The internal architecture of sandbars in modern braided streams has not been adequately documented, especially in medium-scale braided rivers. Identification of the architecture and development of an understanding of the formative processes for these macroforms is important for (1) understanding sedimentation in braided streams, (2) understanding reservoir and aquifer compartmentalization in ancient deposits, and (3) predicting the controls on deposition in similar settings. A 225 MHz GPR survey was conducted within a braided reach of the Wisconsin River near Spring Green, Wisconsin, USA, to characterize the subsurface architecture of a midchannel bar. A 20 × 20 m survey grid consisting...