Sediment Transport at Density Fronts in Shallow Water

The long-term goal of this research is to quantify through observations and modeling how density fronts in shallow estuarine flows impact the mobilization, redistribution, trapping, and deposition of suspended sediments. The specific objectives of this project are as follows: (1) implement a high-resolution, 3-dimensional, finite-volume hydrodynamic model of the tidal flats field site, including advanced sediment transport algorithms; (2) integrate and test a set of field instruments to measure density, velocity, and suspended sediment concentration at density fronts in shallow water (< 1 m); (3) characterize flow and suspended sediment at a density front through the tidal inundation cycle as it travels across the intertidal zone; and (4) combine the observations and model results to quantify sediment suspension, trapping, and lateral circulation at the front, and evaluate and improve the sediment transport model. This research approach combines advanced observational and modeling techniques. In the field, the authors will measure velocity and suspended sediment at high resolution in shallow flows, tracking the evolution of the salinity front through the tidal cycle. The instrumentation will incorporate an acoustic Doppler current profiler (ADCP) to measure currents, and a profiling conductivity-temperature-depth sensor (CTD) to measure water column salinity and density. Suspended sediment concentrations will be determined through a combination of acoustic and optical sensors. An acoustic backscatter sensor (ABS) will measure echo amplitude at three acoustic frequencies, and comparisons between the frequencies will provide information on the suspended particle size distributions. An optical backscatter sensor (OBS) associated with the CTD will provide additional data on the suspended sediment profile.