718
Stauble and Tabar
remained relatively stable with a seaward movement of ap-
The enclosed groin compartment configuration of the Cape
proximately 6.1 m ( 20 ft).
May Point Beachsaver Reef installation, created more of a
At Vero Beach, Florida, from the August 1996 to June 1999
perched beach. A total volume change was given in each cell,
period, the MHW shoreline, showed a relative pattern of sea-
rather than for individual profiles. Over the two-year study,
ward movement in the north control, a landward movement
the eastern Cell 2 between the Leigh and Whilldin Avenue
in the P.E.P. Reef zone and a mixed sometimes landward and
groins had a net gain of sand, with the most pronounced ac-
sometimes seaward movement in the south control zone. As
cretion on the eastern side of the cell. The most gain was
of the December 1999 survey, the shoreline over the entire
found in the nearshore and foreshore portion of the profile
project length moved seaward, reflecting large gains in sand
around 122 m (400 ft) landward of the reef. A smaller net
from post-storm recovery. Over the winter and spring, the
gain in sand volume in Cell 3 between the Willdin and Coral
shoreline continued to average an overall seaward movement
Avenue groins was reported, with sand accretion found in the
trend for the entire project length. Most of the seaward move-
nearshore area. Again, the most gain was measured on the
ment this time was in the south control zone, with a smaller
eastern side of the groin compartment. The downdrift west
but seaward movement also in the P.E.P. Reef zone. The
control Cell 4, measured a volume loss over the study, with
north control zone showed a slight landward movement, but
most of the loss on the western side of the cell and between
the cumulative overall project averaging was the largest sea-
the dune base and 61 m (200 ft) offshore. A similar enclosed
ward movement of the three zones. This shoreline change
groin compartment deployment of the Beachsaver Reef at
analysis may reflect a longshore movement of a sand wave
Belmar/Spring Lake also formed more of a perched beach,
from north to south through the project area in the last year
with an added volume from a truck fill on the backshore area.
of monitoring. The seaward movement of the shoreline in all
This material was retained in the compartment except for a
three zones (with the least seaward movement in the P.E.P.
slight loss of sediment as the fill moved from the berm to the
Reef zone), indicate that the same processes were operating
nearshore portion of the profile landward of the reef struc-
in all three zones, somewhat independent of the Reef struc-
ture.
ture.
The detached and staggered P.E.P. Reef at Vero Beach ex-
hibited a gain in sand volume in the north control, loss in the
P.E.P. Reef area and a mixed volume of gain and loss over
Sediment Volume Response
time in the southern control zone for the first three years.
Another way to assess the performance of these types of
With the gain is sand over the entire project area in the last
breakwaters, was to measure the change in volume of sand
year of the study, sand volume gain was measured in the
along the beach profiles. All projects measured the change in
backshore area of all three zones. The gain in sand volume
profile volume by comparison of temporal profiles. Shoreline
was the least in the P.E.P. Reef area, with most of the grain
position change gives an indication of gain or loss of sand at
in the two control zones. The majority of the volumetric
one point along the profile, and is a function of what ``shore-
changes in the P.E.P. Reef zone occurred landward of the
line'' indicator is chosen. The differences in volume between
breakwater axis and in both control zones landward of the
two dates, gives a measure of cut and fill along the entire
natural hardbottom. Little change was detected in all of the
measured profile, and documents the retention or loss of sand
profile volumes seaward of the P.E.P. Reef axis and over the
from behind the breakwater structure.
natural hardbottom.
The overall change in volume at the Dupont property
showed a variable pattern with gain in the north control, loss
Settlement
behind the P.E.P. Reef increasing to the south, and a gain
just to the south of the reef but loss further to the south. At
Breakwater crest height is important in submerged break-
the Midtown Palm Beach site, the north control area expe-
water design. One of the objectives of these narrow-crested
rienced both erosion and accretion over the monitoring period
breakwaters is to reduce wave height transmission. In order
with overall minimal change in sediment volume. Erosion has
to be effective, the structure freeboard must be shallow
been measured in the lee of the P.E.P. Reef and just to the
enough to trip the incoming waves. Crest elevations on these
units were placed within 1.22 m ( 4 ft) of the surface on
south of the reef zone. Seaward of the reef structure, volume
changes were mixed over the monitoring period but were of
all of the installations. Settlement and movement of the units
much less magnitude than landward of the reef.
were monitored on some of the projects by measuring the
At the Avalon site, individual profile volume data was not
change in elevation of the crest height over time.
presented, but three-dimensional elevation change data in-
No actual measurements were reported on settlement of
dicated that more erosion was found to the south of the
the Dupont Property installation, but it was observed that
Beachsaver reef units. The semi-enclosed jetty attached
some or the larger first generation P.E.P. Reef units moved
northern end of the reef had the lowest erosion rate, followed
seaward during a northeast storm. After realignment, no fur-
by the open southern end of the reef and the highest erosion
ther movement was measured. Settlement occurred from 5 to
rate was found in the southern control area. An outfall struc-
18 months after placement of the second-generation P.E.P.
ture and the backshore parallel bulkhead in this southern
reef units at the Midtown Palm Beach installation. Placed on
area may have contributed to the erosion, as well as changes
a sandy bottom, the settlement ranged from 0.6 to 0.8 m (2
offshore to the southern ebb shoal features of Townsends In-
to 2.6 ft).
let.
Settlement of the Beachsaver Reef at Avalon was highly
Journal of Coastal Research, Vol. 19, No. 3, 2003
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