Local Scour at Downstream Sloped Submerged Weirs
Publication: Journal of Hydraulic Engineering
Volume 144, Issue 8
Abstract
This paper presents an experimental study of local scour at submerged weirs with different downstream slopes. Thirty-three tests of coarse sand () and 24 tests of fine sand () were carried out in a sand-recirculating flume. The tests for each sand type used four weirs with different downstream weir slopes (, , , and to horizontal for the fine sand; , , , and to horizontal for the coarse sand). The results show that the upstream scour depth is independent of the downstream weir slope . For both sand types, the downstream weir slope has no effect on the downstream scour depth when it is greater than the upstream slope of the downstream scour hole . For , the downstream weir surface is partly exposed to flow, resulting in a downstream scour depth at the weir surface , which can be increased by the increase in either downstream scour depth or . In this situation, the upstream water level rises because of the reduced flow cross-section area, and the overflow jet is deflected to be approximately aligned with the downstream weir surface. For the coarse sand tests, when , the effect of the rising upstream water level is predominant because is close to (time-averaged value of ). This results in larger downstream scour depths. When is considerably smaller than , the effect of jet deflection starts to be predominant in the coarse sand tests, generating lower downstream scour depths when . Those two effects balance each other when for , resulting in the same downstream scour depths as those for a rectangular weir. For the fine sand tests, the jet deflection effect is predominant because the downstream weir slope has limited effect on the upstream water level. A conservative design method accounting for both effects is proposed for the local scour at downstream sloped submerged weirs.
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Acknowledgments
The authors would like to acknowledge the valuable suggestions from Mr. Graham Macky and Mr. Conrad Zorn. Also, the first author would like to thank the China Scholarship Council for the financial support of this research.
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©2018 American Society of Civil Engineers.
History
Received: Oct 27, 2017
Accepted: Feb 20, 2018
Published online: May 26, 2018
Published in print: Aug 1, 2018
Discussion open until: Oct 26, 2018
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