Laboratory realizations and numerical simulations of buoyant, gravity-driven coastal plumes are summarized and compared to the inviscid geostrophic theory of Thomas and Linden (2007). The lengths, widths and velocities of the buoyant currents, as well as their internal structure and dynamics, are studied. Agreement between the laboratory and numerical experiments and the geostrophic theory is found to depend on two non-dimensional parameters which characterize, respectively, the steepness of the plumes isopycnal interface (1) and the strength of horizontal viscous forces (Ek(H), the horizontal Ekman number). In general, the numerical and laboratory experiments are in good agreement when conducted at comparable values of land EkH. The best agreement between experiments (both laboratory and numerical) and the geostrophic theory are found for the least viscous flows, though important departures from the theoretical predictions are nonetheless found, particularly in the early development of the plume system. At elevated values of the horizontal Ekman number, laboratory and numerical experiments depart more significantly from theory, e.g., in the rate of plume movement along the coast. A simple extension to the geostrophic theory suggests that the discrepancy between the theoretical and experimental propagation speed should be proportional to the square root of the horizontal Ekman number. The numerical simulations confirm this relationship. For some combinations of the non-dimensional parameters, instabilities develop in the seaward edge of the buoyant plumes. The laboratory and numerical experiments are used together to infer the region within parameter space within which the instabilities occur. Mixing of ambient and buoyant fluids by the plume-edge instabilities is explored using the numerical results. (C) 2011 Elsevier B.V. All rights reserved.

Laboratory experiments simulating gravity-driven oceanographic coastal surface currents are described. In the natural environment such currents develop when estuarine fresh-water discharges into the ocean. Results from three complementing experimental studies are discussed and compared to a new geostrophic model. The first study was conducted in a small-scale (1m diameter) water-filled rotating tank. The other two studies were carried out at the large-scale Coriolis turntables at Grenoble (13m tank diameter) and Trondheim (5m tank diameter). Currents were generated by releasing buoyant fresh water continuously from a small source at the fluid surface. The height, width and length of the currents were studied as a function of the background rotation rate, the volumetric discharge rate at the source and the density difference between fresh and ambient fluid. The small-scale experiments and the Grenoble study focused on the simplest case of currents flowing along a vertical coastlines in an, effectively, infinitely deep ocean. The Trondheim study generalised these results by investigating how the dynamics are affected when the currents flow along inclined coastlines with different inclination angles with respect to the horizontal.

We summarize a study that compares experimental laboratory data for gravity-driven coastal surface currents with corresponding theoretical results obtained from a new geostrophic model describing such currents. It is found that experiment and theory are, generally, in good agreement.