The floods of different probability, sequence, frequency, duration, and the riverbed with different grain sizes, numbers, sequences, and thickness of the layers are one of the reasons for the bridge`s abutments failure because of scour. Although the problem is very topical, the mutual impact of multiple floods and stratified riverbed conditions on scour at the bridge abutments has not been studied. The method for computing scour development in time at bridge abutments was elaborated and confirmed by tests results. The method enables the computer to perform modelling of the mutual impact of unsteady flow and bed layering of scour processes. Computer modelling was made to expand scenarios for tests data in flume for unsteady flow for two steps of hydrograph with different dischargers and for the bed layers with varying grain sizes, numbers, sequence, and thickness. This approach makes it possible to estimate in advance mutual impact, with different scenarios, floods and geological data on the depth of scour at vertical wall abutment, at the design stage or during the maintenance period of the bridge crossing.