Abstract

River discharges that are large enough to be impacted by Coriolis when they reach the coastal ocean create a buoyancy-driven coastal current in the direction of Kelvin wave propagation. This geostrophically adjusted current is a major circulation feature, controlling the transport of riverine waters and associated materials, such as sediments, nutrients and pollutants. Coastal models in areas of large rivers need to accurately represent this coastal current and its variability under the influence of other factors impacting coastal circulation. Coastal altimetry data are an important source of suitable observations to guide modeling and applications. Use of such data around the Mississippi River Delta will be shown, in tandem with in situ data and a high resolution hydrodynamic model that has been optimized for river plume dynamics. During the 2010 Deepwater Horizon incident, this methodology evaluated a period of strong coastal current, which was found relevant to the transport of hydrocarbons from the historically unprecedented Gulf of Mexico oil spill. During the 2015 Mississippi flood episode, the coastal altimetry data confirmed the weak coastal current due to the offshore removal of riverine waters under the influence of oceanic circulation, namely the Loop Current and associated eddies. This variability was captured by both coastal altimetry data and the model, leading to good agreement with in situ data further offshore, along the branches that carried Mississippi waters toward South Florida.