Main Physical Processes Affecting the Residence Times of a Micro-Tidal Estuary

Residence time is an important parameter linked to the water quality in an estuary. In this paper, we identify and analyze the main processes that affect the residence time of the Caloosahatchee River Estuary, a micro-tidal and mixed diurnal-semidiurnal estuary located in western Florida. Multiyear validated hydrodynamic hindcast results were coupled with an offline particle tracking model to compute the residence time of the estuary, which showed a strong seasonality driven by the river discharge. The residence time reduced with increasing river flow. The wind velocity and direction also affected the residence time. The influence of the wind was dependent on the magnitude of the river discharge. In general, upstream-directed wind increased residence time, while downstream-directed wind decreased residence time. Downstream wind during the dry period reduced residence time on average by a week. Processes such as water density gradient-induced circulation and particle buoyancy also influenced the residence time of the estuary. The outcomes of this study can be used to better understand the influence of the main physical processes affecting the residence time at other similar estuaries and to help in the management of the estuaries to improve their water quality.

Automated summary

In this study, the main processes affecting the residence time of the Caloosahatchee River Estuary were identified and analyzed. The residence time showed a strong seasonality driven by the river discharge, and was influenced by wind velocity and direction. Water density gradient-induced circulation and particle buoyancy also played a role in determining the residence time. The outcomes of this study have implications for understanding residence time in other estuaries and improving water quality management.