Evaluating the relationship between channel and scroll bar properties in meandering rivers with migrating chute channels

Abstract:

Scroll bars, curvilinear ridges of sediment deposited as channels migrate laterally, are quintessential features of meandering river environments. Despite their prevalence, it is still unclear exactly which variables control the spacing, height, and curvature of scroll bars, and in turn how these properties record channel migration histories. In this study, we test the relationship between channel and scroll bar geometries in river systems with laterally migrating chute channels that deposit their own scroll bar packages. These chute channels are two to ten times narrower than the associated main channels, allowing us to test the relationship between channel dimensions and scroll properties within each system. We use lidar- and SRTM-derived DEMs to calculate the spacing, curvature and relief of scroll bars in multiple chute-channel-dominated river systems with a range of channel sizes, slopes, and water and sediment discharge regimes, including the Lower Mississippi River (USA), the Red River (USA), the Arkansas River (USA), the Yukon River (USA), and the Strickland River (Papua New Guinea). Results from each case study show that the chute channel scrolls have similar spacing and relief to the main channel scrolls, even though the chute channels have smaller channel dimensions. For example, in the Red River, median spacings are statistically indistinguishable for chute channel (20-85m) and main channel (22-95m) scrolls, even though the chute channels are up to 10 times narrower than the main channels. However, main channel scrolls have consistently higher curvature (for example, in the Mississippi River, width-normalized radius of curvature values for the main channels range from 1.43 to 4.87, whereas chute channel scrolls are much straighter (Rc values ranging from 4.75 to >100)). Additionally, there is no correlation between curvature and scroll bar spacing for main and chute channels. Overall, these results suggest that, in multiple different meandering river systems with significant chute channel development, scroll bar spacing and relief is not controlled by formative channel width or curvature; other variables, such as discharge regime or substrate type, may be the primary controls on scroll bar properties.