Depositional patterns of slowly plugging neck cutoffs from core analysis and estimates of bedload transport, White River Arkansas

Authors: RICHARDS, DEREK - Louisiana State University; KONSOER, KORY - Louisiana State University; Langendoen, Eddy; Ursic, Michael - Mick; CONSTANTINE, JOSE - Williams College

Submitted to: Sedimentology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/4/2021
Publication Date: 2/1/2022
Citation: Richards, D., Konsoer, K., Langendoen, E.J., Ursic, M.E., Constantine, J.A. 2022. Depositional patterns of slowly plugging neck cutoffs from core analysis and estimates of bedload transport, White River Arkansas. Sedimentology. 69(2), 568–591. https://doi.org/10.1111/sed.12915.
DOI: https://doi.org/10.1111/sed.12915

Interpretive Summary: Meander cutoffs and oxbow lakes provide important ecosystem services in agricultural landscapes. Little research has been conducted about oxbow lake formation immediately after a meander cutoff occurs and the hydrologic connectivity between oxbow lake and the main channel. ARS researchers in Oxford, MS, in collaboration with researchers from Louisiana State University and Williams College collected sediment cores and measured bed load at two meander cutoffs on the White River, Arkansas. The studied meander cutoffs showed atypical morphological abandonment from the main channel as plugs did not develop and the ends of the meander cutoff, rather planform-driven scour in the main channel resulted in an elevated abandoned meander bend that remained hydrologically connected to the main channel. These findings can be used by farmers to manage riparian water resources and land conservation along dynamic meandering streams.

Technical Abstract: Meander cutoffs and oxbow lakes are very common features of fluvial landscapes that add complexity and diversity to floodplain alluvial architecture and riverine habitats. Neck cutoffs occur when two segments of a meander bend migrate into one another resulting in bank collapse and the formation of a new channel pathway. Following initial cutoff, sediment accumulates within the entrance and exit of the original bend forming plugs that eventually disconnect the abandoned bend from the main channel. While studies have examined the sedimentology of these plugs once they have fully disconnected from the abandoned bend, fewer studies have detailed the sedimentological processes occurring during the early stages following cutoff initiation. Furthermore, recent studies have highlighted the importance that planform geometry plays in the evolution of neck cutoffs. This study examines the spatial depositional patterns of two neck cutoffs on the White River in central Arkansas that remain hydrologically connected to the main channel. Sediment cores were collected in key locations of each cutoff, including the entrance and exit of the abandoned bends, abandoned bend apices, and newly developed cutoff bars in the downstream channel. The cores were logged and interpreted and grain size analyses and loss-on-ignition were performed. In addition to sediment cores, repeat high-resolution multibeam echo sounding surveys were conducted roughly four hours apart to estimate bedload transport rates and patterns of bedload routing through each cutoff. Results from this research are different from previous studies. Sediment core results show a pattern of deposition typically associated with lower diversion angle chute cutoffs instead of higher diversion angle neck cutoffs. Previous research has indicated plugging of abandoned bends drive disconnection from the active channel, however, this research shows disconnection is more associated with the prevention of sediment from being delivered to the abandoned bends is due to flow being pulled away from the abandoned bends and the evolving channel morphology.