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Samuel Kastner

Graduate Research Assistant




2000-present and while at APL-UW

A conceptual model of a river plume in the surf zone

Kastler, S.E., A.R. Horner-Devine, and J.M. Thomson, "A conceptual model of a river plume in the surf zone," J. Geophys. Res., 124, 8060-8078, doi:10.1029/2019JC015510, 2019.

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1 Nov 2019

We use observations from the Quinault River, a small river that flows into an energetic surf zone on the West Coast of Washington state, to investigate the interaction between river and wave forcing. By synthesizing data from moorings, drifters, and Unmanned Aerial System video, we develop a conceptual model of this interaction based on three length scales: the surf zone width, LSZ; the near‐field plume length, LNF; and the cross‐shore extent of the channel, LC. The relationships between these length scales show how tidal variability and bathymetric effects change the balance of wave and river momentum. The most frequently observed state is LSZ>LNF. Under these conditions the surf zone traps the outflowing river plume and the river water's initial propagation into the surf zone is set by LNF. When the river velocity is highest during low water, and when wave forcing is low, LNF>LSZ and river water escapes the surf zone. At high water during low wave forcing, LC>LSZ, such that minimal wave breaking occurs in the channel and river water escapes onto the shelf. Based on the discharge, wave, and tidal conditions, the conceptual model is used to predict the fate of river water from the Quinault over a year, showing that approximately 70% of the river discharge is trapped in the surf zone upon exiting the river mouth.

A new version of the SWIFT platform for waves, currents, and turbulence in the ocean surface layer

Thomson, J., M. Moulton, A. de Klerk, J. Talbert, M. Guerra, S. Kastner, M. Smith, M. Schwendeman, S. Zippel, and S. Nylund, "A new version of the SWIFT platform for waves, currents, and turbulence in the ocean surface layer," Proc., IEEE/OES 12th Currents, Waves, Turbulence Measurement and Applications Workshop, 10-13 March, San Diego, CA (IEEE, 2019).

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10 Mar 2019

The Surface Wave Instrument Float with Tracking (SWIFT) is a freely drifting platform for measurements of waves, currents, and turbulence in the ocean surface layer. This platform
has been used globally to study wave breaking, wave-current interactions, and waves in ice. A new version (v4) of the buoy has recently been developed and demonstrated in the Office of
Naval Research “Langmuir Circulations” field campaign along the California coast (2017). The new version is built around a 5-beam Acoustic Doppler Current Profiler (Nortek Signature 1000) with a multi-pulse coherent mode for high-resolution turbulence measurements. The new Doppler profiler enables estimates of the turbulent dissipation rate down to 3.5 m below waves, compared with 0.5 m in the previous version, and can measure a much larger range of turbulence levels than the previous version. The new version also uses a broadband Doppler mode to profile the mean currents down to 20 m. Mean Eulerian velocity profiles are estimated from the wave-averaged profiler velocities by applying a wave-following bias correction that scales with the Stokes drift and has twice the vertical decay scale. Finally, the new version supports real-time telemetry of raw sea surface elevations for reconstruction of individual waves by processing a coherent array of multiple SWIFTs, with applications for short-range wave-by-wave forecasting. These combined improvements to the platform are intended to advance understanding of wave processes and applications in the ocean surface layer.

The influence of wind and waves on spreading and mixing in the Fraser River plume

Kastner, S.E., A.R. Horner-Devine, and J. Thomson, "The influence of wind and waves on spreading and mixing in the Fraser River plume," J. Geophys. Res., 123, 6818-6840, doi:10.1029/2018JC013765, 2018.

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5 Sep 2018

This study uses drifter‐based observations to investigate the role of wind and waves on spreading and mixing in the Fraser River plume. Local winter wind patterns commonly result in two distinct forcing conditions, moderate winds from the southeast (SE) and strong winds from the northwest (NW). We examine how these patterns influence the spreading and mixing dynamics of the plume. Under SE winds, the plume thins, spreads, and turns to the right (north) upon exiting the river mouth. Mixing is initially intense in the region of maximum spreading, but it is short‐lived. Under NW winds, which oppose the rightward tendency of the plume, the plume remains thicker, narrower, and flows directly across the Strait with a lateral front on its northern side. Mixing is initially lower than under SE forcing but persists further across the Strait. A Lagrangian stream‐normal momentum balance shows that wind and interfacial stress under NW conditions compress the sea surface height anomaly formed by the river discharge and guide the flow across the Strait. This reconfiguration changes spreading and mixing dynamics of the plume; plume spreading, which drives intense mixing under SE winds, is shut down under NW winds, and mixing rates are consequently much lower. Despite the initially lower mixing rates, the region of active mixing extends further under NW winds, resulting in higher net mixing. These results highlight that the wind, which is often a primary cause of increased plume mixing, can also significantly influence mixing by changing the geometry of the plume.

Acoustics Air-Sea Interaction & Remote Sensing Center for Environmental & Information Systems Center for Industrial & Medical Ultrasound Electronic & Photonic Systems Ocean Engineering Ocean Physics Polar Science Center