Investigation of State of Landslide in Tarom Watershed Using Risk-Vulnerability Superimposed Model

Document Type : Research Paper

Authors

• mojgan entezari ¹
• shokoh Esteki ²
• Hamide Gholamhaydari ³

¹ university of isfahan

² university of I sfahan

³ university of Isfahan

Abstract

Highlights

Methodology

Model introduction

The risk-vulnerability superimposed model has been used to evaluate the landslide risk and vulnerability. Designed by the authors of the present research, this model was first used in this research to analyze landslides in Tarom Watershed, Iran.

Different stages of landslide risk and vulnerability assessment by the proposed model are as follows:

• Preparing the required maps and information layers
• Determining weighting factors for different classes of each factor and index (internal weight)
• Calculating mutual weight (external weight) for factors and indices in MS Excel using embedded formulae like pairwise comparison
• Calculating final weight of the factors by multiplying the wrights by the weight of the corresponding class (internal weight × external weight)
• Introducing the final weights of each layer on the maps to come up with a new map with quantitative values of all factors and indices
• Superimposing the layers of all factors contributing to landslide occurrence to prepare a landslide risk map
• Superimposing the layers of all indices contributing to landslide vulnerability to prepare a landslide vulnerability map
• Preparing a layer out of landslide-affected zones (regional landslide map)
• Compositing and superimposing the risk map, the vulnerability map, and the regional landslide map to produce the final map (e., risk – vulnerability map)
• Given the qualitative nature of the risk-vulnerability superimposed map, inputs to the model include the maps that have been extracted, compiled, and analyzed out of Tarom Watershed to finally demonstrate sensitivity of different points across the watershed to landslide. Results of different stages of the risk-vulnerability superimposed model are as follows.

The following factors were considered as effective for landslide occurrence in this research:

• Topography (slope and height)
• Geology
• Precipitation
• Density of streams
• Land use
• Density of faults

Indices affecting the vulnerability:

• Population density
• Construction density
• Road density

Discussion

Analysis of the factors affecting the occurrence of landslide in the watershed and preparing the landslide risk map showed that, in general, the eastern part of Tarom Watershed exhibits a higher risk of landslide. Investigation of the factors contributing to the occurrence of landslide (e.g., high slope, height, heavy precipitation, dense fault system, and petrological characteristics) showed that the landslide risk is maximum in the northeast of the study area. Focusing on the vulnerability, the northern and eastern parts of the watershed were found to be more vulnerable due to the higher density of constructions, roads, and population, where more fatalities and higher financial losses were expected should a landslide occurs.

Conclusion

According to the model output (i.e., risk-vulnerability map), it was figured out that the eastern and northeastern parts of Tarom Watershed are exposed to higher levels of risk and vulnerability. That is, occurrence of a fatal landslide with financial losses is more probable in these areas, as compared to other parts of the watershed. Higher sensitivity of these areas to landslide was found to be linked to the higher slope, petrological characteristics, inappropriate land use, and hydrographic network. Results of the present research showed that 17%, 35%, 23%, 16%, and 9% of the entire watershed area was exposed to very low, low, moderate, high, and very high levels of landslide risk and vulnerability, respectively.

Keywords

• Landslide
• Risk-Vulnerability Superimposed Model
• Tarom
• Watershed

10.22034/gp.2023.54607.3073

Main Subjects

• Geomorphology