Pacific Adaptation Strategy Assistance Programme (PASAP) : A

4/02/2014
PACIFIC ADAPTATION STRATEGY
ASSISTANCE PROGRAMME (PASAP)
Assessing Vulnerability and Adaptation to Sea Level Rise Lifuka Island, Ha
apai, Tonga
Rise Lifuka Island, Ha’apai,
Tonga
A Water Resources Perspective
DEVELOPING A KNOWLEDGE‐BASED STRATEGY FOR ADAPTING TO SEA‐LEVEL RISE Introduction
• Overview
• Investigation techniques
• Impacts resulting from identified risks
• Water resources Water resources
adaptation and no‐
regrets options
DEVELOPING AN EVIDENCE‐BASED STRATEGY FOR ADAPTING TO SEA‐LEVEL RISE , LIFUKA 1
4/02/2014
Setting
• Lifuka Island • Located in Ha’apai
Group.
• Coral‐limestone island
• Max elevation 15M
• May 2006 earthquake ‐
23 cm subsidence DEVELOPING AN EVIDENCE‐BASED STRATEGY FOR ADAPTING TO SEA‐LEVEL RISE , LIFUKA Lifuka Island
airport
Koulo
Holopeka
harbour
Pangai
hospital
Hihifo
• 500 households
• 3000 people
DEVELOPING AN EVIDENCE‐BASED STRATEGY FOR ADAPTING TO SEA‐LEVEL RISE , LIFUKA 2
4/02/2014
Rainfall
• 1700- 2500mm/yr rainfall
• wet season (Nov-Apr),6070% of rainfall; dry season
(May-Oct)
• Rainfall influenced by SPCZ
• El Nino conditions produce
low rainfall
Geological setting
• Island uplift commenced approx 2Ma • model of uplift, erosion and sealevel
changes to account for the erosive and accretionary geological setting (Dickinson 1994)
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Hydrogeology
•Groundwater thickest in the unconsolidated Holocene
sediments under the main township of Pangai and Hihifo
•Fresh groundwater lens in the permeable Pleistocene
limestone is thin, limited resource potential
Impacts observed from May 2006 earthquake
• Subsidence ‐ 23cm
• Coastal erosion
Coastal erosion
• Inundation
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Hihifo 1968 and 2011
1968 Image with 2011 shoreline
2011 Image with 1968 shoreline
Predicted Water Level Scenarios 2100 Hihifo
Highest
Intermediate‐high
Today
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Basic effect of Storm Water Levels
Present day
g
About 2m wave height
About 2m Storm surge
& wave setup
Present day
high spring
tide level
About 2.5m above MSL
Wharf
Today
Today’ss mean sea level
mean sea level
Present day
low spring tide
level
Rapid Onset: Extreme Event Examples
Trader Jacks, Rarotonga,
Cook Islands
•
•
•
•
•
•
Opened in 1986
Destroyed by Cyclone Sally in 1987
Rebuilt
Destroyed by Cyclone Pan in 1997
Rebuilt
Destroyed by Cyclone Meena in
2005
• Rebuilt
Cyclone Mena - Rarotonga
Extreme Water Level during
Tropical Cyclones =
Tides + Storm Surge + Waves
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Possible Inundation Scenario:
Sea Level Rise and Cyclone by 2100
Hihifo
What about the water resources?
• What if any changes to the groundwater
to the groundwater in response to 23cm subsidence
• Impacts to water resources are under future climate future climate
scenarios
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Lifuka water resources ‐ summary
• 92% of HHs utilise RWH, for drinking, RWH for drinking
cooking, washing clothes.
• 83% of all HHs use groundwater
• Groundwater G
d t
provides 80% of all water needs.
RWH Storage
• Total residential storage 5,279m3 or 5,279,000L, • predominantly cement tanks (75%)
• average of 14,663L/household, (household size no 5.4 people)
• Community perception is need for greater storage
Tank volume per household Tank volume per household (physical)
120
105
90
Frequency
100
80
60
41
40
20
48
25
17
2
Frequency
19
6
5
2
0
Tank volume m3
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Guttering
GUTTERING • 90% of all households are capturing 50% or less of the roof area‐
• 75% of houses require guttering improvements
TWB Reticulated groundwater • TWB water currently services 68% of Lifuka population (264HHs)
• 3 horizontal galleries and one well abstract an estimated 269m3/day of groundwater providing 80%of the daily water needs for connected HHs
• Uneven abstraction from wells/galleries
• Security of water supply during dry Security of water supply during dry
periods
• Used by HHs for garden, and personal bathing needs, smaller % for cooking and washing needs.
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TWB leakage
•Total unaccounted for water (leakage
and other losses included (13% + 20%
+18%)
18%) = 51% off ttotal
t l production
d ti
•Estimated leakage - production to bulk
meter = 13% of total production
•Estimated leakage - bulk meter to HHs
(based on min overnight flow) = 20% of
total production
•Estimated total leakage = 33% of total
production
•Estimated unaccounted for water = 18% of
total production
Water quality
• 95% of sampled wells and TWB treated water tested positive for E Coli
• Poorly designed and maintained “bottomless” septic tanks and animals suspected for high % of contamination
• Only 5% of HHs treat their water (boil) before drinking
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Water Resource Investigations
• Geophysics
– EM34
– Resistivity
• Salinity and water level monitoring
• Infrastructure Infrastructure
and reliance survey
• Water quality
Electromagnetic Surveys‐Location
“Assessing Vulnerability and to Sea‐Level Rise, Lifuka Ha’apai Tonga Adaptation 11
4/02/2014
Resistivity
Freshwater lens mapping
• Conservative due to – extended dry period
– EM34 sensitivity
• Volumes of freshwater (<2,500µS/cm)
– Area 1,005,300m2
– Volume 3,464,520m3
– Available freshwater water 1,212,582m3
• Sustainable Yield – 213,318m3/year
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Impact on the water lens from sealevel rise
•LIF
LIF 7 and
d LIF 9 ((monitoring
it i
bores have water level
measurements pre 2006 and
post 2006 earthquake.
Rainfall residual mass curve
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Impact on the water lens from sealevel rise
• Water
level rises of
55cm and 45cm LIF 9
and LIF 7 respectively in
water level, for 23cm
rise in sealevel.
•Calculated impact on
groundwater of 2.2 times
the unit rate of sealevel
rise.
•A 80cm rise in sealevel
= 1.74m rise in
groundwater level.
Impact on the water lens from sealevel rise
• Average depth to watertable of 2.5m March 2012
0
• Average depth to watertable of 3.5m 1998 (Crennan)
• Assuming a depressed water table due to drought plus a average sealevel rise impact of 0.5m to account for the 1m difference.
• An additional 50‐80cm rise in sea level may result in a 1.1‐1.75m rise in ground water level above current levels
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Impact on the water lens from sealevel rise
Impact on the water lens from sealevel rise
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Impact on the water lens from sealevel rise
Sealevel rise will result in
•groundwater being lifted by an estimated 2 x the sea level
rise
•A shallower water table = reduced barrier to contamination
•Impacts for infrastructure which skim the freshwater now
deeper in the freshwater lens
•Freshwater lens may thicken, with more favourable
sediments holding the freshwater
Table 9. Selected periods of monitoring and their relationship to period rainfall residual mass curve for that period.
Selected monitoring periods –
rainfall residual mass
Period of Monitoring
Position on rainfall residual mass curve
October 98
End of 8 year dry period
April 1999
Approx 5 months of above average rainfall
July 1999
Approx 8 months of above average rainfall
September 2011
Approx 12 months of above average rainfall
March 2012
End of 18 month period of above average rainfall
Julyy 2012
g rainfall
End of a 5 month p
period of below average
October 2012
Period of approx 3 months of average rainfall
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Climate change impacts By 2030 p p
, g
• Temp is predicted to be 0.3‐1.0C, high confidence.
• Expect a general decrease in dry season rainfall, and an increase in wet season rainfall, moderate confidence.
• Expect intensity and frequency of days of extreme rainfall days are projected to increase, high confidence
drought projections are inconsistent
• drought projections are inconsistent.
• Less frequent but more intense tropical cyclones, moderate confidence.
Climate change implications
• Increased reliance on groundwater
– Greater seasonal variability in rainfall
Greater seasonal variability in rainfall
– Hotter temperatures, greater usage
– Possibly increased contamination ‐ shorter travel times from “septic” tanks
• Inundation potential increases – protection of wells and pumps infrastructure
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Sustainable yield versus usage
• Abstraction approx 98,300
98,300m3/y
/yr
• SY = 213,300m3/yr • % of abstraction to SY = 46% however abstraction occurring in 4 places, not across the lens
• Usage set to increase
Water Resource Adaptation Options
• Options specific to impacts of coastal erosion and inundation
and inundation
• No regrets options – regardless of costal erosion and inundation impacts
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Options specific to impacts of coastal erosion and inundation
• Investigate other areas for water supply outside for water supply outside
the inundation area
• Adaptive operational abstraction based on salinity of the lens
• Protection of infrastructure with bunding
No regret options
Adaptation options regardless of coastal erosion and inundation
• Rainwater harvesting
– Guttering maintenance program
– First flush and screens for improved water quality
– Targeted tank installation‐ plastic
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No regret options
TWB – reticulation
(
)
– Reduce losses (33%) and unaccounted for water (18%)
– Abstraction based on salinity in production wells
– Improved water quality sampling – and responsive to results
No regret options
TWB –Buffer zones
– nominal 50m buffer for groundwater protection ‐
groundwater protection ‐
• exclude animals, improved wastewater disposal practice, restrict storage and use of chemicals and fuels
– fencing around well heads ‐
10m nominal – TWB well 4 –
• fencing around depression, bunding and improved surface drainage directed away from well head 20