New Res Dam Plan Would Save Trees
The Arlington Reservoir Committee thinks it has the
perfect solution to the Reservoir dam replacement.
Concerned about the possible loss of trees to build the dam, committee members and the project's Civil Engineer Mark Mitch of Weston and Swanson have struggled to find a way to build an industry standard dam that does not require the loss of the tress that line the current berm. Most agencies, including the Army Corps of Engineers, said an earthen dam like the one at the Res cannot have trees in it, because the root system and animal borrows can compromise the structure.
"It kills me to think about taking all those trees off the dam, but as the engineer of record on this project, if I don't follow industry standards, Weston and Swanson is open to liability if God forbid something happens," said Mitch.
Should the dam breech, the results would be cataclysmic, said Mitch.
"You should expect major property damage and loss of life," he said.
It now appears a compromise solution can be used to save the trees and fortify the dam to modern standards.
"I think I found an exact solution for this," said Mitch.
At a meeting Tuesday night, Mitch proposed using an I-wall inside the existing berm to fortify the dam while limiting the number of trees lost. An I-wall is comprised of metal sheet piles and a concrete cap.
According to Mitch, workers would dig a trench along the walkway on the dam and use vibrating drivers to pound sheets of steel through the soil and into the bedrock below. That steel would be capped with an 18-inch thick concrete block, built to stay level with the ground.
Mitch said an I-wall has recently been installed at a larger reservoir in Minnesota, where residents had similar concerns about losing trees.
"As I looked into this project I said to myself, 'This is the Res,'" said Mitch.
The I-wall would cost an additional $600,000 to $700,000, said Mitch, but that cost would be offset by similar savings on tree removal and other aspects of the original project. Adding the metal, therefore would be a wash on the bottom line.
The project, which would replace the aging dam that let go four years ago and flooded the area, is currently priced between $1.7 million and $2.1 million and will be funded through the town's capital plan.
Driving the sheet piles will be a noisy affair, however. While a vibrating driver is quieter than a pile-driver, it still makes quite a ruckus.
A new spillway will be aligned closer to Mill Brook's bend downstream, near Colonial Village. The spillway will be 50 feet wide, but Mitch said it won't spill out more water than already exits the Res.
The wider spillway allows water to exit the dam only when it exceeds its maximum height and the wider path allows for a slower, more controlled release than the existing gated spillway. The original spillway will remain as the actual control for the Res' water height.
Mitch stressed the new dam and spillway will not increase water release into the surrounding area. The project won't improve flooding either. Committee members agreed, saying the project is to fix the dam, not improve the flooding in the area.
"We're not solving Mill Brook flooding. We're not making it worse either," said Res Committee member Leslie Mayer.
Sharon Stafford lives near the Res. She said the new plan solves most of her concerns.
"You have given me hope again in my life," said Stafford.
A public hearing on the new proposal will be held in April, sometime before Town Meeting, said Mayer. Construction could begin by the fall, said Mitch. Sanchez said the project will likely start in the spring, however.