LTC 109-2002
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CITY of MIAMI BEACH
Office of the City Manager
Letter to Commission No. I Oq - .). 0 0 ~
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FROM:
Mayor David Dermer and
Members of the City Commission
Jorge M. Gonzalez .../
City Manager ~,.r D
MIDDLE BEACH E~OSION CONTROL BREAKWATER PROJECT
Date: April 30, 2002
TO:
SUBJECT:
The purpose of this LTC is to provide the Mayor and Commission with an update
regarding the upcoming start of construction of the Middle Beach Erosion Control
Breakwater Project, an innovative beach erosion control project that will be built
within the beachfront area between 28th and 34th Streets. The construction
operations will start on Monday, May 6, 2002 and will be completed in
approximately 90 calendar days.
The Public Works Department has briefed the Ocean Drive and Miami Beach
Hotel Owners Associations about the project and will continue to provide them
with updated information throughout the project.
Backaround:
Beach erosion has been a problem on Miami Beach since the 1930s. By the late
1950s, the beach had eroded to such an extent that many of the beachfront
properties were forced to construct seawalls to prevent their structures from
being undercut by the encroaching tides.
In the mid-1970s, the U.S. Army Corps of Engineers (ACOE) and Miami-Dade
County entered into a 50-year contract for the joint management of the County's
sandy beaches. In 1979, the ACOE constructed a flood control dike (sand dune)
and an engineered beach along the entire length of Miami Beach. The new,
engineered beach was 200 - 300 feet wider than the native beaches had ever
been. The new beach was a tremendous success and has been credited for
contributing significantly to the resurgence of our local economy.
The sand used to construct the dunes and beaches was pumped or hydraulically
dredged from deposits of sand about a mile off our coast. The renourished
beaches were subjected to the same erosional forces, which depleted the
original beaches. As a result of the continuing erosion, six segments of Miami
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Beach have been renourished since 1980. The original beach construction and
the subsequent renourishment projects have consumed more than 25 million
tons of sand. As a result, the near shore deposits of sand, which have
traditionally been the source for renourishment projects, have been exhausted.
Faced with a continuing need to maintain our beaches and an exhausted supply
of sand, the City's Environmental Resources Management Division initiated an
effort to develop long-term solutions to the beach erosion problem. One element
of that effort involved the development of new technologies, which will slow down
or stop the beach erosion process, thereby reducing the demand for replacement
sand. If the erosion cycle can be successfully slowed or stopped, it would be
worth millions of dollars in cost savings and eliminate many of the environmental
and legal problems related to renourishment projects.
A study of the Miami Beach shoreline was conducted to determine where the
beaches are eroding, how fast they are eroding and why. The study revealed the
presence of several "hot spot" areas along our shoreline, which account for the
majority of our sand losses each year. Analysis of the study data indicated
breakwater-type structures could be designed, which would significantly reduce
the rate of erosion within these hot spot areas and help stabilize large sections of
our beach.
The worst of the identified hot spots exists within the area between 28th and 34th
Streets in the Middle Beach District. This hot spot is responsible for the loss of
more than 120,000 cubic yards of sand each year and in turn accelerates the
erosion of the beach for as much as a mile to the north. With beach
renourishment costs at about $20lton, this hot spot is responsible for the loss of
more than $2 million annually (See Figure 1 attached).
l3ecause of the critical state of erosion that persists in this hot spot area, the City,
the County and the State joined together and designed a series of three
breakwater structures which will redirect wave energies and control the coastal
processes to eliminate the hot spot. The design of the breakwaters has been
completed and construction is scheduled to begin on Monday May 6th, 2002. The
construction will require approximately four months to complete and will cost
approximately $975,000.
The breakwaters will consist of a core structure of tetrahedron-shaped concrete
modules, with a layer of native coral rock boulders across the top and down their
seaward face. The area between the existing waterline and the new breakwaters
will be filled with sand that will be brought up from Lummus Park (See Figure 2
attached).
The tetrahedrons and boulders that will be utilized for the construction of the
breakwaters will be stored in the beachfront area located between 22nd and 28th
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Streets, beginning at the seaward (eastern) limit of the vegetated dune area and
extending 35' eastward, excluding eight, 20'-wide pedestrian access corridors
that shall be maintained for public access at walkways which exit from the
boardwalk at 23rd, 24th, 24.5, 25th, 26th, 27th, 28th and 29th Streets,
respectively.
The heavy equipment, trucks and other construction machinery required for the
construction of the breakwaters will be staged in one of two authorized
equipment staging areas, which will be located east of the vegetated dune area
between 21st and 22nd Streets and in the open sand area adjacent to the beach
maintenance dumpster enclosure, immediately west of the dune area and north
of the 10th Street vehicular beach access corridor, respectively.
The construction of the breakwaters and the sand relocation operations will both
require portions of the beachfront area to be temporarily closed to public access.
Plans for the establishment of a series of daily work zones for the sand recovery
operations and sequential breakwater construction zones have been developed
to allow the contractor adequate space to safely and efficiently complete the
proposed construction activities, while minimizing the area of the beachfront to
which public access will be temporarily prohibited. Provisions for safety
barricades, signage and security personnel have also been included to ensure
public safety (See Figures 3 & 4 attached).
The City has also reserved the right to require minor modifications to the size,
location or use of the project work zones or staging areas if necessary to ensure
public safety, to accommodate special events or if it is deemed to be in the best
interest of the City.
The Middle Beach Breakwater project is the first phase of a master plan to
develop a series of erosion control breakwaters, positioned in key areas along
the shoreline, to widen the beaches and slow the erosion process.
If you have any questions or need any additional information about this project,
please feel free to contact me, or Bruce Henderson in the Environmental
Resources Management Division of the Public Works Department.
JMJa
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Figure 1- 30th Street Beach Erosion Hot Spot
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Figure 4 - Sand Recovery Zone
SAND RECOVERY ZONE
14th Terrace - Northern limit
of sand recovery area
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Typical Daily Work Zone
LU111111US Park
8th Street - Southern limit of
sand recovery area.
CROSS-SECTION OF SAND RECOVERY AREA
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Approximate volume of sand to be excavated.
PRm! ~ 2000 ~ SURYO'i
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High Water Line
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Optimum Beach Profile Line
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400 .... 100 lU)
~ IN FW FROU EROSION CONTR1 lINE
R-MONUMENT 70:.
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