YARMOUTH — Consultants will present the findings of their latest study of restoration of the Royal River at a public forum on Oct. 22, but questions remain about the potential impacts of removing the East Elm Street dam.

The engineering firm, Stantec, recently delivered to the Town Council a 147-page report titled “Royal River Restoration Project: Phase II Analysis and Reporting.” It was prepared by Michael Chelminski, a licensed professional engineer, who will lead next Tuesday’s presentation at 7 p.m. in the Log Cabin on Main Street.

Yarmouth has been looking at ways to improve fish passage and ecological conditions in the river for more than five years. Phase I of Stantec’s study, presented nearly two years ago, determined that removing the Bridge Street and East Elm Street dams, whose fish ladders are barely functional, would provide great help.

The Bridge Street dam impoundment in August 2011 was drawn down, enabling researchers to observe conditions similar to those that would exist if the dam were removed. Drawing down the more archaic East Elm Street dam, however, is not a feasible option, researchers said.

The goal of the latest study was to explore concerns about what the impacts of removing the East Elm Street dam might be:

• How it would affect recreational use of the river.

• Whether it would cause increased sediment delivery to Yarmouth’s harbor.

• And whether that sediment contains harmful environmental contaminants.

Two of the three questions received relatively straightforward answers.

Removing the dam would lower the water surface elevation between the dam and the Route 9 bridge in North Yarmouth by 5 to 6 feet, but boating and swimming would largely be unimpacted, the study concluded. The boat launch behind the Yarmouth Historical Society may no longer be a suitable launch, but the town has already begun investigating a new launch a half-mile upstream.

The study also determined that pollution is not a concern. Contaminants in sediment samples collected upstream from the dam were similar to those downstream, suggesting “minimal potential risk of adverse effects to aquatic life.”

The potential for increased sediment in the harbor is more complicated.

The study says that removing the dam would increase the amount of sediment flowing into harbor, but “the amount of sediment and duration of effects associated with removal of the dam would depend on the number and frequency of flood events following removal of the dam.”

“In the short term, it might add some additional material coming downstream,” Town Manager Nat Tupper said, “but that same material is coming down in the next few storms anyway. So you’re going to reach a new equilibrium pretty quick. (The study) is relatively neutral on the issue of how much silt will come down.”

The biggest concern with removing the dam is that an influx of silt would compound the harbor’s chronic sediment problems and endanger business. A 2008 study by the Greater Portland Council of Governments estimated the annual economic impact of the harbor at over $25 million. Tourism and fishing make up the bulk of that total.

The harbor requires dredging every 10 years to allow maximum navigability, but it hasn’t been done since 1997. The U.S. Army Corps of Engineers, which is responsible for dredging the harbor, issued a press release in February saying it would dredge – when funds become available. When that will be is anyone’s guess.

With the help of U.S. Sen. Susan Collins, Yarmouth approached the Army Corps about sharing costs on the project, but the town’s requests have been largely ignored.

“They said they’d dance with us, but now they won’t get out of their seat,” Tupper said. “We may have to do this all by ourselves, which is frustrating in terms of the cost, let’s say $2 million or $3 million.”

The sediment and navigability problems in Yarmouth harbor are going to be there whether or not the town removes one or both of its dams. The question is whether removing the dams will make those problems appreciably worse.

“Having the dams in place or out is, in the big picture, not likely to make a huge difference in the amount of sediment in the harbor,” said Landis Hudson, executive director of Maine Rivers, one of the project’s partners.

Previous public forums on the Royal River restoration study have drawn a variety of constituents, from sports fishermen and environmentalists in favor of dam removal, to residents worried about dam removal negatively affecting the river’s aesthetic qualities and their own property values.

Tupper stressed that the goal of the study, and Tuesday’s forum, is to provide information.

“It’s not a proposal for dam removal,” he said. “It’s a study of the implications.”

The Town Council will likely take up the issue in November. If the council decides to move forward with removing the dams, it would then work on acquiring removal permits.

“You can’t just say, ‘Oh, I want to take out a dam and then go for it,'” Hudson, who has worked on this project for four years, said. “It’s a lengthy process that involves a number of different agencies and entities. And then of course the funding part of it is quite significant.

“I’d like for it to happen faster,” she added, “but there’s a lot of layers to the work.”

Brendan Twist can be reached at 781-3661 ext. 123 or btwist@theforecaster.net. Follow him on Twitter: @brendantwist.