The orientation, shape, and stability of the Golden Gate sand waves

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Marine sand waves are like underwater sand dunes. They are found worldwide in shallow marine environments such as tidal inlets and tidal banks. They are also found in some estuaries, submarine canyons, and deep shelf environments. They can be important to navigation and the design and placement of submarine cables, pipelines, and wind power generation facilities. For instance, the unintended exposure of a buried pipeline or cable due to the growth or migration of sand waves can cause catastrophic failure resulting in high costs and destructive ecological impacts. The dynamic migration of sand wave crests into shipping channels can render navigational charts inaccurate and be hazardous to shipping and small boats. This project will use models to study sediment transport in the Golden Gate sand waves, one of the earth’s most striking field of sand waves. The project Broader Impacts include an improved understanding of sand wave dynamics that will help inform sediment management in the region. The project would also support a graduate student.The shape and dynamics of sand waves will be investigated through the integration of multiple existing high resolution field surveys of the Golden Gate sand waves and a calibrated numerical model that incorporates physical processes such as fluid dynamics and sediment transport in coastal regions. The hydrodynamic forcing in the region is due mainly to tides and exhibits a powerful tidal jet due to the flow in and out of San Francisco Bay. In combination with ocean waves this results in a complex and energetic sediment transport patterns and bedform morphodynamics. The goals of this project are to evaluate hypotheses to explain several perplexing observations found in various fields of sand waves worldwide, such as: the asymmetric shapes of individual sand waves and their relation to sand wave migration; the dynamics linking the tidal forcing and the orientation of individual sand wave crests; and the occasional appearance and disappearance of a new sand wave crest within a field of sand waves.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.