Residents are concerned that a proposed development on a steep 'Aina Haina hillside could mean more falling boulders and flooding for neighboring houses.

The builder is considering submitting a conservation district use application for a 3,700-square-foot single-family home to be built on the hillside above Manauwea Street next to steep Kului Gulch, which catches much of the drainage from homes on Hawai'i Loa Ridge.

The property, now in escrow, includes land zoned for conservation by the state. Conservation land rules allow a single home of up to 5,000 square feet.

Several homes on Manauwea Street have been affected by flooding in recent years, some were narrowly missed by boulders, and some are slowly slipping down the hill, residents told the neighborhood board last week.

Architect Jim Matichuk of Hawai'i Architects, which intends to build the home and has worked on properties in the area before, said independent cultural, archaeological and biological studies of the area conducted in the last six months did not yield major concerns.

The one-story home will be built 200 to 300 feet from any existing house and "on solid rock," Matichuk said, and there are plans to do a thorough geotechnical study if the permit is approved.

"We're not going to put a house in that is sliding or slipping," he said. "We'll make it stay there forever, basically ... We'll do whatever's required."

Both Matichuk and Michael Horack, the future homeowner, said they would accept a request, time permitting, to appear at the next Kuli'ou'ou/Kalani Iki Neighborhood Board meeting on Sept. 4.

Earlier this month, Linda Rosen, who who has lived at the top of Manauwea Street since 2000, questioned whether enough had been done to study what effects a major construction project would have on neighboring houses.

"They ought to know it's a problem area," she said, standing next to a large boulder in her driveway, nearly as high as her waist, that tumbled onto the property probably in the late 1990s.

Much of the 75-acre parcel where the home will be built is on a 40- to 50-percent grade, she said.

"We're not asking people to take away all the risks," she said. "But don't add to the risks unnecessarily. I would not build on that site, personally."

Like many other homes in the valley, most of the Manauwea Street dwellings were built in the 1950s, Rosen said.

'Aina Haina residents are familiar with unstable soil. In the 1990s, the city paid $6.7 million to buy out a group of homes on Ailuna and Leighton streets when a leaky sewer pipe caused them to slip down the hill.

In 2005, three people escaped injury after heavy rains when their wood-frame home on Ekoa Place slid off its foundation and collapsed.

Last November, a four-foot boulder crashed into a Hao Street home on the other end of the valley after heavy storms.

"We are very, very concerned," Wayson Chow, president of the 'Aina Haina Community Association, said last week.

The group, which represents 1,600 families in the valley, met with Matichuk in early June and has since advised him of its concerns about the project.

"The 'Aina Haina Community Association opposes development on steep slopes in the valley due to concerns about danger to surrounding property and surrounding neighbors," Chow said. "There has been a history of falling boulders, soil movements and homes slipping in the 'Aina Haina area."