City’s six highly-vulnerable landslide zones unearthed

The Geological Survey of India (GSI) has identified six densely-populated zones in the city as “highly vulnerable to landslides and slope failures”, which can lead to loss of life and property. “It is found that majority of the vulnerable inhabited hill slopes are in Bhandup, Vikhroli Parksite (Ghatkopar), Kurla, Mulund, Jogeshwari and Chembur areas,” stated the GSI report, which was accessed by HT.

The Geological Survey of India (GSI) has identified six densely-populated zones in the city as “highly vulnerable to landslides and slope failures”, which can lead to loss of life and property.

HT Image

“It is found that majority of the vulnerable inhabited hill slopes are in Bhandup, Vikhroli Parksite (Ghatkopar), Kurla, Mulund, Jogeshwari and Chembur areas,” stated the GSI report, which was accessed by HT.

The GSI’s study, titled ‘Identification of Vulnerable Inhabited Hill Slopes in Mumbai’, was undertaken at the request of the Brihanmumbai Municipal Corporation (BMC) and took more than two years for completion. Though the excerpts of the study were published from time to time, this is the first time that the entire 435-page report was made public, identifying the exact landslide-prone locations in city and suggesting suitable precautionary measures.

“The preliminary assessment of locations was carried out based on parameters such as physical nature and thickness of slopes, inclination of back slope, the angle of rock-overburden interface, presence of slope instability signatures (such as ground cracks, subsidence, opening along joint planes etc), hydro-geological conditions such as local drainage, sewerage system etc which differ from site to site,” said Akshay Mishra, director (landslide studies), Geohazards Research and Management Centre division, GSI. The scientists also analysed the rainfall from 2006 to 2016 for the study.

After the data was analysed, 46 inhabited locations were identified as “most vulnerable” based on a ‘vulnerability scorecard’, of which 20 were marked as ‘very highly vulnerable’ or ‘highly vulnerable’ locations across the six zones.

The report highlighted that haphazardly-built encroachments, destruction and construction on hill slopes, tree removal and poor drainage network were the main reasons for slope failures and the subsequent debris sliding, mostly during monsoon.

“Change in land-use of the hill slope is the main reason for escalation in calamities. Heavy continuous rainfall in such areas provides the necessary trigger and incorrect day-to-day practices of hill slope utilisation further accelerates disaster,” GSI’s report concluded, adding, “The risk scenario is dynamic and continuous monitoring, timely reporting of increase in adversities and geotechnical evaluation of hill slopes are very important in lessening future risk.”

It recommends formulation of policies to prioritise locals from the most vulnerable locations in the slum rehabilitation plan, prevention of construction in the up slope direction of existing settlement zones in vulnerable areas, making drainage arrangements to manage surface run off and construction of properly-lined drainage system for sewage wastewater and provision of a sufficient buffer zone between hill slope and settlements.

BMC disaster management chief officer Mahesh Narvekar said, “As soon as we received the report, we directed the ward officers concerned, the suburban collector and Maharashtra Housing and Area Development Authority to immediately implement the recommendations mentioned in the report. Each of the bodies will submit a compliance reports to us, and the work will be completed before monsoon.”

Independent experts have criticised authorities and said the lack of administrative will was a cause of concern. “Landslides are predictable and also preventable. It is just a question of stabilising the slopes and the methods are known [to authorities]. However, the lack of intent and responsibility by BMC, collectors etc. is endangering the safety of Mumbaiites every monsoon,” V Subramanyan, former geology professor at Indian Institute of Technology-Bombay.