Landslide Susceptibility of Chittagong City, Bangladesh, and Development of Landslides Early Warning System

Abstract

Chittagong, the second largest city of Bangladesh, is mostly developed in the hilly areas. Hills are mostly covered with loose and weathered tertiary sedimentary rocks susceptible to landslides. Generally, during heavy rainfall within a short time, water infiltrates into the loose rocks and soils, which increase the pore water pressure, and finally exceeds the shear strength of the materials to initiate landslides. Landslides history, slope characteristics, geology and geotechnical properties have been considered to divide Chittagong City and surrounding areas into four landslide hazard zones. Zone I in the east of Chittagong City persists as the most susceptible area for landslides, and the city becomes gradually less susceptible further westward up to zone IV. Prevention of landslides in most cases requires costly engineering solutions. Therefore, mitigation through timely evacuation of people from hazardous areas might be a good solution to combat landslides. Two automated rain gauges are installed at high risk landslide zones with built-in rainfall threshold values. Threshold values for early warning of landslides are set after statistical analysis of past landslides in relation to total amount of rainfall and local geology. The threshold values of rainfall are set to 100 mm in 3 h, 200 mm in 24 h and 350 mm in 72 h.

Analyzing the 27 July 2021 rainfall-induced catastrophic landslide event in the Kutupalong Rohingya Camp in Cox’s Bazar, Bangladesh

“…2). The current threshold value for landslide occurrence is 300 mm and 200 mm for antecedent rainfall for 3-days and 1-day, respectively (Ali et al 2018). During this event, antecedent rainfall for 3-days and 1-day was less…”

Empirical Approach Based Rainfall Threshold Estimation for Landslide Occurrence in Cox's Bazar District, Bangladesh

“…Studies exist where the global rainfall threshold and rainfall threshold for selected climatic zones are well established (e.g., Idrogeologica et al, 2010;Guzzetti et al, 2010;Nazionale et al, 2007). Only a few studies previously tried to estimate the rainfall threshold for Chittagong city (Khan et al, 2012;Ali et al, 2018). However, a rainfall threshold determination attempt is taken for the Cox's Bazar district employing multiple empirical approaches to cross-validate and thus fine-tune the threshold estimation effort.…”

“…We also tried comparing our threshold estimation with similar studies in the Chittagong hill tracts. Ali et al (2018) found that the threshold values for landslides in Chittagong City are 100 mm of rainfall in 3 hours, 200 mm in 24 hours, and 350 mm in 72 hours. This research also indicates that 100mm of rainfall is required to start an event, whereas our study (table 2) reveals that the susceptible rainfall according to maximum threshold value is 34.1mm in 3 hours, 208mm in 24 hours, and 540mm in 72 hours.…”

Disaster Management and Good Governance: A Review on Chattogram Landslides

“…Regarding the angle of the slope, it is found that in the landslide-prone areas of Chittagong, the angle ranges between 34 degrees and 84 degrees; most of them are more than 40 degrees. Several man-made factors such as cutting down the hills and changing the shape of the hills, deforestation, and inadequate drainage system are significantly responsible for this situation (Ali et al, 2018). Fatema (2019) has listed all the areas that are prone to the risk of landslides in Chattogram City based on their severity.…”