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University of Tehran
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Introduction and Objective: Landslides are among the environmental hazards that annually cause significant human and financial losses in extensive mountainous regions of our country. Therefore, identifying the important and influential factors in the occurrence of this phenomenon can be used as a practical tool to reduce potential damages. Consequently, recognizing the environmental factors affecting the occurrence of landslides in forest road networks is of great importance. Due to its mainly mountainous topography and extensive tectonic activity, Ramsar County has a natural potential for widespread landslides within the communication network area. The objective of this study is to assess the susceptibility of landslide occurrence in the Ramsar County area by considering influential factors, especially forest road networks, and utilizing Geographic Information System (GIS) capabilities.
Materials and Methods: To achieve this goal, the locations of landslides were determined using field studies, historical reports, and Google Earth images. A total of 95 landslides were identified in the region, which were divided into two groups for modeling (70%) and validation (30%). Sensitivity analysis of landslide occurrence was carried out based on criteria such as slope, slope direction, land use, distance from residential centers, terrain curvature, precipitation, temperature, erodibility, elevation, vegetation cover density, lithological units, soil texture, drainage density, distance from roads, and topographic wetness index. Land cover density and vegetation greenness were calculated using 16-day products from Landsat 8 satellite in Google Earth Engine, and the final output was calculated using weighted regression methods in GIS and Excel software. Receiver Operating Characteristic (ROC) curves were employed for model evaluation and validation.
Results: The most significant factors affecting landslide susceptibility include soil type, slope of the terrain, vegetation cover, geology, hydrogeological flows, topography, precipitation, and communication lines. Susceptibility zones and landslide density are more pronounced in peripheral areas of transportation corridors. The construction of extensive structures, side effects of road construction, and the disruption of natural terrain balance for road construction and expansion have led to continuous occurrences in these areas. The correlation of parameters influencing landslide occurrence with the landslide distribution layer indicates that approximately 76% of landslides have occurred in slopes ranging from 11 to 38 degrees. Erosion of slopes by high-velocity runoff flows has caused more than 63% of landslides to occur within 500 meters of watercourses. Alongside the three main factors of soil type, natural slope, and slope erosion, landslide occurrence is influenced by road reconstruction and development without considering slope stability principles. More than half of the observed landslides in the area have occurred in a sequence of rock, shale, sandstone, volcanic rock, accompanied by coal layers. The discontinuity of the landslide layer with the distance from the road indicates that landslide occurrence up to a distance of 400 meters from the road has been due to direct effects of road construction and embankment activities, disrupting the balance of slopes adjacent to the road, gradually decreasing with the distance from the main road. The results show that the Frequency Ratio model provides an acceptable accuracy with an area under the curve (AUC) of 0.76 for landslide susceptibility mapping. The final susceptibility map indicates that class 5 with very high susceptibility covers 13.06% of the total area, class 4 with high susceptibility covers 16.35%, class 3 with moderate susceptibility covers 22.32%, class 2 with low susceptibility covers 27.46%, and class 1 with very low susceptibility covers 20.79%. Consequently, 31.79% of the total area is at risk of severe landslides. Considering the final map and the close relationship between road presence and landslide occurrence, it can be stated that the northwestern and eastern forest roads of Ramsar County are more exposed to landslide occurrence.
Conclusion: It appears that removal of vegetation cover, alteration of watercourse routes, modification of natural terrain slopes, and excavation of soils and rocks for road construction in the area have led to landslide occurrences around forest roads. The marginal areas of transportation corridors show a significant discrepancy in susceptibility coefficients, highlighting the potential importance of landslide occurrence in these regions. It can be concluded that providing appropriate recommendations and strategies to reduce landslide risks, improving area management, and implementing preventive measures in this region are highly necessary. This study demonstrates that through accurate analyses and alignment with environmental conditions, effective measures can be taken to reduce the effects of landslides and enhance the stability of operational areas. Therefore, a combination of geological, hydrogeological, topographic, and geographical information analyses can be used as an effective tool for studying, predicting, and managing landslide risks in mountainous regions.
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Type of Study: Applicable | Subject: مديريت حوزه های آبخيز
Received: 2023/08/1 | Revised: 2023/09/8 | Accepted: 2023/09/9 | Published: 2024/07/31

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