Effects of Nonlevel Placement on Accuracy of Long‐Throated Flumes

Tests were conducted to study the effects of nonlevel placement or construction on the calibration of long‐throated flumes. These flumes have previously been mathematically modeled to provide accurate (±2%) calibrations for a variety of cross‐sectional shapes. While cross‐slope can be handled successfully by the modeling procedure, no assured procedure was apparent for longitudinal slope corrections. Laboratory tests were directed to determining errors that a user might experience if a flume crest were placed at various positive and negative longitudinal slopes. The magnitude of systematic errors are shown for portable flumes with either a sidewall gage or a translocated stilling well, and for permanently placed flumes. Correction procedures are suggested.