Submerged Narrow-Crested Breakwaters
697
(BRUNO et al., 1996b). Scour was examined by divers as well
1996b). Scour was measured to the south of the Beachsaver
as from profile data. Waves were measured by two Inter-
Reef during the November 1993 and March 1994 surveys.
Ocean S4 electromagnetic current meters fitted with high-
The outfall structure and the bulkhead may have contributed
resolution pressure sensors mounted 1 m (3.28 ft) above the
to the erosion, as well as changes offshore to the southern
bed. Wave data were recorded over two time periods during
ebb shoal features. Erosion rates were calculated for the area
the monitoring. The first was a three-day period between 12
between the bulkhead and the seaward extent of the reef. The
and 15 September 1993 (BRUNO et al., 1996b). The inshore
average rate of erosion was around 30.6 cu m/m (40 cu yd/ft)
gage was placed 6.3 m (20.7 ft) landward of the reef in around
for the northern 183 m (600 ft) of the reef structure and
3.9 m ( 12.8 ft) MLW. The offshore gage was placed 20 m
around 47.4 cu m/m (62 cu yd/ft) for the southern end of the
(65.6 ft) seaward of the structure in around 3.6 m ( 11.8
reef (Figure 15). South of the reef structure, the profile mea-
ft) MLW. Both meters were about 180 m (591 ft) south of the
sured an average of between 35.9 to 71.1 cu m/m (47 to 93
8th Street jetty. A second deployment occurred over a five-
cu yd/ft) with the highest rates in front of the vertical faced
day period between 20 and 25 May 1995. During this second
timber bulkhead (BRUNO et al., 1996b).
deployment one meter was placed 6.0 m (19.7 ft) inshore of
the reef structure in 3.9 m ( 12.8 ft) MLW depth. The other
Settlement
wave gage was placed 15 m (49.2 ft) to the ocean side of the
Evaluation of the top of reef surveys showed that the set-
structure, in a depth of 3.3 m ( 10.8 ft) MLW. The gages
tlement was highly variable. The settlement measurements
were further north along the reef at 123 m (404 ft) south of
covered a 21-month period from November 1993 to May 1995
(BRUNO et al., 1996b). Settlement was measured at around
evaluated in the May 1995 deployment. An additional study
0.37 m (1.2 ft) at the northern end to around 1.52 m (5 ft) on
of circulation around the reef was done with the deployment
the southern end (Figure 16). Most of the settlement was
of Rhodamine dye in November 1993. Dye was released land-
measured during the first 9 months after installation. Even
ward of the reef around 180 m (591 ft) south of the 8th Street
with the settlement, the reef units remained interlocked to-
jetty and in a control area 585 m (1,919 ft) south of the reef
gether. The reef units were placed on top of a 2 m (6.6 ft)
structure.
thick layer of medium sand. A thin veneer of cohesive sedi-
ment was located 0.91 m (3 ft) below the sand bed and may
Monitoring Results
be the reason for the settlement. The settlement stopped once
the fine material was eroded beneath the structure (BRUNO
Shoreline Response
et al., 1996b).
Beach fill was placed between the May 1993 and Septem-
ber 1993 surveys. The reef was also installed at that time.
Scour
The seaward movement of the shoreline is in response to the
fill. Subsequent shorelines surveys showed a retreat as the
A scour zone was identified on the landward side of the
fill adjusted to the waves and tidal currents in November
Beachsaver units. This narrow zone is adjacent to the land-
1993, January 1994 and March 1994 (BRUNO et al., 1996b).
ward base of the concrete units. After the new beach fill
By May 1994, the beaches south of the submerged breakwa-
placement in June 1995, monitoring continued around the
ter had retreated back to the pre-fill location, but the shore-
southern end of the reef. Scour was measured inshore of the
line behind the reef was still seaward of the pre-fill shoreline.
southern end of the reef in the post-fill survey of July 1995.
A seasonal accretion occurred between May 1994 and Sep-
The fill had buried the reef, but the crest quickly became
tember 1994 during the calm summer months. Little change
exposed, with a scour to the south of the end unit (BRUNO et
was measured through November 1994, with additional ac-
al., 1996b). This scour zone inshore of the southern end of the
reef continued to grow to a depth of 0.91 m ( 3 ft) as of
cretion in the north. Between November 1994 and February
1995, several winter storms eroded much of the beach fill
September 1995 and extended some 12.19 m (40 ft) landward
material. Sand was transferred mechanically from the north-
of the structure. By December 1995, the scour zone deepened
to 1.22 m ( 4 ft) below the crest of the reef.
ern end of the project to the southern area (BRUNO et al.,
1996a). With the limited surveys in 1995, profiles behind the
Beachsaver Reef (AC) showed more stability than the pro-
Wave Attenuation
files to the southern open end of the reef (FG) (BRUNO et
Inshore and offshore directional wave data were collected
al., 1996b). The northern profiles were approximately 15.2 m
to determine the wave attenuation by the Beachsaver units
(50 ft) wider than the pre-fill beach, while the southern
for a 3-day period in September 1993 and a 5-day period in
beaches returned to a pre-fill width (Figure 14).
May 1995. This wave data was supplemented with 1) a Na-
tional Weather Service surface wind speed and direction me-
Sediment Volume Response
ter deployed at Atlantic City some 40 km (25 miles) north of
Volume data were not presented, but elevation change data
the site; 2) a deepwater NOAA directional wave buoy located
were presented between the September 1993 post-installa-
some 72 km (45 miles) to the SSE of the site; and 3) in 1993,
tion/fill survey and the last full survey in November 1994.
a U.S. Army Corps of Engineers directional wave gage de-
Erosion was measured in the nearshore area. Several north-
ployed 3.2 km (2 miles) south of the site as part of the beach
easter storms were reported during this time (BRUNO et al.,
fill monitoring (BRUNO et al., 1996b). With the close prox-
Journal of Coastal Research, Vol. 19, No. 3, 2003
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