Submerged Narrow-Crested Breakwaters
703
Figure 19. Volume change between profiles at Cape May Point, New Jersey (after Herrington et al., 1997).
Scour
et al. (1997) concluded that the reef structure did
RINGTON
not adversely impact the circulation in the east cell.
Scour of up to 0.6 m (2 ft) was observed just landward of
the reef in the form of a reef-parallel trench in the western
Project Performance
Cell 3. The eastern Cell 2 had a well-defined trench at the
landward base of the reef structure up until September 1995.
With the gain in sand on the landward side of the Beach-
The trench has filled in since then on the eastern end but is
saver Reef, particularly on the east cell the reef has stabilized
still present on the western profiles (B thru E). Surveys taken
the beach between the three groins at Cape May Point (HER-
in March 2002 indicate that a scour trench is still present
RINGTON et al., 1997). Profile monitoring indicated that the
along the landward side of the Beachsaver Reef in both cells
beach lost sand from the dune base and backshore but gained
with a depth of from 2.7 to 4.6 m ( 9 to 15 ft).
sand in the foreshore and nearshore out to the reef position
and responded to the typical seasonal cycle of the area. The
Wave Attenuation
MLW shoreline moved seaward within the two groin com-
partments with the reef on average 13.4 m (44 ft) for the east
With only a one-day deployment, the wave attenuation por-
cell and on average of 4.6 m (15.13 ft) for the west cell. The
tion of the study was limited. The study was done on 25 July
control groin compartment shoreline retreated landward on
1995 during the summer months with low wave heights, but
average 4.6 m (15.13 ft), while the profile showed erosion and
they increased as the day progressed from an offshore Hs of
no seasonal signal. After monitoring the project for two years,
0.28 to 0.31 m (0.92 to 1.02 ft). Wave attenuation coefficients
the cumulative volume in the two cells protected by the
between 0.86 and 0.96 were measured over the last three
Beachsaver Reef gained sand volume, with the east cell gain-
hours of the study (HERRINGTON et al., 1997). A wave height
ing a net 2,111 cu m (2,761 cu yd) and the west cell gaining
reduction was thus estimated at around 10 percent for the
a net 380 cu m (497 cu yd). Over the same period the control
Cape May Point installation.
cell in the next groin compartment lost a net 660 cu m (863
cu yd) (HERRINGTON et al., 1997). Settlement of the units was
Dye and Current Studies
prevented by the use of a thick filter cloth placed under the
Under the influence of the incoming tide, the first measure
units. Measurements of the unit tops showed that the settle-
of dye on 27 September 1994 remained close to where it was
ment was negligible over the two- year monitoring (HER-
first placed both behind the reef units in the east cell and in
RINGTON et al., 1997). Scour was measured on the landward
the control area to the west. As the tide reversed, the dye
side of the Beachsaver Reef with the formation of a trench of
was quickly dispersed to the east on the ebbing tide. HER-
0.61 m (2 ft) deep located at the landward side of the reef.
Journal of Coastal Research, Vol. 19, No. 3, 2003
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