Considering the long-term nature of the ongoing project, it is necessary to adopt regulatory and monitoring mechanisms at the vulnerable slopes
The geology of the area cannot be changed; however, the innovation of new and emerging technologies and ideas will mitigate the situation. Representative photo: iStock. Parts of this article were used in a special edition on the Himalayas, published in February 1-15, 2023, issue of Down To Earth magazine
A large landslide that struck the Tupul Railway station building site on June 30, 2022, resulted in 61 fatalities and 18 injuries. The incident occurred at the campsite at Maranching, located at Makhuam village in Noney district.
Extreme rains, long-term exposure to hill slopes cut for development projects, debris obstructing the flow of Ijei river and shifting land use patterns, such as deforestation, are thought to have contributed to the tragedy in the seismically active western Manipur region.
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The incident pushed railway authorities to devise methods for monitoring hill slopes cut for massive development projects.
The landslide was caused by an “extensive slope cut for the construction of the railway station, presence of break in slope in the upslope area, affluence convergence of water and unprotected slope cut for long duration (from 2014 onwards),” according to a preliminary study by the Geological Survey of India’s (GSI) Imphal office.
The hilly districts of Manipur have witnessed unprecedented natural calamities in the last decade due to rampant exploitation and mismanagement of natural land resources for different economic purposes and infrastructural development.
Since Manipur is located at the extreme corner of the country, the state’s road connectivity is in bad shape due to its topography.
The state has faced immense hardship for many years. It relies on two national highways (Imphal-Jiribam and Imphal-Dimapur). In light of expanding connectivity, the state government proposed constructing a railway line from Jiribam to Imphal.
The 111-kilometre-long project was sanctioned in 2003-2004. The broad gauge railway line passes through five districts: Jiribam, Tamenglong, Noney, Kangpokpi and Imphal west.
The project's estimated cost is in tune with Rs 140 billion, of which the majority of the work is nearing completion (89% completed, according to a 2022 report). The railway lines of the project span 140 bridges, 11 stations and 52 tunnels.
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The total length of the tunnels is 62.59 kilometres and the longest tunnel is about 10.2 kilometres. The project is expected to complete in December 2023. It was finally taken up in 2008 and was declared a ‘National Project’ owing to its importance.
This project, a part of the Act East policy, is executed through Northeast Frontier Railway (NFR). It aims to build connectivity with the member nations of the Association of Southeast Asian Nations.
A major factor that caused the landslides was the debris restricting the normal water flow of Ijei river. The materials dumped at the railway construction sites and improper drainage made the hills geologically weak.
The incident occurred nearly 325 metres north of Ijei river. Heavy rainfall might have triggered the landslides. In June 2022, the rainfall received by Noney district was 329.9 millimetres, according to Manipur’s Directorate of Environment and Climate Change.
A Manipur-based Environmentalist Salam Rajesh while visiting the tunnels in 2017-2018, noticed that a small landslide could become fatal. “Steep cutting was not advisable to the area,” he said.
Hill land is formed of soft red earth, sandstone, sedimentary rocks and silt. So, when there is rainfall or earthquake, landslides are common phenomena, he added.
Contour cutting/ gentle slope cutting per hydrological aspect can prevent huge water flow from uphill to downhill. Any distortion in the original land formation can cause landslides.
Adai Gangmei, chairman of Longmai villages council, Noney, termed the landslide a human-made disaster. He said the hard rock soil, which acts as a protection layer, was all destroyed and tugged out from the surface during high-cutting hill clearance. Reportedly some villagers said having heard an unusual sound before the landslide occurred.
A petition was also written to Prime Minister Narendra Modi, demanding geological studies of the area to avert further disasters, Adai informed.
Manipur University’s Earth Science Department cited multiple reasons for the tragedy. A report by the university reports stated that the rainfall between May (375.60mm) and June (329.9mm) in the district was 60 per cent higher than normal rainfall.
The survey team also found that a large old landslide slump, 1,063m deep with a steep slope of 42 degrees, was present in the area and the slump became oversaturated due to incessant rain in May and June
Few cracks in the cut slopes of the railway yard have also contributed to the disaster, the report added.
The slide was triggered from the crest of a hill and debris slid into the Ijei river bed. And around 31 hectares were affected by the massive landslide in which the open cut and major of the railway yard were devastated, causing casualties.
The approximate volume of the landslide slump (debris) is 4.3 lakh cubic metres, slid due to the landslide. And the current piled-up debris is 6.02 lakh cubic metres, deposited on the slope of the hill from the railway building to the river bed.
Other possible causes may be the geologically non-resistant lithologies (shale interbedded with mudstone, siltstone and sandstone).
The fluctuation in the ongoing precipitation pattern and excessive rainfalls lead to the percolation of water below the slopes.
The fine-grained lithologies (clay and silt), being less permeable, become more plastic-like, reducing the slope’s stability and causing landslides. In contrast, the resistant lithologies (sandstone and mudstone) still hold water in their pore spaces.
The seismic zonation map of India has included Manipur in the High Seismic Hazard Zone. Based on the fault, a few minor cracks were observed in the cut slope of the railway yard.
Changes in the land use pattern on the top hill, caused by deforestation, jhum cultivation and banana cultivation, also accelerate soil erosion and might have triggered landslides.
Considering the long-term nature of the ongoing project, it is necessary to adopt regulatory and monitoring mechanisms at the vulnerable slopes along the railway line where the cut portion and yards are to be exposed.
Reassessment of slope stability (Factor of safety) analysis for open cut and yard of the Jiribam-Tupul railway line, regular drone survey and monitoring to detect mass movement along the open cuts and yard as well as beyond railway land boundary before and after monsoon season without significant failure event, detection of subtle slope movement will likely help mitigate the problem.
Installation of automatic weather stations for monitoring weather data at major railway station sites from Jiribam to Tupul and monitoring slopes with web-enabled equipment can be of great help.
The geology of the area cannot be changed; however, the innovation of new and emerging technologies and ideas will mitigate the situation.
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