Rating Adjustment for Settlement of Cutthroat Flumes

Abstract

A study was performed to examine the effects of flume settlement on the accuracy of discharge measurements, using the cutthroat flume in a free-flowing condition. A series of 111 tests was performed on 10.2 cm × 0.91 m, 30.5 cm × 1.37 m, and 61 cm × 1.37 m flumes. Each cutthroat flume was systematically adjusted to simulate settlement in the lateral, longitudinal, and combined lateral-longitudinal directions. Discharge inaccuracies were recorded for each settlement condition. Flume discharge measurement errors ranged from ±3% to ±23% for lateral, longitudinal, and combined lateral-longitudinal slopes of up to 4%. The greatest errors occurred when the lateral slope and/or the longitudinal slope reached or exceeded 3%. An algorithm was developed to adjust the flow measurements for settlement. A procedure was devised for determining the true flow measurement to within ±3% for free-flowing conditions.