At the February meeting of the Upper Arkansas Water Conservancy District board of directors, District Engineer Chris Manera reported that the he has prepared a bid package for the Cottonwood Dam project.
Time has taken a toll on the 1950s-era dam, and concrete at the base of the structure has deteriorated, necessitating its replacement.
Also, the steel gates used to control water releases have lost functionality due to wear and corrosion, thereby increasing the dead pool – i.e., the amount of water that can’t be released for water management purposes.
Cottonwood was a natural lake, and Manera noted during the January board meeting that the dam, built in the 1950s, increased the depth of the lake by 2-3 feet. In the 1990s, the dam height was increased by 5 inches.
Manera said the active pool is currently 61.7 acre-feet. The natural lake is considered dead pool, but the dead pool attributable to dam limitations is 63.6 acre-feet. A primary goal of the dam expansion is to regain access to that 63.6 acre-feet.
Because the dam is located on national forest land, the project requires a special use permit from the U.S. Forest Service.
Manera said he met with Forest Service officials who indicated that the necessary environmental studies have been completed, and the 40-year permit is expected to be signed off on soon.
District Advisor Terry Scanga noted that the district submitted the permit application in 2017.
The Town of Buen Vista is a project partner and will be the main beneficiary of the dam upgrade.
Another beneficiary will be fish. The existing dam is too high for trout swimming upstream to reach the lake, and the new dam will include a fish ladder that allows trout to navigate between the lake and Cottonwood Creek.
Manera said streamflow rates and other factors require work on the dam to begin in the fall, hopefully in 2026, but the schedule just got more complicated.
The Forest Service recently issued a contract to replace the bridge just downstream from the Cottonwood dam, Manera said. The project footprints overlap, but the bridge contractor is qualified to also do the dam work.
So, the bridge work could delay the dam project by as much as a year, or awarding the dam contract to the same contractor could produce cost savings. Once the Forest Service signs off on the permit and the dam bid is awarded, the project waters should be a bit less muddy.
Photo: The aging dam at Cottonwood Lake limits the reservoir’s operational capacity. The Upper Ark Water Conservancy District is working to replace the dam in order to regain lost storage capacity (photo courtesy of Chris Manera, Colorado River Engineering).
