Halligan Reservoir is an existing drinking water storage facility for the City of Fort Collins. An increase in the capacity of the reservoir was necessary to supply a growing population in Fort Collins. Reservoir expansion design included the construction of a brand-new dam structure just downstream of the existing dam. CSU’s Hydraulics lab was contracted to model and study the outworks jet valve and associated stilling basin. One main goal of the project included slowing the high velocity jet to protect the downstream reach of the North Fork of the Poudre River from erosion all while containing the flow in a limited and confined space. The ensuing optimization study led researchers to test dozens of designs before landing on a solution that included a novel hanging baffle and a recession in the basin that forced water recirculation and energy dissipation before flowing downstream.