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Primary Outlet Works ‘Trashrack’ Replacement at Gross Reservoir

Upgrade is a regulatory requirement to comply with current design criteria

Beginning in late August, Denver Water’s contractor, Global Diving & Salvage, Inc., will begin a project to replace the primary outlet works “trashrack” at Gross Reservoir. The trashrack is a 25-foot by 25-foot structure, built in 1951, at the bottom of Gross Reservoir that keeps trash and other debris (e.g., logs) out of the water passage at the base of the dam. While the structure is still sound, the upgrade is a regulatory requirement to comply with current design criteria that applies to all dams regulated by the Federal Energy Regulatory Commission.

The project is not, in any way, related to the Gross Reservoir Expansion Project, and would be conducted regardless of the expansion effort.

Traffic and Recreation Impacts

  • Deliveries to the site will continue for the next few weeks. Our contractors will be vigilant to ensure safety for residents and recreationalists. Please use extra caution while traveling through this area.
  • There is no public reservoir access from the South Side picnic area and the parking lot will remain closed for the duration of this project. The Windy Point picnic area will remain open but may be subject to increased traffic and restricted parking due to crews working on-site.

Because of the depth of the reservoir, and as it is not possible to drain the reservoir due to water supply needs, saturation diving will be used on this project to ensure it is completed as quickly and safely as possible. Saturation diving allows divers to live in a pressurized environment for long periods and reduces the amount of time divers spend undergoing decompression. Saturation diving work will continue 24 hours a day for an estimated 41 days, beginning Sept. 20 and concluding Nov. 1.

Cranes lower material at Gross Dam for rehabilitation project in 2003.
Global installs a gate on the upstream end of the primary outlet works as seen in this 2003 photo at Gross Reservoir. It's the same location for the current project. Photo credit: Denver Water.


Taking a deep dive


feet below water, at the bottom of the reservoir, is the existing location of the trashrack


specialized saturation divers will live in a pressurized chamber

Work will include:

  • Removing accumulated sediment immediately around the existing trashrack structure to allow for construction access.
  • Underwater demolition and removal of the existing concrete columns and beams, steel beams and braces, and steel trashrack panels.
  • Fabrication and underwater installation of a new steel trashrack frame structure and steel trashrack panels similar to the existing structure.

Residents and recreationalists in the area can expect:

  • Increased traffic along Crescent Park Drive and Gross Dam Road as materials and supplies are brought to the site.
  • Some noise and lights from generators and boats on the water.
  • No public access at the South Side picnic area (the lower parking lot on the south side of the dam).

The safety of our workers and neighbors is a top priority and Denver Water is committed to being a good neighbor, minimizing construction-related disruptions and being transparent in our communications. Learn more about our good neighbor commitment.


Ashley Denault, Denver Water Public Affairs, 303-634-3429