Aspen City Council wades into water shortage scenarios

Whether Aspen needs to build a reservoir to meet water demands in 2065 may depend on whether it wants to keep irrigating its municipal golf course during an apocalyptic drought.

According to a water attorney and an economist working for the city on a risk analysis of future water shortages, Aspen may find itself unable to meet domestic water demands — including both indoor and outdoor water use — anywhere from two out of 25 years in an optimistic scenario to 19 out of 25 years in a worst-case scenario.

The most optimistic scenario can be achieved, in theory, if the city limits outdoor watering by its customers and also stops diverting water from Castle Creek to irrigate the 148-acre municipal golf course and other nearby open space.

Outdoor water use accounts for about 60 percent of current demand for city water.

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The members of the Aspen City Council took a sip of such concepts Monday at a work session on “Aspen’s water future.”

Aspen Mayor Steve Skadron said he expects the council to spend “several months” grappling with the city’s future water needs as part of an exercise to identify alternatives to maintaining conditional water rights for two large reservoirs on upper Castle and Maroon creeks.

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Monday night, George Oamek, an economist with Headwaters Corp., presented three scenarios from a risk analysis he’s been developing for the city.

He told the council that his model is packed with uncertainties, mainly around the severity of climate change, but also around the amount of flow in Castle and Maroon creeks and the future demand from Aspen’s water customers.

In his “worst-case” scenario, runoff would come six weeks earlier in the spring and there would be half as much water flowing in Castle and Maroon creeks, the city’s primary sources of water.

The worst-case scenario also assumes that demand for treated water would be 6,320 acre-feet of water a year, up from about 3,500 acre-feet today.

That’s an aggressive demand assumption, however, as a 2014 water efficiency plan from Element Consulting and WaterDM projects the city will, by 2035, “reduce treated demand by about 583 AF — an overall 14 percent reduction in demand.”

The city has been making solid progress on reducing water demand. In 2012, city staffers told the council the city had reduced water consumption by “over two-thirds over the last 19 years.”

In the most draconian scenario developed by Oamek, the city might not be able to meet all municipal water demands — including both indoor and outdoor use — in 19 of 25 years.

In 15 of those years, water shortages could exceed 100 acre-feet of water.

In four of those years, water shortages could exceed 1,000 acre-feet.

And in one of those years, shortages could exceed 2,000 acre-feet.

The combined storage capacity of the potential Castle and Maroon creek reservoirs, as currently decreed, is 13,629 acre-feet.

But the picture gets much brighter in Oamek’s “intervention scenario.”

Runoff would still come six weeks earlier, and there would still be half as much water flowing down Castle and Maroon creeks.

But demand for city water is projected at 2,280 acre-feet a year, as the scenario assumes the city will curtail the use of treated waters for outdoor purposes during a drought.

In that scenario, there might be 14 years out of 25 when there are water shortages, but only in five of those years would the shortages be over 100 acre-feet and none would produce shortages over 1,000 acre-feet.

For comparison’s sake, Lost Man Reservoir on Independence Pass holds about 100 acre-feet.

And Cindy Covell, the city’s water attorney, told the council, along with Oamek, that if the city also stopped diverting water into three irrigation ditches on lower Castle Creek, it could drive the number of years with water shortages down to just two years out of 25.

However, in each of the scenarios presented, it appears it will be difficult for the city to meet both its policy goal of leaving enough water in Castle and Maroon creeks to meet targeted instream environmental flows while also meeting all municipal water demands.

“There are some significant shortages there,” Oamek said while presenting the the worst-case scenario, noting that the instream shortages could be over 10,000 acre-feet in some extremely dry years.

City staff in the city’s Water Department continue to point out that the city likely needs some level of water storage in the future, and this has gotten the attention of Skadron, who said Monday he wants to make sure future generations have good options to meet future demands.

But it’s not clear yet how the scenarios presented Monday may change the city’s negotiating position with the 10 parties opposing its ongoing efforts in water court to maintain is conditional water storage rights for reservoirs on Castle and Maroon creeks.

Last week, the city announced it now intends to transfer its water rights from Castle and Maroon creeks to two potential reservoir sites in Woody Creek. And a second settlement conference with the opposing parties is set for Aug. 2.

Editor’s note: Aspen Journalism is collaborating with The Aspen Times on coverage of river and water. More at http://www.aspenjournalism.org.