Wave Transformation and Breaking on a Sheared Current

Abstract:

Waves shoaling against tidal currents at river inlets have long been a hazard to navigation. We present measurements of waves, currents, and turbulence from SWIFT drifters at the Columbia River Mouth to diagnose wave transformation, breaking, and the resulting turbulence. In particular, down-looking velocity profiles, measured onboard the drifters, allow for evaluation of wave transformation on a vertically sheared current, for which theory exists but few in situ measurements are available. One consequence of wave transformation is steepening and breaking, which is identified using visual images, increased near surface turbulence, and gradients in wave energy flux. Vertical turbulent dissipation profiles measured during breaking are compared to existing scalings developed for deep and shallow water and expanded to the intermediate depth conditions common at the Columbia River Mouth. The analysis is intended to improve hydrodynamic models, especially two-way coupled wave-current models, and to aid navigation by better predicting dangerous wave conditions.