Relation between freshwater flow and salinity distributions in the Alafia River, Bullfrog Creek, and Hillsborough Bay, Florida

Data on streamflow, tide stage, specific conductance, and chloride concentration were collected in the Alafia River and Bullfrog Creek to describe the salinity and physical characteristics of the saltwater wedge. The location of the saltwater-freshwater interface for both streams was described by multiple regression equations involving streamflow and tide stage. Low-flow frequency data were used with regression relationships to show the effect of withdrawals of freshwater from the Alafia River on the location of the saltwater interface. Examples are presented without storage and with storage and minimum streamflow requirements. In every case, the effect of reductions in streamflow was upstream encroachment of saltwater. Salinity in Hillsborough Bay in the vicinity of the Alafia River and Bullfrog Creek was evaluated using a salt-transport model for various freshwater inflow conditions. Model results indicate that freshwater inflow from these streams has the greatest effect on the salinity of areas closest to the mouth during periods of above average inflow. (USGS)