Landslide risk assessment and analysis of its causes on the new Sardasht-Baneh road between Sardasht and Darsavin

Communication networks are exposed to many and varied environmental risks due to their spatial extent and placement in environments with different specializations. One of the important natural hazards that threaten communication roads, especially in mountainous areas, is slope instability and landslides. The instability of the slopes during the construction of roads shows more frequency due to disturbing the balance of the slopes. Therefore, the identification and analysis of landslides in communication networks and roads can be very effective considering the hazardology aspect of these environments and geographical spaces. The studied route is a part of Baneh-Sardasht road between Sardasht and Darsawin. Part of the route of this old road was changed due to the new Sardasht (Kulse) dam that was built on the Zab river. Considering that various factors and parameters effective in the occurrence of geomorphological processes such as landslides react and act in different ways on the surface of geomorphological units, Analyzing the geomorphic changes of the study path from the perspective of landslides and determining the role of various effective parameters in creating this process is one of the main issues of this research, which has been systematically evaluated and analyzed.

The general method of this research was based on theoretical and library studies along with multiple field studies as well as statistical and software analyzes based on the fuzzy model. For this purpose, topographical and geological maps of the region as well as Aster and Landsat8 satellite images, GPS device, laser meter, Google Earth images, Arc GIS 10.3 software and spss18 software have been used. The model used in this research was the fuzzy model. First, effective parameters in landslides were identified, then they were fuzzified using fuzzy membership functions. In this research, the linear membership function is used, which has 4 parameters that determine the shape of the function. First, layers were created for the effective variables in domain instability, then in order to determine the membership of the layers in the degree of slope instability, the fuzzy membership function of each layer in the model, based on the type of relationship that each parameter has with slope instability in the study area and based on the relationship (Graeme, 1994) was determined. In this method, the area under the curve (ROC), with values between 0.5 and 1, is used to evaluate the accuracy of the desired model. The ideal model shows an AUC value close to 1, while a value close to 0.5 shows the inaccuracy of the model.

The final results of fuzzification of the variables showed that 16 variables were effective in creating instability and landslide hazards with different degrees. In connection with the zoning of landslide risk and its analysis, zoning and analysis was done based on Gamma 0.9. The results showed that the majority of the first part of the road from Sardasht to the Three- Way Qalte road and the second part of the Three- Way Qalte road up to Briso village (the new road) are located in the zone with medium to high and very high sensitivity. The results showed that the lowest level of sensitivity is in the third section, which is caused by the less influence of the effective variables, especially the role of lithology and the morphological unit, along with the increase in the distance from the effective variables, such as the distance from the river and fault, etc. The results of the analysis showed that the value of the area under the curve is equal to 0.811, which indicates the accuracy and efficiency of the used model. The overall results showed that the second part has the highest rate of landslides and the third part has the lowest rate of landslides, while the rate of landslides is high in the first part. The available results are in good agreement with the prepared landslide risk map in most parts, which indicates the accuracy of the study.

The mentioned research was related to the evaluation and zoning of landslide risk in a part of the Sardasht-baneh road centered on the new road. The final analysis showed that in the first boa, the role of variables of height, slope, precipitation and flow power in the process of slope instability corresponding to the road surface was significant. In the second part, the role of rainfall variables, distance from the road, distance from the fault and lithological conditions have been very effective in the instability process. The second part has shown a typical example of instability in the last few years, which indicates the landuse change in line with the construction of a new road after the construction of the Sardasht (Kulse) dam, which is on the surface of the sediments of the young terraces and in the immediate vicinity of the river. The greater stability of the third part is also related to the placement on the surface of the sediments of older terraces with greater resistance and also the further development of forest covers. Therefore, it is necessary to identify geomorphic units and determine their assignments, in other words, to recognize the form and process in environmental activities by humans.