Evaluating a Prefabricated Submerged Breakwater and Double-T Sill
for Beach Erosion Prevention, Cape May Point, NJ
Donald K. Stauble1 and Michael A. Giovannozzi2
ABSTRACT
As part of the US Army Corps of Engineers National Shoreline Erosion Control
Development and Demonstration Program, a demonstration project has been installed at
Cape May Point, NJ to evaluate prototype-scale "innovative" or "non-traditional"
methods of shoreline erosion control. The project consists of placing a linear
prefabricated concrete submerged breakwater called the Beachsaver Reef and a linear
prefabricated concrete sill called the Double-T across the seaward end of two adjacent
groin compartments, in order to assess the effectiveness of these structures in retaining
sand within the groin compartments and to reduce shoreline erosion. The beach site, at
the mouth of Delaware Bay on the extreme southern tip of New Jersey, is subject to both
wave and tidal current interactions and has experienced historic erosion and shoreline
retreat. Nine existing stone groins have created eight groin cells around a curved
shoreline from the Atlantic Ocean into Delaware Bay. The Beachsaver Reef in cell 5 is
the second such structure at this site and new improvements include shallow placement
with a crest elevation of 0 MLW and a geotextile fabric base to minimize settlement and
scour. Placement was in August and September 2002, by barge-mounted crane and
divers, in 2.7 m of water. Some excavation and fill of the bed was required to maintain
the desired depth of placement. The Double-T sill in cell 6 is the first installation of such
a device for erosion control. These units were placed at the same 2.7 m depth in four
days in October 2002 with the same barge-mounted crane and divers. No bed cut/fill was
required and no filter cloth was used. Stone was placed between the side of the groins
and both structures to fully enclose each cell as a perched beach compartment.
Monitoring of the project includes 29 beach profiles in all 8 cells to document shoreline
change and beach volume retention, scour and settlement measurements for structural
stability, sediment samples to assess grains size changes, wave and current monitoring to
measure wave/current modifications and aerial photography to document shoreline and
duneline movements and regional sediment changes. This project will evaluate the use of
two prefabricated concrete structures as coastal erosion control devices and if they retain
sand within the compartments, as well as retain new beach fill sand to be placed in 2004.
INTRODUCTION
The U.S. Army Corps of Engineers Research and Development Center is
authorized under Section 227 of the Water Resources and Development Act of 1996, to
1
U.S. Army Engineer Research and Development Center, Coastal and Hydraulics
Laboratory, 3909 Halls Ferry Road, Vicksburg, MS 39180-6199, (601) 634-2056, (601)
634-3080 fax, Donald.K.Stauble@erdc.usace.army.mil
2
U.S. Army Engineer District, Philadelphia, 100 Penn Square East, Philadelphia, PA
19107, (215) 656-6682, Michael.A.Giovannozzi@nap02.usace.army.mil
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