Quantification of the relationship between surface morphodynamics and subsurface sedimentological product in sandy braided rivers

This paper presents an integrated dataset of digital elevation models (DEMs) and ground penetrating radar (GPR) surveys from the sandy braided South Saskatchewan River, Canada. Data were collected from the same sites in 2004, 2005, 2006 and 2007, allowing the evolution of the surface morphology to be tied explicitly to its associated depositional record. The occurrence of a large flood in 2005 also allowed the influence of discharge to be assessed with respect to the process-product relationship. The data demonstrated that the morphology of the study reach evolved even with modest discharges and could become organized into planforms that were either more compound bar-dominated or unit bar-dominated. The large flood was a trigger for switching between states and caused more erosion than is normally the case. The GPR surveys quantified the extent to which the subsurface deposits (the ‘product’) were modified by the surface morphodynamics (the ‘process). They revealed that during the large flood there was an increase in the proportion of facies associated with bar margin accretion and larger dune sets. Conversely, in subsequent years these facies became truncated and replaced with facies associated with smaller dune sets. In particular, this analysis showed that unit bars generally become truncated vertically but especially laterally. Thus, they lose the high-angle bar margin deposits and the smaller-scale deposits found on their surfaces. As a result, commonly the only fragments that remain are dune sets, thus making identification of the original unit barform problematic. This unique datasets raises implications for what may ultimately become preserved in the rock record.