The Geological Survey of India (GSI) report has stated that the disastrous landslide at the construction site of theTupul Railway Station in Noney district of Manipur was caused by extensive slope cut for railway station construction, presence of break in slope in the upslope area, affluence convergence of water and unprotected slope cut for long duration (from 2014 onwards).
The report also stated that debris dumps limiting the normal water flow of Ijei River, unconsolidated materials dumped and used for temporary construction site, improper hillside drainage along the slope cut region and the site is 350m north of Ijei, as the area is geologically weak zone, were the cause of the landslide.
Preliminary note on the ‘Disastrous Tupul Railway Station Landslide, Noney district, Manipur’ submitted by Nongmaithem Herojit Singh, senior geologist; James Pebam, superintending Geologist GSI, SU: MN, Imphal Office, published on July 8, reported that the landslide occurred at the construction site of the Tupul Railway station, which is 50 km away from Imphal.
It lies on the north-east of Tupul bazar across the Ijei River and the extreme ends of the massive landslide extends from latitudes 24˚48ʹ 08.34ʺ N to 24˚48ʹ 23.93ʺN and longitudes 93˚40ʹ 02.57ʺE to93˚ 40ʹ 33.53ʺE, the report said.
On July 1, 2022 a team of officers from the GSI, Imphal office namely James Pebam, Superintending Geologist and Nongmaithem Herojit Singh, Senior Geologist carried out preliminary assessment of the landslide.
Geologically, the area is covered with sedimentary units of Disang and Barail groups where the Barail Group comprises medium grained sandstone units with minor shale and siltstone layers. The lower portion is multi-storied sandstone units with minor shale, siltstone layers.
The upper part is covered by sandstone with siltstone/shale layers as indicated by the slide materials. Ripple marks, cross beddings are the primary structures observed in the sandstone.
The general trend of the rocks is N055˚E/35˚ towards NW. Three joint sets were recorded in the field. These Barail units are exposed in the northern part of the Ijei River while the Disang sediments are observed on the south of the slide across the Ijai River.
The NE-SW trending Ijai Fault along the Ijai River forms the faulted contact between the Disang and Barail rocks. About 800 meters due west, these rocks are abutted with the Tupul fault exposing the Disang sediments.
The survey report stated that the landslide polygon falls within highly susceptible and moderately susceptible zones. The possible landslide initiation zone falls entirely within the highly susceptible zone.
Dripping to flowing hydrological condition was observed in the entire road section and the cut slopes in and around the slide, as per the survey report.
Loose debris was also observed in the cut slopes adjacent to the slide while steep to very steep cut slopes were observed below the unpaved road which are vulnerable to toe cutting by Ijei River. These factors account for a higher risk of slope failure in the area, the GSI report stated.
Under construction railway platform and station of Tupul railway have been damaged. One (barrack) camp of the Army, one railway camp and a labour camp were totally destroyed. The under-construction railway platform and station of Tupul railway have been damaged, the survey found.
“About 0.60 sq. km area of the slope was damaged with inundation of the Ijai River up to 15 mtr water level”, the report stated.
The slide initiated from the highly susceptible zone, already identified during the NLSM mapping of the area by GSI, the report stated. The complex slide that swept away the 0.60 sq. km area of the hill slope is massive (width-504m, height-450m, length-1150m) and the volume completely blocked the flow of Ijai river. The approximate dimension is 460m in length, 193m in width, as per the GSI report.
Immediate remedial measures can be taken up to allow free flow of Ijei River by clearing the debris while debris materials may be cleared step wise in view of recovering the fatalities, as per the report.
The general public should be prohibited from venturing into the active slide zone while muddy water flowing on either flank of the slide should be made easy passage away from the slide zone, stated the report.
