Yarmouth residents packed the town’s Log Cabin on Aug. 13 to learn how the removal of the Bridge Street Dam and partial removal of the East Elm Street Dam would impact the Royal River. Eloise Goldsmith / The Forecaster

A plan to remove two dams located in the Royal River in Yarmouth would result in lower water levels and narrow the river in multiple locations, according to a presentation from the Army Corps of Engineers. Residents, however, would still be able to use the river for canoeing upstream from the town’s canoe launch.

Roughly 40 Yarmouth residents filled the town’s Log Cabin meeting house on Aug. 13 to hear the results of a hydrologic and hydraulic study that laid out how dam removal would impact water levels, appearance and flow.

The Army Corps is assisting the town with ecosystem restoration of the Royal River and earlier this year outlined a proposal to fully remove the Bridge Street Dam and remove part of – or 120 linear feet of – the East Elm Street Dam.

The plan also addresses a third location of interest, a set of cascades called Middle Falls, where it’s difficult for fish to pass, according to Town Councilor Karin Orenstein.

It didn’t make sense to come up with a solution for the existing dams and not tackle this problem, Orenstein said, so the Army Corps’ temporary selected plan also details installing a structure at the top of Middle Falls that would divert the flow into a side channel.

The Bridge Street Dam is located between Route 1 and Bridge Street and the East Elm Street Dam is located right below East Elm Street, next to Gooch’s Island. Neither dam is being used – though they held multiple industrial functions over their life spans, including hydroelectric production at the Bridge Street Dam. Both structures have fishways, which do not efficiently pass fish upstream, according to the Army Corps.

“Drawdown (of water levels) upstream of the Bridge Street Dam (would be) approximately 3 feet,” said Tom Mihlbachler, an engineer with the Army Corps of Engineers. Water levels right after Elm Street are predicted to drop approximately 4 feet.

When it comes to velocity, their modeling shows “that the largest increases of flow velocity are predicted to occur generally in the steep reach between Elm Street and Bridge Street, with minor increases occurring throughout the East Elm Street impoundment,” said Mihlbachler.

A diagram from the Army Corps of Engineers shows how water levels in the Royal River would decrease around the town’s canoe launch with dam removal. The right side projects water levels after dam removal. Orange represents depths less than 1 foot, and red represents depths less than 6 inches. Contributed / Town of Yarmouth

At the Bridge Street location, the water would be more centered where the dam is removed, but the flow patterns would remain largely the same. At the Beth Condon Memorial Bridge, dam removal would cause water level to drop from 2.5 feet to less than 1 foot. The tentatively selected plan would also reveal a new rock ledge upstream from the Beth Condon Memorial Bridge.

Around Middle Falls, depth is expected to stay largely the same at 1 foot.

At the section of the Royal River where residents launch canoes, near the Yarmouth Historical Society, dam removal could cause low water levels that might be a recreational hazard downstream from the canoe launch, according to Mihlbachler’s presentation. However, the river will continue to be deep and wide enough to launch a canoe and paddle upstream.

“We don’t recommend anybody turn a canoe downstream, because there’s even bigger hazards – there’s waterfalls coming,” Orenstein said in a follow-up call.

“What you’re seeing is a river (where) you can still paddle. It’s still wide enough, it’s still deep enough,” she said.

Mihlbachler said that approximately 300 feet of the Gooch Island back channel would become “intermittent,” and water would likely be diverted south of the island. The Army Corps’ plan would also likely reduce flood threat to properties near the island.

The tentative proposal is a precursor to a much larger project – a “feasibility study” – where the Army Corps assesses the various issues with a water resource, comes up with possible solutions, compares them and makes recommendations.

In September, the Army Corps plans to furnish a draft Detailed Project Report/Environmental Assessment, which the public will have a chance to weigh in on during a public review period and public meeting.

“I want to be really clear: there’s no pre-baked conclusion as to what’s going to happen. The town has not decided. We’re really waiting on the report from the Army Corps and for the public input,” said Orenstein, who also shared that under the current proposal, the town would shoulder roughly $2.1 million of the project costs. She said the town would seek to raise that money through grants.

Both dams were constructed in the 19th century and today are owned by the town.

When first considering the project, the Army Corps found that restoring the Royal River could turn up to 135 miles of river into an area of reproduction and early-life habitat for species like herring, alewife, shad, eels and sea-run brook trout.

But over the years there has been some hesitance to remove the dams. A 2013 report by Stantec, an outside environmental and engineering consultant, listed multiple concerns impacting recreational use of the river, increased sediment delivery to Yarmouth Harbor and potential environmental contaminants in the sediment at the impoundment of the East Elm Street Dam.

Orenstein confirmed there have been concerns about sediment. However, in February, the Army Corps presented its findings from a sediment study, which revealed very little build-up behind the dams, generally low chemical levels in the sediment, and little risk to aquatic life in the Royal River estuary and Casco Bay if the town moved forward with the dam removal plan.

And although any actual dam removal is still far off, it has taken many years to get to this point. In 2008, a Royal River Corridor Study evaluated the history, recreational use and future development of the river corridor and the lands around it. The final report included a recommendation to conduct a study that would weigh the pros and cons of removing the Bridge Street and East Elm Street dams.