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Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EQ, UK
Modifications to standard definitions of braiding and meandering are proposed to indicate the morphology of every river channel reach quantitatively, whether it has single channel or multiple channels. Sinuosity (P) is defined as, P = Lcmax/LR, where Lcmax is the length of the midline of the channel (in single-channel rivers), or the widest channel (in multi-channel rivers), and LR is the overall length of the reach. Braiding is a measure of channel multiplicity and a new term ‘braid-channel ratio’ (B) has been defined as, B = Lctot/Lcmax, where Lctot is the total of the mid-channel lengths of all the channels in a reach. Another expression for the braid-channel ratio which gives the same numerical result is, B = Pctot/P, where the total sinuosity, Pctot = Lctot/LR, and P has been defined above. Scatter plots on braid-channel ratio/sinuosity axes show a negative correlation between these parameters, as would be expected from the above relationships. Single-channel rivers (B = 1) have relatively higher sinuosities and the upper limit of these is the point at which cut-off becomes highly probable. For multi-channel rivers (B > 1), sinuosity remains low, reflecting the limiting effect of braid bars on the development of fully developed spiral secondary flow. Data analyses showing that increases in channel slope and bankfull discharge are associated with changes from meandering to braided morphology are diverting attention from the importance of the increased availability of bed-load-grade sediment as a control.
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