Risk Assessment of Geological Hazards in the Alpine Gorge Region and Its Influencing Factors: A Case Study of Jiulong County, China

By inergency On Feb 27, 2024

1. Introduction

Geologic hazards are geodynamic activities or phenomena, such as landslides and mudslides, that are formed by the interaction of natural or human-made factors and cause a loss of human life and property and environmental damage [1,2]. Geohazard risk evaluation mainly studies the probability and distribution of the occurrence of geohazards due to the combination of multiple influencing factors in a certain area [3,4]. The Alpine Gorge region in southwestern China, with its abundant rainfall, steep topography, and active tectonic movements, is the most vulnerable area to mudslide disasters in China [5,6]. Geological hazards often have serious consequences, causing social and economic disruption, destroying the environment, and causing enormous losses of life and property, with serious implications for the sustainable development of the region [7,8,9]. In order to mitigate the losses resulting from geohazards, geohazard risk assessment emerged as a major area of interest for academics and a crucial component of global catastrophe prevention and mitigation plans [10,11,12,13]. However, the systematic analysis and research on the evaluation of the risk of geologic hazards in an Alpine Gorge region near Sichuan and Tibet and the factors affecting them are not thorough enough. Therefore, conducting a risk assessment of mountain geohazards in the Alpine Gorge region of Sichuan Province and an examination of the elements that influence them is extremely important, both theoretically and practically.

Currently, with the rapid development of geographic information system (GIS) technology, people have conducted much research on geohazard risk assessment and achieved fruitful results [14,15]. Scientific and accurate geohazard risk assessment is the key to the research of geohazard prevention and control. A large number of scholars carried out in-depth research and practice in this regard [16,17]. In terms of research content, the analysis of the key factors and the best combination of the main influencing factors in the formation of geohazards is relatively insufficient. From the perspective of research methods, the development trend of geohazard risk evaluation methods evolved from qualitative methods to quantitative methods [10]. The most popular ones are the Analytic Hierarchy Process (AHP) evaluation system [18,19,20,21], Information Value (IV) [22,23], Logistic Regression (LR) [24,25], Artificial Neural Networks (ANN) [26,27], Random Forest (RF) [28,29,30], and so on. All of the evaluation techniques described above have limitations and cannot fully capture the geographical pattern of geohazards in the Alpine Gorge region and their affecting factors. To directly represent the degree and severity of geological hazard risk in the research region and avoid natural catastrophes, many academics examine the geological hazard risk assessment through the comparison of various models [31,32] or improve a single model to achieve higher accuracy [33]. However, all of them have certain limitations, mainly focusing on a certain defined area as the main research subject and rarely studying a certain type of area from a macroscopic point of view. In order to meet the needs of sustainable development and environmental improvement in the future, future research should pay more attention to the difficult geological elements that are seldom studied at present, and this will be an important research trend [34,35].

In summary, this study takes Jiulong County, Sichuan Province, as the study area, analyzes the spatial and temporal distribution characteristics of geologic hazards in the Alpine Gorge region and their influencing factors by comparing three different models, and arrives at the best applicable model for evaluating the risk of geologic hazards in the Alpine Gorge region by comparing the Receiver operating characteristic (ROC) curves of the three algorithms. Finally, disaster prevention and mitigation countermeasures are proposed based on the evaluation results to develop effective disaster prevention strategies for local governments to ensure environmental safety and ultimately promote sustainable regional development.

3. Results

3.1. Characteristics of the Temporal Distribution of Geologic Hazards

Figure 3 represents the distribution of the number of geologic hazards by month in Jiulong County during the period from 1999 to 2020, where yellow, blue, and red correspond to debris flows, collapses, and landslides, respectively. Statistics show that when the annual rainfall is less than 920 mm, the proportion of earthquake disasters is 22.85%. When the annual rainfall is greater than 920 mm and less than 940 mm, the proportion of earthquake disasters is 41.08%. When the annual rainfall is greater than 940 mm, the proportion of earthquake disasters is 36.7%. In recent years, precipitation has played an important role in geological disasters. As one of the important inducements of regional geological disasters, its influence on geological disasters in Jiulong County is mainly based on the dividing line of annual rainfall 920 mm. Years greater than this value are more prone to geological disasters. Moreover, the occurrence of geological disasters has a certain fluctuation. During the period from May to August every year, geological disasters have an overall increasing trend, which is positively related to the monthly rainfall. The increase in precipitation destabilizes the slopes and increases the possibility of geologic hazards. The possibility of geohazards is higher in areas with relatively high rainfall because rainfall causes rainwater to erode the geotechnical body, which increases the gravitational force on the material on the slope, leading to an increase in the downward force. At the same time, the water content also increases, the geotechnical body becomes softer, the shear strength becomes lower, and the stability decreases and, ultimately, induces geohazards.

3.2. Characteristics of the Spatial Distribution of Geologic Hazards

The interplay of elements, including the natural environment and human activity, affects the formation of geologic hazards. Due to the complex geological conditions in the whole study area, geologic hazards are characterized by a large number and wide distribution. As analyzed in Figure 2, the geologic hazard sites in Jiulong County are mainly distributed between elevations of 2000 and 2800 m, slopes between 10 and 30°, and slope aspects due east and southeast.

3.3. Analysis of Factors Affecting the Occurrence of Geologic Hazards

Analyzing the causes of geologic disasters can clarify the spatial distribution characteristics of geologic disasters, reduce the losses of geologic disasters, promote sustainable development in the region, and provide a basis for successful disaster prevention and mitigation. The influencing factors of geohazards in the Alpine Gorge region are mainly divided into two aspects, including natural factors and human activity factors. For example, heavy rainfall, as an important natural factor, is the main cause of geohazards such as landslides, avalanches, and mudslides, which, in turn, lead to serious casualties and economic losses; at the same time, since heavy rainfall occurs mostly in May–August, May–August is also the most frequent period of geohazards. From the viewpoint of human activity factors, engineering construction, slope excavation, mining, and other human engineering activities will have a certain impact on the topography and geomorphology. Engineering construction will increase the burden of the slope body, make the slope body lose its original stability, and under the combined influence of various factors, lead to slope instability, thus inducing geological disasters.

Table 3 describes the construction time of hydropower plants in Jiulong County, average annual energy production, etc. The mainstream section of Jiulong River adopts the “one reservoir, five stages” gradient development program, which consists of Xigu Reservoir, Wuyiqiao, Shaping, Pianqiao, and Jiangbian Hydropower Station from top to bottom, and the first-grade tributary of Taca River on the left bank, which consists of two graded hydropower stations, namely, Xieka Hydropower Station and Taca Hydropower Station, from top to bottom. These hydropower plants generate an average of about 150 Billion kwH per year, guaranteeing sustainable development in the region. The water system of the basin is developed in the form of feathers, and the rock layer along the river is strongly weathered, cut, and broken. The stability of the bank slopes is poor, coupled with the frequent development of hydropower along the coast as well as the construction of large- and medium-sized projects, the basin suffers from landslides, avalanches, mudslides, and other geologic hazards, which are becoming more and more serious.

Figure 4 indicates that the annual number of geological disasters that occurred in Jiulong County from 1999 to 2020 will be a disaster year every few years. The number of geological disasters in Jiulong County was higher in 2005, 2008, and 2012, during which several hydropower stations began to be constructed. It can be visualized that in the early stages of hydropower plant construction, geohazards increased to a certain extent. The frequent development of hydropower projects in the Alpine Gorge region makes geologic disasters in the region inevitable, and it is indispensable to analyze the factors affecting geologic disasters in the Alpine Gorge region to guarantee a stable power supply every year, promote economic development, and facilitate the sustainable development of the region.

5. Conclusions and Recommendations

5.1. Conclusions

The temporal and spatial distribution and influencing factors of geohazard risk in the Alpine Gorge region are analyzed based on three different models and validated for comparison. The main conclusions are as follows.

The Alpine Gorge region experiences geological disasters as a result of human activity and the environment working together. The natural environment is mainly reflected in the fact that the development of disasters coincides with the cycle of precipitation, which is mainly concentrated in May–August. Human activities together are mainly reflected in the fact that the years of heavy disasters often correspond to the early stage of hydropower project construction in the Alpine Gorge region. Precipitation and human engineering activities are the main factors inducing geohazards in the Alpine Gorge region.
Geological hazard sites in Jiulong County are mainly distributed between elevations of 2000 and 2800 m, with slopes between 10 and 30° and slope aspects due east and southeast. The high-risk areas are more in the south than in the north, more in the center than in the east and west, and are mainly concentrated in densely populated areas such as rivers and highways.
The IV model, LR model, and RF model can be applied in the risk assessment of Alpine Canyon. The LR model was verified by the ROC curve to be the most accurate and more suitable for the Alpine Gorge region.

5.2. Recommendations

The western part of Sichuan Province is characterized by complex geological conditions, high mountains and steep slopes, complex topography and geomorphology, special climatic conditions, infertile soil, and a fragile ecological environment. The frequent occurrence of geologic disasters and severe disaster situations seriously hinder social and economic development and affect the life and safety of residents, and the development of geologic disaster risk assessment is a need for the sustainable development of the region. Future studies should focus more on the challenging geological elements that are currently understudied. Additionally, to conduct research appropriate for particular global regions, data fusion, processing, and association mining must be investigated to enhance and compare the accuracy of various models.

This study can improve the scientific nature of the government’s geohazard prevention and control strategy formulation, and the specific recommendations are as follows: local governments should formulate targeted regional sustainable development strategies around the core areas with large geohazards; additionally, the government needs to pay more attention to ecological and environmental issues, avoid the impact of human engineering activities on the sustainable development of energy resources in the region, strengthen the awareness of geohazard prevention, and improve preventive capabilities in the development of hydroelectricity and the construction of large- and medium-sized projects. Moreover, the government should improve preventive capacity and increase the frequency of emergency drills during the rainfall season to improve the residents’ awareness of geologic disaster prevention and emergency response. In the case of disasters, timely forecasts and warnings of geologic disasters will be made to reduce the possible hazards caused by geologic disasters.