Kerala landslides: GSI advocates land use and zoning regulations

It is time to look at land use planning and zoning regulations to reduce damages from landslides and strengthen disaster preparedness, say experts at Geological Survey of India in the wake of the devastating Kerala floods and landslides that claimed nearly 400 lives.

Torrential rains (second spell of southwest monsoon) hammered the state from August 8 to 19 this year, displacing millions and killing many in rain-related events. Government officials estimate losses due to the floods and landslides at more than the state’s annual plan outlay (Rs. 26,500 crore for 2017-2018 fiscal).

According to data provided by GSI, the coastal state in the Western Ghats has experienced 67 major landslide events and hundreds of minor ones, in half a century.

“Landslides have caused substantial damage to life and property in Kerala. Between 1961 and 2013, more than 270 valuable lives were lost in 67 major landslide events. Kerala is vulnerable to landslide hazard,” Dinesh Gupta, director general of GSI told Mongabay-India.

Gupta stressed that people have been living with floods and landslides since ancient history but it is the “unregulated human interference” that is adding to the vulnerabilities.

“Land use zoning regulation (incorporating landslide susceptibility data) should be made mandatory. It is time that we look into land use policies and land management systems in terms of susceptibility and we should also understand that the climate is behaving differently. High rainfall is not very uncommon these days,” he said. Zoning is the term used for designating permitted uses of certain parcels of land by local governments.

Elaborating further, Pankaj Jaiswal, director, Landslide Studies Division, Geohazards Research and Management Centre (GHRM) at GSI, referred to the National Landslide Susceptibility Mapping (NLSM) programme that was launched in 2014, which would aid in prioritising use of resources and framing zoning regulations based on landslide inventories.

The mapping targets an area of 18,854 square km spreading over 64 topographic maps that cover parts of Western Ghats and its foothills.

“These maps are for regional planning and can be used by the state governments for their land use-zoning policy, highlighting the landslide-susceptible areas and what kind of activities can be allowed in these zones. These are being used in Nainital and the Nilgiris as part of their zoning regulation,” said Jaiswal.

GSI has completed landslide susceptibility mapping of around 8920 square km area covering 21 topographic maps in Kannur, Kozhikode, Wayanad, Malappuram, Palakkad, Pathanamthitta, Kollam and Thiruvananthapuram districts.

Among the 14 districts of Kerala, 13 are prone to landslides. Idukki is the worst affected with 217 landslides.

“Kerala has population density of 860 people per square km in comparison to Uttarakhand which has 189 people per square km. Thus, even small landslides can result in huge damage and casualties,” Jaiswal said.

Modified hill slopes failed

As a major land use concern, Jaiswal pointed to failures of hill slope modifications (cut slopes), carried out for developmental activities and plantations, in disaster prone areas.

“More of the disasters (across India) are coming due to cut slope failures and this is something that you have to address first. The cut slope has to be treated and stabilised and the drainage has to be maintained. We have to look at more critically how to manage the drainage water,” he said.

The GSI recommends that all cut slopes be properly managed and retaining walls should be made mandatory along road cuts.

“Things to be considered include how much slope is really needed for plantation and on which type of slope we should not plant and if you are planting on slopes then drainage is the most important factor to consider. Drainage management is crucial. If you can drain the water then the cut slope will not fail,” Jaiswal said.

There are more than 300 landslide incidence reported by the media and the actual numbers of landslides are anticipated to be more. Similar, events were recorded in 2013 when very high rainfall triggered about 145 landslides in Idukki area

“These were of shallow failures along the road wherein the steeply cut slope faces have failed, and also debris flows resulting due to torrent stream conditions in the dissected hill slopes,” said Jaiswal.

Out of the approximately 39,000 square km area of Kerala, the hill area having slopes higher than 10 degree constitutes about 19,000 square km.

Within this the Western Ghats scarps facing west (characterised by thin soil cover and modified heavily by anthropogenic activity) is most vulnerable to landslides. Here, landslides occur mostly as debris/ earth slides or debris flow (‘urul pottal’ in Malayalam), triggered by rainfall during both southwest and northeast monsoons, the GSI said. 

“These are invariably associated with cut slopes along settlements or roads, or torrent stream along nala (drain) or even channelised debris/earth flow due to very high rainfall,” said Jaiswal. 

As an example, Jaiswal drew attention to the landslides that were triggered by the first spell of rainfall (June-July 2018).

Landslides in vulnerable tracts

The post-disaster landslide assessment carried out by GSI (from June 28 to July 7, 2018) revealed that a total of 59 landslide events were recorded in Kozhikode, Idukki, Malappuram, Wayanad, Palakkad and Kannur.

It was observed that 86 percent of the landslides coincided with zones marked as moderate and highly susceptible as per the NSLM map.

“Some of these landslides occurred due to cutting the toe of the hill for road construction or due to bank erosion by river, which resulted in near vertical slopes with no provision of lateral support. There are also a few incidences where the location data of the debris flows were collected at runout areas or at the area of deposition/accumulation, due to inaccessibility of the source areas,” he said.

Moreover, for disaster preparedness, the run-out distance of the landslide is also significant.

“We can use the susceptibility maps to understand what type of landslide size we expect in a specific area and how it behaves in the area and then we can interpret these maps logically in terms of settlement, in terms of any infrastructure. This will help to prioritise resource management, prioritise awareness programmes in villages and prioritise resources at the regional level,” informed Gupta.

“Awareness is equally important. In cases of casualties in remote areas accessibility is a challenge. So awareness generation is important to lessen the impacts of such disasters,” he added.

Banner image: Furniture flung out of a home in Nilambur, Kerala. Photo by Murali Iris.

Article published by S. Gopikrishna Warrier

Floods, Monsoons, Mountains, Rivers

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