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Transcript
Sea-level changes and their impacts
on critical infrastructure in South
Tarawa
Doug Ramsay, Scott Stephens & Rob Bell, NIWA
Kabure Yeeting, Mike Foon, Taouea Titaake-Reiher, Takaia Tekaie, Raitiata
Cati, Robite Teaete, Ueneta Toorua, Kien Teteki, Mikaere Neemia, Bauro
Ukitoori, Kataebati Bataua, Ruoikabuti Tioon, Tenae Atera, Itienang Timona,
Kaiarake Taburuea
Government of Kiribati
Coastal infrastructure and adaptation
• Long lifetime of infrastructure investments
• Robustness of present infrastructure highly variable
– incomplete or outdated climate information used in design
• A seeming desire to build critical infrastructure in
exposed or dangerous locations.
• Construction industry, building codes and standards nonexistent and if available don’t incorporate climate change
• Kiribati Adaption Project Phase II: Climate Information for
risk management
– Aimed to develop climate risk information to be adopted as
national standards for option assessment and technical design
(“climate-proofing” parameters)
Climate information for risk management
• Coastal component:
• Analysis of sea-level data and derivation of extreme
water levels in Tarawa lagoon (10%, 2%, 1% AEP’s).
• Extreme wave conditions on ocean and Tarawa
lagoon shorelines
• Joint occurrence of extreme waves and water levels
around Tarawa lagoon shoreline
• Wave run-up and overtopping on different types of
shoreline.
• How these parameters may change by 2025, 2050 and
2100 for different emission scenarios.
Data, tools &
methodology
•
NOAA/NCEP
Wavewatch III dataset
•
Kiribati Met Service:
wind & sea level
pressure dataset
(1978-present)
•
SEAFRAME / UH tide
gauge record (1974 –
present)
•
Hydrodynamic model
of Tarawa lagoon
•
SWAN wave model of
Tarawa lagoon
Joint occurrence of waves & water levels
Low probability
High Probability
Joint occurrence of waves & water levels
+ 0.48 m
+ 0.79 m
Present Day
X
X
X
Coastal calculator
Acts as a database
•
Extreme offshore significant wave heights around each island in
Kiribati and at 23 locations around the Tarawa lagoon shoreline
•
Extreme storm tide levels at 23 locations around the Tarawa Lagoon
shoreline and representative of Tarawa ocean shoreline.
•
Joint occurrence of extreme wave heights AND storm tide levels at 23
locations around Tarawa lagoon shoreline (and off the east, south and
west Tarawa ocean coasts)
•
Annual Mean Level of the Sea (MLOS) data from the University of
Hawaii and SEAFRAME tide gauges from 1974 to present (updated
to December 2009).
•
5%, central estimates and 95% range of sea-level rise for the six
emission scenarios used by the IPCC AR4 and allowance for
additional ice sheet discharge based on IPCC AR4 guidance.
Coastal calculator (ocean side)
Wave overtopping
Effect of beach
rock outcrops
Wave run-up
Wave height at
the shoreline
Wave translation
Wave set-up
Wave breaking
X
Database of extreme
wave & water levels
Flow-path through the
calculator
Coastal Calculator Applications
•
Climate proofing land and development planning :
– Assessing areas at potential risk from inundation (both in terms of frequent
events, e.g. high tides, to less frequent storm-related events) and how these may
change.
– Setting minimum ground levels or floor levels for development activities.
– Establishing the extent of existing building inundation risk and how this may
change in the future.
•
Coastal engineering:
– Deriving seawall design wave / water level conditions that account for climate
change effects.
– Assessing adequacy of the design of seawall permit applications.
– Basic seawall profile design optimisation (to optimise performance in reducing
wave overtopping)
– Basic assessments of how overtopping of existing seawall structures may change
and how these relate to dangerous overtopping limits
Zone where overtopping
rates become dangerous for
cars
Percentage increase in
overtopping volumes
How much higher does the causeway
need to be to maintain the present
level of overtopping performance?
Tarawa datum issues
Assumes that University of Hawaii Datum ≠ SEAFRAME
Gauge datum (0.42 m difference)
Informing climate-proofed
infrastructure in coastal margins
• Sufficient (but only just) wave & water level datasets to
be able to make:
– Probabilistic assessments suitable for engineering purposes.
– Evidence-based information on the potential impacts of climate
change on Pacific Island coastlines.
• Infrastructure design in coastal margins needs to
consider both waves and water levels
– how they interact
– and the effects of climate change on these drivers and interactions –
it is so much more than just mean sea-level rise!!
What about the rest of the Pacific?
• Few, easily accessible examples, where robust
analysis of coastal extreme design conditions have
been derived, including measures of their accuracy
and uncertainty.
• Less examples of where climate change impacts have
been factored in to the derivation of probabilistic
design conditions.
• Lack of appropriate or locally relevant design
standards, building codes and processes that provide
guidance and processes for accommodating climate
extremes, variability and change.
Lessons learned and science gaps…….
• Changes in frequency of episodic events (overtopping,
inundation) often of more interest than changing
magnitude.
• Probabilistic methodologies for extreme wave analysis that
incorporate bimodal considerations.
• Robust modelling approaches that can simulated the
complex wave - water interactions and feedbacks across
fringing reef environments
– wave breaking, wave set-up, wave grouping and infragravity
waves, wave reformation and transformation.
• Empirical methodologies for:
– wave run-up and overtopping on fringing reef shorelines
– episodic event inundation zones from run-up information.
Kam rabwa