Abstarct: An investigation of local scour at pier groups has been conducted with the aim of developing design recommendations and scour depth prediction equations for the bridge pier groups. A comprehensive series of steady uniform flow experiments was performed on groups of 3 piers. All tests were conducted under clear-water scour conditions. Parameters governing local scour depth around bridge piers include: flow characteristics, sediment properties, and pier size and shape. The effects of these parameters on the maximum local scour depth for a single pier (ds), have been thoroughly investigated in the past. However, when design criteria developed for single piers are applied directly to pier groups, this approach ignores the following important group effects: 1) sheltering, 2) reinforcement, and 3) horseshoe vortex (HSV) compression. Furthermore, the group effects will alter with changes in pier spacing, G. This study, which investigates the local scouring process for the aforementioned groups of model bridge piers, and presents a design relationship for predicting the corresponding maximum local scour depth, is an attempt to address this limitation in current design practice. Initially the local scour was examined for three different single pier diameters (0.06 m, 0.08 m, and 0.01 m). Having current famous single pier relationships such as those introduced by Melville and Chiew (1997), Ettema et al (1999), Richardson and Davis (CSU, 2001) and Sheppard (2004), groups of 3 spaced piers were examined while altering the separation distances. For these piers in line with the flow direction, downstream piers are sheltered by the upstream ones resulting in reducing scour depth around downstream piers. The reinforcement effect is also significant in the front piers resulting the front piers are scoured more than that of a single pier. Moreover, the scour depth of downstream piers, which are less than that of a single pier, differs with increasing the ratios of pier spacing/ pier diameter (G/d). The compressed horse shoe vortex (HSV) affects the local scour depth significantly if piers are staggered and G/d≤5. In this range of G/d, the HSV are intensified, resulting in a deeper scour hole. However, this effect also becomes insignificant with increasing G/d. The data for pier groups were analysed using a multiple regression model, to develop a local scour depth prediction equation for front pier. The regression model includes a dimensionless parameter (G/d) associated with pier groups as a regressor. The results showed that replacing u/uc with pseudo flow intensity (u⁄(u_c ) ̂ ) or Froude number in the equation proposed by Sheppard et al. (2004), improves the accuracy of scour depth prediction The proposed prediction equation estimated the observed data reasonably well, within marginal error. Furthermore the equations proposed in this research return better results for single piers in comparison with those by Melville (1997), Ettema et al (1999), CSU/HEC-18(2001) and Sheppard (2004). Finally a three-dimensional CFD FLUENT model is used to simulate clear-water local scour around group of circular piers. The numerical model assumes the sediment-laden flow as a two phase (water-sand) flow and uses a standard k-ε turbulence closure to predict turbulent parameters in the fluid phase. Two-phase domain (water in the channel with a region of sand at the bottom of the channel) is solved using FLUENT’s multiphase formulation, called the Eulerian method in order to resolve the scour depth around the group of piers. In the present study a standard k-ε turbulence model which is supplemented with additional terms that take into account the interphasial turbulent momentum transfer, is employed to predict turbulent quantities for the water phase. To predict turbulence in the solid phase, Tchen’s theory [Hinze 1975] on the dispersion of discrete particles in homogeneous and steady turbulent flows is used. The interface between water and sand in the physical experiments was taken as that corresponding to the sediment volume fraction αs = 0.5 of the numerical experiments. The calculations confirm the theory of Wang and Chien, which indicated the “laminar behavior” of two-phase flows for αs ≥ 0.5. A good agreement between the results of both measured data and numerical simulations exists which validates the reliability of the numerical model.