ABSTRACT
Two different phenomena act at the same time, are coupled and depend on each other. This kind of process controls the three different stages that the scour goes through during time. One of them is the action of the vortex that is created in front of the pier due to the shock of the flow with the pier. The other phenomenon is the crumbling of the wall of the pit due to geotechnical instabilities. This last phenomenon occurs in
frequent collapses that lead the sediment to the zone where the vortex acts. From now in advance the two phenomena are known as active the first and passive the last.
