The guide banks can be used to protect bridge abutments by redirecting stream flow through a bridge opening, and transfer scour away from abutment to prevent scour potential damage. But scour hole does not disappear, it is developing at the head of a straight guide bank and according to some studies can be greater in size than that at abutment. According to experimental data a streamline concentration, a local increase in flow velocity, vortex and eddy structures, flow separation, an additional flow contraction by a separation zone, and a scour hole were observed at the head of the straight guide banks. The equilibrium scour at the straight guide banks was studied and new method for equilibrium depth of scour calculation was elaborated and verified by experimental data. Hybrid modelling of scour depth development in time and experimental data were used for validation of the method. Equilibrium scour depth reflects the maximum value of the local scour hole that can be reached at the guide bank at a certain flood probability. Equilibrium scour depth should be calculated at the straight guide banks for design and extreme flood events to ensure the reliability of the structure for a lifetime.