1. Sediment Dynamics in the Energetic Nearshore Zone: Acoustic Remote Sensing and Model Validation.
- Author
-
Wilson, G. W., Dickhudt, P., and Aldrich, J.
- Subjects
WATER waves ,VERTICAL mixing (Earth sciences) ,BEACH erosion ,SUSPENDED sediments ,COASTAL engineering - Abstract
Acoustic backscatter data were collected in the shallow nearshore environment under breaking and non‐breaking waves, using a multi‐frequency sonar at 0.5, 1.0, and 2.0 MHz. The data are used to develop and test an acoustic inverse model for measuring suspended sediment concentration (SSC) in the presence of bubbles generated by breaking waves. The model leverages the contrasting frequency dependence of acoustic scattering by bubbles and sand, to simultaneously estimate SSC and bubble void fraction. Validation against in situ sediment measurements shows the acoustic technique can recover sediment concentration with good accuracy in both breaking and non‐breaking waves, unlike existing algorithms which only perform well in non‐breaking waves. Finally, data from the experiment are used to validate existing theories for suspended sediment dynamics under breaking waves, for which few previous data sets exist. Plain Language Summary: The surfzone is the energetic region of the coast where waves break, causing strong currents, mixing, and sediment transport. An understanding of fundamental sediment transport processes in the surfzone is essential to coastal engineering applications, for example, mitigating coastal erosion and flooding. However, theories for nearshore sediment transport suffer from a lack of direct field validation, owing to inadequate measurement techniques. The measurement challenges are many, including the need to detect sediment concentrations within centimeters of a moving seabed. Here, we introduce and validate a multi‐frequency sonar technique capable of obtaining the necessary measurements, including in bubbly flow under breaking waves where field data are arguably most critical. The method is validated with field data collected at Duck, NC. Results from the experiment are used to test existing theories for the vertical distribution of suspended sediment. The data show wave breaking has a strong influence on sediment vertical mixing, with implications for sediment transport predictions. Key Points: Novel observations of mobile sediment in the energetic nearshore zoneNew acoustic remote sensing technique for detecting sediments under breaking wavesField validation of models for near‐bed sediment concentration and vertical mixing, in breaking and non‐breaking waves [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF