A large-scale test facility, the United Kingdom Flood Channel Facility, has been used to compare observations of a range of overbank flows in straight compound channels and meandering compound channels with similar geometries, floodplain roughnesses and mobile main channel bed material. For straight and meandering channels with smooth floodplains, the single channel Manning's n values were similar, but single channel Manning's n values for the meandering channel with roughened floodplains are approximately 50% greater than those for the straight channel with similarly roughened floodplains. At higher relative depths, Y-r > 0.25, the floodplain Manning's n values become similar for both the straight and meandering channels indicating that most of the overbank flow for the meandering channel is in the valley direction at these depths. The meandering main channel with roughened floodplains was found to have the largest mobile bed features.