River plumes

Freshwater transport in coastal currents

We recently investigated the processes controlling the freshwater transport in buoyant coastal currents. It is well known that only a fraction (30-70%) of freshwater from a river source is carried downshelf by coastal currents. Presence of ambient tidal forcing was known to enhance the net transport. However, a mechanistic understanding of the transport variability is not well established. Chen (2014) showed that the partition of freshwater into downshelf coastal currents and upshelf return flow is dynamically analogous to a baroclinic jet split by a wall (see the jet bifurcation movie below) . When outflow is strong, the plume is displaced offshore, and the jet contacts the coast at a small angle (nearly wall-normal). Hence, less momentum and volume fluxes are needed in coastal currents to satisfy the overall momentum conservation. A baroclinic jet theory was shown to provide good estimates for the costal current freshwater fluxes.

Reference: Chen, S. N., 2014: Enhancement of along-shore freshwater transport in surface-advected river plumes by tides, Journal of Physical Oceanography, 44, 2951-2971.