Evolution of the mid-channel bars in the middle and lower reaches of the Changjiang (Yangtze) River from 1989 to 2014 based on the Landsat satellite images: impact of the Three Gorges Dam

Three-decadal dynamics of mid-channel bars in downstream of the Three Gorges Dam, China

“…As an essential geomorphic unit and component in fluvial system, MCBs dynamics directly influences river's morphological evolution and sediment archiving through their interaction with the flow and sediment transport (Ashworth, 1996;Hooke, 1986;Xu, 1997;Wintenberger et al, 2015). Therefore, MCBs dynamics under the context of damming intervention are considered as special importance in maintaining the stability of river channels (Lou et al, 2018;Sanford, 2007) and ecosystem functions (e.g., biodiversity and habitat providing) of the related hydro-ecosystems, including the island ecosystem, adjacent riverbed and wetland (Tonkin et al, 2018;Tabacchi et al, 2009).…”

“…Generally, the dynamic behavior of single MCB in short term tends to be less informative (Xu, 1997). When considering the long-term and long-reach river at a given frequency of discharge, the MCBs, however, might illustrate some statistical characteristics of dynamic behaviors, and thus remarkable variations between different MCBs can be observed (Lou et al, 2018;Wintenberger et al, 2015). Besides, it is possible to explore the longitudinal and temporal dynamics of MCBs, to reveal the response of bar development to the associated impact factors (e.g., damming, water flow, sediment load, and boundary conditions), and eventually, to project the MCB evolution in the future scenarios (Xu, 1997;Dai and Liu, 2013).…”

“…The survey in very early 1980s found hundreds of MCBs with a total area over 1000 km 2 in the downstream of the TGD (downstream of Yichang) (Sun, 1984). These MCBs are often considered as important land resources for channel dredging, habitat providing, and even agricultural development and urbanization, depending on the areas and geographical conditions (e.g., stability, vegetation and soil) (Lou et al, 2018). Over the past decades, the hydrodynamics in this reach, however, experienced huge changes due to various anthropogenic activities, and the most significant influence is the construction of the world's largest dam TGD (Gao et al, 2013a;Hu and Hou, 2015).…”

“…Since 1980s, researches on MCBs dynamics in the context of long reach and long-term temporal span, however, are paid increasingly wider attentions (Hooke and Yorke, 2011;Wintenberger et al, 2015), thanks to the rapid development of Remote Sensing (RS) technology and the sophisticated requirements for river regulating (Baki and Gan, 2012;Gao et al, 2013b). Among these studies, the common observations are that the area and number of MCBs tend to decrease due to the dam-induced sediment supply reducing (Freyer and Jefferson, 2013;Wang et al, 2018a;Raška et al, 2017;Lou et al, 2018). In other cases, however, different dynamical patterns have been observed.…”

“…Most of the topics are focused on the changes in flow and sediment regime and channel morphology (Han et al, 2017;Lyu et al, 2019;Yang et al, 2011). However, only few works are conducted on the MCBs dynamics using time-series RS images (Gao et al, 2013b;Wang et al, 2018a;Lou et al, 2018;Wang et al, 2018c). For example, in the immediate downstream of the TGD, the total area of MCBs extracted from Landsat images reduces drastically by 19.23% from 2003 to 2016, accompanied with an increase in water surface width (Wang et al, 2018a).…”