GOOSE PASTURE TARN DAM REHABILITATION
The Town of Breckenridge is beginning a two year project that is focused on rehabilitating the Gary Roberts Goose Pasture Tarn Dam in Blue River. Construction to rehabilitate the dam is planned to start in May 2021 and be completed by the fall of 2023. The rehabilitation, which primarily includes replacement of two existing spillways with a single larger spillway, is intended to improve the safety and long-term operation of the dam. This project is planned for joint funding by FEMA, the State of Colorado, and the Town of Breckenridge.
The Goose Pasture Tarn Dam is a 57-foot high zoned earthen dam located on the Blue River, 2 miles south of Breckenridge. It was constructed in 1965 and has been owned and operated by the Town of Breckenridge since 1970. An emergency spillway was constructed in 1990 to provide additional spillway capacity above that provided by the concrete service spillway included as part of the original dam. This dam provides water to the Gary Roberts Water Treatment Plant serving residents of Breckenridge.
It is one of 429 Colorado dams classified as “High Hazard” based on estimated consequences if the dam were to fail and is not on the condition of the dam (2018 National Inventory of Dams, US Army Corps of Engineers). In 2016, safety issues with the use of the concrete service spillway during high flows were identified. The Town of Breckenridge took immediate steps to ensure the safety of the dam. Colorado Dam Safety imposed a reservoir storage restriction, lowering the water level that could be stored in the reservoir by 4 feet to a safer level, and restricted flows down the service spillway. The previously unused emergency spillway has been lowered 4 feet below the service spillway and can handle up to 100-year flows without spilling into the restricted service spillway. There have been investigations into the causes for deterioration of the service spillway identified dam safety concerns regarding the spillway and dam requiring rehabilitation.
The Town Public Works staff regularly monitors dam conditions through visual observation, and a series of monitoring wells (aka piezometers) and drains. Colorado Dam Safety personnel and engineers working for the Town inspect the dam on a yearly basis. The reservoir will be kept at the restricted level imposed by Colorado Dam Safety until a new spillway has been constructed. A plan to safely divert river flows around the dam during construction will be implemented. A recently updated emergency action plan for quickly addressing any unanticipated dam safety issues was developed jointly by the Town, Colorado Dam Safety, and Summit County Emergency Management.
Environmental studies are underway to assess wetlands, endangered species, and cultural resource impacts. Engineers for the Town are working with the Federal Emergency Management Agency (FEMA), the State Historic Preservation Officer (SHPO), and the U.S. Army Corps of Engineers to complete these assessments and obtain necessary permits for construction.