WAIMANALO — The state will tear down the Kailua Reservoir dam in Waimanalo after an inspection showed that recent erosion made it dangerous.

"The current condition of Kailua Reservoir is unsafe, and we need to take immediate action to protect the people downstream of the reservoir," said Sandra Kunimoto, Department of Agriculture chairwoman.

The state also said it will close indefinitely one lane of Kailua Road while it makes the area safe from rockslides. Crews will install a net over the hillside near the entrance to the Kailua business district and install concrete barriers to catch falling rocks.

The sidewalk and one Kailua-bound lane of Kailua Road will be closed between Hamakua Drive and St. John Lutheran Church until the work is done. Yesterday's closure caused a big backup during afternoon rush hour

The Department of Agriculture owns the reservoir and wants work to begin this week, especially because a sinkhole developed during the last heavy rain. With wet trade-wind weather predicted for this weekend, the department wants to move quickly, said Kunimoto.

"If there's another rain event, and it's unusually heavy as the last two were, we don't know if those walls will hold up, given that sinkhole," Kunimoto said at a news conference yesterday.

The reservoir, which hasn't been operating since 1993, was inspected two weeks before the downpours that soaked Waimanalo on Sunday, she said. For all these years it has been kept open so any water collecting in it would flow through, but the recent rains overwhelmed the structure and water started backing up, she said.

Erosion above and around the outflow pipe has created a sinkhole about 20 feet wide on the dam crest that wasn't there on the previous inspection, Kunimoto said.

Twelve families living below the reservoir were evacuated Sunday when water flowed over the spillway.

State Civil Defense, the Army Corps of Engineers, the state Department of Land and Natural Resources, and county agencies support this action, Kunimoto said.

The DLNR and the Corps of Engineers inspected the reservoir Monday, although it is not regulated by the department, said Peter Young, DLNR director.

"We did have our people go out and do the inspection, and they also concur that it is a reservoir that needed immediate attention," Young said.

The reservoir was built in the 1930s for agriculture use. It was designed to hold 6 million gallons but now can only hold 4 million to 5 million gallons.

In 2000, a private company prepared a draft environmental assessment for the state and recommended partial removal of the reservoir, but public opposition halted the project. Residents saw it as a way to control floods.

The Corps of Engineers conducted computer-generated dam-break scenarios and concluded that removing part of the reservoir will make the area around the reservoir and downstream safer, said Maj. Gen. Robert Lee, director of Civil Defense.

"If there should be a need for flood control ... if the experts and the engineers determine that is necessary, then the Kailua Reservoir will be built back up to 2006 standards."

Also at the news conference, state officials said: