Investigation of Landslides and Geoenvironmental Analysis in Rangamati and Adjoining Areas of Southeastern Hilly Districts, Bangladesh

Abstract

Landslides that pose significant challenges to the development of Bangladesh have become a common threat, particularly in the southeastern region of the country. This study focuses on an area that stretches from Rangamati Sadar to Kawkhali Upazila, encompassing the surrounding regions of Rangamati District along the Chittagong-Rangamati National Highway. This research utilizes both fieldwork-based landslide inventory data and laboratory experimental analysis of slope soils to better understand disaster loss reduction strategies. A total of 40 landslides has been selected for this study, and 10 soil samples collected from different hills have been tested in the laboratory to characterize landslide slope materials. Field observations show that the slope materials primarily consist of sand, silt and clay. Laboratory test results indicate moisture content of soil samples ranging from 2.61% to 14.19%. The percentages of sand silt and clay-sized particles are 12-34%, 44-70% and 6-22%, respectively. Cohesion and friction angle values from the direct shear tests range from 2 to 24 kPa and 31 to 39 degrees, respectively. The low cohesion and steep slopes increase the likelihood of landslides. A landslide susceptibility map has been developed by integrating the landslide inventory with various factor maps using the Modified Frequency Ratio model. This map classifies the study area into different susceptibility categories: 9% high, 33% moderate, 41% low, and 18% very low landslide hazard-prone areas. The assessment indicates that the Chittagong-Rangamati National Highway and nearby areas in Rangamati District exhibit low vulnerability but face a high risk of landslides. Rainfall-induced landslides in the Rangamati District have increased significantly due to climate change, which has altered rainfall patterns. Besides geotechnical factors, other contributing causes of landslide hazards include extreme short-term rainfall and human activities such as hill cutting, deforestation and unplanned urbanization. This investigation will help the local authorities, stakeholders and policymakers in planning for landslide risk resilience.