Cohesive Sediment Erosion in a Shallow, Wave- and Current-driven Flow
Galen Egan1, Marianne Cowherd2, Frank Spada3, Kara Scheu4, Andrew James Manning5, Craig Alexander Jones3, Grace Chang3, Oliver B Fringer6 and Stephen G Monismith7, (1)Sofar Ocean, San Francisco, United States, (2)Stanford University, Stanford, United States, (3)Integral Consulting Inc., Santa Cruz, CA, United States, (4)Integral Consulting Inc, Marine Science and Engineering, Portland, OR, United States, (5)University of Hull, Energy & Environment Institute, Hull, United Kingdom, (6)Stanford University, Stanford, CA, United States, (7)Stanford University, Stanford, California, United States
Abstract:
Cohesive sediment erosion is affected by numerous physical factors, including bed properties, interactions between waves and currents in the bottom boundary layer, and sediment-induced stratification. The predictive capabilities of sediment transport models rely heavily on accurate parameterizations of these features. Historically, it has been difficult to measure these processes in the field due to the millimeter scales over which they act, leading to parameterizations that may not represent
in situ physical conditions.
We present results from field measurements based on three deployments in South San Francisco Bay. Sediment profile imaging transects provided detailed characterizations of bed properties, while a high-resolution profiling acoustic Doppler velocimeter measured wave- and current-induced shear stresses within the boundary layer and the associated cohesive sediment erosion. Our analysis shows that waves, rather than tidal currents, are the dominant driver of erosion on the shallow shoals, though this dependence varies with relative depth and roughness. We also show that the turbulent sediment flux can be limited by near-bed sediment-induced stratification. These results can be applied towards improving the accuracy of erosion parameterizations in sediment transport models.
