The devastating debris flow in Kattipara panchayat in Kozhikode district in the early hours of June 14 which snuffed out 14 lives and caused extensive damage to crops and property was not wholly unexpected, given that it occurred in an area classified as vulnerable to landslips.
However, the magnitude of the disaster and the contrast with landslip-prone areas in Idukki and Kottayam districts, which received more intense rainfall in the same period, was not lost on scientists and disaster management experts who feel that the land use pattern on the slopes and the density of population in the foothills had amplified the human tragedy.
The hazard zonation map of Kerala prepared by the National Centre for Earth Science Studies (NCESS) in 2010 identified the western flank of the Western Ghats as one of the major landslip-prone areas in the country. The most prevalent and disastrous type of landslip in Kerala is the ‘debris flow’ characterised by the swift and sudden downslope movement of highly water saturated overburden ranging in size from soil particles to boulders, destroying and carrying with it everything in its path.
Case studies by the NCESS have shown that most of the debris flow events are triggered by excess rainfall and influenced by terrain factors like slope, soil thickness, land use, disposition of streams and landforms at micro level. More than 5,600 sq km representing 14.4% of the total land area of the State is classified as ‘landslip prone’, with 1,847 sq km ‘highly vulnerable’. Wayanad and Kozhikode districts are prone to deep-seated landslips while Idukki and Kottayam are prone to shallow landslides.
Deforestation
“A landslip is a natural process triggered by heavy rainfall that raises pore water pressure and reduces shear strength in saturated soils”, explains K.P. Thrivikramji, former Professor, University of Kerala, and consultant on environmental issues. According to the Kerala State Disaster Management Plan 2016, the processes leading to landslides were accelerated by anthropogenic disturbances such as deforestation since the early 18th century, terracing and obstruction of ephemeral streams and cultivation of crops lacking the capability to add root cohesion in steep slopes. The events have become more destructive given the increasing vulnerability of population and property. The majority of mass movements have occurred in hill slopes greater than 20 degrees along the Western Ghats scarps.
Between 1961 and 2016, a total of 295 lives were lost in 85 major landslip events. The most severe, in terms of fatalities, was the one at Amboori in Thiruvananthapuram on November 9, 2001, that claimed 38 lives. According to the document, the population of 10 taluks of Kerala are highly vulnerable to landslips in terms of population density; 25 taluks are listed as moderately vulnerable and 14 fall in the least vulnerable category.
Human intervention
“Kattipara is a classic case of human intervention aggravating the vulnerability of a landslip-prone area”, points out a highly placed official in the State Disaster Management Department. “Various activities such as cultivation of shallow-rooted crops, construction of water impounding structures and blocking of natural drainage channels over the years, have turned the slopes into a highly landslip-prone area. People should realise that allowing accumulation of water on steep terrain can destabilize the slopes. The high soil depth and the density of population in the foothills would amplify the magnitude of the tragedy.”
Raising the issue in the Assembly, Leader of the Opposition Ramesh Chennithala had termed it a man-made disaster triggered by a check-dam constructed on private land uphill. The government has set up a committee to investigate the allegation. However, it is significant that the landslip-prone areas in Idukki and Kottayam, which received more intense rainfall, with a high of 32 cm in 24 hours in Peerumedu, witnessed only minor incidents, officials point out, attributing it to the changes in land use that have rendered the slopes less vulnerable. “Today, farmers in these places have changed their agricultural practices and many residents have relocated elsewhere,” they observe.
Experts also point out that Kattipara had paid the price for violating the restrictions prescribed on development activities in the Ecologically Sensitive Areas (ESAs) identified by the Kasturirangan committee. The absence of a disaster mitigation and response plan for local self-government institutions is pointed out as another major lapse that contributed to the death toll and damage to property.
K.S. Sajin Kumar, Associate Professor, Department of Geology, University of Kerala, who co-authored a landslip atlas of Kerala published last year, stresses the need for a landslip prediction system based on the rainfall threshold analysis. “By studying the correlation between the rainfall and landslip history of a region, it will be possible to come up with the combination that triggers a landslip. Based on the information, the government should map landslip-prone areas and prescribe regulations on activities that could trigger such events,” Dr. Kumar says.
Dr.Thrivikramji sees the need for cadastral scale mapping of landslip-prone areas in the Western Ghats. The Kattipara incident has led to the demand for more refined prediction systems and technological solutions like electronic sensors. However, a section of officials feel that it would be more practical and cost-effective to enforce strict regulations on development activities and encourage farmers to change land use pattern. “But that is easier said than done, if shortsighted political compulsions are allowed to dictate government policies,” they admit.
