WAIMANALO — Fearing a deadly breach of a rural dam yesterday, police, fire and civil defense authorities evacuated 12 families below the Kailua Reservoir and closed a portion of Kalaniana'ole Highway in Waimanalo town as a mid-afternoon thunderstorm pounded the area.

Residents were allowed back into their homes several hours later, but 34 people still chose to stay at a shelter set up at Waimanalo District Park, said John Cummings, spokesman for O'ahu Civil Defense.

The dam scare was part of yet another stormy day in which furious bouts of rain closed roads, caused landslides and contributed to at least one power outage. As much as 8 inches of rain fell on parts of O'ahu in a 24-hour period.

The forecast is for clearer skies this week, but not before the Islands were expected to get hit by more rain late last night.

"We're in the middle of a lot of severe weather overnight," said Tim Craig, lead forecaster for the National Weather Service. "It's improving for Kaua'i and O'ahu but there are still flash-flood warnings for Windward O'ahu, Maui, the Big Island and Kaua'i. We're looking at severe weather for Maui County and the Big Island."

A flash flood watch was in effect for all islands until at least 4 a.m. today.

In Waimanalo yesterday, more than 2 feet of water was reportedly flowing over the spillway of a 4-million-gallon reservoir that is no longer used and usually empty, prompting the 3:30 p.m. evacuation and road closures.

No one was injured. Police reopened the mauka-most portions of Waikupanaha and Kumuhau streets and Kalaniana'ole Highway at 5:30 p.m.

But the threat of another dam-related catastrophe like the one that left three people dead and four missing on Kaua'i last month will have state authorities seriously reviewing the situation this week, said Cum-mings.

The reservoir is owned by the state Department of Agriculture, which for several years has not maintained a gate on it that allows water from Waimanalo Stream to flow out a drain pipe, he said.

"It was off the radar screen," Cummings said. "It was an unused dam in an unoperating reservoir."

Civil Defense officials were told that the floodgates to the reservoir were open and it was never supposed to fill again, Cummings said. Two Department of Agriculture engineers were inspecting it yesterday, he said.

Area residents said they have been complaining for years about the condition of the drain pipe. But it was not until Friday, when water also flowed over the spillway, that civil defense authorities learned of the problem, Cummings said.

Officials scrambled to create an evacuation plan, which they used yesterday, he said.

David Kalama, who grew up in the area and lives in the shadow of the reservoir, said he stood atop the overflowing spillway yesterday and watched with alarm as water roared through his property. Fortunately, it took a course that spared homes and found the nearby stream.

Kalama said the drain pipe had been recently clogged by a chunk of concrete, which contributed to erosion above. About a week ago, the ground above gave way, dropping a large plum tree across the mouth of the pipe and blocking drainage, he said. That allowed the reservoir to fill again.

He said he has seen the reservoir overflow in the past, but that the speed at which it rose yesterday was alarming. It took 12 minutes to rise about 10 feet and over the spillway, he said.

"The water rose so quickly and didn't seem normal," he said. "That told me this tree was blocking it and we were in danger."

His wife, Kim, was below the reservoir making telephone calls to friends who lived downstream, warning them of a possible breach. She knew it wasn't a good place to be.

"Luckily we've been spared again," she said. "Hopefully something will be done soon to repair the gate so we can have a controlled release."

Landslides again closed a section of Round Top Drive that has been plagued by earth movement. "It's not safe. It's going to take a major effort to fix it," said Cummings. "There's a lot of road and mountain damage."

The section of Kalaniana'ole Highway that leads to Kailua also was partially blocked yesterday by landslides next to the Kailua-bound lanes near Kapa'a Quarry Road. During the afternoon, sections of Kamehameha Highway in Waikane and Sunset Beach were closed temporarily because of rising flood waters.

In Kalihi Valley, a chunk of backyard broke off into Kalihi Stream from Camilo and Celestina Villanueva's home at 2600 Kalihi Street.

Celestina Villanueva said it may have occurred sometime Saturday but she wasn't aware of it until yesterday, after neighbors on the other side of the stream on Jennie Street called 911 to report it.

"I'm so nervous right now, I cannot sleep. This is like a nightmare. I don't know what to do," Celestina said. "It's caused by the rain because the current of the stream is so strong."

Cummings of Civil Defense estimated that an amount of dirt and rocks equivalent to five to six dump truck loads had fallen into the stream.

A tree fell on an electrical transmission line in the Sunset Beach area about 3:30 p.m., knocking out power to about 270 customers, said Jose Dizon, spokesman for Hawaiian Electric Co. Power was restored at 9:35 p.m.

On Kaua'i, Hanalei Bridge was closed at about 7 last night because of flooded conditions. Water in the area was receding but the bridge remained closed late last night.

Reach Mike Gordon at mgordon@honoluluadvertiser.com and Rod Ohira at rohira@honoluluadvertiser.com.