## 4 Results and Analysis
### Evolution of River Planform Morphology
#### 4.2.1 River Width
Subsequently, with the weakening of hydrodynamic forces combined with natural adjustment processes, the channel widths at these sections contracted by 75.9%, 18.2%, and 63.3% by 2024. The phenomenon reveals the differentiated driving mechanisms of short-term intense disturbances (such as engineering interventions and flood-driven channel cutoffs) and long-term water-sediment equilibrium processes in the morphological adjustment of river channels. As shown in Figure 7c, Type III cross-sections are located at river bends and transition sections (Cross-sections DD, GG, LL, and NN), as well as in sensitive zones of river evolution (Cross-section HH). The channel width at Cross-sections DD and NN remained stable, primarily due to the combined effects of homogeneous lithology along both banks, flat terrain, and a low stream gradient. Clay with strong erosion resistance suppresses lateral erosion. The straight river channel and low flow velocity weaken the lateral erosive force, maintaining transverse stability. Cross-section LL showed a 175.3% widening from 1993 to 2017. This was mainly due to concave-bank erosion from lateral circulations in bends. The average lateral migration rate was 18.7 m/a. After 2017, bank-protection projects reduced the erosion rate to 4.2 m/a, showing that human intervention effectively controlled the river's lateral migration. Cross-section GG experienced a 44.1% widening from 1993 to 2015 due to lateral circulation erosion. Continued erosion led to a narrowing of the meander neck, and in 2016, a high runoff (with a runoff of 5.242 \(\times\) 10\({}^{9}\) m\({}^{3}\) and sediment transport of 2.2696 \(\times\) 10\({}^{7}\) tons) breached the neck, resulting in a channel cutoff and straightening. The new channel showed a widening trend under the erosive action of flowing water from 2017 to 2024. Cross-section HH exhibited an evolution characteristic of \"shrinkage followed by expansion\". From 1993 to 2015, width reduction occurred due to an imbalance in water and sediment transport (similar to the mechanism observed at profile EE). However, in 2016, a high runoff upstream caused a channel cutoff and straightening, which triggered an increase in downstream hydrodynamic forces, driving continuous widening of the profile. By 2024, the width had reached 1264.5 m.  
In the Xinjaman-Kelelik section of the Tarim River, the main causes of shrinkage are the strong siltation of the convex bank due to the weakening of hydrodynamics and vegetation sand fixation (net siltation of 7.72 km 2 on the north bank), and the limitation of the artificial revetment project on the erosion space of the concave bank (net erosion of 4.49 km 2 on the south bank). This \"deposition-dominated shrinking\" model is different from the erosion-deposition dynamics observed by [PERSON] [13] in the Tana River, which highlights the unique morphological constraints and contradictions of rivers in arid areas under the high-intensity agricultural development (water diversion and bank protection) on both sides. The aggravation of undercutting and the rise in the water level (the increase of flood risk in the flood season) caused by shrinkage are new challenges in river management in arid areas. It is necessary to draw lessons from [PERSON] [34] and others in the regulation of water and sediment to seek a more precise balance between the method of artificial flood and sediment discharge in the Colorado River and the layout of revetment engineering, which is very important to ensure the safety of water diversion sluice and downstream ecological water conveyance, as noted by [PERSON] [25], 2007.