KOCHI: The spell of torrential rain, raging floods and devastation unleashed by the landslides have indeed come as a warning for Kerala. The state should put brakes on rampant constructions in ecologically-fragile areas or it would face more catastrophic natural calamities, cautioned two experts from the US National Science Foundation (NSF)- sponsored Geotechnical Extreme Events Reconnaissance (GEER) Association, who toured the flood-affected areas and documented the factors that led to the devastation.
“Around 90 per cent of the landslides occurred at places where new construction projects were under way. It is evident human intervention in ecologically-fragile areas has led to extreme events like debris flow and earthflow. Cut-slope excavation for construction of buildings, without considering the slope characteristics has exposed the sub-surface drainage channels. The strength of the soil in Munnar is very low and as water accumulates in the sub-surface water channels, it breaks leading to massive flow of mud and water,” Michigan Technological University associate professor Thomas Oommen told Express.
He said the earthflow at Munnar Government College was a typical example of human-induced geological hazard. “A study conducted by Kerala University associate professor K S Sajin Kumar in 2012 had cautioned the college was located on terrain which was prone to extreme geological events. A landslide had occurred on the same terrain in 2005, which partially damaged the college building.
A series of concentric cracks were visible above the crown of the landslide in 2012 itself. This was indicative of an imminent landslide. The college was shifted from the campus for five years following the 2005 landslide. But it was brought back to the campus ignoring the recommendations. Another crown or scarp has developed on the left side of the earthflow. It may fail any time in the event of a heavy rainfall and will wash away the physical education department building of the college,” said Thomas Oommen.
Depletion of water in rivers and wells
During the floods, the heavy flow of water eroded the top layer of the soil in the river bed, increasing the depth of rivers. The top layer of the river bed had low permeability and could hold water. When the top layer was washed away, the rocky bottom layer might have got exposed. The increase in the river depth has led to depletion of the ground water table. This explains the drying up of wells. But we can’t say these are signs of a severe drought, said Thomas Oommen.
Mass death of earthworms in Wayanad
The earthworms live in the topsoil which is rich in organic matter. They might have wriggled out of the burrows as the floodwater entered their habitats. They live in moist soil and cannot survive in warm climatic conditions. Once the earthworms emerge from the burrows they die, said Thomas Oommen.
‘Opening of dams aggravated floods’
According to Thomas Oommen, it was the extreme rainfall that led to the flood situation in Kerala. But the opening of dams created a situation where the water level rose dangerously. “I think there should be better coordination between the Met Department and the authorities operating the dams. People do not take the weather warnings seriously due to inaccuracy. Steps should be taken to conduct flood susceptibility mapping. You can use digital elevation map to mark the areas prone to flooding. We should have rain gauges to monitor rainfall on an hourly basis. The data from the rain gauges should be compiled by a control room,” he said.
‘Floods have destabilised building foundations’
Kochi: The floods have destabilised the foundation of many buildings, including houses, in Kuttanad. After the flood situation eased, several houses developed a tilt towards the direction of the draining water. This points to the weakening of the foundation. As the soil in Kuttanad is weak, many houses have asbestos roofing to reduce building load. Even these houses have tilted, said University of Arkansas associate professor Richard Coffman, who toured Kuttanad to study the impact of the flood. The foundation of houses has moved or shifted due to flooding, causing intense foundational and structural damage, he said.