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FitzGerald and Pendleton
subsequently transported seaward becoming part of the ebb-
Short-Term Processes
tidal delta and spit platform. Some of the sand also fed the
A review of yearly vertical aerial photographs and field
spit system that eventually attached the downdrift inlet
observations of New Inlet between 1989 and 2001
shoreline to the mainland.
demonstrate that the outer portion of the main ebb channel
Almost from the beginning the main ebb channel has been
switched locations on several occasions and a number of
located along the downdrift side of the inlet. This position is
small swash bars, 100 to 300 m in length, migrated onshore
a result of ebb-tidal flow approaching the inlet only from the
(Fig. 5). As described by FITZGERALD et al. (2000) these
north (Pleasant Bay) (FITZGERALD and FITZGERALD,
processes at a migrating inlet indicate that sediment is
1977), due to the fact that the downdrift spit attached to the
moving past the inlet mouth. At New Inlet the dominant
mainland closing off access to the southern bay tidal prism.
southerly longshore transport of sand produces an extension
Since the latter part of 1988, the inlet mouth has consisted
of the spit platform and a deflection of the distal part of the
of an expansive updrift spit platform (1.0 to 1.3 km in
main ebb channel past the downdrift inlet shoreline. This
length) and downdrift channel thalweg. From 1990 to 1996
gradual lengthening of the main channel decreases flow
the spit platform maintained approximately the same
efficiency between the ocean and bay, eventually resulting
configuration and aerial extent, except for small-scale
in the breaching of a new shorter channel through the ebb-
changes associated with the formation and migration of
delta. The breaching event commonly occurs during a storm
swash bars and minor channels. In 1997 the northern
when elevated water levels and a stronger than normal ebb
recurved spit began accreting southward 600 m across the
intertidal platform, a process that continues to the present
directly across the outer ebb shoals. Once the outer main
time. Re-initiation of spit growth may be a consequence of
channel occupies the new short-cut channel, the sand shoals
increased supply of sand to the inlet and/or a period of mild
that have been displaced to the downdrift side of delta are
northeast storms during the past five years
moved onshore by wave action. This process of outer
(ZHANG et al., 2001;
channel shifting has occurred repeatedly at New Inlet with
http://ocean-beach.com/weather_norester_history.htm).
The ebb-tidal delta is composed of the spit platform and
an arcuate group of sand shoals associated with the main
Spit Platform Breaching
ebb channel. Ebb flow through the main channel causes a
The sediment bypassing process described above
seaward excursion of the delta lobe beyond the limits of the
involves the transfer of relatively small volumes of sand
spit platform. Throughout most of the nineties (1990-1999)
(2,000-10,000 m3) to the downdrift shoreline. A potentially
the outer portion of the main ebb channel was skewed along
much larger volume of sand would bypass the inlet if the
the downdrift shoreline. This asymmetry was a result of the
main channel breached a new pathway through the spit
southerly longshore transport system and the preferential
platform. KANA and MASON (1988) and FITZGERALD
accumulation of sand on the updrift side of the ebb delta
et al. (2000) have discussed this mechanism of inlet
(FITZGERALD, 1988). Changes in the configuration of the
sediment bypassing. Sequential aerial photographs of New
ebb-tidal delta during past few years are evidence of a more
Inlet illustrate that subtle changes in the backbarrier
active sediment-bypassing regime.
dramatically influenced flow patterns through the ebb-tidal
delta.
INLET SEDIMENT BYPASSING
As seen in figure 5, when the downdrift spit attached to
When a new inlet is formed, sand is withdrawn from the
the mainland cutting off the southern bay tidal prism in
longshore transport system until the ebb-tidal delta attains
1991, the throat position of New Inlet effectively shifted
northward to a location between the updrift spit and
New Inlet the decade-long retreat of the downdrift inlet
adjacent mainland. In this configuration the exchange of
shoreline is evidence of sand sequestering by the ebb-tidal
water between Pleasant Bay and the ocean was through a
delta. Littoral sand has also been diverted into Pleasant Bay
long and circuitous pathway between the spit platform and
enlarging the flood-tidal delta and other sand shoals
adjacent mainland. This channel pattern is analogous to
(PENDLETON and FITZGERALD, 2001; STAUBLE,
flow through a river meander bend consisting of a point bar
2001). During the past five years the southward extension of
(spit platform) and channel cut bank (downdrift side of
the updrift recurved spit has trapped additional sand.
main channel). A much shorter route would be formed if a
Reduction in sand nourishment to the downdrift beach
new channel were cut through the northern spit platform.
amounted to 200 to 300 m of shoreline recession between
However, for New Inlet to achieve this shorter course would
1990 and 2000 (Fig. 4). The rate of erosion lessened slightly
require a radical change in flow direction of the ebb
in the mid- to late nineties when greater quantities of sand
currents. During the early and mid-1990's the orientation of
began bypassing the inlet.
Journal of Coastal Research, Special Issue 36, 2002