Finite volume modeling of variable density shallow-water flow equations for a well-mixed estuary: application to the Río Maipo estuary in central Chile Modèle en volumes finis des équations d'un écoulement en eau peu profonde de densité variable dans un estuaire bien mélangé: application à l'estuaire de Río Maipo au centre du Chili

Strong advective flows in well-mixed estuaries can produce abrupt fronts and density gradients, which cause secondary circulation and affect the ecosystem by generating recirculation or accumulation of pollutants inside the estuary. To model these complex phenomena, a method capable of adequately representing the dynamics of the flow by considering the salt as an active tracer, influencing the transport within the estuary, is required . A numerical model based on the finite volume MUSCL-Hancock method is used to solve the shallow-water flow equations in combination with an advection/diffusion of salt equation, to simulate two-dimensional unsteady flow in a vertically well-mixed estuary. The salt transport equation is coupled to the momentum equations via the hydrostatic term, which permits simulation of baroclinic secondary circulation. A series of benchmark test problems are used to validate the model and demonstrate its capabilities. The model is then used to simulate the saline intrusion within the Rio Maipo estuary, a well-mixed tidal river in central Chile. The numerical results predict that the presence of a littoral bar at the river mouth preclude s the upstream transport of salt, resulting in an almost negligible salinity intrusion in the system. This result is validated with field measurements o f salinity, taken from within the estuary.