Cofferdams in one form or another have been around for quite some time. Of course, centuries ago, they were not made of vinyl or geosynthetic materials. In 539 BC, King Cyrus of Persia used earthen cofferdams to divert the Euphrates River temporarily. By using this tactic, his armies were able to capture the city of Babylon and expand the territory he ruled.
Cofferdams of various materials were used by the Romans and by Napoleon’s troops. Although they were made differently, the reasons for their use were essentially the same as today’s: to move water out of the way for a time while work is done, then let the water return to where it was.
One recent project took place in Michigan. In early summer 2015, R.L. Morris & Sons Construction Co. of Kalkaska, MI, repaired a natural gas line for its client Consumers Energy Co. of Jackson, MI. The project was in Grand Blanc, MI, and work lasted for about three weeks.
R.L. Morris & Sons specializes in gas pipeline projects. The company works primarily in Michigan, doing such work as construction, repair, and replacement of valves, meters, regulator and compression stations, and gas lines.
Consumers Energy provides natural gas and electricity to 6.6 million of Michigan’s 10 million residents. It serves customers in all 68 of the state’s Lower Peninsula counties. The energy company runs a million-dollar smart tool with a sensor into its pipelines to check for the integrity of the pipes. The tool senses even small cracks, corrosion, wrinkles, or dents in the metal, explains Tyler Morris, vice president of R.L. Morris & Sons.
“If any of these anomalies are found, the gas company wants them repaired right away,” he says. “There was just a little bit of corrosion in the line [at this site], but the company didn’t want to take risks in a high-consequence area near homes.”
This particular gas line extends for about 20 miles. Two hundred feet of the line had to be replaced.
The pipe to be replaced “was 80 feet long in one spot and 110 feet in another separate spot,” says Matt Besaw, project manager with R.L. Morris & Sons.
A big component of the project was a cofferdam made by Dam-It Dams of Grand Blanc, MI. The cofferdam was 8 feet tall and 520 feet long.
At first, Morris wasn’t sure that the cofferdam would work on this project. He met with Jack Nichols, the CEO of Dam-It Dams, to discuss details of the project. “Jack said, ‘I’ve done these [types of projects] before. It will work,’” recalls Morris.
After thinking about the project, Morris says, he “took a risk. I said I would not charge Consumers Energy if the cofferdam didn’t work.”
That decision put considerable pressure on Morris and his team. “If it hadn’t worked out, I would have had to pay $200 a foot, and the cofferdam ran for 500 feet. But we were successful, and Consumers paid for the cofferdam.”
“We moved 30 million gallons of water,” says Besaw. “That took three to four days. Then a huge rainstorm hit and filled one-fourth of the site. It took another two to three days to dewater the area again.”
The work area under which the pipeline was buried occupied about one-third of the site. The water was moved over to the remaining two-thirds section.
“We were working in the bottom of a stormwater detention pond [that held drainage from nearby homes] at the low spot of the area. The pipe was four to five feet deep in the pond, and the deepest part of the pond was about five to six feet,” says Morris. “We saw lots of catfish and turtles.”
“We were doing five or six projects in the same area at the same time. We had a crew of about 30 men, but the number of workers at each site varied from day to day,” explains Besaw. “We had a setup crew, a digging crew, a welding crew, a backfill crew, and a restoration crew all rotating through each project.”
Access to the actual work area was a challenge. Even after dewatering, the area was too soft to dig.
“We had to make a road [for the equipment],” recalls Morris. “We used timber mats that were 16 feet long by four feet wide by eight inches thick. Usually, people use sheet piling on each side of the pipe. We had the timber mats on top, across the sheeting, holding the machines up.”
The timber mats created a road about 2,000 feet long, which protected the ground from erosion as the heavy machines traveled over it.
Other erosion control measures used on the project included straw bales and silt fences. Pumps were put in containment units. Kiddie pools and plastic containers kept gasoline from being spilled into the water.
“We pumped the water through a filter bag, so we were controlling sediment before the water went through a silt fence and then back into the pond,” says Morris.
“We’ve done maybe a dozen projects using Dam-It Dams,” says Besaw. “We’ve always had good luck with them. Their product seems to be top notch for us.”
Morris agrees. “We use these dams all the time. We’re using one redoing the marina on Torch River, in my town. They’re a safe, environmentally friendly way to block the water off. Cofferdams are an amazing innovation.”
Morris notes that the dams can often be reused. “The first few times we destroyed them, trying to roll them back up, but now we know how to roll them up safely.”
This project is just one example of the strong working relationship between R.L. Morris & Sons and the energy supply company. Morris says that his family’s firm “just completed our 1,000th dig for Consumers Energy in the last five years. They sent us a thank you note.”
Removing the Bradford Dam
Work to remove the Bradford Dam on the Pawcatuck River in Bradford, RI, began in July 2017. It was expected to last until just before winter weather set in. Final restoration work and revegetation of the cleared area will take place during spring 2018. The site will then be back to something close to its pre-dam state.
The Pawcatuck River runs for about 34 miles. The Bradford Dam removal project is part of a larger effort to enhance migratory fish passage from Little Narragansett Bay to Worden’s Pond in South Kingston.
Like many dams, the Bradford was constructed in the mid-1800s to harness water power. A mill to grind grain into flour was built adjacent to the dam. The mill hasn’t been active for years, but it will be restored and preserved for its historic value.
The Bradford Dam was 6 feet high and 200 feet wide. To demolish it, a 10-foot-wide bypass channel was created first. Demolition and restoration are being done by Sumco Eco-Contracting of Salem, MA. Engineering assistance was provided by Fuss & O’Neill of Providence, RI.
The purpose of removing the Bradford Dam was to improve access to upstream spawning areas for fish. Because the dam was in such bad condition, the risk of its collapsing—potentially causing major flooding during a storm—was another reason for its removal.
The fish are not game fish for people to catch and eat, but rather baitfish. The native species here include alewife, river herring, American shad, American eel, and sea-run trout. When the numbers of baitfish are increased, more food is available for game fish, increasing their population.
Improving the fishes’ access to spawning areas required constructing a fish ladder they could use to travel upstream. A series of weirs, channels, and pools formed by locally sourced natural boulders form the ladder.
The major challenge on the project has been “as always, dealing with the river,” says Steve Fuller, team leader for Sumco Eco-Contracting.
A second challenge was a tight window of time in which to work. Fuller says that the crew “mobilized onsite the first of June and set up access. We were not allowed to be in the water until July 1.”
Weather posed another potential challenge. A late summer hurricane threatened, so “we started our emergency plan. We were prepared to flood the site and secure it,” recalls Fuller. “We’d flood the site ourselves and drop the cofferdams to allow the river to come through,” but that step turned out to be unnecessary; fortunately the hurricane veered away, causing only a scare.
“The job, on the whole, has gone well,” says Fuller. “The problems have been small, everyday ones, such as finding the right stone. It’s a water diversion that not only acts well, but looks good.”
To hold the river back from the work site, two Portadam cofferdams totaling 500 feet in length were used on the project. The upstream Portadam was placed in 9 feet of water. The downstream Portadam was in 3 feet of water.
The company has used Portadams before, Fuller says. “Portadam in the right application is the best product for temporary water removal in up to 10 feet of water. We use Portadam on 20 to 30 percent of our jobs.”
He adds that each choice must be matched to the specific job, taking into account such factors as “water depth and what’s underneath the water.”
Sumco arranged for Portadam’s crew to install the cofferdams and to remove them. “Portadam is both a sub and a supplier for us,” says Fuller. “They’re very responsive to our questions. They get into the water and see for themselves before they make a recommendation.”
Fuller characterizes the Bradford Dam removal project as “a design-build. We worked with the engineers to come up with something that would work well. I recommended Portadam and met with Portadam employees several times to evaluate the project.”
Working with the cofferdam involved three phases. The first, which took about a week, involved installing the Portadam to hold back the Pawcatuck River while the temporary bypass was being constructed.
The second phase of work was removing the cofferdam from the bypass channel, opening it so that the river was flowing through it. Then the cofferdam was set up to block the river and bypass channel from the work area. This phase took four days to accomplish.
The final phase will take place near the end of the project. The bypass channel will be closed back off and filled in, and the cofferdam will be removed so that the river is back in its natural path. This third phase will take about a week.
Fuller says that fishing within 150 feet of a fish ladder is prohibited, but water travel is permitted. When the project is finished, kayakers and canoeists will still have to portage their watercraft. However, their portage path will be shorter and more easily accessible.
The cost of this project was about $1.8 million. Of that amount, $821,000 came from federal Superstorm Sandy recovery funds. The rest was raised by the Nature Conservancy from several foundations and other sources.
The US Fish and Wildlife Service partnered with the Nature Conservancy on the project. Other partners include the Rhode Island Coastal Resources Management Council, the Rhode Island Department of Environmental Management, the National Oceanic and Atmospheric Administration, the US Army Corps of Engineers, the Wood-Pawcatuck Watershed Association, and the Rhode Island Coastal and Estuary Habitat Restoration Fund.
“The public support is one of the best things about this job,” says Fuller. “There is a bridge just upstream of the dam. Everyday working people, not just members of environmental groups, pull over in their cars and stop to watch the work.”
Saving Water, Saving Energy
The Sweeney-McCune Creek Outflow Recovery and Automation Project is located near Dixon, CA, in an unincorporated rural area of Solano County. The approximately 3-acre site is at the confluence of Sweeney and McCune Creeks.
The two creeks currently supply about 32,000 acre-feet of water per year, used by area landowners for agricultural irrigation. This US Bureau of Reclamation project is being done for the Solano Irrigation District. Its purpose is to retain irrigation tail water or unused irrigation runoff. This surface water will then be available for later redistribution to the irrigation district’s customers. The project will help the Solano Irrigation District in its effort to conserve water. The district’s goal is to conserve 12,360 acre-feet of water each year.
The project will lead to more efficient water usage for the district’s landowner customers, who will begin using drip and micro-sprinkler systems to irrigate their land with the reclaimed water when the next growing season begins.
A third benefit from the project will be the improvement of the district’s management of its water resources. This benefit will occur via more accurate measurement of the disbursement of water.
A Supervisory Control and Data Acquisition (SCADA) system will manage automatically controlled discharge gates. The system will measure flow where water savings are not presently quantifiable.
The project will also help the Solano Irrigation District save energy. With the reclaimed water available to supply to its customers, the district will not have to use as much energy to draw water from its deep groundwater wells.
To achieve the project’s goal of retaining irrigation tail water for the district, Shimmick Construction of Oakland, CA, is installing a long-crested weir. This concrete weir will have walls that are 8 feet tall. Other essential components of the project include integrated flume meters, the SCADA system, and four automated discharge steel gates within the channels.
“Without this structure, a downstream water company would take the water,” explains Tyler Shell, project manager for Shimmick Construction.
The part of the weir that lies within Sweeney Creek is about 139 feet by 57 feet long. The part of the weir within McCune Creek is approximately 72 feet by 59 feet long. The weir is designed and constructed so that any drainage that occurs during the non-irrigation season will pass through or across it. Excavation depth is 7.5 feet.
Shell says challenges on the project include high groundwater; in addition, “Accessibility is very difficult. We have to sequence our work differently because primarily we work in the creek.”
As for the weather being a factor, he says, “Whatever the weather brings, that’s what we’ll deal with. We always hope we don’t get a lot of rain.”
Dewatering the work area required installation of two cofferdams from Aqua Dam Inc. of Scotia, CA. One AquaDam is 10 feet tall by 21 feet wide by 90 feet long. The other is 10 feet tall by 21 feet wide by 85 feet long.
“It took two days to get them installed,” says Shell. “I was surprised at how fast they filled with water and dewatered the site.”
Water within the channels will bypass the dewatered area through HDPE gravity pipelines. In Sweeney Creek, the drainpipe beneath the AquaDam is 42 inches in diameter. In McCune Creek, the pipe under the AquaDam is 36 inches in diameter.
Although this was the first time that Shell has used AquaDams, he says, “They definitely go through and do exactly what you want them to do. They retain the water. They’re a good alternative to driving sheet piles in an environmentally sensitive area.”
Other erosion control measures used on the project include silt fencing and orange ESA fencing to mark environmentally sensitive areas. Straw wattles surround the stockpiles of equipment. More covering will be added as the chances of rain increase. The covering also keeps out wildlife.
“We’re in California, so we are used to using lots of BMPs and measures to protect the environment,” notes Shell.
The last part of the project will be revegetating the site. “All areas will be revegetated before we leave the site,” he says. “We’ll use a hydroseed mix that the owner chose, with grasses native to the area.”
Total estimated cost of the project is $1.6 million. It is partially funded by the US Bureau of Reclamation Assistance Agreement. Local funding came primarily from the Solano Irrigation District.
As these three different projects show, cofferdams work well for a variety of projects where water needs to be removed temporarily from a work site, often saving time and money. With increasing federal, state, and local regulations to make sure that the environment is protected, cofferdams offer erosion control specialists an obvious solution in many applications.