Tree Cutting is an Unwelcome Idea
Among the issues we must weigh in the months ahead are the high costs of repairing and properly maintaining the reservoir as currently operated, the need for a quality outdoor public swimming facility, and the natural role of this lake in the greater watershed.
The state Department of Environmental Management (DEM) has recommended that Arlington cut down all the trees and bushes on top of the reservoir's earthen dam and take other steps to resolve possible structural weaknesses. The prospect of clear-cutting so many trees in one of our last remaining large green spaces is unwelcome.
Under the auspices of the Vision 2020 Environment Task Group, an ad hoc working group has come together to work with the Department of Public Works Director Richard Bento and the Arlington Conservation Commission to better understand the problems and opportunities associated with the dam.
Why take the seemingly extreme measure of cutting down so many trees? The state's engineers worry that root structures of mature trees and other vegetation create zones of saturation in the sub-soil, thus weakening the structural integrity of the earth dam. In addition, a severe storm such as a hurricane could topple the trees, they say, and as their root structures were pulled up, the dam's water-holding ability could be compromised. The inspection of the dam, by hydraulic and water resources engineers for DEM's Office of Dam Safety, also identified possible evidence of seepage near the dam's emergency spillway.
Fortunately, the inspectors concluded that "based upon the visual examination and the dam geometry, the dam is considered stable at this time." The state inspectors recommended repairs to the dam and extensive tree and brush removal at an estimated cost of at least $188,000 to $270,000.
Of course we must squarely investigate and address any genuine safety concerns (we don't yet know whether any are real). But the report's wake-up call coincides with other pressing challenges posed by the condition of the reservoir and swimming area:
* Water chestnuts, an invasive and fast-growing aquatic plant, are covering 50 to 60 percent of the reservoir's surface in summer, choking off sunlight and oxygen required by native aquatic plant and fish species. The most enduring way to reduce their growth is to control excessive nutrients (e.g. fertilizers) washing in from upstream. Such a solution requires an extensive public education effort to convince residents and businesses in the watershed to use less fertilizer on their lawns and gardens. The Conservation Commission, led by chair Susan Brent, understands that such all effective education campaign is a longer term project, and plans to simultaneously harvest the chestnut seed pods over at least three successive seasons -at an estimated cost of $60,000. The Conservation Commission has rightly ruled out applying herbicides to solve the problem - effective though that may be - because of the resulting exposure of children and the environment to such poisons.
* The swimming area at the reservoir is the only outdoor public swimming facility in town, and has a large following (including my family). Yet our town swimming hole faces its own challenges. The mini-berm which surrounds the swimming area has trouble holding water. And the area attracts a flock of ducks and geese, which leave a trail of floating feathers and fowl waste.
By way of a little background, the 65-acre reservoir was created in 1871 by the damming of Monroe Brook. The dam consists of an earthen embankment some 600 yards long and as much as 14-feet high. A crest gate spillway is designed to allow the DPW to raise and lower the reservoir's elevation, and a separate emergency spillway provides relief when heavy rains raise water levels too quickly. Both spillways empty into Mill Brook.
The dam was originally built to supply drinking water for the town. However, as early as 1899 Arlington joined the then Metropolitan Water District and began receiving its water supply from sources outside the town. For years the reservoir served as a popular swimming hole. But as its water quality began to suffer, the current swimming area was enclosed by a berm in 1981 to segregate it from the remainder of the reservoir.
The swimming area is filled each year by water from the town's drinking water source, the Massachusetts Water Resources Authority (MWRA). Water pressure from the reservoir on the other side of the berm helps keep the swimming area's water level high.
The reservoir and its surrounding riparian lands are a popular habitat for water birds and songbirds -- almost 150 species have been spotted, including grebes, herons, osprey, turkey vulture, hawks, sandpipers, woodpeckers, warblers and orioles. The path around the reservoir is a popular walking and jogging venue, away from traffic and crowds.
In order to investigate and verify the potential safety issues with the dam, DPW director Bento has hired Weston & Sampson Engineers to complete a "dam breach analysis" to identify any actual safety problems and, if the dam were to fail, what downstream areas might be inundated with water. Weston & Sampson will also write a repair plan to bring the dam into compliance with state requirements. The engineers will consider two options: 1) maintain the dam and make the required repairs of 2) drain the reservoir and decommission the dam.
To do its work, Weston & Sampson's crew must cut away some of the brush which has grown up around the spillways and other parts of the dam. They will not cut down any trees. The study is expected to be completed by late fall.
Once in receipt of engineer's work, the town must decide which' course of action to take. The options at this point are purely hypothetical. They could include spending the money to cut down the trees, repair the dam, harvest the water chestnuts and maintain the status quo. Another could be to keep the water level low at all times, reducing the pressures on the dam and, creating a safety buffer. This option might save the trees but may still require structural repairs to the dam and ongoing maintenance.
A third, bolder option could be to permanently drain the reservoir, permitting the 65 acres to revert to a wetland. This would avoid the need to spend hundreds of thousands of dollars in dam repairs, tree cutting, and water chestnut removal (the chestnuts can't grow without ample water surface). The earthen berm could be left in place to provide passive flood management in the event of a catastrophic storm. A restored wet land, with its considerable absorption abilities, could provide the best flood management of all. The result could be an area of enhanced natural beauty, on par with Great Meadows.
Draining the reservoir, however, could weaken the swimming area's ability to hold water. The town might be able to reline the area to better hold water (as noted, it can be filled independently of the reservoir's level) and continue the area as currently designed. Or the town could raise state and local funds to build an outdoor swimming pool with appropriate water quality maintenance -- perhaps even at same location as the current swimming area.
The coming year will be critical to the reservoir's future. The Vision 2020 Environmental Task Force Reservoir Committee needs wider representation -- from the neighborhoods downstream and upstream, faithful users of the swimming area, and Lexington. Those interested in helping shape this future are invited to join the next meeting of the Reservoir. Please call or email Chair Gene Benson (641-0911; Ebbenson@aol.com or me (643-8623; firstname.lastname@example.org) if you'd like more information or have questions.
Later this fall, we hope to organize a town wide session in order to envision and plan a future for the reservoir. We need to combine our best efforts and collective wisdom to implement a plan that considers the reservoir's role in the surrounding watershed while providing open space, recreation, flood management and wildlife habitat benefits that will serve Arlington well for many years to come.
Arlington resident Kevin Knobloch is a member of the Reservoir Committee
of the 2020 Vision Environmental Task Force.