Connecting geologically mapped data to numerical modelling can help in understanding river landscape evolution. This study focuses on flood-induced breaching of the coversand ridge in the IJssel valley floodplain (Rhine delta, the Netherlands). The development of the breach would explain why this river branch came into existence in early medieval times. Prior to the breaching, the coversand ridge formed a barrier for the Rhine River to discharge towards the north. A palaeoflood model was coupled to a local sediment transport model to predict sediment transport rates in two competing coversand ridge breaches. The results show that the breach at the current IJssel River location was expected to expand earlier and faster in time for various upstream discharge waves and initial breach dimensions. This provides quantitative argumentation for the IJssel river avulsion case to have been triggered by the breaching of the coversand ridge during a large palaeoflood.