Lateral processes contribute significantly to circulation and material transport in estuaries. The mechanisms controlling sediment transport may vary spatially such that shallow and deep regions of an estuary contribute differently to the total transport. This project describes the spatial and temporal variability of sediment transport in the Delaware estuary, providing insight about the 3-dimensional structure of the estuarine turbidity maximum (ETM).

Figure adapted from McSweeney et al. (2016). Schematic of the three-dimensional ETM structure influenced by lateral variability of along-channel sediment transport  

Observations:  Seven moorings were deployed across the channel in the region of the ETM zone from April to August 2011. Timeseries of along-channel sediment transport reveal a consistent pattern of sediment export across the entire estuary during periods of high river discharge, followed by a transition to import within the channel and export on the flanks during low river flow. Along-channel transport is driven primarily by mean advection, with tidal pumping contributing to about 30% of total transport. Tidal pumping, linked to tidal asymmetries in stratification and sediment resuspension, was shown to drive both ebb-driven export and flood-driven import depending on the tidal variability of stratification.  Across-estuary sediment is driven by the mean circulation and can rework sediment from the flanks into the channel.

Modeling: A 3-dimensional Regional Ocean Modeling System (ROMS) coupled hydrodynamic and sediment model is used to look at the spatiotemporal variability of the ETM structure.  We model 3 noncohesive sediment types: silt, fine sand, and medium sand.  The model provides  insight about the spatial variablity of the mean cross-estuary circulation, which has important impacts on lateral sediment transport  and the trapping efficiency of the ETM.

McSweeney, J. M., R. J. Chant, and C. K. Sommerfield (2016), Lateral variability of sediment transport in the Delaware Estuary, J. Geophys. Res. Oceans, 120, doi:10.1002/2015JC010974.

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