B 1: Physical resources 1.3: Oceanographic assessment

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

Ha’apai, Tonga

B 1: Physical resources

1.2: Groundwater resources assessment

CONTACT DETAILSSecretariat of the Pacific Community

Email: [email protected]: www.spc.int

SPC Headquarters BP D5,

98848 Noumea Cedex,New Caledonia

Telephone: +687 26 20 00Fax: +687 26 38 18

SPC Suva Regional Office Private Mail Bag,

Suva,Fiji,

Telephone: +679 337 0733Fax: +679 337 0021

SPC Pohnpei Regional OfficePO Box Q,

Kolonia, Pohnpei, 96941 FM,Federated States of

MicronesiaTelephone: +691 3207 523

Fax: +691 3202 725

SPC Solomon Islands Country Office

PO Box 1468Honiara, Solomon IslandsTelephone: + 677 25543

+677 25574Fax: +677 25547

Aseri Baleilevuka, Jens Krüger, Salesh Kumar, Zulfikar Begg and Hervé Damlamian

Oceans and Island Programme

B 1: Physical resources1.3: Oceanographic assessment

Secretariat of the Pacific CommunitySuva, FijiMay 2012


Ha’apai, Tonga

ii

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Original text: English

Secretariat of the Pacific Community Cataloguing-in-publication data

B 1: Physical resources 1.3: Oceanographic assessment / Aseri Baleilevuka, Jens Kruger, Salesh Kumar, Zulfikar Begg and Herve Damlamian

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

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

I. Baleilevuka, Aseri II. Krüger, Jens III. Kumar, Salesh IV. Begg, Zulfikar V. Damlamian, HervéVI. Title VI. Secretariat of the Pacific Community VII. Series

363.738 740 996 12 AACR2

ISBN: 978-982-00-0703-1

DISCLAIMER

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

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

IMPoRtAnt notICE

This work and report were made possible with the financial support provided bythe Government of Australia under the Pacific Adaptation Strategy Assistance Program.

SPC undertook the workin collaboration with the Government of Tonga’s Ministry for Lands, Survey, Natural Resources and

Environment and Climate Change.

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

Private Mail BagGPO SuvaFiji Islands

Telephone: (679) 338 1377Fax: (679) 337 0040

www.spc.intwww.sopac.org

Design and layout: SPC Publications Section, Noumea, New Caledonia

www.spc.int

http://www.sopac.org

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

B 1: Physical resources 1.3: Oceanographic assessment

iii

Contents

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

1. EXECUTIVE SUMMARY ............................................................................................................................. 1

2. INTRODUCTION. ...................................................................................................................................... 3

3. METHODOLOGY ....................................................................................................................................... 4

Instrument deployments ................................................................................................................... 4

4. RESULTS ................................................................................................................................................ 10

AQD north lagoon ............................................................................................................................. 10

AQD north shore ............................................................................................................................... 11

AQD south shore ............................................................................................................................... 13

AWAC offshore ................................................................................................................................... 14

TWR Lifuka reef ................................................................................................................................ 15

TWR wharf (September 2011–February 2012 deployment) ............................................................ 16

TWR Holopeka lagoon ...................................................................................................................... 16

TWR south lagoon ..............................................................................................................................17

TWR causeway ...................................................................................................................................17

TWR west of the wharf ...................................................................................................................... 18

iv

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

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

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

Rising oceans, changing lives: Final report is the overview report in a series of technical reports that have been written for the project on Lifuka Island. Accordingly the section titles in the final report correspond with the names of the respective technical reports. The full series of technical reports is listed below.

A: Rising oceans, changing lives: Final report

B: Mapping the Resources


1.1: Shoreline assessment


1.3: Oceanographic assessment

1.4: Benthic habitat assessment

1.5: Beach sediment assessment

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

B 2: Community assessment

2.1: Community engagement strategy and community assessment manual

2.2: Community values and social impact analysis

C: Vulnerability and hazard assessment

1.0: Coastal hazards

2.0: Coastal rehabilitation – Lifuka Island, engineering options report

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

Lifuka, Ha’apai, Kingdom of Tonga: Volume 1 – Least cost analysis

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

Lifuka, Ha’apai, Kingdom of Tonga: Volume 2 – Cost benefit analysis

D: Adaptation options and community strategies



1

EXECUTIVE SUMMARY

The SPC Applied Geoscience and Technology Division (SOPAC) carried out an oceanographic survey of Lifuka from September 2011 to May 2012, with the objective of assessing wave impact that deteriorates the existing coastline and exacerbates inundation of infrastructure.

Current velocities (speed and direction of water flow) were measured in situ using three Nortek Acoustic Doppler Aquadopp Profilers (AQDs) and one Nortek Acoustic Wave and Current Meter (AWAC). Data from the AQD in the North lagoon show the predominant direction of water flow as towards the south at a mean speed of between 0.06 and 0.08 m/s while the AQD on the north shore shows the direction of water flow as towards the northwest at an average speed of 0.05 to 0.1 m/s. The AQD on the south shore shows predominant current direction as towards the southwest averaging 0.06 to 0.08 m/s. Wave measurements by the AQDs on the north and south shore demonstrate the importance of water level for wave processing using the PUV method. When there is insufficient water depth, the cell used for velocity measurement in the PUV method hits the water surface so there are no wave measurements by the instruments during those periods. The AWAC deployed offshore shows predominant water flow direction as towards the northeast at mean speeds of 0.6 to 0.7 m/s.

Six RBR Tide and Wave Recorders TWR-2050P pressure sensors were deployed to measure surface wave parameters and water elevation. The TWRs deployed on the reef and at the wharf from September 2011 to February 2012 show a significant offshore wave event at the end of September, while the TWRs deployed from April to May 2012 show a significant wave event on April 26. The TWRs on the reef, in the south lagoon, Holopeka lagoon and the TWR west of the wharf recorded wave heights of approximately 0.2 m with an average period of 11 seconds, while the TWR at the causeway recorded wave heights between 0.1 and 0.5 m and periods from 6 to 14 seconds. The TWR fixed to a pile at the wharf recorded low wave heights averaging 0.05 m, as expected, but reached close to 0.3 m during the November wave event, and there were also swell events measured in early 2012.

2



3

1. INTRODUCTION

This report describes an oceanographic survey of Lifuka Island in Tonga’s Ha’apai group. The survey was a component of the PASAP (Pacific Adaptation Strategy Assistance Programme) Project entitled Assessing vulnerability and adaptation to sea-level rise: Lifuka Island, Ha’apai, Tonga, conducted by the Applied Geoscience and Technology Division of the Secretariat of the Pacific Community in collaboration with the Government of Tonga’s Ministry for Lands, Survey, Natural Resources, Environment and Climate Change.

The purpose of the project was to enhance the capacity of partner countries to assess key vulnerabilities and risks, formulate adaptation strategies and plans, and mainstream adaptation into decision-making.

This part of the project comprised the following activity:

o acquisition of oceanographic data to assess wave impact, particularly at high tide, that will rapidly deteriorate the existing coastline and exacerbate inundation of infrastructure along Lifuka’s western shoreline.

This report describes the details of the oceanographic instrument deployment data from September 2011 to May 2012. Further analysis and interpretation of the results are in technical reports C.1.0 (Coastal hazards) and C.2.0 (Coastal rehabilitation).

Figure 1: Lifuka Island within the Ha’apai group relative to the region on the left. On the right is a Lifuka topographical map.

4

3. METHODOLOGY

Instrument deployments

To measure current velocities (speed and direction of water flow), three Nortek Aquadopp current profilers and one Nortek Acoustic Wave and Current Meter (AWAC) were deployed. One Aaquadopp was deployed on the reef flat north of the wharf, one in the channel south of the wharf and one Aquadopp was deployed in the middle of the lagoon, while the AWAC was deployed offshore.

The Aquadopps and AWAC (mid-lagoon) were programmed to profile current speed and directions and the AWAC was programmed to record directional waves. All instruments were also programmed to record water pressure and temperature at the instrument head.

Surface wave parameters and water elevation were measured in situ using six RBR Tide and Wave Recorders TWR-2050P pressure sensors. Four TWRs were deployed in the lagoon: one in front of the causeway to the north, one in Holopeka lagoon, one in front of Pangai and one to the south. The fifth TWR was fixed to a pile at the wharf while the sixth was deployed close to the AWAC offshore, on the reef (see Figure 2 for locations).

All the instruments recorded good data. Details of the instrumental operating parameters are listed in the tables below and typical deployment frames are shown in Figure 3.

Figure 2: Lifuka WorldView2, June 10, 2011. Satellite image with oceanographic instrument deployment sites



5

Aquadopp in the north lagoon Aquadopp on the north shore

Aquadopp on the south shore AWAC offshore

6

TWR on Lifuka reef TWR at the wharf

TWR in Holopeka lagoon TWR in the south lagoon



7

Table 1: Instrument summary

Instrument AQD AWAC TWRDescription Acoustic Doppler Profiler Acoustic Wave and Current Meter Tide and Wave Recorder

Make Nortek RBR

Model AQD AWAC-AST TWR-2050

Type Acoustic, 2000 kHz Acoustic, 600 kHz Pressure sensor

Digital recorder Internal

Data recorded Current speed and direction, directional waves,

temperature, pressure

Current speed and direction, directional waves, temperature and

pressure

Tides, temperature, waves

TWR at the causeway TWR West of the wharf

Figure 3: Instrument deployments

8

Table 2: Lifuka instrument settings

Instrument AQD north lagoon

AQD north and south

shore

AWACoffshore

TWR(Sep 11–

Feb 12deployment)

TWR(Apr–May 12deployment)

Default temperature (°C) Measured

Default salinity (ppt) 35.0 35.0 35.0 N/A N/A

Magnetic declination (deg) 12.1 12.1 12.1 N/A N/A

Sampling interval(s) Max. rate Max. rate Max. rate 2Hz 1Hz

No. of samples/bursts 1024 1024 1024 2048 for waves 1024 for waves

Averaging interval(s) 10,800 (waves)60 (currents)

10,800 (waves)60 (currents)

60 120 for tides 60 for tides

Record interval(s) 600 900 600 600 for tides and 10,800 for waves

600 for tides and 3600 for waves

Number of cells in profile 20 50 20 N/A N/A

Blanking distance (m) 0.1 0.1 0.5 N/A N/A

Cell size (m) 0.5 0.1 2 N/A N/A

The raw binary files from the current profile instruments were converted to readable ASCII listings in their respective Nortek softwares; the raw binary files from the Aquadopps in the AquaPro v1.34 software and the AWAC file in the AWAC software. These raw files were then loaded into the software, Nortek Storm Ver.1.09, and processed. A Matlab script was used to plot the processed data as shown in the results section.

For the wave gauge instruments, the downloaded raw data (.hex files) were opened in the RBR software Ruskin v1.7.3 and exported to readable ASCII listings. A Matlab script was also used to generate plots from these data. These plots are also available in the results section.



9

Tabl

e 3:

Lifu

ka in

stru

men

t dep

loym

ent s

umm

ary

Loca

tion

nam

eIn

stru

men

tSe

rial

No

East

ing

(m)

Nor

thin

g (m

)w

ater

de

pth

(m

)

Hei

ght

abov

e se

abed

(m)

Date

, loc

al

time,

num

ber

of fi

rst g

ood

sam

ple

Dura

tion

(day

s)

Date

, lo

cal t

ime,

nu

mbe

r of

last

goo

d sa

mpl

e

Raw

dat

a fil

enam

e

Nor

th la

goon

AQD

9440

7767

74.1

978

0878

7.02

7.6

0.2

311

/04/

2012

, 6:

00:0

0 PM

, 24

842

23/0

5/20

12,

9:00

:00

AM

, 56

62Li

f_N

_lag

oon_

4799

.prf

Nor

th s

hore

AQD

9471

7775

60.7

978

0846

6.64

1.1

0.21

11/0

4/20

12,

6:00

:00

PM,

237

3617

/05/

2012

, 12

:00:

00 P

M,

4862

Lif_

N_s

hore

line_

4828

.prf

Sout

h sh

ore

AQD

6550

7770

44.4

978

0703

1.42

1.5

0.2

111

/04/

2012

, 6:

00:0

0 PM

, 64

048

29/0

5/20

12,

4:20

:00

PM,

6487

Lif_

S_sh

orel

ine_

4453

.prf

Offs

hore

AWAC

-AST

WPR

030

177

3617

.96

7811

010.

5427

.30.

5419

/04/

2012

,

10:0

0:00

AM

, 12

431/

06/2

012,

2:

30:0

0 PM

, 51

64

LIF0

1_01

0620

12.w

pr &

LIF0

1_01

0620

12.w

pb

Lifu

ka re

efTW

R-20

5015

483

7739

04.1

678

1107

3.69

15.0

0.10

12/0

9/20

11,

9:

00:0

0 A

M,

466

149

8/02

/201

2,

2:50

:00

PM,

1343

5

Feb_

2012

_Lifu

ka _

reef

_fix

ed.h

ex

Wha

rfTW

R-20

5015

486

7774

87.9

478

0816

6.88

3.3

1.5

12/0

9/20

11,

9:

00:0

0 A

M,

448

866/

12/2

011,

9:

30:0

0 PM

, 12

311

Feb_

2012

_Lifu

ka_w

harf

.he

x

Wha

rfTW

R-20

5015

483

7774

87.9

478

0816

6.88

3.3

1.5

16/0

4/20

12,

6:

00:0

0 PM

, 19

4329

/05/

2012

, 3:

50:0

0 PM

,620

9

0154

83_2

0120

529

_161

6_w

harf

_201

2052

9.he

x

Hol

opek

a la

goon

TWR-

2050

2157

277

6923

.94

7810

855.

3010

.70.

1011

/04/

2012

,

6:00

:00

PM,

108

522/

06/2

012,

2:

50:0

0 PM

,744

3

0215

72_2

0120

602_

1512

.he

x

Sout

h la

goon

TWR-

2050

2157

577

4495

.24

7806

654.

6414

.00.

1011

/04/

2012

,

6:00

:00

PM,

113

544/

06/2

012,

4:

20:0

0 PM

,772

4

0215

75_2

0120

604_

1628

.he

x

Caus

eway

TWR-

2050

2157

777

8209

.90

7812

748.

5016

.20.

1011

/04/

2012

,

6:00

:00

PM, 9

952

4/06

/201

2,

2:50

:00

PM,7

438

0215

77_2

0120

602_

1500

.he

x

Wes

t of w

harf

TWR-

2050

2157

877

5875

.05

7807

943.

218.

90.

1011

/04/

2012

,

6:00

:00

PM,

119

544/

06/2

012,

5:

50:0

0 PM

,773

0

0215

78_2

0120

604_

1617

.he

x

10

4. RESULTS

AQD north lagoon

Figure 4: Time series plot of pressure, temperature and depth-averaged current speed as measured by the AQD in the north lagoon. Direction is given from true north in oceanographic convention (going toward).

Figure 5: Rose plot of depth-averaged direction, as measured by the AQD in the north lagoon. Direction is given from true north in oceanographic convention (going toward).



11

Figure 6: Time series plot of significant wave height (Hm0), peak wave period (Tp) and peak wave direction (DirTp) as measured by the AQD in the north lagoon. Direction is given from true north in meteorological convention (coming from).

AQD north shore

Figure 7: Time series plot of pressure, temperature and depth-averaged current speed as measured by the AQD on the north shore. Direction is given from true north in oceanographic convention (going toward).

12

Figure 8: Rose plot of depth-averaged current direction as measured by the AQD on the north shore. Direction is given from true north in oceanographic convention (going toward).

Figure 9: Time series plot of significant wave height (Hm0), peak wave period (Tp) and peak wave direction (DirTp) as measured by the AQD on the north shore. Direction is given from true north in meteorological convention (coming from). Note the gaps in the plots for peak wave period and wave direction because water level is too shallow. The cell used for velocity measurement hits the water surface as there is insufficient water depth to process waves with the PUV method (see Table 3 for water level measurement for the instrument).



13

AQD south shore

Figure 10: Time series plot of pressure, temperature and depth-averaged current speed as measured by the AQD on the south shore. Direction is given from true north in oceanographic convention (going toward). Note that there is no plot for wave parameters as there is insufficient water level to process waves with the PUV method (see Table 3 for water level measurement for the instrument).

Figure 11: Rose plot of depth-averaged current direction as measured by the AQD on the south shore. Direction is given from true north in oceanographic convention (going toward).

14

AWAC offshore

Figure 12: Time series plot of pressure, temperature, and depth-averaged current speed as measured by the AWAC. Direction is given from true north in oceanographic convention (going toward).

Figure 13: Rose plot of depth-averaged current direction, as measured by the AWAC. Direction is given from true north in oceanographic convention (going toward).



15

Figure 14: Time series plot of significant wave height (Hm0), peak wave period (Tp) and peak wave direction (DirTp) as measured by the AWAC. Direction is given from true north in meteorological convention (coming from).

TWR Lifuka reef

Figure 15: Time series plot of depth (m), significant wave height (Hs), significant wave period (Ts) and temperature (°C) as measured by the TWR on Lifuka reef. Direction is given from true north in oceanographic convention (going toward).

16

TWR wharf (September 2011–February 2012 deployment)

Figure 16: Time series plot of depth (m), significant wave height (Hs), significant wave period (Ts) and temperature (°C) as measured by the TWR at the wharf. Direction is given from true north in oceanographic convention (going toward). Note: The TWR was deployed at the wharf from April to May 2012, but the pressure sensor malfunctioned, so the instrument did not return good data.

TWR Holopeka lagoon

Figure 17: Time series plot of depth (m), significant wave height (Hs), significant wave period (Ts) and temperature (°C) as measured by the TWR at Holopeka lagoon. Direction is given from true north in oceanographic convention (going toward).



17

TWR south lagoon

Figure 18: Time series plot of depth (m), significant wave height (Hs), significant wave period (Ts) and temperature (°C) as measured by the TWR at the south lagoon. Direction is given from true north in oceanographic convention (going toward).

TWR causeway

Figure 19: Time series plot of depth (m), significant wave height (Hs), significant wave period (Ts) and temperature (°C) as measured by the TWR at the causeway. Direction is given from true north in oceanographic convention (going toward).

18

TWR west of the wharf

Figure 20: Time series plot of depth (m), significant wave height (Hs), significant wave period (Ts) and temperature (°C) as measured by the TWR at the west of the wharf. Direction is given from true north in oceanographic convention (going toward).


Ha’apai, Tonga



CONTACT DETAILSSecretariat of the Pacific Community

Email: [email protected]: www.spc.int

SPC Headquarters BP D5,

98848 Noumea Cedex,New Caledonia

Telephone: +687 26 20 00Fax: +687 26 38 18

SPC Suva Regional Office Private Mail Bag,

Suva,Fiji,

Telephone: +679 337 0733Fax: +679 337 0021

SPC Pohnpei Regional OfficePO Box Q,

Kolonia, Pohnpei, 96941 FM,Federated States of

MicronesiaTelephone: +691 3207 523

Fax: +691 3202 725

SPC Solomon Islands Country Office

PO Box 1468Honiara, Solomon IslandsTelephone: + 677 25543

+677 25574Fax: +677 25547

Documents

B 1: Physical resources 1.3: Oceanographic assessment