On July 30, a series of landslides hit Meppadi in Kerala’s Wayanad district, claiming over 200 lives, while over 200 are missing. Soon after, a cloudburst triggered landslides in Uttarakhand. Mumbai, too, is no stranger to landslides with a landslide in Vikhroli’s Panchsheel chawl killing at least 10 people in 2021. The city has over 290 landslide-prone locations and the Brihanmumbai Municipal Corporation (BMC) has this year listed 74 high-risk, vulnerable zones to landslides. The maximum number falls in the eastern suburbs. In light of the recent events, Chair Professor and former Head of the Civil Engineering department at IIT Bombay, Deepankar Choudhury, who is the chairman of the technical committee on disaster resilience and capacity building under the State Disaster Management Authority (SDMA) of the Maharashtra government, speaks to Nayonika Bose. Edited excerpts: What makes a metropolitan city like Mumbai so susceptible to landslides? While the landslides across the country may have different landslide patterns in terms of technical aspects, the outcome is generally the same where a large portion of the ground slides down and devastates everything along its path. Soil layer thickness, texture that varies from location to location, and man-made activities such as unplanned constructions or even paddy cultivation can damage the stability of slopes. When these man-made activities get added to natural activities such as heavy rainfall or tectonic movement, the ground moves. In the Mumbai region, the natural flow path of the water on the slopes has been altered for development, which is a major factor triggering landslides. The water may flow in our new given route for some time but when there is extreme rain, water will go back to its original path and wash away everything along the way. Are extreme weather events and climate change adding to it? Yes, certainly. While climate change cannot be singled out as the only factor, it is certainly one of the major causative factors leading to landslides. Many regions are witnessing extremely heavy rainfall, which was not the case even a few years ago, owing to climate change. Many of the finite slopes that were earlier stable may not be stable anymore. Last year, a landslide in Raigad's Irshalwadi claimed over 80 lives. In 2021, there was the Taliye landslide in Mahad which wiped out the village. What makes the Western Ghats prone to landslides? The typical nature of the landslides in the Western Ghats is similar. In the aftermath of the Malin landslide in 2014, our technical fact-finding committee constituted by the Indian National Academy of Engineering (INAE), New Delhi, conducted an investigation. We found that some of the major reasons were the diversion of the natural path of water, unplanned constructions and paddy stepped cultivation. They hold true even for the Irshalwadi landslide. Some of the areas fall under this eco-sensitive area categorised in the Kasturirangan Committee report, which concluded that the natural flora and fauna of the Western Ghats region need to be protected. What interventions should be taken in planning and construction in Mumbai to make the city landslide resilient? Whenever planning a construction on a slope or even near a slope, an engineering study must be done on its stability. Once the slope is found stable, houses should be constructed in such a way that it does not add to instability, for which the additional load of a structure must also be studied. Factors such as extreme rain or even mild tremors should be taken into account. Slope protection systems can also be adopted such as the geonet and wire meshes. Most importantly, the natural flow path of water on slopes should be maintained. The InSAR (Interferometric Synthetic Aperture Radar) data, which is a real time monitoring system, can give an idea of how the slope is moving. What can be done to improve landslide forecasting in the country to minimise damage to life and property? There are three typical methods to forecast a landslide with one being the numerical-analytical approach. Secondly, there is direct monitoring of slopes and then finally, the the satellite imagery (InSAR) data. The third method is the best way to predict a landslide. While there is a lot of work happening in forecasting through state and national agencies, there is always a scope for further improvement. Researchers are equipped with better knowledge and we need to bring these new technologies to implement proper forecasting for landslides.
