Laboratory modelling of surface buoyant plume interaction with grid obstruction

Freshwater point sources originating from terrestrial streams and gullies, discharging into quiescent, semienclosed coastal regions, such as estuaries, tidal inlets, or lagoons, typically provide a source of nutrients (e.g. nitrates, phosphates) and contaminants (e.g. pesticides, pathogens) into these sheltered coastal waters. Dynamically, these freshwater flows behave as surface buoyant jets or plumes due to the salinity-induced density gradients within the coastal saline or brackish receiving waters. Many sheltered coastal regions also increasingly support aquaculture operations (e.g. finfish, shellfish, or seaweed farms), the infrastructure for which can provide obstructions to these surface freshwater flows. Similarly, physical understanding of this flowstructure interaction is clearly crucial to assessing the potential contamination risk to the aquaculture products. The aim of the current study is therefore to explore through laboratory experiments the parametric dependence of physical obstruction effects caused by a vertical grid structure on the flow evolution of an incident surface buoyant plume. The results prove that the presence of the obstruction in coastal domains can have a considerable influence of the turbulent mixing process and transfer of substances in the vertical direction, but have relatively minimal impact in the final dispersion of the plume.