I have previously written about Boston surveyor John Hales and his useful 1821 book A Survey of Boston and Its Vicinity; Shewing the Distance from the Old State House, at the Head of State Street, to all the Towns and Villages Not Exceeding Fifteen Miles Therefrom; Also the Intermediate Distance from One Place to Another, Together with a Short Topographical Sketch of the Country. Today's post shows a map of the completed Mill Dam from the same book. What follows is Hales' description of the Mill Dam. The letters in the text refer to points on the map, so click on the map to see a larger version.
"The Mill Dam a. b. c. d. e. just completed by the Boston and Roxbury Mill Corporation [note: initial construction was approved in 1814], from Beacon Street in Boston to Sewall's Point in Brookline, is composed of solid materials and made watertight; its surface is horizontal about three or four feet above high water mark, fifty-feet in width and one mile and a half in length. This Dam cuts off and incloses about 600 acres of the southerly part of the Back or Great Bay, (over which the tide before regularly flowed) and renders the water that is now admitted therein subservient and manageable.
At c. f. there is a cross dam running from the main dam to Gravelly Point, which is also water proof, and divides the part of the Great Bay cut off by the long dam into two parts; the westerly part containing about one hundred acres is intended as a full basin, or reservoir of water. The easterly part contains about five hundred acres and is intended as an empty or receiving basin.
In the long dam at b. there are five pair of flood doors grooved in massy piers of hewn stone, each pair moves from their opposite pivots towards the centre of the aperture on a horizontal platform of stone until they close in an obtuse angle on a projected line cut on the platform from the pivots in the piers to the centre of the space, with their angular points northerly on the open or uninclosed part of the bay. The object of these doors is to close against the flow of tides and prevent the passage of water into the empty basin, consequently at high tide that basin will be empty, with the exception of the waste waters received, during the flow of the tide, from the full basin after having supplied the mills, which is calculated will not rise to a height sufficient to impede the power necessary to carry the works.
At d. there are six watertight sluices leading into the full basin. These sluices are to open every tide when the water in the outer or uninclosed part of the bay hath the ascendancy over the water in the full basin, in order to admit the flow of tide into the reservoir, and to be closed immediately at high water; by this process the full basin will be left full of water every tide as high as the tide has flown, if so high it is needed.
Gravelly Point in Roxbury is intended as the scite [sic] whereon mills or factories are to be erected, somewhat in the line g. g. g. between the full and receiving basins, and sluice ways are to be built from the full basin at h. h. & c. of a size sufficient to admit so much water as will move and keep in motion the power contracted for. The waste water therefrom falling into a raceway which conducts it to the empty basin, and this empty basin discharges itself every tide at low water through the flood doors, so that the reservoir is filled at high water and the receiving basin emptied at low water, by which means there will be a continual supply of water through the sluice ways from the full basin, to set and keep at all times in motion the mills, factories, or other water powers that are erected between the basins, and there will be a sufficient fall from the water in the full basin to the water in the receiving basin to prevent the mills from choaking [sic], so that the powers may with propriety be said to be perpetual.
There are two roads leading from the long dam, one west by north to the Brighton road, the other south-westerly to the Punch Bowl village in Roxbury, both whereof considerably shortens the distance to Boston from the west and south-westerly parts of the country, and there is one road leading from the short dam to Roxbury Street."
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