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

Abstract

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.

Estuarine Channel Evolution in Response to Closure of Secondary Basins: An Observational and Morphodynamic Modeling Study of the Western Scheldt Estuary

“…Many existing estuaries were formed during the rapid sea level rise in the early Holocene when existing paleo‐valleys flooded during the postglacial sea level rise (Dalrymple et al, ; Schubel & Pritchard, ). Side embayments appeared along the fringes of many estuaries, resulting from the drowning of (1) paleo‐valleys (Dabrio et al, ; Fletcher et al, ; Perillo, ; Woodruff et al, ; Yellen et al, ) or (2) coastal plains that experienced major human‐induced subsidence due to intensified agriculture use of peat areas (Pierik et al, ; Syvitski et al, ; Törnqvist et al, ). After the formation of these estuarine systems, the interplay between sea level rise, sediment availability, and sediment distribution by waves, tides, and rivers determined their subsequent morphological development (Pierik et al, ; Pye & Blott, ; Rossi et al, ).…”

“…The side embayments are typically hundreds to thousands of meters wide and hundreds of meters to tens of kilometers long. Note that, in the literature, side embayments are also referred to as bays (Sherwood et al, ), tributary valleys (Dalrymple et al, ), off‐river coves (Woodruff et al, ; Yellen et al, ), branching or secondary channels (Alebregtse & de Swart, ), etc. In this study, following Roos and Schuttelaars (), these side embayments are referred to as secondary basins.…”

“…Secondary basins are usually low energy environments compared with the high energetic main estuary, and therefore, they provide the vertical accommodation space necessary to trap sediment and reduce the net sediment delivery to the ocean (Van Maren et al, ; Woodruff et al, ; Yellen et al, ). A reduction in secondary basin area due to human interventions will likely influence the entire estuarine sand budget and morphodynamics.…”

High‐turbidity events in Western Lake Erie during ice‐free cycles: Contributions of river‐loaded vs. resuspended sediments

“…Given that suspended sediments from river loading and resuspension have distinct ecological functions and driving mechanisms, it is critical to understand their relative contributions to HTEs by tracking their origins explicitly. At present, however, this understanding cannot be fulfilled through field or satellite observations (e.g., Saldías et al 2012;Mendes et al 2017;Valipour et al 2017), nor has it been sufficiently investigated thoroughly in the modeling studies that have been conducted to date (e.g., Lou et al 2000;Liu and Wang 2014;Morales-Marin et al 2017;Yellen et al 2017).…”

Seasonal, tidal, and geomorphic controls on sediment export to Amazon River tidal floodplains

“…Hydrodynamic and sedimentary studies of estuarine tidal channels often overlook temperature because salinity is far more important in determining dynamics; for example, the presence or absence of salt in tidal-river systems can enhance sediment trapping within the tidal floodplain (Yellen et al, 2017). In freshwater fluvial systems, the ecological importance of temperature heterogeneity is well established (e.g.…”