Wednesday, December 16, 2020

Draining the Mill Pond

People walking across the drained frozen mill pond 1916-17.
Trestle and flume visible, left; St. Bridget's spire, right.
One wonders what is on the bottom of the mill pond. No one is allowed to swim in it, or boat on it, so people who own a diver’s face mask, or have the ability to look over the side of a boat on a calm day, cannot fathom what lies on the bottom.

What we do know is that the mill pond is not a ‘kettle pond.’ The most famous kettle pond in Massachusetts is Walden Pond, 65 acres in area and more than 100 feet deep at its deepest. Kettle ponds closer to Maynard, not famous and not as deep, include White Pond (Concord), Crystal Lake, Sudbury (old name “Bottomless Pond”), and possibly White Pond (Hudson), for which Maynard owns water rights, and until 1999, sourced some of its tap water from there.

Toward the end of the last ice age, when the glaciers of ice as much as two miles thick were melting in place there were many instances in which large (LARGE!) blocks of ice remained as a remnant while the ice surrounding it melted, leaving an ice ‘island’ separate from the face of the glacier. As the glacier melted, meltwater would carry sand- and gravel-sized particles to settle around the ice blocks. On occasion, meltwater lakes were contained behind an ice dam, the sudden failure of which would release a vigorous flood of water that would move sizeable rocks.  When the remnant ice blocks finally melted, what remained were open depressions surrounded by deep layers of sand and gravel and rocks. Wherever the groundwater table is high enough, these kettles become permanent ponds, replenished by rain falling on the surrounding sandy plain. Walden Pond has no surface streams flowing into it, nor an exit stream leaving it, yet it persists, with a surface level that averages 158 feet above sea level. It rises or drops several feet above or below that based on previous years’ rainfall and snowmelt.

Maynard’s mill pond and its water level are artifacts of the mill’s construction and management. When Amory Maynard and William Knight came looking for a site for a woolen mill in 1846, they each had mill ownership in the past. They deeply understood water power. Key to the attractiveness of Assabet Village as a potential mill site was the fact that at Rockbottom (not yet renamed Gleasondale), the site of the nearest existing dam upstream, was more than four miles away, so that if they could figure a means to dam the Assabet River to their advantage, they could back up a large enough volume of water for year-round operation without interfering with the operation of the Rockbottom dam.

Where the mill pond is now was originally a swamp; by building a large dam upstream from where there had been a modest dam at Mill Street, and also constructing a canal to where the first mill building was built, they were able to flood the swamp. Lost to unrecorded history (?) is whether a dike or other construction was needed to prevent the newly elevated body of water from finding a route to the river that was not through the mill’s waterwheel. The net result was getting the equivalent of 50 horsepower of ‘free’ power, six days a week, 52 weeks a year. This was enough initially, but by 1862, coal-fired steam engines began to augment, and then finally replace, water power.

Wait, wait, where were we? Considering draining the pond. Which is exactly what was done in 1916-17, when what is now numbered as building #3 was being built. A temporary dam was erected near the Sudbury Road bridge. A wooden pipe, a “flume,” resting on a wooden trestle, conveyed water to the mill for washing the raw wool, providing water for the steam engines, and washing wool again after it was dyed. There are photographs in the collection of the Maynard Historical Society showing the pond drained. In winter, people walked across the ice- and snow-covered bottom. From the photos, an estimate can be made that the refilled pond is no more than 30 feet deep at its deepest.

Trestle visible in 1977 when the mill pond was
partially drained for building repair (photos
courtesy of Maynard Historical Society) 
When construction was completed in 1918 the temporary dam and flume were removed, but the trestle was left in place, partially submerged, in case there was a future need to drain the pond again. In 1977, the pond was partially drained to allow for building repairs. The trestle top was visible and still looking in good shape. At present, the tops of a few remaining wooden piles can be seen breaking the water’s surface when viewed from between buildings #3 and #5. Without knowledge of the original intent, many people assume that these are the remnants of a railroad trestle. Most of the time, the pond’s water level is maintained within a small range.

Could, should, the pond be drained again? There is no real reason to. There is little sediment build-up, because most of the silt carried by the Assabet Rive to the body of water retained by the Ben Smith Dam settles miles upstream from the canal. One hundred years ago, people swam in the pond or skated on the ice. According to town records, some died doing so, but the bottom of the pond is not strewn with bodies. There are rumors that desktop computers and other equipment were defenestrated when Digital Equipment Corporation abandoned the buildings. This has not been confirmed. Unlike the river, the pond was never a dumping place for old tires. Draining it would surely reveal bottles and cans, but nothing that is impacting the quality of the water.

Remnants of trestle (2001)
The pond does not stagnate because it is managed; during times of high river flow, fresh water is allowed in through the canal gatehouse (visible from the Route 117 bridge) and let out via the old mill works tail race, visible from Walnut Street. The water level can drop during summer droughts because no water is allowed to be diverted into the pond when the river flow drops below 39 cubic feet per second. There was a problem the summer of 2017 when the pond would repeatedly fill to almost overflowing into the Main Street parking lot even though the canal gate was closed. Turns out a sunken log had prevented the gate from being completely closed. Scuba divers were hired to remedy the problem.   

Mark envisions an annual kayak day sponsored by Mill & Main, perhaps with a launch fee going to a local charity.  


  1. I never heard it called a "flume". It has always been called the pipe "cradle" by the locals. Also, there is a rail siding along the pond side of what was known as Building 1 that was used to store empty coal cars. It can be seen at "low tide".

  2. The flume would have been the pipe itself. What was left in the pond was the trestle/cradle.