© 2015 Taylor & Francis Group, London.In river bridges, one of the most common reasons of bridge failures is attributed to excessive local scour around bridge piers and/or abutments. Therefore, it is important to investigate the scouring mechanism around their foundations to assess safety levels of bridges. Many empirical equations have been derived to express the maximum scour depth around single piers. However, the scouring mechanism around the group of piers gets more complicated relative to the case of single piers, such that the available equations become invalid to formulate the interaction of flow structures around piers. In this study, experimental investigation of the temporal variation of scour hole topography around dual cylindrical piers is carried out. To this end, the effects of size of piers and the spacing between them are studied in the range of clear water conditions. The findings of the study will be considered as relevant input parameters needed to characterize scour countermeasures.