Caribbean-Florida Water Science Center
Evaluating the Potential Effects of Deepening the St. Johns River Shipping Channel on Saltwater Intrusion in the Surficial Aquifer, Duval County, Florida
Project Chief: Rick Spechler
Jacksonville’s main shipping channel is a 20-mile stretch of the St. Johns River extending from the Atlantic Ocean at Mayport, Florida to the Jacksonville Port Authority’s (JAXPORT’s) Talleyrand Marine Terminal just north of downtown Jacksonville (fig. 1). The United States Army Corps of Engineers (USACE) is in the process of evaluating the costs and benefits of a proposed plan to deepen the shipping channel in the St. Johns River to 48-53 feet below North American Vertical Datum 88 (NAVD 88) to permit new Panamax ships to dock at the JAXPORT ship terminals. Currently, the 20-mile stretch of the shipping channel from the mouth of the river to Talleyrand Marine Terminal is maintained by the U.S Army Corps of Engineers at a depth of about 41-43 feet below NAVD 88 to allow existing deep-draft ships to dock at JAXPORT terminals.
The USGS used a variable density groundwater flow and transport model to quantify the range of water-quality changes expected to result from deepening of the St. Johns River shipping channel. The model was used to simulate saltwater intrusion in the surficial aquifer, and identify areas that could be susceptible to groundwater quality degradation and that would require water-level and/or water-quality monitoring.
In order to estimate the potential effects that deepening of the St. Johns River will have on saltwater intrusion in the surficial aquifer, a numerical model, SEAWAT, was used. The SEAWAT model is capable of simulating advective and dispersive transport in a three-dimensional, variable-density, groundwater flow system. Like most commonly used groundwater modeling programs, SEAWAT is based on Darcy’s Law and requires that model properties be assigned using the assumption of an equivalent porous medium.
Not yet available.
A USGS Scientific Investigation Report (SIR) will summarize the potential effects of deepening of the St. Johns River Shipping Channel on saltwater intrusion in the surficial aquifer in Duval County, Florida.