This paper presents an investigation of dam break flow in a channel with lateral contraction. An experiment was carried out in a laboratory flume by instantaneous removal of a plate. The problem was studied in a smooth prismatic channel of rectangular cross-section over horizontal dry bed. At a certain distance downstream from the dam location, two symmetrical triangular-shaped lateral sidewall obstacles were installed to generate converging diverging channel reach. Thus, it points out the abrupt variation of topography in floodplain for practical applications. Adopted measuring technique, digital image processing, detected the flood wave propagation quite well thereby synchronous recording of the flow through the entire channel with three cameras. The continuous free surface profiles and stage hydro-graphs were obtained without disturbing the flow. The experimental data were compared with the results of RANS-based numerical simulation. Comparisons between measured and computed results show good agreement. (C) 2012 Elsevier B.V. All rights reserved.