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The Honolulu Advertiser
Posted on: Monday, April 21, 2003

Flash-flood warning system considered

By Timothy Hurley
Advertiser Maui County Bureau

Could technology have saved Kevin Brown and his daughter, Elizabeth?

The U.S. Geological Survey says it's possible to install the kind of warning system that could have alerted the visitors from Louisville, Ky., to the flash flood that swept them to their deaths over a Kipahulu waterfall April 10.

Should the project go forward, it has a head start: The agency maintains an 'Ohe'o Gulch stream-flow gauge that relays readings to a computer by way of a satellite every 15 minutes.

Haleakala National Park officials are expected to discuss the warning-system issue in the coming days as they conduct an internal review of the 'Ohe'o tragedy. Searches for the 39-year-old schoolteacher and his 8-year-old daughter were called off on Tuesday, and daily patrols of the area have turned up nothing.

Officials from the national park and the Geological Survey have been in contact in recent days and are expected to talk further after the formal review.

"I'm tired of hearing about people dying over there," said Gordon Tribble, Pacific Islands director of USGS Water Programs, based in Honolulu.

Tribble described one example of an early warning network that would employ a series of rain and stream-flow gauges and rely on computer modeling to factor variables such as the intensity of rain and moisture in the soil to measure watershed absorption rates.

A study would have to figure out where to place the gauges and then determine the thresholds needed to trigger a warning. Radio technology could relay warning signals to the Kipahulu visitor center or automatically set off sirens placed along the stream, he said.

Two years ago, the USGS installed a flood-warning system on the Kawainui Marsh, with gauges providing data in real time to the National Weather Service Flood Forecast Office in Honolulu using cellular telephones.

Questions remain for the National Park Service in setting up a similar system, including the cost, not only in dollars — estimated in the $200,000 range — but in the effect on the wilderness.

"There will definitely be some environmental degradation to the park," Tribble said.

How much degradation may be the key to whether Haleakala park officials proceed. The mission of the National Park Service is to protect natural wild areas for public access. Would a series of sirens and gauge stations ruin the wilderness experience for visitors? Would people even know what to do when they hear a siren?

Haleakala Superintendent Don Reeser said park officials have discussed a warning system but never pursued the idea.

It's uncertain whether such a system would have saved the Browns, he said, since they were hiking about a half-mile up from the famous coastal pools and visitor center. The flooding caught just about everyone by surprise, even the National Park Service, which posted a flash-flood warning only minutes before the hikers were swept downstream.

Nevertheless, Reeser said, the park needs to revisit the issue.

Over the years 'Ohe'o Gulch has had its share of fatal accidents, many linked to flooding or swimming and diving. Park employees said there have been a couple of deaths each year for the past several years, such as the thrill-seeking Kihei man who jumped off the 184-foot Makahiku Falls Jan. 28.

Holly Brown, the wife and mother of the victims, described "a massive wall of water" that swept her loved ones over Makahiku Falls "without any possible chance of warning" at about 4:30 p.m.

According to raw data from the USGS 'Ohe'o stream gauge — situated a few hundred yards downstream of the waterfall — water flow jumped from 21 cubic feet per second to 2,190 cubic feet per second between 4:30 p.m. and 4:45 p.m., topping out at 3,650 cubic feet per second an hour later.

Water levels rose from 1.7 feet to 5.9 feet during the same 15-minute period, peaking at 7.2 feet an hour later.

Because the gauge there records in 15-minute intervals, the water levels between intervals are unknown. Park rangers said they found vegetation on the stream bank bent back from 15 to 20 feet above the normal stream level.

While the April 10 measurements are exceptional, they are not unprecedented. A survey of data collected between 1989 and 1997 reveals that similar levels were recorded an average of three times a year. The last time 'Ohe'o topped 7 feet was this past Oct. 15. (The gauge was inoperable between 1997 and September 2001.)

In a show of even greater power, the recorded stream flow at 'Ohe'o on the night of Sept. 18, 1994, was 14,700 cubic feet per second — about four times the April 10 peak discharge.

Rick Fontaine, a hydrologist and surface water specialist for the USGS Pacific Islands office, said many visitors to Hawai'i are unaware of the dangers of flash flooding in Island streams. Flooding rivers on the Mainland generally rise slowly, he said, while streams here are steep, narrow and pack a lot of water from intense rains.

These fierce rainstorms, sometimes localized high in the mountains, can cause stream waters down the line to rise dangerously fast.

Once, while taking measurements in the Hanawi Stream in East Maui, Fontaine noticed the water level rising rapidly. It was a beautiful day, but he couldn't see the upper slopes of Haleakala in the narrow valley. So he grabbed his gear and ran as fast as he could downstream, escaping just in time.

"It's deceiving," he said. "My job is to observe the stream. I'm attuned to what's going on. The average Joe is just relaxing and not looking for those things.

"People don't understand the power of the streams and how fast they can change."

Contact Timothy Hurley at thurley@honoluluadvertiser.com or (808) 244-4880.