||Dunes and vegetated beach ridges - Unconsolidated sand
or gravel deposits capping beach environments. Dunes are subject to
storm waves and winds, while gravel beach ridges are subject only to
storm wash. Each may be vegetated with salt-tolerant vegetation.
||Fresh-brackish water - Ponded water behind beach
ridges, man-made constrictions on former tidal embayments, or on marsh
surfaces transitional between upland and salt marsh environments.
Salinity of the water is less than 5 parts per thousand (ppt).
||Fresh-brackish marsh - water-saturated, organic-rich
sediments characterized by broad-leafed vegetation tolerant of constant
submergence in fresh water. Salinity of interstitial water is less than
||Man-made land - Structures or fill emplaced by man in
the nearshore environment.
||Landslide excavation and deposits - natural excavation
into shoreline upland slopes created by large-scale slumping or sliding
of bank material and the resulting deposits at the base of the slopes.
||Eolian flat - Partially vegetated sand flats adjacent
to dune fields. Subject to generally northwest winds and occasional
||Washover flat - Sand deposits covering salt marshes
behind inlet mouths which originate from storm washover or inlet delta
deposits on salt marshes. Subject to storm washover and spring tide
||Fluvial marsh - Vegetated river floodplain and bank
environments. Characterized by fresh-water pond vegetation such as pond
lilies, reeds, and wild rice. Subject to daily tidal flooding as well
as inundation during high river discharge periods.
|Marsh environments - Vegetated
environments or isolated depressions within vegetated environments
located above mean tide level in protected coastal areas.
||High salt marsh - Organic-rich sediments densely
vegetated by the salt marsh grass Spartina patens (salt-meadow
grass). High salt marshes are at the same level as mean high water.
||Low salt marsh - Mud or muddy sand embankments
sparsely to densely vegetated by the salt marsh grass Spartina
alterniflora (salt cord-grass). Low salt marsh exists between mean
tide level and mean high water.
||Marsh levee - Channel-margin sediments vegetated with
salt-meadow grass which exist up to several tens of centimeters above
the salt marsh surface. The marsh levee consists of sandy silt or
silt-size sediment deposited from flood waters rising above channel
margins, either from high river discharge into estuarine embayments or
from storm-surge influenced flood tides from the ocean.
||Salt pannes and salt ponds - Salt-water filled,
non-vegetated depressions on the high salt marsh surface (salt pannes)
or salt-water filled depressions anywhere in the intertidal zone (i.e.
tidal pools). Salt pannes may be dry and covered with algae during late
|Beach environments - Deposits
of unconsolidated sediment which extend shoreward from the lowest tide
line to the upland or vegetated dune field or beach ridge. Dominated by
||Sand beach - Beaches consisting of sand-size sediment
which are subject to high or moderate wave energy (waves generated in
the Gulf of Maine).
||Mixed sand and gravel beach - Beaches consisting of
sand and gravel-size sediment which are subject to high or moderate
||Gravel beach - Beaches consisting of gravel-size
sediment which are subject to high or moderate wave energy.
||Boulder beach - Beaches consisting of boulder-size
sediment which are subject to high or moderate wave energy.
||Low-energy beach - Beaches consisting of a wide
variety of sediment sizes which are protected from high wave energy.
Sediment characteristics are dependent upon sediment source, which is
usually from upland scarps immediately shoreward of the beach.
Low-energy beaches may exhibit growth of salt marsh grass when there is
little sediment movement.
||Boulder ramp - Sloping surfaces in the lower
intertidal zone veneered by large boulders. This environment is seaward
of gravel or boulder beaches on high wave energy shorelines. Boulders
are remnant lag deposits of eroded glacial tills. Boulder movement is
limited to periods of intense storm wave activity.
||Washover fan - Fan-shaped deposits of gravel located
behind gravel beach ridges and covering portions of marshes. Few
washovers have been recognized as mappable units on sand beaches.
Washover fans are deposited by storm waves. Fan sediment is derived
from the beach itself.
||Spits - Partially-submerged beach ridges which extend
offshore into open water. This category includes tombolos (spits
joining an island with the mainland).
|Flat environments - Gently
sloping or level environments composed primarily of fine sand, silt,
and clay accumulated in relatively quiet water. Flats are depositional
areas controlled primarily by tidal currents and sediment settling from
the water column. Flat environments may be eroded temporarily by storm
||Mud flats - Flats comprised of sediment finer than
||Coarse-grained flat - Intertidal flats where sand or
larger-size material comprises most of the sediments. Coarse-grained
flats are subject to higher tidal-current velocities than mud flats.
||Seaweed-covered coarse flat - Coarse-grained, shallow
subtidal and low intertidal flats which act as a stable substrate for
seaweed such as Ulva, Enteromorpha, Ascophyllum,
||Mussel bar - Low mounds of living mussels, Mytilus
edulis, and/or disarticulated and broken mussel shells accumulated
by wave shoaling. Mussel bars generally occur at the mouths of
estuaries or embayments at tidal channel margins where nutrient-laden
oceanic waters first flood flat environments. Mussel bars accumulate on
||Channel levee - Linear accumulations of sediment along
margins of tidal channels built several tens of centimeters above the
surrounding intertidal flats. Channel levees are constructed from
sediment deposited on the flat as the tide rises above the channel
||Algal flats - High, coarse and fine-grained intertidal
flats covered with the green algae, Enteromorpha erecta.
||Veneered Ramp - Former boulder ramps presently covered
by fine-grained sediment settling out of the water column.
||Ledge - Subaerially or subaqueously exposed bedrock.
||Fluvial-estuarine channel - Transitional channel
between river and estuarine channels. The fluvial, tidal fluvial, or
estuarine state depends upon the volume of river discharge entering the
||Point or lateral bars - Accumulations of sediment
adjacent to intertidal channel margins at channel bends (point bars) or
along straight segments (lateral bars).
||Swash bars - Accumulations of sediment which occur
where waves shoal onto intertidal flats.
||Flood-tidal delta - Lobate bars of sediment which
accumulate landward of an inlet separating a back-barrier estuary or
lagoon from open-ocean water.
||Ebb-tidal delta - Lobate bars of sediment which
accumulate seaward of an inlet separating a back-barrier estuuary or
lagoon from open-ocean water.
||Fan delta - Coarse-grained, fan-shaped deposits which
accumulate on intertidal flats where upland streams drain onto high
||Spillover lobes - Lobate bars of sediment which extend
from flood-tidal deltas into estuarine or tidal channel areas.
|Flat environments - Submerged,
gently sloping, or level environments composed primarily of fine sand,
silt, and clay. Includes subaqueous exposures of coarse-grained,
Pleistocene glacial sediments.
||Mud flat - Fine-grained subtidal flats.
||Coarse-grained flat - Coarse-grained subtidal flats.
||Eelgrass flat - Fine-grained and coarse-grained,
shallow subtidal (low intertidal) flats which support dense stands of
eelgrass (Zostera marina).
||Seaweed community - Coarse-grained subtidal flats and
bedrock ledges which support seaweed growth.
||Upper shoreface - The inner subtidal slope which
extends seaward from large exposed sand beaches where sediments are
actively transported by bottom currents generated by storm waves. The
upper shoreface is a sandy environment of constant wave shoaling under
normal wave conditions.
||Lower shoreface - The outer subtidal slope which
extends seaward from the upper shoreface. The lower shoreface is
affected only by currents generated by storm waves. Lower shoreface
sediments grade from sand to mud in a seaward direction.
|Channel Environments - Linear,
intertidal, and subtidal depressions carrying tidal-current water.
||High-velocity tidal channel - Tidal channels where
maximum flow velocities probably exceed 2 meters per second (m/s).
||Medium-velocity tidal channel - Tidal channels where
maximum flow velocities probably attain values between 1 and 2 m/s.
||Low-velocity tidal channel - Tidal channels where
maximum flow velocities probably do not exceed 1 m/s.
||Estuarine channel - Tidal channels where ocean and
river waters mix. Estuarine water salinities range between 0.5 ppt and
||Estuarine flood channel - Estuarine tidal channels
where flood-tide current velocities greatly exceed velocities attained
during ebb tide.
||Estuarine ebb channel - Estuarine tidal channels where
ebb-tide current velocities greatly exceed velocities attained during
||Inlet channel - High current-velocity channels cut
through barrier beaches and connecting back barrier estuaries or
lagoons with the open ocean.
||Dredged channel - Man-made, artificially-deepened or
widened tidal channel.
||Channel slope - Gently to moderately sloping wall
margins of large tidal channels. Channel slopes are confined to channel
wall margins composed of sediment.
||Abandoned tidal channel - Former tidal channel no
longer carrying flow sufficient to erode the channel floor or margin
walls. Abandoned channels usually occur in salt marsh tracts where
meandering of the central drainage channel cuts off former channel
||Tidal fluvial channel - Lower portions of river
channels under tidal influence but not carrying estuarine waters.
|Tidal creeks - Small tidal channels draining salt
marshes or intertidal mud flats.
|Marsh drainage ditch - Man-made, rectilinear ditches
dug into marshes to facilitate marsh surface drainage.
|Approximate transition boundary between estuarine and marine
(30 ppt salinity) waters and between estuarine and river (0.5 ppt)