CLIMATE RISK VULNERABILITY ASSESSMENT

CLIMATE RISK VULNERABILITY ASSESSMENT

TA-9519 SAM: Preparing the Central Cross Island Road Upgrading Project - 001 Consulting Firm/Team (51268-002) Contract No. 143151-S53251 Prepared for the Asian Development Bank 17 February 2019

PROJECT REFERENCE NO. 5040020

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CLIMATE RISK VULNERABILITY ASSESSMENT TA-9519 SAM: Preparing the Central Cross Island Road Upgrading Project - 001 Consulting Firm/Team (51268-002) Prepared for Asian Development Bank

SMEC Internal Ref. 5040020 17 February 2019

Table of Contents 1 INTRODUCTION ........................................................................................................................................................ 1

1.1 Description .................................................................................................................................................... 1 1.2 Climate Change Context to Project ............................................................................................................... 1 1.3 Previous Studies ............................................................................................................................................ 1 1.4 Current Status ............................................................................................................................................... 1 1.5 Report Objective ........................................................................................................................................... 2 1.6 Report Structure ........................................................................................................................................... 2 1.7 Previous Vulnerability Assessment Report Limitations ................................................................................ 2

2 RISK SCREENING ....................................................................................................................................................... 3 2.1 Key Climate Risks .......................................................................................................................................... 3 2.2 Project Components and their Vulnerability ................................................................................................ 5

3 ADAPTATION MEASURES ......................................................................................................................................... 6 3.1 Road Surfacing .............................................................................................................................................. 6 3.2 Road Pavement ............................................................................................................................................. 6 3.3 Embankment Slopes ..................................................................................................................................... 6 3.4 Drainage ........................................................................................................................................................ 6 3.5 Roadside Objects .......................................................................................................................................... 7

4 CLIMATE CHANGE IN CURRENT DESIGN (UNDER ERAP) .......................................................................................... 8 4.1 Overview ....................................................................................................................................................... 8 4.2 ERAP General Approach ................................................................................................................................ 8 4.3 ERAP Reporting relevant to Climate Change ................................................................................................ 8 4.4 ERAP Review by Project Component ............................................................................................................ 8 4.4.1 Road Surfacing ........................................................................................................................................... 8 4.4.2 Road Pavement ......................................................................................................................................... 8 4.4.3 Embankment Slopes ................................................................................................................................ 11 4.4.4 Drainage .................................................................................................................................................. 11 4.4.5 Roadside Objects ..................................................................................................................................... 13

5 CLIMATE CHANGE ADAPTATION COSTS ................................................................................................................. 14 5.1 Road Pavement Design – Cement ............................................................................................................... 14 5.2 Road Drainage Design ................................................................................................................................. 14

6 CONCLUSION .......................................................................................................................................................... 18

7 APPENDIX 1 ERAP VULNERABILITY ASSESSMENT SUMMARY ................................................................................ 20 7.1 Introduction ................................................................................................................................................ 20 7.2 Hydrology Investigations ............................................................................................................................ 20 7.2.1 Information Sources ................................................................................................................................ 20 7.2.2 Rainfall Analysis ....................................................................................................................................... 21 7.3 Climate Change ........................................................................................................................................... 24 7.3.1 Climate Projections ................................................................................................................................. 24 7.3.2 Sizing Culverts for Climate Change .......................................................................................................... 25 7.4 Use of Samoan Data in the Future .............................................................................................................. 26 7.5 Conclusion................................................................................................................................................... 26

8 APPENDIX 2 ERAP DRAINAGE DESIGN VS VULNERABILITY ASSESSMENT SUMMARY ............................................ 28 8.1 Using Apia Station ....................................................................................................................................... 28 8.2 VASRN Correction Factor – Elevation ......................................................................................................... 30 8.3 VASRN Correction Factor – Rain Shadow Effect ......................................................................................... 31 8.4 VASRN Correction Factor – Future Projections ........................................................................................... 32 8.5 Other ........................................................................................................................................................... 33 8.6 Conclusion................................................................................................................................................... 33

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Table of Acronyms ACRONYM EXPLANATION ADB Asian Development Bank ADF Asian Development Fund AOGCM Atmosphere-Ocean Coupled General Circulation Models ARI Annual Recurrence Interval ARRB Australian Road Research Board BCC Brisbane City Council BOQ Bill of Quantity CCIR Central Cross-Island Road CCIRUP Central Cross-Island Road Upgrading Project – the Project CRRS Climate-Resilient Road Strategy CRTP Climate-Resilient Transport Project CRVA Climate Risk Vulnerability Assessment D&D Design and Documentation DALA Damage and Loss Assessment EMP Environmental Management Plan ERAP Enhanced Road Access Project GCF Green Climate Fund GHG Green House Gasses IPCC Intergovernmental Panel on Climate Change km kilometer km2 square kilometer LTA Land Transport Authority m meter mm millimeter MASL metres above sea level MNRE Ministry of Natural Resources and Environment MWTI Ministry of Works, Transport and Infrastructure p.a. per annum PACCSAP Pacific-Australia Climate Change Science and Adaptation Planning Program PPCR Pilot Program for Climate Resilience RCP Representative Concentration Pathway ROW Right of Way RRP Report and Recommendation of the President to the ADB Board of Directors SAMET Samoa Meteorology Division SMEC Snowy Mountains Engineering Corporation SPCR Strategic Program for Climate Resilience SPREP Secretariat of the Pacific Regional Environment Programme TA Technical Assistance TCE Tropical Cyclone Evan, 2012 UN United Nations UNDP United Nations Development Programme VASRN Vulnerability Assessment of the Samoa Road Network – World Bank funded ERAP TA Project VAGST Value Added Goods and Services Tax VA-FR VASRN Final Report – commonly referred to in this report WB World Bank WMO World Meteorological Organization WST/SAT Samoan Tala $ United States Dollar

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1 Introduction 1.1 Description Samoa’s land transport depends on key arterial roads that serve the two main islands, Upolu (where capital Apia is located), and Savaii. Upolu is served by three cross-island roads strategically located at the eastern, western, and central sections. The Central Cross Island Road (CCIR) is the key arterial road connecting the West Coast Road in Apia with the South Coast Road in Siumu. The project road is 19.7 km long. It provides access to eight villages enroute.

The project road climbs to almost 780m above sea level and is subject to increasingly heavy rainfall, particularly during tropical cyclones. For example, during Tropical Cyclone Evan (TCE) in December 2012 connectivity was lost, with several sections being washed away.

The upgraded Central Cross Island Road (CCIR) will increase access to social services (education, health) and economic and employment opportunities for the communities served, contributing towards inclusive growth and development of these areas. The climate resilient road will also be a major contribution to the island’s disaster preparedness as it will provide a sustainable alternate route for evacuation, post disaster relief and rehabilitation work between the northern and southern coasts.

1.2 Climate Change Context to Project The impacts of climate change to project were rated by the ADB as high1. In the context of country objective’s, Goal 2 of the government’s Transport Sector Plan2 is to “improve, sustain, and climate-proof [the] road transport network”. Being one of Upolu Island’s key arterial routes, a key element for upgrading the CCIR is accounting for the impacts of climate change.

1.3 Previous Studies The most relevant studies to project were part of the World Bank funded Enhanced Road Access Project (ERAP). A framework for ERAP was prepared based on a Damage and Loss Assessment (DALA) following TCE. The ERAP objective was formed to restore key road sector assets that have been damaged by extreme weather events and to enhance the climate resilience of critical roads and bridges in Samoa. As a result, the most specific sub-projects of ERAP to the CCIR were the following:

1. Central Cross Island Road Upgrading (CCIRU) 2. Vulnerability Assessment of the Samoa Road Network (VASRN).

Both projects were delivered by SMEC from late-2015 to mid-2017. The CCIRU was a road specific study, design & bidding documentation assignment. The VASRN was a nation-wide climate vulnerability assessment study. Due in most part to complex cadastral survey issues, the CCIRU project prematurely ceased in May 2017. At this time, project deliverables were well advanced (about 80%), but it also meant that plans for project implementation (civil works and supervision) to also be funded under ERAP would have to be cancelled. The VASRN was however fully completed around this time, with the final report being issued in May 2017.

It should be noted that due to the parallel project timing and advancement of differing project milestones, it was at the time impractical to ensure that all VASRN report recommendations had been fully assessed and accounted for under the CCIRU. CCIRU project re-start has however now provided an opportunity for this to occur. As such, a gap analysis between the two projects has now been performed, with details included in this report.

1.4 Current Status As the government has now requested ADB support for resumption and completion of the CCIR upgrading, the ADB has initiated a technical assistance (TA) assignment for the purpose of conducting its own due diligence/fact finding. This is a necessary prerequisite to secure ADB funding approval for project implementation (civil works and supervision).

Design and documentation (D&D) completion for bidding purposes is the responsibility of the government, through its implementing agency, the Land Transport Authority (LTA). This project will soon commence, and will be funded through the Green Climate Fund (GCF) administered by the United Nations Development Programme (UNDP).

Both the TA and D&D completion assignments are being delivered by SMEC. This report is a deliverable under the TA.

1 ADB. 2018. Project Concept Paper, Proposed Grant Samoa: Central Cross Island Road Upgrading. Manila.

2 MWTI. 2014. Transport Sector Plan 2014–2019. Apia.

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In order to differentiate the ADB funded project-chapter from that of the World Bank, the project is now referred to as the Central Cross Island Road Upgrading Project (CCIRUP). This is also consistent with the terminology of the ADB Project Concept Paper.

1.5 Report Objective In recognition of the importance of climate change to project (Section 1.2), a key deliverable of the TA is to specifically report on it. Recognising the previous efforts already made under ERAP (Section 1.3), this report serves to summarise relevant climate vulnerability findings and recommendations to the current project status (Section 1.4).

This report also estimates costs that can be attributed to climate change adaptation measures. These are included in Section 5 and summarised in Section 6.

1.6 Report Structure This report has been structured in a similar manner to the separate Climate Change Assessment, being a standard RRP3 linked document reporting template of the ADB. It therefore seeks to:

• Screen the project for identification of key climate risks • Identify means of addressing these risks i.e. adaptation measures.

Risk Screening: This includes identifying key climate risks e.g. increased rainfall and temperatures, and key project components sensitive to climate change e.g. road pavement. For risk identification, as VASRN was a detailed climate risk vulnerability assessment project of the Samoan road network, it will be referred to and summarised, bringing it into direct context with the current project (CCIRUP). Any risks not necessarily covered by the VASRN have been added by the TA consultant.

Adaptation Measures: Possible climate change adaptation options have been presented against each of the defined project components. This includes recommendations of the VASRN, as relevant to the CCIRUP. This is followed by a summary of what is already contained/accounted for within ERAP CCIRU documentation. Collectively, their comparison will take the form of a gap analysis for identification of any additional measures that may be required during the D&D completion exercise, under separate contract.

1.7 Previous Vulnerability Assessment Report Limitations In compiling this Climate Risk Vulnerability Assessment (CRVA) report, the VASRN final report4 (VA-FR) has been commonly referred to. In doing so, it is however observed that the primary VASRN focus is on rainfall. Topics of temperature and storm surge are also covered, but the former is bought into context of rainfall, and the latter is irrelevant to the CCIRUP as the project road is well above sea level (18m at its lowest point, rising to 771m at its highest). Wind, volcanic eruption, and earthquakes are briefly mentioned, but are not subject to analysis in the report. VA-FR footnote 13 explains why for volcanic eruptions (along with tsunamis), reasoning that these are not related to climate change. The same can be said for earthquakes.

As a result, this CRVA accounts for all possible climate risk vulnerabilities, including brief mention of natural disasters, (Section 2), but above all else, presents a more in-depth summary on the rainfall orientated focus of the VA-FR (Appendix 1), which is also considered to be the main climate change risk to the CCIRUP. Table 2-3 demonstrates this point.

Additionally, the VA-FR primarily focuses on climate change adaptation measures for drainage. For this reason, this topic is also subject to more in-depth reporting review than for other project components (Appendix 1 and 2).

3 RRP - Report and Recommendation of the President to the Board of Directors

4 SMEC. 2017. Vulnerability Assessment of the Samoa Road Network, Final Report. Apia.

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2 Risk Screening 2.1 Key Climate Risks The VA-FR reported on climate change for Samoa in 15. Annex D. The Current and Future Climate of Samoa5 brochure was firstly assessed, and deemed to be too qualitative to derive meaningful changes in rainfall intensity from. The remainder of this Annex moved its focus to more quantitative publications, and technical details that focus on climate model projections for temperature and rainfall. The brochure does however provide a simple and useful starting point for understanding the general climate change situation for Samoa, including the past, present, and future. Its finding are generally summarised in Table 2-1, along with conclusions of the VASRN.

Table 2-1: Summary of Current and Future Climate of Samoa

ELEMENT CURRENT CLIMATE CHANGING CLIMATE FUTURE CLIMATE

Temperature Generally consistent throughout the year, with small seasonal changes ranging from 23 to 30 OC. Can vary considerably from year-to-year to the El Nino Southern Oscillation. La Nina is usually cooler.

No evidence of changed air temperatures, but data gaps are recognised. Sea levels have risen.

Mean annual temperatures will rise. VA-FR confirms this (15.4.2). Extremely high daily temperatures will rise. VA-FR does not report on this. Sea levels expected to continue rising. VA-FR confirms this (3.3)

Rainfall Greatly influenced by position and strength of the South Pacific Convergence Zone, and band of heavy rainfall. Samoa’s mountains greatly influence rainfall distribution, with the north-west areas being drier than the south-east. Can vary considerably from year-to-year to the El Nino Southern Oscillation. La Nina is usually wetter. Droughts have had impacts in the past. Flooding has had impacts on the past.

Annual rainfall has increased, but little change in extreme daily rainfall

Small change in mean annual rainfall. VA-FR confirms this (15.4) but concludes that it is directly proportional to temperature rise (3.2.2, 11). More extreme rainfall events (more likely to occur, and to be more intense). VA-FR confirms this (3.2.4). Droughts expected to decline or remain the same. VA-FR contradicts this (3.2.4, 15.4). Tropical cyclones expected to be less frequent, but more intense. VA-FR confirms this (3.2.4).

Wind Trade winds cause wind-driven waves, and although not mentioned, would be strongest during tropical cyclones, and be a cause of damage.

Reduction of wave period expected, but not wave height. VA-FR reports on storm surge (4.9, 17). Tropical cyclones expected to be less frequent, but more intense. VA-FR confirms this (3.2.4).

Source: PACCSAP (2015), SMEC VASRN consultant (2017).

In summary, Samoa is expected to experience an increase in temperatures (average and extremely high days), an increase in more extreme rainfall (more often, and more intense), and high winds can be expected to become more intense but less frequent (as associated with tropical cyclones).

5 Pacific-Australia Climate Change Science and Adaptation Planning Program (PACCSAP). 2015. Current and Future Climate of Samoa.

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The VA-FR mentions many potential vulnerabilities that the Samoa road network faces (20.10). This includes natural disasters, as was contained in the VASRN TOR. These vulnerabilities are reflected in Table 2-2 along with some additions of the TA consultant, and relevance comments to the CCIRUP.

Table 2-2: CCIRUP Vulnerabilities (Climate and Natural Disasters)

POTENTIAL VULNERABILITIES RELEVANCE TO PROJECT (CCIRUP)

Climate

High tides Negligible – lowest point is 18m above sea level.

Sea level rise Negligible – lowest point is 18m above sea level.

Storm surge Negligible – lowest point is 18m above sea level.

Increased mean annual rainfalla

High – For any given road with similar traffic use, one that receives and sheds more rainfall will deteriorate quicker because of the destabilising and deteriorating effects of water over time on road building materials.

Extreme rainfall events High – Damage sustained by TC Evan, December 2012 severed the road in several locations, requiring major emergency works.

Flooding Moderate – Temporary surface flooding possible during extreme rainfall events (including tropical cyclones), but moderate due to generally steep and unconstrained (free draining) topography of the road and its surrounds.

Landslips Low – Frequency and extent of high/unstable embankments adjacent to the road are limited.

Increased air temperaturea Low – Samoa’s temperature is projected to rise by 2OC over the period from year 2000 to 2100b, but the design period of the road upgrade is only 20 years.

Extreme winda Moderate – Damage sustained by TC Evan, December 2012 caused debris to enter/fall on the road corridor.

Natural Disasters

Tropical cyclones High – Damage sustained by TC Evan, December 2012 severed the road in several locations, requiring major emergency works. Of all natural disasters, this presents the highest risk to the CCIR. Climate risk vulnerabilities associated with TCs include extreme rainfall events, flooding, and extreme wind.

Tsunamis Low – Although Samoa is highly susceptible to tsunamis (rated extreme by the MNRE), the lowest road point is 18m above sea level, and the closet point to the coast line is 0.5km (CCIR end point at South Coast Road intersection, Siumu). Likelihood is very low, would only be isolated to only a very small section of the road, and road damage would be minimal.

Earthquakes Moderate – Samoa is at high risk from earthquakes, but the road does not span any fault lines, major water crossings, or have high adjacent embankments. The road is however adjacent to steep ravines in both the north and south, which in the event of a major earthquake, could feasibly slip and impact the road. Likelihood is however very low.

Volcanic eruptiona Low – Like tsunamis, Samoa is highly susceptible to volcanic eruptions (rated extreme by the MNRE), but the road is inland, generally of high elevation, and does not span any major waterways.

Note: a added by TA consultant b VA-FR Figure 14-5 Source: TA consultant

As the report focus is on climate risks, vulnerabilities associated with natural disasters are not further analysed.

Climate risk vulnerabilities of low relevance include landslips and increased air temperatures. For landslips, although the CCIR is a steep and winding road, the extent (frequency, height and slope) of major embankment cut and fill sections is minimal. This is because the road alignment generally follows the natural terrain, as opposed to cutting through it. This also explains why the road is so steep and winding in the first place. Although the upgraded road will slightly improve (smoothen) the alignment, such changes are minimal, resulting in little-to-no change to landslip vulnerability. For air temperature

Increased air temperature presents its highest risk to the project through extreme daily temperatures (Table 2-3).

Moderate relevance vulnerabilities include flooding and extreme wind. Flooding is typically a result of extreme rainfall events, commonly associated with tropical cyclones. Tropical cyclones also bring extreme wind conditions.

High relevance vulnerabilities include extreme rainfall events (not necessarily associated with a cyclone), and increased mean annual rainfall. They increase ground saturation, cause flooding and landslips.

These vulnerabilities are compared to key project components in Section 2.2.

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2.2 Project Components and their Vulnerability Project components include physical works features. Of relevance to CCIRUP climate risks are road surfacing, road pavement, embankment slopes, drainage structures and paths, and roadside objects (trees, signs, utility poles, street lighting, and overhead wires). They are bought into context so that each component can be assessed in terms of its vulnerability to climate risks.

These key project components are reflected in Table 2-3, along with a comment for each against the key climate risks identified in Section 2.1.

Table 2-3: CCIRUP Project Components and their Vulnerability to Identified Climate Risks

PROJECT COMPONENT

VULNERABILITY TO CLIMATE RISK

EXTREME DAILY TEMPERATURES EXTREME RAINFALL EVENTSa HIGH MEAN ANNUAL RAINFALLa EXTREME WIND

Road Surfacing Moderate – Deterioration and road-user nuisance due to softening of bituminous material (not applicable to concrete surfacing)

Low – Failure can occur, but usually resultant of underlying or adjacent granular material failure (refer below)

Low – Failure can occur, but usually resultant of underlying or adjacent granular material failure (refer below)

Negligible

Road Pavement

Negligible Moderate – Can cause immediate rapid damage, but more likely to occur following periods of prolonged rainfall, and in close proximity to drainage paths

High – Prolonged ground saturation causing instability and failure, with or without extreme rainfall

Negligible

Embankment Slopesb

Negligible Moderate – Can cause immediate rapid damage, but more likely to occur following period of prolonged rainfall, and in close proximity to drainage paths

High – Prolonged ground saturation causing instability and failure, with or without extreme rainfall

Negligible

Drainage Negligible High – Short-term or immediate rapid damage caused and capacity exceeded by intense periods of rainfall

High – medium-to-long term sustained damage caused by prolonged rainfall

Negligible

Roadside Objects

Negligible Low – In isolation, but when combined with prior ground saturation and/or wind, can cause roadside objects to fall over

Moderate – Ground saturation combined with extreme rainfall and/or wind is a common cause of roadside objects falling over

Moderate – Vertical objects becoming unstable and falling on to footpaths, driveways, and road

Note: a Refer to Appendix 1 for further VA-FR assessment summary. b In the context of this assessment, refers to all cut and fill slopes within the road right-of-way (ROW), whether directly supporting the road pavement, or

within the verge area. c Trees, signs, utility poles, street lighting, and overhead wires. Source: TA consultant.

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3 Adaptation Measures The following sub-sections provide possible adaptation measures per project component. Measures already adopted in the current design version (under ERAP CCIRU) are summarised in Section 4.

3.1 Road Surfacing Risk focus (Table 2-3) is on extreme daily temperatures.

Possible adaptation measures:

• Review and if deemed required, improve LTAs standard technical specifications for road surfacing. This includes LTA Specification R-51 Sprayed Bituminous Surfacing and R-55 Dense Graded Asphalt. Focus on bituminous material sub-components, especially penetration grade/softening points.

• Consider adopting alternative low-risk surfacing options. A concrete pavement (including surfacing) would be the most low-risk alternative, but it comes with high capital construction costs, would take longer to build, has a higher carbon footprint than flexible pavement surfacings, and is observed to be highly uncommon in Samoa.

3.2 Road Pavement Risk focus (Table 2-3) is on extreme rainfall events, and high mean annual rainfall.


• Elevate the road pavement to be higher than surrounding natural terrain, especially for flood prone areas. • Provide a robust drainage network that especially enables any pavement entrained water to easily drain out i.e. provide

positive drainage. Such measures include providing sufficient crossfalls, crowning the outside shoulder on horizontal curves, and designing side drains with an invert lower than the base of the road pavement.

• Provide sub-soil drains within the pavement. This is, for example, common road authority practise in Queensland, Australia, a region that also receives high rainfall and experiences extreme rainfall events.

• Stabilise road pavement layers. The industry is starting to recognise this as a measure that can be adopted into immediate practise. For example: “Consider the use of moisture insensitive materials (stabilized materials versus unbound materials) throughout the pavement structure to minimize the reduction in structural capacity that occurs when pavements are submerged”. FHWA (2015)6. “A move to stronger foundations incorporating hydraulically bound materials (Chaddock and Roberts, s2006) will make the road foundation less susceptible to moisture”. TRL (2008)7.

• Seal (surface) road shoulders.

3.3 Embankment Slopes Risk focus (Table 2-3) is on extreme rainfall events, and high mean annual rainfall.


• Minimise slopes as much as possible, as they will be less susceptible to erosion. • Line and/or vegetate all slope surfaces, including the consideration of using geotextiles. • Reinforce at-risk slopes e.g. soil nails, gabion baskets, retaining walls. • If possible, off-set at-risk slopes away from the carriageway as much as possible.

3.4 Drainage

Risk focus (Table 2-3) is on extreme rainfall events, and high mean annual rainfall.


• Design drainage network for increased rainfall capacity. • For rural drainage, control drainage path flow velocities, and provide suitable erosion control measures. • Wherever possible, train surface runoff flow-paths to drain away from the road as opposed to towards road side-drains,

which are typically at the road shoulder edge e.g. use interceptor drains.

6 Federal Highway Administration. 2015. Climate Change Adaptation for Pavements. FHWA-HIF-15-015. USA.

7 Transport Research Laboratory. 2008. The effects of climate change on highway pavements and how to minimize them: Technical report. PPR184. UK.

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3.5 Roadside Objects Risk focus (Table 2-3) is on combined extreme rainfall events, high mean annual rainfall, and extreme wind.


• Review and if deemed required, improve LTAs standard technical specifications for road signs and street lighting. This includes LTA Specification R-63 Signs and P-5 Street Lighting. Focus on sign post and street light footing details, and without compromising safety or lighting effectiveness, offset distances from the carriageway.

• Review and if deemed required, request utility owners to improve their standard technical specifications for utility poles and overhead wires. For the CCIRUP, this includes for power and communications. Focus on pole footing details, stays e.g. anchoring cables, and overhead wire/pole connections.

• Offset all utility poles as far away as possible from the carriageway, and minimise the extent of overhead wire road-crossings.

• Remove all trees from the ROW.

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4 Climate Change in Current Design (under ERAP) 4.1 Overview As mentioned in Section 1.3, project design was already well advanced at the conclusion of the World Bank funded ERAP CCIRU project. Remaining design tasks will focus on some scope changes since the previous design effort under ERAP, and completion of outstanding tasks.

4.2 ERAP General Approach The ERAP terms of reference (TOR) did not detail any specific inputs or considerations for climate risks or change impacts. It did however generally state the expected project outcome of ERAP; being “restoration of key road sector assets damaged by extreme weather events, and to enhance the climate resilience of critical roads and bridges in Samoa”. SMEC’s ERAP CCIRU Inception Report (January 2016) did however present the following general approach to mitigate climate change impacts:

• Increase capacity of transverse drainage system by providing additional cross culverts or larger culverts so they can handle greater runoff from higher intensity rainfall events.

• Improve longitudinal drainage by including lined drains, wider side drains, and outlet drains to shed the expected higher volumes of water away from the road.

• Raise the vertical gradeline where road sections are subject to inundation during flooding. • Integrate physical engineering and bio-engineering solutions for high risk erosion areas as combined measures providing

the most cost-effective treatment options. • Minimise clearing of established vegetation in order to protect steep slopes. • Provide kerbing on urban roads and below-ground (buried) storm water drainage pipes to cater for run-off. • Provide erosion and scour protection measures at drain outlets.

As the CCIRU and VASRN both came under ERAP and commenced in parallel, LTA and World Bank expectation was that the CCIRU design team and VASRN study team would work closely together in order to adopt appropriate climate change adaptation measures. This indeed occurred, but as the two projects were progressing in parallel, the CCIRU design team had to adopt some of its own methods and assumptions in order to meet deliverable timelines. All such specific details relate to rainfall and drainage. These are further discussed in Appendix 1 and 2.

4.3 ERAP Reporting relevant to Climate Change Relevant to the topic of climate change and aside from the aforementioned Inception Report extract, the CCIRU consultant also finalised a Preliminary Design Report (February 2017). This included an appended detailed Drainage Design Report, Package 2 (February 2017). No further reports apply, but sets of substantially complete detailed engineering design (DED) drawings do, as these reflect the agreed design intent with the LTA and World Bank based on preliminary design stage reporting, including preliminary engineering design (PED) drawings.

4.4 ERAP Review by Project Component 4.4.1 Road Surfacing

Current Status: Client approved preliminary design outcome was to adopt 50mm thick asphaltic concrete (AC) for the urban area, and a 2-coat chip seal for the rural area. LTA standard specifications would apply. Current technical specifications are generally fine, but will still need further and final review.

Gap Analysis: As compared to possible adaptation measures (Section 3.1): • Review and possibly improve LTA Specification R-51 Sprayed Bituminous Surfacing and R-55 Dense Graded Asphalt. Focus

on bituminous material sub-components, especially penetration grade/softening points. • Although highly resistant to extreme daily temperatures, a rigid (concrete) pavement alternative is for numerous reasons

considered impractical for this project. All other surfacing options contain bitumen, the surfacing sub-component that is vulnerable. Focus therefore needs to be on bitumen grade/softening point, for which the above specification review and possible improvement is sufficient.

4.4.2 Road Pavement

Current Status: The PED drawing road alignment closely resembled the existing alignment, smoothing out both vertical and horizontal profile wherever possible (as balanced with the competing objective to minimise resettlement impacts). Some further alignment improvements were made during DED development, albeit for isolated sections only. More recently, a post-ERAP site assessment of the current urban area DED drawings revealed a need to make some further modifications to

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accommodate an LTA requested revision (around Myna’s supermarket in the urban area), and to minimise some vehicle crossing roll-over slopes from the design carriageway into private properties. Furthermore, a select few sharp corners within the rural area will also be reviewed with a view towards alignment improvement related to design speed changes.

Only one section of the project road is a known or anticipated flood prone risk. This location is KM 2+040, adjacent to the Robert Luis Stevenson Memorial fence line (Figure 4-1).

Figure 4-1: Typical Rock Weir and Drop Structure Details

The existing twin-barrell pipes are blocked by the recently built house on the opposing side. In addition to overall improved drainage up-grade and at this location (new fully piped drainage network), installing a newly aligned cross-drain of adeqaute capacity will alleviate this problem. Final design solution details will be addreesed under the seperate D&D completion servcies contract.

Providing a robust drainage network solution that also accounts for the impacts of climate change (Appendix 2) is a highly effective method of reducing climate risk to the road pavement structure. Additional positive drainage measures already accounted for in DED drawings through geometric design include: • Crowning the outside shoulder for horizontal curves i.e. adverse shoulder crossfall (Figure 4-2)– surface runoff and any

pavement layer entrained water will flow to the side-drain, instead of towards to the more critical carriageway pavement.

Figure 4-2: Crowned Outer-shoulder

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• Extending the width of road surfacing over this crown. See following from typical section drawings (0.15m overlap).

Figure 4-3: Sealed Shoulder Crown

Figure 4-2 and 4-3 both reflect a side-drain invert lower than the base of the road pavement.

Client approved preliminary design outcome was to adopt a flexible road pavement designed according to TRL ORN 318. This included an unbound granular basecourse (base) layer over an unbound subbase layer, over an unmodified but uniformly prepared subgrade layer. In addition, granular unbound and unsealed shoulders for the rural area (no shoulders applied to the urban area). LTA standard specifications would similarly apply, but with a minor technical modification to be made to R-40 Pavement Base and Subbase. This has been carried through to the current DED drawings (including notes referring to the relevant LTA specifications).

Current DED drawings exclude pavement sub-soil drains, stabilized pavement layers, and sealing (surfacing) of road shoulders.

Gap Analysis: As compared to possible adaptation measures (Section 3.2): • For the whole alignment, elevating the road to be generally higher than the surrounding terrain would be a complex and

impractical undertaking, as it would not only require full length review and redesign, but would create an additional set of complex challenges that would then need to be overcome. For example, in the urban area, it would present untold technical and social challenges with tying in the many existing driveways and side roads. From a rainfall and runoff/drainage perspective, it would shift the problem elsewhere i.e. the road asset would be well protected, but would be at the detriment to adjacent private properties. Because of this, in principal, it is better to have the road lower than adjacent properties for an urban setting. For the rural area, these problems are less pronounced due to lower adjacent development and more flexible opportunities for providing drainage outfalls, but required additional investigations and design effort compared to possible benefits that may stem from reduced climate risk exposure quickly negate this as a practical measure. Elevating the road is not therefore recommended.

• For the flood prone area of KM 2+040, elevating the road is not a favoured design solution either. Rather, installing a completely new cross-drain at a new alignment to avoid the house is. Like all pipework, this will have sufficient additional capacity accounting for climate change, amongst some other site-specific measures.

• Positive pavement drainage considerations are already well embedded in the design, so no further action is needed. • Pavement sub-soil drains are used to control pavement moisture content in order to maintain pavement strength, but

their effectiveness is relative to application. They are for example used beneath surface joins for retrofits (where a new pavement section abuts existing). This protects both old and new pavement. They are also used in high-risk areas such as flood prone road sections, or where groundwater is known or anticipated to be problematic, such as the toe of major embankment cuts, or where a high-water table exists. Draw-backs of utilising pavement sub-soil drains include need to outlet to an adjacent drainage path or structure (not always possible due to level design), ongoing cleaning maintenance, and specific to Samoa, likelihood that they would need to be imported. Under the separate D&D completion services, LTA will be further consulted about the possibility of including these in select locations such as KM 2+040, start and end point of each road section to be upgraded, and some other possible yet TBC locations.

• Similar to sub-soil drains, pavement stabilisation is also an effective means of controlling pavement moisture susceptibility, but on a wider scale. Granular layer cement stabilisation is the most obvious choice, but emulsified or foamed bitumen technologies could also be suitable alternatives. Including stabilisation should be but based on its climate

8 Transport Research Laboratory (TRL). 1993. Overseas Road Note (ORN) 31: A guide to the Structural Design of Bitumen-surfaced Roads in Tropical and Sub-tropical Countries. 4th Edition.

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risk management merits versus an array of potential downside that includes but is not necessarily limited to: (i) added constructability challenges including available machinery and experienced construction and supervision personnel9, (ii) increased safeguards issues (cement is caustic and can be hazardous waste), (iii) longer build time frames (additional construction task), and (iv) likely additional construction costs (material, transportation, equipment, and labour). If adopted and designed according to the current pavement design standard (TRL ORN 31), it would need to be for the subbase only and not basecourse. There may still however be merit in stabilising the basecourse instead of subbase. A third alternative is stabilisation of the road shoulders only – the only granular pavement layer exposed to the elements (unsurfaced/covered by an overlaying layer) i.e. not only is it susceptible to pavement-entrained moisture, but also surface scouring caused by excessive rainfall runoff. Cement quantities for shoulder stabilisation is about 1/3rd of the requirement for full pavement width stabilisation. Premixing for shoulders prior to transport and placement may be required, and perhaps even desirable, but of all granular road pavement components, stabilising of shoulders would appear to be the most effective and economical way of mitigating granular pavement layer climate risk vulnerability.

• As road shoulders are already adversely sloped (away from the road centreline) and additional full-width shoulder surfacing costs would be of significance for the 12.9 km of full-width rural road upgrade (estimated $500,000), there is little perceived benefit to project in doing so. It is not therefore recommended.

4.4.3 Embankment Slopes

Current Status: Client approved preliminary design outcome was to adopt LTA standard specification requirements, and recommendations of the ERAP Preliminary Design Report. This report recommended adopting 3:1 (H:V) desirable/2:1 maximum slopes for embankments. Detailed design development did however later reveal that it was largely impractical to comply with these parameters due to the targeted narrow ROW, and need to avoid embankment slopes within private property. As a consequence, a maximum slope of 1:1 was adopted in DED drawings. This was deemed to acceptable on the basis that observed existing slopes of the CCIR are stable at similar or even steeper slopes, and that there is minimal-to-negligible occurrence of high cut or fill slopes stemming from the design.

All embankment slopes are to be grassed lined, with no additional need for further engineering solutions such as geotextiles, bio-engineering (e.g. grasses, shrubs, trees), or other such intervention measures. There is no identified need for specific structural treatments such as soil nails, gabion baskets, or retaining walls to aid in erosion control.

Gap Analysis: As compared to possible adaptation measures (Section 3.3): • Obtain LTA approval for revised maximum embankment slope design of 1:1. • Conduct final review of all embankment slopes during separate D&D completion services contract. If required, make any

necessary adjustments.

4.4.4 Drainage

Current Status: Client approved preliminary design outcome was to adopt the recommendations of the ERAP Preliminary Design Report, including appended Drainage Design Report, Package 2. This has been carried through to the current DED drawings (including notes referring to the relevant LTA specifications, and client accepted Australian standard details e.g. Brisbane City Council). Urban area drainage design is a fully piped network with 4 outfalls. It is almost complete (final review and revisions, plus consolidation of all final inventories and calculations only). Rural area drainage design is also well progressed, but requires more work to complete than for the urban. Both drainage schemes have accounted for the impacts of a climate change, but not necessarily in strict accordance to the recommendations of the ERAP VASRN project. No inceptor drains are specified, as deemed not required.

Gap Analysis: As compared to possible adaptation measures (Section 3.4): • Current design has accounted for increased rainfall and runoff due to climate change. Further analysis of the current ERAP

CCIRU design against recommendations of the VA-FR are provided in Appendix 2. Gap analysis conclusions include: − Confirmation that use of Nafuana and Afiammalu stations instead of Apia station are more appropriate for the

project. − Review required for overly conservative rainfall intensity estimations for the central-northern part of the alignment

from KM3+604 to about KM8+000, when compared on the basis of increased rainfall with increased elevation.

9 One local contractor only (OTT) has a cement stabiliser. This was used for one recent project only (Vaitele St). Bearing this in mind, if cement stabilisation was to be specified, competing firms would likely need to hire this machinery from OTT, or import. It creates a distinct market advantage for OTT, but at least this capability/resource is already available in Samoa.

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− Review required for both under and over conservative rainfall intensity estimations for the entire southern part of the alignment (crest at KM 9+788 to end point at KM19+686) when compared on the basis of rain shadow effect + elevation.

− Confirmation that despite being different, the CCIRU adopted correction factor for estimating future rainfall projections is consistent with the results of the VASRN method. No change is therefore required.

− Confirmation that CCIRU proposed pipe sizes accounting for the climate change are appropriate. • For the rural drainage scheme, frequent use of rock weirs in side-drains are specified in standard drawings to mitigate

erosion by controlling flow velocities, and rock mattresses/rip-rap lining are a common theme for any discharge point. Figure 4-4 reflects both rock weirs and erosion control for a drop structure. These will all be geotextile lined. Geotextile lining of road-side drains to protect the road pavement will be further investigated. Pit openings will include a trash rack to minimise pipe debris blockage. Finalisation of all drainage design details is pending, but no changes to the concepts are anticipated.

• Interceptor drains are a useful way of mitigating rainfall and runoff impacts on a road by minimising the amount of water exposure to the critical part of the road – the road pavement, as road side-drains are typically (but not always) located immediately adjacent to it. In the case of the CCIRUP, width is limited, hence they are all, by default, designed to be adjacent. Due also to width constraints, opportunities for inceptor drains are likewise limited, and would most likely require additional land acquisition. Besides, there is little need for them on this project. Their inclusion is therefore not recommended.

Figure 4-4: Typical Rock Weir and Drop Structure Details

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4.4.5 Roadside Objects

Current Status: Client approved preliminary design outcome was to adopt LTA standard specification requirements for road signs, as no special treatments were considered necessary. This has been carried through to the current DED drawings (including notes referring to the relevant LTA specifications).

Street lighting applies to the urban area. This design, including some specific technical notes on drawings, is substantially complete (subject only to final review and minor changes). The LTA standard specification does however need specialist review and modifications, as appropriate. All street lights are offset from the carriageway by being located behind the footpath.

For utility services, a complete utility corridor master plan was developed and approved. This reflected common utility corridors for both sides of the ROW, and common trench crossing locations nominally spaced at 500m intervals. All corridors were reflected to be a nominal 0.5 m wide. By designating the outer-most limits of the ROW as longitudinal corridors, new and relocated utility poles and overhead wires will be placed as far away from the road carriageway as practically possible.

As part of the Resettlement Plan (RP), most all existing trees within the current and proposed ROW will be removed. As such, any potentially high-risk trees will be eliminated as a hazard.

Gap Analysis: As compared to possible adaptation measures (Section 3.5): • Review and possibly improve LTA Specification R-63 Signs and P-5 Street Lighting. • Review and possibly improve utility owner standard technical specifications for utility poles and overhead wires. • Encourage minimisation of overhead wire road-crossings, and common placement with the currently designated trench

road-crossings.

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5 Climate Change Adaptation Costs Additional project costs attributable to allowing for the impacts of climate change can be quantified for the following two project components:

• Use of cement in the road pavement design. • Differing components on the road drainage design.

These are separately discussed, quantified, and cost estimated in the following sub-sections.

5.1 Road Pavement Design – Cement As per the gap analysis of Section 4.4.2 (bullet point 5 – pavement stabilisation): “stabilising of shoulders would appear to be the most effective and economical way of mitigating granular pavement layer climate risk vulnerability.”

Calculations are provided as follows:

Quantities

Rural area full-width road upgrade length (m): 15,266m less 3,193m for LTA completed road sections = 12,073m

Standard width of road shoulder material (m): 1.85m10 x 2 (each side) = 3.70m

Standard depth of road shoulder material (m): 0.2m (same as basecourse layer thickness)

Area of shoulders (m2): 3.7m x 12,073m = 44,670m2

Costs

Local contractor’s (OTT) contract price for LTA project Vaitele Street (Vailoa – Vaitele) – Reconstruction and Widening, with costed BOQ dated 20 October 2014:

SECTION 6. PAVEMENT AND SURFACING

Item Description Unit Qty Rate Amount (SAT)

Cement Stabilisation of Basecourse

06/3A Stabilise 200mm depth with 2.5% cement, compact, trim and prepare for sealing. Refer specification R42. m2 33,000 10.50 346,500.00

This project was confirmed by the LTA to be the only one where cement stabilisation had been used in Samoa in the past.

Escalated from year 2014 to year 2019 based on ADB’s inflation rates for Samoa11 the unit rate is determined to be SAT 11.41, as per the following table:

YEAR 2014 2015 2016 2017 2018 2019 Inflation Rate 1.9% 0.1% 1.4% 2.0% 3.0%

Unit Rate (SAT/m3) 10.50 10.70 10.71 10.86 11.08 11.41

Total costs attributable to climate change for cement in road shoulders: 44,670m2 x SAT 11.41 = SAT 509,685 ($195,864)12

5.2 Road Drainage Design Table 2-3 identified extreme rainfall events, and high mean annual rainfall as the highest climatic risks to the drainage component of the project.

Generally extreme rainfall events are limited to shorter, high intensity events lasting only minutes rather than hours or days. These events can be in combination with long lasting events, including the occurrence of cyclones, when rainfall prior to the intense event has saturated the catchment and all rainfall essentially runs off, contributing to extreme peak runoff. While time of concentration may be similar for parts of the catchment, because of the high runoff, rutting and scour may occur in places, channelling water down the catchment more rapidly and increasing flows at road crossings.

10 Road shoulders are a standard 2.0m width but in order to provide suitable lateral support to the traffic lane where live traffic loadings are experienced, and additional 0.15m of road basecourse material is included, leaving 1.85m wide remaining as lower-grade specification road shoulder material.

11 https://www.adb.org/data/statistics

12 Forex www.xe.com 14-Feb-19: US$1 = SAT 2.61501

https://www.adb.org/data/statistics

http://www.xe.com/

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Extreme rainfall increases over the life of the CCIR may contribute towards to a 20% increase in peak runoff. However, combined with the increased risk of rutting and scour, this could increase flows at the road alignment to well in excess of 20%; potentially causing flows to concentrate in one area and causing wash-outs.

An increase in high mean annual rainfall is the result of more intense and frequent rainfall events. It does not necessarily increase peak flows; except perhaps where it causes more general saturation of the catchment’s soils, resulting in increased runoff and shorter concentration of flows. However, these two aspects are already addressed under extreme rainfall events so are not considered further.

The anticipated increase in peak runoff due to extreme rainfall events is likely to be in the order of 20%, while consequential factors are likely to contribute a further 5%-10%. This is however more likely to occur at cross drainage locations (culverts) rather than for the longitudinal drainage.

However, at the onset of the design we had adopted criteria which determine the minimum diameter of pipes. In urban areas, the minimum adopted pipe size of 450mm was adopted for all pits and piped drainage. In rural areas, the adopted minimum pipe size for culverts is 900mm and for under road longitudinal drainage, 600mm. With these adopted minimum pipe sizes, inlet pits and outlet headwalls are also a fixed minimum. In other instances, pipe sizes do not change because available capacity of smaller sizes may not be adequate, also for non-climate change flows. Therefore, the scope of change due to climate change for pipe sizes is limited to only the larger pipe diameters of 1050mm, being the only size of pipe greater than 900mm.

Our assessment for change of the design from without to with climate change is therefore limited to the following:

Urban Area: Inlet pit distances reduce by approx. 20%, commensurate with the peak rainfall increase over the catchment. Hence the with climate change scenario (more rainfall) results in closer inlet pit spacing.

Rural Area: Longitudinal drainage channels increase in size to accommodate additional flows. We have assumed channels provide an additional depth of 100mm i.e. with climate change they are 500mm deep and without climate change they are 400mm deep.

Only pipes of diameters greater than 900mm can be downsized by one size. For the CCIR drainage design only 1050mm pipes are greater than 900mm, so the without climate change scenario assumes all current 1050mm size pipes become 900mm.

Where pipe sizes are reduced, connecting structures (headwall/wingwalls, and inlet pits) reduce in size commensurate with the reduced pipe diameter.

Quantities: With and without climate change quantities are provided in Table 5-2.

Unit costs: Unit rates will not change for with and without climate changes scenarios except for open channels in the rural area. Unit rates are reflected in Table 5-2 along with quantities, but are also explained per unit rate in Table 5-1.

All unit rates have been estimated by applying ADB inflation rates for Samoa to historical contracted rates of local contractor OTT for LTA project West Coast Road (WCR) Upgrade Project – Lot 1: Malua to Afega KM 11+900 to 18+500. Rates for this project were received by the LTA 05-Mar-18 and contract signed 14-Sep-18, so the rates are considered to be applicable as of 2018.

Rates from the Vaitele Street Project, 2014 were also assessed, but there was found to be little relevance for comparison to the CCIRUP. As such, ADB’s inflation rate of 3.0% for Samoa in 2019 was used to determine suitable unit rate price escalation for the CCIRUP.

Total costs attributable to climate change for drainage: SAT 453,601 ($175,851).

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Table 5-1: Unit Rate Estimates for Drainage

HISTORICALADJUSTED

HISTORICAL (SEE REMARK)

ESTIMATED

2018 2018 20191 Pipework

1.1 900mm Class 4 1,200 n/a 1,236 2018 price for 900mm class 4. No hist. adjustment needed1.2 1050mm Class 4 2,100 1,900 1,957 2018 price for 1350mm class 4. Assume SAT 200 less for 1050mm2 Structures

2.1 Headwall/Wingwall2.1.1 900mm 1 Cell (HWL900H) 8,500 n/a 8,755 2018 price for 900mm 1 Cell. No hist. adjustment needed2.1.2 900mm 2 Cell (HWC900JZ02) 10,000 0 10,300 2018 price for 900mm 2 Cell. No hist. adjustment needed2.1.3 1050mm 1 Cell (HWC1050JV) 10,500 10,250 10,558 2018 price for 1200mm 1 Cell. Assume SAT 250 less for 1050mm2.1.4 1050mm 2 Cell (HWC1050JZ02) n/a 11,750 12,103 No historical data. Assume SAT 1,500 more than same size 1 cell as reflected for 900mm 2.2 Inlet Pit - rural (no-kerb)

2.2.1 900x1200mm 12,000 12,360 2018 price for chamber to suit single 900mm pipe. No hist. adjustment needed2.2.2 1200x1200mm 14,500 13,667 14,077 2018 price for chamber to suit single 1350mm pipe. Assume 2/3rd of price diff btwn 900 & 1350 mm 2.3 Inlet Pit - urban (kerbed) 14,500 10,875 11,201 2018 price for chamber to suit single 1350mm pipe. Connecting pipes for CCIR design are smaller but

these structures are precast components and more of them so assume 75% of SAT 14,500. 3 Open Channel

3.1 Rock Lined Channel n/a 50 51.50 No historical data. Assume 2.5 times that for grass lined. 3.2 Grass Lined Channel 20 n/a 20.60 2018 price for lineal metres of "swale" including excating, shaping, and seeding. No hist. adjustment

neededDiffering rates for WITH & W/OUT CC for Open Channel

ITEM DESCRIPTION WITH CC W/OUT CC VARIANCE REMARK3 Open Channel

3.1 Rock Lined Channel 51.50 41.20 10.30 3.2 Grass Lined Channel 20.60 16.48 4.12

W/OUT CC: 400mm deep instead of 500mm deep. Assume 1/5 (20%) cheaper than WITH CC

RATE (SAT)

REMARKDESCRIPTIONITEM

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Table 5-2: BOQ-Cost Estimate for Drainage with and without Climate Change

UNIT QUANTITY RATE (SAT) AMOUNT

(SAT) UNIT QUANTITY RATE (SAT)

AMOUNT (SAT)

1 PipeworkInstall underground stormwater pipes including trench excavation, bedding and backfilling, placing all pipework to true depths, lines and grades including all pipe jointing. Connection to structures to be included in those respective cost items.

1.1 900mm Class 4 m 644 1,236 795,984 m 734 1,236 907,5951.2 1050mm Class 4 m 90 1,957 176,717 m - 1,957 02 Structures

2.1 Headwall/WingwallInstall outlet/inlet structure including all excavation, and backfill, bedding and footing, headwalls, wingwalls, apron and pipe connections.

2.1.1 900mm 1 Cell (HWL900H) no. 17 8,755 148,835 no. 18 8,755 157,5902.1.2 900mm 2 Cell (HWC900JZ02) no. 24 10,300 247,200 no. 30 10,300 309,0002.1.3 1050mm 1 Cell (HWC1050JV) no. 1 10,558 10,558 no. - 10,558 02.1.4 1050mm 2 Cell (HWC1050JZ02) no. 6 12,103 72,615 no. - 12,103 02.2 Inlet Pit - rural (no-kerb)

Install inlet structure including open-grate grill cover, all excavation, bedding, backfill, and pipe connections.

2.2.1 900x1200mm no. 1 12,360 12,360 no. 3 12,360 37,0802.2.2 1200x1200mm no. 2 14,077 28,153 no. - 14,077 02.3 Inlet Pit - urban (kerbed)

Install top-entry pit, grill, and precast lintel beam in-line with kerb including all excavation, bedding, footing, backfill, and pipe connections.

2.3.1 2400mm long lintel beam no. 111 11,201 1,243,339 no. 89 11,201 994,6713 Open Channel

3.1 Rock Lined ChannelInstall rock lined channels for road side drains and where applicable outfall channels including all materials and items of works necessary to complete.

3.1.1Excavation, shaping, disposal of earthworks material; preparation including compaction for placement of geotextile & dumped rock (D50 = 150mm, 300mm thick) lm 7,853 51.50 404,436 lm 7,853 41.20 323,549

3.2 Grass Lined ChannelInstall grassed lined channels for road side drains and where applicable outfalls including all items of works necessary to complete. M&P of the works as per the following line items:

3.2.1Excavation, shaping, disposal of earthworks material; preparation including compaction for placement of hydro mulch

lm 10,410 20.60 214,445 lm 10,410 16.48 171,556

3,354,642 2,901,041COMPARISON:

SAT 453,601Equiv. USD 175,851

W/OUT CC: Trapezoidal shaped channels with 1:1 side slopes & 500mm wide base but 400mm deep instead of 500mm deep. Assume 43% of total length rock lined/57% grass lined.

DESCRIPTIONITEM QUANTITY EXPLANATION

W/OUT CC: All pipes > Dia. 900mm become Dia. 900mm (only Dia. 1050 applies)

W/OUT CC: All structures connecting to pipes > Dia. 900mm reduced for connecting to Dia. 900mm

W/OUT CC: spacing of inlets greater. Assumed 20% reduction in nos.

Total (SAT):

WITH CLIMATE CHANGE WITHOUT CLIMATE CHANGE

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6 Conclusion Key climate risk vulnerabilities to the project were identified to include: (i) extreme daily temperatures, (ii) extreme rainfall vents, (iii) high mean annual rainfall, and (iv) extreme wind. Of these, (ii) and (ii) – rainfall was identified as posing the highest risk.

Relevant project components were identified to include:

• Road surfacing • Road pavement • Embankment slopes • Drainage • Roadside objects (trees, signs, utility poles, street lighting, and overhead wires)

These were assessed against the abovementioned climate risks. The most vulnerable project components were deemed to be road pavement, embankment slopes, and drainage. Irrespectively, possible adaptation measures for all five components were presented, their current design status summarised, and remaining adaptation measure tasks identified through a gap analysis.

As the previous project climate vulnerability assessment focused on rainfall, this and the topic of drainage were studied in further detail than other risks and project components. The World Bank funded ERAP Vulnerability Assessment Final Report (May 2017) was referred to as the source document. It was primarily compared to the CCIRU Preliminary Design Report and appended Drainage Design Report, Package 2 (both February 2017).

The overall gap analysis results are presented in Table 6-1. It includes responsible parties and envisaged completion milestones.

Table 6-1: CRVA Gap Analysis Results

PROJECT COMPONENT VULNERABILITY TO CLIMATE RISK

Road Surfacing • Review and possibly improve LTA Specification R-51 Sprayed Bituminous Surfacing and R-55 Dense Graded Asphalt. SMEC – DED completion, Q2 2019.

Road Pavement

• Select and finalise design solution for flood prone area at KM 2+040. SMEC – DED completion, Q1 2019. • Consider select sites for possible inclusion of pavement sub-soil drains, and solicit client input. SMEC/LTA – DED

completion, Q1 2019. • Further investigate possibility of including cement stabilised pavement layer(s). Solicit client inputs.

SMEC/LTA/ADB – TA finalisation, Q4 2018/Q1 2019

Embankment Slopesb

• Obtain client approval for adopting maximum of 1:1 embankment slopes (2:1 was approved in prelim design report). SMEC/LTA – DED completion, Q1 2019.

• Conduct final review of all embankment slopes and make possible final changes. SMEC – DED completion, Q1 2019.

Drainage • Revisit rainfall intensity assumptions for north-side road section from KM 3+604 to KM 8+000, and the entire south-side (crest at KM 9+788 to end point at KM 19+686) with a view towards adopting recommended ERAP Vulnerability Assessment Final Report correction factors for elevation (north-side) and rain shadow effect + elevation (south-side) based on Afiamalu station data. SMEC – DED completion, Q1 2019.

• Finalise both urban and rural drainage designs (rural requiring the most effort). SMEC – DED completion, Q1 2019.

Roadside Objectsa

• Review and possibly improve LTA Specification R-63 Signs & P-5 Street Lighting. SMEC – DED completion, Q2 2019. • Review and possibly request improvement of utility owner standard technical specifications for utility poles and

overhead wires. LTA/SMEC – DED completion, Q2 2019. • Raise and discuss topic of common and infrequent overhead wire crossing locations with EPC (power) and Bluesky

(communications). LTA/SMEC – DED completion, Q1/Q2 2019. Note: a Trees, signs, utility poles, street lighting, and overhead wires. Source: TA consultant.

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Additional civil works costs associated with design measures that account for the impacts of climate change are reflected in Table 6-2, along with brief explanations. Further explanations are provided in Section 5.

Table 6-2: Cost Attributable to Climate Change

PROJECT COMPONENT COST ATTRIBUTABLE TO

CLIMATE CHANGE EXPLANATION

Cement for Road Shoulders (rural) SAT 509,685 ($195,864) • Stabilised instead of unstabilised road shoulders.

Drainage SAT 453,601 ($175,851) • All pipework greater than Dia. 900mm becomes Dia. 900mm for the without climate change scenario. Dia. 1050mm only applies.

• All structures connecting to pipes greater than Dia. 900mm are reduced in size commensurate with pipe size reduction.

• Inlet pits for the urban area (fully piped network) are spaced further apart for the without climate change scenario, meaning less of them.

• All open channels (road side drains and where applicable, for outfalls) are 400mm instead of 500mm deep for the without climate change scenario.

TOTAL SAT 963,286 ($371,715)

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7 Appendix 1 ERAP Vulnerability Assessment Summary 7.1 Introduction The Vulnerability Assessment of the Samoa Road Network Project (VASRN) made a comprehensive assessment of the road transport network across Samoa. It identified areas vulnerable or susceptible to climatic influences and reviewed current practices (2016) in road development, maintenance and asset management.

The CCIR was included in this assessment. Blackvue video recordings were made (also repeated under the ERAP CCIRU Project, and this, the ADB funded CCIRUP TA). The VASRN hazard-mapped roads according to (i) coastline proximity, (ii) waterway crossings, and (iii) landslide vulnerabilities. The CCIR only featured in (ii), for which 15 such crossings were recorded. All were culverts, and included the following comment “Robust, concrete culvert with pipes, constructed as part of emergency repairs. Not a climate change hazard.”. This is because none of them are major waterways. Rather, they are tributaries leading to major waterways, and for the most part, only convey notable runoff during or following heavy rainfall events.

The following is a direct extract from 1. Executive Summary/1.2 Summary of Newly-Introduced Assessment Methodologies of the VA-FR:

“Detailed analysis […] has determined the following:

• IDF curves have been prepared that can form the basic starting point for any future drainage design in Samoa. • A rain shadow exists in Samoa with locations in the south of both islands receiving 25% more rain intensity that in the

north. • An elevation factor exists whereby 10% should be added to the rainfall intensity for each increase in height of 100m. • Hourly rainfall is approximately 27% of daily rainfall.

In addition to the above correction factors, climate change scenarios have been modelled for RCP6.0 from 2016 through 2055 until 2090. These indicate that a peak in global temperatures will occur around 2055 and then decrease. Rainfall is directly proportional to temperature and a 10% increase in precipitation intensity can be anticipated for each 1oC increase in temperature. Therefore, a 20% increase in rainfall intensity should be added to existing rainfall patterns to allow for climate change.”

Further details behind these conclusions are summarised in the following sub-sections. A conclusion is provided in Section 7.5.

7.2 Hydrology Investigations This refers to 13. Annex B Hydrology Investigations of the VA-FR. 3.1 Rainfall Analysis of the VA-FR is also covered in Section 7.2.2 Rainfall Analysis.

7.2.1 Information Sources

The following information formed the basis for hydrology investigations.

Previous Reports: A number of previous reports on meteorology, flood estimation, and climate change were sourced and studied. Principal among these were:

• Kammer. 1978. Samoa Meteorology Report • Burgess. 1985. Study of Samoa Meteorology • New Zealand Met. Service. 1987. The Climate and Weather of Western Samoa • Samoa Meteorology Division, 2007. Climate Risk Profile for Samoa • BECA. 2010. West Coast Road Design • Pacific-Australia Climate Change Science and Adaptation Planning Program (PACCSAP). 2015. Current and Future Climate

of Samoa • Roughton International Ltd. 2015. Design Completion Report, Enhancing Climate Resilience of the West Coast Road

These reports provided background, but none of them provided specific information on short duration rain storms using data from Samoa, nor on the extent to which storm rainfall would be modified by climate change. Some of the information presented in tables and charts was extracted and digitised, then used to complement other data sets.

Existing Data: Three main data sets were provided by the LTA to the VASRN consultant:

• Daily rainfall data for Apia and Faleolo, 1984 to 2014 • 10-minute rainfall data for Afiamalu and Nafanua, 2010 to 2015 • Monthly rainfall from five weather stations, 1984 to 2014 (some earlier than 1984).

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Rain shadow: The four sites on Savaii were selected to show the north-south rainfall variation across the island, known as the “rain shadow”. The site at Matautu, together with data from Apia, gave the north-south comparison across Upolu i.e. the rain shadow.

Elevation Influence: The sites on Upolu at Afiamalu and Nafanua are at low and high elevations respectively, showing rainfall variations with elevation.

Short-duration Rainfall: Afiamalu and Nafanua also had 10-minute data. This was analysed to give short duration rainfalls.

7.2.2 Rainfall Analysis

Three key conclusions of the VA-FR were drawn from the rainfall analysis. These are reflected in green boxes13 in the following sub-sections.

Long-term to short-term rainfall conversions

Long-term data revealed that the highest annual rainfall ever recorded in Samoa was 9,359mm at Afiamalu in 1949. The highest daily rainfall ever recorded in Samoa was 671mm at Tapatapao in January 1939.

For monthly rainfall records, the example of Fogapoa on Savaii was given (Figure 7-1). This shows monthly data going back to 1932.

Figure 7-1: Monthly Rainfall at Fogapoa, Savaii (1932 to 2015)

This shows occasions when the equivalent of half a year’s rainfall fell in one month, which could also have fallen over just a few days.

The daily data enabled the rainfall amount which would have occurred within a specific frequency of occurrence (recurrence interval) to be calculated. The data for Apia was found to be of good quality and being of 31-years duration, was considered adequate to calculate daily rainfall maxima for an annual recurrence interval (ARI) of 1-in-100 years. It was therefore decided by the VASRN consultant to use Apia data sets as a first step for calculating storm rainfall of shorter durations.

This allowed establishment of some “Rules of Thumb” for rainfall, whereby long-term data could be used to estimate short-term data. These included conversion of:

• Annual rainfall to hourly rainfall = 3.6-7.2% (VASRN consultant) as compared to 4-8% (ARRB) • Daily rainfall to hourly rainfall = 33% (VASRN consultant) as compared to 40% (ARRB) • Hourly to short-term (30 minutes, 10 minutes, etc.) = used for small catchments of less than 1 km2.

13 Emphasis given, as-is consistent with the VASRN Final Report.

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Figure 7-2 shows correction factors (blue line) applied to known hourly figures to get short-term values. These were based on the 10-minute intervals from Afiamalu. The orange line shows similar figures estimated by Kammer (1978) for comparison, being slightly higher. The two curves were however found to be consistent.

Figure 7-2: Hourly Rain Fall to Short-term Correction Factors (Blue)

Applying these correction factors to hourly rainfall figures enabled short-term rainfall intensity figures to be derived. These could then be used when calculating runoff from small catchments in the order of less than 1 km2.

CONCLUSION 1: For hourly rainfall use the greater of 5% of annual rainfall (average of 3.6 to 7.2%), and 30% of daily rainfall (rounding of 33%). For less than 1-hour use graph values as set out in the following figure

For less than 1-hour, the graph values reflected in Figure 7-3 were referred. These values are also reflected in Table 7-1.

Figure 7-3: Correction Factors – One-hour to Short-term

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Table 7-1: Correction Factors – One-hour to Short-term

TIME 5M 10M 15M 30M 1H

Correction 0.24 0.34 0.46 0.62 1.00

Elevation Effect on Rainfall

The Climate Risk Profile for Samoa, 2007 contained charts showing storm rainfall increase with elevation, but it was not in sufficient detail to be quantified.

In order to quantify, the VASRN consultant analysed data for Apia, Nafanua and Afiamalu. Table 7-2 compares Afiamalu at 796 metres above sea level (MASL) with Nafanua at 113 MASL.

Table 7-2: Rainfall difference with Elevation

STATION PAIR MASL RAINFALL (MM) RATIO

Afiamalu – Nafanua 796 to 113 331 to 206 1.61

Afiamalu – Apia 796 to 2 332 to 186 1.78

Comparison of Afiamalu and Nafanua data is reflected in Figure 7-4.

Figure 7-4: Rainfall Difference with Elevation (2 Sites)

The VASRN consultant found that daily storm rainfall increases by 10% for every 100m rise in elevation. Further analysis, combining data from these stations with other data from earlier reports, showed that the same rate of increase could be used for both islands. Storm rainfall at the highest point of the CCIR (771m) is 80% higher than in Apia.

CONCLUSION 2: Add 10% to the rainfall intensity for every 100m increase in elevation

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Rain Shadow

Reports prior to the VASRN had shown that rainfall stations on the south of both major islands of Samoa recorded more rain than those to the north of the islands. This was the well-known rain shadow effect. It is visually represented in Figure 7-5. Previous reports had not shown to what extent storm rainfall varied in a similar way.

Figure 7-5: Climate Maps of Samoa showing Rain Shadow

The VASRN consultant confirmed that there is a pronounced rain shadow effect. Analysis of available data showed a 25% difference between north and south, with the north being lower.

CONCLUSION 3: Add 25% to the long-term rainfall values measured in the north (Apia) for sites in the south of both islands

7.3 Climate Change This refers to 15. Annex D Climate Change and 3.2 Climate Change Projections of the VA-FR. Key points are summarised in the following sub-sections.

7.3.1 Climate Projections

Representative Concentration Pathways (RCPs) Selection

Four Representative Concentration Pathways (RCPs) are referred to. Each foresee a different pattern of development of greenhouse gas emissions. At one end is RCP2.6, which is based on greenhouse gas emissions being strictly controlled, and at the other is RCP8.5 which assumes less control of emissions or “business as usual.” They are graphically represented in Figure 7-6.

Figure 7-6: Radiative Forcing for Different RCP Values

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The VASRN consultant chose RP6.0 for its subsequent analysis, being moderately conservative i.e. some emission control is exercised, albeit less than for RCP4.5.

Annual Rainfall

Three models were compared for projections of annual rainfall. These included two CSIRO models, the GFDL model, and the HadGem model. This analysis revealed projected highest annual average rainfall for the period 2055 to 2075.

Monthly Rainfall

Three different time horizons for monthly rainfall were analysed. These horizons were out to 2030, 2055, and 2090. The analysis revealed little change in annual rainfall, increases from October to February (when most rain falls), and decreases in the drier part of the year (March to September). This revealed a likelihood that droughts would actually increase, rather than decrease (as reflected in Table 2-1).

Annual Maximum Daily Rainfall

For daily rainfall, the projection known as RX1 was studied. It concluded that both annual and maximum daily rainfall would increase up to 2055, level out until 2075, then decline. It also observed that this effect was more prominent for higher return period rainfalls.

Temperature

Based on RCP6.0, the VA-FR reported that temperatures are expected to continue rising throughout this century at a rate of about 2OC per century.

Daily Rainfall Projections

In order to project daily rainfall (and for practical application to Samoa), an appropriate climate model downscaling method had to firstly be adopted. This is necessary due to the large cell (or grid) size of climate models, being about 18,000 km2 – 10 times larger than Samoa’s largest island. Downscaling follows the dynamic or statistical method. The dynamic method was ruled out as it can only be developed by major modelling centres, and used if already developed. Of the two main statistical methods, one that fits a mathematical curve to the shape of a series of grid cells surrounding the area of interest was ruled out as it assumes that no features would invalidate the downscaling assumptions. This is not the case for Samoa as it is surrounded by vast ocean with hills having a major impact on the climate. The other statistical method was the delta method. It assumes that although the weather might change within the area of a grid cell, the changes will be the same over the whole cell. These grid level changes are then applied to the local parameters. The delta method was considered to be the most appropriate for Samoa, and was subsequently used for further analysis.

Based on applying the downscaling delta method for RCP6, and applying the O’Gorman14 conclusion that for every one degree rise in air temperature, rainfall would increase by 10%, current observed maximum daily rainfall data (mm/day) was projected out to year 2030, 2055, and 2090 for return periods 2, 5, 10, 25, 50, and 100 years. It concluded that 2055 projections would be used, being representative of the highest rainfall intensities for this century. Based on this, it concluded that current maximum daily rainfall (mm/day) intensities would increase by 17% for different frequencies of occurrence (recurrence intervals), with a standard deviation of 7%.

7.3.2 Sizing Culverts for Climate Change

VA-FR 3.2.3 Methodology for Sizing Culverts based on RCP6 refers. Based off the assumed 17% increase in maximum daily rainfall for different recurrence intervals, the well cited paper of O’Gorman and large uncertainty involved, a 20% increase in allowance for rainfall intensities was recommended for both islands of Samoa.

CONCLUSION 4: Add 20% (17% rounded up) to the short-term rainfall intensity values to allow for climate change

The VA-FR notes that a 20% increase in required flow capacity practically means a 20% increase in pipe wetted area (or perimeter), as opposed to a 20% increase in culvert diameter or 20% increase in drainage-related costs.

For ease of maintenance, the VA-FR recommended a standard minimum culvert pipe size of 0.9m diameter.

14 P. O’Gorman. 2012. Sensitivity of Tropical Precipitation Extremes to Climate Change, Nature Geoscience Letter. Cited 66 times in other peer reviewed literature. The author has published many other peer reviewed papers which confirm his findings.

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7.4 Use of Samoan Data in the Future The VA-FR provided a report section of the above-titled (3.2.5). In this, Apia was recognised to have the longest record of rainfall data, including over 30 years of daily data from 1984. It was therefore used by the VASRN consultant to interpolate down to short-term durations using 10-minute data relationships from two other stations. These were Nafanua and Afiamalu. This data was then used to form a set of intensity-duration-frequency (IDF) curves (Figure 7-7) with accompanying table (Table 7-3) that, along with three correction factors, could be used for future rainfall predictions anywhere in Samoa.

The three correction factors included:

1. Elevation: Add 10% for every 100m rise in elevation (Apia is at sea level) – Section 7.2.2. 2. Rain shadow: Add 25% for locations on the southern side of both Upolu and Savii Islands (as being in the north, Apia is in

the rain shadow) – Section 7.2.2. 3. Future Projections: Add 20% for rainfall intensity to account for climate change (Apia VA-FR data valid as of 2016) – Section

7.3.1.

Figure 7-7: IDF Curves for Apia (2016)

Table 7-3: IDF Curve Values for Apia (2016)

RETURN PERIOD RAINFALL INTENSITY (MM/HOUR)

DURATION (HRS): 0.08 0.17 0.25 0.50 1.00 2.00 3.00 4.00 6.00 12.00 24.00

2-years 104.5 76.6 67.3 48.8 38.7 26.6 20.7 17.2 13.5 9.12 6.05

5-years 155.7 114.2 100.3 72.6 57.7 39.7 30.8 25.6 20.2 13.6 9.01

10-years 189.6 139.0 122.2 88.5 70.3 48.3 37.6 31.1 24.6 16.5 11.0

25-years 232.4 170.4 149.8 108.4 86.2 59.2 46.0 38.2 30.1 20.3 13.4

50-years 264.2 193.7 170.2 123.3 98.0 67.3 52.3 43.4 34.2 23.1 15.3

100-years 295.7 216.8 190.6 138.0 109.7 75.4 58.6 48.6 38.3 25.8 17.1

7.5 Conclusion Because of its more reliable data, the VA-FR recommended using Apia station data as the basic starting point for any future drainage design, anywhere in Samoa.

The four ‘emphasized’ conclusions of the VA-FR are consolidated, as follows:

CONCLUSION 1: For hourly rainfall use the greater of 5% of annual rainfall (average of 3.6 to 7.2%), and 30% of daily rainfall (rounding of 33%). For less than 1-hour use graph values as set out in the following figure CONCLUSION 2: Add 10% to the rainfall intensity for every 100m increase in elevation CONCLUSION 3: Add 25% to the long-term rainfall values measured in the north (Apia) for sites in the south of both islands CONCLUSION 4: Add 20% (17% rounded up) to the short-term rainfall intensity values to allow for climate change

Conclusions 2, 3, & 4 are captured in the VA-FR recommendations for future use in Samoa (Section 7.4). Conclusion 1 is not as apparent in Section 7.4, but is implied through use of the IDF curve data.

1.0

10.0

100.0

1000.0

0.01 0.10 1.00 10.00 100.00

Rain

fall

inte

nsity

-m

m/h

our

Storm duration - hours

Intensity/duration/frequency curve - Samoa

2-years 5-years 10-years 25-years 50-years 100-years

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Two other notable recommendation of the VA-FR not already covered by the above included (i) utilisation of Blackvue for future road assessments and record keeping, and (ii) adopting a standard minimum culvert pipe size of 0.9m diameter.

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8 Appendix 2 ERAP Drainage Design vs Vulnerability Assessment Summary

8.1 Using Apia Station Due to its superior data set, especially long-term data, the ERAP Vulnerability Assessment Final Report (VA-FR) recommended using the Apia station as a starting point from which interpolations could be made through use of conversion factors to other parts of Samoa. It used 10-minute data from nearby Nafanua and Afiamalu stations to interpolate shot-term data from the long-term data, and thus produce a set of intensity-duration-frequency (IDF) curves scalable from Apia.

Due to their close proximity and elevation relevance to the project, the ERAP CCIRU consultant used Nafanua and Afiamalu stations. IDF curves and tables for both were supplied by the VASRN consultant. The following is a direct copy from the CCIRU Drainage Design Report (February 2017):

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Using these two stations instead of Apia was considered to be more accurate application of available data.

8.2 VASRN Correction Factor – Elevation VA-FR: Add 10% to the rainfall intensity for every 100m increase in elevation

As can be seen from the CCIRU Drainage Design Report extract (Section 8.1), Nafanua data was adopted for the project road section from KM 3+604 (310 MASL) to KM 5+500 (483 MASL). It was also used from the start point at KM 0+000 (55.5 MASL) to KM 3+604. Afiamalu data was used from KM 3+604 through the crest of the CCIR at KM 9+788 (771 MASL) to the end point at KM 19+686 (18 MASL).

the Nafanua station (113 MASL) and Afiamalu station (796 MASL)

As part of its ‘elevation effect on rainfall’ analysis (Section 7.2.2), the VA-FR (14.5.2) used mean annual maxima daily data (mm) to determine:

• 21% increase per 100m between Nafunua/Apia • 9% between Afiamalu/Nafanua • 13% between Afiamalu/Apia.

It also compared 1-hour rainfall intensities of Afiamalu/Nafanua (Figure 12-9).

A comparative analysis of both CCIRU adopted and VASRN recommended scaling methods is reflected in Table 8-1 (along with rain shadow correction factor – Section 8.3). This compares singular values for a 1-hour duration (same as the VA-FR

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comparison for both stations), and a 25-year return period or ARI. 25-years from the IDF tables has been chosen based on the adopted drainage design period for the CCIRU of out to 205015, being about 30 years (50% longer than the road design life of 20 years).

The comparison reveals similar results for the Nafuna/Afiamalu interface at KM 3+604. But the CCIRU values are about 20% more conservative for lower elevations. Nafuna data still however more reliably used, so should still be adopted. From KM 3+604 upwards, rainfall intensities are also conversative for the CCIRU when compared to NASRN. This is because of applying the Afiamalu data from a high elevation to lower elevations. Two equidistant additional ‘waypoints’ between KM 3+604 and the crest were similarly compared to understand the extent of this.

In conclusion, the CCIRU method has been conservative for estimating rainfall intensities from KM3+604 to about KM8+000. This will be further assessed during the separate D&D completion services, with a view towards adopting a correction that is more consistent with the recommendations of the VA-FR.

8.3 VASRN Correction Factor – Rain Shadow Effect VA-FR: Add 25% to the long-term rainfall values measured in the north (Apia) for sites in the south of both islands

According the VA-FR, the rain shadow effect would apply to the CCIR as it spans Upolu Island from the north to south coast. Simplistically, the rain shadow effect can be considered applicable from the CCIR crest to the end point at Siumu. Adopting the same approach for elevation correction, 1-hour Apia data for a 25-year ARI at 86.2mm/hour is projected by 25% to give 107.8mm/hour. As Apia is at 2 MASL, this is understood to be applicable to sea level on the opposing southern coastline. This is close enough in elevation to the CCIR end point (18 MASL), so considered scalable to this point, but the elevation correction factor can still be applied, as would be the case for further alignment estimates at higher elevations, so the value becomes 109.4mm/hour. This and other values are reflected in Table 8-1.

Table 8-1: VASRN & CCIRU Elevation & Rain Shadow Comparison

STATION/ CCIRU CHAINAGE (KM)

ELEVATION (MASL)

RAINFALL INTENSITY (MM/HOUR)a VASRN LESS THAN

CCIRU (MM/%) VASRN METHOD (10% PER 100M)

CCIRU METHOD (IDF CURVES)

Apia 2 c86.2 N/A N/A KM 0+000 (start) 55 91.5 d118.4 26.9/22.7% Nafanua 113 95.8 d118.4 22.6/19.1% KM 3+604b 310 112.7 d118.4 5.7/4.8% KM 5+500 483 134.5 e172.8 38.3/22.2% KM 7+750 683 154.5 e172.8 18.3/10.6% Afiamalu 796 165.6 e172.8 7.2/4.2% KM 9+788 (crest)f 771 184.7 e172.8 -11.9/-6.9%

ADD RAIN SHADOW EFFECT: (25% + 10% PER 100M) KM 13+000 586 210.0 e172.8 -37.2/-21.5% KM 16+500 259 166.9 e172.8 5.9/3.4% KM 19+686 (end) 18 109.4 e172.8 63.4/36.7%

KM = kilometre mark (chainage location). IDF = intensity-duration-frequency. MASL = metres above sea level. MM = millimetres. Note: a 1-hour duration/25-year return period b Nafanua/Afiamalu station coverage boundary for CCIRU drainage design c From IDF Table 7-3 d From CCIRU Drainage Design Report Table 4-1 e From CCIRU Drainage Design Report Table 4-2 f Being the crest, rain shadow effect considered not applicable Source: TA consultant

The comparison reveals a high degree of conservatism from coast-to-coast. This is because Afiamalu has been extrapolated to the coast line by the CCIRU consultant; a station with a much higher amount of rainfall due to elevation16, as confirmed by comparison of IDF data specific to each of the 3 stations. Two equidistant additional ‘waypoints’ between KM 9+788 and the end point (KM 19+686) were similarly compared to understand the extent of this. Consistent results are apparent at KM 16+500 (259 MASL), but from here upwards the CCIRU results are less conservative with elevation increase.

15 As per the VA-FR, based on RCP6.0, peak global temperatures (and thus peak rainfall) are anticipated to occur in 2055.

16 Afiamalu station is on the north side of the Upolu mountain range.

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In conclusion, the comparison reveals that the CCIRU method has been overly conservative for estimating rainfall intensity at lower elevations of the southern part of the alignment (about 1/3rd of the total 9.9km south-side road length), but is then less conservative for higher elevations (the balance 2/3rd). Being only 25 MASL higher than the crest, using Afiamalu station as per the CCIRU method is considered more appropriate than using conversion factors from Apia station (VA-FR method), but is still less conservative when accounting for the rain shadow effect at high elevations. This is possibly due to the fact that the Afiamalu station is on the northern side of the Upolu mountain range i.e. it possibly does receive lower rainfall than comparative elevations on the opposing south-side. As a result, application of rainfall intensity data to the entire south-side CCIR alignment requires further assessment, with a view towards adopting new figures based on appropriate use of rain shadow effect + elevation correction factors.

8.4 VASRN Correction Factor – Future Projections VA-FR: Add 20% (17% rounded up) to the short-term rainfall intensity values to allow for climate change

The following CCIRU Drainage Design Report extract refers:

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As can be seen from the conclusion of 4.5.2.4, the CCIRU consultant opted to adopt a different approach for consideration of increased rainfall intensity than that recommended by the VASRN consultant, but still checked and confirmed very similar results (Table 8-2). Table 4-16 presents the CCIRU consultant’s recommendation to the client. This was subsequently approved and adopted in the detailed design.

Table 8-2: VASRN & CCIRU Future Projections Comparison

RETURN PERIOD RAINFALL INTENSITY (MM/HOUR)a

DURATION (HOURS): 0.08 0.17 0.25 0.50 1.00 2.00 3.00 4.00 6.00 12.00 24.00

Nafanua (no correction factor)

5-years 189.8 149.6 130.1 100.6 79.0 54.7 41.2 33.9 27.2 18.1 11.8

10-years 231.5 182.5 158.8 122.7 96.4 66.7 50.2 41.3 33.1 22.1 14.4

20-years 266.7 210.2 182.9 141.4 111.1 76.7 57.9 47.6 38.2 25.5 16.5 VASRN correction (20%)

5-years 227.8 179.5 156.1 120.7 94.8 65.6 49.4 40.7 32.6 21.7 14.2

10-years 277.8 219.0 190.6 147.2 115.7 80.0 60.2 49.6 39.7 26.5 17.3 CCIRU correction (5 to 10 ARI/10 to 20 ARI)

5-years (longitudinal) 231.5 182.5 158.8 122.7 96.4 66.7 50.2 41.3 33.1 22.1 14.4

10-years (transverse) 266.7 210.2 182.9 141.4 111.1 76.7 57.9 47.6 38.2 25.5 16.5 CCIRU less VASRN

5-years (longitudinal) 3.7 3 2.7 2 1.6 1.1 0.8 0.6 0.5 0.4 0.2

10-years (transverse) -11.1 -8.8 -7.7 -5.8 -4.6 -3.3 -2.3 -2 -1.5 -1 -0.8 MM = millimetres. Note: a Using Apia station data Source: TA consultant

In conclusion, both methods are deemed to be suitable.

8.5 Other The only other notable recommendations of the VA-FR were (i) utilisation of Blackvue for future road assessments and record keeping, and (ii) adopting a standard minimum culvert pipe size of 0.9m diameter (Dia. 900).

Using Blackvue is not a climate risk mitigation measure, but was included as a recommendation for the LTA to adopt for future road vulnerability risk assessments. Blackvue was however also utilised by the CCIRU consultant, and more recently by the TA consultant.

Pipes sizes adopted for the CCIRU design have varied from Dia. 450 up to Dia. 900 for the piped urban drainage network, and from Dia. 450 to Dia. 1050 for rural pipes (including for side roads). The piped urban network is a specially designed system that has already accounted for the impacts of climate change, as shown in preceding report sections. For rural drainage, pipes have been sized relative to calculated runoff and rainfall intensities. Most are Dia. 900, some larger, and some smaller, but all are suitably sized for their catchment. Trash racks are also specified for all gully-pit openings.

Pipes for rural vehicle crossings are to span open side-drains conveying runoff to a cross-drain our outfall location. Adopting circular pipes sizes of Dia. 600 or above will detract rather than enhance the drainage system they would either require excessively large side-drains, or water would pond in-and-around each of them. Instead, the CCIRU design reflects standard 450w by 300h box culverts, giving a cross-sectional opening area of 0.135 sqm or equivalent to a Dia. 600 circular pipe.

Although not clearly stated in the VA-FR, the ease of maintenance basis for recommending a min. Dia. 900 pipes size or greater appears to be aimed at situations where debris accumulates around the inlet and in the pipes. This is a typical occurrence for cross-drains conveying waterway flow from one road side to another. Although there is some instance of these in the CCIRU, they are not common. Most CCIRU cross-drains purely convey runoff from road side-drains to the opposing side; typically terminating in an outfall. Risk of blockage is therefore low.

In conclusion, the CCIRU design reflects appropriately designed pipe sizes that allow for the impacts of climate change.

8.6 Conclusion Using Apia Station: Given the close proximity and elevations of Nafanua and Afiamalu stations to the project road, these have been and are more appropriate to adopt for the project. This conclusion is also supported by the following:

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VASRN Correction Factors – Elevation & Rain Shadow Effect: Based on increased rainfall with elevation, the CCIRU method has been overly conservative for estimating rainfall intensities from KM3+604 to about KM8+000. Based on combined rain shadow effect and elevation considerations, the CCIRU method has been overly conservative for estimating rainfall intensity at lower elevations for the southern part of the alignment (about 1/3rd of the 9.9 km south-side alignment), but comparatively, is under reporting for the southern highlands area. Use of the high elevation Afiamalu station instead of the north-coast Apia station is considered to be more appropriate for high elevations of the CCIR, but it is also noted to be on the south-side of the Upolu mountain range. Therefore, the road section from the crest at KM 9+788 to the end point at KM 19+686 should be further assessed for appropriate application of rainfall shadow effect + elevation conversion factors.

VASRN Correction Factor – Future Projections: Both VASRN and CCIRU methods reveal very similar results. As they complement, both are considered suitable. No change is required for the project.

Pipes sizes: The CCIRU design reflects appropriately designed pipe sizes that allow for the impacts of climate change.

The following is proposed from alignment start to end point:

• KM 0+000 to KM 3+604 – North side. Adopt Nafanua station rainfall intensity figures, as per the CCIRU method. No change required.

• KM 3+604 to KM 8+000 – North side. Revisit assumptions/figures based on elevation, with a view towards less conservative figures.

• KM 8+000 to KM 9+788 (crest) – North side. Adopt Afiamalu station rainfall intensity figures, as per the CCIRU method. No change required.

• KM 9+788 to KM 19+686 – South side. Revisit assumptions/figures based on rain shadow effect + elevation, with a view towards adopting less conservative figures for lower elevations, and possibly higher figures for higher elevations.

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CLIMATE RISK VULNERABILITY ASSESSMENT

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