Correlation of freshwater discharge and subtidal salinity in Apalachicola River

Modification of river flow from engineering activities often affects salini ty and the mixing of fresh and saltwater in tidal rivers. In this study, an empirical relation between subtidal salinity and gradually varying freshwa ter inflow at a given station in the Apalachicola River, Florida, was devel oped and tested with field observations. A time series of subtidal salinity was obtained by low-pass filtering of the instantaneous salinity to elimin ate the tidal signal. Based on the one-dimensional balance theory between a dvection and diffusion of salt, the time series of subtidal salinity was di rectly correlated to the gradually varying freshwater input by an exponenti al equation. With field observations obtained from the Apalachicola River, the empirical constants were obtained by regression. The correlation betwee n observations and the results from the empirical equation were very good. This simple empirical relation may be used by water resource engineers and managers in preliminary studies to quickly estimate the potential impact of water resource planning on subtidal salinity at a given location in a tida l river.