Water Circulation & Dilution Projects
   Florida

Overview
As water circulates in surface water bodies, it can transport waterborne contaminants and dilute initial concentrations of release materials. As part of a large investigation at Key West Harbor, Water & Air personnel used drogues to measure current speed and direction over a one-month period to determine typical transport pathways for turbidity plumes that might be generated by ship traffic or dredging activities. At a bayou in Pensacola, Florida, drogues were used over three days to determine the potential for stagnation in the inner portion of a former shipyard that was planned to be converted into a marina and boat storage facility. A Water & Air field team used drogues before and during a dilution investigation in Lake Harris near Eustis, Florida, where dye was released to simulate dilution of a released contaminant. Development permit requirements specified that any contaminant spills, e.g., sewage, must become diluted to 10% of the initial concentrations within 96 hours.

Details

• Water & Air deployed drogues to collect speed and direction data for water masses in an ocean-harbor area, a lake, and a bayou.
• To fulfill permit requirements, dye was released and its dispersion monitored until all concentrations were demonstrated to be less than 10% of the initial value.
• All collected data were reported to clients in graphical and tabular formats with appropriate text.

Results
Current data from the area in and around Key West Harbor showed that water movement was predominantly tidally driven, although wind is a force that can strongly influence both speed and direction. The Key West data were used to formulate a monitoring program for turbidity plumes that potentially might be related to planned dredging activities. Circular flow patterns similar to gyres were documented at the bayou site. Consequently, after regulatory review, an additional dye release investigation or hydrological modeling might be required to demonstrate or indicate that the requirement for the 10% dilution in 96 hours would be met. At Lake Harris, circulation patterns during calm conditions and figures of dye concentration isopleths demonstrated that dilution of released contaminants was achieved within a few hours.