‘Human activity’ main cause of landslides

By Isuri Kaviratne

Many AGA divisions of Sri Lanka are being affected by natural disasters and some have been identified as being unsuitable for human habitation due to landslides, floods and cyclones. A key factor in all these disasters was rain, as heavy downpours caused most of these natural disasters.

Landslide Studies and Services Director of the National Building Research Organization (NBRO), R.M.S. Bandara said some areas in Badulla, Nuwara Eliya, Hambantota, Galle, Matara, Kalutara, Ratnapura and Kegalle Districts could be referred to as areas highly vulnerable to landslides and not suitable as human habitat. He explained that even though landslides occur in Kandy and Matale Districts as well, most vulnerable areas could not be specifically identified.

“The areas which receive the heaviest rainfall are those most endangered. The problem is compounded when buildings have not been constructed according to appropriate mitigation structures. This increases the danger of landslides”, he said.

He added landslides occurred as a result of natural causes as well as due to human activity. Some areas vulnerable to landslides have been identified. But, research conducted by the NBRO revealed that 4/5th of landslides occur due to human activity. “Hence, good habitats constructed on unstable land too could become inappropriate later”, he explained.

“We moved people from some areas due to the danger of landslides but when moving them out of these areas becomes problematic, we educate people in those areas on how to minimize the danger”, he added.

The Hydrological division of the Irrigation Department too confirmed the reason behind the recent flooding as being due to illegal constructions. Floods reaching heights of 5 - 7 ft. are considered minor floods, 7 - 9 ft. major floods, 9 – 12 ft. dangerous floods and over 12 ft. is considered a critical flood.

A Hydrological division engineer said most floods in Sri Lanka are considered minor floods and a major flood had been a very rare occurrence. The Kelani, Kalu, Bentara, Gin and Nilwala rivers have been prone to flooding in recent times. Certain areas in Kelaniya, Biyagama, Kalutara, Ratnapura, Deniyaya, Morawaka, Bentara, Akuressa, Athuraliya were recognised as being flood-prone.

Despite floods occurring twice within a single month in the same area this year, such instances were rare and added the lands could not be identified as being unstable. The Deputy Director of the Meteorological Department, S.H. Kariyawasam said lightning also posed a major problem and occurred particularly when heavy rain fell.

Studies have revealed lightning occurred more frequently on the slopes and at the foot of mountains. The Uva, Sabaragamuwa districts and interior parts of Galle and Kalutara were particularly vulnerable to lightning.

According to the Meteorological Department, flooding would occur in the southeast and northwest due to heavy rains brought by the southwest and northeast monsoons respectively. Accordingly the eastern slopes and western slopes of Nuwara Eliya district become vulnerable to landslides.

“Cyclones are associated with heavy rain and thunderstorms. Strong winds are to be expected during the southwest monsoon. Areas in the south and west of the country would be affected he said. Spokesperson for the Geological Survey and Mines Bureau (GSMB) said though minor tremors were reported at Sigiriya this April and at Beralihela in the Hambantota district, last year the areas could not be identified as being earthquake prone.

Regarding the possibility of a recurrence of a tsunami, the GSMB said despite predictions being made of earthquakes near the Makran Strip, near Pakistan, so far none had been confirmed.

The Indonesian area the GSMB said had been identified as a zone prone to earthquakes due to the movement of the earth’s tectonic plates moving over each other. The agency said this created a negative impact on coastal areas.

However though tremors had occurred in the south, they had never recorded level 5 on the Richter scale which was insufficient to impact Sri Lanka.

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