**8. Conclusions**

The main cause of landslides in and around Chittagong City is heavy rainfall in a short span of time. At the same time, geotechnical properties of the slope materials (loose, well-graded sand, high permeability and porosity, low internal friction angle and weathering characteristics) are also responsible. In several cases, hill cutting accelerates the process of landslides but was not the main cause of landslides.

Depending on the locations of landslides, geology and geotechnical properties of rocks, Chittagong City and its surrounding areas have been classified into four landslide hazard zones. Of these, Zone-I is very much susceptible to landslides and Zones-II, -III and -IV are progressively rather less vulnerable.

Rainfall becomes the primary triggering factor of landslides, and it is statistically calculated that 100 mm of rainfall in 3 h, 200 mm in 24 h (1 day) and 350 mm in 72 h (3 days) can be the threshold values of rainfall to initiate landslide occurrence. Event-based statistical analysis of rainfall data is still taking place to rectify these threshold values for the city.

Accordingly, two automated rain gauges have been installed in and around Chittagong City. If threshold values exceed, the system automatically sends landslide early warning to 10 selected mobiles of local administration and the first responding organizations so that they can alert people in advance before landslides. GSB is also working to increase the number of such systems especially in other landslide-prone areas of the city. The ultimate goal is to save the people from landslide disaster and build a landslide resilience community.
