A study was conducted in the Hydraulics Laboratory of Colorado State University to evaluate how settlement affects the accuracy of 30.5- and 61.0-cm (1- and 2-ft) prefabricated metal Parshall flumes. The flumes were installed and tested for lateral, longitudinal, and combined lateral-longitudinal slopes settlements. Flume slopes varied +/- 7%, and were conducted for free outfall conditions. The results indicated that the Parshall flume accuracy is slope-dependent. The flume rating was in error approximately 28% for longitudinal slopes of +/- 5%, and approximately 10% for lateral settlement of +/- 5%. Flow rates used in this study ranged from 0.01 to 0.20 m3/s for the 30.5-cm flume and 0.03-0.28 m3/s for the 61.0-cm flume. A procedure was presented to adjust the flow rating for lateral, longitudinal, and combined lateral-longitudinal settlement as a function of the flume slope, flow depth, and flume throat width. The results of the 30.5- and 61.0-cm flumes were compared to the results of similar tests with 2.54-, 5.08-, and 7.62-cm Parshall flumes.119610811091