c. vulnerability and hazard assessment: 3.0 preliminary

Assessing vulnerability and adaptation to sea-level rise: Lifuka Island

Ha’apai, Tonga

C. Vulnerability and hazard assessment3.0: Preliminary economic analysis of adaptation strategies to

coastal erosion and inundation

Volume 1 - Least cost analysis

CONTACT DETAILSSecretariat of the Pacific Community

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C. Vulnerability and hazard assessment3.0 Preliminary economic analysis of adaptation strategies to


Volume 1 — Least cost analysis

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Secretariat of the Pacific Community Cataloguing-in-publication data

C. Vulnerability and hazard assessment 3.0 Preliminary economic analysis of adaptation strategies to coastal erosion and inundation: Volume 1 — Least cost analysis / Anja Grujovic, Paula Holland and Anna Rios Wilks

(Assessing vulnerability and adaptation to sea-level rise: Lifuka Island, Ha’apai, Tonga / Secretariat of the Pacific Community)

1. Sea level — Climatic factors — Tonga.2. Climatic changes — Social aspects — Tonga.3. Lifuka Island (Tonga) — Social conditions.

I. Grujovic, Anja II. Holland, Paula III. Rios Wilks, Anna IV. TitleV. Secretariat of the Pacific Community VI. Series

363.738 740 996 12 AACR2

ISBN: 978-982-00-0689-8

DISCLAIMER

While care has been taken in the collection, analysis, and compilation of the data, they are supplied on the condition that the Secretariat of Pacific Community shall not be

liable for any loss or injury whatsoever arising from the use of the data.

IMPoRtAnt notICE

This work and report were made possible with the financial support provided bythe Government of Australia’s Department of Industry, Innovation, Climate Change, Science,

Research and Tertiary Education.

Secretariat of the Pacific CommunityApplied Geoscience and technology Division (SoPAC)

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www.spc.int

http://www.sopac.org

Assessing vulnerability and adaptation to sea-level rise: Lifuka Island Ha’apai, Tonga

C. Vulnerability and hazard assessment 3.0 Preliminary economic analysis of adaptation strategies to coastal erosion and inundation


iii

Contents

List of technical reports for the Lifuka project: ............................................................................................... iv

Abbreviations ..................................................................................................................................................... v

Acknowledgements ............................................................................................................................................ v

1. Executive summary ................................................................................................................................. 1

2. Background .............................................................................................................................................. 3

2.1 The Pacific Adaptation Strategy Assistance Program ................................................................ 3

2.2 Tonga ............................................................................................................................................ 3

2.3 Ha’apai Group ............................................................................................................................... 4

2.4 Coastal erosion on Lifuka ............................................................................................................. 6

2.5 The Lifuka project ......................................................................................................................... 6

2.6 Least-cost analysis ........................................................................................................................ 7

3. Methodology ............................................................................................................................................ 7

4. Results ...................................................................................................................................................... 9

4.1 Adaptation options ....................................................................................................................... 9

4.2 Costs of the adaptation options................................................................................................. 15

5. Discussion .............................................................................................................................................. 23

References ................................................................................................................................................... 29

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List of technical reports for the Lifuka project: Assessing vulnerability and adaptation to sea-level rise: Lifuka Island, Ha’apai, Tonga

As part of the Australian Government’s International Climate Change Adaptation Initiative (ICCAI), the Pacific Adaptation Strategy Assistance Program (PASAP) aims to assist the development of evidence-based adaptation strategies to inform robust long-term national planning and decision-making in partner countries. The primary objective of PASAP is: ‘to enhance the capacity of partner countries to assess key vulnerabilities and risks, formulate adaptation strategies and plans and mainstream adaptation into decision making’ (PASAP, 2011). A major output of PASAP is: ‘country-led vulnerability assessment and adaptive strategies informed by best practice methods and improved knowledge’.

The Lifuka project was developed in conjunction with the Government of Tonga Ministry for Lands, Survey, Natural Resources, Environment and Climate Change (MLSNRECC), PASAP and the Secretariat of the Pacific Community (SPC) to develop an evidenced-based strategy for adapting to sea-level rise in Lifuka Island.

Many technical reports were written for the project on Lifuka Island. They are listed below. They complement, and should be read in conjunction with, the final report : Rising oceans, changing lives.

A: Final report: Rising oceans, changing lives

B 1: Physical resources

1.1: Shoreline assessment

1.2: Groundwater resources assessment

1.3: Oceanographic assessment

1.4: Benthic habitat assessment

1.5: Beach sediment assessment

1.6: Household survey to assess vulnerabilities to water resources and coastal erosion and inundation

B 2: Community assessment

2.1: Community engagement strategy and community assessment manual

2.2: Community values and social impact analysis

C. Vulnerability and hazard assessment

1.0: Coastal hazards

2.0: Coastal rehabilitation – Lifuka Island, engineering options report

3.0: Preliminary economic analysis of adaptation strategies to coastal erosion and inundation:

Volume 1 – Least cost analysis

4.0: Preliminary economic analysis of adaptation strategies to coastal erosion and inundation

Volume 2 – Cost benefit analysis

D. Adaptation options and community strategies




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Abbreviations

ADB Asian Development BankDIICCSRTE Department of Industry, Innovation, Climate Change, Science, Research and Tertiary

EducationDCCEE Department for Climate change and Energy Efficiency GNP gross national productICCAI International Climate Change Adaptation InitiativeLiDAR light detection and rangingMLSNRECC Ministry of Lands, Survey, Natural Resources, Environment and Climate Change (Tonga)NGO Non-governmental organisationPASAP Pacific Adaptation Strategy Assistance ProgramPICs Pacific Island countriesPCRAFI Pacific Catastrophe Risk Assessment and Financing InitiativeSOPAC Applied Geoscience and Technology Division (SPC)SPC Secretariat of the Pacific CommunityTOP Tongan pa’anga

Acknowledgements

The following individuals and departments are gratefully acknowledged for their assistance in implementing this analysis:

o Fuka Kitekei’aho, National Project Coordinator, Tonga MLSNRECC, for his efforts to collect the data on construction costs and value of land;

o Technical Working Group for the Lifuka project based in Tonga; o SOPAC staff for advice on technical aspects of options and data on housing, topography, elevation

and housing materials; o Ministry of Lands, Survey and Natural Resources of Tonga for providing records of previous land

transactions on Lifuka; o Staff of the Ministry of Lands, Survey, Natural Resources, Environment and Climate Change and

the Ministry of Infrastructure; o Staff of KTEC Engineering, Civil Engineering for providing input to costing of options; o Lina Civil Engineering Construction Services, Lifuka, for providing quotes on costs of revetment

construction; o Worley Parsons Engineering for costing of options; o Pacific Catastrophe Risk Assessment and Financing Initiative for sharing their estimates on

replacement values of different building types in Tonga; o Jens Kruger, Team Leader, Oceanography team, SOPAC/SPC for providing scientific input into the

analysis and a tutorial in using Quantum GIS; o Litea Biukoto, Hazards Adviser, SOPAC/SPC, for assistance with PCRAFI data; and o The Government of Tonga and Anna Rios Wilks for reviewing the report.




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1. Executive summary

As part of the Lifuka project — and at the request of the Government of Tonga — SPC has modelled the possible storm surge associated with a tropical cyclone with a one in 100-years return frequency (1:100 year event). Such an event — equivalent to a tropical cyclone category 5 — would be expected to be highly damaging to the lives and livelihoods of the Lifuka community.

This report documents a provisional costing of possible options to address the coastal threats arising from this 1:100 year event. On the basis of consultations conducted with the community of Lifuka, the Government of Tonga and other partners, several options to adapt to coastal inundation and storm surges were identified and provisionally costed:

o revetments (as a means to protect the foreshore);

o relocation inland of families in the most hazard-prone areas; and

o elevating houses in the most hazard-prone areas.

As the discussion on possible options to adapt to inundation was still early, their specifics were not confirmed, so several scenarios were provided and costed for comparison:

o six revetment possibilities;

o two relocation possibilities; and

o two elevation possibilities.

Provisional costing indicates that the cheapest option after 50 years would likely be the establishment of a short coral-block revetment, such as exists along the main coastline of Tongatapu (Table 1). By comparison, elevating houses in the hazard zones by building new (elevated) ones is expected to be the most costly.

Table 1: Provisional costing indicating options after 50 years

Cost after 50 years Cost per capita Rank

(cheapest first) Other costs

Short rice-bag revetment 4.7 m 1,601 4

Possible environmental

damage;Possible enhanced erosion in localised

areas

Short block revetment 0.7 m 229 1

Long rice-bag revetment 22.8 m 7,686 8

Long block revetment 3.3 m 1,101 3

Long combination revetment 18.8 m 6,325 7

Highly resilient coral-block revetment 12.3 m 4,159 6

Build new higher buildings (total) 36.6 m 12,321 11

Build new higher buildings (extra) 2.2 m 744 2

Elevate existing buildings 9.2 m 3,125 5

Immediately relocate 34.7 m 11,700 9

Gradually relocate 34.7 m 11,700 10

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These provisional costs barely tell half of the story and are insufficient to determine the best adaptation strategy for Lifuka for several reasons:

o Environmental costs associated with the cheapest options have not been costed. Revetments could, in fact, exacerbate coastal erosion in some areas along the Lifuka coast and the scale of these negative impacts could be large or small. Accordingly, an environmental impact assessment — as per Tonga’s Environmental Impact Assessment Act of 2003 (Government of Tonga 2003) — would need to be conducted to identify any negative impacts and plan for their mitigation (such as attaching environmental conditions to the works).

o Costs are not necessarily reflective of the ability of the options to protect the community. As an example, depending on the design, revetments may still permit the permeation of water to low land, with the effect that the community may still become inundated. This compares with elevating houses or relocating inland, where communities would not be exposed to the same degree of hazard. Accordingly, it may be practical to consider elevation or relocation of infrastructure away from the most hazard-prone areas. Alternatively, combinations of options (such as partial revetments and partial relocation) may be the most effective to combat coastal inundation and harm to livelihoods. It is therefore critical that an assessment of the possible benefits from the options is considered before options are selected. Options that do not protect the community and livelihoods should not be pursued.

In the long term, infrastructure may need to be renovated, replaced or newly established around Lifuka. In the interests of protecting possessions, lives and livelihoods, the government should consider establishing and enforcing:

o building standards such as minimum building heights to accommodate severe storms;

o a long-term zoning plan in which development in the most hazard-prone areas is minimised and new developments are located on safer (elevated) ground;

o gradual relocation of critical amenities to safer ground;

o existing development controls, such as the minimising of beach mining in sensitive areas.

To adapt to a 1:100 year storm event, and in the face of climate change and rising sea levels, it is improbable that any single adaptation option will be a ‘silver bullet’. The desirability of options will rely not only on affordability but also on (i) the effectiveness of the option to protect lives and infrastructure, (ii) the attitudes of the community, and (iii) different combinations of options. The next step in considering the desirability of the options will be the potential benefits of the options. This will be considered in a follow-up economic assessment report.




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2. Background

2.1 The Pacific Adaptation Strategy Assistance Program

As part of the International Climate Change Adaptation Initiative (ICCAI), the Pacific Adaptation Strategy Assistance Program (PASAP) aims to assist the development of evidence-based adaptation strategies in partner countries. The programme is being implemented by Australia’s Department of Industry, Innovation, Climate Change, Science, Research and Tertiary Education (DIICCSRTE), with the primary objective of enhancing the capacity of partner countries to assess key vulnerabilities and risks, formulate adaptation strategies and plans and mainstream adaptation into decision-making.

In Tonga, the Australian Department for Climate Change and Energy Efficiency (DCCEE) is implementing the Island Vulnerability and Adaptation to Sea-Level Rise Project on Lifuka Island, Ha’apai. The project is intended to develop an evidence-based strategy for adapting to sea-level rise while supporting the capacity of the Government of Tonga and relevant non-governmental organisations to conduct similar assessments of coastal and social vulnerability and adaptation to sea-level rise in the future.

DIICCSRTE contracted SPC’s Applied Geoscience and Technology Division (SOPAC) to conduct work on climate change adaptation strategies appropriate to Lifuka and with application to other parts of Tonga and the Pacific. The project sets out a sequence of activities, which includes a scientific analysis of coastal process dynamics and inundation modelling, topographic and groundwater resource mapping, analysis of community values and exposure to risk, and an economic analysis of different adaptation options. Outputs from the project consist of reports from each of the project components that will serve as primary inputs into the project’s final report. The final report will draw important conclusions between related pieces of work and will capture lessons learned from the various processes.

As part of the Lifuka project, a least-cost analysis was carried out to provide a costing of different adaptation strategies available to Lifuka. The goal of the analysis is to inform the decision-making of the community of Lifuka, the government and the donors, by presenting a comparative economic assessment of possible adaptation options in Lifuka.

As one of the deliverables of the project, this document outlines a preliminary assessment of the cost of several adaptation options for the community of Lifuka to cope with a tropical storm surge with a 100-year return interval (1:100 year event) including:

o coastal protection (revetments, beach renourishment);

o relocation (retreat); and

o elevation of floors of coastal infrastructure.

2.2 Tonga

The Kingdom of Tonga is an archipelago of approximately 170 islands, with a population of 102,000, inhabiting 36 of the islands (Figure 1). The total land area is 650 km2. The main island of Tongatapu is home to 71 per cent of the population and has the highest population density of 277 people/km2. The population of the Ha’apai Group (the region of concern for this project), is 7,570 people at a density of 69 people/km2

(PASAP 2011).

The climate of Tonga is tropical, with rainfall varying between the wet and dry seasons. The wet season lasts from November to April, and the wettest months are usually January, February and March. Rainfall may

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exceed over 250 mm per month during this period. In the wet season, the average temperature in Tonga is around 25–26°C, and in the dry season around 21–24°C (Government of Tonga 2005).

Tropical cyclones usually develop during the hot wet season and are a regular occurrence in Tonga. Over the period 1960–2004, 32 tropical cyclones passed over Tonga. In general, Tonga is affected by one tropical cyclone annually, resulting in millions of dollars’ worth of damage over the years (Government of Tonga 2005).

2.3 Ha’apai Group

The Ha’apai Group of islands consists of a series of 60 small, low-lying islands grouped into six administrative districts. The region’s administrative centre is the town of Pangai, on the island of Lifuka (Figure 2). Lifuka is home to 2,967 people, some 40 per cent of the population of the Ha’apai group (PASAP 2011).

Lifuka houses the region’s airport and main harbour. All islands have primary schools (often with fewer than 20 students), catering for children up to Class 6. Families then raise funds to send the children to high

Figure 1: Map of Tonga

Source: http://en.wikipedia.org/wiki/File:Tonga.jpg

//en.wikipedia.org/wiki/File:Tonga.jpg

//en.wikipedia.org/wiki/File:Tonga.jpg




5

school and college in Pangai or Nuku’alofa. The isolation of the Ha’apai islands constrains the delivery of core services and access to markets, exacerbated by the increasing cost of transport, consumable goods and education (PASAP 2011).

High migration rates from the Ha’apai group have resulted in negative population growth. There has been an overall decrease in population of 7 per cent within a decade. While the urban district population has not decreased, the four remote districts have experienced population decreases of between 14 and 20 per cent. Villages and towns report that up to 30 per cent of homes are uninhabited as people have moved to Tongatapu or overseas (PASAP 2011).

Families rely on subsistence agriculture (root crops, fruits and green vegetables), fishing, pigs and some goats for food security, although there is limited production of fresh vegetables. Some of the small islands have very little fertile soil for agriculture. A few villages have horses for transportation. Gender roles are quite defined, with men exclusively doing fishing, ploughing, planting and harvesting of crops, and preparation of the umu (earth oven). Women do the day-to-day food preparation, treating pandanus and weaving (PASAP 2011).

Income on the outer islands is almost exclusively from fishing and weaving (including the sale of pandanus), with the annual sea-cucumber harvest bringing in a large income in September. While fishing is a vital income source, most islands do not have refrigeration or ice-block machines for storing fish before selling (PASAP 2011).

Figure 2: Map of Lifuka

Source: Itzstein et al. 2012.

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2.4 Coastal erosion on Lifuka

The Ha’apai Group experienced an earthquake on 3 May 2006 that measured approximately 7.9 on the Richter scale, and resulted in subsidence of 23 cm of Lifuka Island (PASAP 2011). In the past four years, the island has experienced significant coastal erosion (Figures 3 and 4), impacting on infrastructure over a three kilometre section of the coastline (PASAP 2011). The infrastructure under risk includes the harbour, residences, a broadcasting tower, a church, the Lifuka hospital, and several government offices.

Sea levels are likely to continue to rise due to climate change during the 21st century, and the resulting wave impact is likely to lead to further erosion of the coastline in Pangai, leading to increasing inundation of and damage to infrastructure along the shoreline. There are related potential impacts on groundwater, health, and food production, and it is notable that some septic systems are below mean high-tide levels (PASAP 2011).

2.5 The Lifuka project

Coastal erosion on Lifuka Island has been identified at the national and community level as a concern (PASAP 2011). In light of this, the goal of the Lifuka project is to develop an evidence-based strategy to adapt to sea-level rise on Lifuka Island, which can be used as a case study for other parts of Tonga and the Pacific.

The objectives of the Lifuka project are several. In the first place, the project aims to assess the impacts of seismic subsidence on the coastal zone and on the people of Lifuka. Secondly, it intends to analyse the vulnerability of the coastal zone and the people of Lifuka to future rises in sea level, and to propose and assess a range of adaptation strategies for adapting to sea-level rise in Lifuka. The intended outcomes are to enhance government and local community understanding of the opportunities, risks and costs associated with various strategies for adapting to sea-level rise, and to support the capacity of the Government of Tonga, and relevant non-governmental organisations to conduct assessments of coastal and social vulnerability and adaptation to sea-level rise in the future.

Figure 3: Coastal erosion in front of the Lifuka Royal Palace




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Figure 4: Southwest shoreline of Lifuka

2.6 Least-cost analysis

Part of the Lifuka project will be an economic analysis component of a range of adaptation strategies to cope with a 1:100 year storm surge event. In the first instance, the cost of different adaptation options will be identified and analysed for implications over time. The outcomes of this analysis are intended to inform decision-making and will subsequently be used in a preliminary cost-benefit analysis of options.

3. Methodology

Material for this report came from consultations, data sources and personal communications.

Consultations

Consultations with the community of Lifuka (Sinclair et al. 2013) revealed that the community was supportive of several types of adaptation to cope with sea-level rise and coastal inundation in the face of climate change, including:

o establishment of a foreshore (most popular);

o relocation (less popular);

o development controls; and

o cessation/control of coastal mining (removal of sand from the beaches that is linked to coastal erosion).

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Consultations with government officials in Tonga, coastal scientists from SOPAC and officials from DCCEE led to the decision to assess the following adaptation strategies:

o revetments or beach renourishment as a means to establish/protect the foreshore;

o relocation of households from the most hazardous areas supported by zoning as a means of both relocation and development control;

o elevation of houses as a form of development control.

These adaptation options are not mutually exclusive; however, for the purposes of this analysis, the cost of each option is presented separately. Other issues (development controls and enforcement of sand-mining legislation) are discussed in Section 5.

Consultations were held with construction companies situated in Tonga and with an international engineering firm with experience in coastal protection in the Pacific

Consultations with key stakeholders and coastal scientists from SOPAC/SPC were conducted to define the scope of the analysis (which type of costs to include) as well as the specificities of each option (See Section 4.1 for a description of the characteristics of each adaptation option) and the assumptions made when costing each of them.

Data sources

Data on the value of land came from the Ministry for Lands, Survey, Natural Resources and Environment and Climate Change in Lifuka.

Data on the preliminary size of setback zones and the location and extent of revetments were based on models of coastal processes conducted specifically for this project.

Data on coastal infrastructure were obtained from the infrastructure mapping exercise carried out by SOPAC/SPC, in collaboration with Tonga Statistics Office, in March 2012. The infrastructure mapping was done as part of the Lifuka Household Survey carried out to assess the vulnerabilities to water resources and coastal erosion and inundation on the island, and was one of the components of the PASAP project in Lifuka.

The replacement value of different types of infrastructure on Lifuka was sourced from the Pacific Catastrophe Risk Assessment and Financing Initiative (PCRAFI), a joint initiative between the SPC/SOPAC, the World Bank, and the Asian Development Bank, with financial support from the Government of Japan and the Global Facility for Disaster Reduction and Recovery (GFDRR — see World Bank (2011)). PCRAFI has developed an exposure database which includes a comprehensive inventory of residential, commercial, public, and industrial buildings in Tonga, as well as estimates of unit replacement cost values for different buildings (see AIR Worldwide 2011).

Indicative costs of elevating floor height were sourced from a previous SOPAC technical report on flood risk reduction measures in Samoa (Woodruff 2008).




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Personal communications

Data on costs of revetments and land value were obtained from personal communication with:

o MLSNRECC, EIA Section;

o Ministry of Infrastructure, coastal engineers;

o KTEC Engineering, Civil Engineering; and

o local engineering company Lina Civil Engineering Construction Services.

Data described and used in this report are based on that which was available at the time. As data and research progresses over time, the costs estimated in this report must be regarded as preliminary estimates which are subject to change.

Material versus non-material costs

Only the material costs related to each option are considered in this costing analysis. Material costs include initial investments to purchase materials and labour, as well as any maintenance costs over the time span of the analysis considered relevant by the Government of Tonga. These costs can be obtained directly from the market values and, in this analysis, most of such costs are obtained from experienced engineers working for the Government of Tonga and/or quotes from engineering companies.

Non-material costs (such as environmental impact costs) are not included due to the lack of available data; however, these are noted where they are likely to be relevant.

Treatment of time (social costs)

In this document, the costs are assessed nominally. The costs of establishing an option and maintaining it over a number of possible periods is considered. The time span for conducting an economic analysis is generally the engineering life of the longest-lasting component used in a project (Woodruff 2008). In the case of this analysis, the setback zone is the longest component, which is considered over a 50-year planning period. For illustration purposes, where relevant, the results in the analysis are displayed on a 10, 20 and 50-year lifespan.

In the second part of this analysis (Holland 2013), consideration is given to the effect of time on the costs. This is because the options considered have different durations and the flow of costs and benefits over time for each will differ. To enable comparison of the pay-off from investing in options (benefit-cost pay-off), discounting will subsequently be applied to costs and benefits.

4. Results

4.1 Adaptation options

Revetments

The community of Lifuka is interested in the construction of a physical barrier to protect the coastline against erosion in the most vulnerable areas of the island (Sinclair et al. 2013). Such revetments could take various forms, depending on the materials used and the length of the coastline to be protected. In this report, two revetment lengths and types are assessed.

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Length of coastline protected

Historically, Lifuka has made previous efforts to establish coastal protection extending the length of the shoreline, starting from the wharf and reaching the Royal Palace (Figure 5). Some parts of the present revetment in this area is made of coral rubble cemented together, while other parts are formed by a low-lying brick wall. However, strong currents and waves from past cyclones and tsunamis have broken through the existing revetment, exposing the shoreline and infrastructure alongside it to sea water. Coastal erosion in front of the Royal Palace is evident even beyond the existing revetment (Figure 4). Noting that the existing revetment is in urgent need of reconstruction. This shoreline length of 475 m is considered as a first scenario for analysis (Table 2).

Figure 5: Scenarios for revetment

Alternatively, the whole shoreline of Pangai and Hihifo combined might be protected by a revetment. In this case, the revetment would start at the wharf, and continue south to the end of the Hihifo beach (Figure 5). Theoretically, this scenario would provide protection to more infrastructure and a greater part of the community.

Table 2: Scenarios for revetment length

Distance of the revetment (m)

Scenario 1 475

Scenario 2 2,281

Material of the revetment structure

Revetments can be constructed using a variety of materials which have different strengths and resilience to wave action. Presently in Tonga, two types of material are used for revetments: rice bags containing cement (Figure 6) and coral blocks (Figure 7) – see Box 1.




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Rice-bag cement revetmentsA strip of this type is already in place at several sites around Lifuka including the road outside Holopeka (Jens Kruger, SOPAC Division, personal communication, 24 September 2012). The revetment is made out of ordinary flour/rice bags filled with concrete and sand which are stacked on top of each other.

A rice-bag cement revetment such as this is easily constructed by the community, and is less expensive than the coral-block type. However, it is also less durable. The Holopeka road revetment was constructed in 2012. It is unlikely this form of revetment will remain intact for long. Following consultations with engineers at SOPAC/SPC it is assumed that this type of construction typically has a lifespan of 5–10 years, after which time a new revetment would have to be rebuilt unless maintenance is conducted.

On the basis of information provided by international engineers (Worley Parsons 2013), it is expected that this type of revetment would not withstand a 1:100 year event.

Coral-block revetmentsA revetment of this type was established along the coast of Nuku’alofa in 1983. According to a report by Saimone Helu (Assistant Government Geologist at Ministry of Lands, Survey and Natural Resources at the time), the structure was rebuilt with the following characteristics:

At the toe of the slope, a trench at least 0.5 m deep was dredged in which the first layer of coral blocks (weighing up to 1.0 ton) was placed up to a height of approximately 0.3 m above the reef flat. Above this height, the cover layer was changed from single- to double-layer, and continued to a crest height of approximately 2.8 m above the reef flat, using blocks weighing from 1.0 ton to 0.5 tons, reducing in size with increasing height. This was extended back in three to five layers corresponding approximately to a 2.5 m crest width. A first filter layer of quarry spall and a second double filter layer of coral stones of 45–100 kg weight were placed below the first cover layer. Behind a concrete retaining wall, the landward side of the structure was filled with small coral blocks or stones and covered with filter material before this backfill was finished with quarry material and topsoil (Helu 1991).

An example of a coral-block revetment is in place on the shoreline of Nuku’alofa. The revetment in Nuku’alofa was constructed in 1983, following the destruction of the old sea wall by 1982 Cyclone Isaac. The old wall was also made of coral blocks but was thin and nearly vertical. When the storm surge from Cyclone Isaac resulted in over-topping the offshore reef, parts of the sea wall were destroyed immediately, while other parts collapsed due to the washing out of the fine fill material behind the wall (ibid.). The 1983 revetment was built by the Government of Tonga with funding from the Federal Republic of Germany (ibid.).

In the case of the Nuku’alofa revetment, the structural materials such as cement, bitumen, artificial filter material and reinforcing steel were imported, and coral blocks were provided locally (ibid.).

Box 1: types of revetments used in tonga

Coral-block revetments are generally more durable as a coastal protection option than rice-bag revetments. As an example, the Nuku’alofa revetment is durable enough that it remains in place today after almost 30 years. As with any other structure, maintenance may nevertheless be required at some point to ensure the revetment remains intact. Following consultations with engineers at SOPAC/SPC, this revetment is assumed to have a lifespan in the range of 30–50 years.

Despite this background, independent assessment by international engineers (Worley Parsons 2013) suggests that this type of revetment would probably not withstand a 1:100 year event.

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Figure 6: Rice-bag cement revetment in Lifuka

Figure 7: Coral-block revetment in Nuku’alofa




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In addition to the “pure” rice-bag and coral-block revetment types presently in use in Tonga, two options for a revetment could be considered.

o A combination of rice-bag and coral-block revetment. Upon the advice of the Government of Tonga (Fuka Kitekei’aho, National Coordinator, PASAP Project, Lifuka, Ministry of Environment and Climate Change, personal communication 20 February 2013), a coral-block revetment might be considered for the short area extending from the wharf to the Royal Palace while a rice-bag revetment might be used for the remainder of the Pangai and Hihifo shoreline.

o An augmented coral-block revetment which is higher and wider than the present coral-block revetment form presently in use in Tonga. In this case, Worley Parsons (2013, p. 43) observe that coral presently used in the block revetments on Tongatapu are of a material “generally considered to be inferior to igneous rock as a material for revetment … to achieve the same level of protection against wave attack [from a 1:100 year event], a revetment constructed of coral rock armour would need to include much larger primary armorous stones that one constructs using igneous rock”. In other words, existing coral and rice-bag revetments in Tonga would not be expected to withstand a 1:100 year event. In order to do so, they would require a more substantial structure. A possible structure to withstand the force of a 1:100 year event is present in Worley Parsons (2013) and will be costed.

Cost of retreat

Coastal retreat refers to the movement of infrastructure and communities from a hazardous area. While the implementation of retreat can vary considerably from one situation to another, coastal retreat in this assessment is considered as occurring through zoning, where all or certain types of development are prohibited in areas deemed hazardous. Development would then have to occur in areas deemed safer. For example, areas along the coastline which are assessed as particularly exposed to severe storm surges could be designated restricted, and communities and infrastructure would retreat from the area. In this way families and infrastructure can be protected against coastal flooding and erosion by ensuring that they are not located in the risk-prone area. For the purposes of this analysis, it is assumed that retreat would be supported by a fixed “setback” zone which prohibits development for a fixed distance landward of the defined shoreline.

The establishment of setback zones is a common policy worldwide as it can be effective in protecting the population against the risk of submersion and erosion (Rochette et al. 2010). Generally, following the establishment of a setback zone, existing infrastructure is allowed to remain, though rebuilding in the event of future damage may be prohibited. In some cases, private landowners might be compensated for lost land or development potential. The nature of any setback zone for Lifuka has not been determined at this point.

The economic cost of a setback zone for Lifuka would theoretically reflect (i) the cost of acquiring replacement land and similar buildings elsewhere, and (ii) any other costs from surrendering existing land and assets that remain useable.

Modelling work conducted as part of this study (Kruger and Damlamian 2013) has identified three zones around Lifuka:

Null zone Areas around Lifuka Island which would not be susceptible to inundation in a 1:100 year tropical cyclone event

Hazard zone Areas that would be inundated during a 1:100 year event and which could be subject to wave action of waves <1 m in height

High hazard zone Areas that would be inundated as a result of a 1:100 year event and that would be subject to damaging waves of =>1 m in height.

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Null zone areas are those that are located above 6 m in height. All other areas would be liable to inundation to various degrees.

Figure 8 illustrates the three zones across Lifuka as modelled under the conditions in which a 1:100 year tropical cyclone event occurs. It is notable that the vast majority of critical infrastructure (including the hospital, police station, part of the airport and some schools) are located in the hazardous and highly hazardous zones.

Figure 8: Hazardous zones in Lifuka under 1:100 year event

Source: Kruger and Damlamian 2013.

Elevation of coastal infrastructure floors

To avoid inundation-related damage, coastal infrastructure could be built higher using wooden or concrete columns (see Figure 9 as an example). By raising the floor height of buildings, either using concrete slabs or stilts, the area below is left open to allow ocean water to flow under the building, reducing structural damage to the building or its contents.

Figure 9: Conventional house elevated on columns

A study on coastal inundation from tropical cyclone waves is currently under way by SPC/SOPAC. For the purpose of this least-cost analysis, it is assumed that all of the households within the identified hazard or high-hazard zones would benefit from elevation.

The costs to elevate infrastructure can be incurred for new buildings as part of their design, or through retrofitting. Both cases will be considered in this analysis.




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4.2 Costs of the adaptation options

Cost of revetments

General assumptions

o Rice-bag revetments have a lifespan of 5–10 years with an assumed average of 7. On the advice of Government of Tonga engineers, no maintenance is conducted on such revetments. As a result, it is assumed that such revetments would need to be replaced after seven years if they are to continue to protect the shoreline.

o Coral-block revetments of the type presently used in Tonga have a lifespan in the range of 30–50 years with an assumed average of 40, after which they would need to be replaced unless maintained. On the advice of the Government of Tonga engineer, coral-block revetments would be maintained at 5 per cent of establishment costs every 15 years and would then not require replacement.

The material costs of revetments take two forms — financial and environmental. The financial costs of revetments are estimated below. The environmental costs of revetments relate to the fact that the construction may ultimately negatively impact coastal ecosystems. Generally, revetments require a wide footprint to be effective, and can have a detrimental impact on the coastal marine habitats they are located near such as seagrass beds and coral colonies. This is due to the increased levels of turbidity or burying that would occur during construction.

Rice-bag cement revetments

Data on costs of a rice-bag cement revetment in Lifuka were sourced from MLSNRECC, Ministry of Infrastructure and KTEC Engineering. It was quoted that 4 km of coastline using concrete rice bags would cost in the vicinity of TOP$4,999,000 — or an average TOP$1,250/m. This estimate is based on, “the cost for production of aggregate, the price for compressive strength of concrete to be mix[ed] is 25MPA and the slope and level that the calculation is based from” (Pesalili Tuiano, Ministry of Infrastructure, Civil Engineering, personal communication, 20 February 2013). Maintenance was not envisaged for the rice-bag revetment and it would therefore require regular replacement. With an assumed lifespan of the structure of 5–10 years, replacement was presumed for every 7 years.

Coral-block revetments

Estimates were sought on the cost to establish a coral-block revetment, similar to that found in Nuku’alofa. These were provided by MLSNRECC, Ministry of Infrastructure and KTEC Engineering. The estimate places the cost of construction of four kilometres of coral-block revetment in the vicinity of TOP$5,209,000 — or an average of TOP$1,302/m. According to the Ministry of Environment and Climate Change, maintenance of a coral-block revetment is not normally considered such that, “the rock revetment in Nuku’alofa which everyone refers to has not been maintained for about 30 years. It came up in our meeting but we did not pay much attention to it. Nevertheless, the government suggested that perhaps a 5 per cent of total cost for maintenance every 15–20 years will be warranted in order to maintain and prolong life of project” (Fuka Kitekei’aho, National Coordinator, PASAP project, Lifuka, Ministry of Environment and Climate Change, personal communication, 20 February 2013). As a result, maintenance costs of 5 per cent of total construction cost were imputed every 15 years, with no replacement provided for as per the advice of the government.

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Highly resistant coral-block revetments

Cost estimates for a coral-block revetment able to withstand a 1:100 year tropical cyclone event were provided by Worley Parsons (2013). At this stage, no costs were indicated for maintenance and costs did not include transport and shipping of any imported materials. These costs are therefore likely to be a conservative estimate.

Total cost comparison

Estimates of total material costs for the construction and maintenance of different types of revetments are presented in Table 3.

Table 3: Total cost estimates of revetments (TOP)

Scenario 1: 475 m Scenario 2: 2,281 m Scenario 3 Scenario 4

Rice-bag cement block

Coral block Rice-bag cement block

Coral block Combination coral block and rice bag

Highly resistant rock standard

Total initial construction cost

593,631 618,569 2,850,680 2,970,432 2,875,617 12.34 million *

Annual maintenance cost

Nil — replaced every 7 years

5% every 15 years, no replacement

Nil — replaced every 7 years



Not available

* Worley Parsons (2013). As no figures exist as to maintenance, the use of this value as a total cost is highly conservative.

Cost of retreat

The costs to withdraw from hazardous zones around Lifuka would reflect two types of costs: (i) the cost to replace land and houses; and (ii) the value of any useable land and assets (buildings) that the community may have to abandon.

The costs of retreat would in practice be determined by the way retreat was implemented. For example, an immediate “no-go” zone might be established in which occupancy or use of existing buildings is prohibited due to risk. This would seem to be a costly approach for Lifuka where families presently use infrastructure in the area and have invested in it on the expectation of ongoing access. Alternatively, a retreat might be applied to the establishment of any new buildings only, in which case these would need to be constructed outside of the area. There again, families might be encouraged to move gradually out of a specific area as their existing homes age, rebuilding replacement homes in a “safer” area — effectively a “staged” retreat.




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Area of land covered by houses in the hazardous zones

It was noted in Section C that inundation modelling work conducted as part of this study resulted in the identification of three zones around Lifuka:

Null zone Areas around Lifuka Island which would not be susceptible to inundation in a 1:100 year tropical cyclone event

Hazard zone Areas that would be inundated during a 1:100 year event and which could be subject to wave action of waves <1 m in height

High hazard zone Areas that would be inundated as a result of a 1:100 year event and that would be subject to damaging waves of =>1 m in height.

Based on a household and technical building survey also conducted as part of this study, it would appear that at least 272 homes around Lifuka are located in hazardous/highly hazardous inundation areas (Table 4).

Table 4: Number of houses in the hazard zones

Houses listed in the high hazard zone 157

Houses Listed in the hazard zone 115

Total 272

The area of total land on which the houses are situated was calculated using satellite imagery and is estimated at around 35,000 m2 (Table 5).

Table 5: Area of housing in the hazard zones m2

Houses listed in the high hazard zone 19,884.71

Houses listed in the hazard zone 15,116.40

Total 35,001.11

Value of land

The unit value of land on Lifuka is not easy to estimate as the market for land is not highly active. Most individuals living on the island occupy land assigned to their families for long periods and is therefore not bought and sold.

Instead, estimates for value of land were sourced from the Ministry of Lands, Survey and Natural Resources in Lifuka, which reported that the latest land transaction in Lifuka was at TOP$8,000 for a land parcel of 760 m2. The land parcel was in the community of Ha’ato’u (situated below the community of Pangai). The ministry also noted that the unit price of land in the communities is much higher than the unit price of farming land behind the communities, which would have sold at around TOP$5,000 per 760 m2. For the purposes of this report, the price of land in the communities is used since land is scarce and families would now have to compete for access. Additionally, community land is the area any setback zone would engulf.

Using these data the unit price of land for the area within a setback zone is estimated to be TOP$10.5/m2. This unit price is assumed constant across all communities in Lifuka.

With this value, it is estimated that the value of land under housing in the hazardous zones in Lifuka is in the vicinity of TOP$367,512.

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Replacement values of coastal infrastructure

Data on the cost of infrastructure within the setback zone were sourced from the infrastructure mapping carried out as part of the household survey in March 2012 combined with the unit cost of buildings provided by the Pacific Catastrophe Risk Assessment and Financing Initiative (PCRAFI) — Box 2.

Box 2: PCRAFI

PCRAFI is a joint initiative of SOPAC/SPC, World Bank, and the Asian Development Bank with the financial support of the Government of Japan and the Global Facility for Disaster Reduction and Recovery (GFDRR), and technical support from AIR Worldwide, New Zealand GNS Science, Geoscience Australia, Pacific Disaster Centre (PDC), OpenGeo and GFDRR Labs.

The programme aims to provide the Pacific Island Countries (PICs) with disaster risk modelling and assessment tools. It also aims to engage in a dialogue with the PICs on integrated financial solutions for the reduction of their financial vulnerability to natural disasters and to climate change. The initiative is part of the broader agenda on disasterrisk management and climate change adaptation in the Pacific region.

The Pacific Disaster Risk Assessment project provides 15 countries with disaster risk assessment tools to help them better understand, model, and assess their exposure to natural disasters. It builds on close collaborations between SPC through its Applied Geoscience and Technology Division (SPC/SOPAC), World Bank andAsian Development Bank, with technical inputs from GNS Science, Geoscience Australia and AIR Worldwide.

Among other things, the programme includes a Regional Georeferenced Exposure Database which contains components for buildings and infrastructure, agriculture, and population.The exposure development leveraged remote sensing analyses with high- and medium-resolution satellite imagery, field visits, and country-specific data sets. For the building andinfrastructure data set, more than 400,000 building footprints for structural classification were digitised from high‐resolution satellite images. These buildings represent about 30 per cent of the estimated total number of buildings in these nations. About 500 imagery scenes were collected and organised.

Approximately 80,000 buildings and major infrastructure (such as roads, bridges, airports and power generation facilities) were inspected during field visits in 11 out of 15 PICs. Field surveys provided ground-truthing data on characteristics such as structural system, construction material, occupancy, number of stories, roof shape and material type, and wall material type. In addition to the digitised and field verified features that capture individual structures, remote sensing techniques were applied to derive aggregate estimates for the quantity and spatial distribution of structures not detected by other methods.

The resulting building and infrastructure database is therefore a resource to characterise the building environment in these nations. Lastly, a property exposure database is derived from the building and infrastructure database in combination with expert research on property value and reconstruction costs.

Source: SPC (2012a).

A household survey of Lifuka was conducted in March 2012 as part of this project. In so doing, it conducted infrastructure mapping of all buildings in Lifuka, which included taking the GPS coordinates and categorising each building. Housing types were:

a) single-storey timber walls; b) single-storey masonry or concrete walls;c) multi-storey timber walls;d) multi-storey masonry or concrete;e) other (Figure 10).




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a) One-level timber walls

b) One-level masonry or concrete walls

Figure 10: Building types in Lifuka

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The vast majority of housing types on Lifuka are single-storey timber houses that form over 80 per cent of homes (Table 6).

Table 6: Housing types in the hazard zones

House type High hazard zone Hazard zone Null hazard

zone TOTAL % in combined hazard zones

A 131 98 59 288 84

B 16 15 8 39 11

C 4 0 1 5 1

D 3 1 0 4 1

E 3 1 1 5 1

Total 157 115 69 341

The replacement costs of houses in the area were estimated using:

o the type of each house derived from the household survey;

o the surface area each house covers, derived from satellite imagery; and

o PCRAFI models of the per metre replacement costs per building provided by the PCRAFI project.

Combining these data allowed for calculation of the estimated total replacement value of each building.

Under different conditions, total costs for replacing each building could have been sourced directly from PCRAFI. However, the replacement values allocated to individual buildings in the exposure database for Lifuka had been based on extrapolated values using satellite imagery, and had not been field verified. Instead, only average replacement costs/m2 of surface area were calculated from PCRAFI for each building type, as provided in Table 7.

Table 7: Estimated building replacement costs from PCRAFI (TOP)

House type Estimated replacement cost/m2 *

Single-storey timber frame $486 850

Single-storey concrete, masonry $626 1,182

Multi-storey timber frame $800 1,399

Double-storey concrete masonry $1,252 2,364

Triple-storey concrete masonry $1,878 3,546

* Based on US$ estimates and exchange rates as of 13 March 2013

These values are province-specific.

By combining the unit replacement values of building types with the surface area they cover (from satellite imagery), the total costs to replace each building in the setback zone was estimated at around TOP$34 million (Table 8).




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Table 8: Estimated replacement value of housing in the hazard zones

Listed houses Estimated house replacement cost TOP

High hazard zone 157 20,136,156

Hazard zone 115 14,211,670

Total 272 34,347,825

These estimated replacement costs for housing underestimate the true cost of housing in the hazardous areas because they do not include the value of sanitary and electric infrastructure, nor furnishings and belongings in houses. Additionally, these values do not reflect the value of all infrastructure in the setback zone, such as the hospital and roads. Third, they do not reflect any cultural or intangible values associated with the buildings such as the cultural value of the Royal Palace situated in the area, or the cemetery which similarly falls in this area.

Total cost of retreat

The total cost to re-establish communities from the hazard zones to an area of 6 m or more in elevation would be around TOP$35 million, if families were to stay in the same kind of housing they have now (Table 9). In a population of 2,967 people (see household survey), this is a cost per capita of TOP$11,700. Naturally, if families had access to existing houses or land in the safe zone, the costs would be lower. Alternatively, if people were only asked to relocate from the high hazard zone and not the hazard zone, too, the costs would be lower.

Table 9: Estimated cost to relocate families (land and houses) (TOP)

Est’d house replacement cost

Est’d land cost Total

High hazard area 20,136,156 208,789 20,344,945

Hazard area 14,211,670 158,722 14,370,392

Total 34,347,825 367,512 34,715,337

The cost of TOP$35 million reflects the estimated cost to relocate families at a single point in time (at once). In practice, this is unlikely to be either practical or acceptable. Further, if families were asked to move immediately, it is possible that it would likely mean abandoning infrastructure that was still useable at that time.

In practice, development constraints in the hazardous zones would mean that abandoned buildings would have little economic use if they cannot be used for habitation or business. It is possible that the buildings could be used for recreation or be stripped for construction elsewhere. The opportunity cost of surrendering “useful” land in these cases is not clear although it could reasonably be expected to be low. Nevertheless, this underscores the fact that the cost of relocation from the hazardous zones is a minimum estimate, not including the economic loss of any valuable land to infrastructure.

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Staged retreat

In practice, it is likely that relocation of a community from a hazardous area would need to take place over time. For example, relocation might be applied first (or only) to the establishment of new buildings, or the community might be given a long time period (e.g. a generation) over which to move. In such a case, the cost of relocation would be lower to begin with and possibly more manageable. In practice, the community has given little consideration to relocating (Sinclair et al. 2013) and therefore the costs associated with this would depend on a scenario that has not been developed in any detail. Presently, outward migration on Lifuka exceeds immigration so it is unlikely that many new buildings would be established. Nevertheless, existing buildings would presumably need to be replaced eventually.

To generate some idea of the potential magnitude of relocation, it is considered that (for illustrative purposes) families are invited to relocate gradually over 30 years. With 272 houses in the hazard zones, this might occur at an average of 10 households relocating a year for 27 years with the last remaining two moving in the 28th year. If 10 households relocated a year, the nominal cost to relocate the community in the hazard zones would be in the vicinity of around TOP$1.3 million per year.

Cost of elevating floor height of buildings

The cost of raising floor heights of buildings varies depending on the type of the structure and the height to which it is raised (Woodruff 2008). In principle, the cost of raising the floor height is expected to be cheaper for new buildings than for existing ones, because raised floors can easily be introduced into the design of a new building. To raise the floor height of an existing building would require jacking the building up and setting it on cribbing in order to build the new foundations underneath (Woodruff 2008).

The cost of raising the floors for new and existing buildings is taken from a previous SOPAC publication by Woodruff (2008), which originally sourced the costs from Williams (1978). Though the original publication is dated, it is assumed that the proportional costs of raising the floors relative to the total value of the house remain constant over time. The costs for elevating floor heights are provided in Table 10.

Table 10: Proportional (%) cost of raising floor heights for new and existing structures of less than 150 m2

Structure type New structure Assumed % Existing structure Assumed %

Single storey 2–12 7 11–50 31

Multi-storey 2–4 3 2–4 3

Source: Williams (1978) cited in Woodruff (2008).

To obtain an initial indication of possible costs, elevating houses in the hazardous zones of Lifuka was conducted using averages (Table 10).

Tables 11 and 12 give estimates for the average costs of elevating existing buildings and the average extra costs incurred if (i) new buildings were established and elevated during construction, and (ii) existing houses were elevated. The cost to elevate all “new” buildings in the hazardous zones of Lifuka would be an extra TOP$2.2 million on top of the cost to rebuild the houses — although this cost is not insubstantial. By comparison, if existing homes were retrofitted (say, because people were unprepared to move or could not access land elsewhere), the cost would be in the vicinity of TOP$9.3 million.




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In all reason, it would appear logical that any substantial investment in housing — the construction of new houses or retrofitting of existing ones — would take place in a “safe” zone, away from the hazardous areas.

Table 11: Estimated cost to establish new elevated houses in the hazard zones

Estimated house replacement cost

Additional cost to elevate replaced house

Estimated total cost of a replaced elevated house

Total 34,347,825 2,207,993 36,555,818

Table 12: Estimated cost to retrofit (raise) existing houses in the hazard zones

Estimated house replacement cost

Retrofit value

Total 34,347,825 9,273,341

5. DiscussionSetting up the adaptation

Figure 11 illustrates the difference between the nominal establishment costs of the different adaptation options. Establishment costs do not include rebuilding or maintenance fees.

Considering establishment costs only, the cheapest option to adapt to coastal inundation would be the establishment of a short rice-bag revetment, followed closely by a short coral-block revetment. All other options have an establishment cost of around TOP$1 million or more (Figure 11). Establishing new houses in the hazardous zones and making them elevated would be the most costly in total although, if families were to cover the cost of replacing the houses (say, when the old houses need to be replaced), this would actually be relatively cheap compared with other options, making it the fourth cheapest.

Figure 11: Establishment costs (TOP$ nominal)

Note: The revetment costs include only initial construction costs, and not the ongoing maintenance fees.

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The impact of ongoing costs

Establishment costs are felt at the beginning of an adaptation solution. Over time, some of the solutions would require maintenance (such as revetments generally) whereas others would not (such as no-go zones). The total costs of options over time — including any maintenance — are indicated in Figures 12–14.

Over a 10-year period, ongoing replacement of revetment structures would render them more expensive than a coral-block revetment, so that more durable revetments would become less costly (Figure 12).

After 50 years, the establishment of a short coral-block revetment is likely to remain the single cheapest option to the community, due to its low establishment cost and relatively infrequent need for maintenance. This option is also likely to appeal to the community on the grounds that this is an option that would normally be supplied by the government, at nil financial expense to the community. The benefits of this option in terms of reduced inundation would need to be assessed.

Due to the costs of maintaining Tongan-style rice-bag and coral revetments, a highly resilient revetment becomes less costly relatively speaking over time (Figures 12–14). After 50 years, the prospect of elevating existing houses in the hazardous zones (retrofitting) is relatively cheap compared with extensive revetment work or relocation from the hazardous zones.

Figure 12: Financial costs over 10 years (TOP$)




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The costs of the 11 options expressed after 50 years are summarised in Table 13. Do note that only material financial costs have been quantified. Other costs — such as environmental costs — have not been quantified.

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Table 13: Summary of costs of adaptation options

Cost after 50 years

Cost per capita

Rank (cheapest

first)Other costs

Short rice-bag revetment 4,749,050 1,601 4

Possible environmental

damage;Possible

enhanced erosion in

localised areas

Short block revetment 680,426 229 1

Long rice-bag revetment 22,805,438 7,686 8

Long block revetment 3,267,475 1,101 3

Long combination revetment 18,767,742 6,325 7

Highly resilient coral-block revetment 12,340,000 4,159 6

Build new higher buildings in hazard zones (total cost)

36,555,818 12,321 11

Build new higher buildings in hazard zones (extra)

2,207,993 744 2

Elevate existing houses in hazard zones 9,273,341 3,125 5

Immediate relocation from hazard zones 34,715,337 11,700 9

Gradual relocation from hazard zones 34,715,337 11,700 10

At establishment, the least-cost option to attempt to manage coastal threats in the face of climate change and rising sea levels is that of establishing a short rice-bag revetment. However, these forms of structures have a relatively short life and therefore need to be replaced regularly. After 50 years, the cheapest option is instead a short coral-block revetment. Revetments — which are a form of coastal foreshore protection — are already an initiative popular with the local community.

While the financial costs of revetments may be comparatively low, revetment work may also have negative impacts associated with it. First, depending on the slope, revetments can still cause erosion on the seaward side of the structure (Worley Parson 2013). Second, eddying around the edges of hard structures such as revetments could result in some increased erosion at their edges, resulting in increased hazard levels for some part of the Lifuka community. Third, revetments may have negative environmental impacts upon shoreline and coastal ecosystems. Such potential costs associated with revetments around Lifuka were not costed in this assessment. It is not clear how large they would be. According to Tonga’s Environmental Impact Assessment Act of 2003 (Government of Tonga 2003), “all major projects shall be supported by an appropriate environmental impact assessment, conducted as required under [the] Act” so that the suitability of projects can be fully assessed. Accordingly, consideration of any revetment work would logically require an environmental impact assessment first, as per government protocols.

The same need to conduct an environmental impact assessment would also apply in theory to any work on substantial beach nourishment (supplementation of sand from elsewhere and the use of groynes to keep the sand in place), where clouding of waters and smothering of coastal flora may occur.

According to the provisional assessment conducted, the most expensive option to address coastal threats over a 50-year period is to establish new houses in the hazard zones and ensure that they are elevated. In practice, the most practical way to ensure elevation would be by requiring families that replace houses with




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new ones to elevate to them to a required standard. The additional (marginal) cost to elevate new houses is relatively low and is the second-cheapest option after a short coral revetment. In this case, it would seem reasonable for the government to consider minimum heights in all future development planning. The Technical Working Group for this project (SPC 2012b) does acknowledge that building development codes for Tonga exist, and that these are often ignored in the interest of saving money. Minimum heights for new houses would therefore require some policing and enforcement.

On the basis of the provisional costing conducted, relocating families away from the hazardous zones identified in this project is likely to be highly expensive (unless families were planning to move anyway). An immediate requirement for families to relocate to higher ground away from coastal hazards is, for the most part, impractical because of the time and costs required to acquire new land and buildings, even assuming that alternative land existed for them (or the government) to purchase. More logically, families would require time to move gradually out of the hazardous zones and re-establish themselves in the elevated areas.

Nevertheless, land access is likely to be a challenge. The Act of 1882 established the right of every Tongan male over 16 years to be allocated part of the land both for residence and farming. However, increasing population and urbanisation have led to most of the available agricultural and town land being used up, resulting in land allocation becoming one of the major issues in Tonga today (Mimura and Pelesikoti 1997). This is one of the factors which has prevented people from moving to safer land (Mimura and Pelesikoti 1997). As a result, the feasibility of establishing and enforcing a setback zone in Lifuka is under question.

In any event, the introduction of zoning and development controls — whether this be for all activities or only for new buildings — would rely on the acceptance of relocation by the local community, which is not guaranteed. The household survey carried out on Lifuka as part of this project (see Sinclair et al. 2013) indicated that only 9 per cent of households in the coastal zone considered relocation (inland or abroad) as a possible solution to sea-level rise.

On the other hand, the concept of relocating might be more palatable to the community if critical amenities existed in the “safe” areas. Presently, the vast majority of amenities critical to the community are located in the hazardous zones of Lifuka. These include the hospital, police, several of the schools and many government buildings. In the event that a 1:100 (or even 1:50) year event occurred, these critical amenities would be susceptible to severe damage. Those amenities such as the hospital that would be most needed following a severe event would also be those most likely to have operations affected.

It is therefore likely to be wise in the long term to have such facilities relocated to ensure continuous provision of service, with and without a severe event hitting Lifuka. Moreover, assuming that land could be provided, the idea of relocating families might be more palatable to the community if critical amenities were also in the vicinity of any new, safer destinations. In general, given the likely scale of damage from storm surge and inundation modelled from a 1:100 year event (Kruger and Damlamian 2013), there would appear to be logic in the government considering a long-term zoning system for Lifuka, and introducing this to its existing infrastructure plan. Logically, new amenities should be planned away from the coastal hazards. Similarly, new or substantially renovated housing should also be considered away from the hazard zones, to protect lives and livelihoods, although the issue of land tenure remains a challenge in this.

In addition to possible relocation of critical amenities, it is logical for the government to consider the introduction of other development controls. Presently, activities such as coastal mining (removal of sand from the beaches, which is linked to coastal erosion) persist in sensitive areas around Lifuka, despite the existence of legislation to control this. Several times the community raised the need to control coastal mining (Sinclair et al. 2013). Enforcement would need to be increased.

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Who pays?

Aside from the scale of costs, the question of affordability of adaptation options will hinge in part on who would need to bear the costs. Most of the options considered in this analysis would, under normal circumstances, be borne by the government. For obvious reasons, this would make those options more palatable to the community. By comparison, issues such as elevating houses or relocation would need to be borne, to various degrees, by the community (Table 14). The affordability of community-borne options would need to be considered by the government. Families might need financial support to implement some of these options and increase their acceptability. In so doing, the government would need to consider:

o the efficacy of options in reducing inundation; and, where options are effective; o ways of making community-borne options more affordable, such as subsidies, education or tax

breaks on relocation, building costs and/or elevation of buildings.

Table 14: Who pays?

Adaption option Who pays? CommentShort rice-bag revetments Government

Short block revetments Government

Long rice-bag revetments Government

Long block revetments Government

Long combination revetments Government

1:100 year event resilient revetments Government

Build new higher buildings (total) Government

Build new higher buildings (marginal) Community Financial support to the community might be needed

Elevate existing buildings Community Financial support to the community might be needed

Immediate relocation Community Financial support to the community might be needed

Gradual relocation Community Financial support to the community might be needed

Next steps

This costing assessment considers, in isolation, different options to adapt to coastal inundation in Lifuka in the face of a 1:100 year storm event and in the face of climate change and rising sea levels. The options are widely variable in cost. In practice, any single option is unlikely to be the “best” one to mitigate inundation. The desirability of options will rely on:

o their efficacy in mitigating coastal inundation; o total costs and pay-off for investment; and o acceptability to the community.

It is critical now that an assessment of the possible benefits from the options is considered. Options that do not protect the community and livelihoods should not be pursued.

In practice, it is possible that no one adaptation option will eventuate as offering a “silver bullet” solution to address coastal threats such as inundation. Rather, it is likely that different packages of solutions will need to be considered by the government and community. It is hoped that the information presented in this analysis will assist in those deliberations.




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References

AIR Worldwide 2011. Replacement Costs and Damage Estimations, excerpt from Pacific Catastrophe Risk Assessment and Financing Initiative (PCRAFI) Component 3: Country Catastrophe Risk Profiles. Technical Report Submitted to the World Bank by AIR Worldwide, 1 December 2011.

Government of Tonga, 2003. Environmental Impact Assessment Act 2003, No. 16 of 2003. Available online at: http://legislation.to/Tonga/DATA/PRIN/2003-016/EnvironmentalImpactAssessmentAct2003.pdf.

Government of Tonga 2005. The Kingdom of Tonga’s Initial National Communication In response to its commitments under the United Nations Framework Convention on Climate Change, May. Available online at: http://unfccc.int/resource/docs/natc/tonnc1.pdf

Helu, S. 1991. Seawall construction and coastal development at Nuku’alofa, Tonga (abstract). In: Workshop on Coastal Processes in the South Pacific Island Nations, Lae, Papua New Guinea, 1–8 October 1987, SOPAC Technical Bulletin 7: 193.194. Published by the SOPAC Technical Secretariat in 1991, Suva, Fiji. Available online at: http://ict.sopac.org/VirLib/TB0007.pdf.

Holland 2013. Preliminary Economic Analysis of Adaptation Strategies to Coastal Erosion and Inundation: Lifuka, Ha’apai, Kingdom of Tonga: Volume 2 – Cost Benefit Analysis, SOPAC Technical Report.

Itzstein, G., O’Hagan, B., Port, A., 2012. 2011 Tongatapu and Lifuka Islands, Topographic and Bathymetric LiDAR Data Capture Project. AAM Project Number 18924A. 430p.

Kruger, J. and Damlamian, H. 2013. Coastal Hazard Mapping and Adaptation Options. Lifuka, Ha’apai, Kingdom of Tonga. SOPAC Division Published Report 161.

Mimura, N. and Pelesikoti, N. 1997. Vulnerability of Tonga to future sea-level rise. Journal of Coastal Research, Special Issue No. 24, 1997.

PASAP, 2011. Pacific Adaptation Strategy Assistance Program, Assessing Vulnerability and Adaptation to Sea-Level Rise Lifuka Island, Ha’apai, Tonga, project proposal.

Rochette J., Puy-Montbrun, G., Wemaëre, M. and Billé, R. 2010. Coastal setback zones in the Mediterranean: A study on Article 8–2 of the Mediterranean ICZM Protocol, IDDRI SciencesPo, n°05/10 December 2010.

Sinclair, P., Singh, A., Grujovic, A., Kruger, J., Begg, Z., Holland, P. and Leduc, B. 2013. Household Survey to Assess Vulnerabilities to Water Resources and Coastal Erosion and Inundation, Lifuka, Ha’apai, Kingdom of Tonga, SOPAC Technical Report.

SPC, 2012a. PCRAFI: Better Information for Smarter Investments, available online at: http://pcrafi.sopac.org/PCFRAI.

SPC, 2012b. Assessing vulnerability and adaption to sea level rise Lifuka Island, Ha’apai, Tonga – Technical Working Group meeting #3: Minutes.

http://legislation.to/Tonga/DATA/PRIN/2003-016/EnvironmentalImpactAssessmentAct2003.pdf

http://ict.sopac.org/VirLib/TB0007.pdf

http://pcrafi.sopac.org/PCFRAI

http://pcrafi.sopac.org/PCFRAI

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Williams, G. 1978. Flood Proofing: A Component of Flood Damage Reduction. Report Prepared by J. F. MacLaren Ltd. for Department of Fisheries and Environment, Gatineau, Canada. Available online at: http://www.nrc-cnrc.gc.ca/eng/ibp/irc/cbd/building-digest-198.html.

Woodruff, A. 2008. Samoa Technical Report – Economic analysis of flood risk reduction measures for the lower Vaisigano catchment area. February 2008. EU EDF – SOPAC Project Report 69g. Reducing Vulnerability of Pacific ACP States. Available online at: http://ict.sopac.org/VirLib/ER0069g.pdf.

Worley Parsons, 2013. Coastal Rehabilitation Lifuka Island, Tonga – Engineering Options Report, report to the Secretariat of the Pacific Community, 29 April 2013.

World Bank, 2011. Pacific Catastrophe Risk Assessment and Financing Initiative, Better Risk Information for Smarter Investment, Available online at: http://www.pacificdisaster.net/pdnadmin/data/original/WB_2011August_PDRFIS.pdf.

http://www.nrc-cnrc.gc.ca/eng/ibp/irc/cbd/building-digest-198.html

http://ict.sopac.org/VirLib/ER0069g.pdf

http://www.pacificdisaster.net/pdnadmin/data/original/WB_2011August_PDRFIS.pdf

http://www.pacificdisaster.net/pdnadmin/data/original/WB_2011August_PDRFIS.pdf


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