Lateral variability of sediment transport in the Delaware Estuary

Abstract

Lateral processes contribute significantly to circulation and material transport in estuaries. The mechanisms controlling transport may vary spatially such that shallow and deep regions of an estuary contribute differently to the total transport. An observational study was conducted to explore the importance of lateral variability in sediment transport mechanisms in the Delaware Estuary. Seven moorings were deployed across the channel in the region of the estuarine turbidity maximum (ETM) zone from April to August 2011. Time series 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. There is a persistent divergence of across‐channel sediment fluxes on the Delaware side, where sediment from the flank is transported toward both the channel and wetland coast. Decomposition of the fluxes highlight that across‐channel sediment transport is driven by mean lateral circulation, whereas along‐channel transport is driven primarily by mean advection, with tidal pumping contributing to about 30% of total transport. The spatial and temporal variability of mean advection and tidal pumping were generally complementary, with both contributing to the observed sediment transport pathways. 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. The spatiotemporal patterns of sediment transport highlight the three‐dimensional structure of the ETM and shed light on the variability of sediment transport mechanisms.

Three‐Dimensional Sediment Dynamics in Well‐Mixed Estuaries: Importance of the Internally Generated Overtide, Spatial Settling Lag, and Gravitational Circulation

“…The suspended sediment concentration at the seaward boundary of the physical domain ( C m ) is prescribed to be a constant. The value of C m is determined by prescribing the averaged sediment availability in the physical domain to be constant, such that a maximum residual SSC of ∼200 mg L −1 representative for the observed ETM in the Delaware estuary under a relatively small river discharge (∼288 m s −1 ; see McSweeney et al, ) is obtained.…”

“…Nevertheless, since the SSC and a are strongly related (following equations and ), the reliability of a can be assessed by comparing the simulated SSC's to observations. It is found that the main features of the ETM in the Delaware estuary observed by McSweeney et al () are qualitatively reproduced. First of all, the ETM is centered around 100 km for the river discharge used here (288 m s −1 ), with the region of elevated SSC distributed between approximately 80 km and 120 km from the mouth.…”

“…Therefore, it is reasonable to believe the simulated a for the sediments considered in this experiment is realistic. Moreover, the spatial sediment transport patterns observed by McSweeney et al () are qualitatively reproduced, with sediments transported into the estuary from the left side of the deep channel, and transported down‐estuary on the right flanks. The model also confirms that the lateral depth‐integrated residual sediment transport is mainly due to the advection of the residual SSC by the residual currents, while sediment transport contributions due to both tidal pumping and residual advection of residual concentration contribute significantly to the longitudinal residual sediment transport.…”

Three-Dimensional Salt Dynamics in Well-Mixed Estuaries: Influence of Estuarine Convergence, Coriolis, and Bathymetry

“…It is found that the stratification in the central region of salt intrusion increases with increasing river discharge, consistent with model studies (Ralston et al 2008;Lerczak et al 2009) andobservations (McSweeney et al 2016). The top-to-bottom salinity differences (less than 1.5 psu), however, are much smaller than the observed values during large river discharges (McSweeney et al 2016). This implies that the relatively strong stratification in case of large river discharges is not resolved in this model, which is probably the reason for the overestimated impact of river discharge on salt intrusion.…”

Influence des conditions hydrométéorologiques sur les flux et bilans sédimentaires en estuaire de Seine

“…YU et al, 2014 ;MCSWEENEY et al, 2016 ;JALON-ROJAS et al, 2016 ;TOUBLANC et al, 2016). De plus, la remise en suspension des sédiments sur les bancs à l'embouchure et les opérations de dragage le long des chenaux de navigation jouent un rôle très important (AVOINE et al, 1981 ;LE HIR et al, 2001 ;MARMIN et al, 2014).…”