Water Trust had already met with water rights holders in the Crystal River watershed, and some appeared interested in signing their rights over to the group.
If the Colorado Water Trust can find a way to keep more water in the rivers this coming summer, there may also be a need for additional gauges to keep track of that water.
According to Mason, the two lowest flow points he measured during the summer of 2012 were not in the vicinity of any existing gauges.
“If the goal is to characterize the lowest flow conditions on a particular segment, new gauging infrastructure may be necessary,” said Mason.
New gauges, though, are expensive, and Brundich said funding for them will be easier to find when the Water Trust has a concrete plan in place to keep water in the river.
“There is going to be more support for gauging when we can demonstrate how it will be used more specifically,” she said.
If water levels stay low next summer, Sharon Clarke of the Roaring Fork Conservancy said her group may consider other methods of improving flows, such as deepening and narrowing parts of the river channels or planting vegetation on the banks to add shade and reduce erosion.
“One of the things we want to look at is restoring the channel to function better at low flows,” she said.
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