Spillways are essential dam safety structures, as they prevent uncontrolled overtopping and help protect both the dam and downstream communities. However, the bulletin notes that spillways have often received less systematic surveillance than the dam structure itself, despite the fact that inadequate spillway capacity or performance has contributed to many dam incidents and failures, as illustrated by the Oroville incident in 2017.

The bulletin proposes a structured, systematic approach to spillway surveillance. It recommends understanding each spillway’s design, components, operating history, vulnerabilities and potential failure modes, supported by regular visual inspections, monitoring instruments, periodic testing, and post-flood or post-earthquake inspections. It also stresses the importance of good documentation, clear procedures, specialist expertise and attention to human and organisational factors.

Overall, the bulletin calls for spillways to be treated as critical dam safety components in their own right. Regular, site-specific and well-documented surveillance should help detect deterioration early, guide maintenance and repairs, improve operational readiness, and reduce the risk of major incidents.