Internal wave Observations and Modeling: Inner-shelf Experiment 2017
Abstract
Previous laboratory and field experiments (e.g., Carr at al., 2017, Zulberti et al., 2020) suggest that internal waves evolution on the continental shelf can cause measurable sediment transport (e.g., Boegman and Stastna, 2018), and consequently play a role in the formation of shelf bedforms, and the redistribution of pollutants and biological material. Quantifying sediment transport by internal waves requires field monitoring of flow, density stratification, and sediment transport, covering the entire water column, with high-vertical resolution near the bed, and also covering temporal and spatial scales characteristic for internal wave (days and tens of km). Although technology is continuously improving, such experiments remain prohibitively expensive. However, stratification information is comparatively easily monitored, e.g., by R/V sounder scans. This raises the question whether, and under what conditions, it might be possible to characterize sediment transport under internal waves from stratification data.
The opportunity for this study is provided by the observations collected by NRL during the ONR Inner Shelf Dynamics Experiment 2017 (https://innershelf.sioword.ucsd.edu/), a multi-institution collaboration that deployed a variety of instrumentation monitoring the vertical temperature, flow velocity, and surface waves on the shelf off point Sal, CA, in August-September 2017. Here, we use two-dimensional, analytical, linear flow models of internal waves to investigate the relationship between the stratification profile and flow near the bed, and use standard sediment transport models to estimate bed shear stresses and incipient sediment transport. Analytical results are compared with field measurements of near-bed flow and suspended sediment concentration near the 35-m isobath. The comparison shows that simple potential flow models using point measurements of stratification capture with reasonable accuracy the observed flow associated with internal waves of approx 15 min periods, and may be used to infer sediment transport characteristics. However, the approach fails for larger scale oscillations (e.g., semi- and quarter-diurnal bores, whose dynamics seem to deviate significantly from the potential flow description. Further research is needed to understand the applicability and limitations of the method at different internal oscillation scales.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2022
- Bibcode:
- 2022AGUFMOS53B..06Q