Three-Dimensional Numerical Modeling of Deltas
Deltaic systems are controlled by a complex interaction of sediment supply, accommodation, and coastal energy, each varying in time and space, making three-dimensional study necessary. Numerical simulation models of such complex systems are thus also required to be 3D. This paper evaluates the state of 3D delta modeling and demonstrates that existing forward simulation models are still too limited to be applied to the full range of deltaic environments. Floodplain dynamics, as well as longshore transport, are generally lacking in present models. Many models lack the capacity to deal with multiple grain-size classes.
Two advanced 3D models, AquaTellUs and 3D-SedFlux, illustrate how quantitative theoretical experiments provide insight into the dominances of processes acting and the evolution of a fluviodeltaic system. Depositional architecture and coastal progradation patterns depend strongly on the frequency of channel switching. Results from the AquaTellUs model suggest that channel switching may be an even more important control then the rate of change of sea-level fall.
To further develop predictive 3D sedimentary models there is a need for field-test cases with quality input data, and with estimates of their associated uncertainties. Furthermore, process descriptions require efficient quantification and appropriate scaling. Only then will numerical models be able to address the responses of complex delta systems to specific forcing variables.
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Deltas are amongst the most environmentally and economically important coastal sedimentary environments. Studies of deltas lag behind research in both fluvial and deep-water depositional systems, as well as more geomorphologically oriented land studies. This knowledge lag reflects both a reorientation of the petroleum industry in the last two decades toward deep-water systems, as well as the difficulty of working across the shoreline with the traditional tools used for oceanographic or land-based work. However, deltaic studies are experiencing a renewed focus, because of their global importance in environmental and other societal concerns. This volume stems from a special session: Deltas: Old and New, held at the Annual Geological Society of America conference in October 2002, that was convened to highlight these new directions in deltaic research.