Posted on: Tuesday, July 15, 2003

Flash-flood warnings for streams considered

By Timothy Hurley
Advertiser Staff Writer

After recent deaths caused by flooding in Hawai'i streams, state and federal officials have formed a working group to examine the possibility of setting up a statewide network to better alert authorities about potential flash floods.

In a separate initiative, Haleakala National Park wants to explore the possibility of installing a warning system at 'Ohe'o Gulch, where two visitors from Louisville, Ky., were swept to their deaths in the state's latest flash-flood tragedy April 10.

Superintendent Don Reeser said the park hopes to use National Park Service emergency money to pay for a study.

"It happened so quickly," he said of the 'Ohe'o Gulch flood, which was described as a 6-foot wall of water. "It would have to be a pretty sophisticated system to have prevented something like that. But we're going to see if there's something feasible out there."

Meanwhile, officials with the U.S. Geological Survey, the National Weather Service and the state Department of Land and Natural Resources recently began meeting to discuss implementing a statewide system.

Barry Hill, assistant district chief with the U.S. Geological Survey's Pacific Islands Office, said the effort was prompted by "a realization we could do a better job" with warning technologies.

There have been at least 27 deaths in Hawai'i because of flash flooding between 1970 and 2001. In addition to the two 'Ohe'o deaths in April, three people were killed in January 2002 trying to cross a rain-swollen stream in an automobile in Waiehu, Maui.

Floods and flash floods are the No. 1 weather-related killer in the United States, according to the National Weather Service, with more people dying annually from flash floods than from lightning, tornadoes or hurricanes.

While flash floods are not unique to Hawai'i, the Islands do have their own set of conditions to consider, Hill said, including streams that are steep, narrow and pack a lot of water from intense rains.

The working group is hoping to develop proposals in two related areas: rainfall runoff modeling and a flood-warning network of gauges.

The rainfall modeling would allow officials to examine the hydrological condition of a watershed and determine the likelihood of flooding. If, for example, a watershed endures rain four days in a row, the ground may be saturated to the point where another intense rain could trigger a flash flood.

As for the actual warning system, a range of technologies is available, some reasonably cost-effective. One possibility, Hill said, is the use of line-of-sight radios, connected to stream gauges, with repeater stations that would relay information to a personal computer.

Hill said the working group hopes to launch the project next year by outfitting the technology on one or two streams. The Hanalei River on Kaua'i is a good candidate, he said, as are the Waihe'e and the 'Ohe'o Gulch streams on Maui. How many streams ultimately get warning systems would depend on money, he said.

Reeser said Haleakala plans to install additional warning signs at the 'Ohe'o stream.