Assessing Dam Performance During a Non-Failure Incident: Hurricane Fiona’s Impact on Puerto Rico Dams

Evaluating dam performance after significant flooding events – even those not resulting in dam failure – provides opportunity for dam owners and community representatives to evaluate the impact of dams on flooding and related consequences, leading to a better understanding of dam risk and the need to enhance emergency preparedness.On September 18, 2022, Hurricane Fiona made landfall in Puerto Rico dumping more than 20 inches of rain across much of the island and resulting in widespread flooding and storm-related damages. Many communities were left without power and/or clean water for several days. The island’s thirty-six dams survived the flooding without major failure. However, FEMA is interested understanding the influence – both positive and negative – that the dams and their operations may have had on flooding during the event and how the emergency management personnel responded. This presentation will discuss FEMA’s Incident Specific Technical Assistance (ISTA) in Puerto Rico, specifically highlighting work that is evaluating dam performance during Hurricane Fiona in three watersheds – Rio de La Plata, Rio Grande de Loiza, and Rio Jacaguas. These watersheds include a total of seven dams and represent numerous affected communities across the island. Project efforts developed a suite of hydrologic and hydraulic models calibrated to the Hurricane Fiona rainfall to compare flood impacts with and without the dams in place. Through a robust post-event data collection process, conducted in close collaboration with federal, regional, and state partners and local stakeholders, FEMA and the ISTA project team conducted more than 30 interviews and site visits, developed detailed models, performed spatial mapping, and created illustrative graphics to represent hurricane-related flooding and an understanding of the dams’ influence on flood damages. From these findings, the project team determined a number of lessons learned, best practices, challenges, and potential mitigation strategies to support Puerto Rican dam owners and downstream communities at risk for flooding to better plan and prepare for future extreme weather events, thus improving overall resilience. The positive benefits of performing the Puerto Rico ISTA study will be highlighted, as well as specific actions that resulted from the effort.