YARMOUTH­ — Removing two outdated dams on the Royal River would improve fish habitat and spawning conditions, but would not solve the need for dredging in Yarmouth Harbor, where the Royal empties, a river study commissioned by the town said Tuesday night.

The town wanted to study the effects of removing the East Elm Street and Bridge Street dams. Although there is approximately 110,000 cubic yards of sediment behind the East Elm Street dam’s nearly six-mile-long impoundment, scientists who studied the river said removing the dam would not significantly increase the flow of sediment into the harbor.

“There is plenty of sediment moving downstream into the harbor (presently) and it will continue,” said Michael Chemlinski, one of the study’s authors. Most influential to the rate of sediment movement are major flood events, which are responsibly for ushering large amounts of silt and sand downstream quickly.

A smaller amount of sediment escapes through the dams downstream now.

The study should alleviate some fears by harbor business owners, who have concerns that dam removal would release the material and hasten the harbor’s worsening situation. Although Chemlinski and others said there is a potential short-term dump of sediment, the rate that it reaches the harbor should remain nearly unchanged. Most sediment movement is controlled by floods, which no one can predict.

The harbor supports roughly $25 million in annual economic activity, according to the town, and has not been dredged in 18 years. Town Manager Nat Tupper said the need to perform the work is getting dire, with a possibility that, absent federal dollars, the town may have to take on the project, if the public so desires it.

“You, the taxpayer, will probably face a choice soon over whether we go it alone dredging the (harbor) or we watch our marine economy go away,” said Town Manager Nat Tupper, at a discussion of the study’s findings Tuesday.

“The ideal solution would be an integrated, coordinated project,” Tupper said.

The harbor dredging project shelved by the Army Corps. of Engineers would remove 67,000 cubic yards. The town has sought approval and funding of the project since 2004, but federal-level budget woes have forced the Corps to give other projects a higher priority.

Other effects of removing the East Elm Street dam would be a dramatic reduction of water levels by an estimated five to six feet.

The river would flow faster and some placid areas would turn into small rapids.

Most directly, a public launch area behind the Yarmouth Historical Society would be rendered useless, and kayakers or canoers looking for a place to access the river would have to go farther upstream.

Matt Byrne can be contacted at 791-6303 or at:

mbyrne@pressherald.com