CLIMATE CHANGE DIVISION

Ministry of Environment, Climate Change, Disaster Management & Meteorology

Siota Provincial Secondary School Shoreline Assessment

Coastal Processes, Vulnerability and Risk Assessment

Report compile by

Malachai Bate’e, Reginald Reuben, Marlchom. Z. Row, Thaddeus Siota, Henry Tufa and David Tufi

9/19/2017

i | P a g e

Acknowledgement

The assessment team would like to thank the Provincial Government of Central Province for

accepting us to conduct this assessment on Siota Provincial Secondary School. On the same

note, we would like to thank the school for the hospitality provided during our stay.

We would like to thank the US Government through American Museum of Natural History

(AMNH) for providing Satellite image datasets for the study site. The National Government

and aid agencies are very supportive and we would like to thanks them for providing the

needed funds to conduct this assessment.

Lastly, we acknowledge PS MECDM, Dr. Mataki for conducting a preliminary assessment

on the study site providing baseline information and guidelines that directs us in designing

and conducting the field assessments.

ii | P a g e

Summary

Coastal erosion and inundation pose significant threats to essential infrastructures and

facilities that are located on low-lying coastal areas. This becomes a challenge in developing

island nations like Solomon Islands as adapting to such threats is expensive as a result of

limited resources. This assessment shows Siota PSS as one of the essential public facility that

is at risk to coastal erosion and inundation. The overall goals of this assessment are; 1),

assess the shoreline adjacent to Siota PSS to collect data on elevations AHWM and BHWM

and identify which section of the shoreline is at high risk to coastal hazards, 2) determine the

direction and movements of currents, wind waves and sediments Within Mboli Passage and

Siota shoreline.

The assessment identifies tidal currents to be a major threat to the shoreline apart from wind

wave. Using the CVI approach, Transect 5, 6 and 7 is the segment of the shoreline at ‘very

high’ vulnerability. By considering ‘element at risk’, this section of the shoreline is classified

as ‘very high’ risk to coastal erosion since staff houses are located too close to the beach

scarp. If there’s a need to build coastal protection, this section of the shoreline should be

prioritized.

The use of remotely sensed data such as Satellite imageries proves to be effective given the

limited time and resources to conduct a detail assessment. In this assessment, the direction

and movement of wind waves, tidal currents and sediment transport is determined by visually

interpreting the alignment and deposition of sand on the reef flat, along the shoreline and on

the floor of Mboli Passage. The information gathered from visually interpreting Satellite

images from 2010, 2013, and 2016 is re-traced giving a general description of water and

sediment movements around Siota and within Mboli Passage.

iii | P a g e

Table of Contents

Acknowledgement ...................................................................................................................... i

Summary .................................................................................................................................... ii

Table of Contents ..................................................................................................................... iii

Figures and Tables .................................................................................................................... iv

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

1. Introduction ........................................................................................................................ 1

2. Study Site ............................................................................................................................ 2

2.1. Brief Background ........................................................................................................ 2

2.2. General Physical Geography ....................................................................................... 3

2.2.1. Coastal Environment ............................................................................................ 3

2.3. Asset and Infrastructure .............................................................................................. 3

2.3.1. Existing Structures ............................................................................................... 4

3. Methodology ....................................................................................................................... 4

3.1. Ground Truthing and Visual Image Interpretation ...................................................... 4

3.2. Coastal Survey and cross section mapping ................................................................. 4

3.3. Coastal vulnerability Index and risk assessment data ................................................. 5

4. Results ................................................................................................................................ 6

4.1. Asset Inventory and Coastal Processes Analysis ........................................................ 6

4.2. Coastal Levelling and Profiling Survey ...................................................................... 8

4.3. Coastal Vulnerability Index and Risk Assessment ................................................... 10

5. Discussion ......................................................................................................................... 11

6. Conclusion and Recommendations .................................................................................. 12

References ................................................................................................................................ 13

Appendices ............................................................................................................................... 14

Appendix 1: Map showing transects and stations ................................................................ 14

Appendix 2: Transect Profiles Excel Output........................................................................ 15

Appendix 3: Score and Weighting Matrix used to generate input values for Equation 1 .... 19

Appendix 4: Siota Coastal Vulnerability Index and risk assessment map .......................... 19

iv | P a g e

Figures and Tables

Figure 1: A general overview of Siota PSS in Nggella, Central Province. ............................... 2

Figure 2: Map of Assets and Infrastructures ............................................................................. 6

Figure 3: The map indicates the movement of water and sediments within Siota and Mboli

Passage ...................................................................................................................................... 7

Figure 4: The graph shows heights AHWM and BHWM and the length of each Transect

starting from Reef Crest. ............................................................................................................ 8

Figure 5: The graph shows the relationship between LWM and Gradient ............................... 9

Figure 6: Output of Linear Regression Statistical Analysis. ..................................................... 9

Figure 7: The map shows the section of Siota's shoreline that was surveyed. ........................ 14

Figure 8: The map shows the level of vulnerability for the surveyed shoreline ...................... 19

Table 1 Shows LWM, HWM and Gradients of each Transects.................................................. 8

Table 2 Shows CVI Matrix Output for Attribute score and Variable Weighting ..................... 10

Table 3: A score and Weighting Matrix used in the study ....................................................... 19

v | P a g e

Abbreviations

AHWM – Above High Water Mark

BHWM – Below High Water Mark

CRISP - Community Resilience to Climate and Disaster Risk in Solomon Islands Project

CVI – Coastal Vulnerability Index

GPS – Global Positioning System

HAT – High Astronomical Tide

HWM – High Water Mark

MECDM – Ministry of Environment, Climate Change, Disaster Management and

Meteorology

NIWA – National Institute of Water & Atmospheric Research

PACC – Pacific Adaptation to Climate Change

PCCSP – Pacific Climate Change Science Program

PS – Permanent Secretary

PSS – Provincial Secondary School

SLR – Sea Level Rise

1 | P a g e

1. Introduction

Coastal hazards posed significant threats to low-lying coastal areas in the Pacific Island

Countries (Nurse et al., 2014). This constitutes a challenge as coastal developments often

happen without prior investigation on the severity of projected impacts of coastal hazards due

to climate change. Sea level rise is projected to exacerbate the severity of coastal erosion and

inundation in certain locations in addition to extreme hydro-meteorological events and

inappropriate coastal developments (Albert et al., 2016).

Severe coastal erosion, coastal flooding, inundation and storm surges have been documented

in Solomon Islands (Albert et al., 2016; Gillie, 1992; Mataki et al., 2013; PACC Technical

Report 4, 2014; PCCSP Country Report, 2014). There is very high confidence in the direction

of long-term changes in sea level in Solomon Islands with projected impacts on coastal areas

(PCCSP Country Report, 2014).

In Solomon Islands, essential public infrastructures like schools and clinics co-exist with

communities, and usually located in coastal areas (areas within 10m elevation and 100m

inland from HWM). Impacts of coastal hazards onto these infrastructures are becoming an

issue. A recent visit to schools in Ngella by Dr. Mataki and Central Province Education

Authority state coastal erosion, coastal flooding and inundation, amongst threats confronting

schools and their infrastructures in the province (Mataki, 2016). Assessing the likely impacts

of these hazards in areas where such developments are taking place (especially on low-lying

coastal area), should be prioritized.

Siota Provincial Secondary School is one of these schools initially assess. A rapid coastal

vulnerability and risk assessment has been conducted within Siota provincial secondary

school by Dr. Mataki and retreating shoreline and severe coastal erosion is reported at certain

spots adjacent to the school (Mataki, 2016). The report suggests the need to conduct a detail

assessment on coastal environments and wind movement around Siota, as well as, climate

change/disaster risk awareness raising programme to be conducted at schools. It also suggests

shoreline protection in which, hard engineering solution could help address the situation as

other adaptation measures are expensive.

The assessment outline in this report is conducted in respond to recommendation suggested in

the initial assessment. The five objectives of this assessment are; 1) to understand coastal

processes, 2) to conduct coastal vulnerability and risk assessment using coastal vulnerability

index (CVI) approach, 3) to quantify actions suggested in the preliminary assessment report

in order to protect eroded sections of coastline adjacent to Siota PSS, 4) To conduct

awareness on causes and effects of climate change and disaster risk, and 5) to collect baseline

data that would be used in the design of a shoreline protection project.

The assessment comprises of two major activities; 1) coastal vulnerability and risk

assessments, 2) educational awareness to schools. These activities are undertaken to achieve

the outline objectives of this assessment. The content of this report is based on coastal

vulnerability and risk assessment activity. The variables needed as input data for CVI, are

collected onsite and used to assess the vulnerability of the shoreline.

2 | P a g e

2. Study Site

This section of the report provides detail descriptions on the assessment site. It outlines and

describes the history, site conditions, existing structures, coastal environment, and assets

observe during ‘transect walk’. The map below shows an overview of the area.

Figure 1: A general overview of Siota PSS in Nggella, Central Province.

2.1. Brief Background

Siota School is located on the north coast of small Nggela at the eastern end of Mboli

Passage. Siota School is the only premier secondary in the Central Islands province. It enrols

more than 200 hundred students from different provinces of the Solomon Islands and having

20 teaching and auxiliary staff. It offers forms 1 (year 7) to form 6 (Year 12) levels of

secondary education. Siota is one of the first missionary schools in the Solomon Islands,

having a very old but rich history.

It was here in the late 1800s that the Anglican’s first attempt to establish a permanent boys'

school in the British Protectorate, St. Luke's. They purchased Siota in 1893 for £10

(SBD$88.08) from the Belaga people (The University of Queensland, 2013). The first

buildings were erected in 1896. There were forty-seven boys in 1897 when a dysentery

epidemic killed eleven of them. The swampy low-lying grounds at the back of the school,

was thought to be unhealthy leading to its closure just after four years of operation. When the

Mission moved to the Solomon from Norfolk Island in 1920, Siota became its new

headquarters and remained until the protectorate headquarters were transferred from Tulagi to

3 | P a g e

Honiara, when the Anglicans also shifted their headquarters there. Subsequently in the early

1970’s Bishop Patteson Theological College was relocated to Kohimarama and Siota was

handed back to the Central Provincial government (The University of Queensland, 2013).

2.2. General Physical Geography

The site is located on the northern side of Nggela Pile Island and at the eastern end of a

Passage. The northern coast of Siota is partly facing Indispensable Strait and towards Malaita

while the western end lays adjacent to the Mboli passage. Few coconut palms grow near the

beach on both the eastern and western ends of the site. Strands of woody coastal vegetation,

beach shrubs and creepers protect certain section of the shoreline. The interior is generally a

tangle of luxuriant tropical swamp vegetation growing on a swampy belt that surrounds the

entire site. Beyond the swamp is mainly grass land.

The general topography of the site is generally flat with a mound of approximately 20m

AHWM, situated at its centre. Soil composition (sandy loam) observe within a 100 metres

inland from HWM is mostly unlithified deposits of coralline sediments. Surrounding the

mound, composition of top soil is mostly red clay with very fine particles and is deposited on

a limestone bed rock.

2.2.1. Coastal Environment

The coastline is basically sandy beach and a very narrow fringing reef with few hard corals.

The wave’s height is minimal and become ripples on a very fine day but strong tidal currents

persist all throughout the year. Located at the end of a very narrow but long passage means

currents move in to fill the passage and out to empty the passage twice in a 24 hour period.

The strength of the current within the passage is however determined by factors such as high

swells, storm surge, wind and the size and bathymetry of the passage. A time-lag between

high tides and low tides within the passage is an area of further studies.

The sediment built up on the coastline indicates a short shore sediment transport from the

nearby reef flats on the northern end, to the southern end of the shoreline. There is visual

evidence of erosion. The beach is basically flat with a mixture of medium to large sediment

sizes. There are no beach or bed rocks on the northern end as observe during ground truthing.

Vegetation is basically coastal shrubs and grass except for the southern and far north ends

which have some coastal trees and coconut palms. Runoff or storm water fare emptied into

the swamp and eventually into a subsequent stream that surround the entire site.

2.3. Asset and Infrastructure

All of the infrastructure (students dormitories, classrooms, staff houses, clinic, church and

essential services) except for a few staff house are at risk of flooding and continuous erosion.

Most of the infrastructures are found within 150 meters inland beyond the high water mark

covering an estimated area of 67586 square metres. The elevation where most classrooms,

dormitories, church, essential services and staff house are located is less than 3 metre high

making the site prone to inundation and coastal flooding during storms and extreme high

tides.

4 | P a g e

2.3.1. Existing Structures

An old jetty and a gabion built decades ago are now being disintegrated as a result of high

corrosive nature of the environment. Coastal processes such as tidal currents and wind waves

contribute to the disintegration process.

The gabion mostly lime stone, was built purposely to support the base of the jetty, however,

over time, it cannot withstand the wind, wave action, and currents surges around the area.

Materials used for the gabion are mostly small sized limestone. Land area behind and beyond

the destroyed gabion is now subjected to regular overtopping and erosion. Other structures

noticed, is a basement of a semi-circular building. This is one of the remains of an old

American style building and relates the site to an army base during World War two.

3. Methodology

This study focussed on Siota Secondary School, the Premier Secondary School of the Central

Province. A preliminary report was done for the school thus, we did a scoping exercise to

validate the findings of the report but also, to see what other factors the School needs. We

surveyed the North-west and North-south shoreline of the school since it was where most of

erosion mentioned in the preliminary report occurs. This section outlined in detail, the

activities conducted, data collected, and instrument used to collect the data including the

approach used to analyse the data.

3.1. Ground Truthing and Visual Image Interpretation

Ground truthing and visual image interpretation was conducted as an initial part of the

assessment purposely, to get a general overview of the physical setting and the environment

surrounding the assessed site. The assessment team conducted ‘transect walk’ within the

school boundary to observe school infrastructure, water source, soil type, vegetation,

topography and its exposure to natural and climate change related hazards. Remote Sensing

was used to obtain information the assessment team could not collect during ground truthing.

Interpretation of Multi-Spectral Satellite Imageries from 2010, 2013 and 2016 provided data

and other useful information used in this report. The sets of imageries were ortho-rectified

before overlaid. Interactive Band Stretch technique using Image Analysis tool in ArcGIS

10.2.2 was used to improve visual interpretation and analysis of the Satellite imageries.

3.2. Coastal Survey and cross section mapping

Rotating Laser and Levelling equipment was used to determine heights above and below high

water mark (HWM). Once HWM was identified, it was used as a vertical reference point (z)

to determine specific elevation of each station along the transects when post-processing of

field data.

The levelling equipment used in the assessment comprised of a rotating laser, laser detectors,

a tripod stand and two measuring staff graduated in metric units. The rotating laser projected

laser beams horizontally at 360 degrees clockwise. When mounted onto a tripod stand, the

5 | P a g e

height of the beam above the ground can be detected by a laser detector clipped onto the

measuring staff and the height of the ground surface relative to the height of the laser was

recorded. This was later, subtracted from the vertical reference point (z) to determine the

actual elevation of each station from HWM. Using this concept, the elevation above and

below the vertical reference point (z) for the stations along the transects were collected.

The section of the shoreline surveyed consisted of 8 transects. The number of stations along

the transects varied. Two Trimble Geo 7x GPS receivers with sub-metre accuracy were used

to collect and record the field data at each station along the transects. The map in Appendix 1

shows the section of the shoreline surveyed including the transects and stations. The data

were analysed in ArcMap and MS Excel to determine elevation and slope of each transect.

3.3. Coastal vulnerability Index and risk assessment data

Coastal Vulnerability Index (CVI) approach was chosen for this assessment. CVI had been

used widely to identify areas most vulnerable and will be at risk to the impacts of projected

sea level rise, providing data, maps and information to support coastal management decision

(Goodhue et al., 2012; Murali et al., 2013; Pendleton et al., 2010). It combines variables

which strongly influence coastal system’s response to coastal hazards providing a

quantitative measure of the coastline’s vulnerability to these hazards.

In this assessment, six variables that influenced coastal responses to sea level rise and

associated coastal hazards were selected from the dataset collected in the field. The six

variables were: 1) Sediments and substrate types, 2) sea level rise, 3) coastal slope, 4)

hydrodynamics (tidal marks and wave height), 5) elevation, and 6) Vegetation. A score of 1 –

5 (5 being the most sensitive) was assigned to the attributes of the six variables. A Weight of

1 – 5 (5 being most important) was assigned to the variables based on their ability to enhance

SLR and Coastal Hazards. The weight once assigned, did not undergo any change.

The coastline was divided into transect and data for the outlined variables, were collected on

each station along the transect using Trimble Geo 7x GPS. The variables were used as input

datasets to create a simple score and weighting matrix producing a vulnerability index for the

coastline (See Matrix Table in Appendix 3). The CVI was generated based on the equation

used by NIWA (Goodhue et al., 2012). In this Assessment, the Equation (Eq.1) was modified

to suit local condition and data limitation.

The Equation: CVI = (∑ 𝐴𝑛 . 𝑊𝑛𝑛1 )÷Ʃ (At . Wt) (Eq.1)

Where;

CVI = Coastal Vulnerability Index

A = Attribute Score

W = Variable Weighting

At = Overall Attribute Score (Total)

Wt = Overall Variable Weighting (Total)

n = Number of Variables

6 | P a g e

4. Results

4.1. Asset Inventory and Coastal Processes Analysis

Ground truthing provides information on school assets and buildings, including the physical

geography of the site. Building types, basic inventory on water sources and road network are

some of the information collected and mapped. Buildings are classified into class room,

dormitory, staff house, essential services, church and others. Essential services are buildings

that are commonly used by staff and students. Others are building where its function is not

given during this assessment. The quantity and spatial orientation of the assets and

infrastructures is shown on the map (Fig.2). The school depend on well for water. There are 3

bore holes and 4 open wells (See Fig.2).

Figure 2: Map of Assets and Infrastructures

Other required information that is difficult to collect during ground truthing is captured using

multi-spectral satellite imageries. Currents and wind wave movement around Siota and Mboli

Passage is remotely assessed by visually interpreting Satellite images from 2010, 2013 and

2016 respectively. In this analysis, the alignment of sand on the reef flat and in the channel,

is the main clue used to determine the direction and moment of currents, wind waves, and

sediment transport. Displacement of Sediments is the other clue used to determine direction

and movement of currents and sediment transport. Based on these clues, the information is re-

traced on the map. Properties of water and bathymetry of the channel is also considered in

7 | P a g e

this assessment. From the information gathered, a ‘scenario like movement’ of currents, wind

wave and sediment transport is developed and mapped. Fig.3. shows the information.

Figure 3: The map indicates the movement of water and sediments within Siota and Mboli Passage

Tidal current is the major coastal processes affecting Siota shoreline in addition to wind

wave. Tidal current is the ‘likely’ cause of erosion seen on Siota shoreline. The narrow

entrance to the channel and sand cays to the north of Mboli Passage give rise to a condition

that generates tidal jets at the deeper column of water as observe during high and low tides.

Furthermore, the sand cays act as a ‘barrier’ to the flow of tidal currents into the narrow

channel causing flood and ebb currents to deflect as shown by the arrows on the map. The

deflection of flood and ebb currents is the ‘likely’ cause of erosion seen on Siota shoreline.

Direction of wind wave is the other coastal processes shaping and aligning coastlines. Siota is

somehow, sheltered from the South Easterly Trade Winds meaning that, wind waves

propagating towards Siota shoreline appears to be approaching it from Indispensable Strait in

an easterly direction throughout the year except for Tropical Cyclone seasons. As a result,

transportation, deposition and alignment of sediments around Siota shoreline is in an east-

west direction. Analysis of Multi-spectral Satellite imageries from 2010, 2013, and 2016

confirm the east-west direction of movement. The deep channel and the jetty, is seen as a

‘barrier’ to sediment transport on the surveyed section of the shoreline resulting in a deficit

sediment budget after the old jetty.

8 | P a g e

4.2. Coastal Levelling and Profiling Survey

Most of the data used in this report are collected by conducting coastal levelling and survey.

There are 8 surveyed transects. The number of stations and length varies for each transect.

Heights AHWM and BHWM along the stations at each transect, are used to generate a

general elevation profile of the surveyed section of the shoreline. Transects that indicate a

much steeper gradients are Transect 2 and 3, and Transect 5 to Transect 8. The graph below

summarized the profile or cross section of the shoreline. Elevation profile of each transects

including a map, is also available in the appendices section of this report.

Figure 4: The graph shows heights AHWM and BHWM and the length of each Transect starting from Reef Crest.

It is observed during the survey that active erosion occurs at Transect 5 up to Transect 8. It is

also noticed while post-processing and plotting elevation values that the lower the LWM

from HWM, the greater the value of gradient (slope). This observation prompted the

assessment team to generate a graph of LWM and Gradients values to visualize the

relationship since the information could be useful to Engineers in their decision when

designing coastal structures (see Fig. 5). Table 1 Shows the LWM elevation, HWM

(reference Points) and Gradients for all Transects. Fig.5. shows the visual representation of

the relationship.

Table 1 Shows LWM, HWM and Gradients of each Transects

Transect ID No.of Stations Transect Length

(m)

LWM Elevation

(m)

HWM Elevation

(m)

Gradient (Y/X) % Gradient

1 7 62 -1.08 0 0.7404 74.04

2 6 58 -1.19 0 0.9151 91.51

3 6 50 -1.05 0 0.8906 89.06

4 8 75 -0.9 0 0.6317 63.17

5 5 66 -1.64 0 0.883 88.3

6 4 42 -2.14 0 1.291 129.1

7 5 53 -1.96 0 0.8706 87.06

8 5 45 -2.3 0 0.9795 97.95

9 | P a g e

Figure 5: The graph shows the relationship between LWM and Gradient

A Linear Regression analysis is conducted to test the direction and strength of the

relationship. The analysis indicates a strong linear relationship meaning, the further the LWM

elevation value goes below zero (HWM), the steeper the gradient. The result shows the value

of Multiple R = 0.7124 indicating a stronger positive linear relationship. At 95 % Confidence,

P-value = 0.047 which is less than 0.05 indicating the significance of the relationship. Fig.6.

shows the summary output of Linear Regression Analysis.

Figure 6: Output of Linear Regression Statistical Analysis.

-2.5

-2

-1.5

-1

-0.5

0

0.5

1

1.5

1 2 3 4 5 6 7 8

Transects

Graph showing heights (m) of LWM in relation to slope steepness

LWM Elevation (m)

Gradient (Y/X)

SUMMARY OUTPUT

Regression Statistics

Multiple R 0.712416001

R Square 0.507536559

Adjusted R Square 0.425459319

Standard Error 0.145555485

Observations 8

ANOVA

df SS MS F Significance F

Regression 1 0.131009183 0.131009183 6.183645524 0.047373843

Residual 6 0.127118396 0.021186399

Total 7 0.258127579

Coefficients Standard Error t Stat P-value Lower 95% Upper 95% Lower 95.0% Upper 95.0%

Intercept 0.51813224 0.1620484 3.197391879 0.018661366 0.121614088 0.914650391 0.121614088 0.914650391

X Variable 1 -0.249334591 0.100267512 -2.486693693 0.047373843 -0.494680355 -0.003988826 -0.494680355 -0.003988826

10 | P a g e

4.3. Coastal Vulnerability Index and Risk Assessment

Table 2 shows the summarize results of attribute score and variable weighting done in the

CVI Matrix table (See Matrix Table in appendix 3). A value for An.Wn is calculated by

multiplying ƩA and ƩW. Ʃ (At .Wt) is the overall attribute score and variable weighting for

each transect. The overall attribute score for each transect is At = 6×5 =30. Six is the number

of attributes while five is the highest score. On the other hand, overall variable weighting Wt

is constant and does not change throughout the analysis. Six variables are given weight which

does not change thus; the overall variable weighting Wt is equals to the sum of the total

weight of the six variables. Appendix 3 shows the weights assign to the six variables.

Table 2 Shows CVI Matrix Output for Attribute score and Variable Weighting

Transect ID Ʃ A Ʃ W An.Wn Ʃ (At .Wt) CVI

1 20 20 400 600 0.67

2 23 20 460 600 0.77

3 24 20 480 600 0.80

4 18 20 360 600 0.60

5 21 20 420 600 0.70

6 22 20 440 600 0.73

7 23 20 460 600 0.77

8 23 20 460 600 0.77

The Table is exported into a GIS environment and coastal vulnerability Index values for each

transect is mapped. The output result when mapped (Appendix 4) shows the locations of

Transects 2, 3, 7 and 8 at ‘very high’ vulnerability index score. Transects 5 and 6 at ‘high’

vulnerability and Transects 1 and 4 at ‘moderate’ and ‘very low’ vulnerability score

respectively. Considering ‘elements at risk’, the section of the shoreline where Transects 5, 6

and 7 is situated, are ‘very high risk’ to coastal erosion. Considering coastal inundation,

section of the shoreline where transect 1 to transect 4 is at ‘high risk’. Map of CVI and risk

assessment for the assessed section of the shoreline can be seen in Appendix 4 of this report,

11 | P a g e

5. Discussion

The assessment finds, assessing the direction and movement of currents and wind waves

around Siota and within Mboli Passage to be an interesting area of study if further

assessments are to be conducted. It will be interesting to learn the likely impacts of wind

waves onto Siota shoreline if the wind changes its direction blowing from Northwest instead

of east to Southeast direction. During the assessment period, the wind is blowing mainly from

an easterly direction. The impact of wind wave observed at this time is minimal as energy of

the wave reduces when it moves over the shallow depth and bends onto the reef flat before

moving into the channel. Visual interpretation of multi-spectral images from 2010, 2013 and

2016, is somewhat, found to be useful in providing these information given the limited time

we have to assess coastal processes.

Tidal currents are seen as the main causes of coastal erosion on Siota shoreline. This

assessment has identified the possible pathways or direction the flood and ebb currents take

when moving in and out of the Mboli Passage. The velocity and time-lags of these currents is

not assessed during this assessment. To partially understand these components of tidal

currents, depth profiling using drifting buoys will give some data on velocity, direction and

time-lags. Through visual observation, there’s an indication of strong tidal current moving in

and out at the bottom of the passage. A detail assessment on how bathymetry of the passage

and the sand cays will influence the direction of flow is also important to understand.

Coastal erosion and inundation are the main threats considered in this assessment. The level

of exposure to these threats on the surveyed section of the shoreline is mostly equal.

However, this assessment finds the section of the shoreline after Transect 4 (Transect 5, 6, 7

and 8) to be highly eroded compare to Transect 1, 2, 3 and 4. The obvious reason for this is,

the section of shoreline between Transect 2 and Transect 4 are initially protected. Other

possible reasons could be; 1) deficit sediment budget to resupply lost sediments, 2) the

deflection of tidal currents occurs adjacent to Transect 5 to 8 causing a strong vortex near the

shoreline, and 3) the channel running adjacent to the shoreline is seen as a ‘sink’ to

sediments.

If there’s limited resource available to protect Siota PSS from the current threats (coastal

erosion), it is advisable to consider ‘elements at risk’ approach to prioritise which section of

the shoreline needs an immediate action. The assessment finds the section of the shoreline

after Transect 4 (Transect 5, 6 and 7) in need of immediate action. Section of the shoreline

from Transect 2 to Transect 4 is also vulnerable but once we take ‘element at risk’ approach,

we’ll find that the level of risk is lower compare to the section of the shoreline after Transect

4.

12 | P a g e

6. Conclusion and Recommendations

Siota Provincial Secondary School is highly exposed to coastal erosion and inundation. The

assessment finds tidal currents to be the main cause of coastal erosion on the surveyed section

of the shoreline. Obstructions to the flow of tidal currents and sediment transport are

observed during the assessment. Wind waves have a minimal impact to the shoreline during

the South Easterly Trade Wind seasons. Remotely assessing coastal processes using Satellite

imageries proves to be very effective given the limited time to conduct such assessment.

Applications of Coastal Vulnerability Index (CVI) in this assessment provide useful data to

assess the vulnerability of different sections of the assessed shoreline. The result of CVI

provides information that can be utilized to manage coastal hazards that is seen as a threat to

Siota PSS. From this assessment, the team would like to recommend the following:

o A detail assessment of coastal processes within Mboli Passage will provide an

interesting result once conducted.

o A depth profile assessment of Tidal currents within Mboli Passage and near Siota

shoreline is recommended.

o There’s a need to identify HAT water mark during the validation trip.

o Analysis of historical aerial images should provide information on the rate of erosion

thus, it is necessary to conduct such analysis.

o Each transects should have a LWM, HWM, and HAT.

o High risk section of the shoreline identified should be prioritized for protection.

o If coastal protection is to be built, a survey on the current status of marine organism

along the shoreline should be conducted to meet environmental requirements for

coastal developments.

o When designing a propose height for coastal protection structure, elevation of LWM,

HAT, and projected Sea Level rise for the Solomon Islands must be incorporated into

the design.

13 | P a g e

References

Albert, S., Leon, J. X., Grinham, A. R., Church, J. A., Gibbes, B. R., & Woodroffe, C. D.

(2016). Interactions between sea-level rise and wave exposure on reef island

dynamics in the Solomon Islands. Environmental Research Letters, 11, 1 - 9

Gillie, R. D. (1992). Ranadi Beach Coastal Erosion Study Honiara, Solomon Islands. SOPAC

Technical Report 152 (pp. 1 - 157). Suva: SOPAC.

Goodhue, N., Rouse, H., Ramsay, D., Bell, R., Hume, T., & Hicks, M. (2012). Coastal

Adaptation to Climate Change: Mapping a New Zealand Coastal Sensitivity Index

(pp. 43). Hamilton: National Institute of Water & Atmospheric Research Ltd.

Mataki, M. (2016). Gela Schools Preliminary Hazard/Vulnerability Assessment (pp. 1 - 8).

Honiara: MECDM Unpublish Report.

Mataki, M., Solo, G., Donohoe, P., Alele, D., & Sikajajaka, L. (2013). Climate Change

Vulnerability and Adaptation Assessment Report: Securing the future of Lauru now

(pp. 1 - 80). Suva: SPC GIZ SPREP.

Murali, R. M., Ankita, M., Amrita, S., & Vethamony, P. (2013). Coastal vulnerability

assessment of Puducherry coast, India, using the analytical hierarchical process.

Natural Hazards and Earth System Sciences, 13, 3291 - 3311. doi: doi:10.5194/nhess-

13-3291-2013

Nurse, L. A., McLean, R. F., Agard, J., Briguglio, L. P., Duvat-Magnan, V., Pelesikoti, N., . .

. Webb, A. (2014). Small Islands. In C. B. Field, V. R. Barros, D. J. Dokken, M. D.

Mastrandrea, K. J. Mach, T. E. Bilir, M. Chatterjee, K. L. Ebi, Y. O. Estrada, R. C.

Genova, B. Girma, E. S. Kissel, A. N. Levy, S. MacCracken, P. R. Mastrandrea & L.

L. White (Eds.), Climate Change 2014: Impacts, Adaptation, and Vulnerability. Part

B: Regional Aspects. Contribution of Working Group II to the Fifth Assessment

Report of the Intergovernmental Panel on Climate Change (pp. 1613 - 1654).

Cambridge, United Kingdom and New York, USA: Cambridge University Press.

PACC Technical Report 4. (2014). Vulnerability and adaptation (V&A) assessment for

Ontong Java Atoll, Solomon Islands (pp. 1 -56). Apia: SPREP.

PCCSP Country Report. (2014). Climate Variability, Extremes and Change in Western

Tropical Pacific: New Science and Updated Country Reports, Solomon Islands (pp.

259 - 279). Malbourne: Australian Bureau of Meteorology and CSIRO.

Pendleton, E. A., Barras, J. S., Williams, S. J., & Twichell, D. C. (2010). Coastal

Vulnerability Assessment of the Northern Gulf of Mexico to Sea Level Rise and

Coastal Change. (pp. 1 - 30): US Geological Survey.

The University of Queensland. (2013). Solomon Islands Historical Encyclopaedia, 1893-

1978. Retrieved 14 September, 2017, from

http://www.solomonencyclopaedia.net/biogs/E000764b.htm

14 | P a g e

Appendices

Appendix 1: Map showing transects and stations

Figure 7: The map shows the section of Siota's shoreline that was surveyed.

15 | P a g e

Appendix 2: Transect Profiles Excel Output

16 | P a g e

17 | P a g e

18 | P a g e

19 | P a g e

Appendix 3: Score and Weighting Matrix used to generate input values for Equation 1

Table 3: A score and Weighting Matrix used in the study

Variables Very Low - 1 Low - 2 Moderate - 3 High - 4 Very High - 5 Score Weigh

Elevation

(metres) > 20 15 ≥ 20 10 ≥ 15 5 ≥ 10 < 5 4

Sediments Boulder

Cobble +

Gravel Gravel + sand Sand Sand + Mud 3

Vegetation

Trees,

Coconuts,

srubs, vines coconut trees shrubs, vines vines, grass grass 1

Sea Level Rise

(mm/year < 2 2 ≤ 4 4 ≤ 6 6 ≤ 8 ≥ 8 3

Mean Wave

Height

(metres) < 1 1 ≥ 2 2 ≥ 3 3 ≥ 4 > 4 5

Slope (y/x) < 0.3 0.3 ≥ 0.5 0.5 ≥ 0.7 0.7 ≥ 1 > 1 4

Appendix 4: Siota Coastal Vulnerability Index and risk assessment map

Figure 8: The map shows the level of vulnerability for the surveyed shoreline