15. Weir Submergence

Accurate measurements of submerged sharp-crested weir discharges cannot be made because of the spread of measured data when determining correction factors for drowned or submerged weirs. Skogerboe et al. (1967) show plots of correction factor curves for several weirs with actual data points plotted around them. The range of data spread of submergence corrected discharge is "15 percent. Besides complicated hydraulics, submerged weirs also have the problem of precision of head reading relative to head measurement. Despite the form of the correction procedures, discharge is actually based on the difference of two heads. These differential heads are small relative to the ability to measure head precisely. Therefore, submergence correction procedures should be only a temporary emergency procedure to provide estimates. The need for submergence correction should be eliminated directly by maintenance and cleaning of weeds, sediment, and other debris from the downstream channel, changing system operations, raising the crest, or installing another kind of measuring device since correction estimates are only within +15 percent.

Flow cannot be estimated for submerged partially contracted Kindsvater-Carter and Kindsvater-Shen calibrated weirs discussed in sections 6 and 7.