Impact of breaker type on wave dissipation on a natural beach

University Of Washington, Seattle WA

Investigators

Abstract

Wave forcing is the largest energy flux into the surf zone, the shallow nearshore region where surface gravity waves are influenced by the presence of the seafloor, become unstable, and break. The dissipation of wave energy here results in important nearshore processes, including circulation, mixing, sediment transport, and storm surge. An important goal of the nearshore science community is to understand and predict the time and space variability of wave breaking in the surf zone with the aim of deriving and modeling wave forcing over broad areas and with adequate resolution to represent the time and space scales that occur. However, wave breaking is a nonlinear, episodic event that is difficult to capture in a bulk model. The action and forces resulting from wave breaking cause and influence a broad range of processes at the ocean margin including erosion at the shoreline, strong and often dangerous currents, storm surge and coastal flooding, damage to coastal structures, and maritime navigation. Details of wave breaking are still poorly understood although they are parameterized broadly in modeling. Thus, this work will advance understanding of the details of breaking, and results and data from this effort will be used for direct model improvement and testing. This project will fund a graduate student whose dissertation will be focused on analysis and publication of the wave breaking data and it will develop presentations and activities showcasing wave research to the public during the annual outreach activities organized by the University of Washington and the Pacific Science Center. The project will analyze existing remote sensing data collected in the surf zone at the U.S. Army Corps of Engineers (USACE) Field Research Facility (FRF) at Duck, NC. Observations included thermal (infrared, IR), visual, and lidar remote sensing of the ocean waves propagating toward the shore. These data captured information covering a wide range of wave conditions. The aim of the data analysis is to analyze infrared imagery and lidar profiles of the waves to characterize their motion, the way waves break, and parameterize wave energy loss during the breaking process (wave dissipation). The identified need for improving nearshore models is to account for dissipation due to variable wave breaking type in the surf zone (i.e. spilling versus plunging breakers), how wave geometry and parameterizations of the wave physics compare with observations, and how those differences affect our ability to use remote sensing to estimate wave forcing remotely. Existing wave roller and bore-type models commonly used to estimate wave breaking dissipation assume steady state conditions that are violated at the break point where breaking waves form and plunging waves can occur. The inability of these parameterizations to account for the extra dissipation by plunging waves will bias modeling and efforts to remotely measure wave dissipation and wave forcing. Here, a new infrared-based remote sensing technique will be utilized, that has shown skill to remotely characterize individual breaking waves within the surf zone, but has not been tested near the breakpoint. Extension and modification of the method to account for breaking wave type will provide definitive insight into wave breaking, and provide a transformative observational tool that could be used observe breaking waves remotely.