Restoring and Protecting Marine Habitat The Role of Engineering and Technology (1994) / Chapter Skim
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Appendix B: Case Studies
Appendix B: Case Studies
Pages 129-153
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From page 129... ...
habitats. The examination then shifts to initiatives with primarily positive results: enhancement, restoration, and creation projects for the Chesapeake Bay region, Tampa Bay, San Francisco Bay region, and Kiawah and Seabrook islands in South Carolina.
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Artificial reef technology is presented in a separate case study. Many artificial reefs have been constructed in U.S.
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The consequences of not doing so are illustrated by the inadvertently validated construction of two 600-acre diked areas for dredged material disposal in Tampa Bay (Figure B-11. The new placement sites destroyed some of the most important deep overwintering mud bottoms for pink shrimp.
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These fishermen did not divulge the pink shrimp habitat use because of financial competition. Fishing vessels were occasionally observed working the proposed permit area, but apparently no one investigated.
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Intertidal flats and shallow water habitats are found on either side except in areas of industrial development. The cross section is about 10 feet deep across the middle except in the navigation channel.
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Stripped bass have been reintroduced to the ecosystem and spawning of missing age classes is anticipated. CHESAPEAKE BAY PROTECTION AND RESTORATION INITIATIVES The Chesapeake Bay has been under extreme environmental stress for many years as a result of human activity, particularly pollution from point and nonpoint sources within the estuary and its watershed.
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Experience with construction techniques and monitoring provided information about physical energies and colonization that were useful in later projects (Boesch et al., 1978; Lunz et al., 19781. Fifteen acres of fresh intertidal marsh were created with dredged material at Windmill Point in the James River.
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From page 136... ...
Additional wetlands restoration projects were in progress or in planning at Eastern Neck National Wildlife Refuge, Kenilworth Marsh, and Bodkin Island (Maynord et al., 19921. Oyster Beds Oyster beds were created using dredged material at Twitch Cove (Smith Island)
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. Maryland Shore Erosion Control In response to marine habitat losses resulting from extensive shoreline erosion, mostly in Chesapeake Bay, the Maryland General Assembly established the Shore Erosion Control Program (SECP)
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Multipurpose Sites Although not a marine habitat project per se, the Hartmiller Island confined disposal facility project near Baltimore provides useful insights into the difficulties of obtaining approval for projects using dredged material, even if environmental objectives are an element of the project. The Port of Baltimore is a huge economic engine for the state.
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In the absence of a well-planned restoration program, pressures are building for diversion of additional funds for nonrestoration projects (Garrity, 19921. SAN FRANCISCO BAY WETLANDS RESTORATION Land subsidence in the San Francisco Bay system, including the Sacramento-San Joaquin River delta, is a result of extensive diking and pumping to create farmlands over the years.
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Several wetland restoration projects have used sediments dredged from the bay to restore intertidal elevations (Figure B-3~. Four completed projects include Salt Pond Number 3 in south San Francisco Bay (1972)
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Sonoma Baylands, which is being restored by the state, includes an intertidal marsh using sediment from the Petaluma River, a marsh managements unit for waterfowl, and open natural land. Hamilton Antenna Field is planned to become a 300-acre intertidal salt marsh.
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The study encompassed climatology, archeology, history, shallow water physical oceanography, estuarine and freshwater sediments, benthic fauna within the sediments, fisheries, phytoplankton and zooplankton, birds, mammals, herpetology, forest and dune vegetation, coastal processes, oyster populations, and marine turtle nesting. The final report discussed each component in detail and synthesized the results as a holistic view of the island in its ecological surroundings.
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To the degree that beaches are stabilized naturally, associated marine habitat may benefit as well. Many up-to-date geological, hydrographic, and coastal engineering studies were available, providing details of the area.
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The capability to engineer environmentally acceptable modifications to inlets is potentially adaptable to other barrier island locations. MARSH RESTORATION AND CREATION USING DREDGED MATERIALS In some restoration projects there are multiple users to be satisfied, and therefore a multiple-use project results.
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Southwest Pass, Lower Mississippi River, Louisiana Marsh development in southern Louisiana is a dynamic process that can be viewed as a battle to stave off some of the shoreline erosion, subsidence, and sediment starvation from levee systems and navigation channels that are resulting in the annual conversion of about 30 square miles per year of Louisiana wetlands, depending on the estimates used, into shallow water habitats (see Figures 3-1 and 3-2) (Turner and Cahoon, 1988~.
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As a result, sea and wading bird colonies relocated to these artificial islands in large numbers. More than 1 million water birds nest on the dredged material islands annually.
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Thus restoration of dredged material islands has been erratic and is often delayed until water bird nesting has declined markedly, usually owing to loss of or natural changes to nesting habitat. Especially in Louisiana and North Carolina, state and federal agencies responsible for habitat management have improved their flexibility and willingness to consider the needs of diverse coastal species.
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About 17 million cubic yards of silt and soft plastic clay particles were placed along the 40- to 45-foot depth contours parallel to the Dauphin Island shoreline about 2 miles downdrift and about 5 miles offshore. Extensive monitoring includes bathymetric, subbottom profile, and sidescan sonar surveys; sediment analyses; wave, wind, and barometric pressure data collection; benthic microfauna and vertical sediment profiling surveys; and fisheries investigations with trawling surveys, feeding analyses, and hydroacoustic surveys.
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To date the demonstration projects indicate that the technology is well suited for shoreline protection and the creation of marine habitat. Benefits of the feeder berms include the introduction of beach-quality sand into the nearshore profile.
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This capability permits the use of artificial reefs where other restoration technologies, such as those for restoring seagrass beds, might not be suitable. Although prefabricated artificial reef technology is expensive relative to more traditional techniques, it has more flexibility for use under varying water quality and physical energy conditions.
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Then in the 1950s, designed and prefabricated concrete modules were used to make artificial reefs. At the same time, the Japanese government made matching funds available to prefectural and municipal governments and fishing cooperatives (Sheehy, 19821.
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In cost comparisons with traditional engineering structures prepared by the Waterways Experiment Station, these techniques save as much as 90 percent of protection and restoration costs. For example, riprap typically costs approximately $300 per linear foot and erosion control matting (plants included)
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When such data are available, marine habitat management authorities can use them to identify and track changes in habitat profiles, including conversions and alterations of human origin that are not permitted.
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