Submitted to: Journal of Irrigation and Drainage Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/8/2006
Publication Date: 12/1/2007
Citation: Wahl, T.L., Clemmens, A.J., Replogle, J.A., Bos, M.G. 2007. Discussion of "broad-crested weirs with rectangular compound cross sections". Journal of Irrigation and Drainage Engineering. 133(6):616-618. Interpretive Summary: This article is a discussion of an article published in the Journal of Irrigation and Drainage Engineer on Broad-Crested Weirs with Rectangular Compound Cross Sections. The discussers agree that these structures are very suitable for many applications. However, the calibrations provided by the authors are not consistent with the published literature. Since a primary standard was not used to determine the calibration, the discussers suggest that the comparison measurement device was not sufficiently accurate. Unfortunately, the author’s work presents misconceptions regarding these devices, which this discussion attempts to refute. This should be of interest to the Bureau of Reclamation, water resources specialists, and irrigation engineers.
Technical Abstract: The development of interactive, easy-to-use design and calibration software in the past two decades has made broad-crested weirs with streamlined approaches one of the best available structure types for measuring open channel flows. Advantages include excellent accuracy, minimal head loss, adaptability to many channel types, and the ability to measure wide flow ranges through the use of trapezoidal, V-shaped, and compound control sections. The authors have presented a detailed set of experiments on weirs with rectangular compound cross sections. These weirs have a small inner rectangular section for measuring low flows and then broaden to a wide rectangular section at higher flow depths. The investigation considers the head-discharge ratings, discharge coefficients, velocity coefficients, and modular limits of the structures. Some of the work is compared to results from the WinFlume computer program (Wahl et al. 2000) developed by the discussers for the calibration and design of long-throated flumes and broad-crested weirs. Many of the results presented by the authors touch upon subjects previously investigated and documented in detail by the discussers and others. Specifically, comprehensive guides to the theory and practical application of long-throated flumes and broad-crested weirs were provided by the discussers in 1984 and 1993, and most recently were updated in 2001 to include new developments, notably the WinFlume computer program. Unfortunately, the authors’ work also creates misconceptions about the validity of this past work and the WinFlume software, and may potentially lead practitioners to adopt undesirable designs for flow measurement structures with compound control sections. The purpose of this discussion is to set the record straight.