The tallest dam in Colorado in 50 years, incorporating asphalt core technology

Chimney Hollow Reservoir

The Chimney Hollow Reservoir Project aims to secure a reliable water supply for 400,000 residents in northern Colorado through a collaboration with 12 public agencies.

We are responsible for the comprehensive engineering and design of the Chimney Hollow Reservoir. The project features a 360-foot (110-metre) tall hydraulic asphalt core rockfill main dam, a 40-foot (12-metre) high zoned rockfill saddle dam, inlet/outlet works within a tunnel on the right abutment, and an uncontrolled concrete spillway. Additionally, it includes large diameter conveyance piping and a valve house to integrate with the US Bureau of Reclamation’s Colorado-Big Thompson Project, along with access roads.

Our scope encompasses geotechnical investigations, evaluation of alternatives, complete engineering analyses, preparation of intermediate and final designs, creation of bid documents, support during bidding, and engineering services during construction. This work involves a large test quarry and test fill to assess rockfill properties for the final design.

The Northern Colorado Water Conservancy District Subdistrict has secured all necessary federal permits for the project. Upon completion, the main dam will be one of the largest in Colorado. The project is expected to be commissioned in summer 2025.