Wave Breaking Across the Inner Shelf and Nearshore Regions

University Of Delaware, Newark DE

Investigators

Abstract

The inner shelf region, in which the wind and wave-driven upper ocean comes in contact with, and is modified by, the bottom, represents a still poorly understood region of the ocean. The region is important as a pathway for the transport of materials between the surf zone and shelf, and represents the area where surface waves begin to play a role in the mobilization and distribution of sediments. Wave breaking in this region plays an important role in momentum transfer from atmosphere to water column and likely provides a strong control on the form and strength of mean currents which would shift as the nature of breaking events changes with depth. The project will develop a variety of modeling approaches to study wave breaking in the range of depths from deep to shallow water, building on this team's recent experience in high resolution Large Eddy Simulation of breaking events in laboratory settings, and on ongoing work in developing wave resolving and wave-averaged models for dispersive wave processes. The project will also contribute to the training of a Ph.D. student and K-12 outreach activities through laboratory visits and informational scientific talks to the public, web broadcasting of public lectures, and special events at open houses at the University of Delaware. The study will focus on a transition from the topology of deep water breaking, where a vortex ring spanning the underside of the breaking event is generated, and shallow water breaking, where the breaking event is laterally bounded by regions in which vertical vortex cores ending at the surface and bottom are generated. The transition between these two topologies will be denoted as a principal demarcation between intermediate depth and shallow water behavior. In particular, the transition region represents a shift from deeper water, with breaking making a significant contribution to horizontal vorticity generation, to shallow water, where breaking primarily contributes to predominantly vertical vorticity at length scales corresponding to breaking wave crest geometries. This effort will be organized in three main topics: (1) detailed examination of breaking of finite crest lengths in a range of relative water depths spanning from deep to shallow water, using high resolution calculations based on a combined Large Eddy Simulation and Volume of Fluid model previously verified for intermediate depth breaking in wave flume experiments, (2) development of extensions to an existing non hydrostatic, wave-resolving, shock-capturing solver for surface wave breaking to improve the representation of intermediate and deep water wave breaking, for application to larger spatial scales, and (3) development of an impulsive force model for individual breaking waves, together with a stochastic formulation for the distribution of breaking events in space and time, which spans the depth range from deep to shallow water. This last model will be implemented in a non hydrostatic, wave-averaged model for use in describing wave-driven processes in the full range of water depths from shoreline to inner shelf.