Tracer dynamics in two-layer density-stratified estuarine flow

Abstract

This paper considers tidal-driven particle motion in Tampa Bay, Florida, USA under fully stratified conditions with riverine inflow. The flow field is modelled by means of the two-layer shallow-water equations solved on an adaptive quadtree grid using a second-order Roe-type finite-volume scheme. Tracer dynamics are then obtained through Lagrangian particle tracking. The results show that the effect of external forcing is concentrated primarily in the upper layer, with particles in the lower layer less mixed and exhibiting relatively longer residence time in the semi-enclosed tidal bay. Particle flushing from Old Tampa Bay into the open sea is particularly hindered by the narrow inlet, whereas particles in Hillsborough Bay experience rapid transport seaward due to the large influx of river discharge. Particle patches are typically stretched in Middle Tampa Bay and may be trapped in the shallow Lower Tampa Bay region. The study reveals interesting underlying mixing features that cannot be produced by a single-layer depth-averaged shallow-water model.