PALEO-DRAINAGE SYSTEM OF THE NEPONSET RIVER, BOSTON HARBOR, MA

Terrestrial, estuarine, fluvial and marine environments in the greater Boston, MA area have undergone significant landscape changes since deglaciation. These changes have been driven primarily by natural processes until settlement of the New World by Europeans approximately 400 ybp. Coastal zone modifications between 20 kypb and 400 ybp were driven by rising sea level and fluvial erosion or deposition. Post 400 ybp, natural modification has been supplemented by anthropogenic activities including: land reclamation, river damming, dredging, coastal armoring and protection, and construction.

Boston Harbor exhibits a long history of anthropogenic changes and the Neponset River watershed is no exception. The head of tides is artificially defined by a dam, considerably restricting fluvial processes. Land reclamation projects and coastal protection have further altered the environment.

A current proposed dredge in Savin Hill Cove, just seaward of the mouth of the Neponset River, prompted us to expand our site survey to include the area where the Neponset River may once have flowed. Using high and medium-resolution subbottom profiling equipment, we were able to identify several drowned and buried channels of fluvial origin. Channels appear to incise into the glaciomarine sediments and generally underlie the present-day navigation channel. Portions of this channel were dredged prior to 1990 to a planned depth of 4 m below mean low water.

Based on seismic reflection data, we did not observe any sections of paleo-channels that extend under areas of reclaimed land. We did observe areas where dredge projects have cut into and through paleo-channel fill.