Wednesday, May 13, 2020

Assabet River Revisited

Recently, the Assabet River has been deeper than its long-term average for spring the reason being more than average rainfall. April, for that matter most months, averages four inches of rain (or snow equivalent) per month, year-round. Eastern Massachusetts does not have wet and dry seasons typical of some other parts of the country, although in some years there can be lengthy summer droughts. Oddly, after an unseasonably warm and low-snow February and March, this April was one of the coldest on record.    

Kayaker enjoying the rapids between Main Street
and foot bridge, Spring 2014
In the spring the river is exceptionally clear. The bottom is stony, versus how green it will appear in late summer when grown over with water milfoil, filamented algae and other bottom-anchored water plants. Year-round, the water has a low sediment content. This is because the Ben Smith Dam traps all the upstream sediment. A U.S. Geological Survey study completed in 2003 estimated accrued sediment volume at approximately 20,000,000 cubic feet. If ever there was a decision to remove the dam, some form of sediment removal would be required, elsewise vast quantities of sediment would shift down river, increasing the risk of floods in Maynard, Acton and Concord.

This time of the year the river mid-town is also mostly clear of surface plants. By late summer, every rain event that increases volume over the top of the dam brings floating plants like duckweed, watermeal and globs of free-floating algae through the center of town. Upstream of the dam, the near-shore shallows, also currently clear, will be covered by these floaters plus the flat leaves of white and yellow water lilies. Luckily for boaters, most of the river is deep enough to not sustain the surface-leafed, bottom-rooted, water plants.

The kayak and canoe launch dock at Ice House Landing
is back in the water for 2020.
Come winter, the plants will die, returning phosphorus to the bottom sediment. Even though wastewater treatment facilities are enjoined from adding too much new phosphorus to the river, this growth/death process functions as a self-sustaining cyclical phosphorus source, promoting next spring’s growth. Bad now, far, far worse 40 years ago. Ann Zwinger wrote in A Conscious Stillness (1982) "...the reach above the Powder Mill Dam [Acton, next to Route 62] is closed by joint action of the Maynard and Acton boards of health...the river smell is nauseating, reeking like an unpumped-out campground outhouse times ten." The smell emanated from rotting of bacteria, algae and water plants, the consequence of eutrophic growth promoted by the excesses of phosphorus and nitrogen entering the water as either inadequately treated waste water or farm and golf course fertilizer run-off, raw storm sewer discharge, etc.

As for why “Assabet,” once upon a time the Assabet River was known as the Elizabeth River, alternative spellings Assabeth, Asabet, Elizbeth, Elizabet…all thought to be Anglicized versions of a Native American name. One colonial era map had it as the Concord North River, with the Sudbury being the Concord South River. There was a map consensus in 1830 that Elizabeth Brook flowed into the Elizabeth River, but by 1856 it was Assabet Brook flowing into the Assabet River, with the pre-Maynard community identified as Assabet Village. Nowadays it is Elizabeth Brook flowing into the Assabet River.   

Removal of the footbridge, August 2016, in preparation for the new bridge,
installed February 2017 as part of the Assabet River Rail Trail.
The river is 31 miles long, from headwaters in Westborough to its merge with the Sudbury River in Concord to form the Concord River. Seven towns draw their well water from within the Assabet valley watershed and five discharge treated wastewater into the river (Westboro, Marlboro, Hudson, Maynard, Acton). There are six existing, intact, historic mill dams, plus one breached (Damonmill, West Concord) and one flood-destroyed (Papermill, Maynard). And there are two twentieth century flood control dams: George H. Nichols, Westborough, and Tyler, Marlborough. By having limited egress, those function to blunt peak downstream volume during times of heavy rain.

Sadly, in this time when so many people are looking for places to hike, there are few in Maynard or Stow with an actual view of the river. A suggestion: drive west on Concord Road into Acton, south on High Street, veer right onto Old High Street, and park at the trail head. The trail goes west, with water views.  

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