Characterizing coarse sediment grain size variability along the upper Sandy River, Oregon, via UAV remote sensing

In this article we evaluate the hypothesis that multiscale observations of fluvial physical characteristics can reveal systematic patterns that enable more detailed analyses of fluvial process, as well as conceptual models relating local conditions to downstream trends. We map the distribution of coarse sediment within 33 gravel bars along the upper Sandy River and analyze the grain size variability at the river segment and bar scales in relation to active channel width. The results show that grain size is inversely correlated with channel width, but that this relationship is only significant for patches located at bar heads. Additionally, bar scale variability in some cases is nearly equivalent to the grain size variability observed within the 12 km reach. This finding indicates that the application of downstream fining models could have limited application on the upper Sandy River at scales finer than a few kilometers.