While barchan dunes are traditionally associated with aeolian environments, recent efforts now highlight the emergence of barchans in subaqueous environments as well, particularly in rivers. To this end, herein the flow associated with interacting barchan dunes is quantified in the laboratory as a means of understanding a range of morphodynamic issues associated with their evolution. The interaction between barchans of different sizes produces complex processes such as collision, amalgamation and breeding. In this study, idealized, fixed physical models are utilized to permit accurate interrogation of the flow with high-resolution planar particle image velocimetry. Specific simplified geometrical configurations of two fixed barchan dunes in tandem reveal the flow modifications induced by dune proximity as compared to the baseline case of flow around an isolated dune. Initial measurements focused on the latter, followed by measurements of several tandem configurations, while future efforts will focus on configurations which replicate sequential stages in a dune-dune collision.