Estimating the equilibrium scour depth around two side-by-side piers with different spacing ratios in live-bed conditions

The aim of this research was to numerically investigate the flow behaviour and evolution of the local scour around a group of two side-by-side piers in live-bed conditions. A coupled hydro-morphodynamic model was developed in OpenFOAM®. The hydrodynamic part of the model solved the unsteady Reynolds Averaged Navier-Stokes equations. The morphodynamic part of the model entailed solving both bedload and suspended load sediment transport. The model validation was performed for the available experimental data in the literature. The modelling for the pier groups was carried out with three different spacing ratios of G/D = 1, 2, and 3, where G represents the distance between the piers and D is the pier diameter. The results presented detailed information regarding the flow field and scour hole progression adjacent to two side-by-side piers. The dimensionless equilibrium scour hole depths of 1.74, 1.38 and 1.29 were predicted for the pier groups with G/D = 1, 2, and 3, respectively. The results showed an inverse correlation between the spacing ratio and the scour hole depth adjacent to the piers. The results were generalised, and an equation was obtained for the prediction of the equilibrium scour hole depth as a function of the spacing ratio.