Effect of Seepage-Induced Nonhydrostatic Pressure Distribution on Bed-Load Transport and Bed Morphodynamics
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Abstract
Bed-load transport is commonly evaluated in the condition of a hydrostatic pressure distribution of the flow field; while this condition is reasonable for quasi-steady, quasi-uniform rectilinear flows, it cannot be satisfied in a large variety of flow conditions, i.e., near an obstacle as in the case of a bridge pier. The dimensionless Shields number, which contains the assumption of a hydrostatic pressure distribution in its denominator, therefore cannot be strictly applied to evaluate bed-load transport in all the configurations where nonhydrostatic pressure distributions are observed. In the present work, a generalization of the Shields number is proposed for the case of nonhydrostatic pressure distribution produced by groundwater flow. Experiments showing the effects of vertical groundwater flow on the bed morphodynamics are presented. The comparison between the experimental observations and numerical results, obtained by means of a morphodynamic model which employs the new formulation of the Shields number, suggests that the proposed generalization of the Shields number is able to account the effect of the nonhydrostatic pressure distribution on the bed-load transport.
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Acknowledgments
Professor Enio Paris is greatfully acknowledged for his support in the present research and for his precious comments and suggestions. The experiments reported here were performed at St. Anthony Falls Laboratory, University of Minnesota as part of the Ph.D. thesis of the first writer, in partial fulfillment of her degree. These experiments were supported in part by the visitor program of the National Center for Earth-Surface Dynamics (NCED), a Science and Technology Center of the United States National Science Foundation.NSF This paper represents a contribution to the effort of NCED in the area of channel dynamics. Preliminary results of the present work were published in the Conference Proceedings of RCEM 2005 and River Flow 2006.
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Published In
Journal of Hydraulic Engineering
Volume 134 • Issue 4 • April 2008
Pages: 378 - 389
Copyright
© 2008 ASCE.
History
Received: May 5, 2006
Accepted: Aug 8, 2007
Published online: Apr 1, 2008
Published in print: Apr 2008
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