Salinity characteristics and distribution and effects of alternative plans for freshwater withdrawal, Little Manatee River estuary and adjacent areas of Tampa Bay, Florida

The Little Manatee River, a coastal stream that empties into Tampa Bay, Florida, may be used as a source of freshwater. Reduction of streamflow will result in upstream movement of saltwater in the stream. Data on streamflow, tide stage, and specific conductance describe the salinity distribution of the estuary. Vertical conductivity profiles indicate that the river is vertically homogeneous during low flow. The maximum upstream location of the saltwater-freshwater interface (800 micromhos) in the river was described by multiple regression analysis involving mean daily streamflow and high-high tide. The coefficient of determination is 0.94 with a root mean square error of + or - 0.4 mile. The location on the river where the estuarine system ends and the riverine system begins is at about 9.9 miles above the reference station at Shell Point. Duration analysis of conductivity indicates that the maximum upstream location of the interface exceeded 9.7 miles about 17 percent of the days for the period of study. Reduction by 50 percent of streamflow for the 90day, 2-year and 20-year recurrence-interval low flow would relocate the maximum intrusion of the interface at the 2-year and 20-year flows upstream by 0.7 and 0.2 mile, respectively.