Engineers for the City of Newton have chosen a plan to repair the Bullough’s Pond Dam in Newtonville, according to a recent update given to the Newton Public Facilities Committee.

The dam at Bullough’s Pond dates to colonial times and has not been repaired since 1926. In 2018, the state of Massachusetts ordered the City of Newton to reconstruct the dam after an inspection found it to be in poor condition.

According to flood inundation maps, the dam’s failure would disperse floodwaters across a large section of Newtonville, affecting approximately 450 homes, Newton North High School, Cabot Park, and the Massachusetts Turnpike, according to dam engineer Lee Wooten of GEI Consultants.

Wooten warned of the significant risks that a hazardous dam carries in the event of a 100-year storm. A 100-year storm brings excessive rainfall and has a 1 percent chance of occurring in any given year.

“The primary spillway is not big enough for the storm water to go past the dam without overtopping the dam,” said Wooten. “That kind of overtopping will likely lead to a breach of the dam.”

If the dam broke in a storm of that size, it would cause extensive property damage and even risk casualties, according to Wooten.

“It’s not definite that it would cause loss of life, but it is certainly within the realm of possibility,” Wooten said. “The property damage would be pretty big.”

Wooten explained that floods could reach 2 feet in the event of a significant storm.

“It’s a storm of multiple inches over two days,” said Wooten. “At the dam, we estimated the flow over the top of the dam would be two feet deep. You would have two feet of water going over the road, and then down the other side.”

In order to mitigate the likelihood of a failure, Wooten proposed a solution that would stabilize the dam without being inappropriate for the surrounding area.

“The design would put some kind of erosion protection on the downstream slope,” said Wooten. “The area would be covered with an erosion protection system called articulated concrete blocks. They are put down over the slope and then covered with soil and seeded, so you have a grass slope.”

The area’s appearance, however, would be changed significantly due to the large number of trees that would need to be eliminated.

“All of the trees and woody vegetation would need to be removed … from the upstream and downstream slopes,” said Wooten. “The number of trees was about 199.”

Bill Salomaa, the director of the Massachusetts Office of Dam Safety, reiterated the necessity of the tree removal.

“Trees do not belong on dams,” Salomaa said. “They can topple in winds and pull out big root balls that make the dam very susceptible to instantaneous stability issues.”

Wooten added that he had considered three options for the dam’s rehabilitation, but ultimately selected the one that he thought would cause the least disruption to Newton’s infrastructure.

“The first two options involved a lot of work in the road,” said Wooten. “Essentially, most of the construction happens in the footprint of the road, so the road would be shut down for quite a while.”

Further, the selected design would be more fiscally conservative for Newton amid its ongoing debates over the city budget.

“The selected design is less expensive by a million to a little less than two million,” Wooten said.

Ward 7 Councilor-at-Large Marc Laredo sought clarification on the selection procedure.

“I am trying to get the sense of process here,” said Laredo. “Did the Office of Dam Safety say we want the one that you have chosen, or did they say that any of these three alternatives are acceptable?”

Salomaa explained that it would be up to Newton officials to choose how to proceed with the project.

“It’s up to the dam owner to make a selection on which alternative they want to go forward with,” Salomaa said.