Analysis of occurrence potential of the earth/debris flow and shallow landslides using the TRIGRS model (Case study: babolrood Basin, Mazandaran)

In this study, the occurrence potential of rainfall-induced shallow landslides in the Babolrood basin has been investigated. In this basin, due to the mountainous topography and the presence of loose organic soils, the potential of such landslides is high, and landslides of different sizes occur every year after long and intense rainfalls. These landslides, which start with the sliding mechanism in the upper parts of the soil cover, immediately turn into earth/debris flows, and from their joining together, large flows may form downstream of the basin, which is considered a destructive phenomenon. In this research, to investigate the effect of rainfall on the occurrence of shallow landslides and flows, the TRIGRS program, which is a comprehensive and grid-based program for slope stability analysis using the infinite slope method, has been used. In this program, the effect of rainwater penetration into the soil and runoff caused by rainfall, which are important parameters in the occurrence of shallow landslides and subsequent flows, are also fully considered and this natural phenomenon is fully simulated. The input data required for this research includes topographical data of the basin, geological and hydrogeological properties of soil units, and rainfall data in the region, which are prepared in the form of appropriate text files and GIS maps. The output of the Triggers program includes maps of the spatial distribution of the minimum safety factor, the depth of the failure, and the pore water pressure at the failure depth, which are prepared in the form of text files and can be interpreted in GIS-based software. The results of this study showed that in the high and steep parts of the basin, wherever there are soils on a bedrock rich in clay minerals (such as mudstone, marl, and shale), the potential for shallow rainfall-induced landslides is high. In the field studies, a good agreement between the results of this study and the experiences obtained from field observations of landslides caused by rainfall in the region was obtained in terms of their spatial distribution and time of occurrence.