Process-based modelling of morphodynamics and bar architecture in confined basins with fluvial and tidal currents

摘要

Tides affect sediment transport dynamics in many coastal environments. Tidal effects may be particularly large in marine-influenced confined settings due to tidal amplification. Yet, it is largely unknown in what ways the width of confined basins and the strength of tidal currents impact sand deposition, and how this would affect reservoir architecture. This study applies the morphodynamic model Delft3D to systematically test models of bar stratigraphy and preservation in confined basins with mixed fluvial and tidal currents. A unique aspect of the methodology is that morphological as well as subsurface data are considered, thus enabling the tidally-influenced bar morphodynamics to be related explicitly to the associated bar deposits. By systematically varying tidal range in idealized confined basins of varying width, it is shown that bar dimensions are primarily affected by basin width, and that tidal range has a secondary effect. An increase in basin width results in a higher bar braiding index, a larger number of bars as well as longer bars, wider bars and thicker bar deposits. Synthetic architectures that can be compared directly with the sedimentary record show a high degree of stratigraphic complexity within tidally-influenced bars. Statistical distributions, summarizing the internal structure of tidally influenced bars, provide quantification of the preservation of bars and such approaches will improve their three-dimensional characterization in geo-models of tidally-influenced and confined settings.