DECEMBER 26, 2004 TSUNAMI IMPACTS ON COASTAL THAILAND

DECEMBER 26, 2004 TSUNAMI IMPACTS ON COASTAL THAILAND

By Curtis Edwards, PE – Pountney Psomas

Yumei Wang, PE – State of Oregon

On January 31, 2005, the American Society of Civil Engineers (ASCE) sent a

team of engineers to the west coast of Thailand to investigate and document

damage resulting from the December 26, 2004 tsunami. This tsunami was

caused by a magnitude (Mw) 9.0 earthquake off the coast of Sumatra, Indonesia

southwest of Thailand. The investigation covered about 150 km of the coastal

region including the highly impacted areas of Phuket, Khao Lak and Phi Phi Don

Island. Although 10,000 fatalities were suffered, the team focus was to document

damage to coastal lifelines and other coastal facilities incurred by the tsunami

generated from 500 miles to the west.

Rugged cliffs interrupted by pocket beaches characterize the Phuket coastline.

These beaches are highly developed and contain most of the resorts,

commercial support and resident housing for the communities. Many of these

facilities are in close proximity to the beach and were subjected to the most

destructive forces of the tsunami. The tsunami was generally characterized by a

receding wave followed by three surging waves, depending on the location. The

first wave was the smallest but still did a great deal of damage. As a result, the

second and third waves contained large amounts of debris (trees, furniture, cars,

glass, rocks, etc.) that caused far more casualties and damage than the saltwater

waves alone.

High velocity, debris-ladened waves took their toll on many other coastal lifelines.

On Phi Phi Island, the water system consists of many individual public/private

well, reservoir and tank systems. Those located in the low areas were

completely inundated by the saltwater waves. Some systems were temporarily

restored. The lower-lying portions of the sewer system in Patong Beach were

completely flooded by the tsunami waves. This included large portions of the

gravity sewer system and six of their 13 pumping stations. The waves introduced

salt water into the system, which entered the activated sludge type treatment

plant causing it to fail. Many of the electrical power systems were disrupted

along much the tsunami-affected areas. Thailand uses reinforced concrete

power poles, which have been known to do very well during earthquakes.

However, many of these poles were battered by debris and sheared off at the

base.

Most of the bridges in the region are reinforced concrete supported on piers,

abutments and deep foundations. Most of the damage was associated with

abutment scouring and erosion and battering of concrete railings. Minor erosion

was simply repaired using fill to restore the road surface. One bridge in Khao Lak

was reported to have been swept away because of severe approach/pier

erosion.

Khao Lak, a new upscale resort area north of Phuket, was completely devastated

by waves that exceeded 10-m high in places. Resort infrastructure was almost

total destroyed and all hotels are closed for extensive repair. Foundations were

scoured, walls collapsed by wave pressure, and roof tiles removed by wave

impact.

A fishing port, Ban Nam Ken, north of Khao Lak, had extensive damage to

concrete piers and nearly all the fishing fleet either destroyed in place or washed

a km inland. The local Navy base was severely damaged by the tsunami waves.

Ships were beached and shore facilities flooded. The Navy’s water treatment

plant and electrical generation facility were damaged. This hindered the Navy’s

ability to aid in the tsunami response efforts.

Lastly, one aspect of the restoration process found during this investigation,

compared to many others around the world, was that repairs/restoration is

moving very rapidly. Unfortunately for documentation of damages, much of the

debris has been cleared on the 100s of kilometers of inundation areas inspected.

60% of the destroyed/damaged buildings had been demolished and removed.

50% of the remaining buildings are under restoration with over 1% of them

already open. A true honor to the people of Thailand.

In stark contrast to the “mainland” recovery efforts, Phi Phi Island, where

approximately 3,000 people were killed, is only now beginning to recover. This

island is mostly privately owned and requires boats or helicopter access. As a

result, recovery has been slow. Originally, the provincial government would not

allow the disposal of collected debris. This decision was reversed around

February 1 and now clearing and disposal by barge is progressing.

In addition, it was indicated that Phi Phi Island would begin a planning process to

limit construction in the vulnerable areas to avoid future catastrophes. Much of

the formerly developed area that was wiped out will apparently be converted to a

memorial park.

LESSONS LEARNED

Based on local reports and review of the various videos, it is apparent that most

of the tourists and local peoples were not aware of the dangerous waves that

were about to hit them. If there had been a tsunami warning system (or simply

an awareness through education) thousands of lives would have been saved.

One of the greatest lessons learned from the event is that designers need to plan

for tsunami inundation and the force of impact from the waves and associated

debris. Structures can be designed with “flow through” first stories with limited

structural areas facing the tsunami. Another aspect is that drainage control for

the ebbing tide is just as critical. Adequate drainage in facilities could be an

effective means to prevent erosion and impact damage of critical infrastructure

facilities.

INVESITGATION TEAM:

Curtis Edwards, PE, MASCE, EERI – Team Leader; Pountney Psomas, San

Diego

Yumei Wang, PE, MASCE, EERI- State of Oregon, Portland

Tony Dalrymple, PE, MASCE – Johns Hopkins University

David Kriebel, PE, MASCE – US Naval Academy

Robert Lo, PE, MASCE – Klohn Crippen

Robert Barnoff, PE, MASCE

Martin Johnson, PE, MASCE, ABS Consulting

Anat Ruangrassamee, PhD – Chulalongkorn University

Amar Bhogal, ICE – Great Britain

Chitr Lilavivat, ICE – Thailand Representative

PHOTOS:

11Phi Phi Island Damage – 07° 44.379N; 98° 46.335E

11Damaged Fishing Pier - 08° 34.226N; 98° 13.439E

11Khao Lak - 8° 41.45N; 98° 14.49E