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Scale‐Dependent Evanescence of River Dunes During Discharge Extremes
Author(s) -
Naqshband S.,
Hoitink A. J. F.
Publication year - 2020
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2019gl085902
Subject(s) - froude number , flume , bedform , geology , sediment transport , geomorphology , sediment , bed load , hydrology (agriculture) , flood myth , flow (mathematics) , geotechnical engineering , geometry , geography , archaeology , mathematics
During high river discharge extremes, the growth of dunes can reach a maximum beyond which a transition to upper stage plane bed may occur, enhancing the river's conveyance capacity and reducing flood risk. Our predictive ability of this bedform regime shift in rivers is exclusively built upon high Froude number flows dominated by asymmetric dunes with steep downstream‐facing slipfaces that are rare in natural rivers. By using light‐weight polystyrene particles as a substrate in an experimental flume setting, we present striking dune morphodynamic similarity between shallow laboratory flow conditions and deep rivers, preconditioned that both flow and sediment transport parameters are accurately scaled. Our experimental results reveal the first observation of upper stage plane bed in a shallow laboratory flume that is reached for a Froude number well below unity. This work highlights the need to rethink widely used dune scaling relationships, bedform stability diagrams, predictions of flow resistance, and flood risk.