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Little Narragansett Bay Major Soil Landform Units

CONNECTICUT - January 2007

In this section, each proposed major soil landform unit recognized in the mapping area is described. The descriptions are arranged in alphabetical order. Characteristics of the landform, soil and the material in which it formed are identified for each unit.

Barrier Island:

A long, narrow, sandy island representing a broad barrier beach that is above high tide and parallel to the shore, and that commonly has dunes, vegetated zones, and swampy terrains extending lagoonward from the beach; also a long series of barrier beaches (modified from Jackson, 1997). This mapping unit includes small areas of sandy dredge spoils. The sandy soils found in this mapping unit most likely include excessively-drained Udipsamments on the higher, more stable, and vegetated coastal dunes of the Barrier Island. The lower, less stable areas that are subject to frequent storm wash over and have little or no vegetation are dominated by Beaches.

Bay Bottom:

The nearly level or slightly undulating central portion of a submerged, low-energy, depositional estuarine embayment characterized by relatively deep water and sandy textures (1.0 to >2.5 m). The soils in this mapping unit are Haplic Sulfaquents and Typic Psammaquents (Sulfic Psammowassents and Fluventic Psammowassents). Some areas may have gravelly surface layers and few boulders. Wave action and subsurface currents are sufficient to keep silts and clays from settling out of the water column. The soil surface is firm in most places

Navigation Channel:

A roughly linear, deep water area operation for navigation purposes (after Wells et al., 1994; dredged hole). This deep channel has steep sides and a parabolic shape and strong currents in places.

Mainland Cove Loamy:

A loamy, subaqueous area adjacent to the mainland or a submerged
mainland beach that forms a cove or embayment within the larger basin. Sulfic Fluvaquents and Haplic Sulfaquents (Sulfic Fluviwassents and Haplic Sulfiwassents) are the dominant soil types in this mapping unit. Some areas may have a few boulders. Buried terrestrial soil profiles are common in this mapping unit. The soil surface is soft and fluid.

Mainland Cove Sandy:

A sandy, subaqueous area adjacent to the mainland or a submerged mainland beach that forms a cove or embayment within the larger basin. Haplic Sulfaquents (Haplic Sulfiwassents) are the most common soil types. Some areas may have a few boulders. Buried terrestrial soil profiles are common in this mapping unit. The soil surface is soft and fluid in most places.

River Bottom:

The nearly level or slightly undulating watercourse consisting of, or covered by, sandy unconsolidated material. The soils in this mapping unit are Haplic Sulfaquents (Sulfic Psammowassents). Some areas may have gravelly surface layers and few boulders. Wave action and subsurface currents are sufficient to keep silts and clays from settling out of the water column. The soil surface is firm in most places.

Shoal Sandy:

A natural subaqueous ridge, bank, or bar consisting of, or covered by, sandy unconsolidated material rising above the general subaqueous estuarine floor to near the surface. Typic Psammaquents and Typic Endoaquepts dominate this mapping unit. The soil surface is firm in most places.

Shore Face:

A nearly level to gently sloping dynamic and unstable landform seaward of the barrier island that may have small areas exposed at low tide. The soils in these areas are sandy in texture. Dramatic changes can occur in this mapping unit over time resulting from severe storm events. Wave action and strong currents promote the formation of Typic Psammaquents (Fluventic Psammowassents) in this environment. The soil surface is firm and sandy.

Shore Complex:

Generally a narrow transverse area that parallels a coastline, commonly cutting across diverse inland landforms, and dominated by landforms derived from active coastal processes which give rise to beach ridges, overwash fans, beaches, dunes, wave-cut platforms, barrier islands, cliffs, stacks, etc. (Schoeneberger and Wysocki, 2002). Wave action and strong currents promote the formation of Typic Psammaquents in this environment. The soil surface is firm and sandy.

Submerged Headlands:

Bouldery, submerged glacial deposits adjacent to glaciated uplands with numerous boulders and stones, some of them above the high tide mark. Submerged terrestrial soils with a capping of sandy marine deposits are common in this mapping unit. Aeric Endoaquepts and Typic Endoaquepts (Aeric Haplowassents and Typic Haplowassents) are the dominant soil types in this mapping unit. The potential for submarine (fresh) groundwater discharge zones are high in this map unit given the geomorphic links with the surrounding upland land forms. The soil surface is firm in most places.

Submerged Stream Valley:

Linear feature occupying a former stream valley submerged by sea level rise. Submerged alluvial, glacial fluvial, and organic marsh deposits are common in this mapping unit along with a capping of loamy sulfidic marine deposits. Haplic Sulfaquents and Thapto-Histic Sulfaquents (Haplic Sulfiwassents and Thapto-Histic Sulfiwassents) are the dominant soil types in this mapping unit. The soil surface is soft and fluid in most places.

Submerged Tidal Marsh:

Nearly level organic deposits submerged by sea level rise that are adjacent to upland tidal marshes bordering the coast. Formerly a tidal marsh alternately covered and uncovered by the tide is now permanently submerged by sea level rise. Submerged marsh soils with a capping of loamy marine deposits are common in this mapping unit. Typic Sulfihemists and Terric Sulfisaprists are the common soil types in this mapping unit. The soil surface is soft and fluid in most places.

Tidal Inlet:

Any inlet through which water alternately floods landward with the rising tide and ebbs seaward with the falling tide (Jackson, 1997). Haplic Sulfaquents and Sulfic Fluvaquents (Haplic Sulfiwassents and Sulfic Fluviwassents) are the dominant soil types in this mapping unit. The bathometry of this unit is in constant change as storms and tides sculpt the floor.

Washover- Fan Flat:

A gently sloping, fan-like subaqueous landform created by overwash from storm surges that transports sediment from the seaward side to the landward side of a barrier island (Jackson, 1997). Sediment is carried through overwash channels that cut through the dune complex on the barrier spit (Fisher and Simpson, 1979; Boothroyd et al., 1985; Davis, 1994) and spill out onto the lagoon-side platform where they coalesce to form a broad belt. The soils in this mapping unit are Typic Psammaquents (Fluventic Psammowassents) with numerous buried horizons. They provide links to stable periods between catastrophic storm events that breeched the barrier island in numerous places. The history of major storm events along the southern New England coast is entombed in the profiles of the washover fan.

References:
  • Boothroyd, J.C., N.E. Friedrich, and S.R. McGinn. 1985. Geology of microtidal coastal lagoons: Rhode Island. Marine Geology 63:35-76.
  • Davis, R.A., Jr. 1994. Barrier island systems- a geologic overview. p. 1-46 In Davis, R.A. (eds.) Geology of Holocene Barrier Island Systems. Springer-Verlag, New York, NY.
  • Fisher, J.J. and E.J. Simpson. 1979. Washover and tidal sedimentation rates as environmental factors in development of a transgressive barrier shoreline. p. 127-148. In Leatherman, S.P. (eds.) Barrier Islands from the Gulf of St. Lawrence to Gulf of Mexico. Academic Press, New York, NY.
  • Jackson, J.A.. (ed.). 1997. Glossary of geology, 4th Ed. American Geological Institute, Alexandria, VA; 769p.
  • Schoeneberger & Wysocki, 2002.
  • Soil Survey Staff. 2002. Glossary of landforms and geologic materials. Part 629, National Soil Survey Handbook, USDA, Natural Resources Conservation Service, National Soil Survey Center, Lincoln, NE.
  • Wells, D.V., R.D. Conkwright, J.M. Hill, and M.J. Park. 1994. The surficial sediments of Assawoman Bay and Isle of Wight Bay, Maryland: physical and chemical characteristics. Coastal and Estuarine Geology File Report Number 94-2, Maryland Geological Survey, Baltimore, MD.

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