Causative factors of landslides 2019: case study in Malappuram and Wayanad districts of Kerala, India
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Sudesh Kumar Wadhawan I Balmukund Singh I Maneesha Vinodini Ramesh
Causative factors of landslides 2019: case study in Malappuram and Wayanad districts of Kerala, India
Abstract Several landslides and floods were triggered by unprecedented, incessant heavy monsoon rainfall from 4 August 2019 to 8 August 2019, along the northern slopes, at Kavalappara, in the Malappuram district and Puthumala, in the Wayanad district of Kerala, India. The geological and geomorphological field settings were analyzed within the sub-basin wide catchment areas, for a preliminary evaluation of the causative factors of the landslides. This paper provides insights into the causative factors of landslides, together with suggestions on appropriate land use planning and deployment of real-time flood and landslide monitoring systems, besides building an adaptable community resilience model in high landslide-prone areas. The structurally disturbed weakened bedrocks and generally incompetent residual alteration products, exacerbated by nonchalant human interventions, reduction of cohesive strength, on super-saturation of underlying earth material, were inferred to be the primary causes of major landslides, triggered during 5 days of excessively heavy rainfall (400% over the normal average). Additionally, massive toe erosion was observed by streams gushing with course clastic sediments and debris. The destructive nature of such multi-hazards was evoked by unscientific modifications of slopes, mismanagement of water drainage, unplanned residential developments, across the channel courses and within active floodplain of rivers, and lack of early warning schemes for landslide. Keywords Landslides . Floods . Multi-hazard . Chaliyar River basin . Kerala Introduction The state of Kerala, in southern India, pummeled by rainfall deluge during the monsoon seasons of 2018 and 2019, experienced several landslides and ravaging floods in vulnerable tracts; 65 landslides were reported during the seasonal downpour between June 1 and August 16, 2019 (Chandran (2019); Manorama Online, Aug. 2019). Huge losses taking a toll of 81 lives and heavy damage to property were reported. Around 8.0 p.m. of 8 August 2019, Kavalappara (site 1, see Fig. 1) in Puthukkad area of Malappuram district suffered multiple hazards of landslide and floods (Shaju Philip, August 2019). The landslide was initiated along the northfacing hill-slopes. The 4th order stream joining the Chaliyar River, flowing west to east, started flooding since the morning of the same day. At 12 noon, the flood level reached more than 2 m above the bridge at Bhoodanam in the Puthukkad area. Similarly, the upper drainage catchment sub-basins, located in Puthumala area (site 2, Fig. 1), in Meppadi region of Wayanad district, were ravaged by multiple hazard floods and landslide events, around 4.0 p.m. of 8 August 2019. Here, the landslides occurred along the north-facing hill-slope in a structurally controlled sub-basin of the Chaliyar River. A semi-structured interview with the Kavalappara residents settled on
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