Collaborative Research: Swash zone dynamics driven by obliquely incident waves

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Beaches are coastline features that offer economic benefits, ecosystems services, and a natural barrier against flooding. Thus, sustainable management of beaches requires a firm understanding of coastal processes and beach sediment budgets. Such knowledge is particularly underdeveloped in the swash zone, where waves wet and dry the sand with each wave and shift enormous amounts of sediment. This project will investigate these processes as they occur by waves that arrive at an angle, a common scenario on beach beaches. Previous research efforts that have developed new tools, measurement techniques, and knowledge to understand swash zone processes have focused solely on cross-shore dynamics since these studies are easier to perform in small-scale wave flumes and two-dimensional simulations. In this project, an intensive campaign of laboratory experiments, theoretical analysis, and numerical simulations will be used to expand swash zone knowledge to all three spatial dimensions and time. The alongshore dynamics and sediment transport are particularly important in the field where waves approach at an angle, but they are also the least understood. The laboratory experiments will include a range of wave forcing conditions and wave incidence angles and be complemented by numerical modeling using open-source models as well as development of new predictive formulations based on theoretical considerations. The project will aim to develop a new knowledge framework based on studying fundamental aspects of swash dynamics to transform our understanding of the flow and sediment transport patterns on beaches. These will have far reaching implications for researchers and stakeholders since almost half of all beaches in the US (and globally) face management challenges related to sediment transport trends that change unpredictably due to wave action. The project will train two PhD students at UW-Madison and U Delaware, respectively, and numerous undergraduate students across four institutions. The project will also provide partial support to a postdoctoral researcher, who will gain valuable experience and mentoring for a future career as a professor. Additionally, four high-school teachers from different regions will receive a meaningful research laboratory experience and help in developing a new learning module for their classrooms. The project will also start a new collaboration between University of Wisconsin-Madison, the Caribbean Coastal Ocean Observing System, the Center for Applied Coastal Research at University of Delaware, and the Coastal Engineering Laboratory at Queen’s University. Finally, project results will be widely disseminated via journal publications and conferences, including the Young Coastal Scientists and Engineers Conference - Americas, which will be held in the Midwest (Madison, WI) for the first time during the project. All experimental data will be hosted on NSF-funded data repositories and open-source numerical models will be used to promote further development. Using state-of-the-art experimental measurement techniques and numerical modeling tools, the project will discover the physical basis for flow and sediment transport in the alongshore direction under forcing from incident-band waves. The alongshore flow and transport is poorly described in the swash zone, despite its importance in overall beach sediment budgets. Detailed measurements coupled with numerical modeling and theoretical analysis will reveal how bore collapse and flow turbulence drive alongshore currents under different wave conditions and across a range of wave incidence angles. Similarly, detailed sediment concentration profiles and fluxes will reveal fundamentally new insights into three-dimensional sediment transport patterns in the swash zone, including how sheet flow transport in the alongshore may enhance cross-shore erosion/accretion.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.