Connecting the Surfzone and the Inner-shelf
Abstract
Project Summary The exchange of material (contaminants, pathogens, sediment, optical clutter, or biota) across the surfzone and the inner-shelf, important to Navy operations, is poorly understood. Breakingwave driven surfzone processes are radically different from the wind, stratification, (non-breaking) wave, and rotation driven processes in the inner-shelf. The time-scales of the processes in the surfzone (mins) and inner-shelf (hours+) are quite different. In the surfzone, onshore wave-induced near-surface mass flux is balanced by return flow at depth (undertow), driving exchange. Rip currents (both transient and bathymetrically controlled) can exchange surfzone water with the innershelf. Yet, rip ejection events are not well characterized. In addition, over a few hours surfzone tracers and drifters are“retained” within a strip about two surfzones wide. On the inner-shelf in 10 m depth, onshore wave-induced Stokes drift balanced against Eulerian cross-shelf flow at depth (similar to undertow) has recently been shown to be important during weak stratification. Diurnal and semi-diurnal internal waves as well as higher frequency internal bores also can induce across inner-shelf exchange. However, the relative importance of these processes is not understood. The interaction of these processes governs exchange, and depends on the waves, wind, tide, and stratification. Lagrangian tracers and drifters are a natural method for studying cross-shore exchange scales and mechanisms. Natural tracers with known sources and sinks such as temperature and turbidity, combined with velocity observations, can reveal 3D aspects of exchange, whereas Lagrangian drifters focus on horizontal (2D) exchange. To study exchange across the surfzone and inner-shelf, we propose to: 1. Use surfzone/inner-shelf models to help develop an optimal array plan in conjunction with DRI participants. 2. For a 2-month base experiment, deploy an array of 10-m depth Wirewalker+ADCP moorings, 5-m depth tripods measuring currents, waves, temperature, and turbidity, and 25 near bottom temperature sensors to measure cross-shore internal bore propagation into the surfzone. 3. For a 14-20 day intensive experiment, perform Lagrangian drifter experiments, and measure inner-shelf temperature and currents synoptically using jetski and small-boat based platforms. 4. Perform quality control, analysis, and modeling Analysis of our Inner-shelf DRI field observations, coupled with our state-of-the-art numerical modeling capability, will be used to diagnose surfzone and inner-shelf cross-shore exchange timescales, length-scales, and the underlying mechanisms. This will lead to improved understanding of surfzone and inner-shelf cross-shore exchange processes.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Aug 12, 2016
- Source ID
- N000141512631
Entities
People
- Falk Feddersen
Organizations
- Office of Naval Research
- United States Navy
- University of California, San Diego