## 4 Results and Analysis
### Evolution of River Planform Morphology  
#### 4.2.1 River Width  
The width of the river channel is an important parameter to study the change of river channel plane shape, which affects the flow velocity and sediment transport, directly reflects the lateral erosion-deposition balance of river, and then affects flood control and river bank stability. In order to explore the evolution law of river channel width, the cross-section of the river channel was divided according to the following principles, aiming to capture the key factors controlling the change of river channel plane shape and its spatial heterogeneity. Cross-sections (such as Cross-sections BB, CC, EE, FF, and MM) were preferentially set at the key geomorphological units (corner vertices and transition sections) that significantly affect a river's morphology and evolution process. The bend is the most active area of lateral erosion and convex bank deposition. The section was set at the top of the bend (the strongest erosion point) and the upstream and downstream transition section to capture the influence of curvature change on river width and section shape. Priority sections (such as Cross-sections AA, II, JJ, KK, and OO) were set up in the upstream and downstream of artificial building interference sections (embankments, spur dikes, revetments, bridges, diversions, etc.) to evaluate their effects on river channel narrowing, widening or local erosion/deposition. In areas where human activities have a direct or potential significant impact on river bank stability and river morphology (villages, farmlands), encrypted sections (such as Cross-sections DD, GG, HH, LL, and NN) were used to assess flood control risks and protection needs, as well as the impact of agricultural activities (such as water intake, drainage, bank slope reclamation) on river bank erosion, river morphology and stability. In the stable river reaches (such as a straight, slightly curved section, and a controlled river section) with relatively uniform river morphology, slow evolution or less interference, the section spacing could be appropriately increased, and the channel stability between section EE and FF was the largest, reaching 21.9 km. In the vicinity of bends, bifurcations, man-made buildings and villages/farmlands, the cross-section spacing was significantly reduced by a minimum spacing of 2.6 km to more accurately characterize the complex morphological changes and dynamic processes in these key areas. On the basis of satisfying the above principles, it was ensured that the section could reasonably cover the entire study section from Xinqiman-Kelelik in space. A total of 15 representative cross sections were arranged in the study section (see Figure 6 for details), and the section spacing ranged from 2.6 km to 21.9 km. This non-equidistant layout reflects the non-uniform spatial distribution of the river's geomorphological characteristics, the intensity of human activities, and potential evolution risks. Since satellite imagery cannot obtain the cross-sectional shape of the river channel, this study only analyzes the change of the river channel width based on the river channel plane. Figure 7 shows the annual changes in the width of each typical cross-section. Based on the morphological evolution characteristics and driving mechanisms of the river cross-sections, the typical cross-sections were classified. Cross-sections BB, CC, EE, FF, and MM are categorized as meander-driven water-sediment differentiation types, as shown in Figure 7a,and are designated as Type I cross-sections. Cross-sections AA, II, JJ, KK, and OO are classified as engineering-flood composite disturbance types, as shown in Figure 7b, and are designated as Type II cross-sections. Cross-sections DD, GG, HH, LL, and NN are categorized as mixed evolution types, as shown in Figure 7c, and are designated as Type III cross-sections. Figure 6: Schematic diagram of the cross-section river division in the Xinjaman–Kelelik segment study area.