This study explores the link between spatial variability within fluvial sedimentary strata and river channel geometry. This link is then used to determine the macrodispersion coefficients for solute transport in groundwater flow in river deposits. In doing that we combine concepts from sedimentology, geostatistics, and the stochastic-Lagrangian theory of subsurface transport. It is proposed to analyze the spatial variability of river sediments in terms of transition probabilities. The transition probabilities can be determined from the averages and variances of the lengths of stratasets and their volumetric fractions using concepts developed by Carle and Fogg (1996) and Ritzi (2000). Strataset length scales are shown to correlate well with the geometry of the river channel and its bed forms and can be determined indirectly from aerial photogrammetry, and, more directly, through surface ground penetrating radar surveys. Stratal dimensions can also be related, using Lagrangian transport analysis, to macrodispersivity of subsurface transport. This allows relationships between the geometry of river channels and subsurface transport parameters of associated fluvial deposits. For demonstration the longitudinal macrodispersivity in a compound bar deposit in the gravelly, braided Sagavanirktok River was investigated.