The vast majority of Reclamation’s large facilities such as dams, spillways, diversion structures, and canal systems were designed and built over 50 years ago. These large, signature projects were based on the hydrologic data, design standards, and analysis methods of the time. Intensified precipitation extremes and extended droughts challenge the assumptions underpinning the original design criteria. While new operational and societal demands like sediment management, fish passage and environmental low flows require capabilities these structures were never intended to provide. To adapt these legacy structures, both physical and numerical hydraulic modeling are crucial to guiding design modifications and retrofits by evaluating the performance of any proposed modification. New instrumentation and construction methods continue to advance what is possible with physical hydraulic modeling. Complementary to physical modeling, numerical modeling or computational fluid dynamics (CFD) allows detailed simulation of turbulent, three-dimensional flow. These tools enable engineers to reimagine and safely modify aging infrastructure.