News
Geotechnical body wants building activity in high-risk areas halted
View(s):By Nidarshani Wickramasinghe
The National Building Research Organisation (NBRO) has recommended that all construction projects be cleared from high-risk areas demarcated through boundary demarcation maps developed using satellite images following the landslides triggered by cyclone Ditwah in November.
However, the areas and the corresponding landmass affected have not been confirmed, and this will take time, Dr Wasantha Senadeera, senior scientist of the NBRO, told the Sunday Times.
The total number of landslides and natural disasters will be computed after verification.
The Arthur C. Clarke Institute for Modern Technologies was able to locate and delineate about 4,200 rapid mass movements in slope failures in Sri Lanka.
Sentinel-2 satellite images were used.
The nationally consistent landslide boundary data provide vital information in a timely manner. Sentinel-2 satellite data provide free multispectral images with 10-20 metres spatial resolution and high repeat times, which make them suitable for landslide mapping over extensive and remote areas.
The demarcation maps created from these satellite images have now been provided to national universities, the Disaster Management Centre, NBRO and relevant institutions.
Scientists and officers of NBRO are expected to visit those areas for field observations and confirm data provided by satellite imagery. Once risk areas and high-risk areas are identified, corresponding actions are taken, Dr Senadeera said.
The institute said that the number of landslides and natural disasters viewed through satellite data exceeds the numbers reported in the media.
Landslides can occur in both residential and forested areas as well as in other land not used by the public, such as reserves.
The institute reported that when NBRO has completed site investigations, the final estimated number of landslides will be higher than it is now.
Arthur C. Clarke Institute research scientist Mahesh Chathuranga also said, “When we look at those locations and those patterns based on satellite observations, it will give us a very strong basis for predicting their stability in these areas of forested hill country.”
He said the most reliable indication of future landslides would be those that occurred in the past because failed regions would have vulnerable slopes that would frequently fail again.
He said that should landslides occur where there are endemic plant and animal species, those may never be seen again, and it is important to act immediately where landslides have happened before the regrowth of vegetation.
However, Manjula Karunarathne, a Disaster Management Centre committee member and senior lecturer of geography at the University of Ruhuna, said the expert committee strongly recommends that the government implement the Soil Conservation Act.
“The Act contains many provisions to counter land degradation, erosion, and sedimentation,” he said.
He highlighted the importance of proper control of land use in the higher catchment areas, pointing out the unauthorised constructions he noticed along rivers and the rapid depletion of the remaining forest areas because of these activities.
And forests should also have more protected areas, and upland agricultural areas should adopt agroforestry, analogue or a mixed farm system to help agricultural growth become sustainable, he said.
Meanwhile, underlining the significance of modern technology to landslide and disaster management, Dr Gayantha R.L. KodiKara, adjunct professor of the University of Wisconsin, Milwaukee, United States, told the Sunday Times, “Landslides pose a severe and visible threat to Sri Lanka’s hill country, where there is significant damage to lives, the natural environment and the economy.”
With the increase in heavy precipitation events caused by climate change, earth observation by satellite technology has become an important component for early disaster detection, disaster risk mapping, and rapid disaster assessment, he said.
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