RECALIBRATION OF PARSHALL FLUMES AT LOW DISCHARGES

An inspection of the original study that developed the rating equation s for Parshall flumes indicates that the calibration tests were not co nducted for discharges as low as is currently recommended for the flum es' use. A numerical model was developed to predict the effect of flui d viscosity on the depth-discharge relation. An experimental investiga tion for several flume sizes indicates that the original rating equati ons and data overpredict the discharge at flow rates that are less tha n about 15% of the maximum rated discharge for the flume. The discrepa ncy can be as much as 25% for the range of flows for which the flume i s recommended to be used. The numerical model successfully matches the experimental data for the flume sizes studied. Alternative rating equ ations are developed for use at low discharges.