Abstract
Results from measurements are presented that were collected during a full tidal cycle in the Ems estuary, involving two landers and an anchored research vessel. The conditions were characterized by very weak winds, no wave effects, and low river run-off, so that the state was close to tide-only. We find that the lateral (i.e., cross-slope) transport of water and suspended particulate matter (SPM) much of the time shows a vertically layered structure, which is however subject to sudden transitions. Moreover, even on the small spatial scale of these measurements (i.e., within a distance of 200 m), a strong lateral variability is observed in the circulation patterns. We analyze its dynamics by means of dimensionless parameters. In addition, near-bottom peaks in SPM concentration are observed, notably during early flood. However, these episodic events have little effect on the overall transport of SPM, which involves the whole water column: the measurements show a high vertically integrated SPM signal during late ebb, resulting in an ebb-dominance in the transport at this position in the tidal channel.
Highlights
Estuaries, connecting the riverine and marine environment, can be efficient traps for marine and fluvial sediments, resulting in localized regions of high suspended sediment concentrations, a so-called estuarine turbidity maximum (ETM) (Burchard et al, 2018)
We find that the lateral transport of water and suspended particulate matter (SPM) much of the time shows a vertically layered structure, which is subject to sudden transitions
The observed con centrations and specific trapping locations can be strongly influenced by human interventions, such as land reclamation (Van Maren et al, 2016), construction of weirs (Schuttelaars et al, 2013), dredging activities and channel deepening (Chernetsky et al, 2010; De Jonge et al, 2014; Dijkstra et al, 2019a), and water quality improvements (Cox et al, 2019)
Summary
Estuaries, connecting the riverine and marine environment, can be efficient traps for marine and fluvial sediments, resulting in localized regions of high suspended sediment concentrations, a so-called estuarine turbidity maximum (ETM) (Burchard et al, 2018). The observed con centrations and specific trapping locations can be strongly influenced by human interventions, such as land reclamation (Van Maren et al, 2016), construction of weirs (Schuttelaars et al, 2013), dredging activities and channel deepening (Chernetsky et al, 2010; De Jonge et al, 2014; Dijkstra et al, 2019a), and water quality improvements (Cox et al, 2019) These changes, especially when the observed concentrations strongly increase, can adversely affect both the economic and ecological value of estuaries: shipping channels have to be dredged to allow (ever larger) vessels to reach ports, and light penetration and availability of oxygen in the water are reduced, negatively impacting the ecology (De Jonge and Schückel, 2019). On August 28, 2018, the joint German-Dutch campaign EDoM018 took place involving eight research vessels at different locations, be tween Eemshaven and Papenburg (not shown) As part of this effort, the NIOZ research vessel Navicula was anchored at the position indicated in Fig. 1 (red dot) to carry out 13-h measurements, involving two bottom landers at both sides of the ship over the southwestern slope.
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