Slope-induced changes in channel character along a gravel-bed stream: the Allt Dubhaig, Scotland

R.I. Ferguson, Philip Ashworth

Research output: Contribution to journalArticle

Abstract

Changes in channel character along a small river in the Scottish Highlands are described using measurements in seven reaches over a 3 km length with no significant tributaries but a decline in slope from 0.02 to O-OOO15 because of local baselevel control. This decline in slope is associated with rapid downstream fining of the gravel bed followed by an abrupt transition to a sand bed. The channel pattern alters progressively rather than abruptly, in the sequence (1) near-braided, (2) meandering with active point-bar chutes, (3) meandering with active outer-bank talweg, (4) stable equiwidth sinuous. The changes in channel pattern and hydraulic geometry are predicted better by rational approaches based on critical shear stress or other physical cdncepts than by purely empirical discriminant or trend equations. Measurements in five reaches confirm a downstream decrease in shear stress and the amount and calibre of bedload. It is argued that the downstream changes in channel character in this stream are induced by profile concavity inherited from deglacial conditions, are typical of many streams in mountainous areas and can be understood in terms of slope-induced changes in hydraulic properties.
Original languageEnglish
Pages (from-to)65-82
Number of pages18
JournalEarth Surface Processes and Landforms
Volume16
Issue number1
Publication statusPublished - 1 Jan 1991

Keywords

  • Channel pattern
  • Gravel-bed rivers
  • Downstream fining
  • Rational regime theory
  • Hydraulic geometry

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