Environmental Engineering Reference
In-Depth Information
5.3.1 Meandering Rivers
Leopold (1994) indicated that 90% of the alluvial rivers in the U.S. have meandering stream channels.
A simple model of meander geometry is provided by the equation for a sine-generated curve:
sin kx
(5.59)
where T is the channel direction expressed as a sinusoidal function of distance x , 4 is the maximum
angle between a channel segment and the mean down-valley axis, k 2 / S , and O is the wavelength of
the curved channel. However, it is much less applicable to non-regular bends or to lengthy meander
traces in which a string of identical bends is unlikely.
It has long been recognized that consistent relations exist between the meander wavelength and radius
of curvature and channel width ( w ), where the latter operates as a scale variable of the channel system. In
particular, results from a variety of fluvial environments suggest that wavelength and radius of curvature
are respectively about 10-14 and 2-3 times the channel width. Since width is approximately proportional
to the square root of discharge, it is not unreasonable to expect that the meander wavelength will also be
proportional to the square root of discharge. Thus, the following equation is proposed:
1/ 2
12 wKQ
T 4
O (5.60)
In which K is a constant. This relation indicates a self-similarity of meander geometry over a wide range
of scales and environmental conditions.
One important element of the meandering process is the flow pattern through the bends. In meanders,
velocities are highest at the outside edge due to angular momentum (Fig. 5.43). The differences in flow
Fig. 5.43 Velocity distribution at a stream meander (flow direction is from the inner bank to the outer bank on the
surface and in the opposite direction near the bottom) (after FISRWG, 1998)
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