Effect of Flood Recession on Scouring at Bed Sills
Publication: Journal of Hydraulic Engineering
Volume 136, Issue 4
Abstract
The effect of the flood recession time on the local scour depth at bed sills in gravel deposits is examined. Experiments were carried out to study the development of scour holes under time-varying hydraulic conditions with no upstream sediment feed. Triangular-shaped hydrographs, having recession times up to three times the duration of the rising limb, were used. Traditionally, the peak water discharge in any flood event is used as a design value in estimating the final depth of scour formed by a flood. This approach is overly conservative when the flow hydrograph is steep, i.e., during the occurrence of flash floods. The actual reduction of the scour depth from this estimated value is dependent on both the characteristics of the flood event and the characteristics of the stream. The results show that the maximum potential scour depth can be achieved only for hydrographs with long recession times, while the rate of this process can be estimated as a function of the ratio between a characteristic flood time and the steady-state temporal scale of scour development. A method is proposed for the prediction of the scouring process under unsteady flows in terms of two dimensionless temporal parameters. Results obtained for clear-water boundary conditions can be extended to sediment-supply tests if specific supply input conditions hold.
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Acknowledgments
Data analysis was funded by the PRIN project “Models and measurements of flow-sediment interactions at spatial and temporal scales of physical interest” of the Italian Ministry for Education and Scientific Research. The participation of the first writer to the experimental phase was supported through a scholarship offered by the “Ing. Aldo Gini” Foundation. The writers would like to thank Geoff Kirby who lead the instrumentation design, and who took part in setting up and carrying out the experiments.
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Information & Authors
Information
Published In
Journal of Hydraulic Engineering
Volume 136 • Issue 4 • April 2010
Pages: 204 - 213
Copyright
© 2010 ASCE.
History
Received: Mar 3, 2009
Accepted: Sep 27, 2009
Published online: Oct 2, 2009
Published in print: Apr 2010
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