The bed morphology of upland single-thread channels in semi-arid environments: Evidence of repeating bedforms and their wider implications for gravel-bed rivers

D. Mark Powell, Jonathan B. Laronne, Ian Reid, Ronel Barzilai

Research output: Contribution to journalArticlepeer-review

14 Scopus citations

Abstract

Single-thread, gravel-bed streams of moderate slope in the northern Negev are characterized by three channel units: bars exhibit steeper than average slopes and poorly sorted mixtures of small-medium cobbles and coarse-very coarse pebbles; flats are associated with more gentle slopes and well-sorted medium-fine pebbles and granules; and transitional units have intermediate slopes and grain size. In general, all three units are planar, span the full channel width and have well-defined boundaries. Bars and flats are more common than the transitional units and alternate downstream for distances of several hundred metres, forming sequences that are reminiscent of the riffle-pool structure commonly observed in humid-temperate gravel-bed rivers. A notable contrast is the absence of significant bed relief: bars lack crests and flats lack depressions. The relative lack of bed relief in bar-flat sequences is attributed to the high rate of sediment supply from the sparsely vegetated hillslopes which promotes the infilling of depressions and to the erosion of crests under conditions of intense transport. This reduction of bed relief lowers channel roughness, which in turn increases flow velocity and, therefore, the ability of the channel to transmit the large sediment loads it receives. Although our analyses pertain to a semi-arid river system, the results have wider implications for understanding the adjustment of channel bedform to high sediment loads in other fluvial environments.

Original languageEnglish
Pages (from-to)741-753
Number of pages13
JournalEarth Surface Processes and Landforms
Volume37
Issue number7
DOIs
StatePublished - 15 Jun 2012

Keywords

  • Bars and flats
  • Channel units
  • Ephemeral rivers
  • Gravel bedforms
  • Riffles and pools

ASJC Scopus subject areas

  • Geography, Planning and Development
  • Earth-Surface Processes
  • Earth and Planetary Sciences (miscellaneous)

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