Oahu’s tsunami evacuation maps will be updated for the first time in 19 years, in response to updated ocean-floor data.

The city Department of Emergency Management will hold public outreach workshops on the 21 maps outlining zones that must be evacuated. That’s two more zones than in the 1991 set of maps.

Zones with the most significant expanded evacuation area include Waikiki, downtown Honolulu, Maili and Honolulu Harbor. City officials added two more maps that did not have an evacuation plan: Pearl Harbor and Kaneohe Bay.

Overall, more land is covered by the evacuation zones. But some areas, such as Sandy Beach, saw their evacuation zones shrink, Kaku said.

Melvin Kaku, director of the city Emergency Management Department, said the updates, still in draft form until they are presented to the public, will not affect flood insurance rate maps.

The new maps will not be in the 2011 phone books, due to publishing deadlines. But all 21 maps will be available online tomorrow on the department’s website. Also tomorrow, the city will begin holding public workshops throughout the month.

"Most of the areas have not seen significant changes," Kaku said. "With more scientifically available data, we believe this is a more accurate designation of evacuation zones."

Hawaii was the first state to develop tsunami evacuation maps, said Kwok Fai Cheung, a University of Hawaii researcher hired by the state to do tsunami research studies.

The current maps, found in telephone books statewide, were based on studies of five destructive tsunamis in the last century. However, the maps were not comprehensive.

Cheung said the old maps do not take into account ocean-floor topography, which can change wave behavior as it approaches the shoreline.

New computer models use updated ocean floor mapping data. They show that Pearl Harbor and Kaneohe Bay, two harbors once thought to be protected because of their makeup, would be vulnerable in a worst-case-scenario tsunami.

Cheung’s research was funded through about $100,000 to $200,000 per year in federal grants. He had graduate students assist him in drawing the new maps.

"We had most of the data already," Cheung said. "Now we’re using a two-dimensional model where the waves can propagate in all different directions."

Cheung said the old tsunami models displayed waves hitting in one direction. In reality a tsunami would cause waves all around an island, as was seen in the Feb. 27 tsunami that hit the islands after an 8.8-magnitude earthquake in Chile. The waves caused no damage. The tallest surge was in Kahului, at 3 feet, 1 inch.

Cheung said he is now working with Big Island Civil Defense on their evacuation maps. The inundation maps for the Big Island are already complete. He will be assisting Kauai and Maui counties, as well.

John Cummings, spokesman for city emergency management, said Oahu evacuated about 50,000 people during the February event.

Cheung completed his work on inundation areas in 2008, and the city began determining which priority areas to evacuate.

"From a public safety perspective, we looked at what would be reasonable in terms of getting the optimum evacuation sequence in place, as well as convenience or accessibility in terms of the first responders," Kaku said. "Therefore, specific infrastructure or key site features were used as a clear demarcation areas for evacuation zones."

ON THE NET
To download drafts of the new tsunami evacuation maps, visit www.honolulu.gov/dem.