In this study, the effect of the downstream expansion region of a flow measurement flume of rectangular compound cross section on some of the flow properties; such as the discharge coefficient, C-d, the approach velocity coefficient, C and the modular limit, ML were investigated. For this reason, extensive laboratory tests were conducted with nine models of different downstream transitions. The aforementioned hydraulic quantities were then related with the relevant parameters to obtain sets of curves from which one could decide which kind of downstream transition type would produce the highest modular limit. It was found that model type A yielded the highest modular limit with a downstream slope of about 1/7. (C) 2013 Elsevier Ltd. All rights reserved.