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This study presents the physical model experiments on the wave overtopping induced bed level changes at an unprotected rear side of a rubble mound revetment with a crown wall. In the experiments, the wave conditions, the backfill material size, and the backfill depth (vertical distance from the crest level to the rear side bed level) are varied. Two mobility parameters, namely the densimetric overtopping discharge and the relative fall velocity, are introduced to represent the initiation of motion and suspension of the backfill material, respectively. The temporal evolution of scour depth at the rear side is related to the mobility parameter, the number of waves and the backfill depth utilizing regression analyses. The effect of the backfill depth on the scour is found very limited for the available data set. However, the time scale of the scour is found to be related with the backfill depth only. For the present data set, it varied within a range of 1500–16000 number of waves approximately, with an average of 5600 waves. An equilibrium scour profile is reached 3 to 4 times the time scale. The geometry of the scour profile is expressed in terms of the scour depth, based on the equilibrium scour profile data.
•Scour due to random wave overtopping at the rear side of a rubble mound revetment is studied via laboratory experiments.•Time for a substantial amount of scour at the rear side is observed at 5600 waves on average, for the available data set.•The equilibrium conditions for the rear side bed level changes are observed 3 to 4 times the time scales.•Temporal evolution of the scour depth is related to a relative fall velocity parameter, number of waves and backfill depth.