720
Stauble and Tabar
Wave data collected at the Midtown Palm Beach site, in-
outcrop of hardbottom. The Beachsaver Reef placements were
dicated a wide range of data over time from the offshore and
along the New Jersey Atlantic Ocean coast and were placed
inshore wave gages. This was due to differences in tide level,
in close proximity to groins, with the Avalon site being ad-
smaller wave transmissions with higher wave heights and
jacent of an inlet terminal groin but open on the downdrift
greater reflection from existing seawalls and revetments on
end. The Cape May Point site at the entrance to Delaware
the back beach after loss of sand (DEAN and CHEN, 1995c).
Bay and Belmar/Spring Lake sites along a high wave energy
It was determined from a comparison of the wave attenuation
coast, placed the reef as a solid barrier on the seaward end
between the concurrent control and reef gages, that the
between groin compartments, creating a closed cell perched
P.E.P. Reef associated transmission coefficients ranged from
beach. Beach fills were placed concurrently with the Avalon
0.85 to 0.95 at that site.
and Belmar/Spring Lake projects.
Comparing the deeper placement of the Beachsaver at the
The dimensions and triangular configuration were similar
Avalon site with the shallow placement at Cape May Point,
for both types of concrete structure. This narrow-crested de-
the wave measurements indicate that the wave attenuation
sign, with a steeper landward facing slope experienced scour
was a strong function of the water depth over the reef crest
on the landward base with minimal wave attenuating effect
and the incident wave heights. Wave transmission coeffi-
(around 10% at all projects). Filter cloth and a geotextile mat-
cients ranged from around 0.78 to 1.13 at the Avalon site
tress used on two of the New Jersey sites appeared to mini-
(BRUNO et al., 1996a) and around 0.9 at Cape May Point
mize but not eliminate scour and settlement. The most suc-
(HERRINGTON et al., 1997). Wave heights were reduced over
cessful projects as far as retaining sand on the beach profile
the breakwater for periods when the reef crests were near
and maintaining a stable shoreline were the two perched
the water surface and for periods of large incident wave
beach configurations at Cape May Point and Belmar/Spring
heights.
Lake. Fill placed at Belmar/Spring Lake was retained within
Initial wave measurements at the Vero Beach site indicate
the groin compartment and the natural beach at Cape May
a wave transmission coefficient of around 0.88 soon after the
Point was maintained with minimal loss using this closed cell
initial placement before the P.E.P. Reef units settled. After
design, which limits the seaward movement of sand within
the first four-month monitoring period when the most rapid
the compartment. In the more open coastal configurations,
settling took place, the coefficients averaged between 0.91
the reef was less successful in retaining sand on the beach
and 0.92. A control site south of the reef indicated that the
and preventing landward movement of the shoreline. At Av-
wave height difference over the natural bed ranged from 0.91
alon, the northern end of the project was more successful in
to 1.03. The wave studies suggest that once the units had
retaining beachfill sand in a semi-enclosed environment of
settled there was minimal reduction in the waves as they
the reef attached to the inlet terminal groin, than in the
passed over the reef. Only the larger storm wave showed a
southern end of the project where the reef was detached and
significant reduction in wave height on the landward side of
parallel to the shoreline. The three Florida projects were all
the reef.
placed parallel to the coast, detached from any other shore
protection structures and are ineffective in retaining sand or
stabilizing the shoreline behind the reef structures. Currents
Performance Criteria
induced by the single long Midtown Palm Beach configura-
This review of monitoring data of six different installations
tion seem to be responsible for scour along the reef and de-
of prefabricated submerged, narrow-crested concrete break-
position beyond the ends of the structure. The staggered con-
waters has allowed for evaluation of project performance, suc-
figuration of the Vero Beach project with gaps between the
cess or failure criteria and particulars of unique coastal en-
individual segments appeared to alleviate this reef-induced
vironments of placement. The stated objectives of this type
longshore current, but the northern most reef segments still
of breakwater were to a) reduce wave height, b) stabilize the
limited an apparent sand wave from moving alongshore, re-
shoreline position, c) limit sediment volume changes in the
sulting in initial higher erosion and later less accretion be-
vicinity of the breakwater, and d) lower wave energy land-
hind the reef, than in the two adjacent control areas. The
ward of the breakwater during storms.
natural hardbottom configuration and the presence of sea-
Each placement site had some similarities and well as
walls and narrower beach width behind the P.E.P. Reef also
many differences in morphology, underlying geology, prevail-
affected the retention of sand.
ing coastal and inlet processes and proximity to other shore
The most successful projects were when these narrow-
protection structures. The P.E.P. Reef installations were all
crested prefabricated concrete submerged breakwaters were
on open Atlantic Ocean shorelines along the lower central
used to create a closed cell perched beach at the seaward end
Florida coast away from the influence of inlets and shore per-
of groin compartments. While not dissipating much wave en-
pendicular shore protection structures. The units were placed
ergy, the reef structure was able to prevent offshore transport
some distance from the beach in a shore-parallel configura-
of sand from within the compartment, as long as the reef was
tion not in contact with any groins. All of the sites had var-
attached to the adjacent groin or jetty tips by rock. More open
ious configurations of seawalls on the landward end of the
coast placement, where the breakwaters were detached from
profile. The Dupont property and Midtown Palm Beach sites
any shore normal structures, limited the sand trapping effec-
were a single line of reef units landward of any hardbottom.
tiveness by reef induced currents and limited wave attenua-
The Vero Beach site was a staggered inshore and offshore
tion due to scour and settlement.
placement of 11 segments placed at the edge of an extensive
Future placement of these types of submerged breakwaters
Journal of Coastal Research, Vol. 19, No. 3, 2003
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