The city of Aspen’s recently released integrated water resource plan outlines the strategy for an adaptable, phased approach to meet increasing demands and a large pool of “emergency” storage to protect against threats to supplies from Castle and Maroon creeks.
Aspen Utilities Director Tyler Christoff, Utilities Resource Manager Steve Hunter and John Rehring of Carollo Engineers, the Denver-based firm that the city hired to complete the study, presented the IWRP to City Council members at a work session Monday night. The report, which looks 50 years to the future, uses projections about population growth and climate change impacts to determine that the worst shortfalls could occur in two consecutively dry years and be about 2,300 acre-feet total over the course of both years.
To make up for that gap, the report offers six different portfolios of potential new water sources, including storage, nonpotable reuse, groundwater wells, Hunter Creek, enhanced water conservation and drought restrictions. The IWRP says storage is included in five of the six portfolios because no single supply option or combination of supply options can completely mitigate shortages without the use of at least some operational storage.
Two storage pools
The plan proposes two separate storage pools to meet demands under projected conditions in 2070: a 520-acre-foot operational pool and a 5,300-acre-foot emergency-storage pool to provide up to 12 months of water.
Since the report recommends a phased approach with each additional implementation coming after a predetermined trigger is reached, the first phase of operational storage would be for just 130 acre-feet to buffer the seasonal shortage. Streams are highest with runoff in the spring, but demands on Aspen’s water system are highest in late summer, when streamflows are low — and this is the gap operational storage aims to fill.
The construction of the combined 5,820 acre-feet of storage and its associated pipelines and pumps comes with a hefty price tag — it is estimated to cost more than $400 million in 2021 dollars as it is implemented over the coming decades.
“We want to make it flexible and adaptable so that we are ready for that worst-case condition,” Rehring told council members. “We implement as needed as we see those conditions unfold over time.”
The report says the emergency-storage pool must be full and ready for use when the need arises — if, for example, an avalanche makes the city’s supplies in Castle and Maroon creeks unusable. “Regardless of siting and co-location, emergency-storage volumes would be filled and maintained at their defined capacity until needed for an emergency,” the IWRP reads.
Storing water specifically until an emergency occurs is not a decreed beneficial use under Colorado water law. But municipal water providers often have a lot of leeway to plan for future needs, which could include storage projects.
Part of the goal of the IWRP is to narrow the city’s options for moving its conditional water rights for reservoirs in Castle and Maroon valleys. After a lengthy court battle, in which 10 entities opposed Aspen’s plans, the city gave up its water rights in those particular locations. One of the places to which the city could move them is a 63-acre plot of land that it bought in Woody Creek in 2018. If the city stores water there, it would have to pump it back uphill to the water-treatment plant via an 8-mile pipeline.
City Council member Ward Hauenstein asked about the timeline for storage and renewing the city’s conditional water rights.
To keep these rights, the city will have to show, through a 2025 filing in water court, that it still intends to use them and that it is making progress on a project.
“Recent history across Colorado shows that it could take decades to implement a storage project, even after sizing and siting analyses are completed,” the report reads. “Therefore, reservoir planning must start immediately.”
Aspen City Council will vote on whether to adopt the IWRP at a later meeting. Mayor Torre thanked the staff, consultants and community members who weighed in on the plan.
“The work you guys are doing on this is some of the most important work Aspen is going to have the benefit of over the coming 10, 20, 30 years,” he said. “Thank you.”
This story ran in the Nov. 23 edition of The Aspen Times.