The recurrent floods in recent decades have imposed a challenge of embankment dam breaching, which needs great attention through improved design methods that are based on risk approach, the evacuation plans for people at risk, etc. In this study, based on the small-scale model tests a series of experiments were conducted to determine the breaching process of cohesive embankment dam using a simplified physical based breach model due to overtopping; the breach process observed during tests in the laboratory and the results from analyzed parameters are described. Five dam models, three of which were constructed with homogenous clay soil while two were sandy-clay mixture tested. The heights of the embankments dam were 0.45 m, and the widths at the crest were 0.20 m. The data from these examinations indicated that headcut erosion played an important role in the process of breach development. Initiation of erosion, flow shear erosion, sidewall bottom erosion, and distinct soil mechanical slope mass failure from the headcut vertically and laterally were all observed during these tests. In this physical based experimental model, the initial scouring position calculated by applying a hydraulic method, the broad crested weir formula used for breaching flow discharge and flow velocity computed based on breach flow discharge. The stability of the side slope failures was estimated by comparing the resisting and deriving force. Further, using data from laboratory experiments, the calculated peak breach discharge, breach characteristics times, breach widths, and breach flow velocity generally agreed well with the measured data and also the knowledge acquired from observed breach process at several stages. Finally, the accuracy of model was checked by root-mean-square-error.
