Investigation on the dynamics of gravity-driven coastal currents

Numerical simulations of buoyant, gravity-driven coastal plumes are summarizedand compared to the inviscid geostrophic theory of Thomas & Linden (2007) andto laboratory studies for plumes owing along a vertical-wall coastline (those ofThomas & Linden (2007) and additional experiments performed at Warwick University). In addition, results of two new laboratory studies with different scalesfor plumes owing along a more realistic inclined-wall coastline are presentedand compared to an extended theoretical model from the geostrophic theory ofThomas & Linden (2007). The theoretical and experimental results for plumesflowing along inclined-wall coastlines are compared to the inclined-wall experimental studies of Avicola & Huq (2002), Whitehead & Chapman (1986) and Lentz& Helfrich (2002), to the inclined-wall scaling theory of Lentz & Helfrich (2002),and to oceanic observations. The lengths, widths and velocities of the buoyantgravity currents are studied. Agreement between the laboratory and numericalexperiments, and the geostrophic theories for both vertical-wall and inclined-wallstudies is found to depend mainly on one non-dimensional parameter which characterizes the strength of horizontal viscous forces (the horizontal Ekman number). The best agreement between the experiments and the geostrophic theoriesis found for plumes with low viscous forces. At large values of the horizontalEkman number, laboratory and numerical experiments depart more significantlyfrom theory (e.g., in the plume propagation velocity). At very low values ofthe horizontal Ekman number (obtained in the large-scale inclined-wall experimental study only), departures between experiments and theory are observed aswell. Agreement between experiments and theory is also found to depend on thesteepness of the plumes isopycnal interface for the vertical-wall study, and on theratio between the isopycnal and coastline slopes for the inclined-wall study.