Starved versus alluvial river bedforms: an experimental investigation. Issue 5 (17th February 2020)

• Record Type: Journal Article
• Authors: Porcile, Gaetano; Blondeaux, Paolo; Colombini, Marco
• Is Part Of: Earth surface processes and landforms. Volume 45:Issue 5(2020)
• Page Start: 1229
• Page End: 1239
• Publication Date: 2020-02-17
• Subjects: fluvial dunes -- barchan dunes -- supply limitation -- flume experiments -- form roughness; Geomorphology -- Periodicals; 551.4
• DOI: 10.1002/esp.4800
• Languages: English
• ISSNs: 0197-9337

Abstract

Abstract: Laboratory experiments were conducted to investigate the formation of river bedforms under sediment supply‐limited conditions, i.e. when a motionless substratum is bared by the dynamics of the mobile sediments. Three series of experiments were organized in a laboratory flume by fixing all the hydrodynamic and morphodynamic parameters but varying the thickness Δ of the initial layer of mobile sediments which covers the rigid bottom of the flume. At the end of all the experiments, which lasted for the same amount of time, the formation of transverse sand dunes was observed. For decreasing Δ, the rigid bottom of the flume was bared progressively earlier during the experiment and the measurements showed a clear tendency of the bedforms to lengthen, i.e. to increase their crest‐to‐crest distance. Moreover, under strong supply limitation, the two‐dimensional transverse dunes turned into three‐dimensional barchanoid forms and into isolated barchan dunes characterized by an abrupt reduction in bedform heights. A two‐dimensional Fourier analysis of the bottom profile was performed, providing the amplitude of the main streamwise and spanwise harmonic components of the bottom morphology as a function of Δ . © 2019 John Wiley & Sons, Ltd. Abstract : Laboratory experiments were conducted to investigate the formation of river bed forms under sediment supply limited conditions, i.e. when a motionless substrate is bared by the dynamics of the mobile sediment which give rise to the formation of bed forms. Three series of experiments were made by fixing hydrodynamic and morphodynamic parameters and in particular the duration of the experiments but varying the thickness of the initial layer of mobile sediment which covers the motionless substrate. At the end of all the experiments the formation of dunes was observed. When the thickness of the initial sand layer was decreased, measurements showed a tendency of the bed forms to lengthen. Moreover, under strong supply limitation the two‐dimensional transverse dunes turn into barchanoid bottom forms and into isolated barchan dunes. A two‐dimensional Fourier analysis of the bottom profile has been performed that provides the amplitude of the streamwise and spanwise harmonic components of the bottom morphology as a function of the volume of mobile sediment available.