Rating Correction for Lateral Settlement of Parshall Flumes

A 3‐in. (7.62‐cm) Parshall flume is installed in a channel and flow rates are measured with lateral flume crest slopes of 0, 3.6, 6.5, 9.0, 13.3, -3.8,-4.8,-7.2, and -11.8%. The apparent discharge is compared to the measured discharge for each slope with free outfall conditions. The results indicate that the Parshall flume accuracy is in error approximately 7% at a lateral slope of ±10%. It is determined that the flow measurement requires a 0.75% adjustment for each 1% of lateral settlement at the flume crest. A method for correcting the apparent discharge with the measured discharge is presented for variable lateral slope conditions.