Salt wedge dynamics lead to enhanced sediment trapping within side embayments in high‐energy estuaries

• Published in: Journal of geophysical research. Oceans Vol. 122; no. 3; pp. 2226 - 2242
• Main Authors: Yellen, Brian, Woodruff, Jonathan D., Ralston, David K., MacDonald, D. G., Jones, D. S.
• Format: Journal Article
• Language: English
• Published: Washington Blackwell Publishing Ltd 01-03-2017
• Subjects: Accommodation; Accumulation; Bays; Brackish; Brackishwater environment; Channels; Circulation; Computer simulation; Discharge; Dynamics; Ebb currents; Energy; Energy storage; Entrances; Estuaries; Estuarine circulation; Estuarine dynamics; estuarine turbidity maximum; estuary; Fluvial sediments; Freshwater; Geochemistry; Geophysics; Inland water environment; Intrusion; Marine; Numerical simulations; Oceanography; River sediments; Rivers; Salinity; Salinity effects; Salt wedges; Sea level; Sea level rise; Sediment; Sediment concentration; sediment storage; Sediments; Tidal energy; Tidal power; Tides; Trapping; Turbidity; USA, Connecticut R; ANE, Germany, Hamburg
• ISSN: 2169-9275; 2169-9291
• DOI: 10.1002/2016JC012595

Off‐river coves and embayments provide accommodation space for sediment accumulation, particularly for sandy estuaries where high energy in the main channel prevents significant long‐term storage of fine‐grained material. Seasonal sediment inputs to Hamburg Cove in the Connecticut River estuary (USA) were monitored to understand the timing and mechanisms for sediment storage there. Unlike in freshwater tidal coves, sediment was primarily trapped here during periods of low discharge, when the salinity intrusion extended upriver to the cove entrance. During periods of low discharge and high sediment accumulation, deposited sediment displayed geochemical signatures consistent with a marine source. Numerical simulations reveal that low discharge conditions provide several important characteristics that maximize sediment trapping. First, these conditions allow the estuarine turbidity maximum (ETM) to be located in the vicinity of the cove entrance, which increases sediment concentrations during flood tide. Second, the saltier water in the main channel can enter the cove as a density current, enhancing near‐bed velocities and resuspending sediment, providing an efficient delivery mechanism. Finally, higher salinity water accumulates in the deep basin of the cove, creating a stratified region that becomes decoupled from ebb currents, promoting retention of sediment in the cove. This process of estuarine‐enhanced sediment accumulation in off‐river coves will likely extend upriver during future sea level rise.
Key Points:
Side embayments are a primary location of long‐term sediment trapping in high‐energy estuaries
Sediment trapping is amplified 2–3 times during low discharge when ETM penetrates far enough upstream to encounter embayments with available accommodation space
SSC introduced by flood‐dominated, estuarine‐induced circulation is a primary mechanism for off‐river sediment trapping