The physical process of nearshore sediment transport causes coastlines to change whenever there is a change in wave climate — whether during storms, over seasons, or longer-term. Our current research funded by NSF and the US Army Corps of Engineers is applying novel instrumentation combined with numerical models to better understand the physics of sediment transport on beaches. This basic research is necessary since numerical models used by engineers to predict coastal change suffer from a high degree of uncertainty in the wave-driven sediment transport process.
Our goal in these projects is to apply novel observational methods to the time-dependent process of sediment transport under waves. Many previous studies have validated sediment transport theories based on predicted changes in bathymetry over many days, such as sand bar migration — however, models with completely different physical assumptions can often be “tuned” to reproduce such observations. Our goal is to obtain direct validation data that can test the physical assumptions made by the models.
Blasstex (Boundary Layer Acoustic Sediment Transport Experiment): In February and October 2022, we conducted experiments at the US Army Corps of Engineers Field Research Facility (FRF) in Duck NC. There we deployed a number of instruments from the FRF Coastal Amphibious Research Buggy (CRAB), to test the ability to resolve sediment transport processes near the seabed under various wave conditions. The main technique we are studying is multi-frequency acoustic sonar, which can measure vertical profiles of sand concentration and velocity very near the bed, remotely without disturbing the wave boundary layer itself. An important challenge for interpreting the data is developing models for acoustic backscatter that take into account the unique environment of the nearshore zone, including the presence of bubbles and other non-sediment acoustic scatterers.
DragonX (Acoustic Doppler sediment flux measurement): The MFDop, developed by Alex Hay (Dalhousie University) and Len Zedel (Memorial University), is a multi-frequency pulse-coherent Doppler profiler designed to measure the wave boundary layer. It is capable of collecting vertical profiles of 3d turbulent velocity and sediment concentration, at mm-scale vertical resolution and at up to 50Hz. The instrument is ruggedized for use in the nearshore zone. Our current projects are centered around field deployments of MFDop in the surfzone of sandy beaches.
In Aug-Sep 2022, we conducted a field study at Arch Cape, OR, where MFDop was deployed in the intertidal zone (up to 2 m water depth). This was the first-ever deployment of the instrument on a sandy beach, and yielded remarkable data on wave-by-wave sediment flux in the wave bottom boundary layer.
