## 1 Introduction  
Significant dam-break events produce downstream rapidly-varied unsteady flows, which may determine catastrophic consequences in terms of human losses and damages to properties. Severe floods forecasting is necessary for the prevention of these consequences and the creation of emergency plans which may avoid, or at least decrease, casualties and costly damages. In the literature, the dam-break problem has been widely investigated for fixed-bed cases, giving emphasis to the kinematic motion of the water body [1] and neglecting its interaction with the related morphodynamic processes (i.e., sediment transport and bottom evolution). In the fixed-bed problem, dam-break has been studied separately in domains with an initially dry or wet bed, owing to the related significant differences in flow behavior [2]. Analytical solutions are available for only idealized situations. [PERSON] [3] proved that the pressure distribution is non-hydrostatic immediately after dam failure, a result later confirmed by many reports (e.g., [4]). [PERSON] [5] extended the solution of [PERSON] [6], comprehending wet bed conditions downstream by solving the Saint-Venant equations. Since the 1950s, many studies have focused on laboratory experiments of dam-break phenomena, starting with the pioneering works of [PERSON] [7] and [PERSON] [8]. [PERSON] presented experimental data obtained at the US Bureau of Standards, consisting of forward and backward wavefront trajectories in a horizontal rectangular channel for three different channel bottom roughnesses. Further studies (e.g., [8; 9; 10; 11]) focused on resistance effects. [PERSON] and [PERSON] [12] carried out experiments of a 3D dam-break model case similar to the one investigated here, but only for dry bed conditions and with a downstream open boundary, measuring water depths and bottom pressures in order to assess the Shallow Water model and the feasibility of the hydrostatic approximation. [PERSON] and [PERSON] [13] experimentally and analytically analyzed the forward and backward wavefront trajectories in a horizontal smooth and rectangular channel for dry bed conditions as well. The initial stages of dam-break for dry and wet bed conditions have also been investigated in other studies [14; 15; 16]. Other researches of dam-break floods over erodible beds have also studied wave propagation and the influence of forward and backward wavefront celerities [17; 18]. Recently, image analysis techniques have been applied to the experimental flow measurements of dam-breaks. [PERSON] and [PERSON] [19] examined the influence of downstream obstacles on the dam-break wave-making use of resistive gauges and Acoustic Doppler Velocimeters for water level and velocity measurements, respectively. [PERSON] and [PERSON] [20] processed image recordings, correcting tangential and radial distortions using the Calibration Toolbox for Matlab. [PERSON] and co-workers [21] added methylthioninium chloride to the upstream tank water and made use of cold fluorescent lamps in order to obtain as uniform as possible luminance during image recordings. [PERSON] and [PERSON] [22] derived stage hydrographs by processing synchronous video images of three adjacent CCD cameras, using virtual wave probes as an alternative to intrusive instruments for experimental measurements. In most of the above-mentioned experimental works, the flow was considered to be one-dimensional (1D), since no significant wall effects are observed. Therefore, the flow kept the same features in each longitudinal section. Furthermore, and differently from the present work, an open boundary was considered so that no reflections occurred at the downstream channel edge. On the other side, the non-stop increase of computing power in recent years has allowed for software development (e.g., [23; 24; 25; 26; 27]) and solving algorithms to tackle dam-break phenomena in complex geometries over fixed or erodible beds and embankments.