714
Stauble and Tabar
( 3.32 ft) on the inner segments and 0.86 m ( 2.83 ft) on
the volume of sand was gained at the base of the seawalls.
Locally, the nearshore profile was impacted by the placement
the outer segments resulted in only an 8% decrease in wave
of the P.E.P. Reef, as a landward trough developed at the
heights passing over the breakwater. Wave gage records in-
base of all of the breakwater segments. A seaward trough
dicate larger storm waves were reduced in height by around
also formed after storm waves. These troughs at the P.E.P.
12% after settlement. The crest width of 0.31 m (1 ft) of each
segments further reduced the volume of sand in this zone
P.E.P. Reef unit was too narrow to sufficiently reduce wave
relative to pre-placement profiles. The south control profiles
height. Wave and circulation modeling indicated that if the
had an intermediate length profile mostly backed by low
breakwater segments had not settled, they would have atten-
dunes and a few seawalls. The nearshore region was domi-
uated more wave energy and allowed for possible sediment
nated by a shallow outcropping of the Riomar Reef, part of
accumulation up to 15 to 25 cm (0.5 to 0.7 ft) over a 30-day
the natural hardbottom. This reef had the highest relief and
model test (ZARRILLO, 2002).
was the closest to shore of hardbottom in the three zones.
Based on current data collected along with the wage gage
The beaches in this zone exhibited alternating erosion and
deployments, the breakwaters have limited influence on the
accretion, with a large gain in sand at the end of the study
currents. It is noted that, the current data was only collected
on the upper beach and foreshore. Little change in volume
for a short time and under low wave conditions. The P.E.P.
was measured in the nearshore.
Reef appears to be affecting the ability to transport sand in
The relative importance of the breakwaters and the natu-
the longshore direction based on the shoreline and sand vol-
ral non-uniform outcropping of rocky hardbottom on the local
ume analysis. The north end of the reef appears to limit the
coastal processes was evaluated. With natural hardbottom
movement of sand from the north control to the P.E.P. Reef
almost directly alining with the boundaries of the north con-
zone. A large sand accumulation was measured on the south
trol, P.E.P. Reef and south control areas, it was difficult to
end of the north control zone. A bulge in the shoreline was
separate the impact of the P.E.P. Reef from that of the exist-
observed to grow over the study from the aerial photographs
ing hardbottom. Comparison of long-term historical shore-
just to the north of the first P.E.P. Reef segment (STAUBLE,
lines and more recent historical (1972, 1986, 1993) profile
2002). The north part of the P.E.P. Reef zone had the most
data from the Florida DEP with present day shoreline and
landward shoreline and smallest profile volumes throughout
volume changes after installation show a similarity in trends,
the study. For the first two years, the north end of the south
with erosion in the P.E.P. Reef zone and accretion in the
control along with the last two segments of the P.E.P. Reef
north and south control zones. The post-installation changes
also seemed to be limited in sand volume and experienced
appear to be more exaggerated, but follow the long-term
landward movement of the shoreline. It was not until after
trends, indicating that the P.E.P. Reef has only a localized
the tropical storms in fall 1999, that this pattern of recession
effect on the overall coastal processes.
and accretion was changed resulting in sand moving along-
The gain in sand on all three zones at the end of the study
shore through the system.
is problematic, with large sand gain measured on the upper
Early measurements of scour rods indicate that localized
scour at the toe of the breakwater structure was directly re-
portion of the beach after the passage of several tropical
lated to settlement. Most of the segments are now resting on
storms in the fall of 1999. This volume of sand remained
the natural hardbottom. Scour rods placed around the north-
throughout the winter and was only slightly redistributed in
ern-most segments, the center segments and the southern-
the alongshore direction. The large gain in sand in December
most segments documented a high degree of variability over
1999 is suspected to be the result of fair weather waves mov-
time in sand elevation changes adjacent to these units. Scour
ing sand, originally moved into the nearshore by the storms,
started at the southern segments almost immediately after
back onto the dry beach. A large volume of sand also moved
placement and has spread to all segments by the second year.
downdrift from the north control through the P.E.P. Reef
Scour in the gap regions was more pronounced at the begin-
zone, to be deposited on the southern end of the P.E.P. Reef
ning of the study, with accretion measured in the last (May
zone and northern portion of the south control zone. It is com-
to June 1998) scour rod measurement period. Initially, more
mon to have a rapid recovery of sand back onto the dry beach
sand was scoured out from the offshore segments, but as the
after the passage of a tropical system, since most of these
study progressed, scour was present around the inshore seg-
storms are followed by long periods of fair weather waves,
ments also.
that move sand back onto the beach. The volume of accretion
measured after the storms, and the fact that it remained
At the time of this writing, the P.E.P. Reef has remained
through the winter with little change in volume and only
in place. There are no immediate plans for modifying or re-
slight redistribution in both the cross-shore and longshore
moval of the project.
direction was surprising. The frequency of storms during the
CONCLUSIONS
winter and spring of 1999/2000 was about average, however,
the magnitude of the storms was lower than average. The
Objectives
post storm sand that accreted on the back beach was pre-
served and was only moved slightly in a southerly (downdrift)
According to the vendors, there are three primary function-
direction.
al objectives of prefabricated submerged breakwaters along
Wave transmission over the P.E.P. Reef was enhanced by
open ocean coasts (AMERICAN COASTAL ENGINEERING, 1993;
the settlement of all of the segments within the first 14
CRETER et al., 1994). The first is to reduce wave energy trans-
months of the study. An average settlement of 1.01 m
mitted over the structure. The second is to stabilize the
Journal of Coastal Research, Vol. 19, No. 3, 2003
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