Overview
Jacksonville Harbor, a major U.S. port, underwent a general reevaluation study by the U.S. Army Corps of Engineers — Jacksonville District (USACE-SAJ) to evaluate plans for deepening the navigation channel from its existing depth of 40 feet (12.2 m) to a maximum of 50 feet (15.24 m), from the river mouth at the Atlantic Ocean to a point 14 miles (22.5 km) upstream. Deepening would allow larger vessels to access the port — reducing transportation costs and improving navigational safety — while seeking to minimize impacts on environmental resources. To evaluate potential impacts, a three-dimensional hydrodynamic and transport model of Jacksonville Harbor was developed using the Environmental Fluid Dynamics Code (EFDC).
Model Setup
The EFDC hydrodynamic and salinity model was validated for the Jacksonville Harbor deepening project area and used to assess the direct impacts of channel modifications on salinity and circulation in the main stem of the lower St. Johns River. Channel-deepening scenarios were evaluated over a six-year period (1996–2001) that includes the lowest river flow of any three-year period in the river’s 78-year flow record, ensuring that assessed project impacts exceed those of an average year and providing conservative estimates.
Key Findings
The model results examine the effects of the proposed channel-deepening projects on water level, salinity, and water age throughout the model domain, providing tools for analyzing biological, chemical, and ecological impacts. The study presents cumulative impacts 50 years after project completion from the proposed channel-deepening alternatives together with other projects — including the Mayport Deepening Project for the U.S. Navy, freshwater withdrawals from the St. Johns River, and future sea level rise.