Scour Reduction by Air Injection Downstream of Stilling Basins: Optimal Configuration Determination by Experimentation
Publication: Journal of Irrigation and Drainage Engineering
Volume 142, Issue 12
Abstract
Hydraulic structure undermining attributable to scour can cause structural damage or collapse. Experiments were performed in a laboratory channel on scour downstream of a stilling basin of a low-head spillway to ascertain the feasibility of air injection for scour reduction, an idea that has not been previously attempted. Various hydraulic flow conditions without air injection indicate that the condition of stilling basin water elevation lower than the spillway crest, under high headwater-to-tailwater depth ratio, results in the deepest scour. Over 120 experiments were performed to determine the optimal parameters for scour reduction by air injection. It was found that optimal scour-reducing conditions consist of (1) air injection at an air-to-water velocity ratio of 251, (2) vertical air injection at the same elevation as the stilling basin exit point, (3) using diffuser hole diameters corresponding to a ratio of air-to-water velocity equal to 251 spanning the entire width of the stilling basin, and (4) a diffuser hole spacing 0.04 times the diffuser width. Scour can thus be reduced by approximately 59% near the structure. Air compressors and diffuser pipe diameter and hole sizes corresponding to these conditions would be required in prototype installations.
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Acknowledgments
This study was partially funded by the South Florida Water Management District. The opinion expressed or statements made herein are solely those of the authors and do not reflect the views of the agencies of the authors’ affiliations.
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Published In
Journal of Irrigation and Drainage Engineering
Volume 142 • Issue 12 • December 2016
Copyright
© 2016 American Society of Civil Engineers.
History
Received: Sep 14, 2015
Accepted: Jun 30, 2016
Published online: Aug 26, 2016
Published in print: Dec 1, 2016
Discussion open until: Jan 26, 2017
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