Detached Eddy Simulation (DES) is used to investigate the changes in the horseshoe vortex system and the bed shear stress distribution forming around the base of spill-through bridge abutments located at two sides of the channel for two different contraction ratios. DES is conducted at a channel Reynolds number of 45,000, and the incoming flow was fully turbulent that contains resolved turbulence fluctuations. Simulations are conducted at flat bed conditions representing the initiation of the scour process. The horseshoe vortex system is the main mechanism responsible for the local scour around the abutments and once the contraction ratio is increased some changes in the structure of the horseshoe vortex is observed. Moreover, a pair of coherent vortices, which were not present in the low contraction ratio, form in the middle of the channel oriented in the streamwise direction. These changes result in a large difference in the magnitude and pattern of the shear stress and pressure fluctuation distributions on the bed and hence thought to have a huge impact on the sediment entrainment and scour mechanism at the initial stages of scour.