Restoring and Protecting Marine Habitat The Role of Engineering and Technology (1994) / Chapter Skim
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3 The State of Engineering Practice in Marine Habitat Management
3 The State of Engineering Practice in Marine Habitat Management
Pages 31-62
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From page 31... ...
These issues introduce our examination of the state of engineering in marine habitat management, followed by an examination of the application of technology in various marine habitat settings (Box 3-1~. Dredging and dredged material placement technologies and their application in marine habitat protection and restoration are reviewed, as are alternative approaches and technologies that have been or could be used to establish marine habitats or to minimize or prevent deleterious impacts from human activities.
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From page 32... ...
From a coastal engineering perspective, capabilities for dredging and placement of dredged material are important resources that may be used in marine habitat management in conjunction with other important engineering capabilities. These include design expertise, predictive tools, and practical experience with a wide array of engineering technologies and structures.
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From page 33... ...
Use of Dredging and Dredged Material in Restoration Dredged material (see Box 3-1) is used in constructing many marine habitat management projects.
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From page 34... ...
Such uses primarily involve one or more habitat types: upland meadows and woodlands, marshes and wooded wetlands, wildlife islands, and estuarine and marine habitats. For island design and management, all four are often included.
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From page 35... ...
. Under current national policy, who should pay for increased costs if use of dredged materials in marine habitat management is not the least-cost alternative becomes an issue.
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From page 36... ...
. Hardened structures technology is well advanced and could potentially be applied in some circumstances to protect marine habitat (Bruun, 1989a,b; Herbich, 1990, 1991, 1992a; USACE, 1984~.
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From page 37... ...
The sand bypassing technique appears to have only very limited potential for application in marine habitat management projects. The efficacy of beach nourishment projects and their relation to structural protection is controversial; some projects have been considered successful, others not (NRC, 1987a, 1990a; Pilkey, 1989~.
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From page 38... ...
The cost-share requirement may hinder use of beach nourishment technology to benefit marine habitat management (in the absence of a residential or commercial tax bases that benefits from a project) , except where marine life uses the nourished beaches or the objective is to protect parks or preserves.
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From page 39... ...
These techniques are prime examples of a conscious effort to improve marine habitat management through the use of beach nourishment technology. Estuaries The nation's estuaries are of great value as breeding and nursery grounds for post-larval fishes as well as feeding grounds for many young adult oceanic fishes.
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From page 40... ...
Restoration efforts require comprehensive assessments of flushing times to ensure that oxygen demands are identified and accommodated. Seagrass Meadows Submerged seagrass beds are highly productive habitats that are often found in estuaries and are associated with tidal salt marshes and mangrove swamps (Hamilton et al., 1989; Weber et al., 1990~.
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From page 41... ...
Their great value in protecting the shoreline, providing fish and wildlife habitat, filtering pollutants, and providing nutrients to adjacent estuaries was not generally appreciated until the latter half of this century. Despite their critical importance in providing marine habitat, salt marshes and other coastal wetlands were drained and filled to provide more coastal land for development, an important economic consideration in earlier times when natural areas were far more plentiful and seemingly inexhaustible.
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From page 42... ...
The marsh may contain some clay as well as larger particulate matter. Extensive mud flats usually appear along the seaward edge of salt marshes and are exposed only by the lowest tides.
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From page 43... ...
The possible threat of large-scale sea level rise jeopardizes the future of all coastal wetlands (Brown and Watson, 1988; NRC, 1987a)
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Mangrove Forests Mangrove forests are coastal wetlands dominated by mangrove trees; they replace tidal salt marshes along both high and low-physical energy tropical coasts. These habitats have high ecological value but have been long unvalued by society.
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From page 47... ...
Full recovery takes decades even when local conditions are ideal. Thus it is essential to protect coral reefs from damage or loss owing to degradation of water quality or human activity, including recreational boating, commercial vessel operations, and recreational activity on the reefs themselves.
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From page 48... ...
Technology can also be applied indirectly to provide conditions more favorable to natural restoration, principally through measures to improve water quality. Artificial Reefs The use of artificial reefs or artificial habitat enhancement is defined as the manipulation of natural aquatic habitats through the addition of natural structures or structures of human origin (Seaman and Sprague, 19911.
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From page 49... ...
For example, much of the historic inner city areas of Baltimore, Washington, Newark, New York, Boston, Norfolk, Savannah, Charleston, Portland, San Francisco, and San Diego are built on dredged material. But the use of dredged material as fill for development is no longer common practice because of environmental concerns about the quality of the sediments, possible harm to vegetation from chemical changes when dredged material is exposed to air, and the cumulative losses of remaining coastal wetlands and shallow water and intertidal marine habitat.
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From page 50... ...
. When not constrained from doing so by the least-cost environmentally acceptable alternative rule, the Army Corps of Engineers continues to maintain habitats and nourishes eroding both natural islands and those of human origin using dredged material.
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From page 51... ...
The USACE also conducts technical assistance and technology transfer programs. Innovation by the commercial dredging industry is almost exclusively on an as-needed basis for application in marine habitat protection and restoration.
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From page 52... ...
Shallow Water Vegetated Habitats The most difficult habitats to establish using dredged material are shallow water vegetated habitats, such as seagrass meadows. Seagrass species have precise requirements with respect to current action and water quality.
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From page 53... ...
. However, this technique is very expensive in comparison to traditional technology; · use of oil and gas pipelines to distribute sediment (Suhayda et al., 1991~; and · use of coastal engineering capabilities to assist in the management of wastewater and storm water (including the use of natural marsh functions to treat sewage and wastewater and concurrently develop marine habitat)
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From page 54... ...
For example, it may be feasible in some areas to provide a substantial deep to shallow water intertidal habitat from the 25-foot depth contour to the shoreline. Although scale modeling and computer-based shiphandling simulations potentially could be employed to help improve channel design relative to marine habitat needs, counter pressures could reduce design effectiveness for this purpose.
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From page 55... ...
Its purpose is to minimize the area and number of dredging access canals and well slips in wetlands (Scaife et al., 19834. A geologic review meeting can reduce adverse impacts on vegetated wetlands by · shortening access canal or access road lengths by directional drilling to proposed bottom hole locations or to geologically equivalent strata; · eliminating proposed access canals/well slips and board roads/ring levees by directional drilling from open water or from existing slips or ring levees within the directional drilling radius of the proposed bottom hole location; and · allowing advance planning of field-wide exploration from one central drilling location instead of random canal or board road dredging to individual locations.
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From page 56... ...
In addition, the method maintains the low elevations prevalent in coastal wetlands throughout the life of an active oil and gas well. · Spray dredging may result in less damaging impacts on localized hydrologic conditions.
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From page 57... ...
One option, therefore, is for states or the federal government to provide an economic incentive grant to a recognized ACV company or petroleum exploration company that would underwrite the costs of drilling and producing an oil or gas well with ACV equipment where marine habitats could be affected. Some expenses (landowner royalties and lease payments)
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From page 58... ...
They include: limited predictive capabilities for shoreline change; poor performance of some projects, including lack of project monitoring, that undermines the credibility of protection and restoration technology, particu larly for mitigation projects; lack of evaluation procedures and criteria to determine success of resto ration projects, particularly in regard to inherent values of environmental (in cluding ecological) benefits; · lack of national policy and commitment to protect and restore marine habitats; .
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From page 59... ...
Predictions of project performance beyond this time scale have little utility within the present state of knowledge of coastal processes. The traditional coastal engineering time scale is unrealistic for marine habitat projects because of their dynamic nature.
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From page 60... ...
Identification of individuals and organizations qualified to perform marine habitat management work can be difficult. Although all states have license requirements for professional engineers, only about one third of practicing engineers are licensed (Anderson, 1992~.
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From page 61... ...
The more constraining factors in technology application relate to an incomplete understanding of the ecological functions of marine habitats relative to habitat enhancement, restoration, and creation. A substantial body of literature is available describing marine habitat management projects, technologies, and monitoring regimes.
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From page 62... ...
62 RESTORING AND PROTECTING MARINE HABITAT sence of suitable predictive capabilities, project performance is the principal technical factor in determining the appropriateness of restoration technology. This does not provide a suitable basis for resolving uncertainties.
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