On the effects of wind and tides on the hydrodynamics of a shallow mediterranean estuary

Abstract

A study is made of the effect of wind and tides on the hydrodynamics of the shallow inner basins of mediterranean estuaries. The paper includes a case study of Harvey Estuary in southwestern Australia where salinity and temperature data exist for 11 years during the 1980s and 1990s when that estuary experienced massive annual blue-green algal blooms. An analysis is made of salt exchange through the channels that join estuarine basins of this class to either the ocean or, as in the case of Harvey Estuary, to another shallow estuarine basin. A detailed three-dimensional numerical model is also implemented for the basin of Harvey Estuary. It is concluded that exchange through the channel is dominated by the (mainly diurnal) tides, despite the general micro-tidal nature of this class of estuary, although the efficiency of this process is found to be controlled by the length of the channel. Wind set-up in the basin also produces channel exchange and for Harvey Estuary this is about 20% of the exchange due to tides. Baroclinic flow through the channel is also capable of producing significant exchange but this is suppressed by the tidal currents in the channel except immediately after riverflow. Salt transport along the basins of this class of estuary is mainly driven by the longitudinal density gradient and the strength of this process is controlled by vertical mixing from the wind. However, there is also significant salt transport from wind-induced advection, the effect of which changes seasonally with the direction of the salt gradient.