This bulletin focuses on the hydraulic and structural design of spillways, which are critical safety features that protect dams and downstream communities by safely releasing floodwaters without uncontrolled overtopping. Because floods beyond spillway capacity have been a major cause of dam incidents and failures worldwide, the publication addresses the main spillway components, design options, and operational challenges. Following lessons learned from recent incidents such as the Oroville Dam event in 2017, particular attention is given to chute spillways followed by stilling basins, including both smooth and stepped chute configurations. The bulletin examines key issues such as high-velocity flow behavior, aeration, cavitation risk, energy dissipation, and structural resilience.

It also presents practical solutions for upgrading existing spillways to meet increasing safety requirements, especially in the context of improved hydrological assessments and the growing impacts of climate change on extreme flood events.