Landslides, natural as well as man-made

By Justice P. H. K. Kulatilaka

Landslides study belongs to a multi-disciplinary domain, and in order to contain hazardous situations arising from landslides, a concerted effort is necessary. For such an effort, expertise and know how available in our universities should be properly tapped. In this regard the expertise and experience of qualified staff in the State institutions also must be obtained.

Causative factors

Landslides cause destruction of lives and property and also displacement of large numbers of people. There are instances where whole villages being totally destroyed by landslides. Landslides occur due to masses of soil or rocks slipping down slopes, under gravity. When a slope has no proper drainage, rain water is retained within the soil mass. Surface soil becomes heavier with water. Hence, there is a tendency to slide down due to increase in the gravitational pull. If this mass is on slip surface a landslide will occur.

Earth tremors and flash floods also trigger off landslides along lines of weakness. Such phenomenon can occur in the event of the dam-breaking and draw down in reservoir areas. Causative factors could be brought under four heads, namely:

(i) Ground condition, (ii) Geomorphologic process, (iii) Physiological process, (iv) Man-made process.

Apart from the natural factors, man's unwarranted intervention with the environment by way of deforestation, cultivation on slopes (Kandapola is a case in point), non-engineered construction (Ginigathhena) obstructing natural drainage (Kandapola) improper drainage, mining and quarrying causing artificial vibration coupled with continuous heavy rainfall or excessive rainfall may lead to landslides.

In the year 2006 a massive landslide buried the entire Peradeniya town making it a ghost town, just above Mahaweli. Non-engineered constrictions cutting right into the naturally steep slope seems to be the causative factor.

It is estimated that there are about 12,500 square kilometres in the island prone to landslides. In 1986 there had been a series of landslides, 51 people died and 10,000 people were displaced. In 1989 about 31 people died of this disaster. In 1994, landslide at Hela Uda in Ratnapura killed 31 people. In 2003, landslides associated with floods in Ratnapura took away the lives of 120 people and 35,000 families had to be evacuated.

Experts are of the view that this episode was mainly by due to obstructions created by unscrupulous gemming and sand mining and cutting into banks of the rivers and tributaries using heavy equipment such as backhoes.

Timely information

National Building Research Organisation (NBRO) is the institution responsible for giving timely information of an impending landslide. In order to identify landslide prone areas Landslide Hazard Zonation Mapping project is in progress.

This project covers ten districts, namely: Badulla, Ratnapura, Kalutara, Galle, Nuwara-Eliya, Kandy, Matara, Kegalle, Matale and Hambantota.

Research has been undertaken in respect of hydrology, geology, slope, soil types etc. for identification of different hazard potential. Zoning is based on the risk factors involved. Zoning is to the following effect:

1. High hazard zone, 2. Medium hazard zone, 3. Where the landslides are likely to occur and, 4. No risk zones.

Mapping project

1. Mapping of the distribution of landslides hazard potential in the highlands of Sri Lanka.

2. Introduction of standard guidelines and codes on practices for planning human settlements and infrastructure in the landslide prone areas.

3. Establishment of sustained long term and short term mechanism for landslide disaster management in Sri Lanka.

In this regard landslide Studies and Survey Division (LSSD) of NBRO function as a service sector performer as well as research institutions providing necessary information to Divisional Secretaries, Urban Development Authorities, Pradeshiya Sabhas and other local authorities.

Landslide Hazard Zonation map are made available to the aforesaid institutions on payment of a nominal fee. These map cover land use and management slope category and land forms. Further zonal mapping gives an indication as to what the landslide prone areas are.

Hazard zonation maps can be made use of by the local authorities and other institutions to decide areas where potential buildings should be prohibited. It can be used to avoid settlement, development in moderately landslide prone areas.

Any way there is provision for making exception for engineered construction.

In the process of relocation, LSSD has the capacity to investigate land suitable for the relocation by evaluation of stability of soil.

Co-ordination

Landslide occurrences are closely associated with rainfall. Therefore, Meteorology Department also plays an important role by providing weather related information. This is being done via telephone dial up link.

Creation of public awareness about causative factors of landslide and disaster mitigation is also part of the mechanism.

University of Peradeniya had introduced such awareness programmes at Koslanda Maha Vidyalaya in Haputale in the year 1998. Further NBRO has undertaken several awareness programmes.

The factors that should be considered, while being watchful during heavy rainfall, can be summarised as follows:

(i) Big boulders would start moving.

(ii) Tress would slant towards the slope.

(iii) Coconut trees and arecanut trees start showing signs of decay

(iv) Cracks would appear on the walls and other structures.

(v) Springs and water spouts would appear and there will be rise in the water level.

(vi) The earth itself would show cracks and fractures.

Some suggestions

NBRO appears to be the institution in-charge of and responsible for landslides. But a recognised legal structure has not been established. Hence it is necessary recognise the LSSD as the only governmental institution responsible for landslide investigation, mitigation and conducting related research. Presently even the Meteorology Department issues warnings regarding landslides without required experience, expertise and knowhow in landslide. Therefore, if the Meteorology Department is to continue to give media statements, in order to avoid panic situation among people living in these areas, they should do so after consulting Landslide Studies and Services Division of the NBRO. Modern communication systems should be in place to give warning.

Need for legislation

There has to be legislation to prevent people who have been relocated from coming back to the same area from which they were evacuated. In 1994 after the landslide which buried part of Hela Uda village in Ratnapura about 40 families were relocated in 'Pibidunagama' but most of the people had sold the new land given to them 'Pibidunagama' and had gone back to Hela Uda.

Data Base Research Unit

Establishment of the Data Base Research Unit for assessment of potential areas for landslide, seems to be a vital requirement. It is necessary to improve the instrumentation at the Meteorology Department, which would enable the Meteorological Department to provide accurate weather related information to National Building Research Organisation and to the public. According to the Meteorological Department sources, arrangements have been made to install a modern Doplar Radar Station in Sri Lanka. It would enable the Meteorological Department to provide instant weather information relating to any area at any time.

(The writer is a former Judge of the Court of Appeal, Deputy Director, Sri Lanka Judges' Institute, Member of the Tsunami Commission)