Hydraulics Lab Manager Colorado State University Fort Collins, CO, Colorado
The Halligan Water Supply Project (HWSP), located near Fort Collins, Colorado, is being undertaken by the City of Fort Collins (City) to enlarge Halligan Reservoir by approximately 8,200 acre-feet to improve water reliability and resiliency. The existing Halligan dam is a 78-foot high, arch concrete dam that will serve as a cofferdam during construction and then will be demolished. AECOM is designing a new 144.5-ft high Roller Compacted Concrete (RCC) dam, overtopping spillway, and new outlet works for the HWSP.
The outlet works will be designed to convey the large construction diversion flows associated with a 350+ square mile watershed and meet a wide range of operational flows. Outlet flows range from a few cubic feet per second (cfs) to 800 cfs to provide flushing flows to improve the downstream riverbed. The design of the outlet works includes a 48-inch and two 24-inch jet-flow gates that discharge into the adjacent spillway stilling basin. A physical model was developed to evaluate the hydraulic performance of the energy dissipation structure that is based on Reclamation Type VI Stilling Basin.
This paper presents the results of a 1:6 Froude scale physical hydraulic model constructed and tested in support of the proposed unique energy dissipator design that is constrained by space created by the adjacent spillway infrastructure. Iterative model configurations were evaluated at multiple flow conditions to determine the optimal dissipator configuration and air supply to achieve satisfactory hydraulic performance. Final design recommendations and lessons learned during the extent of the study will be presented.
