NBRO to educate public on inherent dangers:

Seventy landslide-prone areas identified

By Mohammed NAALIR

The National Building Research Organisation (NBRO) has mapped out 68 to 70 areas highly vulnerable to landslides in the Kandy, Matale, Nuwara-Eliya, Badulla, Kalutara, Ratnapura, Kegalle, Galle, Matara and Hambantota districts. After the recent heavy rains 300 landslide-prone areas have been identified in these districts, including, Gampaha and Colombo. Eleven locations have been identified in the Gampaha district alone. Landslide Studies and Services Division Head, NBRO, R.M.S. Bandara said.

Mitigation work will be carried out in three phases. The Kandy, Nuwara Eliya, Badulla and Matale districts will be mitigated under the first phase, Kalutara, Ratnapura and Kegalle districts under the second phase and Galle, Matara and Hambantota districts under the third phase, according to the Landslide Studies Division Head.

The NBRO consists of six divisions such as Landslide Research and Risk Management, Building Material, Human Settlement, Environment, Project Management and Geo Technical Divisions. All these institutions are engaged in various studies and provide consultant service to the public, Government and private institutions.

Heavy rains is the cause for landslides in hilly areas. Man-made errors also account for landslides. Geological, hydrological conditions and the angle of slope are natural causes, while bad land use practices, non engineer-consultation during construction and constructing structures obstructing the drainage path are man-made causes for the occurrence of landslides.

The high, medium and low hazard zones have been clearly indicated in the map. Even after the mapping some landslide prone areas have been identified away from these zones. Man-made errors have induced these areas to become vulnerable to landslide. The NBRO will not consider such incidents as landslide even though it comes under the landslide category. Such occurrences are called cutting failures, Bandara said.

Last month the NBRO reported a landslide in the Kadawatha area. Unauthorised building practice was the main reason for this incident, he said.

"Cutting failure" is the term used by the NBRO for such incidents. "Cutting failure" means the slip of unstable land cuts during heavy rains. Unstable cuts are created as a result of bad land use practice during construction. An unstable cut is between two to three metres in width.

Normally, it is believed that only hilly areas are vulnerable to landslide; but Kadawatha, Gampaha, Ja-ela, and Piliyandala areas in the low land has also come under the landslide prone zone due to man-made errors.

Bandara said adjoining districts to the landslide prone districts also experience landslide incidents, for example, in a location where the main hill would be in one district while its slope will appear in another district. A landslide incident was reported at Wathupitiwala in the Gampaha district last month. The main hill is in the Kegalle district while its slope stretched out to the Gampaha district. Several such incidents have been reported in other districts too. A landslide occurred in the Moneragala district, spreading out to the adjoining district, Badulla. Two such incidents occurred in Ridigama and Mawathagama in the Kurunegala district. Kurunegala is an adjoining district to Kandy and Matale. Districts close to landslide prone districts are also affected according to Bandara.

Mitigation work means, to identify the landslide prone areas and take preventive measures by restructuring the soil mess.

The NBRO officers have been kept in the alert in the landslide prone districts to take precautionary measures if an area is identified as vulnerable to landslide. Zoning maps will help commence mitigation work identifying the landslide prone areas.

Besides, the NBRO also carries out mitigation work in areas where already mitigation works were carried out to prevent the extension of the landslide. Various mitigation methods are used in Sri Lanka.

The NBRO used traditional methods to carry out mitigation work. Now gradually, they are using modern technologies with the help of friendly nations. Japan and Canada are helping us in mitigation work.

Peradeniya before mitigation in 2006

The mitigated location in Peradeniya

Elapatha landslide

Thus the NBRO is developing new mitigation methods with the help of modern technology, Bandara said.

He said, mitigation work is not risky. If the reason for the landslide is identified clearly, mitigation work can be carried out easily. If it fails to identify the prime cause mitigation work would be risky. If the mitigation work was carried out blindly the ultimate goal cannot be achieved.

The NBRO conducts proper investigations, works out proper plans and implements suitable mitigation methods at proper locations, Bandara said.

The United Nations, JICA, Austrian Government, Thailand and other countries help Sri Lanka in carrying out mitigation work in landslide prone areas.

The Government has accepted the integrated landslide mitigation plan submitted by the NBRO. Now the NBRO is striving to raise funds to commence mitigation work soon in landslide prone areas.

No landslide has been reported in the mitigated location in Peradeniya. The NBRO mitigated highly vulnerable locations in Peradeniya under the first phase. The mitigation work is progressing and will be completed by end December. There is a landslide prone location on the other side of the mitigated site, with houses, shops and boutiques close to the location.

Even though this area has been declared by the NBRO as a hazard zone the people are yet to evacuate the area. The NBRO is unable to start mitigation work until such time.

The NBRO has submitted a proposal to the Government to mitigate this area. It is not a natural landslide prone location, but has become vulnerable due to man-made errors.

The area housing the Nurses' Quarters in Kandy is still in danger. The NBRO has submitted a proposal to the Government to commence mitigation work in this area soon. Lack of funds is the cause for the delay. However, mitigation work is expected to commence next year, Bandara said.

The NBRO has given a clear recommendation for mitigation work in Haldumulla as there is the possibility of several rock falls behind the Haldumulla town. It has recommended to relocate the Haldumulla town. With heavy rains, rock falls may occur at any moment.

"According to geological denudation process slopes are made with soil, rocks and the mixture of soil. Some slopes consist colluvium deposits. Colluvium deposits mean transported materials. If we visit Haldumulla we could see a big escapement and there is a slope that contains colluvium soil. Colluvium soil means transported material mixed with soil, rock and boulders. It is not compacte soil.

When water drains through the area, if the slope is high it will start to move," Bandara explained.

The NBRO creates awareness among people in grassroots level, schoolchildren, Grama Niladaris, Samurdhi officers, planners and designers. Schoolchildren and the public are the target group of the NBRO.

Sustainable solution means in any construction work in hilly areas, primarily one has to consider landslide threat areas. The NBRO has issued a circular to the authorities to seek its approval when any type of construction is carried out.