breach, the beach eroded
approximately 35 ft. Sediment
supplied by longshore transport
advanced the shoreline east of the
breach by as much at 55 ft within
about 425 ft of the breach
channel.
The beach tended
toward erosion at greater
distances to the east.
Water level was measured on
the ocean and sound side of the
barrier. Current velocity through
the main breach channel was
estimated by timing surface
drifters and measured with an
ADCP
during
two
field
deployments. Maximum current
velocity was on the order of 7 ft/
sec. On the Pamlico Sound side
of the breach channel, the
strongest currents were located
east of the channel centerline,
tended to the center through the
middle part of the channel, and
were located west of the channel
centerline on the ocean side. The
Figure 11. Example ADCP current transect at line 1.
ADCP data correspond to visual
observations and surface drifter
are to the west (left) of the channel center. Ebb current transects
estimates. A more thorough analysis of the current data is
for Line 2 indicate that the strongest currents tend towards the
planned. The collected morphologic and current data will
channel center. On Line 3, the strongest currents are observed to
provide both qualitative and quantitative descriptions of breach
be east of the channel center and sometimes have two distinct
evolution and will be applied in the development of numerical
maxima, one that parallels the main channel and another from the
models of coastal breaching.
margin channel on the northeast side of the breach. This
ACKNOWLEDGEMENTS
preliminary analysis of ADCP transect data corresponds to visual
observations of surface currents, namely, that on ebb flow two
This study was performed under support provided by the Inlet
distinct currents merged at the breach, and on flood flow there
Geomorphology and Channels Work Unit of the Coastal Inlets
was a strong current through the main channel with a more
Research Program, U.S. Army Corps of Engineers (USACE).
diffuse current spread out over the area between the flood shoal
The authors thank Dr. Nicholas C. Kraus of the U.S. Army
and margin channel.
Engineer Research and Development Center, Coastal and
CONCLUSIONS
Hydraulics Laboratory, for his encouragement in this project and
helpful review and John McCormick of the U.S. Army Engineer
Hurricane Isabel breached Hatteras Island by a combination of
District, Wilmington, for his assistance in the field and office.
elevated water level and wave attack from the Atlantic Ocean
Permission was granted by Headquarters, USACE to publish the
side about 6 miles northeast of Hatteras Inlet. The breach
information contained in this paper.
occurred at a location of minimum island width and elevation.
REFERENCES
As described in this paper, the breach was surveyed to provide
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conducted 10 days apart to capture short-term temporal changes
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14
Shore & Beach Vol. 72, No. 2, Spring 2004, pp. 9 - 14
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