Differential bank migration and the maintenance of channel width in meandering river bends

Abstract

AbstractComparison of three bare-earth lidar data sets along 30 consecutive river bends on the Trinity River in Texas, USA, shows that differential migration of river banks in a channel bend counterbalances past bank migrations so that a statistically steady-state channel width is maintained. Two difference maps created from lidar flown in 2011, 2015, and 2017 capture this temporal variability in the relative amounts of inner versus outer bank migration. In 20 of the studied river bends, channel narrowing during 2011–2015 was counterbalanced by widening during the second interval, or vice versa. Only four bends recorded significant (>1%) progressive change in channel width during both measurement periods. Each of these four bends recorded progressive channel narrowing that was connected to floodplain complexity associated with past bend cutoffs or tributaries. Subaerial volumes of sediment deposited on inner banks of bends were smaller for 2015–2017 than for 2011–2015, while erosional volumes associated with the outer banks were similar despite 2015–2017 having had almost twice the number of days under flood conditions. Over time, channel width for the river appears roughly constant because differences in outer and inner bank migration at one time are counterbalanced by compensating differences at a later time. For the Trinity River, this compensation happened over time spans as short as 2–3 yr and would lead to the appearance of invariant channel width at the decadal scale. Tighter river bends with relatively smaller radii of curvature have smaller magnitudes of width change compared to broader bends with larger radii of curvature.