ABSTRACT
Scour development in time at the abutments with stratified river bed is investigated. Tests were carried out with one uniform layer and with two layers of different grain sizes with standard deviation, different thickness and sequence of the layers. The differential equation of the equilibrium for bed sediment movement in clear-water is used and a method for scour depth calculation in time at vertical wall abutments with stratified river bed conditions is elaborated. The method is confirmed by test results. This method allows one to calculate the scour depth in layers with different mean grain size, thickness and sequence combination. The most critical conditions for structures in flow is when fine-sand layer is under a coarse-sand layer. With river bed layering the depth of scour is always greater in the case when a finesand layer is under a coarse-sand layer(s) comparing to the depth of scour measured or calculated with mean grain size which is on the top of the riverbed. The calculation of the scour depth near abutments by using only mean grain size diameter on the top of riverbed and neglecting the stratification, as it is accepted now, can lead to the wrong results and finally to considerable damages and losses.
