GSI team identifies four types of landslides in Nilgiris

It also found a large number of over 200 “landslips/landslides” having occurred following the monsoon rain.

The Coonoor area in the district, at the heart of the tea basket, has recorded the highest- ever amount of rainfall, 82 cm, so far for any single day. It  was the “single-most immediate trigger point” for the landslides. Unplanned “human interventional factors” accumulated over the years have also done in the popular tourist resort of “Ooty,” Queen of Hill Stations.

E Balasubramanian, Director (Project Landslides), GSI, Chennai and C Thanavelu, Senior Geologist, GSI, who have just returned after a preliminary study of the extent of damages in Nilgiris, told Deccan Herald here on Friday that the landslides could be sub-divided into four categories of “soil-slips, landslides proper, debris flow and stream banks failures.”

The “human causative factors” stemming from unplanned development have also substantially contributed to this serious scenario, they pointed out.

These factors  include “vertical cutting” of the slopes for road formation, “loading the slopes” with heavy construction activities, the “bench-cuts” and “terracing” of slopes for construction and agriculture activities (terrace farming).

Maximum damage has occurred in places adjacent to unprotected road-cut slopes and human settlements, the GSI experts said.

“Most (soil) failures happened along the road cuts, bench cuts (L-shaped) for house-sites, along steep slopes and recurrences in old, known landslide sites,” said Thanavelu. The “debris flow (rolling of rocks and soil)” was predominant along the road and railway corridors from Pudukaadu to Coonoor, he said.

The other major problem was encroachment on “stream banks” width to build houses which choked the “natural drainages” in the Nilgiris when rainfall was exceptionally high this year, the GSI scientists said. Creating much larger community awareness about these issues was needed.

While excessive potato cultivation is also believed to be among the factors that loosen the soil in the Nilgiris, the scientists said when “water cannot flow down”, chunks of soil mass over the rocks “slide down.”

Rocks and other objects perched on the soil come tumbling down under tremendous force, even uprooting trees at several places, they pointed out.

The GSI team will forward its report to the National Disaster Management Authority , the State government and other concerned agencies with its recommendations on control and corrective measures, Balasubramanian said.