City of Jacksonville Compound Flood Modeling

The City of Jacksonville appointed a Chief Resilience Officer in 2021 and launched the development of the Resilient Jacksonville Strategy, a comprehensive adaptation plan to guide long-term resilience. A multidisciplinary consultant team, including Halff, was selected to support stakeholder engagement, policy evaluation and infrastructure planning using a structured decision-making framework over an 18-month period.

Halff supported the prime consultant and the Chief Resilience Officer by compiling existing flood adaptation policies, projects and programs to establish a citywide flood resilience inventory. The team also developed present and future flood hazard layers for coastal and riverine flooding, integrating the City’s vulnerability assessment into the strategy to create a baseline for future decision making. The process included extensive coordination with City departments, the Mayor’s Office, City Council and community representatives to align flood adaptation actions with broader resilience initiatives.

As part of The Water Institute’s (TWI) Citywide Probabilistic and Compound Flood Model and Real-Time Forecasting System project team for the City of Jacksonville, Halff led the development of a 2D, rain-on-mesh USACE HEC-RAS hydraulic model to simulate coastal, fluvial, and pluvial flooding and their simultaneous effects.

To simulate flooding in the St. Johns River — including its 100-miles long estuary — the city’s numerous tributaries, and the Nassau River watersheds, Halff defined a model domain encompassing approximately 13,000 square miles, with a maximum resolution of 500 feet that covers both watersheds entirely.

Halff’s role includes development of a seamless topographic and bathymetric digital elevation model; collection of historical flood data; tidal and riverine gauge, wind, and precipitation data; validation and calibration of tropical and non-tropical events; representation of antecedent conditions; quality control and review of production runs by the prime; and support for other modeling tasks.

When complete, this project will provide detailed, citywide mapping of water surface elevations and depths, giving officials and the public a robust tool to evaluate flood vulnerability, assess exposure of critical assets and inform resilient design for current and future conditions.