## 2 Study Area  
The Yangtze River, ranked as the world's third-longest river with an approximate length of 6300 km, is commonly segregated into upper, middle, and lower reaches, delineated according to distinct hydrological attributes and geographical settings [44]. The MYR encompasses a \(\sim\)955 km stretch between the Yichang and Hukou reaches, situated immediately downstream of the TGD, and incorporates floodplain-type lakes, such as Dongting and Poyang [45] (Figure 1). The regional climate of the MYR is characterized by a subtropical monsoon climate, with annual precipitation levels ranging between 1000 and 1600 mm and an average annual temperature of 16-18 \({}^{\circ}\)C [46]. The topography in the MYR is predominantly composed of mountains, hills, and plains. The highest elevation is situated in the mountains of western Hubei, while the lowest is found within the central plains, with mountains and hills constituting over 50% of the landscape. The terrain exhibits a west-to-east gradient, transitioning from higher to lower elevations, with an average altitude of approximately 1497 m. The observed flora encompasses 36 species of annual herbs (e.g., Polypogon fugax), 34 varieties of perennial herbs (e.g., Phragmites communis), 4 types of trees (e.g., Pterocarya stenoptera), and 3 classifications of vines (e.g., Cayratia japonica) [47]. The MYR predominantly exhibits a meandering channel configuration, characterized by numerous bars and a riverbed composition that progressively transitions to finer grain sizes in the downstream direction [48].  
Based on local geographical contexts and channel patterns, nine sub-reaches were demarcated, including Yichang-Zhicheng, Zhicheng-Majaidian, Majaidian-Shashi, Shashi-Shishou, Shishou-Jianli, Jianli-Chenglingji, Chenglingji-Hankou, Hankou-Jiujiang, and Jiujiang-Hukou (Figure 1). Sediment and flow fluxes within each sub-reach were assessed at 10 hydrometric stations. For the analysis, 16 relatively large bars (with an area exceeding 1 km\({}^{2}\)) were selected (Figure 1, Tables 1 and 2). We used ArcGIS Pro to generate maps in this study (Esri Inc., Redlands, CA, USA, (2022). ArcGIS Pro (Version 3.0.2)).  
\begin{table}
\begin{tabular}{l l l l l l l l l l l l l} \hline Sub-reach number & 1 & 2 & 3 & 4 & 5 & 6 & 7 & 8 & 9 & \\ Included & Yichang- & [PERSON] & Mijaidan & Shashi & Shishou- & [PERSON]- & [PERSON] & [PERSON]- & [PERSON]- & & \\ reaches & [PERSON] & [PERSON] & [PERSON] & [PERSON] & [PERSON] & [PERSON] & [PERSON] & [PERSON] & [PERSON] & & \\ \hline Hydrometric station & 1 & 2 & 3 & 4 & 5 & 6 & 7 & 8 & 9 & 10 & & \\ number & & & & & & & & & & & & \\ Hydrometric station name & & [PERSON] & [PERSON] & [PERSON] & [PERSON] & [PERSON] & [PERSON] & [PERSON] & [PERSON] & [PERSON] & Hukou & \\ \hline Bar number & 1 & 2 & 3 & 4 & 5 & 6 & 7 & 8 & 9 & 10 & 11 & 12 & 13 & 14 & 15 & 16 \\ Bar name & [PERSON] & [PERSON] & [PERSON] & [PERSON] & [PERSON] & [PERSON] & [PERSON] & [PERSON] & [PERSON] & [PERSON] & [PERSON] & [PERSON] & [PERSON] & [PERSON] & [PERSON] \\ \hline \end{tabular}
\end{table}
Table 1: Essential information on 9 sub-reaches, 10 hydrometric stations, and 16 bars in the Middle Yangtze River (MYR).