Debris flows are fast-flowing events that are saturated with granular material. They naturally occur in steep creeks and are a threat to local communities. Scientists have turned to numerical models to better understand how they behave. We investigate the accuracy of a numerical model that relies on modelling the debris flow as a mixture of a granular phase and a fluid phase. We focus on a demonstration of the capacity of the model to reliably represent the behaviour of the flow at different scales.