Second boulder dam added to Columbia Canal repair plan

A second boulder dam is being built in the Columbia Canal to slow the rush of water that has hampered construction of another dam that is critical to keeping the downtown water treatment plant operating, a city official told The State newspaper Thursday.

Assistant city manager Missy Gentry said a second dam is part of a larger canal repair effort that includes siphoning water out of the damaged canal and the adjoining Broad River to supply the plant. The plant provides drinking water to about 188,000 customers in the capital city and lower Richland County.

“The plant’s not going to run out of water,” Gentry said. “We’re pumping from the canal and running pipes from the river. The lines we’re running to the river will be activated by Saturday. There are no plans to turn Columbia’s water off.”

But repair work to the dike’s breach caused the water to rush too quickly through the damaged part of the canal. A second dam should help slow the water so work can continue, city officials and private contractors decided Thursday.

South Carolina Electric & Gas Co. workers on Thursday afternoon were moving at least one utility pole and dropping power lines near where the second dam is being built, below the Jarvis Klapman Boulevard bridge.

Gentry said completion of either dam is Job One in the overall repair of the canal wall. In addition to filling a 60-foot breach in the canal dike caused Monday by the raging, storm-fed river, teams are dealing with Wednesday’s partial collapse of another part of the dike.

Placing boulders in a dam gets more difficult as it gets closer to spanning the 125-foot canal because water rushes faster in narrow gaps, Gentry said.

In addition to supplying the plant from the river and the canal above the breach, city officials have amped up the Lake Murray water plant, which generally supplies customers north of I-20.

The Lake Murray plant is connected to the downtown plant through a network of pipes, but that plant is not a full substitute for the older plant at downtown’s Riverfront Park, city officials said.

Gentry said she does not know how much of the 40 million gallons being pumped daily now from the lake plant is going to the downtown plant. But the lake plant is pumping 12 million more gallons daily than it did at this time last year, she said.

The downtown plant is pumping almost 11 million more gallons daily than a year ago, Gentry said. But much of that is to offset water loss to breaks in water lines.

Utilities director Joey Jaco said during a news conference Thursday that inspectors have found no other weaknesses in the canal dike. The canal is being inspected twice daily, he said.

The city on Thursday released its first full written report that details damage and response efforts by Columbia and Richland County officials. It’s the first official accounting of locations of broken water lines, lines under repair and areas of town too flooded four days after the deluge to be accessible to repair crews.

Highlights of the report include:

▪ Three locations are still too flooded to make line repairs: near Monticello and Cedar Creek roads, the 4200 block of Shady Lane and Arcadia Lakes Drive off Carys Lake.

▪ Repairs are under way on a 24-inch line on Kay Street, a 300-foot section of Caughman Road in Hazelwood Acres and Dominion Hills neighborhoods off Garners Ferry Road, the 3200 block of Fernandina Road off I-26 and a 10-inch line off Forest Drive between Trenholm and Percival roads.

▪ Water lines as large as 12 inches have been repaired at Trenholm and Rockbridge roads, in Lost Creek/Chestnut Hill Plantation neighborhoods off the Broad River north of Harbison State Forest, Tall Pines Circle off South Beltline Boulevard, and Earlewood and Sunset drives.

▪ Evaluations or repairs of main lines are under way in the Reflections subdivision, Caughman Road, Quail Creek Road, Westwood Avenue and Summerlea Drive.

In other updates from the briefing near the canal work site, city and Richland County officials said a boil water advisory for all customers except some in the Chapin and upper Lake Murray area will remain in force until the water is safe to drink.

Gentry said the first boulder dam is unlikely to be completed Thursday.

She and other city staffers said the use of pumps and pipes to supply the treatment plant has been a back-up plan for several days.

Mayor Steve Benjamin again on Thursday assured customers the water distribution system will be fixed. “The system is running strong,” he said. “There are no plans to shut off the water system – zero plans.”

This story was originally published October 8, 2015 at 12:49 PM.