To fortify water resources and protect against increasingly severe flood events, Halligan Reservoir is being expanded via construction of a new dam downstream of the existing structure. CSU’s Hydraulics Lab has been contracted to construct and test a 1:24 scale model of the new spillway system.

The model consists of a large wooden headtank with milled bathymetry to simulate approach conditions from the reservoir to spillway, a converging stepped spillway, a flat converging stilling basin with nine modular baffle blocks, and a milled downstream exit channel. Water for testing is supplied via gravity from Horsetooth Reservoir.

The model is tested to perform against a Probable Maximum Flood (PMF) event of approximately 105,000 cubic feet per second. Testing has focused on calibrating the model approach conditions to CFD results using large-scale particle-image velocimetry (LSPIV), measuring water-surface elevations within the stilling basin, and measuring velocity over erosion-critical locations downstream of the stilling basin.