This research studies the complex dynamics of surf zone wave-induced currents and the multi-scale dynamics of the hydro-morphodynamic system that will eventually lead to better predictions in the nearshore environment. Surf zone currents, driven by breaking waves, are the primary agents to transport, mix and disperse water, sediments and pollutants in the near shore. These strongly influence coastal erosion, hence coastal overtopping and flooding, and water quality. Better understanding of the dynamics of these currents is important to the development and protection of coastal environment, economy and ecosystem. Rip currents are widely known as dangerous beach hazards and account for 80% of surf zone rescues in the USA. Theoretical understanding of rip generation mechanisms has not been satisfactory, in particular on beaches lacking alongshore variability. Recent studies have mostly focused on morphodynamic instabilities (feedback between fluid and erodible seabed), not carefully considering the fully dynamical interaction between waves and currents. This effectively models only the slow time scale controlled by the morphology evolution, suppressing the faster time scale of the hydrodynamic processes. To address the significance of the various time scales, the PI plans to thoroughly investigate the multi-scale interactions among waves, currents and morphology, by coupling the hydrodynamic instability due to wave-current interaction (Yu, 2006) and the morphodynamics. The research program will include extended linear analysis of the hydrodynamics instability leading to rip currents, numerical study of the nonlinear developed rip currents, and the coupling with slow-scale morphodynamics. The modeling will be validated through direct and indirect comparisons with available observations. Improvements are needed for development of reliable predictive tools essential to science-based planning, decision-making and mitigation strategies. Coastal evolution has become even more of a concern within the climate change scenarios, as the rise of global sea levels increases the likelihood of storm surges as do the risks of overtopping and flooding. The planned research supports the development of a graduate program. In addition to training two graduate students, research and education will also be fostered through the PI's efforts to develop a graduate curriculum in Coastal Engineering and Environmental Fluid Mechanics. A broader educational impact is also expected through the outreach programs of the PI's collaborators, including the National Weather Service Wilmington, NC Sea Grant and University of North Carolina, Coastal Studies Institute.
