Updating Precipitation Design Standards for Oregon: Precipitation Frequency and Probable Maximum Precipitation

ABSTRACT ONLY - A critical aspect of dam design and operation is determining the amount of rainfall that dams must be designed to capture and safely pass through their hydraulic structures. Additionally, extremely rare events— such as Probable Maximum Precipitation (PMP) or extremely rare events—must be considered due to the potentially severe consequences of dam failures. To support dam owners and operators in Oregon, the Oregon Water Resources Department (OWRD) is updating two key datasets essential for dam design, including global warming considerations and uncertainties estimation: (1) Point and areal precipitation frequency estimates for extremely rare events (e.g. 100,000-year) (2) Probable Maximum Precipitation (PMP) Historically, PMP has been the primary design parameter for high-hazard dams. However, there is a growing shift toward risk-based approaches, which directly link consequences to risk levels (return periods) and explicitly account for uncertainties. We argue that both precipitation frequency estimates (1) and PMP (2) remain invaluable for dam safety. In this presentation, we will outline the technical work involved in updating these datasets and introduce a user-friendly webpage being developed to provide easy access to this critical information.