Evaluation of the factors controlling the spatial distribution of soil piping: a case study from the southern Western Ghats, India

Soil piping (tunnel erosion) is a soil-related natural disaster. It is a type of sub-surface erosion, which involves the hydraulic removal of sub-surface soil causing the formation of an underground passage in landscape. Soil piping significantly affects the most responsive run-off systems of the humid tropics. Southern parts of the Western Ghats have recorded seven incidents of this phenomenon within a period of 1 year, starting from August 2010 to August 2011. Out of the seven incidents recorded from the Ghats regions falling in Idukki District of Kerala, south India, the main aspects and parameters of four locations were evaluated and correlated by synthesizing the physical, chemical, geological and hydrological parameters. The evaluation showed a similar expression of physical, chemical and hydrological components of soil at the sites 1, 2 and 4, which does not normally favour the phenomena of soil piping, while site 3 has chemical components favouring its development. Even though the pipe outlets were observed at or near the foothills, the mechanism behind the recharging is to be clarified further more. The study reveals that the phenomenon has been recorded from a variety of geographical entities with no common contributing system, except the intensity of rainfall and vicinity to prominent structural controls. Hence, the increased periodicity of occurrence of the incidents is attributed to the stress-induced dilatation of the sub-surface water-bearing formations before and after a series of mild tremors recorded contemporaneously from Idukki District, Kerala.