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Abstract: Researchers who study tsunami deposits share common ultimate goals of their work, which are to better assess the magnitude information of paleotsunamis and to contribute to the assessment of future tsunami risks. Numerical modeling of tsunami sediment transport is an important piece of interdisciplinary research that fills the gap between geological studies and practical utilization of tsunami deposits. Forward and inverse numerical models that address tsunami transport of sand and boulders have been developed over the last two decades. Forward models are capable of delineating the time evolution of tsunami hydrodynamics, sediment transport and the resulting morphological changes associated with erosion and deposition. Inverse models estimate tsunami characteristics, such as flow speed and depth, from deposits. Numerical modeling can be used not only to quantify paleotsunamis but also to enhance our understanding of tsunami sedimentology and hydrodynamics. To make progress towards the ultimate goal of improved tsunami risk assessment, development of an in-depth mutual understanding between modelers and geologists of the advantages, limitations and uncertainties in both numerical modeling and geological records is an important challenge. [Copyright &y& Elsevier]

Morphodynamic equilibrium is a widely adopted yet elusive concept in the field of geomorphology of coasts, rivers and estuaries. Based on the Exner equation, an expression of mass conservation of sediment, we distinguish three types of equilibrium defined as static and dynamic, of which two different types exist. Other expressions such as statistical and quasi-equilibrium which do not strictly satisfy the Exner conditions are also acknowledged for their practical use. The choice of a temporal scale is imperative to analyse the type of equilibrium. We discuss the difference between morphodynamic equilibrium in the “real world” (nature) and the “virtual world” (model). Modelling studies rely on simplifications of the real world and lead to understanding of process interactions. A variety of factors affect the use of virtual-world predictions in the real world (e.g., variability in environmental drivers and variability in the setting) so that the concept of morphodynamic equilibrium should be mathematically unequivocal in the virtual world and interpreted over the appropriate spatial and temporal scale in the real world. We draw examples from estuarine settings which are subject to various governing factors which broadly include hydrodynamics, sedimentology and landscape setting. Following the traditional “tide-wave-river” ternary diagram, we summarize studies to date that explore the “virtual world”, discuss the type of equilibrium reached and how it relates to the real world. [ABSTRACT FROM AUTHOR]