The Impact of Fluvial Meander Cutoff on Channel-Bend Migration Patterns: Implications for Predicting River Planform Evolution and Deposit Architecture

Abstract:

Meandering rivers are widespread across the surface of Earth and were present on Mars in the distant past. Although it has been shown that channel curvature and substrate heterogeneity exert a strong control on river planform evolution, not much is known about how perturbations of the channel planform affect subsequent channel migration. Fluvial meander cutoffs are common perturbations that significantly modify local channel shape and the adjacent floodplain. While recent work has shown that cutoffs can alter nearby bend migration rates, their impact on subsequent planform migration patterns, or transformational modes (expansion and translation) has not yet been fully explored. Here we use 40 years of Landsat data and more recently collected, high-resolution imagery, in combination with a newly developed, semi-automated digital channel extraction approach to examine the time-lapse evolution of several modern meander-bend cutoffs on the Trinity River near Liberty, TX that occurred circa 1990. Landsat images over cutoff locations between the years 1980-2019 at low-flow stage are used to extract channel banks. Our semi-automated channel bank extraction workflow employs a dynamic time-warping approach to quantify channel bank and centerline migration rates, as well as characterize changes in planform transformational mode upstream and downstream of the cutoff locations. Early results indicate a marked change from pre-cutoff expansion to post-cutoff downstream translation. We relate this transition to the rapid change in local channel curvature and meander wavelength at the cutoff location. A post-cutoff shortened arc length causes the point of maximum migration to fall close to the downstream inflection point, resulting in downstream bend translation. Additional analysis will explore the extent to which adjacent channel bend shape and scale influence post-cutoff planform bend kinematics and how these processes are reflected in the deposits that are left behind. Improved understanding and quantification of the effect of meander cutoffs on subsequent planform evolution in modern river systems has implications for predicting river position through time, understanding modern fluvial channel-belt heterogeneity, and improving stratigraphic interpretations of the rock record.