Large parts of Kerala are highly vulnerable to land subsidence owing to a widening network of underground tunnels, experts participating in a workshop organised by the National Centre for Earth Sciences (NCESS) here on Monday have warned.
All but three districts
Citing a study conducted by NCESS and the State Emergency Operations Centre (SEOC), scientists from various research institutions across the country said subsurface tunnels, some of them extending across several kilometres, had been reported from all but three districts in the State.
Revenue Minister E. Chandrasekharan, who inaugurated the workshop, said the government had declared soil piping a State- specific hazard, considering the magnitude of the threat to life and property.
The vulnerability to land subsidence is attributed to soil piping, the formation of tunnels owing to subsurface erosion.
According to the study submitted to the National Disaster Management Authority (NDMA), the phenomenon has emerged as a serious problem in Kerala and the adjoining districts in Karnataka.
Kannur and Kasaragod districts are the worst affected while the problem is widespread in Wayanad and Idukki and sporadic in Palakkad, Pathanamthitta, Kozhikode, Ernakulam, Kottayam, Malappuram, and Thrissur.
Experts who addressed the delegates expressed concern over the safety of the Banasurasagar earthen dam in Wayanad because of soil piping in the locality.
In Kannur, Kasaragod
Principal Investigator of the study G. Sankar said scientists had come across gaping underground tunnels, more than 10 feet wide, in Kannur and Kasaragod. Some of the gullies had caved in, damaging roads and farmlands and affecting groundwater storage.
The whole of Udayagiri village in Idukki district was found to be sitting atop a network of tunnels formed by soil piping.
Cases of land subsidence had been reported a few km downstream of the Banasurasagar dam.
Using electrical resistivity studies, ground penetrating radar, push cameras, and geophones, scientists have mapped the areas vulnerable to soil piping in the 11 districts.
The proposed mitigation measures include the use of discarded tyres to trap sediment, diverting water flow, and application of gypsum and lime to soil.
In Karnataka
Soil piping has also been reported from the Kodagu, Mysuru and Chamarajanagar districts bordering the Western Ghats in Karnataka.
M. Rajeevan, Secretary, Ministry of Earth Sciences; D.N. Sharma, Member, NDMA, and Suresh Das, Principal Secretary, Science and Technology, were among those who addressed the workshop.
