RISK ASSESSMENT AND MANAGEMENT FOR TSUNAMI HAZARD

Sri Lanka

RISK ASSESSMENT AND MANAGEMENT FOR TSUNAMI HAZARD Case Study of the Port City of Galle

Empowered Lives. Resilient Nations.

Risk Assessment and Management for Tsunami Hazard

Case Study of the Port City of Galle

The analysis, opinions and policy recommendations contained in this publication

do not necessarily reflect the views of UNDP.

United Nations Development Programme

Asia-Pacific Regional Centre

UN Service Building

Rajdamnern Nok Avenue

Bangkok 10200 Thailand

http:// sia- acific.undp.org

Copyright © UNDP 2011

Cover photo: WHO / Armando Waak

Design and Layout: Inís Communication – www.iniscommunication.com

Dr. S.S.L. Hettiarachchi, University of Moratuwa, Sri Lanka

Dr. S.P. Samarawickrama, University of Moratuwa, Sri Lanka

Dr. N. Wijeratne, University of Ruhuna, Sri Lanka

Risk Assessment and Management for Tsunami HazardCase Study of the Port City of Galle

Published by United Nations Development Programme, Asia-Pacific Regional Centre

in partnership with ICG/IOTWS Working Group on Risk Assessment under the

UNESCO/IOC framework

2011

Galle

ii Risk Assessment and Management for Tsunami Hazard

Key terms

Definitions

Hazard A natural or human-induced threat to people and their welfare

Vulnerability Exposure and susceptibility to losses in terms of deaths, injuries, property,

livelihoods, disruption of economic activity or environmental impacts

Risk The probability of hazard occurrence, associated with people’s vulnerability to

potential damage and losses.

Capacity The means by which available resources, abilities and knowledge are utilized;

the ability of individuals, organizations and societies to perform functions, solve

problems, and set and achieve objectives

Capacity development The process through which the abilities to do so are obtained, strengthened,

adapted and maintained over time

Acronyms and abbreviations

ANUGA This refers to a specific mathematical model for tsunami simulation.

APRC Asia-Pacific Regional Centre

AVI-NAMI This refers to a specific mathematical model for tsunami simulation.

EWS Early Warning System

ICAM Integrated Coastal Area Management

IO Indian Ocean

IOC Intergovernmental Oceanographic Commission

IOT Indian Ocean Tsunami

IOTWS Indian Ocean Tsunami Warning System

ISDR International Strategy for Disaster Reduction

UN United Nations

UNDP United Nations Development Programme

UNESCO United Nations Educational, Scientific and Cultural Organization

UNISDR United Nations International Strategy for Disaster Reduction

USAID United States Agency for International Development

WAPMERR World Agency of Planetary Monitoring and Earthquake Risk Reduction

WG-RA Working Group on Risk Assessment

Risk Assessment and Management for Tsunami Hazard iii

Contents

Foreword ___________________________________________________________________________ 1

1. Risk – Components of risk and its assessment ____________________________________ 3

1.1 Risk __________________________________________________________________________ 3

1.2 Hazards _______________________________________________________________________ 4

1.3 Vulnerability ___________________________________________________________________ 4

1.4 Capacity, preparedness and improvement of community resilience ______________________ 5

1.5 Tools and methods for tsunami risk assessment ______________________________________ 5

2. City of Galle – damage and mechanics of tsunami wave impact _________________ 6

3. Tsunami hazard analysis _________________________________________________________ 8

3.1 Approaches to tsunami hazard analysis _____________________________________________ 8

3.2 Post-tsunami field investigations __________________________________________________ 8

3.3 Deterministic tsunami hazard modelling ___________________________________________ 10

3.4 Probabilistic tsunami hazard modelling ____________________________________________ 13

3.5 Hazard analysis for risk assessment _______________________________________________ 14

4. Vulnerability ____________________________________________________________________16

4.1 From a single dimension of susceptibility to a three-dimensional sector approach ________ 16

4.2 Simplified approach to vulnerability ______________________________________________ 17

5. Risk assessment _________________________________________________________________18

6. Managing Risk – Classification and planning risk management measures ______19

6.1 Classification of risk management measures ________________________________________ 19

6.2 Planning risk management measures via policy and management options _______________ 20

6.3 Classification of physical interventions (artificial and natural) __________________________ 21

6.4 Development of guidelines for tsunami-resistant buildings ___________________________ 21

7. Mitigation and its integration with development projects ______________________21

8. Preparation of disaster management maps _____________________________________23

9. Coastal community resilience ___________________________________________________26

9.1 Coasts at risk __________________________________________________________________ 26

9.2 Establishing the resilience of coastal communities ___________________________________ 26

10. Concluding remarks ___________________________________________________________28

References _________________________________________________________________________30

Risk Assessment and Management for Tsunami Hazard 1

Foreword

IN THE AFTERMATH OF THE INDIAN OCEAN TSUNAMI, the Indian Ocean States decided to establish a

tsunami warning system under the Intergovernmental Oceanographic Commission of the United Nations

Educational, Scientific and Cultural Organization (UNESCO/IOC). Activities in this direction were initiated in

March 2005. The member States decided that the Indian Ocean Tsunami Warning System (IOTWS) would

be a coordinated network of country systems in which each country has the responsibility of identifying

hazards, assessing risk and issuing warnings to its own population. In this respect they will be assisted by

regional tsunami warning centres to be established in some of the Indian Ocean countries. India, Indonesia

and Australia are establishing centres for this purpose. In order to assist the establishment of the IOTWS, six

working groups were formed, one of which was dedicated to risk assessment within a multi-hazard framework.

The Working Group on Risk Assessment (WG-RA) conducted a survey of the needs of its membership and it

was evident that there was a demand for a clear understanding of tsunami hazard in order to develop uniform

guidelines on tsunami risk assessment. It was suggested that the guidelines be developed in full consultation

with the member States and considering the existing knowledge base. In addition it was requested that

training programmes be offered to member States for capacity building in tsunami risk assessment and

mitigation.

The WG-RA adopted a three-pronged approach to its tasks:

1 The Indian Ocean tsunami hazard map was prepared by Geoscience Australia based on probabilistic

tsunami hazard modelling, with funding from AusAID, and in full consultation with regional and external

experts. Geoscience Australia provided leadership for this activity.

2 A tsunami risk assessment guide was prepared and published as UNESCO Manual and Guide No. 52.

This guide was prepared over a two-year period after several workshops with regional and external

experts. The UNDP Asia-Pacific Regional Centre (APRC) in Bangkok, the World Agency of Planetary Monitoring

and Earthquake Risk Reduction (WAPMERR) in Dubai and IOTWS provided funding for these activities. UNDP

supported the development of the guideline. In doing so, priority was given to understanding the existing risk

assessment framework in Indian Ocean countries and to ensuring that the guidelines captured the existing

knowledge base of Indian Ocean States.

3 Several seminars and workshops were held during the preparation of the tsunami hazard map and

the risk assessment guide. After the successful preparation of these two documents, a seminar and

workshop were conducted in Bangkok in November 2009 to provide training to member States on the use

of the tsunami hazard map and the risk assessment guide. The UNDP APRC in Bangkok, the Indian Ocean (IO)

Coast Map Project and IOTWS provided funding for this activity.

UNESCO/IOC has also undertaken a strong initiative within the IO-COAST MAP Project to assist nations in

the acquisition of nearshore bathymetric data and development of shallow water maps which are essential

for modelling of both episodic and chronic hazards and also for coastal development activities. The WG-RA

and UNDP APRC in Bangkok worked in collaboration with the IO-COAST MAP project to organize a successful

2 Risk Assessment and Management for Tsunami Hazard

training workshop in Bangkok in August 2009 on coastal mapping, modelling and risk assessment. UNDP also

sponsored two more national workshops in Sri Lanka and Indonesia in 2010 to provide training and develop

national capacity in tsunami risk assessment.

At the first global meeting of the tsunami warning systems, held in Paris in March 2009, the WG-RA proposed

that case studies of tsunami risk assessment be conducted in cities and regions covered by tsunami warning

systems in the Indian Ocean basin and other ocean basins. This report presents such a case study of tsunami

risk assessment and management in the Port City of Galle in Sri Lanka.


1. Risk – Components of risk and its assessment

Coastal communities all over the world are under severe pressure resulting from planned and unplanned

development, population growth and human-induced vulnerability. Coastal hazards are increasing in

magnitude, with greater frequency of extreme weather events and other impacts of global climate change.

These unprecedented changes are placing communities at increasing risk from coastal hazards such as severe

storms, tsunamis leading to coastal erosion, flooding and environmental degradation.

Planning and implementation of post-tsunami rehabilitation and conservation of coastlines should ideally be

undertaken within a multi-hazard coastal risk assessment framework giving due consideration to all coastal

hazards. Even when risk assessments are undertaken specifically in relation to tsunami hazard, it is important

to conduct such studies on a platform that can accommodate other coastal hazards.

1.1 Risk

Risk is primarily a function of hazard and vulnerability. It is usually expressed by the notation

Risk = Hazard x Vulnerability.

Hazard is understood as a potential natural or human-induced threat to people and their welfare, while

vulnerability is their exposure and susceptibility to losses in terms of deaths, injuries, property, livelihoods,

disruption of economic activity or environmental impacts. Therefore, in this equation, risk can be quantified

as hazard associated with the probability of occurrence, and with people’s vulnerability to potential damage

and losses.

Another popular expression for risk incorporates capacity and is expressed by the notation

Risk = (Hazard x Vulnerability) / Capacity.

Capacity represents the means by which the community utilizes available resources, abilities and their

knowledge base to confront adverse conditions that could lead to a disaster. In this respect community

preparedness is considered the pivotal factor. The strengthening of coping capacities usually builds resilience

to withstand the impacts of hazards, both natural and human-induced. Capacities thus focus on group

measures that are in place to cope with an event.

Prior to the Indian Ocean Tsunami (IOT), Sri Lanka had not adopted a planned approach towards preparedness

and response in relation to mega-disasters, an aspect which is considered vital in saving lives. Hence it seemed

more appropriate to focus on the importance of preparedness in relation to capacity. In this notation risk is

expressed as

Risk = Hazard x Vulnerability x Deficiencies in Preparedness.

The additional term represents certain measures and tasks, the absence of which could increase the loss of

human lives and property in the specific interval of time during which the event is taking place. This term is

also commonly identified as the inverse of capacity.

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For a detailed assessment of risk it is necessary to quantify the three main components of risk, which is a

challenging task. When risk is expressed in the form

Risk = Hazard x Vulnerability.

it is possible to quantify risk in terms of loss. However with the introduction of capacity or preparedness it is

difficult to adopt direct quantification methods.

There is no standard technique for such assessment of risk and a number of methods have been used by

researchers including quantitative and qualitative methods. Quantification based on qualitative description

(ranking methods) and quantification based on detailed analysis of respective parameters have both been

successfully adopted. Although studies relating to risk will be able to capture the significance of all the three

components, there are limitations in the assessment process. However, it is important that risk assessment

studies are conducted within the framework defined by the above formula. This aspect has to be kept in mind

when reviewing the outputs from studies on risk assessment.

1.2 Hazards

A hazard can be defined as a potentially damaging physical event, phenomenon or human activity that may

cause the loss of life or injury, property damage, social and economic disruption or environmental degradation.

Hazards are either of natural origin or induced by human activities. Hazards also include latent conditions

which may represent future threats. Each hazard is characterized by its location, intensity, frequency of

occurrence and associated probability. Therefore, hazards represent the possibility of occurrence of a natural

or human-induced event of a probable magnitude or intensity over a specific geographic area. ‘Exposure’

refers to the geographic area, human life, ecosystems and infrastructure potentially affected by the hazard.

The Indian Ocean Tsunami (IOT) focused global attention on the severe impacts of tsunamis. It was also

recognized that coastal communities are increasingly at risk from a number of hazards, broadly classified as

episodic and chronic hazards. These hazards, which may arise from natural phenomena or human-induced

events, have severe impacts on coastal communities, ecosystems and infrastructure.

Episodic hazards include severe storms, earthquakes, tsunamis and oil spills, all of which have limited

predictability and may result in major disasters. The communities should be made aware of these hazards,

their vulnerability and risks, and should be educated on the importance of preparedness in responding

to potential disasters which usually require long-term post-event recovery efforts. Chronic conditions

include shoreline erosion, flooding, sedimentation, sea-level rise and coastal environmental and resource

degradation. These conditions, which may result or increase from disasters arising from episodic hazards,

relate to processes which can be measured and monitored. They require long-term planning measures and

restoration efforts to reduce risks.

1.3 Vulnerability

Vulnerability represents conditions determined by physical, social, economic and environmental factors

or processes which increase the susceptibility of a community to the impact of hazards. Vulnerability can

be broadly classified into several components, including human, physical, socio-economic, environmental,

functional and administrative. Hence vulnerability is dependent on several factors relating to these


components. These include, among others, population density, building density and status, distance from the

shoreline, elevation and evacuation time. Assessment of vulnerability is complex and can be implemented

at different levels, commencing from very basic to highly sophisticated databases. Several models of

vulnerability are available.

1.4 Capacity, preparedness and improvement of community

resilience

The assessment of risk is an important element of coastal community resilience. In this respect, coastal

community resilience is identified as the capacity to absorb and withstand impacts of hazards, emerge from

disaster events and adapt efficiently to changing conditions. Economic and social development pressure

in coastal areas, increasing population density and distribution, and other human-induced vulnerabilities,

together with increasing frequency and duration of storms, long-term sea-level rise and other hazards,

have created conditions for disasters of high severity to occur more frequently. Under such circumstances,

communities have restricted capacity and reduced time to recover.

Global observations also reveal that the period of time between disasters and recovery is becoming smaller.

Therefore some communities are continuously facing disasters, event after event, depriving them of time to

plan and achieve long-term recovery. In effect, they lead a life of continuous response to varying disasters.

Such communities should be identified as high-risk areas and special area risk assessment and management

studies should be undertaken.

While vulnerability represents the extent to which a community is prone to be affected by the hazard,

deficiencies in preparedness represent the absence of measures and tasks which could reduce the loss of

human lives and property during disaster. In this respect, communities must be made aware of the hazards,

their exposure, vulnerabilities and capacity. The key areas requiring attention are awareness and education,

preparedness, early warning, response, evacuation, safe places and evacuation structures, and hazard-

resilient infrastructure. Enhanced coastal community resilience enables populations at risk to ‘live with risk’,

thus facing a wide range of coastal hazards with a greater degree of confidence.

The United States Agency for International Development in Asia (USAID/ASIA), in support of the IOTWS,

promoted a strategic approach to strengthening coastal community resilience to tsunamis and other coastal

hazards. This approach, which has been developed via a consultative process with national stakeholders,

provides an effective way of assessing coastal community resilience and is recommended for application.

It reflects community understanding of critical risk issues and therefore is linked to capacity. The approach

primarily deals with eight generic elements of coastal community resilience which are considered of pivotal

importance in reducing risk from coastal hazards, efficient recovery and adaptation to change. Resilience

has to be built up in each of these areas to ensure a well-balanced approach to strengthening community

resilience.

1.5 Tools and methods for tsunami risk assessment

Although a considerable amount of work has been carried out relating to tsunami risk assessment of whole

countries, regions and cities, there is no uniform approach to the definition of risk assessment and to

methods of risk assessment. The capabilities of the respective countries vary considerably with respect to the

availability of expertise, tools for analysis and quality of data used for such analysis.


Having recognized the existing knowledge base, the WG-RA of the Intergovernmental Coordination Group

for the establishment of the IOTWS produced two important guidelines with the support of member states

and donor agencies.

• Probabilistic tsunami hazard assessment of the Indian Ocean nations (Burbidge et al, 2009)

• Tsunami risk assessment and mitigation for the Indian Ocean (UNESCO, 2009a)

The latter was published as a UNESCO/IOC Guide.

In addition UNESCO/IOC also published a broad guideline on coastal hazards, entitled Hazard Awareness and

Risk Mitigation in Integrated Coastal Area Management (ICAM) (UNESCO, 2009b).

The three guidelines above provide a broader understanding of coastal hazards in the context of ICAM,

probabilistic tsunami hazard analysis, and tsunami risk assessment and mitigation for the Indian Ocean

states. They provide useful guidance to implementing tsunami risk assessment and mitigation studies within

the broader framework of integrated coastal area management. The guidelines provide sufficient flexibility

in implementing such studies, giving priority to critical variables as applicable to the region or city under

consideration.

The case study presented in this document for the Port City of Galle has made use of these guidelines,

focusing attention on critical parameters and the development of cost- effective risk assessment studies with

the active participation of stakeholders.

2. City of Galle – damage and mechanics of tsunami wave impact

Many coastal cities of Sri Lanka, particularly in the east and the south of the island, were severely affected by

the Indian Ocean tsunami, due to their exposure to the hazard. One of the principal coastal cities devastated

was the historic Port City of Galle located in the southern province of Sri Lanka. Incidentally, the first recorded

tsunami to have affected Sri Lanka was on 27th August 1883, arising from the eruption of the volcanic island of

Krakatoa. On this occasion too, unusually high water levels followed by receding water were observed in Galle

around 1.30 pm. The water level fluctuations were not severe and there was no inundation. The reported time

of the occurrence corresponds well with the travel time for tsunami waves that would have been generated

by the largest eruption of the volcano earlier in the morning. However, unlike this previous occurrence, on

26th December 2004 Galle received the severe impact of tsunami waves, their magnitude having increased

due to nearshore transformation processes. Five hundred persons were killed, 90 others disappeared, 1000

were injured and 8120 people were affected in total. Houses and other buildings damaged numbered 1600

and 1300 respectively. Galle is one of many coastal cities around the world remaining heavily exposed to

tsunami hazard. The presence of poorly constructed buildings and inadequate drainage contributed towards

increased vulnerability.

The tsunami waves which reached the offshore waters of Galle were primarily diffracted waves, diffraction

having taken place around the southern coast of Sri Lanka. In the context of tsunami hazard, the location

of Galle is heavily exposed. It lies beside a wide bay and a natural headland on which is located the historic

Galle Fort with very reflective vertical non-porous walls on all sides. Furthermore, there is the Dutch Canal

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west of the headland, conveying water through the city centre. The waves in the vicinity of Galle, which were

increasing in height due to reduced water depths, were further subjected to a series of nearshore processes

which increased wave heights even further. The canal was a facilitator in conveying the massive wave and

associated flow towards the city centre.

In the vicinity of the headland on which the Galle Fort is located, the wave energy concentrated due to

refraction. These waves then reflected from the vertical solid walls of the fort and moved around the headland.

The walls reflected almost all the incident wave energy with very high wave heights at the wall itself. There

was hardly any dissipation. On the west of the headland the waves moved ferociously into the Dutch Canal.

On the east they moved along the bay. The wide bay in Galle further contributed to the increase in wave

heights by modifying the shoaling process via reduced wave crest width to accommodate the bay shape.

The combined effect of this phenomenon and the wave coming around the eastern side of the fort caused

a massive wave of destruction along the Marine Drive (see Figure 1). It is certainly not surprising that many

survivors referred to a large black moving wall similar to that of the Galle Fort.

The City of Galle is therefore not only exposed to tsunami waves which diffract around the southern part of

Sri Lanka, it is even more exposed to nearshore coastal processes which further increase wave heights. This

aspect is identified as increased exposure within the risk assessment framework.

Figure 1: Galle Bay and headland

Bay – increase of speed, height and circulation

Headland – concentration of energy and spreading around the headland


3. Tsunami hazard analysis

3.1 Approaches to tsunami hazard analysis

Tsunami hazard analysis focuses on three areas: the tsunami hazard sources, exposure and the potential impact

on land. Tools and methods available to study the hazard include field investigations, image analysis and

mathematical modelling. The latter includes both deterministic and probabilistic tsunami hazard modelling.

With respect to tsunami hazard sources, attention is focused on previous events (their location, magnitude

and sequence), seismic gaps and the identification of ‘credible scenarios’.

When examining the exposure at a given location, due attention must be focused on submarine geological

features, the regional location that will identify the influence of key wave transformation processes, and

the location with respect to continental shelf and shoreline geometry. Depending on these aspects, the

amplitude of the tsunami wave may be enhanced, as was observed in the City of Galle.

Tsunami impact on land can be studied by measurements from field instruments, post- event field observations

and satellite images. In the aftermath of the IOT, attention has also focused on paleo-tsunami research work.

3.2 Post-tsunami field investigations

Several studies were undertaken to measure the impact of the tsunami. The universities of Ruhuna and

Moratuwa undertook studies to assess the inundation, flow directions and damage to buildings and

infrastructure.

The assessment inundation was carried out in an organized manner by dividing the area under study into

250m x 250m grids. At least one location was selected for each grid and a total of 138 points were selected for

the study. People living within the respective areas were interviewed for all grids. Information on inundation

depths and flow directions was obtained together with associated parameters of the hydraulic regime. The

collected data were used to identify:

• The inundation profile comprising depth, length, run-up and spatial distribution

• Inundation contours with wave direction and information that could help to estimate the flow speed

• Distance from the sea along the tsunami flow path

• Relevant information for risk assessment.

This data generated a tsunami hazard map for the City of Galle based on field measurements.

Separate studies were undertaken to study the damage to buildings and infrastructure, and the specific

flow regimes generated by the location and spacing of buildings. Those who survived the tsunami were able

to describe devastating impacts of flow regimes, such as jetting effects which occurred along the streets

running between rows of buildings.

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The results of the study were also useful in identifying the following features for the Indian Ocean Tsunami

scenario:

• Evacuation routes and refuge areas

• Safe areas and safe buildings

• Proposed locations for fixing signboards on evacuation routes.

Figure 2 illustrates the data collection points and Figure 3 illustrates the inundation depth and the direction

of incoming wave. Wave directions and inundation heights were established after the interviews with the

people. Figure 4 illustrates the inundation contours established from field investigations. This represents the

tsunami hazard map for the Indian Ocean tsunami prepared from extensive field measurement.

Figure 3: Inundation depths and wave directions

Figure 2: Data collection locations


3.3 Deterministic tsunami hazard modelling

Deterministic tsunami hazard modelling comprising deep water, nearshore and inundation modelling was

carried out with three objectives:

• To study overall exposure of the island to a given hazard source

• To simulate the IOT and compare with field measurements on the height, inundation length and run-up

• To simulate potential tsunamis based on credible scenarios from geologic and seismic studies.

The results from modelling of ‘different credible scenarios’ provide a database of the key parameters relating

to inundation and the flow regime. Inundation height, length, distribution, run-up and velocity are some of

those parameters. These parameters can then be used for the development of critical hazard scenarios by

relating them to threshold values for the security of people and infrastructure.

The modelling studies generated a valuable database which can be used for multi scenario-based risk

assessment. It was evident that the IOT represented a worst-case scenario. The numerical modelling procedure

is described below for a few alternative scenarios.

Numerical modelling of tsunami phenomena was carried out to obtain information on the coastal region of

Sri Lanka that could be affected by potential tsunamis. General coarse-grid modelling was carried out for the

coastal region in the southern parts of the island and detailed fine-grid modelling, including tsunami run-up

and inundation, was carried out for the City of Galle. The results of this exercise were used for the preparation

of hazard maps for the City of Galle for different scenarios based on mathematical modelling.

Generation and deepwater propagation of the tsunami waves were modelled using the AVI-NAMI model.

The module for co-seismic tsunami generation of AVI-NAMI uses the method developed by Okada (1985)

and the module for tsunami propagation solves Non-linear Shallow Water Equations. The ANUGA fluid

dynamics model based on a finite-volume method for solving Shallow Water Wave Equations was used for

the inundation modelling. In the ANUGA model the study area is represented by a mesh of triangular cells.

Figure 4: Inundation contours

Above 3.5 m

3.5–3.0 m

3.0–2.0 m

2.0–1.0 m

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The model has the flexibility to change the resolution of the mesh according to the area of importance.

A major capability of the model is that it can simulate the process of wetting and drying as water enters

and leaves an area, and is therefore suitable for simulating water flow onto a beach or dry land and around

structures such as buildings. High-resolution nearshore bathymetric data obtained for the new Galle Port

Development (2007) and high-resolution topographic data obtained after the 2004 tsunami were used for

study (LIDA Surveys, 2005).

Broad-scale deepwater propagation modelling was carried out for a number of source scenarios selected

from the Sunda/Java Trench. The results of four selected scenarios are presented here. A fault length of

500 km, a width of 150 km, a dip angle of 8°, a slip angle of 110° and a displacement of 40 m was used

for the study. Table 1 gives the source details and the maximum and minimum wave amplitudes from the

propagation modelling. Figure 5 provides snapshots of tsunami propagation for these four scenarios 180

minutes after the earthquake. Figure 6 illustrates the distribution of computed maximum tsunami heights

over the Indian Ocean.

Table 1: Source details and the maximum and minimum wave amplitudes from the propagation modeling

Longitude Latitude Strike angle Max. amplitude (m) Min. amplitude (m)

Scenario 1 92.00’ E 8.52’ N 350’ 2.015 -1.501

Scenario 2 94.26’ E 3.09’ N 329’ 3.477 -2.391

Scenario 3 97.01’ E 2.07’ N 329’ 1.419 -1.33

Scenario 4 97.60’ E -0.60’ N 329’ 2.608 -2.081

Figure 5: Snapshots of tsunami propagation in four scenarios 180 minutes after the earthquake

(a) Scenario 1 (b) Scenario 2

(c) Scenario 3 (d) Scenario 4


Based on the results of the deep water model, inundation modelling was carried out using the ANUGA model.

Modelling results give valuable information about the coastline of Galle that could be affected by potential

tsunamis. The model results are very useful for the preparation of hazard maps. Figure 7 gives the inundation

modelling results in four scenarios.

Figure 6: Distribution of computed maximum tsunami heights over the Indian Ocean

(b) Scenario 2

(d) Scenario 4

(a) Scenario 1

(c) Scenario 3


3.4 Probabilistic tsunami hazard modelling

Probabilistic tsunami hazard modelling seeks to assess the probabilities of certain wave heights being

exceeded due to the arrival of a tsunami at locations studied. These probabilities are expressed in terms of

expected return periods. A probabilistic tsunami hazard assessment of Indian Ocean nations was carried out

under the leadership of Geoscience Australia (Burbidge et al, 2009).

Two views quickly emerged in discussions among the panel of developers. The hazard assessment should,

on the one hand, avoid over-estimating the hazard by considering only those sources for which there is solid

evidence for generation of large tsunamis. On the other hand, the assessment should be careful not to miss

source zones that may generate large tsunamis even if they have not done so historically – as was the case for

the 2004 Indian Ocean Tsunami (IOT). The panel decided these two views could best be accommodated by

developing two assessments, referred to here as low-hazard and high- hazard end-member assessments. This

Figure 7: Deepwater propagation and inundation modelling for Galle

(a) 2m_20min tsunami wave

(c) 4m_20min tsunami wave

(b) 3m_20min tsunami wave

(d) 5m_20min tsunami wave

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3–4

4–5

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affords a clear expression of uncertainty in the degree of hazard, shown as the difference between the two

end-members. It was hoped that any blurring caused by the application of the two assessments to mitigation

would be manageable. The geographic pattern of the low-hazard assessment is broadly reflective of the

impact of the IOT. The high-hazard assessment, on the other hand, highlights areas potentially threatened

by local tsunamis, such as the western Makran and southern Java coasts, which are the areas of highest

uncertainty in the hazard assessment.

These studies led to the development of a range of maps providing the information described below.

• Hazard curves – the relationship between the return period and the maximum tsunami amplitude for a

particular model output point.

• Maximum amplitude maps – the maximum tsunami amplitude that will be exceeded at a given return

period for every model output point in a region.

• Probability of exceedance maps – for a given amplitude, the annual probability of that amplitude being

exceeded at each model output point in a region.

• Disaggregated hazard maps – the relative contribution of different source zones to the hazard at a single

location.

• National weighted disaggregated hazard maps – indication of the source of the hazard to a nation or

region as a whole.

For Sri Lanka, the low-hazard and high-hazard maps are very similar in character, with maximum hazard along

the east coast, and the high-hazard case deviating from the low-hazard case by about 30 per cent. Since

both high-hazard and low-hazard cases for Sri Lanka are dominated by the events in North Sumatra and the

Nicobar Islands, it seems that the IOT was a worst-case scenario.

3.5 Hazard analysis for risk assessment

Hazard analysis for risk assessment can be undertaken either via a multi-scenario-based or an event-based

approach. For risk assessment against the tsunami hazard it is important to assess scientifically and establish

the basis and criteria on which such an exercise is carried out.

In developing hazard maps for risk assessment, it is necessary to develop hazard levels for which many

approaches are available.

In a multi-scenario-based approach, the superimposition of the impact of scenarios will clearly indicate areas

which have a greater likelihood of being affected. The probability of inundation and its magnitude can be

assessed by several methods.

In an event-based approach, attention is focused on individual events, for example, on a worst-case event

with specific frequencies of occurrences and impacts. After a mega-tsunami such as the IOT, it is customary to

focus attention on planning strategically for such events, for example, considering the location of hospitals,

power stations, water treatment plants and other critical facilities. Even if planning is based on observations

arising from a single extreme event, it is important to analyse the impacts of credible scenarios and operate

within a framework of multi-scenario-based approaches. This provides a justification for the use of an event-

based approach.


For the City of Galle, it was decided to develop an initial risk assessment based on the IOT, which represents

the worst-case hazard scenario. Results from both field investigations and deterministic tsunami hazard

modelling were available, and a good comparison existed between the two. These results could be used for

long-term strategic planning and location of important buildings, and for the identification of evacuation

routes and safe places or buildings, preparation of evacuation plans and placement of signposts for the

benefit of the community at risk.

Hazard levels were developed based on inundation and flow speeds. The four hazard levels were classified as

given below.

• High – Inundation level above 0.5m with high flow/current speeds (>1.5 m/sec)

• Medium – Inundation level between 1m and 2m with low flow speeds

• Low – Inundation level less than 1m and low flow speeds

• Very low (zero) – Very small or no inundation impacting humans

Results from investigations conducted by the Ports and Airports Research Institute, Japan, on the resilience of

both men and women against tsunami currents, were considered in developing these hazard levels.

Figure 8 shows the hazard map developed from this analysis.

Figure 8: Hazard map

Hazard level

High hazard

Medium hazard

Low hazard

Zero hazard 1 km


4. Vulnerability

4.1 From a single dimension of susceptibility to a three-dimensional

sector approach

The assessment of vulnerability remains a complex area, in view of the widely varying parameters associated

with a detailed analysis, and also due to the difficulties in defining and quantifying certain parameters. The

basic components of vulnerability can be broadly classified as human, physical, socioeconomic, environmental,

functional and administrative. This approach is primarily a one-dimensional approach. Reviews of recent post-

tsunami vulnerability studies indicate that the greater focus has been on potential loss of life and damage to

houses and dwellings. Only a few studies have considered other aspects in detail.

Villagran de Leon proposed a framework to break down vulnerability assessment into components by analysing

how disasters can impact the different sectors of society (Villagran de Leon, 2008). The sector approach

identifies dimensions of vulnerability in three areas, namely dimensions of susceptibility, sectors and scale.

In effect, the dimensions of sectors and scale are added to the existing dimension of susceptibility. Typical

sectors identified are housing, communications, education, health, energy, government, industry, commerce,

finance, transportation, public infrastructure, environment, tourism etc. Figure 9 illustrates this concept. The

framework proposes differentiation within each sector in terms of several areas relating to susceptibility,

namely human, physical, socio-economic, environmental, functional and administrative factors. These areas

relate to factors identified by the United Nations International Strategy for Disaster Reduction (UNISDR) as

sion of suscept ity tdim thh

ty

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bility

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Figure 9: The three-dimensional sector approach showing dimensions of vulnerability

Housing

Basic lif

elines

Health

Agricultu

re

Energy

Infra

structu

re

Comm

erce

Industr

y

Finance

Tele

com

munica

tions

Educatio

n

Dimension of sectors

Physical

Economic

Human

Environmental

Administrative

Functional

Dimension of components

Geographic level

dimension

National

State or province

District or municipal

Local or community

Single unit or house


increasing the susceptibility of communities to the impact of a hazard. The third dimension of scale expands

consideration from household to national level, including city, district and provincial levels. The advantage

of this approach, in particular from a policy point of view, is that it promotes the effective assignation of

responsibilities relating to the reduction of vulnerabilities. This approach was applied in detail to a benchmark

project for the City of Galle and its advantages are clearly seen. In particular, it is easy to understand the

factors that maintain, reduce or increase vulnerability levels. The application of this method requires a great

deal of data and time. However, on the strength of this study, it is possible to adopt a simplified approach

with reduced but critical parameters, and then compare the output of both single-dimension and three-

dimensional studies.

4.2 Simplified approach to vulnerability

A simplified approach will focus attention on critical parameters of interest identified in consultation with all

stakeholders. The critical parameters applicable to the City of Galle were:

• population and its distribution

• buildings, infrastructure and their status

• exposure to the hazard

• distance from the sea

• elevation

• capacity to evacuate (within the broader framework of awareness, preparedness, early warning, response

and safe evacuation)

• impact on livelihoods.

In addition, attention was focused on the profile of the occupants, their sources of income, household

economic levels, conditions of buildings and infrastructure, and community knowledge.

Based on the above, it is possible to develop four levels of vulnerability, namely high, medium, low and very

low (zero). According to this approach, a level of high vulnerability can be classified as the presence of a

large population within short distances of the seafront, at low elevations with direct exposure to the sea,

within an environment of easily damaged infrastructure, with easily disrupted livelihoods and without the

capacity to evacuate quickly. Similarly it is possible to identify other levels of vulnerability. Figure 10 presents

the vulnerability map developed from this analysis. A comparison between this study and the detailed

study using the sector approach indicated that, provided the critical parameters are duly identified and

evaluated, the simplified approach provided an effective method for vulnerability analysis, based on which

risk assessment can be undertaken with confidence. The selection of critical parameters, through a process

of scientific analysis and stakeholder consultation, has to be given high priority in the simplified approach.


5. Risk assessment

The risk map can be prepared by superimposing the hazard and vulnerability maps. In doing so, the method

adopted must be clearly identified so as to recognize potential limitations in applications. In this study, the

hazard and vulnerability maps, each comprising four levels of classification – high, medium, low and very low

(zero) – have been prepared. For superimposing them, it is necessary to establish the criteria for risk levels. A

high level of hazard superimposed on high, medium or low levels of vulnerability (or vice versa) is classified

as a high level of risk. A medium level of hazard with a medium level of vulnerability is also rated as a high

level of risk. A medium level of hazard with a low level of vulnerability is rated as a medium level of risk or vice

versa. Finally a low level of hazard with low-level vulnerability is rated as a low level of risk. If either the hazard

or vulnerability is very low (zero), then risk is considered to be zero. Figure 11 shows the risk map developed

using the above analysis. It is emphasized that other criteria can also be used for this type of analysis.

It is noted that sufficient information is available to conduct a multi-scenario-based hazard analysis and

levels of risk could have been developed using such an analysis. This study focused on event-based hazard

analysis, which can be used for strategic planning of buildings and infrastructure, and preparedness for safe

evacuation. The IOT certainly represents a worst-case scenario but other scenarios can be used to identify the

potential impacts from events with a higher possibility of occurrence.

perimposing the hazard and v

to rrececogogninizeze ppoto e

abil

tatatioi

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ap

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Figure 10: Vulnerability map

Vulnerability level

High vulnerability

Medium vulnerability

Low vulnerability

Zero vulnerability1 km


6. Managing Risk – Classification and planning risk management measures

6.1 Classification of risk management measures

There are many measures that could be adopted for risk management in coastal zone management when

planning for a tsunami and other coastal hazards that accompany high waves and high inundation. These

include early warning systems, regulatory interventions in the form of extending existing setback defence

lines, and physical interventions such as the protection of structures and utilizing the full potential of coastal

ecosystems. These should be supplemented with public awareness of disaster preparedness and efficient

evacuation procedures incorporating planned evacuation routes.

Measures for risk management can be broadly classified into three categories, namely, those that mitigate the

impact of the hazard, those that mitigate exposure and vulnerability to the hazard, and those that promote

successful evacuation.

6.1.1 Measures that mitigate the impact of tsunami hazard1. The implementation of artificial measures for protection, including tsunami breakwaters, dikes and

revetments

2. The effective use of natural coastal ecosystems including coral reefs, sand dunes and coastal vegetation

(mangrove forests)

3. Hybrid systems of artificial and/or natural systems

6.1.2 Measures that mitigate exposure and vulnerability to the tsunami hazard1. Land-use planning

2. Regulatory interventions such as setback of defence lines

3. Hazard-resilient buildings and infrastructure

Figure 11: Risk map

Risk level

1 km

High risk

Medium risk

Low risk

Zero risk


6.1.3 Measures that promote successful evacuation from tsunami hazard1. Early warning systems (local and regional)

2. Public warning systems

3. Evacuation routes and structures

4. Community education, including community maps and other measures for community preparedness

Hazard, vulnerability and risk maps play a vital role in risk management. In view of the benefits of risk

management measures, it is important to upgrade these maps regularly. These maps can be used for the

production of disaster preparedness or management maps.

6.2 Planning risk management measures via policy and management options

Post-disaster planning should be undertaken in the context of overall coastal hazards, including tsunamis.

Although the chances of an extreme event such as that of 26th December 2004 taking place are low,

the impacts of such events set the agenda for strategic planning and location of key infrastructure. It is

recognized that a coastal hazard protection plan for the city should be an integral part of an overall coastal

zone management plan based on various policy and management options. These options should reflect a

strategic approach to achieving long-term stability, in particular for sustaining multiple uses of the coastal

zone and giving due consideration to the threats and risks of hazards.

Policy and management options should be formulated on a sound scientific basis, preferably within the

prevailing legal and institutional frameworks. However, if the need arises, institutional improvements should

be effected and new laws should be imposed. In this process, a high priority should be given to stakeholder

participation. Extreme care has to be exercised when obtaining the active participation of stakeholders who

have witnessed disaster and suffered heavily in loss of lives, property and livelihoods from one of the most

severe natural disasters to have affected the region. Most of them require a long period to recover completely

from their traumatic experiences.

Policy options identify possible courses of action on shoreline, such as:

• Maintenance of the existing defence line

• Setback of the defence line

• Retreat

• Advance

In order to implement the policy options, various management options are proposed that may be appropriate

for the coastal area. They are summarized as:

• Do nothing

• Reinstate previous conditions

• Modify the existing design

• Develop new design

Once the risk assessment study is completed, mitigation options should be developed within the framework

of policy and management options, giving due consideration to stakeholder consultations.


6.3 Classification of physical interventions (artificial and natural)

In light of the discussion in Sections 6.1.1 and 6.2, mitigation by physical intervention is classified into three

types, depending on location and function in protecting the coast. These interventions may be achieved by

artificial methods via coastal engineering design, and also by harnessing the full potential of natural coastal

ecosystems. The types of interventions and typical examples for each category are listed below.

1. Reduce the impacts of tsunami waves prior to reaching the shoreline e.g. tsunami breakwaters, coral reefs

2. Protect the coastal zone by preventing the inland movement of tsunami waves e.g. tsunami dikes, sand dunes

3. Mitigate the severe impacts of tsunami waves on entry to the shoreline e.g. tsunami dikes, revetments,

mangrove forests

On many occasions, both artificial and natural methods can be adopted in parallel to achieve well-integrated

hybrid solutions satisfying environmental concerns.

6.4 Development of guidelines for tsunami-resistant buildings

The coast is an area of high economic activity and it is not possible to transfer all activities to areas that

are completely free from potential tsunami hazards. For some areas of the coast, safe evacuation areas may

be too far away for citizens to reach on foot, thus necessitating vertical evacuation structures. Therefore

there is a need to develop design guidelines and construction manuals for tsunami-resistant housing and

infrastructure for the benefit of the public.

Given the background of discussion in Sections 6.1.2 and 6.2, two types of guidelines are required:

• Overall design guidelines providing advice on location, layout, orientation, structural configuration, geo-

technical considerations and other considerations relating to good design practice.

• Detailed design guidelines on hydraulic and structural loads, geo-technical issues and detailed design

information.

The overall design guidelines could be developed from the experience gained by damage assessment in

different parts of the country. Such assessment should be analysed in the context of the hydraulic regime

generated by the tsunami at that location. In particular, local effects which can enhance the impact of tsunamis

have to be taken into consideration. Relevant information from other countries affected by tsunamis will be

very useful for this exercise. It is important that damage assessment should cover a variety of infrastructure

that was destroyed or damaged, or that survived with fewer impacts.

7. Mitigation and its integration with development projects

In 2000, Japanese Port Consultants (JPC) developed a master plan for the development of the Port of Galle. In

view of environmental issues, they recognized that development should be restricted to a two-berth medium-

sized harbour. In order to maintain healthy tidal flows for the well-being of the coral reef system located

on the eastern side of the bay, JPC in consultation with environmental specialists incorporated an offshore

detached breakwater, which coincidentally has all the characteristics of an effective tsunami breakwater (see

Figure 12). It must be admitted tsunamis were not part of the agenda of the engineering and environmental

terms at that stage.

egration wntegration wit

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ts integration with d

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On analysing damage in the aftermath of the IOT, the proposed development of Galle harbour and the use of

the offshore breakwater were revisited. Through numerical modelling it was determined that by implementing

this project with a slightly extended offshore breakwater in the direction of Galle Fort, the City of Galle would

have the benefit of a tsunami breakwater as part of a port development project. Considerable reduction of

the inundation area could be achieved. Once this extension is designed, it may be possible to reduce the

length of the revetment protruding near the berth. The construction of a small offshore breakwater in front

of the channel located west of the headland would provide additional protection.

A protection wall (tsunami dyke) of modest proportions along the coastline could supplement the tsunami

breakwater. The design details and the structural configurations can only be determined after carrying out

mathematical modelling and physical modelling to assess the performance of the proposed configuration.

A hybrid approach using both artificial and natural methods seems very appropriate for this situation. These

are some of the physical mitigation measures which can be successfully adopted as feasible options for the

protection of the City of Galle. These measures will also be effective against potential coastal hazards that

have a greater probability of occurrence than an extreme tsunami wave event (see Figure 13).

Figure 12: Master plan for the development of the Port of Galle


8. Preparation of disaster management maps

Hazard, vulnerability and risk assessment maps were prepared based on the investigations conducted

in Sections 3, 4 and 5, and public consultations via meetings with officials of the government and non-

government organizations, affected people and questionnaire surveys. This was followed by the preparation

of disaster management maps. Two maps were prepared, namely maps of safe places and buildings, and

maps of evacuation routes and signposts. These maps will be refined with further investigative studies and

modelling work if necessary. The maps are presented below in Figures 14 and 15 (a), (b) and (c). Figure 16

shows the location of signposts, which are very important in particular if there are people who are visiting or

going through the city during a hazard event for which a warning has been issued.

er managster mana emisaster mana emen

essment maps were prepared

nsultations via meetin

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Figure 13: Hybrid approach using both artificial and natural methods

Road

Housing units

Coral reefs and

submerged sand dunes

Buffer zone

Coastal vegetation

Sand dunes /

revetment


Figure 14: Safe areas and safe buildings

1 km

Figure 15(a): Evacuation places and routes

1 km


Figure 15(b): Evacuation places and routes

1 km

Figure 15(c): Evacuation places and routes

Vulnerable area This way to a safe place This way to a tall building This way to high land


9. Coastal community resilience

9.1 Coasts at risk

The coastal zone, comprising coastal communities, the built environment and ecosystems, are exposed to a

wide range of hazards arising from natural phenomena and human-induced activities. Cities within this zone

are centres of economic development with heavy population density subjected to immense development

pressure. On most occasions this has resulted in unplanned accelerated development leading to high

vulnerability. It is not surprising that coastal communities are increasingly at risk from coastal hazards. This

was evident from the experience of disasters such as the IOT of 2004, storm surges resulting from Hurricane

Katrina in 2005 and Cyclone Nargis in 2008. The events exposed a lack of knowledge regarding hazards and

vulnerability, and deficiencies in preparedness and response. Since then there have been several initiatives to

improve disaster risk assessment and management.

9.2 Establishing the resilience of coastal communities

Risk knowledge is a critical component of coastal community resilience and represents the awareness of

the community regarding potential hazards, vulnerability and the extent to which the community is prone

to hazard impacts. Risk knowledge therefore plays a vital role in building a hazard-resilient community. It

requires a full understanding of hazards both episodic and chronic, the frequency of occurrence, the time

scale over which they occur, and the geographic extent of impact. The community should be aware of the

impacts on human life, ecosystems, agriculture and infrastructure. A hazard-resilient community can only be

developed via an understanding of hazard and vulnerability, leading to improved preparedness. Lower levels

of risk reflect a resilient community and this can be achieved via a three-pronged approach of reducing the

impact of hazards, reducing vulnerability and improving preparedness. The community itself can harness the

full potential of their indigenous knowledge in developing measures to improve preparedness.

USAID/ASIA in response to the development of the IOTWS promoted a strategic approach towards coastal

community resilience to tsunamis and other coastal hazards. This approach was developed in consultation with

national stakeholders and presented as a practical guide, entitled, ‘How resilient is your coastal community?’

(USAID IOTWS, 2007). The guide provides an effective way of assessing the resilience of coastal communities

and is recommended as a very useful rapid assessment undertaken by all stakeholders to identify strengths,

weaknesses and opportunities to improve resilience.

The approach primarily deals with eight generic elements of coastal community resilience considered to be of

pivotal importance in reducing risk from coastal hazards, and in promoting efficient recovery and adaptation

to change. Resilience has to be built up in each of these areas to ensure a well-balanced approach towards

community resilience. This is an ongoing process which in turn will enable the community to ‘live with risk’

arising from a wide range of coastal hazards, with an equally high degree of confidence.

The eight fundamental elements of coastal community resilience identified in the USAID guide to reduce risk

from coastal hazards, accelerate recovery, and adapt to change are:

1. Governance: Leadership, legal framework, and institutions provide enabling conditions for resilience

through community involvement with government.

esiliencernitymunimmu

riis

omm

s

al com

oa

stal c

11

oastCo9. C9


2. Society and economy: Communities are engaged in diverse and environmentally sustainable livelihoods

that are resistant to hazards.

3. Coastal resources management: Active management of coastal resources sustains environmental

services and livelihoods and reduces risks from coastal hazards.

4. Land use and structural design: Effective land use and structural design complement environmental,

economic and community goals and reduce risks from hazards.

5. Risk knowledge: Leadership and community members are aware of hazards, and risk information is

utilised when making decisions.

6. Warning and evacuation: The community is capable of receiving notifications and alerts regarding coastal

hazards and warnings for at-risk populations, and individuals are able to act on such alerts.

7. Emergency response: Mechanisms and networks are established and maintained to respond quickly to

coastal disasters and address emergency needs at the community level.

8. Disaster recovery: Prior to hazard events, plans are in place to accelerate disaster recovery, engage

communities in the recovery process, and minimize negative environmental, social and economic impacts.

Figure 16 gives the results from a survey on coastal community resilience carried out in an area of Galle

District.

Figure 16: Coastal community resilience

Socio-economic status

and livelihoods

3

2

1

0 Coastal resource

management

Land use management

and structures

Risk knowledge

(a) Middle-level managers Governance

Disaster recovery

Emergency response

Warning and Evacuation

(b) Villagers

Socio-economic status

and livelihoods

Coastal resource

management

Land use management

and structures

Risk knowledge

Governance

Disaster recovery

Emergency response

Warning and Evacuation

3

2

1

0

1

000


The results indicate that both middle-level managers and villagers had a good understanding on warning and

evacuation because it has been a major area of community awareness-raising after the IOT. In comparison,

community knowledge regarding land-use management and disaster recovery is comparatively low. Based

on this analysis, appropriate action can be taken to enhance the knowledge base in other areas.

It is recognized that risk knowledge represents one of the key elements on which a hazard-resilient

community can be built. Without this knowledge, the community cannot establish pathways towards

resilience. Risk knowledge is strongly linked to all aspects of coastal community resilience and, as identified

in the guideline (USAID IOTWS, 2009), this knowledge base enables the community, government agencies

and other stakeholders to work in collaboration:

• to incorporate risk-related issues in the decision making process

• to identify measures to reduce impacts of hazards on social, economic and cultural resources

• to manage coastal and environmental resources in an effective manner for sustaining multiple uses,

including for disaster risk reduction

• to adopt safe construction in accordance with hazard-resilient design standards, and to identify safe

locations and construct safe evacuation structures

• to develop effective warning systems, warning dissemination and evacuation plans

• to identify highest-risk areas for immediate disaster response

• to develop disaster recovery plans and mitigation methods against potential hazards.

One of the principal ways of improving the resilience of coastal communities against hazards is to implement

risk assessment studies. This enables them to understand exposure to hazards and issues of vulnerability, and

to undertake planning of emergency response and recovery as well as overall hazard mitigation measures. In

effect, risk assessment studies provide an opportunity to understand hazards before they are translated into

disasters. The outcome of such studies can be used effectively to adopt measures to improve the resilience

of coastal communities. It is emphasised that risk knowledge is the foundation on which all other elements

of coastal community resilience are developed, and community resilience can only be built by giving a high

priority to risk knowledge.

10. Concluding remarks

This report has described in detail and presented the results of an investigative study on tsunami risk

assessment for the Port City of Galle in Sri Lanka. The paper focuses on hazard, vulnerability and capacity

analysis, the principal components of risk assessment followed by risk management measures.

Hazard analysis comprises both probabilistic and deterministic hazard analysis. The probabilistic tsunami

hazard analysis revealed that for Sri Lanka the low-hazard and high-hazard maps are very similar in character,

being subject to influence by events in North Sumatra and the Nicobar Islands. The use of deterministic

tsunami hazard modelling permitted a multi-scenario-based analysis. In terms of hazard impacts, the IOT

represented a worst–case scenario which may be used for long-term strategic urban development planning,

in particular to identify locations for critical infrastructure and installations. However, there are no constraints

on the use of multiple scenarios in preparing an overall hazard map. The multi-scenario modelling carried out

for this study may be used for such an exercise, with the adoption of weightage factors.

The report presents a simplified approach to vulnerability and capacity analysis whereby only the critical

parameters have been used. These parameters were identified in consultation with stakeholders. The report

ks

resented the

mar

ail and esented the results of

e in Sri Lanka. The paper fo

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also refers to a very detailed study on vulnerability assessment undertaken for the City of Galle using the

sector approach. The sector approach demands a very detailed analysis based on an extensive database. It

was evident that the simplified approach provides an effective vulnerability analysis on which risk assessment

can be undertaken with confidence.

The risk assessment has been achieved via the superimposition of hazard and vulnerability maps. It is

recognized that the frequency of tsunamis which may severely affect the Sri Lankan coast is small, and this

aspect has to be given due recognition when adopting measures for risk management. It is in this respect that

the extreme scenario of IOT has been considered, and the results used for strategic planning, as noted earlier.

The report then focuses on tsunami risk management. It presents a three-pronged strategic approach and

identifies the importance of operating within a multi-hazard coastal protection plan. Such an approach

considers measures to:

• Mitigate the impact of the hazard

• Mitigate exposure and vulnerability to the hazard

• Promote successful evacuation from the hazard

In the case of the City of Galle the report presents a case for integrating national port development with

tsunami hazard protection. It recommends that the breakwaters of the proposed new port in Galle be utilised

to provide protection against the tsunami hazard, and that modelling will have to be carried out to estimate

the desired crest height of the breakwater in order to achieve the expected level of protection. The report

has identified the overall approach to be adopted for the design of tsunami-resilient buildings. Appropriate

techniques are being developed under the leadership of the Disaster Management Centre of Sri Lanka. The

report includes disaster management maps that were developed to show safe places and routes. The report

has also focused on the evaluation of the resilience of coastal communities, which is considered one of the

most important goals in risk management.


References

1. Burbidge, D.R. Cummins, P.R. Latief, H. Mleczko, R. Mokhtari, M. Natawidjaja, D. Rajendran, C.P. & Thomas, C.

‘A Probabilistic Tsunami Hazard Assessment of the Indian Ocean Nations’, Professional Opinion No. 2009/11,

Geoscience Australia, September 2009.

2. UNESCO, ‘Tsunami risk assessment and mitigation in the Indian Ocean; Knowing your tsunami risk – and

what do about it’, IOC Manuals and Guides No 52, UNESCO: Paris, 2009.

3. UNESCO, ‘Hazard awareness and risk mitigation in ICAM’, IOC Manuals and Guides No. 50, ICAM Dossier No.5, UNESCO: Paris, 2009.

4. Villagran de Leon, J.C., ‘Rapid assessment of potential impacts of a tsunami: Lessons learnt from the port

of Galle in Sri Lanka’, No. 9, SOURCE Publication Series, United Nations University – Institute for Environment

and Human Security (UNU-EHS): Bonn, 2008

5. US IOTWS program, ‘How resilient is your coastal community? A guide for evaluating coastal community

resilience to tsunamis and other hazards’, U.S. IOTWS Document No.27, 2007.

Empowered Lives. Resilient Nations.

United Nations Development Programme

Asia-Pacific Regional Centre

United Nations Service Building, 3rd Floor

Rajdamnern Nok Avenue

Bangkok 10200, Thailand

Documents

RISK ASSESSMENT AND MANAGEMENT FOR TSUNAMI HAZARD