## 5 Discussion
In contrast, the scatter points for P5 and P7 are distributed across both Region A and Region B, highlighting the influence of rainfall on deformation. This suggests that the reservoir water level and rainfall jointly control deformation velocity in the middle and rear sections of the landslide. This observation aligns with the association rules for the high-level deformation phase presented in Tables 3 and 4, where rules involving moderate-to-heavy rainfall are also evident. Furthermore, the scatter points for P5 and P7 in Regions B and C indicate that deformation velocity under medium-to-low reservoir water levels is generally higher than that under high reservoir water levels, reflecting the significant attenuation of the rainfall effect seen under high water levels. This pattern is consistent with the results from Rule 2 in Table 3, further validating the accuracy of the association rule mining results presented in this study. Figure 10: _Cont._  
Over time, the deformation velocities at P2, P5, and P7 (Figure 11) reveal that the peak values of the displacement velocity curves typically emerge during the water level drop or the stable-fluctuation phase following a decline to low levels. A comparison of the trends around the peak values indicates that the variation trends at P5 and P7 are largely consistent, demonstrating a high degree of agreement. In contrast, the variation trend at P2 diverges from that at the other two monitoring points in most cases, with the peak deformation velocity occurring later than at the others. These results further confirm that the reservoir water levels exert relatively uniform influence across the landslide; a decline in reservoir water level under medium-to-low levels can significantly accelerate overall landslide deformation, while high reservoir water levels and rising water levels can somewhat suppress deformation. Rainfall has a negligible impact on deformation at the front of the landslide, but positively affects the middle and rear sections. Additionally, there is a gradual increase in deformation from the rear to the front, indicating that the impact of rainfall infiltration is relatively weaker, with reservoir water level fluctuations playing a dominant role in accelerating landslide deformation. Several terms have been defined and used to describe the movement pattern of landslides, such as retrogressive, thrust, successive, etc. [41]. Retrogressive-type deformation is characterized by movement being initiated at the front of the landslide due to erosion or load, with the deformation gradually increasing from rear to front. Thus, it can be inferred that the movement pattern of the Huangtupo No. 1 riverside sliding mass is typically retrogressive, where periodic fluctuations in the reservoir water level trigger stress adjustments in the front of the landslide, leading to instability and creeping. These factors in turn induce sliding at the middle and rear sections, resulting in retrogressive-type deformation (Figure 12a), similar to what was observed in the Quchi landslide within the TGRA [42]. Based on the proposed movement pattern of the No. 1 riverside sliding mass under the influence of reservoir water levels and rainfall, the mechanisms of landslide deformation can be further elucidated as follows:  
1. The influence of reservoir water levels is characterized by the following features: (i) a decline in the reservoir water level reduces the hydrostatic pressure on the landslide, decreasing the normal pressure \(\sigma\) on the sliding surface, thereby reducing the resistance force \(\tau_{f}\). This increases the tendency for the sliding mass to slide  
Figure 10: Relationship of monthly deformation velocity at monitoring points in (**a**) P2, (**b**) P5, and (**c**) P7 with rainfall and water level. downward along the sliding surface.