Mill Pond, the historic man-made pond in the heart of West Tisbury, was once again the center of debate this week over what, if anything, should be done to address fears that the pond is disappearing and the health of its species are in decline.
At a public forum Wednesday, representatives from the state division of ecological restoration, The Nature Conservancy and the town’s Mill Pond committee addressed a standing-room-only crowd at Howes House with competing visions for the pond’s future. Options included dredging and dam removal.
The pond, which dates back to the 1600s, was created when a dam was built along the Mill Brook to provide hydropower to the grist and wool mills. Over the years, the pond has been periodically dredged to remove dense aquatic vegetation and accumulated sediment. Though few records exist to provide the frequency and quantity of dredged material, the last time the pond was dredged was reportedly in 1970.
In recent years town leaders have expressed concern that the pond has been shrinking due to increased sediment, with a recent average depth recorded of about a foot and a half. In 2008 the town appointed a Mill Pond committee charged with better understanding the intricacies of the pond and its tributaries. The committee commissioned the engineering firm ESS Group to study the pond, which recommended it be dredged.
“The whole Mill Brook system is one of historical, ecological and cultural significance . . . in our view,” Robert Woodruff, chairman of the Mill Pond Committee, explained of the committee’s backing of the dredge option at the forum. “The average sediment thickness is 2.8 feet, if you pick that up in your hand it’s like going through chocolate cake batter. Even finer — cocoa batter.”
The Mill Pond committee has endorsed dredging 3,150 cubic yards of the pond, which they say would create a retention basin and increase the average depth of the pond from 1.7 feet to four feet. The ESS estimates the cost of dredging at $405,000.
But even among members of the committee there is disagreement as to whether dredging is the best course of action to improve the pond’s health, or whether any action needs to be taken at all.
“The preservation of the Mill Pond depends on understanding and controlling the water flow into and out of the pond,” Kent Healy read from a prepared statement at the Wednesday forum. Mr. Healy, a civil engineer, Mill Pond committee member and the caretaker of the pond, has been a staunch opponent to dredging and believes the pond is not shrinking. He advocates that no action be taken to change the depth or water flow in the pond.
“The change of depth contours by [engineering firms] indicate that the pond has gotten shallower along the west side but has gotten deeper by about a foot in the central part of the pond . . . Google Earth photos show no significant reduction of pond area from 1994 to the present.”
“The Mill Pond dam is in good condition . . . and the town can keep it that way,” he concluded.
Prudy Burt, a West Tisbury resident and stream restoration proponent, advocated a third option: removing the dam. Doing so, she said, would improve water flow and help native fish species.
That approach has been backed by a November 2012 study from a state diadromous fish biologist, which suggested a watershed restoration plan, river herring habitat assessments, replacing the fish ladder at the Mill Pond dam, and further investigation into the removal of the dam. A September 2012 assessment of the state of fish population by the state division of fisheries and wildlife recommended Mill Brook and its several tributaries be listed as cold-water fisheries resources and its un-needed dams or culverts removed.
The watershed includes Mill Pond, Mill Brook, Tiasquam River, Prister’s Pond and Scotchman’s Lane and covers just over 3,000 acres. Mill Pond itself measures 2.5 acres and is fed by the Mill Brook, which flows north and west of the pond basin.
“What we have on Mill Brook is a segmented system with fish and wildlife populations at risk for expirtation because they are isolated populations,” said Ms. Burt, who invited ecologists from The Nature Conservancy and state department of ecological restoration to speak on behalf of dam removal.
Among those Ms. Burt invited was Alison Bowden, freshwater program director for The Nature Conservancy in Massachusetts who works on migratory fish and river restoration projects in order to increase connectivity and flow from rivers to the ocean. Ms. Bowden said dams slow connectivity and impede the health of fish species.
“We want to restore the ecological integrity and a self-sustainable system, recognizing the land use has changed,” she said.
There are 3,000 dams in Massachusetts, most built for mills that no longer exist, she said. “This is a state with a long history” of building dams which were built during the industrial revolution and contributed to “the loss of healthy rivers.”
Beth Lambert, a hydrologist with the division of ecological restoration, said her department has done 80 restoration projects around the state. Many of the projects the group has assisted in were dam removal projects aimed to help restore rivers to full-flowing streams.
She presented several cases where similar mill ponds had been restored to full-flowing streams, causing lush vegetation to grow back in along the banks.
“Because of the large impact that dams have in aquatic systems in Massachusetts, we chose to implement that focus through dam removal because of the cumulative impacts that all those dams have,” she said. Her program removed nine dams in Massachusetts this year, many of which were owned by towns, she said.
Michale Chelminksi, an engineer with Stantec Consulting Services, recommended removing the boards to test the success of a full dam removal.
“As an engineer’s recommendation on public safety it would be to get the boards out of there to test dam removal,” he said.
Dam removal is estimated to cost $580,000, much of which would be funded by state and federal grants.
After lengthy presentations, the floor was open to public comment. Mill Pond committee member Barbara Day said she was opposed to the dam removal option.
“Every year there are more shrubs on either side and eventually, unless you pay to maintain those, it begins to fill in,” she said. “It seems to me that what you would have is nothing but a lot of trees to look at. I don’t know how you handle that unless you want to go to the expense to weed out trees that move inward.”
Town resident Anne Fielder asked for more information on the dredging option.
“The one thing that bothers me about this whole evening is that we haven’t put enough emphasis on what happens if we dredge,” she said.
Shellfish biologist Rick Karney said he wanted the ongoing discussion to include implications on all of the options on shellfish in Tisbury Great Pond. Mill Brook, which feeds the pond, runs from the headwater in the Roth Woodlands just south of North Road to Town Cove in Tisbury Great Pond.
“I would hope part of this discussion includes what impact this is going to have on this very valuable, rare resource that we are so gifted to have in Tisbury Great Pond,” he said.