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Is “morphodynamic equilibrium” an oxymoron?

February 1, 2017

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.

Publication Year 2017
Title Is “morphodynamic equilibrium” an oxymoron?
DOI 10.1016/j.earscirev.2016.12.002
Authors Zeng Zhou, Giovanni Coco, Ian Townend, Maitane Olabarrieta, Mick van der Wegen, Zheng Gong, Andrea D'Alpaos, Shu Gao, Bruce E. Jaffe, Guy R. Gelfenbaum, Qing He, Yaping Wang, Stefano Lanzoni, Zhengbing Wang, Han Winterwerp, Changkuan Zhang
Publication Type Article
Publication Subtype Journal Article
Series Title Earth-Science Reviews
Index ID 70187625
Record Source USGS Publications Warehouse
USGS Organization Pacific Coastal and Marine Science Center