EPISODES OF VERTICAL ACCRETION AND CATASTROPHIC STRIPPING: A MODEL OF DISEQUILIBRIUM FLOOD-PLAIN DEVELOPMENT

This paper describes flood plains formed episodically by vertical accretion along high-energy, laterally stable channels in southeastern Australia. Overbank deposition gradually builds a flood plain of fine-textured alluvium over a period of hundreds or thousands of years, following which catastrophic erosion by a single large flood, or a series of more moderate floods, strips the flood plain to a basal lag deposit from which it slowly reforms. This periodic destruction appears due to the progressive development of large levee banks and flood-plain surfaces of highly variable relief. As the levees and flood plain grow, overbank flow is gradually displaced from the broad flood plain into the main channel and flood-plain backchannels, with a resulting concentraion of erosional energy. Eventually, high flows greatly exceed erosional thresholds, and wholesale scour of the channel boundary and flood plain occurs. Vertical-accretion flood plains at different stages of development result in a wide range of bankfull recurrence intervals, even along the same river. Some of these flood plains are so infrequently flooded that they can be mistaken for terraces formed under a prior flow regime. The almost random but catastrophic nature of this flood-plain erosion means that sediment supply and transport are highly variable and probably impossible to predict. This model of flood-plain formation is seen as only part of a continuum of alluvial environments ranging from vestigial, coarse-grained, traction-load flood plains along high-energy rivers in narrow gorges to extensive low-gradient flood plains in which alluvial stratigraphy is dominated by fine-grained overbank deposition.

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• Corporate Authors:

  Geological Society of America

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  Boulder, CO  United States  80301
• Authors:
  • Nanson, G C
• Publication Date: 1986-12

Media Info

• Features: Figures; Photos; References; Tables;
• Pagination: p. 1467-75
• Serial:
  • Geological Society of America, Bulletin
  • Volume: 97
  • Issue Number: 12
  • Publisher: Geological Society of America
  • ISSN: 0016-7606

Subject/Index Terms

• TRT Terms: Alluvium; Dislocation (Geology); Erosion; Flood plains; Flow; Mathematical models; Scour; Sediments; Soil mechanics; Soils; Stripping (Pavements)
• Uncontrolled Terms: Disequilibrium
• Subject Areas: Geotechnology; Highways; Hydraulics and Hydrology; I26: Water Run-off - Freeze-thaw;

Filing Info

• Accession Number: 00473078
• Record Type: Publication
• Files: TRIS
• Created Date: Sep 30 1987 12:00AM