Tsunami Proofing: Where to Put Walls, Why to Keep Trees

John Roach
for National Geographic News
April 28, 2005
The images from the Indian Ocean tsunami that left nearly 300,000 dead
or missing last December are striking. Amateur video shot in Phuket,
Thailand, for example, shows huge ocean waves ripping across beachfront
swimming pools and crashing through hotel lobbies.

"All of those videos were shot from the upper floors of hotels; [the buildings] survived," said Gerard Fryer, a geophysicist and tsunami expert at the University of Hawai'i at Manoa in Honolulu.

The hotels were among the few buildings left standing along coastal areas in South Asia and East Africa that were hit by the December 26 tsunami.

According to Fryer, the basic architecture of the buildings that survived serves as a take-home lesson from the catastrophe. All were built so that their load-bearing walls would escape a direct hit from incoming waves.

Bearing walls are key to the integrity of any structure. The walls support, in addition to their own weight, other parts of a buildings structure, such as upper floors and the roof. To survive the impact of a tsunami, bearing walls are built perpendicular (at right angles) to the shoreline.

"The building then does not offer much of an obstruction to the waves," Fryer said. "The waves break down the nonbearing walls, but the building is yielding and not collapsing. The building serves also as a wonderful sanctuary for anybody who wants to escape these things."

Forests, Mangroves, Reefs

Planting a forest between a building and the shore can also protect a building from a tsunami, Fryer said, because the trees serve as barriers that slow the water down.

The geophysicists said that, had natural mangrove forests been left intact in Banda Aceh, an Indonesian city that was devastated by the December 26 tsunami, many lives and buildings would have been spared.

According to the WWF, the conservation nonprofit, areas that had healthy coral reefs and intact mangrove forests were less severely impacted by the Indian Ocean tsunami than areas where the reefs had been damaged and the mangroves removed.

"Coral reefs act as a natural breakwater, and mangroves are a natural shock absorber, and this applies to floods and cyclones as well as tsunamis," Simon Cripps, director of WWF's endangered-seas program, said in a media statement.

The Gland, Switzerland-based conservation organization is urging that rebuilding efforts in the wake of the tsunami include rehabilitation and restoration of coral reefs, mangroves, and other natural buffers.

Fryer said, "The shoreline is a very attractive place, and we're prepared to put up with a lot to live there." However, he added, people need to acknowledge that hazards exist and adjust their building habits.

Tsunami "World Capital"

Fryer points to the Hawaiian Islands, describing them as "tsunami capital of the world." The islands earn the moniker because of their proximity to earthquake-prone trenches of the Pacific Ocean. The volcanic islands are also surrounded by undersea volcanoes that are prone to landslides, which can generate tsunamis.

The city of Hilo on the island of Hawaii, for example, was struck by a tsunami in 1946 and again in 1960. After the second set of destructive waves, city residents said enough is enough and moved Hilo inland.

The millions of tourists who flock to the Hawaiian Islands each year, however, have little intention of spending their holidays away from the beach—a reality that requires local officials to prepare escape plans.

Waikiki Beach on the island of Oahu is Hawaii's most popular destination. The beach itself is lined with towering hotels.

In 1986 a tsunami warning caused a full coastal evacuation in Hawaii, Fryer said. Waikiki was evacuated according to the existing escape plan, which quickly resulted in traffic gridlock—which would have been a disastrous situation had the tsunami warning been real.

In the event of a tsunami warning today, civil planners call for Waikiki visitors, residents, and workers to move to the upper floors of beachfront hotels.

"All the hotels in Waikiki were built half with the expectation there would be a big flooding event, so quite intentionally they have breakaway walls facing the ocean," Fryer said.

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