ORRINGTON – A large beaver dam in the south part of town let go early Wednesday, releasing a torrent of water that washed out a half-mile stretch of Swetts Pond Road and created a gully at least 10 feet deep at the entrance of Cemetery Road.

The raging water also temporarily submerged a section of Route 15, closing it for several hours, and washed away a section of the Springfield Terminal railroad bed before making its way into the Penobscot River.

The disaster resulted in as much as $1.5 million in damage, according to Town Manager Dexter Johnson. As of midafternoon, he said, portions of the road were cleared and made temporarily passable for emergency vehicles, though it will be rough going until the road can be rebuilt. “We don’t have a million and a half bucks just sitting around here,” Johnson said.

The beaver dam, located in a largely undeveloped area between the Swetts Pond and Hoxie Hill roads, reportedly let go about 5 a.m., sending torrents of water downhill. Town maps created in the 1970s show the pond created by the dam to be between 15 and 20 acres in area, though locals and others familiar with the area estimate it could be three times that size.

Three households – two on the lower end of the Swetts Pond Road and one on the Cemetery Road, were left virtually landlocked. Deep chasms were left where driveways and culverts once were.

While no one was stranded or injured and no homes were destroyed, it could be some time before residents can leave their properties with their vehicles.

Dick Harriman, the town’s tax assessor and code enforcement officer, said Johnson, selectmen, municipal staffers and engineers spent much of the early part of the day in emergency meetings and working with state and federal officials to develop a strategy for repairing the road.

Harriman said the repair work will be costly. “We’re talking major reconstruction,” he said. Town officials also are working on a temporary fix that would enable affected residents to use their temporarily stranded vehicles.

According to longtime residents, Wednesday’s beaver dam failure marked the second time in recent history that Swetts Pond Road, freshly repaved last summer at an estimated cost of $30,000, has washed out.

“Back in 1954 or ’55, we had a hurricane come through that washed out that road,” Gilbert Betts, 75, said. “It’s surprising how far [the water contained by the dam] came down.”

According to Betts, who lives on the river side of Route 15 not far from Swetts Pond Road, some in the neighborhood heard what “sounded like a big jet plane” whooshing by when the dam let loose what he estimated to be 50 or 60 acres of dammed water.

Measurements taken Wednesday morning showed that a 1,300-foot stretch of Swetts Pond Road was completely washed away, and as much as half a mile of the road was badly eroded.

The water carved a large gully, which the town manager said was 20 to 30 feet deep and about 40 yards across, at the entrance of Cemetery Road, cutting a cemetery and one residence off from Swetts Pond Road. Even larger trenches and gullies were seen on lower Swetts Pond Road, which took the brunt of the damage.

Why the dam let go remained unclear Wednesday. Though several theories abounded, most agreed that it was unusual for a beaver dam to fail, unless there were no beavers around to maintain it. Harriman said he had been told that beavers hadn’t been at the dam for the last six months. Some speculated that the beavers that once lived at the dam had been trapped or relocated, while others maintained the beavers had left for lack of food.

“Beavers are better engineers than many people who’ve gone to college,” said Craig Kosobud, a state Department of Transportation crew supervisor assigned to the area.

According to Kosobud, Route 15 was not damaged in the deluge, though it was submerged under as much as 5 to 6 feet of water during the peak of the flood. His estimate was based in part on watermarks left on road signs in the affected area.

Route 15 was closed from the time of the flooding to about 10 a.m., after the water had abated and DOT workers and Orrington volunteer firefighters had had a chance to clean the highway of debris and silt.

According to Cynthia Scarano of Guilford Rail System in North Billerica, Mass., which owns the affected track, rail service between Brewer and Bucksport was expected to be restored Wednesday afternoon or evening. Damage to the railroad track was minimal, with about a 100-foot long stretch of rail bed washed out, but the track itself was intact. The Springfield Terminal track between Bucksport and Brewer typically is used for two trips a day.