'AINA HAINA — A 100-year flood of Wailupe Stream would wash out Kalaniana'ole Highway, strand thousands of motorists and flood many of the the 819 homes in the valley, the U.S. Army Corps of Engineers has said. Twenty-eight commercial buildings would also be affected.

The eight miles of Wailupe Stream have been the subject of discussion among residents for a quarter-century. From state and federal officials, they have urged such measures as concrete debris basins, concrete channelization of the stream and floodwalls, excavation of the channel 100 feet into the ocean and modifications of the bridge over Kalaniana'ole Highway.

The U.S. Army Corps of Engineers has studied the stream's conditions several times, most recently this year. Last night the corps held a community meeting to fill residents in on what projects it proposes for the eight miles of stream that in a disastrous situation could flood the entire valley floor. While the scope of any project hasn't been determined, the price tag could be $20 million to $38 million, said Steve Yamamoto, U.S. Army Corps of Engineers project manager.

Malama Maunalua, an environmental group determined to restore the health of Maunalua Bay where all the storm water flows, opposes any kind of hardening or lining of the stream with concrete or boulders because it could increase runoff. The group has said it wants the Wailupe to remain a natural stream and not be turned into a drainage canal.

The cost would be shared by the federal, state and county governments. The present timetable calls for a draft decision to be completed by March, a second public hearing in April and a final decision by June. Plans and permits could be completed by 2010.

"This affects a lot of residents," said Art Mori, an 'Aina Haina resident. "The real problem for people living along the stream is the erosion on the steep banks that is occurring.

The last time the stream overflowed its banks in 1967, it flooded much of 'Aina Haina downstream, said Gregg Kashiwa, an 'Aina Haina resident who lives at the mouth of the stream along the ocean.

Residents who live along the stream, particularly in the upper portion of 'Aina Haina, have a steep drop off into the stream behind their house, Kashiwa said.

"We sustained heavy damages then," Kashiwa said. He said residents who went through that storm want the situation taken care of.

In 2001, the city, state and federal government all were on board and had ponied up money to pay for the stream work study, said Bertha Leong, a Kuli'ou'ou /Kalani Iki Neighborhood Board member and former state representative. But the cost-benefit analysis didn't pan out and last year the Bush administration withdrew its financial support until an economic analysis was completed.

"The project is going to move forward," Leong said. "We know that lining the stream will help with sedimentation. The banks of the stream have eroded so much that dirt now rolls into the stream all the time."

Reach Suzanne Roig at sroig@honoluluadvertiser.com.