Relating River Plume Structure to Vertical Mixing

Abstract

The structure of a river plume is related to the vertical mixing using an isohaline-based coordinate system. Salinity coordinates offer the advantage of translating with the plume as it moves or expanding as the plume grows. This coordinate system is used to compare the relative importance of different dynamical processes acting within the plume and to describe the effect each process has on the structure of the plume. Vertical mixing due to inertial shear in the outflow of a narrow estuary and wind mixing are examined using a numerical model of a wind-forced river plume. Vertical mixing, and the corresponding entrainment of background waters, is greatest near the estuary mouth where inertial shear mixing is large. This region is defined as the near field, with the more saline, far-field plume beyond. Wind mixing increases the mixing throughout the plume but has the greatest effect on plume structure at salinity ranges just beyond the near field. Wind mixing is weaker at high salinity classes that have already been mixed to a critical thickness, a point where turbulent mixing of the upper layer by the wind is reduced, protecting these portions of the plume from further wind mixing. The work done by mixing on the plume is of similar magnitude in both the near and far fields.

Penetration of a salinity front into a rotating basin: Laboratory experiments and a simple theory

“…Spreading of density fronts in the ocean is likely to be dominated by processes, such as frontal instabilities and mixing by eddies, which are not considered in this paper. Turbulent mixing appears as an important process for the dynamics of buoyant coastal plumes, as indicated by field observations (e.g., Münchow and Garvine, 1993;Sanders and Garvine, 2001;MacDonald and Geyer, 2004;Pritchard and Huntley, 2006;Horner-Devine et al, 2009) and numerical simulations with circulation models (e.g., Fong and Geyer, 2001;Hetland, 2005;Pimenta et al, 2011). Nonetheless, the notion that interfacial friction leads to seaward spreading of density fronts bounding buoyant water introduced along oceanic boundaries (e.g., Wright, 1989) finds here apparent support.…”

High-resolution satellite turbidity and sea surface temperature observations of river plume interactions during a significant flood event

“…Moreover, flood events are difficult to observe in situ; as with ship-based activities, it is seldom possible to reach river mouths while autonomous vehicles are not operating in shallow waters or in highdensity gradients (Hetland, 2005;Devlin and Schaeffelke, 2009;Tesi et al, 2011). However, observations from instrumented sites or coastal observatories such as AAOT provide detailed information on a large array of variables but do not provide a sufficient spatial coverage and may not happen to be located favourably to observe events of interest (Dickey, 2003).…”

“…The operational systems were forced by the operational highresolution (7 km × 7 km) meteorological model COSMO-I7 (Russo et al, 2013a, b). Following Hetland (2005), at the river mouths' grid cells, momentum was injected, giving a vertical structure to the plume, i.e. injecting most of the freshwater discharge in the surface layers (∼ 80 % in the four uppermost sigma levels, corresponding to about 1.5 m).…”

“…The extent, motion, and general structure of river plumes are mainly determined by the advection and mixing processes of freshwater from the river mouth, while the along-coast transport of the riverborne material is determined by several processes, including stratified-shear mixing, frontal processes, oceanic transport, tide and wind forcing, as well as Coriolis effects (Hetland, 2005;Horner-Devine et al, 2015;Geyer et al, 2004;Nof and Pichevin, 2001). The relative importance of these processes determines the overall fate and transport of freshwater, as well as the associated dissolved and particulate matter within the plume (Horner-Devine et al, 2015;Devlin and Schaeffelke, 2009;Brodie et al, 2010;Syvitski et al, 2005).…”

Effects of bottom topography on dynamics of river discharges in tidal regions: case study of twin plumes in Taiwan Strait

“…Hence, any model of plume evolution is particularly sensitive to how turbulence is parametrized (Luketina and Imberger, 1989;Oey and Mellor, 1993;Ruddick et al, 1995;Garvine, 1995;Kourafalou et al, 1996;Hetland, 2005Hetland, , 2010Schiller and Kourafalou, 2010;Wang et al, 2011;Hwang et al, 2011).…”