Experimental and numerical results relating to dam-break flows are compared. Dam-break waves were generated by the quasi-instantaneous removal of a plate in a smooth prismatic channel of rectangular cross-section over horizontal dry and wet beds. The laboratory experiments were conducted to determine the initial stages of the free surface profiles using digital image processing. The flow characteristics were detected by applying an adequate, simple and economical measuring technique. The experimental results were compared with the results of a commercially available CFD program, solving the Reynolds-averaged Navier–Stokes (RANS) equations with the k–ϵ turbulence model involving the shallow-water equations. Measured and computed free surface profiles during the initial dam-break stages indicate that although both models predict the dam-break flow with a reasonable accuracy, the agreement using the RANS model is better.

Dam-break wave propagation usually occurs over irregular topography, due for example to natural contraction-expansion of the river bed and to the presence of natural or artificial obstacles. Due to limited available dam-break real-case data, laboratory and numerical modeling studies are significant for understanding this type of complex flow problems. To contribute to the related field, a dam-break flow over a channel with a contracting reach was investigated experimentally and numerically. Laboratory tests were carried out in a smooth rectangular channel with a horizontal dry bed for three different lateral contraction geometries. A non-intrusive digital imaging technique was utilized to analyze the dam-break wave propagation. Free surface profiles and time variation of water levels in selected sections were obtained directly from three synchronized CCD video camera records through a virtual wave probe. The experimental results were compared against the numerical solution of VOF (Volume of Fluid)-based Shallow Water Equations (SWEs) and Reynolds-Averaged Navier-Stokes (RANS) equations with the k-ε turbulence model. Good agreements were obtained between computed and measured results. However, the RANS solution shows a better correspondence with the experimental results compared with the SWEs one. The presented new experimental data can be used to validate numerical models for the simulation of dam-break flows over irregular topography.