Impact of embankments after neck cutoff on flow structure of a highly sinuous meandering bend in the Zoige basin

Keywords: Fluvial Geomorphology, River Dynamics, meandering bend, flow structure, cutoff restoration
Abstract Type: Paper Abstract

Abstract

If a highly sinuous meandering bend is restored after neck cutoff, how would flow structure and channel morphology response? This study aims to tackle this issue The studied meandering bend is located in Zoige basin on the eastern Qinghai-Tibet Plateau. It experienced neck cutoff in July 2018. For the purpose of accessing the bend floodplain, an earth embankment was build months, but was quickly breached in 2019, which led to the following establishment of a rock embankment in 2020. We measured the morphodynamic structure of the upstream limb of the bend and the breached cutoff channel in the summer of 2019, 2020, and 2021using ADCP and RTK GPS, leading to the following findings. First, the center of the oxbow channel formed deep pools due to strong bed incision, while the upstream channel was subject much reduced bed erosion. The secondary flows were stronger near the breached earth embankment. Second, the subsequent rock embankment greatly altered flow structure at the entrance of the bend, leading to strong local bed incision, which formed elongate pool along the embankment and the connected downstream bank. Third, the local flow intensity along the embankment was apparently attenuated one year later (i.e., 2021), but the local pool extended downslope gradually. These results suggest that (1) the local flow and channel morphological structures were altered significantly by the restoration of the cutoff bank; and (2) the alteration catalyzed a new pattern of local flows that have reduced flow intensity, such that the rock embankment will remain stable.