Some experimental results from the Fluid Mechanics Water Channel Facility at Birzeit University, Birzeit, Palestine, were used for computing discharge using separate channel methods in asymmetrical compound channels with varying floodplain widths and step heights. Three assumed interface planes (vertical, horizontal and diagonal) between the main channel and the floodplain subsections were considered. Then discharge values in the subsections and in the whole cross-section were evaluated. None of the separate channel methods used estimated the measured discharges accurately for the total range of the floodplain to main channel depths ratio (Y-f/Y-mc) investigated. The best discharge prediction methods with validity ranges of Y-f/Y-mc ratios are presented. (C) 2012 Elsevier Ltd. All rights reserved.