The Falls Lake dam itself is sound and can be made even safer, according to the engineers who run it. But if it ever ruptured because of a structural failure, extraordinarily high water or sabotage, the result would be cataclysmic.

Because of that, Falls Lake's dam recently scored a middle safety rating of "conditionally unsafe."

"You can never discount the possibility of a failure," said Wayne Bissette, chief of engineering for the U.S. Army Corps of Engineers' Wilmington District, which manages the lake.

Falls Lake has been a godsend since its construction 25 years ago. The 28-mile-long federal reservoir north of Raleigh provides the Capital City's drinking water, keeps the Neuse River flowing healthily, enhances recreation, and has prevented more than half a billion dollars in flood damage downstream.

But the federal engineers who manage the lake now are warning of an unlikely but conceivable catastrophe: If the lake's earthen dam ever burst, a freshwater tsunami would swamp the Neuse River valley from North Raleigh to Kinston, blasting away bridges, obliterating riverside homes, inundating parts of Smithfield and Goldsboro, and possibly drowning dozens or hundreds of people -- perhaps with no warning.

Continued development along the river, much of it in popular subdivisions with street names reflecting the watercourse's appeal, worsens the danger.

"It's the downstream development that creates a problem," Bissette said. "As long as encroachment on the floodplain continues, there's always the potential for loss of life and economic impact."

Raleigh Mayor Charles Meeker said the warning was news to him.

"I've never heard anything about the Falls Lake dam failing ... " Meeker said. "We haven't been briefed on that."

Martin Chriscoe, Wake County's emergency management director, said he has no study or report of the likely effects of a dam failure and flood.

No one involved has any estimate of the number of homes and businesses in the flood path.

Nor does the corps, Raleigh, or the state plan to buy and clear the Neuse bottomland, local, state, and federal officials said.

"Unless you have a major disaster, it's hard to do," said Doug Hoell, the state's emergency-management director. "In the meantime, people in the floodplain need to have flood insurance."

A threat to bridges, too

At its normal level, Falls Lake holds about 43 billion gallons. If a storm pushed the lake to its spillway height (as almost happened three times in the 1990s) that would constitute about 115 billion gallons. That's about 101 billion gallons more, if dumped in one day, than what causes flooding in adjacent neighborhoods.

Corps officials say that to deter terrorism, they cannot let the public see their map of the likely extent of the inundation. But they say it would extend somewhat beyond a 500-year-storm floodplain, a line state and local governments use for land-use planning.

Such a deluge also would jeopardize at least the 16 highway bridges and three railroad bridges over the Neuse River between the Falls dam and Smithfield, from Falls of Neuse Road at the dam's foot to Interstate 95, about 50 miles downstream.

"I would expect that there would be some bridge failures, but some of them would survive," said Don Idol, the state Department of Transportation's assistant state bridge inspection engineer. "Nothing's 100 percent."

State and local authorities would establish detours, but losing bridges in a catastrophic flood would make it harder to rescue the injured and recover the dead.

Riverfront life

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