Two years on: How safe are we from a future tsunami?

Peradeniya Engineering Faculty focuses on tsunami risk reduction through education and hazard mapping

Extracts of a keynote lecture delivered by Dr. Janaka Wijetunge of the Faculty of Engineering, University of Peradeniya at the Conference on Rehabilitation of the Tsunami affected coasts organized by the Indian Institute of Technology (IIT), Chennai, on December 12, 2006.)

Two years ago, on December 26, 2004, the coastal belts of several Indian Ocean countries including Indonesia, Sri Lanka, India and Thailand suffered massive loss of life and damage to property due to the tsunami unleashed by the third largest earthquake ever recorded. In Sri Lanka, 13 of the 14 districts lying along the coastal belt were affected: the death toll was over 35,000 with 20,000 injured and about 100,000 housing units either completely or partially damaged leaving half a million people homeless and causing massive disruption to livelihoods. The fisheries and tourism sectors were among the hardest hit with many fishing boats and beach-front hotels damaged or destroyed.

The enormity of this unprecedented tragedy made all of us painfully aware of the potential vulnerability of the coastal belt of our country to the forces of nature, especially to the extreme geological and meteorological happenings in the vast expanse of the Indian Ocean around us.

The way in which we ought to respond to the threat of any hazard depends on its severity as well as how frequently that hazard is likely to strike. Therefore, our approach and strategy in mitigating the risk from a future tsunami should be formulated based on an assessment of the severity and the frequency of the tsunami threat for Sri Lanka. For example, if the December 2004 tsunami were to occur, on average, once in 50 to 100 years, then one may argue that all structures built in the inundation zone be made tsunami-resistant. However, if the December 2004 tsunami was a once in 250 to 500 year or greater event then questions may be raised about the applicability of such tsunami-resistant construction standards, when the life expectancy of a structure may only be 70 to 100 years. Several preliminary investigations based on plate tectonic theory as well as the history of past events in the Andaman–Sumatran earthquake zone seem to suggest that the frequency of recurrence of an ocean-wide tsunami similar to the one that occurred in 2004 is very low. Therefore, we must realize that it is neither economically feasible to mitigate the potential damage due to such low frequency tsunami events through engineering interventions such as building of giant seawalls, nor is it socially acceptable to exclude people and buildings entirely from the damage prone areas. Consequently, what we require is an integrated approach to tsunami risk mitigation, consisting of public education & awareness, early warning & evacuation, hazard & vulnerability mapping, and necessary institutional & legislative initiatives, all of which are non-structural measures.

In connection with early warning, it must be added that the Intergovernmental Oceanographic Commission (IOC) of the United Nations Educational, Scientific and Cultural Organization (UNESCO) has been coordinating the efforts of the international community led by the Government of the United States of America to develop a tsunami early warning system for the Indian Ocean, similar to that currently used in the Pacific, by the end of 2007. The proposed Indian Ocean Tsunami Warning Network, though by no means a foolproof system, will help improve Sri Lanka’s tsunami early warning capability and reliability. Yet, the more difficult and challenging task will be the dissemination of such tsunami warnings fast and effectively to the vulnerable communities so as to enable their evacuation to safe locations before the arrival of the tsunami.

Clearly, evacuation of people to safer locations ought to be done in a predetermined manner lest the result be chaos. Therefore, we need to know which areas are safer and which areas are not in order to prepare such evacuation plans. In other words, it is essential to identify risk areas of the coastal belt of the country through development of tsunami hazard maps which provide a graphical presentation of damage-prone areas with expected degree of damage in case of tsunami attack, and often, such maps also contain information relating to evacuation locations and evacuation routes. However, the short length of the historic record of tsunami in the Indian Ocean does not permit a comprehensive probabilistic tsunami hazard assessment. In such situations, the commonly employed method in Japan and in the USA is to make use of the worst credible tsunami event from the available historic earthquake and tsunami records as the basis of hazard and evacuation maps. The tsunami that occurred in December 2004 can be considered as the worst case scenario for Sri Lanka, so preliminary versions of our hazzards maps for the coastal belt of the island could be based on that event. Such preliminary hazard maps should be refined as further studies of tsunami source areas as well as mathematical modelling of tsunami propagation and inundation yield new information.

As the preliminary versions of tsunami hazzard maps for the country are to be based primarily on the December 2004 tsunami, the Engineering Faculty of the Peradeniya University, with financial support from the National Science Foundation, carried out an extensive field survey in the east, south and west coasts of Sri Lanka to trace the extent of tsunami inundation, that is, how far the surge of tsunami water travelled inland.

The extent of tsunami inundation was determined based on damage to structures, trees and vegetation, lines of debris and location of wreckage as well as eyewitness accounts of overland flow. At many locations, local people could give reliable information about the maximum level of tsunami flooding, for example, “water came up to this step of this temple …”. The furthest limit of tsunami inundation at about 200 to 400 metre intervals along the coastal belt was obtained in this way by employing a hand-held Global Positioning System (GPS). The field measurements have now been processed on a Geographical Information System (GIS) to develop comprehensive inundation maps for the coastal belt of the country with facility for overlaying of topography and land use data, as shown in the sketch, for example, for a short stretch of the south-west coast near Beruwala.

The inundation maps so developed, however, do not provide any information about the depth of flooding, which is essential for a tsunami hazard map. Therefore, Peradeniya University Engineering Faculty in collaboration with the Cornell University, USA and with financial support from the USAID is at present building computer models of overland flow due to the tsunami in December 2004 as well as other probable scenarios. Such computer models of tsunami inundation are used to obtain vital information such as depth of flooding and flood velocity required for delineation of hazard zones. The tsunami hazard maps developed under this project will be made available to the respective local authorities as well as relevant government organizations through the Disaster Management Centre of the Government of Sri Lanka.

The tsunami disaster in December 2004 also revealed the need for a proactive approach to disaster management as well as for building local capacity in disaster risk mitigation and management. Given the inter-disciplinary nature of the subject of disaster management, Peradeniya University with seven faculties spanning a broad spectrum of disciplines was in a unique position to offer an advanced programme of study in disaster risk management. Accordingly, two entities of the University of Peradeniya, the Postgraduate Institute of Science (PGIS) and the Faculty of Engineering pooled their resources as well as expertise from other departments of study to offer a Masters Degree Programme in Disaster Risk Management with continuous support and encouragement from the Ministry of Disaster Management and Human Rights and in collaboration with several overseas institutions including the Asian Disaster Preparedness Centre.

The primary objective of this programme is to support the development of disaster risk management capacity within governmental, non-governmental and private sector organizations in order to improve their ability to manage the variety of disasters. There was considerable demand and enthusiasm from all parts of the country for this programme, and currently, 45 participants from a wide array of backgrounds such as engineering, geology, physical and biological sciences, medicine, public administration, and sociology are reading for their Masters Degree in Disaster Management.

The PGIS has also conducted several short courses, workshops and seminars in the general area of disaster mitigation and management for mid-level professionals engaged in disaster related activities. Moreover, at undergraduate level, the Engineering Faculty of the Peradeniya University regularly offers Disaster Management as an elective course to its final year students with emphasis on the need for sustainable development through disaster risk reduction.

Finally, the country as a whole has taken significant steps towards disaster risk reduction since the tsunami devastation in December 2004. We now have a sound disaster risk management institutional framework underpinned by necessary legislative provisions. A comprehensive and holistic strategy has been formulated to unify, prioritize and coordinate the disaster risk management activities that have been planned to be implemented in the next ten years towards building a safer Sri Lanka. As a result, we as a nation are expected to face disasters better than what we were two years back, yet there is a long way to go to make ourselves disaster resilient.

The writer is Senior Lecturer in Coastal & Ocean Engineering and the Joint Coordinator of the postgraduate degree programme in disaster management, Faculty of Engineering, University of Peradeniya