Journal of Development Innovations

Comparing Frequency Ratio and Analytical Hierarchy Models for Landslide Susceptibility in the Dharan Sub-Metropolitan Region of Eastern Nepal

Manish KC, Champak Babu Silwal, Pratik Dangi, Dinesh Pathak — Mon, 15 Jul 2024 00:00:00 +0000

This study compares the application of Frequency Ratio (FR) (statistical/quantitative) and Analytical Hierarchy Process (AHP) (heuristic/semi-quantitative) for landslide susceptibility analysis in Dharan Sub-Metropolitan Region of eastern Nepal. Nine different thematic layers including slope, aspect, curvature, geology, land use, distance to roads, distance to thrusts, topographic position index (TPI), and distance to streams were used for analysis. A landslide inventory map was prepared by identifying the landslides in recent Google Earth images, and it was then verified by field observations. The resulting susceptibility map with different susceptibility levels was validated using the Area Under the Curve (AUC) method, and the resulting AUC values were determined to be 78% for FR and 76.8% for AHP. Both methods offer a reliable strategy for landslide susceptibility mapping with a good prediction rate. The FR model enclosed 41%, 31%, 20%, 7% and 1% of the area as very low, low, moderate, high, and very high susceptibility, respectively, whereas AHP showed 21%, 24%, 27%, 21% and 7% of the area for the respective susceptibility levels. The specific zones identified within the range from very low to very high susceptibility provide valuable insights for local authorities, planners, and decision-makers, allowing them to identify areas susceptible to landslides and implement mitigation measures to aid in targeted risk management efforts.

Rainfall-induced Landslide in the Lesser Himalaya: A Case Study of the Pallotari Landslide, Lamjung, Central-West Nepal

Basant Bhandari, Krishna Chandra Devkota, Chhabilal Pokhrel, Indra Lamsal — Mon, 15 Jul 2024 00:00:00 +0000

The Pallotari area, located in the Marsyangdi Rural Municipality, Lamjung, central-west Nepal, within the Lesser Himalaya, was impacted by a series of rainfall-induced landslides in July 2020. This study focuses on the Pallotari landslide, one of the major landslides in the area. Geological and engineering geological studies were performed to identify the causes of this landslide, and its impacts to the local community. Our results indicate the major causative factors to be intensive rainfall, steep topography with loose colluvial soil, and some anthropogenic activities such as the construction of the rural roads through the crown area. The study area still has hanging colluvial material on the crown as well as on the left flank of the landslide, and the numerical model for slope stability analysis indicates it to be unstable even in the unsaturated condition. The colluvial material in the middle portion of the landslide also has the risk of failure in the saturation condition which can be due to intensive rainfall. However, the rock slope stability analysis using the kinematic analysis does not show any contribution to the orientation of discontinuities on the slope failure. The presence of several transverse and longitudinal cracks in the surrounding of the landslide are signs of future failure.

Geology of Kerabari - Rajarani Area with Special Emphasis on Geological Structures and Strain Analysis of the Main Central Thrust, the Lesser Himalayan Sequence, and Higher Himalayan Crystalline, Eastern Nepal

Kailash Rai, Sushant Bhattarai, Lalit K. Rai, Kamal K. Acharya — Mon, 15 Jul 2024 00:00:00 +0000

The geological study was carried out in the Kerabari - Rajarani area that covers south-eastern part of Dhankuta district and northern part of Morang district of eastern Nepal. The study was mainly focused on the lithostratigraphy, structural analysis, and strain analysis of the Main Central Thrust (MCT) and its hanging and foot walls by integrating field study and laboratory investigation. Geologically, the study area can be divided into the Sub-Himalaya, the Lesser Himalayan Sequence, and the Higher Himalayan Crystalline, respectively. The Lesser Himalayan Sequence is divided into the Bhedetar Group and the Dada Bajar Group, separated by the Chimra Thrust. The Bhedetar Group consists of the Chiuribas Formation, while the Dada Bajar Group comprises of the Ukhudanda Formation, the Mulghat Formation, the Okhre Formation, and the Patigau Formation, respectively. The key geological structures include the Main Central Thrust, the Chimra Thrust, the Main Boundary Thrust, and the Main Frontal Thrust, from north to south, respectively. The microstructural analysis of the quartz grains from the Lesser Himalayan Sequence and the Higher Himalayan Crystalline on either side of the MCT provide evidence of multiple phases of deformation. Likewise, the strain analysis of quartz grains from the MCT characterizes the MCT as the stretching fault thrust.