The water exchange in estuaries is driven by complex Lagrangian physics which means the tidally-averaged movement of water parcels in an estuary are not driven by residual current vectors that are estimated by averaging tidal currents at fixed locations. One must trace the movement of individual fluid particles to properly estimate water exchange and movement in an estuary. For this reason, the Marine Dynamics Laboratory developed a 3-D Lagrangian particle tracking program and incorporated the new finite-volume Satilla River model.
The particle-tracking experiments were conducted to examine the nature of the water exchange in the Satilla River Estuary. The results show that the movements of particles depend on the times and locations that particles are released, as well as the wind fields. The trajectories of particles released at the high or low water levels, with or without the impact of wind, could differ significantly, as shown in Figures 1-4.
The study suggests that the water movement in the Satilla River Estuary is completely controlled by strong nonlinear physical processes. Therefore, limited drifter measurements made over short time intervals do not represent the general nature of water movement within this estuary. Since water salinity is also driven by the Lagrangian process, we must combine the model and field measurement efforts if we expect to get an objective view of the environmental conditions controlling freshwater and saltwater movements and interactions in the Satilla River Estuary