Posted on: Wednesday, November 10, 2004

Flood relief plans on fast track

By Beverly Creamer
Advertiser Education Writer

With the bulk of Hawai'i's rainy winter weather still ahead, officials are considering an array of high-priority fixes to prevent a recurrence of the flooding on Manoa Stream that did millions of dollars in damage 10 days ago.

The proposals being weighed by the state, city and federal agencies include raising part of Woodlawn Drive to send floodwaters back into the stream, using a secondary drainage ditch as a retention pond in times of heavy rainfall, and installing gauges in the stream that would operate via satellite to give early warning of the potential for flooding.

"It's not a detailed analysis at this point," said Eric Hirano, chief engineer for the State Department of Land and Natural Resources. "But everybody's going to put their heads together and ask 'Does this make sense to at least reduce the magnitude of the flooding?' "

"We can't eliminate the flooding with these measures, but perhaps we can reduce the magnitude."

Long-term measures also are under consideration, but the hope is that by investing $1 million or so in short-term steps, it will prevent a repeat of the damage done Oct. 30 when Manoa Stream overflowed its banks after heavy rain, sending millions of gallons of muddy water through residential sections of Manoa Valley and the University of Hawai'i.

Hirano said the group hopes to have a more detailed outline and cost analysis in time to be included in Mayor-elect Mufi Hannemann's first budget in January, and requests going to the Legislature, which convenes that same month.

"If we can come up with some (final) cost figures by January and reach some type of agreement with the agencies, at least on the staff level, what we have to look at then is how can we get all the parties to kick in something financially," said Hirano.

Resident Gayle Sunabe, whose patio and laundry were flooded and who had a wall at the back of the family property topple in the flood, said it was good to hear the agencies are concerned enough to take such quick action.

"Anything that they can do to prevent anything like this from happening again would be so much appreciated and make us feel so much more secure," said Sunabe.

"I'm just glad they're thinking of new prevention measures because winter is coming," she said.

The suggestions being scrutinized include:

• Replacing the hurricane fences along UH property on Woodlawn Drive with break-away fences that would give way with flood pressure.

"A lot of the fencing along the roadway trapped the debris and almost acted like channel walls that funneled the flood waters in a direction they shouldn't have gone," said Hirano. "As the flood waters came up, all the debris clogged on the chain link and they became like a channel or a canal."

• Elevating Woodlawn Drive by two to three feet for approximately two blocks between the Woodlawn Bridge and Noelani School.

"You would do that to send the waters back into the stream channel," said Hirano.

• Extending the concrete-lined channel of the stream above Lowrey Street, in a wing from 30 to 50 feet longer on the side by the park.

"It appeared the water overwhelmed the channel above Lowrey and went around the channel," said Hirano. "So one of our suggestions is to extend the wing wall of the channel and angle it more toward the park so it will trap the water within the concrete-lined channel and keep it from going around."

This is city property, and Hirano estimates this cost alone would be $20,000-$50,000.

• Installing a flap valve in a secondary drainage ditch that connects with Manoa Stream. During times of heavy rain, the ditch would keep water out of Manoa Stream during peak flow, and feed it back in when it subsides.

• Installing real-time gauges in Manoa stream around Paradise Park and an area where two streams meet near Wa'akaua Street above a pedestrian bridge that was washed away.

"The water levels will be transmitted through satellite to give a forewarning of floods," said Larry Kanda, State Civil Defense hazard mitigation officer. "It will trigger an alarm with the National Weather Service that will call all first responders that we've got a serious problem right now."

Included in the agency partnership working toward solutions have been the city and county, U.S. Army Corps of Engineers, state and O'ahu Civil Defense, the federal Natural Resources Conservation Service and the Federal Emergency Management Agency. The group will also bring the Department of Education and UH into the meetings.

Also under way are plans for long-term fixes. Derek Chow, senior project manager for the Corps of Engineers, is looking at what it would cost to add analysis of flood control in the Manoa, Makiki and Palolo watershed areas to an ongoing study of the Ala Wai watershed and flood prevention in Waikiki.

Reach Beverly Creamer at bcreamer@honoluluadvertiser.com or 525-8013.