Channel morphology and flow structure of an abandoned channel under varying stages

Abstract

Abandoned channels are those channels left behind as meandering rivers migrate over their floodplains and remain among the most enigmatic features of the riverscape, especially related to their hydraulics and geomorphology. Abandoned channels are being considered and implemented as restoration and rehabilitation strategies for large rivers but we do not yet have a sound understanding of their hydromorphodynamics. The overall objectives of this work were to assess the bed morphology and flow structure of a large, dynamically connected abandoned channel (e.g., the channel is inundated during annual or decadal floods through bank overflow) under varying stages. Here we document the hydromorphodynamics of an abandoned channel during 3.4, 9.2, and 37.9 return interval discharges using an acoustic Doppler current profiler. Flow separation was observed along the channel entrance during the lowest flow surveying campaign but was not seen during the higher flow campaign. Width to depth ratio and channel width at the exit both progressively decreased from the first surveying campaign, despite the final campaign having the highest measured discharge. Large zones of flow stagnation and recirculation were observed, with depth‐averaged velocity vectors not aligning in one direction, in the abandoned channel where water from the entrance was meeting water coming up from the exit during moderate discharges. The abandoned channel has been maintained for at least 25 years due to its low diversion angle and it being perched above the Kansas River. Results of this study provide insights of how flow hydraulics and physical characteristics of abandoned channel change under varying stages.

Morphologic adjustments of actively evolving highly curved neck cutoffs

“…A considerable amount of work has been done on meandering river cutoffs, ranging from the long-term behaviour and organization of meandering rivers (Stolum, 1996(Stolum, , 1998Hooke, 2004;Camporeale et al, 2005Camporeale et al, , 2008Constantine and Dunne, 2008;Micheli and Larsen, 2011), mechanisms of cutoff initiation (Ratzlaff, 1981;Gay et al, 1998;Constantine et al, 2010b;Grenfell et al, 2012Grenfell et al, , 2014, rates of infill and sedimentology of oxbow lakes and floodplain alluvial architecture (Petersen, 1963;Erskine et al, 1982;Bridge et al, 1986;Piégay et al, 2002;Brooks and Medioli, 2003;Wren et al, 2008;Citterio and Piégay, 2009;Toonen et al, 2012;Dieras et al, 2013;Ishii and Hori, 2016), cutoff types and distribution within meandering rivers (Lewis and Lewin, 1983), hydrodynamics of cutoffs and the abandoned channel (Constantine et al, 2010a;Le Coz et al, 2010;Zinger et al, 2013;Costigan and Gerken, 2016;Richards et al, 2018), and morphologic changes following cutoff (Johnson and Paynter, 1967;Mosley, 1975;Gagliano and Howard, 1984;Hooke, 1995;Fares, 2000;Fuller et al, 2003;Han and Endreny, 2014). Based on the work mentioned above, several factors can be identified that provide first-order constraints on the morphologic evolution of meander cutoffs, namely (1) length of channel removed via...…”

Characterizing sedimentary processes in abandoned channel using compositional data analysis and wavelet transform

“…Meandering channels are omnipresent features of the Quaternary fluvial system. Abandoned channels are distinct meandering sub-environments that result from complex channel migration over the floodplain (Shen et al 2021); they develop through consecutive processes of cutoff initiation, plug bar formation, and channel disconnection (Costigan and Gerken 2016;Sedláček et al 2019;Ielpi et al 2021). Therefore, understanding abandoned channels' sedimentary processes can contribute significantly to understanding Quaternary fluvial systems.…”