An inspection of Thai villages and ports struck by
tsunami waves has uncovered some engineering lessons that
might reduce casualties and destruction in future oceanic
upheavals, a Johns Hopkins researcher said.
Robert A. Dalrymple, an internationally recognized
expert on water waves and coastal engineering, was part of
a nine-member team that recently toured southern Thailand,
examining landscape and structural damage in areas that had
been battered by waves up to 10 meters (more than 30 feet)
high. The research trip to Thailand, along with similar
expeditions to Sri Lanka and India, was organized and
funded by the American
Society of Civil Engineers in cooperation with the
Institution of Civil Engineers.
An earthquake in the Indian Ocean triggered the Dec.
26 tsunami, which killed more than 200,000 people in 11
nations and caused immense property damage. "The force of
the fast-moving waves on structures was tremendous," said
Dalrymple, who is the Willard and Lillian Hackerman
Professor of Civil
Engineering in the Whiting School. "We wanted to see
which buildings and other structures held up against the
waves — and which didn't."
The American Society of Civil Engineers is preparing a
detailed technical report. But Dalrymple said team and
personal observations in post-tsunami Thailand led him to
compile a list of general lessons for builders in coastal
areas where future tsunamis may occur:
Elevated structures survive better. The waves were
powerful enough to smash through a building's ocean-facing
wall and break out the opposite side, and high enough to
inundate a second-story level. Elevated buildings that
allowed the moving water to pass through the lower level
with little interference fared better than those with solid
first-floor walls. Taller buildings that allowed people to
reach heights above the wave's crest helped reduce
casualties.
Materials matter. Reinforced concrete structures were
more likely to survive the wave forces. In general, masonry
(brick) and wooden structures did not fare as well.
Orientation is important. Walls facing the ocean,
allowing perpendicular impact from the waves, sustained
more damage. Walls oriented in the direction of the flow
sustained less.
Strong foundations are necessary. In addition,
landscaping and other features can protect the foundations
against scouring, which is soil erosion caused by the
moving water.
Seawalls can be a very effective way to reduce wave
damage. The structures must be continuous, however, with no
gaps for pedestrian crossings. Also, such structures should
not slope inland, allowing waves to slide up and over the
walls like a skier.
Debris in the flow is hazardous. Many tsunami victims
were injured or killed by debris pushed along by the
powerful waves. Debris can be minimized if vehicles are
parked and heavy items stored on the inland side of
buildings.
Ports are particularly vulnerable to tsunami waves.
Boats and piers in a harbor hit by a tsunami have little
protection.
Beaches in Thailand recover rapidly. The ASCE
researchers discovered that within weeks of the disaster,
natural ocean forces had returned the sandy beaches nearly
to their pre-tsunami condition. The beaches have reopened,
Dalrymple said, and Thais are encouraging tourists to
return.
Dalrymple said several questions raised during the
trip require further research. These include why the height
of the tsunami varied dramatically along the coast of
Thailand and how engineers can construct a mathematical
model of wave forces as they pass through coastal
structures.
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