Summit County Government

Posted on: August 13, 2015

Summit County, Towns of Dillon and Silverthorne Unveil Reservoir Expansion Project

Photo of six public officials cutting a ribbon in front of a reservoir.

Old Dillon Reservoir expansion provides flexibility and certainty for local water rights and municipal water supplies

Gary Martinez, Summit County Manager

SUMMIT COUNTY – Summit County and the towns of Dillon and Silverthorne cut the ribbon on Old Dillon Reservoir Thursday, celebrating the completion of a major project to shore up local water rights and municipal water supplies.

The project, which broke ground in 2011, expanded the capacity of Old Dillon Reservoir from 46 acre-feet to 303 acre-feet. Reservoir construction was completed in 2014, and the reservoir filled for the first time this summer.

“The newly expanded Old Dillon Reservoir gives Summit County, Dillon and Silverthorne new flexibility and certainty in managing our water rights and our municipal water supplies,” Summit County Manager Gary Martinez said. “We’ll be able to put this water to great use in a variety of ways throughout the county, including river restorations, workforce housing projects and emergency preparedness.”

Old Dillon Reservoir, located between Dillon Dam Road and Interstate 70, was originally constructed in the 1930s as a municipal water supply source for the Town of Dillon. In recent years, the reservoir became unusable, as its dams required major upgrades to meet modern safety standards.

Summit County, the Town of Dillon and the Town of Silverthorne came together to form the Old Dillon Reservoir Water Authority, which undertook the extensive renovation and expansion of the reservoir. The project included the draining of the old reservoir, removal of its dams and construction of new dams using onsite materials. To facilitate the expansion, crews relocated the Salt Lick Gulch headgate upstream from its original location. Crews also constructed a new spillway and outlet to Salt Lick Gulch, as well as a new outlet to Dillon Reservoir.

“This new outlet to Dillon Reservoir opens up a tremendous number of options for us to conduct water exchanges,” Martinez said. “For example, we could release Old Dillon Reservoir water into Dillon Reservoir in exchange for water upstream that we would use to improve riparian habitat or restore wetlands.”

The water in Old Dillon Reservoir could also serve as an emergency municipal water supply for the Town of Dillon in the event of contamination of Straight Creek, the town’s primary drinking water source.

The project cost totaled $5.7 million, or about $18,000 per acre-foot of storage. In some years, the water authority will have access to more than 303 acre-feet because of approved refill rights. Now that the reservoir is filled, on-going operating costs are estimated to total about $50,000 per year, to be divided among the three partners.

Colorado Parks and Wildlife has stocked Old Dillon Reservoir with golden trout in efforts to create a thriving fishery. While fishing is not yet allowed, biologists anticipate opening the reservoir for catch-and-release fishing of golden trout once the fish population is mature enough. A screen at the reservoir intake prevents predator species from entering the water from Salt Lick Gulch.

The expansion project included creation of more than 2 acres of adjacent wetlands, planted in 2013 and 2014. Some of the water supply from Salt Lick Gulch is directed into the wetlands to ensure it remains viable habitat.


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