Gross Reservoir expansion gets approval
July 11, 2017
This year has provided several watershed — no pun intended — moments for a pair of permits issued by the Army Corps of Engineers for development of reservoirs on the eastern slope.
Officials from Denver Water late last week announced the Army Corps of Engineers has issued the long-awaited 404 Permit related to the expansion of Gross Reservoir. Denver Water will receive the permit 14 years after starting the process.
To expand Gross Reservoir, located in Boulder County near Twin Sisters Peak and is one of Denver Water's main storage reservoirs, officials plan to raise the Gross Dam by 131 feet to accommodate the storage of an additional 77,000 acre-feet of water, easily tripling the reservoir's capacity.
Of the 77,000-acre feet of additional storage, 5,000-acre feet will be set aside as an environmental pool to mitigate low flow periods on South Boulder Creek.
Officials estimated the cost of the project, including design, management, permitting, mitigation and construction, at around $380 million. Officials from Denver Water noted that no tax dollars will be directed to the project, instead it will be funded through rates and new tap fees on Denver Water ratepayers, as well as the sale of hydropower.
Denver Water stated in a news release Friday that additional water stored in Gross Reservoir will help prevent future shortfalls during drought and helps offset an imbalance in Denver Water's collection system.
Denver Water's CEO Jim Lochhead was happy with the permit approval.
"Denver Water appreciates the Corps' dedication and commitment to careful study of the anticipated impacts of this project," Lochhead said. "We will complete this project responsibly, as evidence by our actions during the public process and the resulting robust environmental protections we've agreed to along the way. We're proud to be doing the right thing."
Local conservation groups like Trout Unlimited, which works closely with Denver Water on the Grand County-based adaptive water management program called Learning By Doing, was also happy with the permit approval, albeit for different reasons.
"Issuance of this permit will unlock significant resources that will allow us to do good things for the river and the environment," said Mely Whiting, counsel for Trout Unlimited.
Preconstruction work, including dam design and geotechnical work, is expected to begin in 2018 according to officials from Denver Water. The entire project is scheduled for completion in 2025.
Officials from Denver Water said an additional 10,000 acre feet of water will be diverted through the Moffat Tunnel during average and wet years. This is an increase of 15 percent, Denver Water officials stated no increaesd diversions would occur during dry years, which are defined as any year when reservoirs are not full due to insufficient snowpack and runoff, with exmaples being 2002 and 2012.
Under the 404 Permit, and other existing agreements including the Colorado River Cooperative Agreement and Learning By Doing, Denver Water must meet specific conditions related to mitigating diversion impacts in Grand County. According to Denver Water, the Gross Reservoir Expansion Project means Denver Water will restore approximately two miles of the Williams Fork River, and will be working with Colorado Parks and Wildlife, U.S. Fish and Game and the U.S. Forest Service to restore and expand cutthroat trout habitat at several locations in Grand County.
The Gross reservoir was originally built in the early 1950s and was designed to allow for expansion to allow for additional water storage. The 404 Permit approved by the Corps of Engineers is part of the National Environmental Policy Act.
Officials from Denver Water are still waiting on the approval of a hydropower license amendment application for the reservoir's dam. They anticipate receiving approval of that application some time next year.