From On Track Magazine Winter 2016
A Sargent Corporation crew led by superintendent Adam Tenan spent a month at Second Roach Pond last fall replacing a rock dam that had been built too high. The prior dam effectively raised the water level in Second Roach Pond and created unstable conditions in large rainfall events. The dam’s owner (Appalachian Mountain Club) was issued a notice of violation from the Maine Land Use Planning Commission in 2014 and was required to reconstruct the dam to resolve a variety of environmental concerns.
Adam and his crew started demolishing the old dam on September 10 and finished the new dam on October 9, six days ahead of the October 15 environmental deadline for in-water work.
The old dam, which was built in 2014 for the Appalachian Mountain Club, stood three feet above the water level. A hydrological study concluded that even a 100-year flood would not overtop the dam; however, it would result in water flowing around both ends of the dam. The resulting uncontrolled flow of water flanking the dam could have resulted in damage to wetlands and undermined the stability of the Roach River channel.
Additionally, state and federal agencies were concerned about the raised water levels. In particular, their concerns focused on flooding associated with valuable wading bird and waterfowl habitats around the shoreline of Second Roach Pond.
The new dam matched the historic spring water surface levels and also preserved summer levels to protect both the recreational value for canoeing and swimming and the wetlands that the dam creates, while allowing water to flow over the dam naturally.
Many casual observers would not necessarily recognize the new structure as a traditional “dam,” since it was designed and constructed as a “nature-like” rock ramp.
“The new dam looks like a bunch of cobbles strung across Roach Pond,” said project manager John Sturgeon. “That’s what the Appalachian Mountain Club wanted.”
This “nature-like” rock-ramp style has been utilized in a variety of remote locations in Alaska and the Western United States; however, few of these structures have been built in Maine or the Northeast.
The dam includes a small low-flow channel fishway, also made of cobbles but a little deeper, so the fish can pass during periods of low water. The primary spillway, which is the central 70-foot-wide section of the dam, is also roughened with rocks and boulders to provide for passable conditions at high flows. This “nature-like” rock ramp allows for a variety of fish and aquatic species, particularly native brook trout and landlocked salmon, to freely pass across the dam and extend their range across the Roach River and Pond system.
Second Roach Pond is located in northern Piscataquis County, about 28 miles northeast of Greenville. The Roach River below the dam is described as prime nursery habitat for landlocked salmon and brook trout.
The first step was to install some temporary culverts to ensure that there was a constant flow of water to the Roach River while the dam was being reconstructed.
The next step was to put in a coffer dam made of sandbags with a poly cut-off sheet.
“The sandbags were the barrier, but we had to put in the poly to seal off the water,” said Adam. “There were gaps between the sandbags, and the poly provided a solid sheet to keep the water out.”
Installing the coffer dam required Adam and his crew, including laborer David Theriault, to spend a lot of time in the water.
“Placing the sandbags—getting them in and out of the water—the only way to do it was for us to be in the water,” Adam said. “We used waders most of the time, as long as we were only in chest deep. But if we were going in where the water was over chest height, we’d just bring some extra changes of clothes, so we could change into dry clothes when we were done.”
Work on the coffer dam was even more challenging when the streambed was disturbed and the water became dirty.
“When that happened, we couldn’t see what we were doing,” he said. “We had to do it all by feel.”
Getting the coffer dam to work properly and provide a dry work area was another challenge.
“Unfortunately, the coffer dam was not entirely effective as the pond and river bottom consisted of a very gravelly material,” Adam said. “When we pumped down the inside of the coffer dam, which was our work area, the pressure of the water on the outside would blow out the material under the sand bags. This required constant maintenance and a lot of pumps in order to continue working on the dam construction.”
The biggest problem was a pool formed by a rock-crib dam about 800 feet downstream, which kept the water elevation higher than anyone thought it would be.
Because of environmental regulations, no one could do anything about it.
“It was hard for us to get water downstream when water in lower part of stream was so high,” said John.
Eventually, the crew was able to create a work area that was dry enough to excavate the cut-off trench and construct the dam.
The new dam included a 60-mil HDPE liner, similar to a landfill liner, which was placed vertically all the way across the dam to help keep the water going over the dam and not through it.
“The whole purpose of building the coffer dam was to be able to do that work in dry conditions,” Adam said. “We had to backfill the HDPE liner with clay, and in order to get that material placed and compacted, the area had to be dry.”
He said it was ironic that the crew had to build a dam—the coffer dam—in order to build the permanent dam.
“The temporary part of the job was the most challenging part,” Adam said. “The actual dam construction—the finished product— was the easy part.”
John said the dam reconstruction at Second Roach Pond was a successful job that was completed under very adverse conditions “due to the persistence and diligence of the people working there.”
Mike Gordon started as the superintendent for Sargent, but very early in the project Adam became available and Mike was needed to oversee a project in Danforth.
Tim Folster was the operations manager. Mike Thibodeau was the estimator.
Wright-Pierce of Topsham was the owner’s representative on the project.
Joe McLean, project manager for Wright-Pierce, said Sargent Corporation did an outstanding job on the project.
“The Sargent crew was diligent, effective, and professional,” Mr. McLean said. “The owner couldn’t have asked for a better contractor to reconstruct this dam and restore the site. When challenges arose, particularly during dewatering efforts, the Sargent crew never wavered and simply solved any problem they encountered. Even with some surprisingly heavy rainfall, including one storm with over 6 inches of rain in 24 hours, Sargent always maintained control of the site and limited environmental impacts during construction.”