Effect of Cross-Sectional Shape on Free-Surface Instability
Publication: Journal of Hydraulic Engineering
Volume 121, Issue 4
Abstract
The effect of cross-sectional shape on free-surface instability is characterized by the dimensionless relative kinematic wave celerity c drk, defined as β− 1, in which β is the exponent of the normal discharge-flow area rating Q =αAβ. The value of c drk is a function of the type of friction (Manning or Chezy) and the cross-section parameter δ, the exponent of the wetted perimeter-flow area relation P =κAδ. A stable channel is defined as that which features a constant δ. Two types of stable channels are formulated: (1) unconditionally stable, for which δ= 1 and the Vedernikov number V = 0 for all Froude numbers; and (2) conditionally stable, for which δ< 1, and V ≤ 1 for Froude numbers in the range F ≤Fns, in which Fns is a design neutral-stability Froude number. Given a suitable choice of initial hydraulic radius R o and Fns, a stable yet relatively narrow channel cross section may be designed following the methodology described here. Provided the Froude number remains in the range F ≤Fns, such a channel should be largely free from roll waves and kinematic shock waves.
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Published In
Journal of Hydraulic Engineering
Volume 121 • Issue 4 • April 1995
Pages: 376 - 380
Copyright
Copyright © 1995 American Society of Civil Engineers.
History
Published online: Apr 1, 1995
Published in print: Apr 1995
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