The purpose of this study is to investigate the effect on flow hydrodynamics of grading of the bed and the mining of sand from the river bed around a bridge pier group. In total, 22 experiments with two different bed gradings (‘A’ and ‘B’), three different discharge rates, and Froude numbers were performed. In order to investigate the effect of mining on scour rate, the mining of material was carried out both upstream and downstream of the pier group. It was observed that the mining from downstream locations led to an increased scouring around the pier group. At a Froude number of 0.5, the existence of a pit hole downstream of the pier group causes a 3% and 9.7% increase in the maximum scour depth for grading ‘A’ and ‘B’, respectively. On the other hand, mining materials from upstream locations and for the same Froude number decreased scouring by 9% for ‘A’ grading and 8.1% for ‘B’ grading. A regression method was used to provide an equation that can be used to estimate the scour depth.
