Abstract
Among the 135 or more estuaries on the southeast Australian coastline, 45% are intermittently open. A number of others, which would normally have an intermittently open entrance, are kept permanently open to improve the flushing and water quality that are functions of the horizontal dispersion of the estuarine system. Field studies that investigate the dynamics and horizontal dispersion processes of open and closed states of Intermittenly Closed and Open Lakes and Lagoons (ICOLL) are conducted. Clusters of Lagrangian drifters were used to characterise the surface flow. Horizontal dispersion coefficients (K) under study varied significantly for different tidal phases; the mean ebb tide K (~4.7 ± 3.8 m2 s−1) is an order of magnitude higher than that of the flood tide. During the closed state, K values were up to two orders of magnitude lower than those observed in the open state. These results highlight the contribution of tidal dispersion to transport and mixing processes within an ICOLL. The results showed that tidal pumping effects and tidal-induced horizontal velocity gradients are responsible for the horizontal surface transport and dispersion occurring during the open inlet state. The horizontal surface dispersion processes identified at different inlets and environmental conditions within this site are valuable for managing transport of particles, freshwater mixing, larvae transport, waste, and pest control.
Highlights
Closed and Open Lakes and Lagoons (ICOLLs) are a subcategory of coastal lakes and lagoons, which exhibit limited exchange with the ocean and river flows [1]
The purpose of this article is to present estimates of dispersion coefficients and dominant dispersion mechanisms from field studies in an Intermittenly Closed and Open Lakes and Lagoons (ICOLL) that provide an insight into transport of material in the systems during open and closed conditions, for time scale less than a tidal cycle and length scale in the order O [1 m]
The analysis of drifter deployments, Acoustic Doppler Velocimeter (ADV) observation, and physiochemical properties highlight a significant contribution of tide in the flow dynamics of the channel
Summary
Closed and Open Lakes and Lagoons (ICOLLs) are a subcategory of coastal lakes and lagoons, which exhibit limited exchange with the ocean and river flows [1]. Of the more than 135 estuaries along the southeast Australian coast, about 45% of these are intermittently open and a number of others, which would normally have intermittently open entrances, are kept permanently open. The permanent open state is facilitated by mechanical means to maximize the flushing and water quality that are functions of the horizontal dispersion of the system [2,3]. Many prior studies on ICOLLs have focused on the change in ecological processes caused by their dynamic opening and closing [4,5]. Hydrodynamic processes including vertical mixing, and horizontal dispersion, flushing, and recirculation patterns control the ecological processes [6,7].
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