This work explores the potential of UAV imagery to map grain-size distribution (GSD) of 12 well-preserved braided reaches of the Southern French Alps and Prealps. A strong calibration curve has been developed to predict the grain-size from photogrammetric point clouds. Grain-size calibration has been obtained using 129 close-range photos of 1 m² homogeneous grain-sizes patches computed on Digital Grain Size (Buscombe, 2013). The D50 of each photos was then fitted with the mean roughness height (Vázquez-Tarrío et al., 2017). Distributed grain-size maps of the D50 can be produced by rasterizing the average surface roughness in a 1 m pixel and applying the calibration curve for each pixel. The procedure has potential for rapid and con-tinuous GSD characterization over braided reaches. Qualitative examination of a grain-size map shows great correspondence with sedimentary mosaics visible on SfM ortho-images, even in sub-merged conditions. Therefore, it allows for characterizing morpho-sedimentary signatures of braided reaches, which can have important applications for management of braided rivers.