## 4 Results and Analysis
### Evolution of River Planform Morphology
#### 4.2.1 River Width
(**a**) The overall schematic diagram from Cross-section AA to Cross-section OO. (**b**) Schematic diagram of Cross-section AA. Cross-section AA is located near the Xinjaman Bridge, which belongs to the typical section of the artificial building interference Cross-section. (**c**) Schematic diagram of Cross-sections CC, DD, and EE, located at the apex of the bend and the transition section of the Cross-section, belonging to the key geomorphic unit’s typical cross-section that significantly affects the river channel morphology and evolutionary process. (**d**) Schematic representation of Cross-sections II, JJ, and KK, typical of Cross-sections in areas where anthropogenic activities have had direct or potentially significant impacts on stream bank stability and channel morphology. Figure 7: Width changes of typical cross-sections: (**a**) cross-sections BB, CC, EE, FF, and MM; (**b**) cross-sections AA, II, JJ, KK, and OO; (**c**) cross-sections DD, GG, HH, LL, and NN. As shown in Figure 7a, Type I cross-sections exhibited a significant contraction trend from 1993 to 2024, with a contraction rate ranging from 62.1% to 79.5%. These cross-sections are primarily located in the transitional sections of river bends (Figure 6). The contraction mechanism of the cross-sections is primarily driven by the water-sediment dynamic differentiation in river bends. The concave bank undergoes continuous lateral erosion, leading to shoreline retreat and threatening the safety of adjacent farmland and villages, thus necessitating the intervention of artificial bank protection measures to limit channel widening. In contrast, the convex bank experiences a significantly higher deposition rate than the erosion intensity of the concave bank due to reduced flow velocity, sediment deposition, and the root-induced stabilization effect of vegetation, driving an overall narrowing of the cross-sectional morphology. The \"Recent Comprehensive Management Plan for the Tarim River Basin\" began implementation in 2001, and by 2011, the plan entered its final stage. After 2011, the implementation of bank protection projects and flow regulation, along with other systemic management measures, effectively slowed down the dynamic evolution of the river, and the lateral instability of the riverbed was brought under control [52]. As shown in Figure 7b, the morphological evolution of Type II cross-sections exhibited a non-steady \"expansion followed by contraction\" pattern. This is because such cross-sections are mainly located in areas with dense hydraulic engineering structures and river evolution-sensitive zones (see Figure 6). The temporal and spatial variations of these cross-sections are primarily attributed to the dual disturbances of human activity interventions and extreme hydrological events on the hydrodynamic conditions. At Cross-section AA, which is predominantly influenced by human activities, the construction of the Xinqiman Bridge (2007-2008) altered the local flow regime, triggering erosion along the right bank and sediment deposition on the central shoal of the left bank. As a result, by 2018, the river channel had narrowed to 37.9% of its original width. Cross-section OO widened from 1993 to 2006, reaching a peak width of 1246.6 m in 2006, driven by sediment-water separation in bends. However, due to water diversion upstream and bank-protection projects, the channel width reduced by 56.6% to 541.5 m by 2024. Affected by the high runoff event in 2002 (runoff volume of 5.04 \(\times\) 10\({}^{9}\) m\({}^{3}\) and sediment load of 2.1823 \(\times\) 10\({}^{7}\) tons), the river channel near the upstream Yueliangwan Scenic Area Reach underwent meander cutoffs and channel straightening. This morphological change led to a significant increase in downstream flow velocity, triggering severe erosion. Consequently, Cross-sections II, JJ, and KK reached their maximum widths of 877.9 m, 915.7 m, and 1458.2 m in 2006, 2012, and 2013, representing increases of 61.1%, 77.2%, and 2.1%, respectively.