EM 1110-2-1100 (Part V)
31 Jul 2003
(Breakwaters International, Inc., Flemington, New Jersey). Independent monitoring over 18 months revealed
significant structure settlement with the maximum over 1.2 m and average about 0.6 m (Sorensen & Weggel
1992). Most settlement occurred the first two months after installation. A large scour hole was found
landward of one section and the sand trapping volume in two salients was only about 300 m3, before
settlement (Sorensen & Weggel 1992).
(b) The Town of Palm Beach, Florida, in the early 1990s, experimented with another design labeled the
"Prefabricated Erosion Protection" or P.E.P. reef system by its developer, American Coastal Engineering,
Inc., West Palm Beach, Florida. Each unit is 3.7 m long, 4.6 m wide, 1.8 m high and is placed on a cloth filter
fabric. Each unit weights about 22 metric tonnes with crest elevation below msl to act as a thin-crested,
submerged, reef-type breakwater. One long breakwater/reef system, 1,270 m in length, placed 76 m offshore
(msl) in 2.9 m National Geodetic Vertical Datum (NGVD) water depth consisting of 330 interlocking units
was constructed. The submergence was 1.1 m at msl. Monitoring by the University of Florida's, Department
of Coastal and Oceanographical Engineering included nearshore profiles and wave gauges landward and
seaward of the structure (Dean and Chen 1996). About 17 percent of the units settled 0.8 m with the
remainder settling 0.5 m. Wave transmission coefficients ranged from 0.65 for normal conditions (tide range
1.0 m) to 0.85 for storm conditions. A detailed analysis of the leeward project area revealed that wave
overtopping, wave setup, pounding, excess longshore currents and sediment transport (both directions)
resulted in an increased erosion trend relative to that present before construction (Dean and Chen 1996;
Martin and Smith 1997). The conclusion, that the reef breakwater provided little benefit, resulted in its
removal. The units have since been salvaged and used to construct a groin field with beach nourishment at
the site (Erickson 1998).
(c) These negative results at West Palm Beach, Florida, resulted in a staggered and gapped, planform
l
configuration being the modified plan for the next P.E.P. reef installation at Vero Beach, Florida, in the late
1990s. Monitoring is being conducted by the USACE (Stauble and Smith 1999) with the latest results
reported by Wooduff and Dean (2000). Analysis of nearshore profiles over 25 months (August 1996 - June
1999) when compared with historic volume change (1972 - 1986) revealed that erosion has increased
landward of the reef. And, background erosion decreased north but remained the same south in control areas
outside the reef area (Stauble and Smith 1999).
(d) The Beachsaver breakwater unit and P.E.P. reef unit shapes are similar, namely triangular with flatter
slope on the seaward side than on the landward end. The have been called pyramid-shaped. Both have a thin
crest width. In contrast, a vertical, cylindrical shape (circular, concrete pipe) combined with a concrete base
forms the Hollow Core Reef System (HCR) as patented by Hollow Core Reef Enterprises, Inc., Newport
News, Virginia. Each unit is typically 3.6 m long at its base and 1.7 m wide, but the height varies (pipe
length) and is specifically designed for intertidal regions with 1-3-m tidal range. Since 1996, a 116-m-long,
nearshore breakwater consisting of 46 units, 2.6 m in height has been installed at Sea Island, Georgia, on the
Atlantic Ocean (tide range 1.8 - 2.7 m). Each unit weighs about 22 metric tonnes. Freeboard above msl is
unknown. The foundation is timber cross-members to form a subbase and initial settlement was measured
at less than 0.5 m. The units have been stable since construction and remain in place after several hurricanes
along the south Georgia coast (Oertel 1999, 2000, personal communications).
(e) In summary, crest width, planform configuration, siting and foundation design appear to be the
weakest aspect as revealed by field monitoring of precast, concrete, modules for breakwaters and submerged
reefs.
Shore Protection Projects
V-3-89
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