Shoreline Enhancement for MacDill
AFB; Phase II
I.
Summary
MacDill
Air Force Base (AFB), Tampa Bay Watch, Inc. and the United States Fish &
Wildlife Service (USFWS) are working to continue restoration of the Interbay
Peninsula shoreline. The partnership
between MacDill and Tampa Bay Watch to install oyster habitats along the
shoreline is a continuation of a community-based restoration project that began
in 2003, known as Phase I. Phase II
work will provide protection along 800 linear feet of shoreline. MacDill AFB is located at the southern tip
of the Interbay Peninsula (Figure 1), and receives substantial wave energy from
large vessels navigating the channels as well as natural storm-driven
waves.
This community-based enhancement project involves
the placement of 1500 Lo-Pro Reef Ball™ units and 500 linear feet of oyster shell bars along
the southeast corner of the Interbay peninsula, at Gadsden Point. These Lo-Pro reef balls are marine-friendly,
hollow, concrete oyster domes that will provide shoreline stabilization for the
currently eroding coastline and habitat for marine life. Sediment accretion landward of the domes will
eventually provide the substrate for Spartina
alterniflora, or salt marsh and other native coastal vegetation to further
stabilize this eroding shoreline. This area
contains large black mangroves, Spartina
sp., palms and live oaks that are being destroyed by the pounding waves. Future enhancement and restoration plans
include community-based plantings of the salt marsh along the southeast
coastline of MacDill AFB.
II. Background
Phase
I of this multi-stage project commenced in early 2004 with the installation of
910 Lo-Pro Reef Ball™ units protecting 800 linear feet of MacDill AFB shoreline. Along with two 100’ oyster shell bars, the
oyster domes protect the southeastern shoreline midway between Catfish and Gadsden
Points (Figure 2) from continuous wave action.
Monitoring of this project is currently underway and will continue
through the first half of 2006.
Observations thus far have shown excellent sediment accretion behind the
domes and bars, a positive sign of shoreline reestablishment.
The photo on the left identifies the substantial
oyster growth after four months on both the domes and the oyster shell bars
constructed in Phase I. Besides helping
to stabilize the shoreline, oyster dome communities provide environmental
enhancement in the form of hard-bottom habitats for fish and wildlife resources.
Expansion
of hard bottom surfaces will create a greater surface area for settling spat
(oyster larvae), and create habitat niches for other benthic organisms. In addition to wave relief, these domes promote
the following community benefits:
§
The oyster communities
improve our local water bodies, as oysters are filter feeders, capable of
surviving in a variety of water quality conditions are found throughout the
estuarine portion of the Tampa Bay ecosystem.
Oysters can filter up to 37 liters (9.8 gallons) of seawater every hour
(Friese, 1973) providing a natural filter, primarily for algae, in the nutrient
laden waters of the Bay.
§
Oyster communities
provide diverse food sources or foraging areas for a variety of important fish
species, birds and other wildlife species.
The constructed oyster communities provide recreational opportunities
related to these species.
§
Initially, the oyster
domes provide increased surface area for the attachment of sessile organisms
and provide protective habitats for larger invertebrates and fishes. Oyster communities also help stabilize
bottom sediments, which reduces turbidity levels and lowers erosions rates of
shoreline areas.
Once
the shoreline stabilizes, restoration efforts along this area will include planting
native salt marsh grass, or Spartina
alterniflora, to further protect the shoreline from constant wave
energy.
Plans
for Phase II provide protection of an additional 800 linear feet of shoreline
at Gadsden Point. Figure One
illustrates the Hillsborough Channel Cut A, the large vessel access to Tampa
Bay that is approximately 2000 yards (approx. 1.25 nautical miles) off Gadsden
Point. According to Port Operations at
the Tampa Port Authority, 3,313 vessels utilized this channel from September 2002
to October 2003. This equates to one
large vessel (tugs, barges, cargo or cruise ships) passing by Gadsden Point every
2.6 hours. These ships cause
substantial wave energy; effectively moving sediment along the shorelines of
the peninsula, as the short distance from the ship channel does not allow the
waves to dissipate.
III. CORE Description
The
goal of Tampa Bay Watch’s Community Oyster Reef Enhancement (CORE) program is
to increase the oyster population in Tampa Bay and at the same time, provide
habitats for small organisms, prevent shoreline erosion, improve water quality
and promote fish and wildlife habitats.
In addition, this project benefits the Tampa Bay community by promoting
environmental awareness and offering hands-on experience in habitat
restoration.
Oyster
shell bars will be constructed similar to natural oyster communities found
along shoreline areas throughout Tampa Bay.
Fossilized oyster shell from local shell mines provides a hard surface
for oyster larvae to settle upon and grow, eventually forming a natural reef. Mesh bags filled with fossilized shells will
be used to create the oyster bar habitats.
Each oyster shell bag is 20 inches long by eight inches in diameter and
made of diamond oriented tubular mesh filled entirely with fossilized (oyster)
shell. The design has been used
extensively by the South Carolina Department of Natural Resources (SCDNR) to
reduce movement of deployed shell for many of their oyster restoration
projects. This type of mesh does not
unravel and has not been shown to cause adverse affects to fish and wildlife
resources.
No
oyster shell or oyster bags will be placed in seagrass areas or in any areas
containing any significant benthic infauna.
Typically, natural oyster beds are located in the tidal flats from +1.5
mean low water (MLW) and lower, which is periodically exposed and limits
seagrass growth. All new oyster bars
(and domes) will be constructed landward of MacDill AFB “Do Not Enter/Boater
Exclusion Zone” signs posted approximately 100 feet offshore.
Over the last four years, Tampa Bay Watch has
created multiple oyster shell bars at five locations in and around Tampa
Bay. The picture on the right depicts a
one layer, two bag wide oyster bar constructed at Palonis Park, a City of Tampa
Park on the eastern shore of Old Tampa Bay at the Gandy Bridge. These shell bars have been successful at
both sediment accretion as well as new oyster recruitment.
Lo-Pro
Reef Ball™ units will be placed to provide wave attenuation to assist with
erosion control and to provide habitat for marine life. The oyster dome units are half-round in shape
and are made from marine-friendly concrete (additives are added to the concrete
to neutralize the pH, making it compatible to marine life). The oyster domes are 24” in diameter and 18”
tall and weigh about 75 lbs. These
reef balls are well suited for the establishment of oysters that are common
throughout Tampa Bay and along MacDill AFB shoreline. Placing the Lo-Pro’s in approximately two feet of water would
allow the units to be mostly exposed during low tide and totally submerged at
high tide; conditions which are optimum for oysters in Tampa Bay. Reef ball units will create habitat by
encouraging oysters and other filter feeders to attach.
The submerged oyster domes are covered with large holes
on the perimeter with a large opening in the middle, extending to the top of
the dome. These holes enable waves to
penetrate the unit and allow an easy flow of wave energy. Water enters the holes on the sides of the reef
balls and then is dispelled out the top.
The diagram illustrates how the water exits out the top of each unit. This movement of water will keep the unit
stable and immobile. The waves, in
essence, will not reflect backwards; but in all directions, more effectively reducing
the waves.
IV. MacDill AFB Phase II Description
Oyster
Shell Bars
Tampa
Bay Watch staff, MacDill AFB staff and volunteers will construct 500 linear
feet of oyster shell bars along the southeastern corner of MacDill AFB in the
following manner:
§
Pile of old
cable ↑ and old fence post →
Oyster shell bars created at the southeast point of
the Interbay Peninsula will assist with protecting 800 linear feet of salt
marsh and mangrove shoreline. Erosion
and tidal influence has affected the cluster of mangroves at the inlet opening
and warrants shell bag construction. A
200 foot oyster shell bar will be constructed, beginning at the southeast point
and extend 200 feet east-northeast, mimicking the natural shape of the
shoreline (Figure 3).
§
The remaining 300 feet
of oyster shell bars will consist of six 50’ bars constructed landward of the
Reef Ball communities. Two of these shell
bars will encompass existing marine debris—an old fence post and a tangle of
old cable—in their design and construction (Figures 3 and 4).
§
All oyster shell bars
will be built in shallow water using oyster bags placed approximately 15’ from
the shoreline. Figure five (5)
illustrates each oyster bar measuring 5’ wide and 0.66’ tall (three rows of
bags = 5’ width). Typically, natural
oyster beds are located in the tidal flats from +1.5 mean low water (MLW) and
lower. All new oyster bars (and domes)
will be constructed landward of MacDill AFB “Do Not Enter/Boater Exclusion Zone”
signs posted approximately 100 feet offshore (Figure 7).
Reef
Ball Units
A
total of 1500 Lo-Pro Reef Ball™ units will help protect 800’ of shoreline at the
southeast corner (Gadsden Point) of the Interbay Peninsula. This particular corner of the AFB receives
constant wave energy from the two ship channels (Hillsborough Cuts A and C,
Figure 1) that run parallel to the east and south coastline of the peninsula.
The
proposed plan is to purchase the oyster domes from Reef Innovations in Sarasota
and have them delivered the day of each event.
When the domes are complete, they will be placed by community volunteers
along the shoreline in the following manner.
The project will be constructed where the water is typically 1.5’ to 2’
deep at mean high water (MHW).
§
The reef balls will be
placed on the sandy bottom along the most southeast shoreline of the Interbay
Peninsula. There are no signs of
seagrass beds or intertidal vegetation or other significant natural resources
in the project area.
§
Figure four (4)
illustrates how the oyster domes will be placed along the shoreline. Seven serpentine lines of domes will be
installed, beginning at the stand of mangroves at the southern tip, following
the coastline 800 feet north.
§
Each 150’ line
consists of 195 domes per line and will protect 120’ of shoreline. Two and three rows of Lo-Pro Reef Balls™
touching at the base will measure 4’ and 6’ wide (1 row = 2’) and 1.5’ high
(Figure 6).
§
Two of the serpentine
lines (lines 4 and 6, Figures 7,8) will be constructed differently. This area of the shoreline has two mature Quercus virginiana (live oak tree) which
have exposed roots due to erosion.
Extra wave attenuation protection for this area will prevent additional
erosion and hopefully allow for the survival of these trees. A double row of domes (approx. 60 per line)
will ‘enclose’ the bend of the serpentine line.
§
Approximately
twenty-five oyster units will be randomly placed near the vicinity of lines 4
and 6. These domes will provide additional
habitat for marine life, as well as substrate for oyster recruitment.
§
Oyster shell bags will
be placed in the ‘interior’ of the enclosure for two reasons; to help stabilize
the landward domes, and to provide habitat for oyster and marine wildlife. The estimated number of shell bags needed
for the two ‘interiors’ is approximately 970 bags (Figure 8).
§
Each serpentine line
will overlap the next by 20’ and will feature a 10’ gap to allow marine animal
species to access shallower and calmer waters (Figures 4 and 6). This extended overlap will prevent sediments
from washing out. The oyster shell
reefs landward of these reinforced dome lines will provide additional defense
from wave action and allow for sediment accretion.
V.
Materials:
§
1500 Lo-Pro Reef Balls™
§
49.1 tons of cleaned,
local, fossilized shell
§
to assemble 2975 shell
bags
VI. Task Description:
The
project is designed to be accomplished in the following manner:
Task
1. Permitting and Interagency
Coordination
Permit
applications will be submitted to the Tampa Port Authority from MacDill
AFB. The Environmental Protection
Commission of Hillsborough County also reviews the application. Permit application will also be prepared by
MacDill AFB and submitted to the Florida Department of Environmental Protection
and the US Army Corps of Engineers.
Task 2.
Schedule Project Dates
Based
upon receipt of the appropriate permits, the project dates will be scheduled. The project is anticipated to commence in
the spring of 2005 and be completed by the end of 2007.
Task
3. Arrival of Materials / Area
Preparation
The
oyster reef material of choice is clean, washed 3” fossilized oyster shell that
is mined locally and can be delivered to each oyster shell bagging site the day
prior to the event. Tampa Bay Watch
will coordinate with MacDill AFB for delivery to an appropriate area.
Marine-friendly
Lo-Pro Reef Ball™ units will be constructed by Reef Innovations of
Sarasota and Tampa Bay Watch staff and then delivered to the site at MacDill
AFB the day of the event.
Task
4. Event Coordination
Volunteers
will shovel the shell into pre-cut PVC pipe “sleeved” with the mesh. The PVC form is removed; creating an oyster
shell bag that is tied at both ends.
These “bags” are then loaded onto an ATV and delivered to the shoreline. Staff from Tampa Bay Watch and MacDill AFB
will be on-site to ensure proper placement of the oyster shell, and to minimize
human impact on shoreline vegetation.
Lo-Pro Reef Ball™ units will be unloaded from
the delivery vehicles and carried to the water by volunteers, Tampa Bay Watch
and MacDill AFB staff then positioned into place.
Task
5. Follow-up Monitoring and Reporting
Tampa
Bay Watch will monitor the newly deployed oyster reef units and constructed
oyster shell reefs every six months for two years for the following
parameters: oyster shell migration, new
oyster colonization, changes in erosion patterns, sediment accretion and
wildlife usage of the new oyster communities.
Tampa Bay Watch and MacDill AFB will publish the results of the effort
and distribute to program participants, permitting agencies, program sponsors
and environmental organizations.
VII. Timeline
MacDill
AFB and Tampa Bay Watch will begin the process of applying for permits in the
fall of 2004. Volunteer coordination
and equipment accumulation will take place two months prior to each event. The construction of these shallow water
oyster bars and dome deployment will be scheduled between February and May 2005
to coincide with natural oyster recruitment in Tampa Bay. The newly created oyster communities will be
monitored every six months for a two-year period. A final report will be prepared at the end of the two-year
period.
Figure 1
Hillsborough Channel
Cut C Catfish Point Hillsborough Channel
Cut A
Figure 2
MacDill AFB Catfish Point N
