Geology Reference
In-Depth Information
Fig. 12.1
Ebb- and fl ood-tidal delta models (From Hayes
1979
). Aerial photograph of Essex Inlet, MA. Inlet cross-section model
from FitzGerald (
1996
)
Commonly, the sides of the inlet are formed by the
recurved ridges of spits, consisting of sand that was
transported toward the backbarrier by refracted waves
and fl ood-tidal currents. The inlet throat is the con-
stricted, deepest part of an inlet normally coinciding
with the minimum channel width and maximum tidal
current velocities. The strength of the tidal currents in
the throat section is generally suffi cient to remove sand
from the channel fl oor leaving behind a lag deposit
consisting of gravel or shells, or in some locations
revealing bedrock or consolidated mud.
The stability of an inlet is related to the framework
geology of the region and littoral sediment transport
trends. Migrating inlets occur along coasts having a
pronounced net longshore transport system and where
the channel erodes through unconsolidated sediment
(e.g. Kiawah River Inlet, SC, Tye and Moslow
1993
) .
Conversely, natural stable inlets are situated in chan-
nels that resist lateral erosion such as those scoured into
former river valleys (Virginia; Halsey
1979
) , cut into
limestone (Florida; Zarillo et al. 2003), or abutting bed-
rock or till outcrops (New England; FitzGerald
1993
) .
Several classifi cations of tidal inlets have been
published based on the distribution of intertidal and
subtidal sand bodies and the general morphology of
the ebb-tidal delta and inlet shoreline including Oertel
(
1975
) , Nummedal and Fischer (
1978
) , Hubbard et al.
(1979), Hayes (
1979
) , Davis and Gibeaut (
1990
) , and
Galvin (
1994
). A discussion of these schemes can be
found in FitzGerald (
1996
) .
