Prioritizing and Zoning the Factors Affecting the Landslide Model Entropy (Case Study:Bajgiran, Ghochan)

IntroductionLandslide is one of the natural phenomena causing many financial losses and casualties in Iran every year (Kamranzadeh, 2014, p.101). This phenomenon occurs when the force of the materials’ weight is higher than the soil's sheer force (Memarian et al., 2006, p. 105). The Shannon entropy is a function of probability distribution and a standard for measuring uncertainty in the information content of a parameter. In addition, by considering the frequency of the occurrence of the subgroups of that parameter, it shows the heterogeneity level. As a result, it calculates the effect of each parameter on the results of the system (Hosseinpour Mil Arghadan et al., 2014). The purposes of the present study are the selection of criteria and standards, preparation of the digital factors layers, preparation of the landslide hazard zonation map, diagnosis of the high risk points via the Shannon entropy, presentation of the strategies appropriate for preventing possible risks, and solutions to reduce damages in the study area. Bajgiran is the central district of Bajgiran Country and a part Doulatkhaneh Rural District of Ghouchan Township. According to climatological divisions, Bajgiran has a moderate mountainous climate. Moreover, geologically and structurally, it is part of Kopeh Dagh Sedimentary Basin. In terms of stratigraphy, outcrops from the Jurassic rock units to the present era can be observed in the study area.
Materials and methodsIn the present study, first of all, the factors affecting the occurrence of the landslides including height, precipitation, slope, slope direction, slope shape, distance from the waterway, distance from the road, distance from the fault, land cover, and lithology were identified, and the mentioned maps were digitized in GIS. To this end, using the topographic map on a scale of 1:50000, the Digital Elevation Model Map (DEM), factors of slope degree, slope direction, slope shape, height level, distance from the waterway, and distance from the road were prepared. In addition, using the land-use map on a scale of 1:25000, information layers of land use were extracted. Then, to draw the lithological map, the distance from the fault of the geological map on a scale of 1:50000 was used. Finally, to draw the precipitation map, the statistics of the rain gauge stations of five Daroungar, Mohammad Taghi Beig, Aman Gholi, Kikan, Hey Hey Ghouchan, and Bahman Jan Stations were used.
Results and DiscussionAfter converting the criteria into integers and the formation of the initial matrix, the values of Pij and K were respectively calculated via equations 1 and 2. To calculate Ej for each criterion, equation 2 was used. The results are indicated in table 2. In this equation, the value of E is a function of n. For each n, where Pi is equal, the value of E becomes maximum which is statistically calculated via probability distribution of Pi. Then, the uncertainty or the degree of the deviation of each criterion (dj), obtained from the fraction of the value of Ej, from 1 were calculated per each indices effective on landslides of the study area (table 2). After that, using equation 5, the weight of each parameter, used in the entropy matrix of landslides (Wj), including height (0.02113), precipitation (0.031142), shape of slope (0.0116110), slope (0.011342), distance from the waterway (0.045161), distance from the road (0.113401), distance from the fault (0.099871), land use (0.997110), and lithology (0.095148) were obtained. After that, the regional model of the landslide hazard degree in the area was obtained via equation 6. Hi is the landslide hazard degree in the area (equation 7).
ConclusionThe aim of the present study was to prioritize the factors affecting the occurrences of landslides and to zone their sensitivity in Bajgiran Region via the Shannon entropy. The results of the study showed that the most important factors affecting landslides in the study area were slope layers, slope direction, lithology, distance from the fault, and height. After weighing the parameters and formatting the entropy matrix, the zonation mappings were conducted. To this end, the information layers were prepared in Arc GIS and converted into Raster formats. With regard to the zoning maps obtained from the entropy model, 15 landslides have occurred in the area, of which 9 landslides have occurred in a high risk zone (42%), 4 landslides in a moderate risk zone (31%), and 2 landslides in a low risk zone (27%). Regarding the slope factor, it can be said that most of the landslides have occurred in slopes with 60% because of the lack of the soil-formation process prone to the slippery movements. In case of the slope direction, most of the landslides have occurred in northern domains and in heights with 1600 m high. This result is compatible with the faults and calcareous, marl, and Pyura Chilensis organizations of the area. The results of the present study also show that the entropy model has appropriate performance in identifying risk areas and their zonation. In addition, the results can be used in decision making and management of the land use and urban planning.