Séminaire EPOC "Effects of seasonal, local and remote forcing on a point-source submarine groundwater discharge" Sabrina PARRA (University of Florida, US)22/06 : 10h45
Lundi 22 juin 2015, 10h45 en Salle Stendhal
Effects of seasonal, local and remote forcing on a point-source submarine groundwater discharge
Sabrina PARRA (University of Florida, US)
The seasonal variability of local and remote forcing on a point source submarine groundwater discharge located within a fringing reef lagoon were investigated using three different time series. The local forcing considered to affect discharge and turbulent kinetic energy (TKE) variations were tides, precipitation, and waves. Jet velocities and TKE were primarily driven by semidiurnal tides and seasonal precipitation patterns, followed by semi-monthly tidal variations, and intermittently by wave events and sea level changes caused by the Yucatan Current variability. While the wet period produced consistent subinertial spring outflow, the dry period produced consistent saltwater intrusion at high tides. During the wet period, saltwater intrusion events were generated when the tidal range exceeded 0.2 m, during wave setup events and variability in the geostrophically-balanced Yucatan Current. As the discharge intensified during low tides, jet temperatures decreased and jet salinities increased. Decreasing temperatures suggested that waters originated further within the aquifer, while increasing salinities suggested mixing of aquifer and seawater. Therefore, it is proposed that the jet conduit is connected to a stratified chamber with seawater below brackish water. The spring discharge was quantified using a modified Bernoulli energy equation that included the Darcy-Weisbach friction term. This model used the aquifer elevation and the friction factor as the free parameters to match the observations. The model worked best during the dry period, when aquifer levels were less variable because of decreased rainfall. The wet period most likely led to a more variable aquifer level, thus reducing the variance explained by the model that assumes a constant aquifer elevation. Nevertheless, the model predicted saltwater intrusion events reasonably well with a relatively simple approach.