Standard specifications for flow measurement structures

The performance data given in existing standards for open channel flow measurement structures are qualified by strict limitations derived from the original supporting research. This research did not anticipate the more extensive range of conditions used today. Commonly used measurement structures often operate outside the limits specified in the current standards and this can lead to gross inaccuracies in measured flows. This paper describes an investigation carried out to extend the range of conditions where the performance of particular structures can be predicted, thereby permitting the extension of the scope of certain flow measurement standards. Current flow measurement standards were scrutinised and the key limitations were identified. Additionally, a review of the current usage of flow measurement structures was undertaken based on registers of measurement structures, reports and papers on studies undertaken, asset surveys and the views of individual experts. This information was then drawn together in order to determine what laboratory tests might be undertaken to provide data which would enable the standard specifications to be extended. Following this review, the research programme was formulated to cover three of the more important issues identified namely: to extend the range of permissible flow conditions in terms of head to weir height ratios; to evaluate the performance characteristics of compound weirs without divide piers; and to extend the availability of drowned flow performance data.