Tony L. Wahl. 2002. "Performance Limits of Width-Contracted Flumes". Bureau of Reclamation, Report Number PAP-893.
Abstract: Long-throated flumes and broad-crested weirs are economical and flexible devices for measurement of open-channel flows. These structures produce critical depth flow in a throat section created by a raised sill, contracted width, or a combination of floor and sidewall contractions. Flumes that are solely width-contracted are especially suitable for sites where bed load must be transported through the measurement structure. The hydraulic theory used to predict the contraction required for critical flow and determine the head-discharge rating of a structure assumes that width contractions and floor contractions are equally effective. In most cases this is true, but in width-contracted flumes whose throat sections are very wide compared to their length, the flow disturbance created by the side wall contraction may not propagate sufficiently across the channel before the flow exits the throat. The effect of the side walls is not felt at the centerline of the throat section and critical depth may not occur uniformly in the throat section. To examine this phenomenon, a series of flumes with similar geometry but with different throat length to width ratios was tested to determine operational limits of width-contracted flumes. The modular limits of the widest flumes were found to be lower than the values predicted by theory. Guidelines for design of width-contracted flumes are provided.
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