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Dam blasting set for Wednesday to sound like boom of 20 cannons

One hundred and thirty years of industrial history is about to open like a flood gate.

An explosion tentatively set for 3 p.m. Wednesday is to fracture a granite stone and masonry dam that has stood across the Chattahoochee River since 1882, when upon its completion the Sunday Enquirer newspaper called it “the largest granite dam in the South” and boasted, “It is fully accomplished and generations yet to come will see its durability.”

Some will see the durability of the Eagle & Phenix dam as Wednesday’s blast loosens its dense granite so the heavy stone crumples into the stream. Fragments may be propelled into the air, from whence they could plummet upon bystanders, were any allowed to stand by.

Columbus police Capt. J.D. Hawk, who’s heading security for this event, warns motorists frequenting downtown Columbus that at any time between 2 and 4 p.m., Front Avenue and the 13th Street river bridge could be shut down for 30-40 minutes.

Officers will sweep the streets and both the Columbus and Phenix City riverwalks for pedestrians, east and west clearing safety zones from Broad Street in Phenix City and Broadway in Columbus to the river’s edge. Broadway and Broad Street will remain open, Hawk said.

In Columbus, Front Avenue and Bay Avenue will be swept clear and closed down, from 14th Street to Dillingham Street. Hawk notes drivers with vehicles parked along those avenues won’t be able to leave during the blast time. If they want to travel between 2 and 4 p.m. that day, they should park outside the safety zone.

Along with Columbus and Phenix City police on the streets, Coast Guard and Georgia Department of Natural Resources officers will be out on the river to ensure no one fishing or boating goes into the blast area, Hawk said. A police helicopter will be overhead.

“In addition, the police helicopter will have infrared, and it will be flying over and checking to see if anybody might be hiding,” said Newt Aaron whose Aaron & Associates firm is managing the whitewater project for which the dam is being breached.

If anyone ventures into the cleared safety zone, the work will stop until the intruder is removed, Hawk said.

Uptown Columbus Inc. is arranging a safe viewing area in Woodruff Park, at 10th Street and Bay Avenue behind the Columbus State University Theatre Complex. Uptown Columbus President Richard Bishop suggests spectators park in the RiverCenter parking garage and walk. Signs will direct them to the viewing area, he said.

The blast

When completed in October 1882, the Eagle & Phenix dam was a formidable structure. The Sunday Enquirer put its length at 1,009 feet, its width 17 feet at the base and 15 feet above that.

“The height of the dam above the river bed is various, owing to the inequalities of the granite rock upon which it is built, ranging from 16 to 27 feet high,” the newspaper reported.

Today it is not its former self. Voids became apparent when water recently was diverted through the Eagle & Phenix powerhouse, Aaron said. Water started leaking through the dam’s downstream face.

“After they did drilling for the explosives, it seemed to tie some of those voids together and even more leaks sprang out,” Aaron said.

The Scott Bridge Company of Opelika, Ala., has drilled about 100 vertical holes through the dam from the top down. The bottom half of each will be packed with 2-inch sticks of dynamite, topped with a 2- to 3-foot layer of crushed gravel, and then more dynamite.

That layering puts most of the explosive power at the dam’s base, where it’s most needed, said Stephen Summers and Charles Davis of the Scott Bridge Company. Summers is the construction firm’s senior project manager. Davis is its vice president over engineering.

They anticipate this:

The explosion will be like a chain reaction, with 20 milliseconds between each tunnel blast. The effect is that one blast blows a gap that the next explosion widens, and the one after that widens both, similar to a zipper coming undone. This makes the most of the energy being expended, and it reduces the risk of flying rock that could result from an instant burst.

Further cutting that risk will be a blanket of heavy silt screen, reinforced with sections of chain link fence, that will cover the dam’s blast site. This first breach is to be 50 feet long, with the intent of creating a channel that drains half the dam’s backwater, narrowing the river.

Pressed by the river, the big rocks in the dam are expected to topple like blocks. Because of all the precautions, viewers needn’t expect to see a spectacular, action-movie eruption of debris, which would be dangerous.

But they can anticipate a boom that sounds like 20 cannons fired at once, the sound waves reverberating off the riverbanks.

Some flying debris still is possible within about a quarter-mile of the blast site. The designated viewing area at the end of 10th Street is more than a third of a mile away.

The aftermath

After the blast, crews will use heavy equipment to remove the rock and other debris. Then they’ll get ready for the next breach.

That could be as soon as next Sunday, when the same safety precautions would be taken as the Scott Bridge Company fractures a larger section of dam, about 75 feet.

Between the two gaps will be left standing about 100 feet of dam that, once isolated, can be removed through heavy equipment alone.

All of that work will be west of a concrete berm the company built in the riverbed to divert water from where they sculpted rapids near the Alabama bank.

Still left after that will be a section of dam on the Georgia side, adjacent to the Eagle & Phenix powerhouse and Columbus’ Chattahoochee RiverWalk. The breach on the Alabama side will so narrow the river that crews can install a service road along the eastern bank from a staging area at 14th Street, bring in equipment and start sculpting whitewater rapids for the river’s eastern channel.

That last section of dam is to be removed only with heavy equipment. Left on either side of the river will be wings of the former dam, each about 45 feet long, so that future generations can imagine what used to be.

The engineering

The explosive that’s to destroy the dam is the same used to build it: An estimated 3,000 pounds of dynamite went into the construction, said the 1882 Enquirer: “On some occasions as much as 75 to 90 pounds of dynamite was thus simultaneously discharged causing the whole earth in the city to tremble with the upheaval.”

Other tools were more primitive: Steam rock drills bored holes into the granite for dynamite, and sometimes hand drills were used. Eight boom derricks, each about 50 feet tall, together employing about 5,400 feet of wire rope for guy lines, were used to haul granite. A railroad track across the dam’s crest took three cars, each hauling about 2 tons of mortar, to where the granite blocks, each with a weight of 185 pounds per cubic foot, were sealed in place. More than a million tons of granite, 4,800 barrels of cement and 1,200 barrels of lime went into the dam, which took 250 workers to build.

Holes drilled into the bedrock were used to anchor guy wires for the boom derricks, precursors to modern-day cranes. “We found lots of pins, iron pins and drilled holes in the bedrock below there,” said Aaron. The pins anchored the wires.

Built to withstand floods that continually blew out early wood dams, the stone dam was designed, and its construction supervised, by John Hill, a gifted engineer who also designed and specially ordered equipment to fit Eagle & Phenix Mill No. 3. That’s the 19th century mill complex’s southernmost building, the one now remodeled into loft apartments -- where residents Wednesday will be warned to stay off their balconies as Hill’s dam is reduced to rubble.

Davis, the Scott Bridge engineering vice president, said the old dam remains a striking piece of industrial-age construction:

“It’s very impressive when you consider the tools that the men had at their disposal to build that back in that time,” he said.

Over the years the company has done a lot of demolition, at times undoing what took considerable effort to achieve decades ago.

“It’s always a solemn event,” Davis said, “because you’re undoing the work, the hard work, of a lot of good men.”