Environmental Science and Engineering Seminar

Breaking waves in shallow water generate low-frequency eddies within the surf zone. These rotational flows alter the transport and mixing of contaminants, bacteria, larvae, and other materials in coastal environments. Surf-zone eddies are driven by several mechanisms, including instabilities in mean flows and spatial gradients in wave forcing. This talk describes experimental and numerical investigations into surf-zone eddy generation mechanisms and their dependence on wave forcing. We first characterize vorticity injected by individual breaking waves through wave-basin experiments and depth-averaged wave-resolving model simulations. We then quantify the relative roles of surf-zone eddy-generation mechanisms in tracer dispersion with three-dimensional wave-resolving model simulations, highlighting the role of a recently identified mechanism: instabilities in vertically sheared undertow. A quantitative understanding of these processes is critical to predict material exchange between our shoreline and deeper waters.