# Soil and Rockfill Dams Safety Assessment for Henan Province: Monitoring, Analysis and Prediction
## 5 Discussion
### Correlation Analysis of Reservoir Water Level, Rainfall and Deformation  
The Xiaolangdi Dam was analyzed based on the deformation of five randomly selected points, as shown in Figure 16. The dam deformation trend exhibits a stepped shape. Moreover, the upstream water level of the Xiaolangdi Reservoir undergoes annual cyclical  
Figure 14: (**a**) Deformation at points 10 and 11 at the bottom of Xiaolangdi Dam; (**b**) deformation at points 12 and 13 at the left shoulder of Xiaolangdi Dam; (**c**) deformation at points 14, 15, and 16 at the right shoulder of Xiaolangdi Dam; (**d**) deformation at points 17, 18, and 19 at the floodgate of Xiaolangdi Dam. Figure 15: (**a**) Cross-section A-A1 of Xiaolangdi Reservoir Dam; (**b**) cross-section B-B1 of Xiaolangdi Reservoir Dam. changes. As the water level continuously varies, the dam deformation trend becomes more apparent during high water levels and slower during low water levels. This suggests that the water level plays a critical influence on the deformation behavior of the dam. From the analysis in Figure 16, during the stages of 1\(\rightarrow\)2, 3\(\rightarrow\)4, 5\(\rightarrow\)6, 7\(\rightarrow\)8, and 9\(\rightarrow\)10, the deformation curve slope was steeper, indicating a higher deformation rate. During these stages, the water level of the reservoir is in a state of rising or falling. However, during the stages of 2\(\rightarrow\)3, 4\(\rightarrow\)5, 6\(\rightarrow\)7, and 8\(\rightarrow\)9, the slope of the change curve was small, the deformation rate was slower, and the reservoir water level was in a storage state, causing less significant deformation. This illustrates that the water level has an impact on the deformation of the dam. In addition, during the stage of 9\(\rightarrow\)10, Henan Province experienced an unprecedented extreme weather event with rainfall exceeding the historical maximum of the past five years. The water level of the reservoir has rapidly increased, and the Xiaolangdi Dam has also experienced abnormal deformation with a sharp decrease (slope significantly greater than the previous four years) compared with the same period in previous years. The research area is located near 34\({}^{\circ}\)55\({}^{\prime}\)N and belongs to the warm temperate zone, with a continental monsoon climate throughout the year. It has the characteristics of distinct four seasons, simultaneous rainfall and heat, complex diversity, and frequent climate disasters. Summer rainfall is high, while winter rainfall is small and intermittent. The annual rainfall is concentrated from July to September, with the characteristics of concentrated rainfall and large instantaneous rainfall, which can easily cause short-term rapid rise of reservoir water level, especially in July to September 2021, with an average monthly rainfall of 280 mm. Meanwhile, it can be observed that during the low water level stages 1\(\rightarrow\)2, 3\(\rightarrow\)4, 5\(\rightarrow\)6, 7\(\rightarrow\)8, 9\(\rightarrow\)10, it is in summer, with more local rainfall and a larger slope, resulting in accelerated deformation, as shown in the red box in Figure 16. During the stages of 2\(\rightarrow\)3, 4\(\rightarrow\)5, 6\(\rightarrow\)7, 8\(\rightarrow\)9, when the water level continues to rise, it is in winter. The local rainfall is relatively low, the slope is small, and the deformation slows down. The seasonal characteristics of dam deformation are significant. Therefore, soil and rockfill dam generally presents the deformation law of \"quick summer and slow winter\" with distinctive seasonal characteristics. From mid-June through early July each year, the Xiaolangdi Reservoir opens its gates to discharge water to adjust the water and sediment of the Yellow River basin. During  
Figure 16: Relationship between rainfall, reservoir level, and deformation of Xiaolangdi Reservoir Dam. this period, the reservoir water level drops by approximately 50 m. Figure 16 shows that after the discharge process, the deformation rate of the Xiaolangdi Dam slows down, and a slight uplift occurs.