![]()
RACR![]()
Application of slope unit for rainstorm-induced shallow landslide hazard zonation in South China
Qinghua Gong, Guangqing Huang & Jun Wang
Guangdong Open Laboratory of Geospatial Information Technology and Application, Guangzhou, China Guangzhou Institute of Geography, Guangzhou, China
Junxiang Zhang
Tourism College, Huangshan University, Huangshan, China
ABSTRACT: In South China, shallow landslides result in enormous casualties and huge economic losses in mountainous regions. The landslide hazard zonation is to offer planners with overview information of landslide prone areas which is very important in disaster mitigation since both disasters drastically increase in recently years. The slope, rock types and land use type were the main controlling factors in the shallow landslide formation process. Based on landslide formation mechanism and characteristics in small watershed region; this paper puts forward a method for landslide hazard zonation. Firstly, this paper selected the slope-unit which contains a set of ground features same in the unit and different from the adjacent units as the basic cell for landslide zonation. The partition and distinguish of slop units were made by the Digital Elevation Model (DEM) and GIS system. Secondly, the index system of hazard assessment of landslide was established by analyzing the factors that affect landslide hazard. Nine variables was imposed to create the landslide hazard risk evaluation map including topography relief, slope, slope aspect, slopeshape, soil type, thickness of weathering layer, road density, construction intensity and NDVI are chosen for landslide hazard. Finally, Landslide hazard zonation by means of GIS automatically was overlaid on the nine data layers of hazard. Through the hazard assessment model for the calculation of degree of hazard, the hazard map was deduced.
Keywords: Slope unit, Rainstorm-induced Shallow Landslide, hazard
1 INTRODUCTION
Extreme rainfall-induced landslides usually gathered in a small watershed caused great harm in South China. Those landslides formation mechanism are essentially different from general rainfall pattern of landslides. Geological environment has a unique regional characteristic in South China. Hazard assessment and management has been recognized as an important component of disaster risk reduction strategy. The risk management of landslides began in the late 1980s and became a popular approach in landslide management in the late 1990s. And the risk zoning has become a hotspot in the field of disaster prevention and control in recent years. Experts and scholars have made many exploratory achievements in landslide risk zoning. Landslide hazard risk zoning developed gradually from qualitative to quantitative, from macro to micro, from two-dimensional to three-dimensional (Jin, et al. 2007; Zhou, et al. 2008; Zhu, et al. 2003; Gao, et al. 2011; Qiao, et al. 2008; Tang, et al. 2011). Most of landslide disasters are small shallow landslides, but the landslide hazards are densely distributed in a small watershed in south China. Because of the unique formation mechanism and characteristics of landslide hazard in South China, the existing landslide zoning method cannot meet the spatial accuracy requirements of landslide hazard zoning in South China. There are four spatial division cells used in landslide hazard zonation including grid cell, administrative zones, river basin and slope cell (Guzztti, et al. 2007). Each of the spatial units has its advantages and disadvantages as shown in Table 1.
Table 1. Advantages and disadvantages of spatial division unit used in risk mapping.
Cell type | Advantages | Disadvantages |
Grid cell | Easy to operate, simple and efficient operation | The grid unit does not reflect the disaster mechanism. The correlation between grid cells and hydrology, geology, topography and other environmental factors is poor. |
Administrative zones | The use of administrative zones for risk zoning is more conducive to administrative management | The use of administrative zones to carry out risk zoning ignores the natural attributes of disasters |
River basin | Using the river basin as a unit for risk zoning can reflect the characteristics and laws of the geological environment | The spatial scale of risk zoning based on river basin is large, which cannot meet the spatial accuracy requirement of small—scale shallow landslide in South China. |
Slope cell | Theoperation process is complex, and requires a higher data accuracy using the slope as the smallest unit for risk division. | The slope cell can reflect the disaster mechanism of the landslide and can meet the precision requirements of the small landslide risk zoning. |
Each landslide is associated with the slope, and each slope has a clear terrain border (Ermini, et al. 2005). The slope has a different terrain feature (terrain, streamline, and slope) with its adjacent slopes (Tian, et al. 2013). And terrain and geological conditions within the slope unit are basically same. Based on the mechanism, the slope cell is identified as the basic cell of disaster risk zoning. Based on the analysis of meteorological, hydrological and human processes and mechanism of rainstorm-induced shallow landslides in small watershed in south china, this paper established a risk assessment index system for rainstorm-induced shallow landslides. The risk evaluation index of each slope unit is calculated, and the database of rainstorm-induced shallow landslide risk analysis based on slope unit was constructed. Finally, the hazard grade of each slope unit is determined by comprehensive hazard index calculation. On the one hand, both the index system and the spatial unit are based on the mechanism of rainstorm-induced shallow landslide formation, and the result of zoning is more objective and scientific. On the other hand, it provides spatial precision for disaster prevention.
2 STUDY AREA AND METHODS
2.1 Study area
The landslide hazard zonation was tested on the Magui town which is located at the south-east of china, with a total area 162 km2 and the elevation ranging from 186 to 1627.3 m. (Figure 1). There are widespread mountains in the study area with complex geological conditions and str...
