UNB, Dhaka :
Amid the growing trend of heavy rainfall induced by climate change in Chittagong region, an early landslide warning system has been set up in Chittagong, aiming to save lives and property from impending landslides.
“The Geological Survey of Bangladesh (GSB) with support from the Norwegian Geotechnical Institute (NGI) is working to reduce landslide risks and losses in the port city. We’ve already developed an early warning system to forecast rainfall-induced landslides in the port city,” GSB director Reshad M Ekram Ali told UNB.
He said, automatic rain gauges for the landslides early warning have been installed in the port city and at Chittagong University, which record precipitation data after every five minutes and send it to an online system.
Before installation of the automatic rain gauges, the GSB conducted a survey analysing event-based rainfall data to determine the rainfall threshold values for the landslides. The survey selects rainfall threshold values for Chittagong City — 100 millimetres of rainfall in 3 hours, 200 millimetres in 24 hours and 350 millimetres in three days.
When the rainfall thresholds, which set up in the system, are exceeded, the automatic rain gauges send SMS immediately to the registered mobile phones of the 10 organisations and personnel.
The rain gauges send the real time early warning to the registered mobile phones so that the first responding organisations can take action before landslides happen. This intends to facilitate the evacuation of the people residing close to landslide-prone areas.
These automatic rain gauges receive power from solar panels to charge batteries and require only mobile telephone coverage at the installed location. The stations work with standard
mobile phone SIM cards, sources at the GSB sources. Chittagong, the country’s second largest city, is mostly developed on hilly areas with tropical monsoon climate. The yearly rainfall is about 280 millimetres. About 90 percent of yearly monsoon occurs during June to October, triggering landslides in the region.
According to the GSB survey, external factors like excessive precipitation within a short period of time, hill slope cutting and deforestation are triggering landslides in Chittagong region. The magnitude, intensity, and duration of the rainfall play a role in determining whether a hill slope will fall or not.
Rainfall lubricates and increases the weight of slope materials. Excessive rainfall weakens soil materials by replacing air and increasing the water pressure along shear surfaces.
Identifying the causes behind the landslides, the survey says due to heavy rainfall, rainwater easily gets into the slope materials that ultimately increase the pore water pressure. As a result, crown cracks develop on top of the hill and cracks allow more and more water to infiltrate into the materials.
The resulting pore water pressure exceeds the shear resistance of the slope materials and landslides begin to start when the shear resistance threshold is exceeded by pore water pressure.
Reshad M Ekram Ali, also the head of the GSB Urban Engineering Geology branch, said rainfall is the main triggering factor of landslides and it is statistically calculated that 100 mm rainfall in 3 hours, 200 mm in 24 hours and 350 mm in 72 hours can be threshold values of rainfall to warn people before landslides hit.
“If the threshold values are exceeded, the system automatically sends landslide early warning to the authorities concerned so that they can alert people in advance to save people from landslide disaster,” he said.
Bangladesh is one of the most vulnerable countries of the world to suffer from various natural disasters like flood, cyclone, earthquake and landslide.
In Bangladesh, the incidents of landslide have increased both in frequency and intensity, and have assumed catastrophic and disastrous proportions, causing extensive damage to life and property.
In and around the Chittagong city, more than 200 people were killed in landslides during 2006-2013 with over 127 killed in a single catastrophic landslide in 2007.
