The latest report from the Army Corps of Engineers recommends upgrading the barrier's electrical system, but says the structure "is generally in good shape."

01:00 AM EDT on Sunday, July 16, 2006

BY BRUCE LANDIS
Journal Staff Writer

PROVIDENCE -- If a major hurricane threatens the East Coast this summer, images from the Hurricane of 1938 will come to mind -- downtown Providence flooded, street cars stalled with water up to their windows.

And the question will arise: will the Fox Point Hurricane Barrier -- dedicated in 1966 to keep downtown from going under water -- protect the city?

This season, officials say, after $3 million in repairs, the barrier's five massive pumps are ready to run and the convex steel gates, intended to keep a storm surge out of downtown, will open and close properly. The hurricane barrier could fail if it loses electric power, something National Grid, the utility company that supplies most of the state, says is possible but unlikely.

The report from the Army Corps of Engineers' last inspection, in December, made some recommendations, notably an upgrade for the barrier's electrical system, but said the structure "is generally in good shape."

The barrier is a single structure at the mouth of the Providence River, but it consists of two elements, one for each of the threats a hurricane presents to the city's downtown -- flooding from a storm surge or from rainwater backed up behind the barrier.

The most visible element is the barrier itself, a massive 25-foot-tall dam across the river, with dikes extending on the shore to higher ground on both sides of the river. In a storm, the gates close three 40-foot-wide openings that normally let boats in and river water out.

The half-mile of barrier and dikes is intended to keep a storm surge of up to 20.5 feet from continuing up the river and flooding an estimated 280 acres of the city.

A storm surge is the bulge of water, created by a hurricane's winds and the low pressure accompanying it, that could be driven up Narragansett Bay. The surge from the Hurricane of 1938 was estimated at 15.7 feet. The one during Hurricane Carol, which swamped the downtown again in 1954, was estimated at 14.5 feet.

Where roads, such as Allens Avenue, cut through the dikes, steel gates will be closed to block the water. Other gates are underground, to keep flood water from backing up through storm sewers into the city.

Will it work?

The Army Corps of Engineers, which inspects the barrier twice a year, thinks there's little reason to expect the barrier to fail. "It was a very conservatively designed project," said James Law, a civil engineer with the Corps' New England District. He referred to both its height, to contain an enormous surge of salt water, and its pumping capacity. He said that the barrier was designed to hold back and pump enormous amounts of water well beyond what could be expected during a hurricane.

The pumps are needed because when the gates are closed, the river's flow backs up behind them.

Inside the pump house, the raised western end of the barrier, are five 55-foot-tall pumps. Together, they can pump an extraordinary amount of water -- more than 3.1 million gallons per minute -- out of the river inside the barrier, and eject it into the harbor outside the barrier.

The barrier has been used to keep the river higher during low tides, for the benefit of WaterFire Providence, and during the filming of an episode of the TV show Providence.

Hurricanes are usually accompanied by a deluge of rain, adding enormously to the runoff from the watershed feeding the Providence River. While the barrier is blocking the storm surge from the south, the pumps are needed to keep the rainwater runoff from flooding Providence from the other direction.

The five pumps are mounted vertically, each with a 4,500-horsepower electric motor on top turning a drive shaft reaching down to the bottom of the pump, where it turns a propeller-like impeller. That drives the water up the cylindrical pump shaft, over the top of the barrier and into the Bay.

The operating principle is pretty simple, the way City Public Works Director John D. Nickelson explains it. Tide gauges in the pump house measure the water level inside and outside the barrier. The idea is to keep the water level inside the barrier "not too high, not too low."

When it rises, he said, "you turn on a pump. When the water comes up some more, you turn on another pump."

The amount of water to be pumped, and for how long, would depend on the interaction of many variables, including the timing of the storm surge, the timing and amount of the rain and the timing of high tide.

The surge and heavy runoff coinciding would put the maximum strain on the system. If the rain and storm surge came at different times, little or no pumping might be needed. If a surge occurred at low tide, the resulting water level would be from 3.5 to 5 feet lower than at high tide.

Law said it isn't known how much changes since the barrier was designed, such as increased runoff due to development in the watershed, would increase the river's flow.

But he said that the barrier's conservative design makes it unlikely that Nickelson's staff would ever need to use all five pumps. In fact, three pumps would probably do the trick, he thinks.

Many of the sporadic reports over the years that some pumps weren't ready for the next storm were prompted by a lack of regular maintenance and repairs. Law said that many of the problems stemmed from overheated bearings.

The pumps bearings have periodically overheated, but Law said the problem has apparently been cured by adding a water-cooling system and a better method for distributing grease to the top bearings.

The city also replaced the impeller in Pump 3, at a cost of about $400,000.

IF THE BARRIER holds up and the pumps run, the remaining critical element is electricity, enormous amounts of it -- so much that officials say providing backup generators isn't practical.

That leaves National Grid, which supplies power through two underground feeds from its nearby Franklin Square substation.

Ordinarily, one feed supplies two pumps and the other feed supplies the other three pumps. But Nickelson said that in a pinch, the pumps can all run off one feed.

The barrier is next to the Manchester Street Station, a power plant operated by Dominion Resources, and is so close that the pump house is longer than the distance to the generating plant's nearest smoke stack. But that doesn't help ensure the barrier's power supply. The two aren't connected.

The plant feeds the regional power grid, not local users, said Edward Paluch, manager of operation planning for National Grid. If there is a massive regional power failure, he said, the generating plants fail, too, and have to be restarted, a time-consuming and complicated job. That would leave the grid unavailable and the barrier -- and everything else -- without power.

But that sort of cascading power failure usually happens at times of peak demand, such as when every air conditioner is running, not during a hurricane, Paluch said.

A hurricane could damage the power-distribution system, cutting off power to the substation, or damage the substation itself, Paluch said.

In September 1999, an explosion at the substation cut off power to the Hurricane Barrier for eight minutes. The same explosion contributed to a lengthy power failure at Rhode Island Hospital, during which an elderly man in a critical-care unit died.

Three high-voltage lines feed the Franklin Square substation, Paluch said: one from the East Bay on the big towers that cross India Point Park, another line underground from Johnston, and a third from Woonsocket.

But again, failure isn't likely. "It would truly take a catastrophic event at that substation to knock it out," Paluch said. "I don't think that station has gone down in the past 15 or 20 years."

blandis@projo.com / (401) 277-7487