Abstract: Four institutions were involved in the“Sediment movement”IMPACT work package. Laboratory experiments were carried out and a huge amount of data were gotten. Those experiments resulted in high-quality data sets for the validation of the numerical models. Meanwhile, the Lake Ha! Ha! case study helped identifying and understanding the key features of the geomorphological changes induced by a dam-break flood. Besides, an assessment of the capabilities and the uncertainty of current numerical models was achieved through comparison between the modeling data and the observations in laboratory experiments and the specific case. At last, some conclusions and recommendations were presented, for reference.