Skimming, Nonaerated Flow on Stepped Spillways over Roller Compacted Concrete Dams
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VIEW THE REPLYPublication: Journal of Hydraulic Engineering
Volume 138, Issue 10
Abstract
The nonaerated region may occupy a large portion of the skimming flow in steep, stepped spillways, particularly for relatively high unit flow rates. In spite of the numerous contributions on the hydraulic properties at both the inception point of air entrainment and the aerated region, much less is known regarding the flow in the nonaerated region. In this paper, new empirical evidence, based on an extensive data set obtained during several years in a large-scale facility, sheds light on the features of the nonaerated-flow region. Diverse ways to locate and estimate the main hydraulic properties at the inception point are first discussed and compared. Then, expressions capable of characterizing the main flow variables along the nonaerated region are presented, namely, the boundary-layer development, the velocity distribution, the equivalent clear-water depth, the characteristic depth taking into account the free-surface unsteadiness due to turbulence, and the energy dissipation. The energy dissipation is observed to be larger than that for smooth spillways, although much smaller than values typically reported for aerated flows at the toe of stepped spillways.
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Acknowledgments
Inês Meireles was Visiting Scholar at the University of California, Davis, for two periods of 6 months in 2007/2008 (financially supported by Fulbright/Luso-American Development Foundation—FLAD) and in 2009/2010 (financially supported by the Portuguese National Science Foundation—FCT). The financial support granted by Fulbright and FLAD and by FCT, through Project PTDC/ECM/108128/2008 and Grant No. SFRH/BD/38003/2007, and the support granted by the National Laboratory of Civil Engineering (LNEC), Lisbon, are gratefully acknowledged.
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Published In
Journal of Hydraulic Engineering
Volume 138 • Issue 10 • October 2012
Pages: 870 - 877
Copyright
© 2012 American Society of Civil Engineers.
History
Received: Jul 30, 2011
Accepted: Mar 8, 2012
Published online: Mar 12, 2012
Published in print: Oct 1, 2012
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