Sedimentation Effects on Triangular Short-Crested Flow-Measurement Weirs
Publication: Journal of Hydrologic Engineering
Volume 22, Issue 8
Abstract
Flow-measurement weirs in natural channels experience sedimentation. Removing accumulated sediment is often impractical, prohibitively expensive, or both. This paper describes the results of hundreds of laboratory experiments conducted over a 6-year period to quantify the effect of sedimentation on the discharge coefficients for short-crested 120° and 140° triangular weirs over a range of flows, channel slopes, and different measurement positions along and across the channel. Two weir crest geometries were tested. These included the U.S. Department of Agriculture, Agricultural Research Service (ARS) design, and a modified ARS-type weir crest intended to reduce the frequency of plugging by floating debris called the Panama crest design. Two different weir crest thicknesses were tested in a hydraulics laboratory in two different flumes, with and without horizontal planar sedimentation, to identify the effects of sedimentation on discharge coefficients. Sediment transport was not considered. Results showed that in all cases sedimentation reduced the discharge coefficient by up to 10%. Channel slope had a relatively minor effect provided that the channel slope was less than or equal to 2% with a horizontal planar bed above the weir. Depth measurement position was of minor importance provided that the measurement was made out of the region of drawdown near the weir. The findings reported in this paper extend the usefulness of short-crested triangular weirs to conditions where the upstream pool is filled with sediment to the weir invert.
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Acknowledgments
This study was largely funded using discretionary funds provided to the first author by the University of Wyoming as the Cline Distinguished Chair of Engineering, Environment, and Natural Resources at the University of Wyoming. Support for graduate, undergraduate, and high school student participation was provided by the U.S. National Science Foundation through Grants EAR-1045166, EPS-1135483, and EAR-1360384. This study was conceived and managed by the first author, who is responsible for the analysis presented in this paper. Coauthor Jesse Creel earned his M.S. thesis based on his study of the 120° Panama weir crest. Coauthor Ed Kempema served as laboratory manager during this study and kept the study and the students moving. Coauthor Trey Crouch and former M.S. student Juan Carlos Briceno showed the patience to reliably collect high-quality data day after day. Others who contributed to data collection in the lab from time to time include Michelle Ogden, former postdoctoral associate Nawa Raj Pradhan, former Ph.D. student Guy Litt, M.S. student Jason Regina, former M.S. student Nels Frazier, undergraduates Cornelus “Casey” Valkenburg, Samantha Marquard-Ogden, and Drew Herrera, and Emma Erikson and Fritz Ogden when they were high school students. This study would not have been possible without all their effort. Sherry Hunt and Ron Tejral of the USDA-ARS Hydraulic Engineering Research Unit provided key historical literature to aid in interpretation of past results. Reviewers Dave Goodrich and Tony Wahl contributed to the quality of this paper. Their attention to details is greatly appreciated.
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Information & Authors
Information
Published In
Journal of Hydrologic Engineering
Volume 22 • Issue 8 • August 2017
Copyright
©2017 American Society of Civil Engineers.
History
Received: May 25, 2016
Accepted: Jan 25, 2017
Published online: May 2, 2017
Published in print: Aug 1, 2017
Discussion open until: Oct 2, 2017
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