There had been a great deal of speculation regarding what was below the surface of the Mattapoisett Harbor waters, just what was supporting Long Wharf. Comments on the materials that might have been used decades ago ran the gamut from poor-quality dirt from construction sites to sunken boats, cement, rocks and more.
Documentation from the late 1800s failed to give a clear picture of what might be found underwater. The August 8 report from Childs Engineering confirmed that most speculation was correct.
Childs, which has been hired by the Town of Mattapoisett to study the current state of the historic Long Wharf and the material composition that supports it, completed test borings, a necessary process before decisions can be made on next steps in the proposed rehabilitation of the waterfront asset. On August 31, members of the Marine Advisory Board discussed the findings.
Soil explorations took place in June and July. Three soil borings along the top deck and five borings underwater next to the wharf were taken, the report stated. The purpose is to obtain sufficient data that will support a design and various considerations needed for the rehabilitation project.
The condition of the wharf has deteriorated over time, primarily due to exposure, the engineers wrote. There was an assumption that sunken, wooden barges had been used, barges filled with local fill materials, including boulders. At an early point in its history, Long Wharf was extended to accommodate a ferry. The exterior seawall comprised granite blocks. Time, tides and storms have penetrated the seawall, washing out fill.
The field exploration statements include, “The boring operation on the wharf was difficult and slow. Most of the wharf was constructed from boulder rich fill underlain by a thin layer of organic marine settlement on top of glacial-fluvial deposits overlaying dense lodgment fill.” (Subglacial lodgment tills are deposits beneath the glacier that are forced or “lodged” into the bed below.)
Subsurface conditions were described as dense till consisting of silty sand and gravel with cobbles and boulders; thicknesses of the various layers change with distance from the shore.
The report documents findings at the surface of the wharf and underwater along the seawall. The team found confirmation of its assumptions, thus supporting Childs’ earlier construction suggestion, although design has not begun.
The test-boring report notes that from zero to 10 feet glacial-fluvial, dense, fine-to-coarse sand of varying colors and gravel, were found. From 10 to 25 feet, lodgment till and very dense, moist blackish-tan, fine-to-coarse gravel was present.
“Overall, the recommendations provided by Childs remain valid and are now supported by field observations and testing,” MAB concluded. Next steps include review of the Childs’ report by the Select Board.
The next meeting of the Mattapoisett Marine Advisory Committee is scheduled for Thursday, September 28, at 7:00 pm.
Mattapoisett Marine Advisory Board
By Marilou Newell
