New England tidal inlets with special reference to riverine-associated inlet systems

Tidal inlets along the glaciated coast of New England exhibit a diverse morphology due to widely different physical and geological settings and sediment abundance. Except for the glacial sediment coasts of Cape Cod, Nantucket Island, and Marthaʹs Vineyard, most regions of New England are rocky, and barrier and tidal inlet development is related to isolated glacial and riverine sediment supplies. Inlet-connected bays and marshes encompass many different origins, including drowned river valleys, glacial lake discharge channels, indented bedrock and glacial sediment coasts, kettles, and groundwater sapping channels. Generally, inlet size is correlated to tidal range; the largest inlets (width >300 m) occur along mesotidal coasts, whereas most inlets along microtidal coasts are small (width <100 m). Exceptions occur along microtidal coasts where large bay areas produce large tidal prisms. te of their diversity, New England tidal inlets can be grouped into three broad categories based on their morphology, hydrographic regime, and sediment transport characteristics. These classes include the wave-dominated and mixed-energy tidal inlets, and riverine-associated tidal inlets. Wave-dominated inlets tend to occur in microtidal settings and are found primarily in southern New England. They contain flood-tidal deltas of variable morphology and poorly developed or absent ebb-tidal deltas. They have histories of migration, closure, and reopening during storms. Mixed-energy tidal inlets occur mostly along the mesotidal shorelines of central and northern New England. These inlets exhibit well-developed ebb- and flood-tidal deltas. They are backed by extensive marshes and tidal creeks and, in some cases, by a broad system of tidal flats. ne-associated tidal inlets coincide with major rivers that have significant freshwater discharge, especially during late winter and early spring. The throat cross-sections are large in comparison to other inlets in New England and are a function of their tidal prism. They contain well-developed subtidal ebb-tidal deltas and variable developed flood-tidal deltas. Ebb-oriented bedforms, grain size, and mineralogical analyses of channel sediments, and hydraulic data have been used to demonstrate that the estuaries are exporting sand to the nearshore, a process that has likely been ongoing since deglaciation. The mechanism for downstream movement of sand in the estuaries is moderate to large spring freshets and major floods when freshwater discharge supplants the saltwater tidal prism. During these periods, there are unidirectional seaward currents in the estuaries that may last for several days or weeks.