Environmental Engineering Reference
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thalweg , the line of maximum water or channel depth, itself meanders. Flow or channel
sinuosity is measured as the ratio between the channel and straight-line distances between
two points and = 1 in straight channels, increasing with sinuosity. Meandering is
arbitrarily considered to occur where sinuosity is greater than 1ยท5.
Many theories have been advanced for meandering, including chance deflection by
obstacles leading to destabilization of stream flow with repeated downstream over-
correction. Recent studies emphasize temporal changes in sediment supply and bed shear
stress, stimulating local erosion/deposition and hence new channel geometry. Since
channel efficiency increases downstream to counteract lower potential energy, and
velocity remains constant, a downstream increase in discharge must require adjustments
to the channel. Meandering consumes surplus energy by lateral erosion and friction with
the larger wetted perimeter implicit in sinuous channels (Figure 14.21 and Plate 14.14).
Bars , riffles and pools are large-scale, dynamic bed forms implicit in the morphology
and formation of meanders and it is useful now to assume that the thalweg is also the line
of average maximum velocity. Alternating bars develop by deposition in slower, less
competent flow either side of the sinuous mainstream. Arguably, random deposition in an
area of lower bed shear stress could
Plate 14.14 Stream-flow meandering in an iron quarry drain,
even where its banks are not erodible.
Photo: Ken Addison.
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