Exploration of Salt Wedge Dynamics in the Columbia River Estuary Using Optical Measurements of Internal Ship Wakes.

In May of 2013 and beyond, Argus optical measurements of the mouth of the Columbia River estuary and plume were collected as part of the RIVET II multi-investigator field experiment. One surprise was the strength of eddy and internal wave signatures observed in movies computed from one-minute averages of high-frequency snapshots (such that gravity waves were averaged out but slicks and variable surface roughness remained). In particular, passing ships left wakes that propagated away at speeds on the order of 0.5 m/s, much slower than gravity waves and presumably surface manifestations of internal waves associated with the time-varying salt-wedge. Thus, these internal ship wakes appear to act as probes of internal stratification dynamics. This paper will explore the time variations of these internal wakes and relate them to corresponding variations in the estuary salt wedge.