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Reservoir to Include State’s Highest Non-Federal Dam

Mon February 12, 2007 - Southeast Edition
James A. Budd

Two government agencies have teamed up in the Atlanta area to build a $36 million, 411-acre (166 ha) reservoir that will help bolster water supplies needed for two booming metro counties already approaching a combined population of 1 million residents.

The Hickory Log Creek Reservoir near Canton, Ga., will feature a huge roller-compacted concrete (RCC) dam towering 180 ft. (55 m) high and stretching 980 ft. (299 m) across a rocky ravine.

The reservoir and dam, touted as the highest non-federal dam in Georgia, is expected to help meet the water needs of the area until the year 2050.

The impoundment will allow removal of up to 44 million gal. (166.5 million L) of water a day (mgd) for use by the city of Canton and the Cobb County-Marietta Water Authority (CCMWA) which will share 25 percent and 75 percent of the total cost, respectively.

Canton is the county seat of Cherokee County, which has a population of approximately 200,000. The city of Canton grew from 7,709 residents in 2000 to 17,685 in 2005, according to U.S. Census figures. CCMWA is the primary supplier of water in Cobb County, located just southwest of Cherokee County, and has a population of 654,900, according to U.S. Census figures.

Canton City Manager Bill Werner said both the city and county have experienced a tremendous rate of growth recently and a corporate campus-type technology park under development near the reservoir is expected to lure thousands of workers to the area. Cherokee County government also is planning to construct administrative buildings and a convention center nearby. Massive residential developments also are sprouting up in the vicinity.

“This project takes us out to 2050 to meet the water needs of the area,” said Werner. “It has been a very effective partnership with Cobb County-Marietta Water Authority.”

Once completed, the city planned to build a recreation area at the reservoir that will include fishing, picnicking and the use of self-propelled watercraft such as canoes.

“We’re working on plans for the park right now,” he said.

A pump station, which will be built for an additional $15.5 million under a separate contract, will be used to draw water from the nearby Etowah River to help fill the reservoir and allow release of water from the reservoir into the river for treatment at a water treatment plant located downstream.

A combination of 72-, 42- and 32-in (183, 107 and 81 cm) pipe — along with smaller piping — will be used for the project.

The Etowah River and the Chattahoochee River are the two major sources of drinking water for the entire metro Atlanta area and much of northern Georgia.

Thalle Construction Company Inc. of Hillsborough, N.C., was awarded a $36 million contract for construction of the second phase, according to Rick. T. Miller, Phase II project manager of Thalle. Brown and Caldwell of Atlanta and Schnabel Engineering Inc. of Alpharetta, Ga., are engineers of the project.

Phase II Gears Up

Construction of the Hickory Creek Dam project, which started in summer 2006 and is expected to be completed in November 2007, includes two phases. After the dam is completed later this year, officials said it will take approximately one year to fill the reservoir.

Phase I, which has been finished, entailed the prep work and required the clearing and grubbing of 36 acres (15 ha), removal of 200,000 cu. yds. (153,000 cu m) of earth and blasting approximately 10,000 cu. yds. (7,600 cu m) of rock. Phase II involves the actual construction of the dam and auxiliary facilities.

ASI Constructors Inc. of Pueblo West, Colo., is the contractor for mixing and placing the RCC, which will be manufactured at an on-site pugmill. More than 235,000 cu. yds. (180,000 cu m) of RCC, which is a dry mixture that includes aggregate, cement, No. 4 stone and fly ash, will be used for construction of the dam, according to Miller. Rotec Inc. headed up construction and operation of the massive conveyor system that is transporting the RCC from the pugmill to the actual dam site.

The Rotec conveyor is 950 ft. (290 m) in length to the right abutment of the dam and a lateral conveyor travels another 800 ft. (240 m) from the right abutment to the left abutment, Miller said.

A Manitowoc 888 230-ton (209 t) lattice-boom crawler crane is already on site and has begun lifting the first of 1,500 pre-fabricated concrete lateral face panels to their location on the dam wall. A Liebherr 1100 120-ton (109 t) crawler utility crane also is on site and will be used at the top of the reservoir in latter stages. A Manitowoc 4100 is expected to arrive on site shortly and also will be used for lifting panels.

The pre-cast concrete panels with Carpi liner are being manufactured on site by a subcontractor, Mike Johnson of Johnson Poured Walls of Canton, Ga.

A Soosan SD 1300E boom-extension crawler rock drill is drilling 4-, 5-, and 6 in. (10, 13 and 15 cm) bores for gallery drains and piezometers.

Other equipment includes a fleet of Volvo A35D off-road trucks used to transport a massive amount of on-site materials. Cat 950 wheel loaders, Cat 267 skid steers and Kawasaki 95ZV and 85ZV loaders also are used extensively to haul materials.

Approximately 450 tons (408 t) of rebar will supply the project, along with 217 linear ft. (66 m) of 72-in. (183 cm) pipe; 1,440 linear ft. (440 m) of 42-in. (101 cm) pipe; 36 linear ft. (11 m) of 32-in. (81 cm) pipe; 182 linear ft. (55 m) of 16-in. (41 cm); and 373 linear ft. (114 m) of 8-in. (20 cm) pipe.

Approximately 150 workers are employed on the project, including 65 workers and technicians from Thalle, 50 from ASI and 12 from Rotec, said Miller.

Work will soon be stepped up as RCC is placed at a rapid pace.

“We are getting in the phase of this project where we will be running RCC 20 hours a day,” Miller said. “Our intent is to run all the RCC by May so we don’t get into warm weather and have to refrigerate the RCC. Our goal is to place it in cool weather.”

Miller, who returned from Iraq last summer after serving as a U.S. Department of Defense engineering manager for two years, said the rough terrain of the project has caused a few problems because space is limited.

“The critical path of the job for the past few months has been mobilization and procurement,” he said.

In addition to the ASI pugmill for manufacturing of the RCC, Thalle has its own batch plant to make conventional concrete for different aspects of the project. More than 100,000 cu. yds. (76,000 cu m) of aggregate has been stockpiled on jobsite.

“We are having to schedule the materials as we go along,” Miller said. “Space is at a real premium.”

A nearby plant operated by LaFarge is supplying aggregate for the RCC and concrete.

“We keep 18 to 30 dump trucks running six days a week to the quarry,” said Miller, adding each truck will haul approximately 200 tons (181 t) a day.

“We will use about 4,000 cubic yards to 6,000 cubic yards a day of RCC when we go on a double shift [at the end of January] so it will be needed,” Miller said.

An interesting part of the project, he said, is the installation of bi-directional flow piping draw water from the Etowah River and release water into the river.

Hickory Log Creek, a tributary of the Etowah, doesn’t have the capacity to fill the reservoir. A 42-in. (107 cm) line will link the reservoir to the Etowah River.

A 42-in. (107 cm) riser is being installed in the face of the dam, which ties into the 72-in. (183 cm) pipe that terminates at the spillway valve vault, where it is reduced from 72 to 42 to 30 in. (183 to 107 to 76 cm) at the ring jet valve. There is a 42-in. (107 cm) tee before the ring jet valve and the bi-direction 42-in. pipe ties in and is routed downstream.

“The permanent 72-inch pipe runs from the face of the dam to the valve vault,” said Miller. “At this time only 140-feet of permanent 72-inch pipe has been installed. We have a temporary 72-inch corrugated pipe tied into the permanent as water control during dam construction.”

W. Mark Harber, an engineer of Brown and Caldwell, said the pump storage system incorporated at the facility will allow both the city and the CCMWA to pull more water out of the Etowah River basin that includes Lake Allatoona just downstream from Canton.

“They will be able to withdraw more water from Lake Allatoona than they would have been permitted [by EPD] to remove because of the reservoir,” he said. “Neither entity needs the water now, but it will be needed for the city’s growth.”

To facilitate the construction, a cofferdam will be built on the north side of the Etowah River, giving workers a dry environment to excavate part of the riverbed for the raw water intake. The cofferdam will extend approximately one-third of the way into the river so the flow won’t be stopped. A tunnel will connect the intake to the pump station and then a 42-in. diameter pipe, approximately 1-mi. (1.6 km) long, will connect the pump station to the reservoir.

Harber said the project has proceeded at a good pace and communication is a key to ensuring a smooth operation.

“From my perspective, there hasn’t been any surprises or issues,” he said. “The key is communication.”

Keeping an Eye on El Nino

An unusual weather pattern created by an El Nino event in the Pacific has been blamed for keeping rainy weather in northern Georgia for much of the late fall and early winter.

The frequent rains have forced crews into a contingency plan to move equipment and extensively clean the area where the concrete will meet the bedrock of the earth.

“We’ve had to clean up a lot every time it rains,” Miller said. “You want a good clean seal. You can’t have any weak points at the base of this dam. You have to get everything right and make sure all silt and organic materials are removed so you get a good base. All of us watch the radar.”

If weather reports indicate more than a half-inch of rain, crews move equipment and once it’s over, the clean up begins.

After the wall gets up approximately 930-ft. (280 m) above sea level, Miller said he will sleep easier because weather won’t be as much of a factor.

“After the dam hits 930 feet we will be okay if there is a flood,” he said. “In the meantime, we are watching the radar.”

Approximately 3 to 5 ft. (0.9 to 1.5 m) in height each is expected to be added and rolled by vibratory equipment.

“We want to get away from using articulated trucks and want to use conveyors and rollers,” he said. CEG

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