Landslides 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.

Author Reply to Reviewer 1

“…For example, at north-east Bangladesh, in pre-monsoon season, more than 150 mm rainfall event over a 6-day period can lead to an early flash flood (Ahmed et al, 2017). On the other hand, at south-east parts of Bangladesh, in monsoon season, more than 350 mm rainfall events over a 3-day period is enough to cause a landslide (Ali et al, 2014). Whereas, for a wide-spread river flooding e.g., the Brahmaputra River Basin flooding in August 2017, 10-day extreme rainfall event is considered (Philip et al, 2018).…”

Risks of seasonal extreme rainfall events in Bangladesh under 1.5 and 2.0 °C warmer worlds – how anthropogenic aerosols change the story

“…National Aeronautics and Space Administration (NASA)'s near-real time Integrated Multi-satellitE Retrievals for Global Precipitation Measurement, GPM (IMERG) data estimated the heaviest rainfall accumulation of more than 510 mm in only 3 d, 12-14 June, 2017 (Gutro, 2017). Further, in north-east Bangladesh, more than 150 mm in 6 d during the pre-monsoon season led to early floods (Ahmed et al, 2017); 350 mm in 3 d during the peak of the monsoon season caused a landslide in south-east Bangladesh (Ali et al, 2014); and exceptional 10 d rainfall in August 2017 led to widespread flooding in the Brahmaputra River basin (Philip et al, 2018).…”