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Electronic journal of the International Association
for Environmental Hydrology
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JEH Volume 8 (2000), Paper 13, August 2000
Posted August 12, 2000
CHANGES OF BED TOPOGRAPHY IN MEANDERING RIVERS AT A NECK CUTOFF INTERSECTION
Y. R. Fares
Department of Civil Engineering University of Surrey Guildford,
Surrey United Kingdom
ABSTRACT
On the basis of a field survey on bottom topography changes in the
meandering river Allan Water at the cutoff (lateral overflow) section,
a detailed study of velocities and boundary shear stresses in an idealized
rigid bed model was undertaken. The characteristics of curved channel flows,
i.e. secondary circulation and superelevation at the water surface, have
been included in the formulation. The effect of lateral overflow on the
curved flow is formulated by a spatially varied flow equation with decreasing
discharge. The analysis of results has shown that continual reductions
in velocities and shear stresses occurred in the channel at the lateral
overflow region. Maximum reduction of velocities and shear stresses was
18 percent and 37 percent for cases of low lateral overflows, and 58 percent
and 82 percent for cases of high side overflows respectively. These reductions
were attributed to the development of stagnation and separation zones at
the intersection associated with strong lateral outward currents. Finally,
an explanation is provided for the marked bed topography changes in the
Allan Water situation. The changes in shear stress field are found to be
responsible for the initiation of a longitudinal bar in the middle of the
channel and a deep scour hole close to the outer bank.
Reference: Fares, Y.R.; Changes of Bed Topography in Meandering
Rivers at a Neck Cutoff Intersection, Journal of Environmental Hydrology,
Vol. 8, Paper 13, August 2000.
Y.R. Fares
Department of Civil Engineering
University of Surrey
Guildford GU2 7XH
Surrey, U.K.
Email: y.r.fares@the-vine-freeserve.co.uk