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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: spc@spc.intWebsite: 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
Assessing vulnerability and adaptation to sea-level rise: Lifuka Island
Ha’apai, Tonga
ii
© Copyright Secretariat of the Pacific Community 2014
All rights for commercial / for profit reproduction or translation, in any form, reserved. SPC authorises the partial reproduction or translation of this material for scientific, educational or research purposes, provided that SPC and the source document are properly acknowledged. Permission to reproduce the document and/
or translate in whole, in any form, whether for commercial / for profit or non-profit purposes, must be requested in writing. Original SPC artwork may not be altered or separately published without permission.
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
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
B 1: Physical resources
1.1: Shoreline assessment
1.2: Groundwater resources assessment
1.3: Oceanographic assessment
1.4: Benthic habitat assessment
1.5: Beach sediment assessment
1.6: Household survey to assess vulnerabilities to water resources and coastal erosion and inundation
B 2: Community assessment
2.1: Community engagement strategy and community assessment manual
2.2: Community values and social impact analysis
C: Vulnerability and hazard assessment
1.0: Coastal hazards
2.0: Coastal rehabilitation – Lifuka Island, engineering options report
3.0: Preliminary economic analysis of adaptation strategies to coastal erosion and inundation:
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
Assessing vulnerability and adaptation to sea-level rise: Lifuka Island Ha’apai, Tonga
B 1: Physical resources 1.3: Oceanographic assessment
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
Assessing vulnerability and adaptation to sea-level rise: Lifuka Island Ha’apai, Tonga
B 1: Physical resources 1.3: Oceanographic assessment
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
Assessing vulnerability and adaptation to sea-level rise: Lifuka Island Ha’apai, Tonga
B 1: Physical resources 1.3: Oceanographic assessment
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
Assessing vulnerability and adaptation to sea-level rise: Lifuka Island Ha’apai, Tonga
B 1: Physical resources 1.3: Oceanographic assessment
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.
Assessing vulnerability and adaptation to sea-level rise: Lifuka Island Ha’apai, Tonga
B 1: Physical resources 1.3: Oceanographic assessment
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).
Assessing vulnerability and adaptation to sea-level rise: Lifuka Island Ha’apai, Tonga
B 1: Physical resources 1.3: Oceanographic assessment
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).
Assessing vulnerability and adaptation to sea-level rise: Lifuka Island Ha’apai, Tonga
B 1: Physical resources 1.3: Oceanographic assessment
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).
Assessing vulnerability and adaptation to sea-level rise: Lifuka Island Ha’apai, Tonga
B 1: Physical resources 1.3: Oceanographic assessment
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).
Assessing vulnerability and adaptation to sea-level rise: Lifuka Island Ha’apai, Tonga
B 1: Physical resources 1.3: Oceanographic assessment
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).
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: spc@spc.intWebsite: 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
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