Pile scour is the main cause of bridge failure. A physical model used in this research to study scour around a group of piles in clear-water conditions. The study examined changes in stream bed, volume and area of scour holes due to changes in pile spacing and arrangements. For this purpose, width, length and depth of scour hole variation and also changes in channel bed formation owing to pile groups, their arrangement and spacing were studied. An experimental channel with a length of 10 m, a width of 0.83 m and a depth of 0.5 m was used. The channel bed was covered with medium-sized uniform sediments for 0.9 mm. The discharge and flow velocity were adjusted to clear-water conditions. In each experiment, the channel bed changes and the scour hole were recorded and analysed. The results showed that the piles’ arrangement and their spacing affected the area and volume of scour hole so that with increasing pile spacing, despite the scour depth, volume and area of the scour hole increased. The channel bed formation and movement of sedimentation areas and scour was also affected by the arrangement and spacing of piles. The results of this study can be used by engineers to optimize the design of bridges and determine the zones around piles for scour protection.

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