General mitigation measures Scope - CCOP

Tsunami Risk Reduction Measures
International Dissemination Seminar
9 March 2006, Bangkok
General mitigation measures
presentation by
Kjell Karlsrud
Norwegian Geotechnical Institute (NGI)
Scope
• Establish practical guidelines for land use and
re-construction in consideration of future
earthquake and tsunami risk along the west
coast of Thailand.
• Propose alternative measures that may be
taken to reduce future risks to life and property
to an acceptable level
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Conclusions from risk assessment
• The potential for a new megathrust M 9+ event
will after 100-200 years give highly
unacceptable risk
Potential for very large consequences,
possibly even worse than 2004
It should be the responsibility and
duty of present generations to take
steps to minimize consequences of
such long term events
Types of mitigation measures
• Awareness building and warning systems
• Land Use and Master Plans
• Building Codes
• Site and Project Planning
• Functional network of escape routes to safe
places
• Establishment of safe places (elevated land,
buildings or other structures)
• Physical protection barriers
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Warning systems are not covered
by this study, but:
• Considerable efforts have been made in
Thailand as well as regionally
• It is important to have proper understanding of
future tsunami scenarios
• Look for simplicity-”what is good enough now”
• In the long term new and improved technology
will come!
How to ensure
lasting awareness is
a key issue
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Lasting awareness measures
• ”Monuments” which also could be part of
protection structure
• Curriculum in schools?
• National tsunami or hazard day?
Detailed measures must be suited
to the local setting
Memorial wall- Hiro village, Japan
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Example of memorial under
construction in Thailand
Memorials must cover all areas potentially affected
5

Masterplans and regulations may:
• Prohibit developments in high risk zones
• Ban buildings that represent high vulnerability
or hazardous facilities, and avoid important
infrastructure in the most hazard-prone areas
• Set requirements (in master plans, building
codes etc) to reduce vulnerability in hazard
prone areas
Building measures
H max
• Upper floor safe from tsunami surge
• Easily accessible escape to safe floor
• Bedrooms at safe level (H max )
• Main structure shall not collapse
• Front and back walls at ground levels may be
designed to collapse
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Tsunami forces against a building
When a surging
tsunami hits a
building, the force
might appear as
a slamming force
with relatively
high intensity and
short duration
Farmers house typical Ruen
Krueng Pook
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Elevated areas for housing
L 1
L 2
H
•Required height in relation to tsunami
inundation level
•Fill from dredging or land pits
•Can also function as escape pods
Protection barriers
• Dikes
• Vertical seawalls
• Moles or breakwaters in the sea
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Dike or sand dune type barrier
•Practical upper limit of height?
•Core and protection material
•Outlets through dike
•Limited overtopping may be acceptable
Example of dike built to protect
Hiro village Japan in 1854
After Ohta,2005
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Protection dike- Hiro village
After Ohta, 2005
Vertical seawalls
• Practical upper limit of height?
• Requires arrangement for outlet of
normal run-off from areas behind.
• Limited overtopping may be acceptable
10

Ancient portuguese fortification- The city
walls of El Jadida, Morocco
The Patong
Bay could in
principle be
protected by
breakwater,
but….
11

Model:
Breakwater across the bay
(Case of Patong City)
Potential breakwater along the Patong City beach,
approximately 1 km offcoast, with a 100 m wide
opening
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