Sediment Dynamics in Wind Wave‐Dominated Shallow‐Water Environments
Abstract
Sediment dynamics driven by waves and currents in shallow‐water estuarine environments impacts many physical and biological processes and is important to the estuary‐wide sediment budget. Observational restrictions have limited our ability to understand the physics governing sediment entrainment and mixing in these environments. To this end, we use direct numerical simulation to simulate sediment transport processes in shallow, combined wave‐ and current‐driven flows. Simulations are run with depth‐averaged currents ranging from 0 to 9 cm/s, while wave conditions are held constant with a bottom orbital velocity and period of 10 cm/s and 3 s, respectively. Our results indicated that for wave‐dominated conditions, waves reduce vertical momentum fluxes and the associated bottom drag, thereby accelerating mean currents. Conversely, currents do not significantly affect the wave velocity field. However, they increase the bed shear stress and change the timing and duration of sediment entrainment throughout the wave cycle. Counterintuitively, these effects lead to lower suspended sediment concentrations near the bed for a portion of the wave cycle. By analyzing sediment fluxes, waves are shown to drive near‐bed sediment dynamics while currents control vertical mixing above the buffer layer, where downward settling is predominantly balanced by the current‐generated vertical turbulent sediment flux. In the absence of currents, sediment concentrations are negligible above the wave boundary layer because mixing is weak. We show that the time‐ and phase‐averaged sediment concentration profiles for wave and current conditions resemble the theoretical Rouse profile derived for equilibrium conditions in statistically steady, unidirectional turbulent channel flow.
Document Details
- Document Type
- Pub Defense Publication
- Publication Date
- Oct 01, 2018
- Source ID
- 10.1029/2018jc013894
Entities
People
- Kurt Nelson
- Oliver B. Fringer
Organizations
- Office of Naval Research
- Stanford University