INBUCOC

Interacting Buoyant Coastal Currents

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 Obiettivo del progetto (Objective)

'Buoyant coastal currents strongly influence coastal circulation and ecosystems and, on a global scale, the redistribution of freshwater. The interaction of buoyant currents from different river sources is a common phenomenon; for example, the western Adriatic Sea coastal current. The manner in which buoyant currents interact will influence the downstream coastal distribution of waterborne materials contained in individual currents, with ecological and societal importance. While clearly an important phenomenon on many coasts, the dynamics of interacting buoyant coastal currents, and the impacts of such interactions, remain poorly understood. As researchers, we are interested in investigating the dynamics of buoyant current interactions in a series of idealized and process oriented analytical studies and laboratory experiments. The principle objective of this study is to determine the details of the cross-shore and vertical structure of buoyancy and velocity within two interacting buoyant coastal currents and their dependence on control parameters including density anomaly, current transport, bottom slope, and rotation rate. Both surface-trapped currents, which do not feel the bottom, and slope-controlled currents, which are steered by the action of the bottom boundary layer, will be examined. Analytical studies will look at the structure of coupled, geostrophically-adjusted currents. Rotating tank experiments will be conducted to track the interaction of two buoyant currents, and to test the predictions of the analytical model. The laboratory and analytical studies will complement each other allowing for a robust assessment of the final results. This study will lead to a greatly improved understanding of the dynamics of buoyant coastal currents and their interaction, and will advance our capability of modeling buoyant currents. In addition, this project will allow the transfer of extensive experience, knowledge, and expertise of Dr. Cenedese to the host institution.'

Introduzione (Teaser)

Despite being an important phenomenon, the dynamics and impacts of interacting buoyant coastal currents are poorly understood. Researchers joined forces to clear the waters in this respect by investigating the dynamics of these interactions in a series of studies and laboratory experiments.

Descrizione progetto (Article)

Buoyant coastal currents strongly influence coastal circulation and ecosystems as well as the redistribution of fresh water on a global scale. One example of a common interaction of buoyant currents from different river sources is the western Adriatic Sea coastal current. The way in which buoyant currents interact influences the downstream coastal distribution of waterborne materials contained in individual currents. This has significance in both ecological and societal terms, and calls for an understanding of how coastal waters can transport pollution, harmful algal blooms (HABs) and sediments away from a populated coastline.

Against this backdrop, the 'Interacting buoyant coastal currents' (INBUCOC) project set out to investigate the effects of multiple river plumes on the formation and dispersal of coastal waters. Researchers focused on the importance of the boundaries and relative location of these plumes, given the possibility of waters from one river being polluted or carrying harmful algae. To achieve their goals, they employed a simplified scenario involving two hypothetical rivers, the North River and the South River.

To determine various scenario outcomes whereby one river contained pollution or harmful algae, INBUCOC set a series of questions. These covered the possibility of effects to the populated coastline, whether one river acts as a barrier to such threats reaching the coast, and if the two water masses align relative to each other in the vertical and horizontal.

Primarily, the study aimed to quantify the possible horizontal and vertical alignment scenarios as a function of dynamically relevant non-dimensional numbers, using an analytical model. Laboratory results and analytical calculations showed that the frontal position, the depth profile, and the horizontal and vertical alignments of two buoyant fluids with different densities can be characterised by an important length scale, the Rossby radius of deformation.

Laboratory rotating experiments revealed that, after reaching equilibrium, the two buoyant currents align mainly horizontally. Alternatively, if the extent of the fronts between three different fluids is similar, the buoyant currents align mainly vertically.

INBUCOC provided insights on how the water masses of two individual buoyant coastal currents align relative to each other vertically and horizontally. While this can enhance our understanding of coastal current interactions, researchers cautioned that project results should be interpreted with care, due to their modelled, speculative, laboratory-based nature.