Posted on: Monday, January 17, 2005
Call builds for new Hawai'i tsunami maps
By Jan TenBruggencate
Advertiser Science Writer
The technology exists to produce more accurate tsunami inundation maps, but there hasn't been enough money to make them quickly.
That may be changing, thanks to increased local and national anxiety about tsunamis in the wake of the Indian Ocean catastrophe.
The best Hawai'i tsunami inundation maps now available — the ones in the phone book — are based on a technology that is 15 years old.
Now, state Civil Defense officials have received indications that both state and federal financial resources might be available. National Oceanic and Atmospheric Administration officials have called, asking what resources are needed. And Hawai'i state legislators have indicated they're prepared to kick in money if the feds don't come up with enough.
"If we had more funding available, it would be an option to look at parallel projects going on," and that could produce a new statewide set of tsunami maps much faster than the six to 10 years now being predicted, said Brian Yanagi, tsunami program chief for state Civil Defense.
State Sen. Fred Hemmings R-25th (Kailua, Waimanalo, Hawai'i Kai), said he has discussed the issue with other legislators and believes there is bipartisan support.
"It's one of those basic necessities; a thing that government should do. I don't see how anyone could deny a need for it. We're going to make sure it's in the budget," Hemmings said.
The development of a new set of statewide tsunami inundation maps started last year with $150,000 from NOAA's National Tsunami Hazard Mitigation Program.
Of that sum, $100,000 goes to a University of Hawai'i tsunami inundation modeling program run by ocean and resource engineering professor Kwok Fai Cheung. The remaining $50,000 goes to the state Department of Land and Natural Resources, which takes Cheung's modeling results and works with county Civil Defense agencies to determine whether existing tsunami evacuation maps need changing.
For the coming year, the amount of money is the same: $150,000.
State and federal authorities may be ready to add something to that sum, but just increasing the money may not be sufficient to speed the process dramatically, researchers say.
There are not many scientists trained to do tsunami modeling work, and Cheung said trained personnel, not cash, is the primary limiting factor. He said he has classes to teach and administrative work to do, and his graduate students have their studies, exams to take and their own research projects.
"If you give me 10 times as much money and ask me to do it in one year, I can't do it. But with twice as much, we might be able to double the speed," he said. That could cut the completion time to three to five years, he said.
Cheung said the process takes a great deal of time and immense computing power. For each section of coastline, his researchers must calculate the inundation from multiple distant earthquakes around the Pacific basin. Then they must modify the waves' force based on detailed coastal topographic data.
To decide what data to put in, Cheung's team reproduced every tsunami that hit Hawai'i from a distant point in the past 100 years.
The team started working on its first section of coastline — from Ka'ena Point to Kahuku Point on O'ahu — last year, and expects to finish that section by this coming summer. Civil Defense authorities will dictate which coastline on which island will be the next to be prepared.
All the wave inundation calculations need to be done in advance because the work is so complex that it can't be done within a few hours during a tsunami threat.
"The computers are many orders of magnitude too slow to do that," said University of Hawai'i geophysicist Gerard Fryer, who several years ago prepared some preliminary inundation maps using updated data for a tsunami generated by an earthquake off the Big island.
Cheung and Fryer said the difficulty with the older tsunami inundation maps is that they don't take into account the effect of the shape of the underlying ground on the movement of water in a tsunami. A sloping bottom, a steep undersea canyon, a bay — those features can cause water to move laterally as well as directly makai-mauka. That means that certain areas can get much deeper tsunami inundation than others.
"If you have a rugged headland over here and a quarter-mile away you have a sandy beach, there will be a very different impact," Fryer said.
The phone book maps of tsunami run-up were based on the best technology available at the time, and based on that limitation, they are very good. But the new models more accurately reflect what is actually likely to happen, Cheung said.
Even with all the updated technology that will go into the new maps, they have limitations, he said.
"Nothing is absolute. If the tsunami is bigger than what we had from the last 100 years, then it's a different story," he said. Inundations in that situation could be deeper than the zones shown on the maps. For that reason, he said it is fortunate that Civil Defense authorities generally move evacuation map lines inland from predicted inundation lines, to family landmarks like major roadways, which residents will easily recognize.
"When we produce our inundation maps, it's already conservative. Evacuation maps are even more conservative," Cheung said.
Still, these maps are based on distant tsunami. A locally generated tsunami provides residents with little time for evacuation, and the phone book maps may not accurately reflect actual inundation because the characteristics of locally generated events can be so different.
"If there is a Big Island earthquake, there is no time for an orderly evacuation. People should just start walking inland."
Reach Jan TenBruggencate at jant@honoluluadvertiser.com or (808) 245-3074.
