Estuaries are a critical interface between land and coastal ocean across which freshwater and suspended particulate matter (SPM), and consequently terrestrial carbon, nutrients and anthropogenic contaminants are exchanged. Estuarine water quality is in part mediated by its suspended particulate load; and sediments continually interact with biogeochemical processes, thus influencing estuarine ecosystem functioning. A range of physical processes in estuaries typically result in trapping of SPM that form Estuarine Turbidity Maximum (ETM) zones, and in estuaries acting as sediment sinks. In spite of this conceptual understanding of estuarine sediment transport, predictions of SPM concentrations and distributions still remain elusive (e.g., Fitzsimmons et al., 2011), in particular at time scales of seasons and longer, and there is a pressing need for improved predictions of estuarine SPM and its transport.
Estuarine sediments typically include significant fractions of cohesive material, such as mud, whose transport is subject to a range of complex processes, including flocculation, hindered settling, consolidation, liquefaction, turbulence damping, and bioarmouring (Winterwerp and van Kesteren, 2004). There is, however, a lack of simple and computationally efficient formulations unified across varying hydrodynamic regimes and seasons to describe cohesive behaviour in estuarine numerical models (e.g. Amoudry and Souza, 2011a). This project will address this critical gap and generate new improved process-based modelling approaches for simulations of estuarine cohesive sediment transport over time scales ranging from seasons to decades.
In spite of significant efforts towards three-dimensional modelling of estuarine cohesive sediment transport in the past decade (e.g. Baugh and Manning, 2007; Kombiadou and Krestinitis, 2012; Ramirez-Mendoza et al., 2014), studies investigating both the estuarine spatial scale and timescales of seasons and over remain very scarce. In such three-dimensional process-based models, cohesive behaviour impacts two critical model components: particle settling rate (due to flocculation and hindered settling for example), and bed sediment resuspension and deposition (Amoudry and Souza, 2011a).
The studentship aims to increase the predictive ability of estuarine SPM at seasonal to decadal timescales and will focus on the following objectives:
derive novel formulation(s) for settling rate applicable across seasons,
implement formulations for bed resuspension and deposition that include bioturbation, consolidation and armouring,
test, calibrate, and validate model against in situ estuarine observations,
determine mechanisms controlling transport of estuarine cohesive sediments over seasons to decades.