Understanding the Effects of Sediment Stratification In Shallow Wave and Current Driven Environments
Abstract
Sediment entrainment and mixing processes in shallow coastal waters and estuaries are complex because of nonlinear coupling of the wave and current boundary layer. The physics is further complicated by the tendency of sediment to self-stratify, and hence, modulate turbulence. In this work, resolved, large-eddy simulation (LES) is employed to simulate sediment dynamics using an Eulerian-Eulerian approach in combined wave and current driven flows. Simulations are forced with different combinations of a constant (100 < Reτ < 500 without waves) and time varying (50 < ReΔ < 1,000 without current) pressure gradient that resembles conditions common in coastal waters and estuaries. Assigned sediment properties are based on measured values collected in San Francisco Bay. We illustrate the primary effect of sediment stratification is to suppress vertical turbulent transport of mass and momentum. This suppression manifests as reductions in vertical Reynolds fluxes when compared to sediment-free simulations. When wave conditions are moderate yet currents are weak, we show sediment suspends into the water column but remains near the bed. As the magnitude of the current increases, current generated turbulence suspends additional sediment and increases vertical mixing. However, increases in shear can be accompanied by increases in sediment stratification, suggesting sediment concentrations can self-regulate.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2016
- Bibcode:
- 2016AGUFMEP53F1052N
- Keywords:
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- 1862 Sediment transport;
- HYDROLOGYDE: 1902 Community modeling frameworks;
- INFORMATICSDE: 3022 Marine sediments: processes and transport;
- MARINE GEOLOGY AND GEOPHYSICSDE: 4568 Turbulence;
- diffusion;
- and mixing processes;
- OCEANOGRAPHY: PHYSICAL