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Restoring and Protecting Marine Habitat: The Role of Engineering and Technology (1994)

Chapter:3 The State of Engineering Practice in Marine Habitat Management

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Suggested Citation:"3 The State of Engineering Practice in Marine Habitat Management." National Research Council. 1994. Restoring and Protecting Marine Habitat: The Role of Engineering and Technology. Washington, DC: The National Academies Press. doi: 10.17226/2213.
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3
The State of Engineering Practice in Marine Habitat Management

Whether marine habitats can be protected or restored has stimulated considerable debate; so too has the application of technology in protection and restoration. Major issues include the functioning of habitats following application of protection or restoration technology, dredging impacts, the efficacy of using dredged material in restoration work, and the placement of dredged material. 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. The chapter concludes with an overview of various factors that affect the use of technology for habitat protection and restoration. A categorized list of major references is included as Appendix C. A summary of regional perspectives on the state of practice is provided in Appendix D.

RESTORATION TECHNICAL ISSUES

Functionality Following the Application of Technology

The technology to enhance, restore, or create the physical or three-dimensional structure of marine habitats is generally well developed. (For marine wetlands see Kirkman, 1992; Kusler and Kentula, 1990; Landin et al., 1989b; Seneca

Suggested Citation:"3 The State of Engineering Practice in Marine Habitat Management." National Research Council. 1994. Restoring and Protecting Marine Habitat: The Role of Engineering and Technology. Washington, DC: The National Academies Press. doi: 10.17226/2213.
×

and Broome, 1992; Simenstad and Thom, 1992; and Zedler, 1992. For coral reefs see Maragos, 1992. For artificial reefs see Lewis and McKee, 1989; Seaman and Sprague, 1991; Sheehy and Vik, 1992. For shallow water submerged seagrass see Fonseca, 1990, 1992; Lewis, 1987; Lewis et al., 1985. For kelp forests see Schiel and Foster, 1992. For mangrove systems, see Cintron-Molero, 1992; Hamilton et al., 1989; Lewis, 1982.) Technology also exists for shore protection and water quality control, although its application by coastal managers and the engineering community is not uniform (Crewz and Lewis, 1991; Roberts, 1991). Regardless of the technology used, the capacity of enhanced, restored, or created structural components to function as refugia or filter contaminants or to serve as sources of carbon and food for marine organisms is seriously debated (NRC, 1992a). For example, Lewis (1992) and Landin et al. (1989c) support the hypothesis that restored marine habitats can function as if they had not been disturbed or altered from preexisting natural conditions; the Pacific Estuarine Research Laboratory (PERL, 1990) disagrees.

There is a general acknowledgement that use of existing protection and restoration technology and regulatory enforcement to offset or mitigate permitted losses of marine wetlands has not resulted in "no net loss" of ecological functions (Lewis, 1992; Redmond, 1992; Roberts, 1991). In light of continuing loss of aquatic habitat, the NRC encouraged a dedicated program to reverse historical and current loss of wetlands. The NRC recommended that

inland and coastal wetlands be restored at a rate that offsets any further loss of wetlands and contributes to an overall gain of 10 million wetland acres by the year 2010. … In the broadest terms, aquatic ecosystem restoration objectives must be a high priority in a national restoration agenda; such an agenda must provide for restoration of as much of the damaged aquatic resource base as possible, if not to its pre-disturbance condition, then to a superior ecological condition that far surpasses the degraded one, so that valuable ecosystem services will not be lost.

(NRC, 1992a)

Despite of the controversy over how fruitful marine habitat projects are, they continue to be launched and implemented, and technology continues to be applied. 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. These capabilities may be used for integrating marine habitat objectives into coastal development, improving channel design to reduce dredging requirements, control of hydraulic conditions and sedimentation, planting marsh and submerged vegetation, stabilizing and restoring beaches, and designing and operating sewage and other waste disposal facilities to minimize environmental impacts. It is with this range of tools that the coastal engineering profession can aid in the

Suggested Citation:"3 The State of Engineering Practice in Marine Habitat Management." National Research Council. 1994. Restoring and Protecting Marine Habitat: The Role of Engineering and Technology. Washington, DC: The National Academies Press. doi: 10.17226/2213.
×

improved stewardship of vital coastal resources. Dredging and the placement of dredged material, although important, are also the source of much controversy, whether applied in marine habitat management or more traditional coastal engineering work.

Use of Dredging and Dredged Material in Restoration

Dredged material (see Box 3-1) is used in constructing many marine habitat management projects. Thus, in practice, marine habitat management depends heavily on its availability and suitability. Material is obtained either through dredging or water control structures that regulate the natural movement of suspended sediment. In some cases, shore structures have been modified, such as breaching levees (creating artificial crevasses) to reestablish or improve water transport of sediments into areas where they will settle to the bottom and accrete to form emergent wetlands.

Substantial quantities of sediments are dredged to maintain federal navigation projects (shipping channels). Disposal of material dredged from such projects is often complicated by controversy over placement because of potential environmental impacts. Lesser quantities of sediments are moved for private navigation projects, such as maintenance of marinas but can still result in a placement problem. Dredging is also conducted during construction of new navigation projects and port facilities and for some commercial and residential developments in shore areas either to provide or improve water access or for fill, although this latter activity is less common today.

The placement or disposal of dredged material often creates considerable controversy, regardless of its source (Hamons, 1988; Kagan, 1990; Lethbridge,

BOX 3-1 COMPOSITION OF DREDGED MATERIAL

Dredged material varies substantially in composition. It may be clean or may contain pollutants (NRC, 1985d, 1989a), affecting its potential use as a resource in marine habitat management. There are five general categories: rock, gravel and sand, consolidated clay, silt and soft clay, and mixtures of the four. Silt and soft clays are of particular interest for use in marine habitat restoration. They form much of the material obtained through maintenance dredging and are potentially useful for habitat development in and out of marine settings. Also of interest are gravel and sands that may be used to stabilize or improve turtle nesting beaches, construct bird nesting islands, and provide elevations necessary for restoring wetlands (Herbich, 1992b; Landin, 1992b; PIANC, 1992a). Rock and consolidated clay obtained through dredging have potential applications as well as construction material for offshore berms and artificial reefs (PIANC, 1992a), for example.

Suggested Citation:"3 The State of Engineering Practice in Marine Habitat Management." National Research Council. 1994. Restoring and Protecting Marine Habitat: The Role of Engineering and Technology. Washington, DC: The National Academies Press. doi: 10.17226/2213.
×

1988; Stromberg, 1988). Dredged material is treated as a resource or a spoil, depending on one's point of view. Concerns over use of dredged material outside its natural marine environment include the chemical changes that occur when marine sediments are exposed to oxygen and contamination of sediments by pollutants (Davies, 1988; Engler et al., 1991a,b; Herbich, 1985; Lee and Jones, 1992; NRC, 1985d, 1989a; 1992a; USACE, 1984). Relatively few navigation project areas are heavily contaminated by pollutants that typically have emanated from nonpoint sources into affected ecosystems. These occur near major coastal cities (Robertson and O'Conner, 1989; Zarba, 1989). About 95 percent of all dredged material is classified by the U.S. Army Corps of Engineers as suitable for open water disposal, although some materials with small amounts of pollutants may require capping, depending on the nature and level of contaminants present. Much of this material is therefore potentially suitable for use as a nourishment and construction resource for habitat enhancement, restoration, and creation projects (Engler, 1988; Landin and Smith, 1987; Murden, 1989b; OTA, 1987) (see Box 3-2). Another relevant concern is the fact that organic and inorganic materials are lost to the dredged material in varying degrees when

BOX 3-2 THE ARMY CORPS OF ENGINEERS APPROACH TO USING DREDGED MATERIAL

Historically, the Army Corps of Engineers was concerned primarily with the disposal of dredged material. In the past two decades, applied research and dredging interests within the Corps have emphasized dredged material as a resource for habitat protection, enhancement, restoration, and creation (Landin et al., 1989c; PIANC, 1992a; USACE, 1986, 1989a). This approach is referred to as the beneficial uses of dredged material. 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. The environmental and engineering technology for using dredged material for habitat purposes has been developed, published, examined in conferences, demonstrated through field applications, and monitored since the 1970s by the Corps of Engineers. Landin (1992a) and Landin et al. (1989c) found that the performance of projects using dredged material can be predicted reliably for salt and fresh marshes. Where feasible, USACE regulations now encourage inclusion of wetland restoration and creation in dredging projects under Section 150 of the Water Resources Development Act (WRDA) of 1986, 1990, and 1992. The Corps has not widely implemented regulations based on these acts; the acts authorize regulations but did not include appropriations to enable widespread implementation. Further, the acts only regulation of wetlands, thereby excluding all the other habitats associated with natural progression in a coastal ecosystem. Another limitation on the use of dredged material is the Army Corps of Engineers policy requiring least-cost, environmentally acceptable placement.

Suggested Citation:"3 The State of Engineering Practice in Marine Habitat Management." National Research Council. 1994. Restoring and Protecting Marine Habitat: The Role of Engineering and Technology. Washington, DC: The National Academies Press. doi: 10.17226/2213.
×

sediments are disturbed, depending on compaction and local conditions. This affects its quality for use in habitat restoration.

The nation's ports are vast economic engines and access by modern ships is fundamental to their efficient operation. Despite economic and environmental controversy over dredging issues, as discussed in the preceding paragraph (Kagan, 1990; NRC, 1985d, 1992b), past history has shown that bottom sediments will continue to be moved to maintain federally authorized navigation channels as an economic necessity. When this occurs, environmental objectives established by law and regulation need to be met constructively and responsibly (Hamons, 1988; Harr, 1988; Murden, 1989b; NRC, 1985d, 1992b; Rhodes, 1988; Stromberg, 1988). For example, dredging operations could be planned and conducted to disrupt ecosystems as little as possible, such as by maintaining biologically active shallow water and intertidal areas where feasible. In some cases, this might even reduce the amount of material to be moved and the costs of construction and maintenance, all of interest for improving waterway design (NRC, 1992b). Nevertheless, the materials obtained from dredging can provide the very resource needed to reduce or reverse habitat losses. In fact, in the Mississippi River delta region of Louisiana, the controversy is not over whether to use bottom sediments as a resource but about how to overcome federal policy and budgets that constrain wider productive use. Such use, however, may be more costly than least-cost, environmentally acceptable placement options (Landin, 1993a, in press-b). 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.

APPLYING TECHNOLOGY

This section reviews the general ecological settings within which the various technologies are often applied; it is intended to be illustrative but not exhaustive. The discussion begins with an examination of the relationship between the ecology of barrier islands and estuaries and traditional coastal engineering practices and includes problem areas affecting the application of coastal engineering technology. A similar treatment of marine wetlands follows, including seagrass meadows and tidal marshes. The role of coastal engineering is not as well defined for these habitats. The section concludes with a summary of artificial reef technology.

Shoreline Engineering

An almost continuous chain of barrier islands, and in some areas beaches extending from headlands, stretch along the Atlantic and Gulf Coasts. When undisturbed, these areas develop complex, dynamic ecosystems. Barrier islands are especially dynamic, shifting and migrating in response to tidal, wind, wave,

Suggested Citation:"3 The State of Engineering Practice in Marine Habitat Management." National Research Council. 1994. Restoring and Protecting Marine Habitat: The Role of Engineering and Technology. Washington, DC: The National Academies Press. doi: 10.17226/2213.
×

and storm energies. These coastal barriers are a first line of defense for back bay areas and uplands against winter storms and hurricanes. The beaches serve to dissipate storm wave energy. The sand dunes protect against storm surges, and when breached, result in overwash that naturally raises upland elevations behind the dune line. The stability and health of barrier island ecosystems depends on this flexibility (Amos and Amos, 1985; Mendelssohn, 1982; Perry, 1985; Platt et al., 1992; Rose et al., 1878; Weber et al., 1990; Williams et al., 1990).

However, human activity has disturbed the physical processes that caused barrier islands to shift and migrate by replacing sand dunes with homes and commercial properties, and through construction of shoreline protection and beach and inlet stabilization structures. Nevertheless, barrier beaches continuously respond to the influence of waves, currents, and wind. The net effect has often been erosion that threatens both fragile barrier island ecosystems and shore-front properties (NRC, 1987a, 1989a,b).

Faced with a challenge from the sea to coastal development, there is strong public interest in stabilizing eroding shorelines. Several strategies are used in shoreline management. Permanent structures (''hard" projects), such as seawalls, groins, jetties, and offshore parallel breakwaters have been used for many years. They create an effective barrier between the sea and land but interrupt the littoral flow of sediment (Charlier et al., 1989; USACE, 1991, 1992). This change perpetuates erosional problems in some instances and creates new ones in others, such as accelerated erosion on downdrift sides of jetties. In extreme cases where the barrier island is forced landward, marshlands behind the island are lost. Permanent shoreline protection structures, although popular in the past, are used less extensively except to protect harbor entrances and port facilities because of actual and perceived adverse effects on erosion (Charlier et al., 1989; Hall and Pilkey, 1988; Pilkey and Wright, 1988; USACE, 1994). Some coastal engineers have concluded that properly engineered seawalls and revetments can protect the land behind them without adversely affecting the fronting beaches (NRC, 1987a, 1990a). There is evidence that beach change near seawalls is like that on beaches without seawalls in both magnitude and variation (Kraus, 1988; NRC, 1990a). 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). For example, breakwaters could be constructed to dissipate wave energy that threatens wetlands in large estuaries. However, effects on sediment transport would need to be considered.

An increasingly popular shoreline engineering technique is to nourish an eroding beach by adding sand of suitable size and quality. In the United States, normally dredged material is used. The main purposes of beach nourishment are to increase the capability of beaches to act as storm buffers to protect structures in the coastal floodplain and on barrier islands and peninsulas and to provide attractive recreational "habitat" (Anderson, 1980). Periodic replenishment is needed to maintain the desired beach platform and profile. Secondary benefits

Suggested Citation:"3 The State of Engineering Practice in Marine Habitat Management." National Research Council. 1994. Restoring and Protecting Marine Habitat: The Role of Engineering and Technology. Washington, DC: The National Academies Press. doi: 10.17226/2213.
×

include possible locations for placement of beach-quality material dredged from some navigation channels (presently institutionally constrained) and enhancement of nesting beaches for sea turtles. Improving the performance of beach nourishment projects is sometimes attempted by anchoring the beach with terminal structures such as groins. Some practitioners prefer beach nourishment as a preferred management solution from an environmental perspective; nonstructural ("soft") measures could replace hard structures (Charlier et al., 1989). Beach nourishment is a nonstructural measure with some potential for use in marine habitat management. However, much remains to be learned about the physical performance of these projects, and whether they can be effectively considered a long-term solution to shoreline erosion (USACE, 1994).

Another aggressive approach is to dredge and fill, or dike and pump, thereby altering the configuration and characteristics of estuaries. This approach is practiced most extensively in the Netherlands (Charlier et al., 1989; Verhagen, 1990).

Beach nourishment involves excavating large quantities of sand from one site (usually offshore or from ebb tide shoals, but the source could be sand deposits in an estuary, for example, a flood tide shoal). The sand is placed on an existing beach to advance the shoreline seaward. The beach is essentially moved back in time so that an earlier sequence of shoreline change can be repeated (O'Brien, 1985).

Beach nourishment projects are typically site-specific. Although some projects have covered 10 or more miles of shoreline, most are much smaller. Landscape (regional) perspectives have generally not been employed in planning and design to address effects on downdrift beaches or on sand budgets for long-term maintenance including periodic renourishment. However, it is recognized that the greater the length of the beach segment that is nourished, the longer will be the duration of retention of the placed sand (Dean and Yoo, 1993).

Another approach to beach nourishment is sand bypassing. Sand is artificially transported from one side of a shoreline protection or inlet stabilization structure or from a sand deposit in an inlet to the other side of the structure or inlet in order to restore the sand budget for the downdrift beach. Typically, special pumping systems are installed to dredge the sand and transport it by pipelines to downdrift beaches. The few applications of this technique in the United States have been principally for beach nourishment purposes. The beach nourishment projects have used hydraulic pumping systems for sand transport and are used intermittently as needed. Special pumping systems have recently been developed for continuous bypassing. However, these are currently being tested at only a few locations. Data on their efficiency and effectiveness are minimal (Mehta, 1993). 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). Success is determined by the

Suggested Citation:"3 The State of Engineering Practice in Marine Habitat Management." National Research Council. 1994. Restoring and Protecting Marine Habitat: The Role of Engineering and Technology. Washington, DC: The National Academies Press. doi: 10.17226/2213.
×

volumetric loss, loss rates, planned versus actual renourishment intervals, and project objectives, including whether a project was designed as direct nourishment or to serve as a feeder beach for natural nourishment of other beaches. Some coastal engineers trace failures to inappropriate siting (such as attempting projects where there are high background erosion rates) or inappropriate application of the technology (such as less than optimal design) (NRC, 1990a). Critics attribute failures to gaps in knowledge of shoreline processes and consistent underestimation of the volume of sand required to maintain beaches near their design dimensions (Pilkey, 1989). The technical controversy is fed by the fact that

  • shoreline processes are complex, and their effects are highly site specific, making case histories difficult to apply to broader applications;

  • data interpretation methods are not consistent, so that what appears to one person as erosion may appear as accretion to another; and

  • arguments are sometimes advanced to support a point of view.

Decision making about beach nourishment is undergoing major change. Recent changes include a 50 percent cost-share requirement by local sponsors for shoreline improvements. As a result, states and municipalities now have a substantial and direct interest in the cost and performance of shoreline projects. Further, the Water Resources Development Act (WRDA) of 1990 [Public Law (P.L.) 101-640] linked federal participation in the planning, implementation, or maintenance of any beach stabilization or nourishment project with a state's establishment of or commitment to a beach front management program. The act accentuates the controversy over beach nourishment. 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.

Some nourished beaches along the South Atlantic have enhanced sea turtle nesting habitats. This result was effected by placement of dredged sand in advance of turtle migration to the beach for reproduction. Timing is critical so that sorting and settling of materials occur before the migration. Improving turtle habitat was unanticipated but has now been incorporated in beach nourishment project planning and implementation (Nelson, 1985; Nelson and Dickerson, 1988). Typically, material is placed in late fall or early winter to satisfy nesting requirements. Costs of placement may increase if more sturdy equipment is required or if placement is hampered by environmental conditions in the winter months.

Although knowledge of project performance has improved considerably over the past few decades, prediction of the loss rates associated with a beach nourishment project is still probably no better than about 30 percent (NRC, 1990a).

Suggested Citation:"3 The State of Engineering Practice in Marine Habitat Management." National Research Council. 1994. Restoring and Protecting Marine Habitat: The Role of Engineering and Technology. Washington, DC: The National Academies Press. doi: 10.17226/2213.
×

However, the associated design methodology and placement technologies continue to evolve in an effort to improve the longevity of fill. Although potentially negative environmental impacts may result from beach nourishment, they may be offset by implementing management techniques, such as relocation of nests, tilling of compacted sand, use of compatible sand, smoothing of scarps, and placement of dredged material prior to the nesting season (Nelson and Dickerson, 1988). 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. The estimated value of estuary-based commercial fisheries in the late 1980s was $5–6 billion. The recreational fishing industry generated more than $8 billion in 1986. Recreational fishing activities are believed to have increased an estimated 40 percent since then (Bell et al., 1989; Brown and Watson, 1988; Kelley, 1991; Water Quality 2000, 1992; Weber et al., 1990). The importance of estuaries and the need to preserve and improve those that remain were recognized in 1987 when Congress established the National Estuary Program (NEP) as part of Clean Water Act amendments. The NEP builds on earlier and continuing programs for the Great Lakes and Chesapeake Bay ecosystems. Twenty-one major estuary projects are in progress under the program (EPA, 1992).

Estuarine health depends on complex interactions among physical, chemical, geological, and hydrological factors. These interactions are not fully understood, and they differ among estuaries and within specific locations of an estuary. Process-oriented and empirically based predictive models are available, but not well developed (Bell, 1989; NRC, 1983a).

Salinity gradients are important to marine and estuarine life in associated marshlands. Any engineering practice that alters estuarine salinity patterns can severely impact the functioning of the ecosystem. For example, altered by hydraulics and salinity in the Savannah River estuary related to channel maintenance adversely impacted some fish species and invertebrates (Weber et al., 1990). Water diversion (that is, removal from the system) also threatens the health of estuaries. Fresh water removal alters the salinity gradient, making the area that is affected unsuitable for fresh water vegetation, fishes and other organisms that are suited to fresh or low salinity waters. For example, dams and water diversions have eliminated 80–100 percent of fish migration and spawning areas in northern California rivers. In the Sacramento River, Columbia River, and Chesapeake Bay systems, dams have eliminated hundreds of miles of anadromous fish spawning areas in the main streams and eliminated access to tributaries; hatchlings are not able to successfully migrate downstream (NRC, 1992a; Stroud,

Suggested Citation:"3 The State of Engineering Practice in Marine Habitat Management." National Research Council. 1994. Restoring and Protecting Marine Habitat: The Role of Engineering and Technology. Washington, DC: The National Academies Press. doi: 10.17226/2213.
×

1992; Williams and Tuttle, 1992). Effects of water wells and diversions, particularly in times of low rainfall in the watershed, are being felt in the Delaware River system as well. Salinity in the estuary has increased because the salt water wedge penetrates more deeply into groundwater and freshwater marshes. The oxygen content of the estuary water has changed substantially. The severity of effects on marine life depends on the amount of water removed from the system, particularly on a continuing basis.

Flushing time is an important factor in maintaining a favorable oxygen concentrations in an estuary. Any activity that slows the flushing rate probably will decrease the oxygen supply when all plants are macrophytes (that is, large plants), and thus produce conditions deleterious to aquatic life. 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). Eelgrass (a macrophyte) dominates the more northern coasts, and turtle grass dominates the coast of Florida and isolated places on the Gulf Coast. Seagrass beds may develop from coral or rock reefs or from sand and mud substrates. Many species of invertebrates, such as crabs, mollusks, and shrimp, and also larval and juvenile fish, use seagrass beds for habitats and nursery grounds. Turtles also use these areas extensively. Because submerged seagrass beds hold sediments in place, their removal or loss can lead to severe erosion. The restoration of seagrass habitat has grown increasingly important, and considerable experimentation has been attempted (Merkel, 1990a,b, 1991; Phillips, 1990; Thorhaug, 1990). Seagrass restoration includes plantings using plugs, tufts, seeds, grids, or sprigs. Thorhaug (1990) identified the literature available on specific projects. Successes have been achieved with lessons learned reported by Hoffman (1990), Merkel (1990a, 1991), and Nitsos (1990) for seagrass restoration work performed in southern California.

Evidence shows that simply installing seagrass sprigs on an unvegetated bottom or bare spot in an existing seagrass meadow does not usually work (Fonseca, 1990; Lewis, 1987). Seagrass meadows require good water quality characterized by low dissolved nutrient and suspended sediment levels, and high light transparency. The increasingly eutrophic conditions in coastal waters have caused major declines in the areal cover of extant seagrasses in the Chesapeake Bay (Orth and Moore, 1983), Tampa Bay (Lewis et al., 1985), and Galveston Bay (Pulich and White, 1991), among other water bodies. The precise mechanisms causing these losses may vary somewhat among estuaries, but without significant improvements in existing water quality, the planting of seagrasses could fail. Many losses are due to an increase in nutrients and sediments from point

Suggested Citation:"3 The State of Engineering Practice in Marine Habitat Management." National Research Council. 1994. Restoring and Protecting Marine Habitat: The Role of Engineering and Technology. Washington, DC: The National Academies Press. doi: 10.17226/2213.
×

and nonpoint sources, causing eutrophication and increased turbidity. The subsequent reduction in light penetration has eliminated many seagrass beds. Dredging activities for developing and maintaining ports and navigation channels have mechanically removed many acres of seagrass beds and increased turbidity. When water quality management improves conditions appropriate for natural seagrass recolonization, planting efforts often succeed (Johansson and Lewis, 1992; Merkel, 1990a).

Intertidal Marshes

Intertidal salt marshes occur along all U.S. coasts, particularly along the Atlantic and Gulf Coasts (Amos and Amos, 1985; McConnaughey and McConnaughey, 1985; Perry, 1985; Weber et al., 1990). Intertidal marshes are among the most productive vegetative areas in the world, supporting abundant fish and wildlife populations. 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. Water diversion projects and other activities upstream from estuaries have degraded or destroyed intertidal marshes as well (Brown and Watson, 1988; GAO, 1991; Gooselink and Baumann, 1980; Kusler, 1983; OTA, 1984).

Ecological Considerations

Intertidal marshes usually develop on coasts with low physical (wave and current) energy; accordingly, they are frequently within the protected confines of estuaries or on the landward side of barrier islands or barrier beaches extending from headlands. Mature coastal intertidal marshes have many functions (Box 3-3) and are complex ecosystems that usually developed over long periods. They are the result of a wide range of chemical, biological, and physiological processes, including sediment deposition and erosion, nutrient and other organic cycles, and tidal energies. These forces define the structure of marsh ecosystems. Tidal energies are particularly important. The diversity of species depends a good deal on the individual marsh characteristics and, in the long term, on marsh stability.

Intertidal marsh typically has a much higher primary productivity rate than the higher marsh, which is less frequently inundated. These grassy marshlands are also important in the production and export of detritus to coastal areas, where it comprises a main portion of food available to many invertebrates and fish. These marshes are also effective in removing excess nutrients and in the production of oxygen.

Suggested Citation:"3 The State of Engineering Practice in Marine Habitat Management." National Research Council. 1994. Restoring and Protecting Marine Habitat: The Role of Engineering and Technology. Washington, DC: The National Academies Press. doi: 10.17226/2213.
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BOX 3-3 INTERTIDAL MARSH FUNCTIONS

  • Fish and shellfish habitat

  • Wildlife habitat

  • Storm protection

  • Sediment stabilization

  • Water quality improvement

  • Containment sinks and purifiers

  • Recreation and aesthetics

Coastal marsh, which is regularly inundated and drained by the tides, consists of an expanse of salt-tolerant grasses and a network of tidal creeks. Tidal creeks are excellent breeding, nursery, and feeding grounds for many invertebrates and fish. Each creek has a complex structure with regard to salinity gradient, depth of flow, and type of sediment present. The extent and frequency of tidal rhythms may profoundly effect the value of a marsh as a nursery and breeding ground.

In some marshes, tidal pools known as salt pans maintain water during low tides. While they are inundated with salt water from tides, they may also receive varying amounts of freshwater from groundwater. Thus they support vegetation distinct from the surrounding marsh.

The substrate of a coastal wetland is highly variable in structure because it contains sediments of various-sized particles, a considerable amount of organic matter formed mainly from plant debris, and peat. 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. Nutrients in the soil or substrate of a coastal marsh come mainly from river deposition and tidal action. In some cases, groundwater greatly influences nutrient concentrations. A substrate favorable to plant growth is essential when a wetland is restored or created.

Increasing a marsh's stability, such as by laying down the right mix of different sized sediments and organic material, is important to its ultimate development. Stability depends on a system of accretion and subsidence. The combined effects of accretion and subsidence result in an RMSL for each location that is typically different than the absolute change in sea level. Long-term causes of a rise in the RMSL are

  • eustatic (global) rise of world sea level,

  • crustal subsidence or uplift due to neotectonics,

  • seismic subsidence caused by earthquakes,

Suggested Citation:"3 The State of Engineering Practice in Marine Habitat Management." National Research Council. 1994. Restoring and Protecting Marine Habitat: The Role of Engineering and Technology. Washington, DC: The National Academies Press. doi: 10.17226/2213.
×
  • subsidence resulting from compaction or consolidation of soft underlying sediments,

  • subsidence of human origin caused by oil, gas, and water extraction or structural loading, and

  • variations due to climatic fluctuations (Barnett, 1990; NRC, 1987a, 1991).

These factors may work separately or in combination. Salt marshes are relatively stable along the northern Atlantic Coast because accretion is keeping pace with RMSL. In contrast, autosubsidence due to compaction and downwarping of delta sediments along the Gulf Coast is causing the marshes there to subside and disappear (NRC, 1987a, 1991; Saucier, 1992). The possible threat of large-scale sea level rise jeopardizes the future of all coastal wetlands (Brown and Watson, 1988; NRC, 1987a).

Restoring Intertidal Marshes

In creation of a wetland or the alteration of water flow or estuary size, great care is necessary to ensure that the functioning of other processes important to fish and wildlife are not adversely affected. For example, placement of structures could alter the rate of water exchange between areas, affecting salinity and sedimentation, such as that which occurred in modifications to the Savannah River estuary (Appendix B).

Success in establishing vegetation in tidal marshes is quite high when appropriate technology is applied (Broome, 1990; Josselyn et al., 1990 Landin et al., 1989c; Lewis, 1990a; Shisler, 1990). When creating a habitat for organisms that form the basis for fisheries is an objective, success appears to include the need for higher ratios of marsh to open water edge. Many small creeks and channels may be necessary to establish a marsh-water interface that replicates the functions of a natural marsh (Minello et al., 198y). However, in the evaluation of mitigation projects requiring vegetation, credit is often not given for inclusion of small creeks and channels even though they may be more biologically productive than the marsh surface.

Kusler and Kentula (1990) note that for all wetland types in the United States, "in general, the ease with which a project can be constructed and the probability of its success are … greatest overall for estuarine marshes." The capability to establish all the functions of a natural tidal marsh has been demonstrated; for example, fish utilization of restored or created marshes is generally equal to that in natural marshes in 3–5 years (Landin et al., 1989c; Lewis, 1992). Other functions may lag behind faunal colonization (Zedler and Langis, 1991). Certain approaches, such as creating artificial crevasses in levees, thus diverting riverine sediments to adjacent marshes, rely on nature for the restoration once hydraulic regimes are provided (Brown and Watson, 1988; Fritchey, 1991). There is a localized sediment buildup, referred to as splays, as a consequence of breaks

Suggested Citation:"3 The State of Engineering Practice in Marine Habitat Management." National Research Council. 1994. Restoring and Protecting Marine Habitat: The Role of Engineering and Technology. Washington, DC: The National Academies Press. doi: 10.17226/2213.
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in the levee. These buildups usually take the shape of a small delta. With splays, wetlands accrete in the same manner as if the river had cut a new channel (Figures 3-1 and 3-2), and they appear to achieve equal quality. In some demonstration projects, substantial biological activity approaching that found naturally has been achieved in 5–15 years, depending on conditions at the project site.

Practitioners do not agree on what level of interdependent biological activity constitutes full restoration of natural functions. Nor is there agreement on the baseline criteria for making comparisons. One attribute of full ecological restoration might be the capacity for self-maintenance or self-perpetuation, although measurable attributes that could be robust indicators of the capability for self-maintenance have not been identified (NRC, 1992a). The question becomes whether to wait until research finds solutions or to undertake projects given the present state of knowledge, using the projects to increase scientific and engineering knowledge about marsh restoration. Full functional replacement as a concept is desirable, and it may be mandatory for marsh mitigation projects. Full functionality is not necessarily a limiting factor when restoring wetlands for other objectives, including species-specific goals.

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. Hamilton et al. (1989) provide a comprehensive description of mangroves and their value as a natural resource.

Most mainland U.S. mangrove forests are in Florida, although they also occur in Louisiana and Texas. The red mangrove typically dominates the intertidal zone because it can tolerate high salt concentrations. The arching prop roots of these trees help hold the substrate in place. Black mangroves appear behind the red mangroves in areas exposed to high tides. Both the black and white mangroves feature special structures in their root systems that serve as respiratory organs. The structures, known as pneumatophores, contain bodies of cells, known as lenticles, which serve as pores for the respiratory system. These morphological features allow mangrove species to live where other plants cannot. The tangled masses of prop roots and pneumatophores are havens for many forms of aquatic life. Important recreational and commercial fish feed in these relatively protected areas as well.

Mangrove swamps export much organic material to adjacent estuaries (Heald, 1969). Mangrove detritus is the primary food source for many estuarine animals and is important to the sport and commercial fisheries in the Gulf of Mexico. Primary consumers that use mangrove swamps as nursery and breeding grounds also serve as prey for game fish, such as tarpon, snook, sheepshead, spotted sea trout, red drum, jack, and jewfish.

Suggested Citation:"3 The State of Engineering Practice in Marine Habitat Management." National Research Council. 1994. Restoring and Protecting Marine Habitat: The Role of Engineering and Technology. Washington, DC: The National Academies Press. doi: 10.17226/2213.
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FIGURE 3-1 Status in 1978 of three selected splay totaling 559 acres in Lower Mississippi River Delta following levee breaches (USFWS, 1992, unpublished data).

Suggested Citation:"3 The State of Engineering Practice in Marine Habitat Management." National Research Council. 1994. Restoring and Protecting Marine Habitat: The Role of Engineering and Technology. Washington, DC: The National Academies Press. doi: 10.17226/2213.
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FIGURE 3-2 Status in 1988 of selected splays development of lower Mississippi River Delta after 10 years. Intertidal wetlands acreage increased from 559 to 1.756 acres (USFWS, 1992, unpublished data).

Suggested Citation:"3 The State of Engineering Practice in Marine Habitat Management." National Research Council. 1994. Restoring and Protecting Marine Habitat: The Role of Engineering and Technology. Washington, DC: The National Academies Press. doi: 10.17226/2213.
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Like tidal salt marshes, mangrove wetlands preserve the coastline by mitigating the effects of floods and violent storms. Protection of these coastal wetlands is therefore essential. The general techniques for successful restoration or creation of the plant community have been demonstrated for mangrove forests (Cintron-Molero, 1992; Crewz and Lewis, 1991; Lewis, 1982, 1990a). Mature propagules are harvested directly from the trees, surrounding grounds, or naturally planted propagules. Early maturity of transplanted specimens is a problem that can be offset by transplanting them at the young tree stage. Relocation of mature tress is possible, but it requires extensive top and root pruning. Cost is a constraining factor (Thorhaug, 1990).

The equivalency of all functions has not been demonstrated, but evidence shows that the potential to restore mangrove habitats and provide good habitat for fish and epibenthos exists (Roberts, 1989, 1991). Alteration of mangrove systems often results in unanticipated severe effects because the natural shoreline protection provided by these systems is typically degraded or lost. For example, destroying red mangroves on a high-energy coast will eventually lead to erosion of the area. It is the active growing of these trees with their root and stem systems that makes possible the stabilization of the sediments there.

Coral Reefs

Reef corals grow principally in clear tropical waters. Fringing reefs, the only major type of coral reef in continental U.S. waters, are found only in southern Florida, primarily off the southeastern keys. Coral heads are scattered elsewhere off Florida's west coast, and in a few areas off the Texas coast. Coral reefs and heads consist principally of calcium carbonate deposits from stony corals, and coralline algae. They are utilized as habitats by a diverse array of other organisms. These creatures require clear, clean water; they tolerate little pollution. The growing portion of a seaward fringing reef is essential for survival and maintenance of the entire reef system. The coral reefs and the astonishing variety of marine life that depends on them combine to form a most unique habitat. In addition, fringing reefs provide highly effective natural protection against waves generated by hurricanes and other episodic storms (Amos and Amos, 1985; Guilcher, 1987; Maragos, 1992; Wiens, 1962).

Restoration of coral reefs or heads once damaged or lost relies on natural restoration, although recolonization can be assisted. 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.

Various techniques documented by Maragos (1992) for aiding in coral reef restoration include:

Suggested Citation:"3 The State of Engineering Practice in Marine Habitat Management." National Research Council. 1994. Restoring and Protecting Marine Habitat: The Role of Engineering and Technology. Washington, DC: The National Academies Press. doi: 10.17226/2213.
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  • transplanting reef corals, including cementing reef substrates with reef coral attached in damaged areas;

  • construction of artificial reefs to provide both habitat for reef fishes and suitable substrates for recolonization;

  • construction of reef quarry holes to provide suitable depths for recolonization;

  • placement of rubble mound revetments and breakwaters for recolonization;

  • cementation to restore reef frameworks in order to protect adjacent undamaged areas and promote recolonization;

  • removal of diseased organisms;

  • control of fisheries;

  • replanting of seagrasses and mangroves to restore ecosystem links; and

  • protective regulations.

Although favorable results have been achieved with these approaches, their application is expensive (Maragos, 1992). 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, 1991). More than 250 artificial reefs have been established in the coastal waters off most states, primarily off the South Atlantic and Gulf coasts. Many of these projects are characterized by placement of old ships, rubble, and other materials of opportunity rather than by specific design and construction for certain fish species. Nevertheless, the technology for artificial reefs is well developed (Bell, 1986; Bell et al., 1989; Lewis and McKee, 1989; McGurrin and Reeff, 1986; McGurrin and ASMFC, 1988, 1989a,b; Sheehy and Vik, 1992; Shieh et al., 1989).

Use of artificial reefs in fisheries management raises serious questions about what constitutes success. Artificial reefs can increase the efficiency of harvesting fish by concentrating them around an easily identifiable site. Less clear is the functional equivalency of artificial reefs compared with natural reefs and their real capability to increase standing stocks rather than attracting those that already exist (Alevizon and Gorham, 1989; Gorham and Alevizon, 1989; Seaman and Sprague, 1991; Wendt et al., 1989). Lack of long-term monitoring and controlled experimental studies are cited as factors limiting understanding of artificial reef ecology (Bohnsack, 1989; Bohnsack et al., 1991).

The United States took a major step in coordinating artificial reef activities through passage of the National Fishing Enhancement Act of 1984 (P.L. 98-623).

Suggested Citation:"3 The State of Engineering Practice in Marine Habitat Management." National Research Council. 1994. Restoring and Protecting Marine Habitat: The Role of Engineering and Technology. Washington, DC: The National Academies Press. doi: 10.17226/2213.
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The act's purpose is to promote and facilitate responsible and effective efforts to establish artificial reefs in specific waters. It provides a formal mechanism for reef development and encourages state activity, and the number of permitted reefs has increased substantially since 1983, but there is only moderate continuity in habitat construction (McGurrin and Reeff, 1986; McGurrin et al., 1989a,b).

In a comparative study of the U.S. and Japanese development of artificial reef technology, Grove and Wilson (in press) concluded that the United States regulates reactively and Japan takes a proactive approach. Both approaches are advancing construction techniques and understanding of artificial habitat. The Japanese are focused much more on carefully engineered structures for commercial production of selected species, and they have conducted considerably more applied research to determine species life histories (Bell, 1986). Japan provides substantial funding yet offers little latitude for experimentation; the United States, in contrast, provides encouragement and great latitude that leads to indecision and works against focused development of reef technology. A further difference is resource ownership. In Japan, fishery resources at private reefs are treated as property of the reef owner. In the United States, coastal and riverine fishery resources are, with few exceptions, treated as public property. Thus there is little incentive for private development of reefs as a fisheries resource.

DREDGING AND DREDGED MATERIAL PLACEMENT

Historical Uses of Dredged Material

Use of dredged material dates back to harbor development and mariculture impoundments by the Chinese, Greeks, and Phoenicians. A substantial body of literature details techniques and methodologies for its application (Landin 1988a,b; Landin and Seda-Sanabria, 1992; Landin and Smith, 1987; Lazor and Medino, 1990; PIANC, 1992a; USACE, 1986).

The United States and Canada have used dredged material since colonial times. It was generally used to fill shallow water and wetland areas for urban, aviation, port, farm, industrial, and other interests. Until recent decades, these uses were acceptable. 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. Today the most extensive use of dredged material as a resource in coastal areas is the placement of beach-quality sands in beach nourishment projects to protect shorelines. Further, the use of

Suggested Citation:"3 The State of Engineering Practice in Marine Habitat Management." National Research Council. 1994. Restoring and Protecting Marine Habitat: The Role of Engineering and Technology. Washington, DC: The National Academies Press. doi: 10.17226/2213.
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dredged material to aid in restoring wetlands in areas such as Louisiana, which are experiencing severe changes in wetland character and acreage, is being explored.

Another important use of dredged material in marine habitat management over the past 100 years is the creation of some 2,000 estuarine islands. They have become important to nesting water birds as natural shorelines and islands disappeared under the pressures of coastal population increases and development. More than 1 million water birds nest on these islands each year. These habitats have been studied to determine the best ecological and engineering designs, soil types, configurations, slopes, and other features. Technical guidelines for island creation, additions, enhancement, and protection for wildlife habitats have been published by both the Army Corps of Engineers and the National Park Service (Herbich, 1992a; Landin, 1980, 1992b). 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. Nesting islands are an example of restoration and creation in a landscape scale (that is, a category or habitat lost in an ecological landscape is replaced within the landscape, but not necessarily at the site where the loss occurred). Ecological improvements are more likely to persist and to be self-maintaining if they can be carried out in a landscape context.

Dredged material use as a resource has historically included extensive development of recreational facilities and parks throughout the U.S. waterways systems, in Washington, D.C. (much of the Mall was created by filling intertidal wetlands), the Great Lakes, the lower Columbia River, and San Diego. Other historical applications have been shoreline protection, sediment stabilization, beach erosion control, and storm protection, primarily along the Gulf coast, in the Chesapeake Bay, and in the Great Lakes. It has not been used to the fullest extent technically possible where extensive erosion is occurring, however. At the same time, alternative uses have continued to surface in recent decades, such as in the creation of oyster beds, fishing reefs, and clam flats (Landin, 1989, 1992a).

Dredging and Dredged Material Placement Technology

Herbich (1992b) details dredging technology and methods, including their application in environmentally sensitive coastal areas. Generally, specialized dredges and equipment have been developed nationally and internationally for custom placement of dredged material for wildlife islands and other upland habitats, as core material for large placement facilities, berms, wetlands, oyster reefs, clam beds, fishing reefs, and beaches. A broad range of dredging and dredged material placement equipment, such as multihead pipe heads, diffusers (for better dispersement material), perforated pipes, and flexible pipes, is used for (precise) placement of material at intertidal elevations. Booms are used to reach

Suggested Citation:"3 The State of Engineering Practice in Marine Habitat Management." National Research Council. 1994. Restoring and Protecting Marine Habitat: The Role of Engineering and Technology. Washington, DC: The National Academies Press. doi: 10.17226/2213.
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placement locations without traversing sensitive wetlands. Light foot-pressure floating and tracked equipment can ''walk" in water up to 6 feet deep and in wetlands with minimal adverse affects. Abandoned oil and gas pipelines have been used experimentally in coastal Louisiana to distribute sediments in coastal wetland restoration sites. Specialized equipment and techniques are used for construction of barrier islands, sediment entrapment to form marshes, substrate stabilization using bioengineering,1 and planting.

Innovative dredging and dredged material placement technology in the United States is primarily the result of USACE dredging and wetlands research since 1973, and is well documented (USACE reports are generally available from the agency or through the National Technical Information Service). Research areas include dredging equipment, dredged material placement technology, structures, habitat protection and restoration, long-term fate of dredged material, contaminated sediments, and long-term monitoring criteria. 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. The national, privately based dredging industry currently has no ongoing research and development program to support this work further.

Application of Dredged Material to Habitat Protection and Restoration

Dredged material has been used extensively in protection and restoration. Care must be taken to ensure that the dredged material intended for use in restoration work is suitable for this purpose (NRC, 1989a; PTI Environmental Services, 1988). Suitability can be determined through existing risk analysis and sampling techniques. Ecotoxicological evidence that indicates the presence of contaminants needs to be carefully assessed with the objective of minimizing risk. The examples that follow describe some of the more well-known current uses.

Underwater Berms

The USACE has built 23 underwater berms for storm wave attenuation, shoreline nourishment, bottom topographic relief, and fisheries habitat improvement. The Corps periodically monitors the berms for engineering stability and project performance. Only three have been monitored for environmental purposes (Clarke and Pullen, 1992; Hummer, 1988; Murden, 1988, 1989b):

  • the deep water and nearshore berms off Mobile Bay as part of a national demonstration project for underwater berms, and

1  

Bioengineering is the coupling of traditional engineering technology with living plant material.

Suggested Citation:"3 The State of Engineering Practice in Marine Habitat Management." National Research Council. 1994. Restoring and Protecting Marine Habitat: The Role of Engineering and Technology. Washington, DC: The National Academies Press. doi: 10.17226/2213.
×
  • the offshore underwater berm at Norfolk, Virginia, south of the entrance of Chesapeake Bay, primarily for its physical performance and, as an adjunct, for fisheries production (Clarke et al., 1988; Langan, 1988).

To date, data from these three berms indicate that

  • the deep water berm off Mobile Bay is stable and, in effect, is providing artificial reef-like fisheries habitat and a refuge for numerous species of several age classes;

  • the nearshore berm off Mobile Bay, consisting of beach-quality sand, is slowly moving with the current to nourish the beach; and

  • the Norfolk berm is providing habitat to over wintering blue crabs from the Chesapeake Bay, among other fisheries benefits (Clarke and Pullen, 1992).

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. With few exceptions, mitigation and restoration of seagrasses have not been successful. In Mission Bay near San Diego, a dredging project provided ideal habitat conditions. Eelgrass plantings there established and multiplied extensively around lagoons (Merkel,1991; Merkel and Hoffman, 1990). This area might have recovered on its own over time. Based on observations of seagrass restoration efforts, a rule of thumb is that seagrasses will become established in areas where they had previously occurred naturally regardless of whether dredged material is used (USACE, 1986). Dredged material can be used in seagrass restoration projects to provide elevations suitable for seagrass recolonization and to construct berms to provide protection.

Oyster Beds

One recent application of dredged material involves raising bottom elevations and covering the new areas with suitable culch or gravel to provide oyster beds. These habitats were built both accidentally and intentionally in Galveston Bay. The USACE and the NMFS cooperated in building similar habitats in Chesapeake Bay. Early findings of ongoing research indicate that intentionally built oyster bed habitats are achieving project objectives (Earhardt et al., 1988). The overall effect of these projects on function and balance within the ecosystem has not been determined.

Suggested Citation:"3 The State of Engineering Practice in Marine Habitat Management." National Research Council. 1994. Restoring and Protecting Marine Habitat: The Role of Engineering and Technology. Washington, DC: The National Academies Press. doi: 10.17226/2213.
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ALTERNATIVE APPROACHES AND TECHNOLOGIES FOR MINIMIZING OR AVOIDING IMPACTS TO MARINE HABITAT

Adverse impacts on coastal habitats may be minimized or avoided through use of non-traditional and innovative methods for dredging and minerals exploitation. Some alternatives are:

  • refinement of channel design and maintenance operations to minimize impacts to marine habitat and, if possible, to improve existing habitat;

  • directional drilling (drilling several oil or gas wells from one location instead of dredging individual canal slips for each drilling location);

  • spray dredging (spraying the dredged material over the wetland in layers under hydraulic pressure so that no spoil bank is formed);

  • hovercraft (use of air-cushion vehicles (ACVs) to lift seismic or drilling equipment over the wetland on a cushion of air, thus eliminating the need for dredging). 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).

Improving Channel Design and Maintenance

The principal objective of channel design is to provide for safe and efficient transits by vessels. The design vessel is, in effect, the largest vessel that the channel is designed to accommodate safely. Channel cross sections are based on engineering guidelines and rules of thumb for design, which are sometimes supplemented by physical scale modeling or computer-based shiphandling simulations. The latter offer more precise channel dimensions required for design vessels. This precision may reduce requirements for dredging and placement of dredged material. Shiphandling simulations are also used to address environmental concerns about channel adequacy for tankers and other large vessels (NRC, 1992b). Potentially, reduced dredging requirements could reduce turbidity and impacts on shallow water and intertidal habitats.

Sedimentation of navigation channels is a continuous process that is traditionally addressed through dredging to maintain project depths necessary to support marine commerce. Each port and waterway system is unique, necessitating site-specific examinations to determine the sources and extent of sedimentation, requirements for channel maintenance, and the potential effects of dredging operations on the local environment. Alternatives that potentially could be used to reduce sedimentation include stopping or diverting sediments before they reach

Suggested Citation:"3 The State of Engineering Practice in Marine Habitat Management." National Research Council. 1994. Restoring and Protecting Marine Habitat: The Role of Engineering and Technology. Washington, DC: The National Academies Press. doi: 10.17226/2213.
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navigation channels or keeping material in suspension as it passes through. These alternatives could be employed to reduce sedimentation from many existing facilities, although such action would be costly. Alternately, sediment management could be incorporated into the site selection, design, construction, and maintenance of new waterway projects and facilities. More complete and accurate hydrographic data would be needed than are normally available (NRC, 1987b). Attempts to manage sedimentation need to be carefully formed to avoid unintended side effects (Appendix B).

Physical scale modeling has been done for both channel design and environmental purposes. Cross sections could be modeled to determine their effects on an estuary's hydraulics. If the cross sections create an area of greater volume than the tidal prism, then the water flow through the system is reduced, changing the salinity, temperature, oxygen content, and sedimentation rates. A better understanding of these effects and their accommodating design could potentially lead to a reduction of impacts on existing marine habitat.

Shiphandling simulation technology has apparently not been used to determine whether equivalent safety performance in maneuvering could be achieved using cross sections designed to (1) mitigate wave or current action on contiguous habitats, (2) serve as habitat for vertebrates and invertebrates, or (3) provide migration routes for various species. It may be possible to provide cross sections that support all three uses. 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. For example, channel improvements lag years behind changes in ship technology. The result is that channel configurations are routinely stressed well beyond design ship parameters because of economic pressures and competition between ports. Even where improvements are authorized, there is great pressure to minimize costs because of increased cost sharing responsibilities of local sponsors (NRC, 1992b). Thus, sloping a channel wall to the 25-foot depth contour could increase dredging requirements, increasing project cost. Other alternatives to modify channel design to satisfy habitat objectives would be subject to similar pressures. Another issue is who would pay for the added modeling, simulation, or construction costs associated with the marine habitat objectives.

Alternatives to Access Canals for Mineral Exploration and Production in Coastal Marshes

The construction of access canals for oil and gas exploration and production in coastal marshlands results in significant direct and indirect losses of marine habitat. Canals can also lead to salt water intrusion in estuaries and blockage of

Suggested Citation:"3 The State of Engineering Practice in Marine Habitat Management." National Research Council. 1994. Restoring and Protecting Marine Habitat: The Role of Engineering and Technology. Washington, DC: The National Academies Press. doi: 10.17226/2213.
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natural channels. Alternatives for substantially reducing the need for canals and reducing the impacts of those that are constructed include directional drilling, spray dredging, and the use of air cushion vehicles.

Directional Drilling

Directional drilling is a subsurface mineral-recovery process that usually creates a nonlinear wellbore track from the surface to a recovery zone beneath, occasionally several miles from the drill site. Directional drilling is often used in coastal Louisiana to avoid disturbing sensitive environmental features (such as barrier islands, endangered species, or wetlands). This technology could also reduce the number of drilling sites needed in a given field.

Directional drilling is more complex than drilling straight downward because of the increased and variable pressures on the subsurface equipment, loss of lubricants, and increased chances of well blowout. Drilling angles are usually less than 30° (<2° per 30-meter change in the vertical) for vertical drilling and less than 20° with multiple curvatures (<1.5° per 30-meter drop). Directional drilling is generally 15–70 percent more costly than conventional methods (Louisiana's average cost is 30 percent or more).

The technical feasibility and safety of using directional drilling for certain oil and gas wells have been evaluated in Louisiana since mid-1982; the procedure, known as a geological review, involves a state petroleum geologist and petroleum engineer. Its purpose is to minimize the area and number of dredging access canals and well slips in wetlands (Scaife et al., 1983). 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.

Directional drilling engineering practices succeed because

  • an appropriate technology is applied in a mixed institutional setting of environmental managers, geologists, and permit applicants;

  • the additional costs of directional drilling assumed by the permit applicant are generally known and acceptable to the applicant; and

  • knowledge of the coastal ecosystem affected (primarily wetlands and barrier islands) is sufficiently understood to be persuasively applied as a management and regulatory tool.

Suggested Citation:"3 The State of Engineering Practice in Marine Habitat Management." National Research Council. 1994. Restoring and Protecting Marine Habitat: The Role of Engineering and Technology. Washington, DC: The National Academies Press. doi: 10.17226/2213.
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Spray Dredging

High- and low-pressure spread dredging are the two types of hydraulic dredging being used infrequently in the Louisiana coastal zone to construct oil and gas access canals and well slips. Cahoon and Cowen (1988) provide a comprehensive assessment of these technologies. The advantages of spray dredging over conventional bucket dredging include:

  • It creates no spoil banks, resulting in less wetland habitat destruction. 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. Sheet flow across vegetated wetlands and tidal interchange through surrounding waterways may be less affected by spray dredging. Further, spray dredge barges are usually smaller and require less draft than bucket dredge barges. More remote and shallower areas may be accessed with less disturbance of water bottoms.

  • Spray dredging may result in slower or less compaction of underlying sediments, thereby slowing subsidence rates.

The disadvantages of spray dredging include:

  • It is less efficient than conventional dredges, thereby increasing placement costs for dredged material.

  • Costs can be 2–14 times higher than bucket dredging.

  • Pollution risks increase when an oil spill or well failure occurs (the lack of spoil banks may allow contaminants access into surrounding wetlands).

  • It is considerably less effective in aquatic substrates and wetland swamp habitats and where underwater obstructions (such as logs and stumps) are common.

  • Equipment breakdowns are frequent, especially where organic materials occur in the sediments. Options for improving the technology and use of spray dredging include:

  • Spray dredging costs reported during geologic review meetings could be evaluated to determine whether the habitat value and acreage of wetlands to be impacted by a proposed project justify the added costs to the applicants.

  • Additional funding could be provided for scientific research to examine

Suggested Citation:"3 The State of Engineering Practice in Marine Habitat Management." National Research Council. 1994. Restoring and Protecting Marine Habitat: The Role of Engineering and Technology. Washington, DC: The National Academies Press. doi: 10.17226/2213.
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the elements of projects that use spray dredging for the purpose of developing data and analysis to better understand the potential of this technique.

  • Equipment could be more efficient and cost effective.

Air-Cushion Vehicles

The use of ACVs to avoid long-term impacts on coastal tundra wetlands of the North Slope arctic oil fields has been discussed in both general and technical publications (Sikora [1989] is a substantial review). Both drilling barges and smaller support craft that utilize ACV technology are in regular use in that region. The advantages of the ACV technology are:

  • It would eliminate the majority of the dredging for exploratory wells.

  • The need for maintenance dredging is likely nil.

The obstacles to their use are:

  • No demonstration or field tests in other coastal habitats have been conducted for more expensive alternative equipment.

  • No minimal regulatory or economic impetus exists for oil exploration companies to consider their general use.

  • Substantially increased transport and placement costs for the excavated material (the cost per cubic yard is two to five times that of traditional placement technology).

Industry practices will likely continue to rely on a proven infrastructure in the absence of a workable and cost-effective or required alternative.

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) could be minimized by conducting the project on state-owned lands. If a well were productive, then grant expenses could be recouped from production profits. Such a project could provide a unique opportunity for determining the technical feasibility of using ACVs as placement equipment, conducting an in-depth economic analysis of production costs associated with the ACV use, and determining the degree to which impacts on habitat are avoided or mitigated.

Management of Wastewater and Storm Water

The management of wastewater and storm water, especially in coastal urban areas, is a large and complex problem. Essentially, estuaries and coastal ocean areas are, in effect wastewater and storm water disposal areas. Although considerable

Suggested Citation:"3 The State of Engineering Practice in Marine Habitat Management." National Research Council. 1994. Restoring and Protecting Marine Habitat: The Role of Engineering and Technology. Washington, DC: The National Academies Press. doi: 10.17226/2213.
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efforts have been undertaken to control and treat wastewater including the use of freshwater wetlands for natural treatment of wastewater in some locations (EPA, 1985; Gearheart and Finney, 1982; Gearheart et al., 1982; Reddy and Smith, 1987), these remain major sources of nutrients and sedimentation which affect water quality, and ultimately, the fate or quality of marine habitats. The need for integrated coastal management to systematically and effectively address wastewater and storm water issues was examined by the NRC(1993). Coastal engineering capabilities are resources that could potentially be applied to controlling wastewater and storm water, and thus to improve water quality. Because this report addresses engineering capabilities to restore and protect marine habitat, the use of marine wetlands and engineering capabilities for other purposes, such as treatment of wastewater and storm water, were not assessed. Although there might be potential applications in select locations, perhaps using marine wetlands as a final stage of treatment, there are significant concerns that any pathogens and pollutants that were introduced into an ecosystem could threaten the health of wildlife, fish, and nearby human populations. There are also significant concerns that water quality could be degraded. Therefore, in order for such applications to be environmentally acceptable, they would have to be seriously examined with respect to policy, legal, human and environmental health, scientific, and technical considerations.

IMPLEMENTATION FACTORS AFFECTING USE OF TECHNOLOGY

The foregoing discussion centered on the present use of technology in marine habitat management as seen by practicing experts (Yozzo, 1991; Appendix D). Several important factors have restricted the use of protection and restoration technology. 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, particularly for mitigation projects;

  • lack of evaluation procedures and criteria to determine success of restoration projects, particularly in regard to inherent values of environmental (including ecological) benefits;

  • lack of national policy and commitment to protect and restore marine habitats;

  • uncertain professional qualifications of individuals or organizations engaged in protection and restoration work resulting in a range of technical expertise that affects project performance;

  • a relatively young and rigid regulatory framework in which adaptive management is basically nonexistent;

Suggested Citation:"3 The State of Engineering Practice in Marine Habitat Management." National Research Council. 1994. Restoring and Protecting Marine Habitat: The Role of Engineering and Technology. Washington, DC: The National Academies Press. doi: 10.17226/2213.
×
  • lack of technical qualifications needed for decision making about and oversight of restoration technology applications among regulatory personnel (discussed in Chapter 5);

  • limited information transfer and training for practitioners (discussed in Chapter 5; and

  • cost.

Shoreline Change Predictive Capabilities

The capability for predicting shoreline change relative to temporal (time) and spatial process scales is limited, and confidence levels tend to be low. Research that enabled even those accuracies that are attainable is are only about a decade old. Limited prediction capabilities are directly related to limitations in the knowledge of coastal processes, discussed in Chapter 2.

Time Scale Predictions

Storm-related dune erosion can occur in a single day. Localized beach erosion may take a month to a year. Effects of sea level change can take on the order of 10–100 years or longer. The predictive capability (and confidence in the result) decreases as the time scale increases. In coastal engineering, 30–50 years is generally used as the project life span. 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. The understanding of their natural functioning relative to coastal processes is even less well developed. Although near-term predictions are possible for some marine habitat protection and restoration, their appearance and performance much beyond the near term cannot be estimated with reasonable confidence.

Spatial Scale Predictions

Predicting spatial scales is problematic. Coastal engineers deal with orders of magnitude ranging from 10 meters to 10 kilometers. Generally, predictions with moderate confidence levels relative to coastal processes can be made on the 1-kilometer scale relative to specific structures, such as a groin. Broad predictions on any scale have relatively low confidence levels and are particularly difficult on the 10-meter scale. For example, it is difficult to determine if, when, or where a barrier island will move over the long term. With the exception of beach habitat that coexists with traditional coastal engineering work, the coastal engineering profession has not focused much attention on spatial relationships between coastal processes and marine habitat or ecosystem dependencies.

Spatial scale relationships are being vigorously developed within an emerging

Suggested Citation:"3 The State of Engineering Practice in Marine Habitat Management." National Research Council. 1994. Restoring and Protecting Marine Habitat: The Role of Engineering and Technology. Washington, DC: The National Academies Press. doi: 10.17226/2213.
×

discipline referred to as landscape ecology (Turner, 1989). Ecologists have achieved moderate confidence levels in predicting habitat change in the near term on a small scale. Spatial relationship predictions for areas over the 1-meter scale are less reliable. Mathematical models and simulations are just beginning to be developed.

Performance of Habitat Protection and Restoration Projects

In the absence of reliable predictive capabilities for all time and spatial scales, project performance, from an applied technology perspective, is the single most important factor in determining the appropriateness and effectiveness of protection and restoration technology. Failure of a project to achieve its objectives does not establish the track record or credibility needed to advance the state of practice, although lessons can be learned through careful documentation and analysis. Inadequate performance of mitigation projects, in particular, has resulted in challenges to mitigation as an environmentally acceptable approach to destruction of habitat in return for a promise of full restoration of a degraded habitat elsewhere (NRC, 1992a). Views on mitigation range from stopping all wetland impact permitting and the associated required mitigation to requiring full execution of all permitted marine wetland restoration (for mitigation) projects prior to authorizing the activity for which mitigation was the tradeoff. Because success in marine habitat protection and restoration is critical to advancing the state of practice, an approach to attaining project goals and objectives is described in Chapter 6.

Professional Qualifications of Practitioners

The qualifications of individuals and organizations performing habitat protection and restoration work directly influence the effective application of scientific knowledge and engineering capabilities and, ultimately, project performance. Application by less than fully qualified individuals compounds problems associated with limitations in knowledge and capabilities. 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). Few licensing requirements pertain to environmental work; those that do have been enacted by local jurisdictions often lacking the professional expertise necessary to operate a credible specialty licensing program (Anderson, 1992; Eisenberg, 1992). A recent explosion in the number of voluntary registration and certification programs, including some with no professional credibility, has undermined the perception of certification as a means of identifying qualified practitioners (Eisenberg, 1992). These issues are discussed in Chapter 5.

Suggested Citation:"3 The State of Engineering Practice in Marine Habitat Management." National Research Council. 1994. Restoring and Protecting Marine Habitat: The Role of Engineering and Technology. Washington, DC: The National Academies Press. doi: 10.17226/2213.
×

Regulation of Restoration Projects

Based on practical experience, regulatory programs have not been particularly successful in ensuring project performance to design objectives. This situation is attributed in part to the cost of conducting monitoring to determine project performance, the cost of enforcement, the relatively young status of regulatory programs directed toward habitat protection and restoration, and turnovers in federal and state regulatory enforcement personnel. These factors make it difficult to maintain a cadre of qualified regulators.

General Status of Restoration Regulation

The U.S. Fish and Wildlife Service, Forest Service, Soil Conservation Service, and Army Corps of Engineers have been conducting nonregulated habitat restoration for more than 70 years. Regulations governing the type of habitat restoration permissible and its design are less than two decades old. As with most new regulations, permitting issues have dominated the concerns of regulators, regulated industries, and third-party interests (such as environmental groups).

Recently several ad hoc and regulatory agency-sponsored wetland mitigation permit compliance reviews in Florida, Oregon, Louisiana, and New England, received wide notice and third-party comments. All these compliance reviews involved a nonrandom selection process based on projects that could be easily identified and located. Because the criteria used were not part of the original project goals and objectives, a percent failure figure or percent success is meaningless. It is generally accepted that problems exist in most permitted marine wetland habitat restoration projects. No other habitat types were reviewed.

SUMMARY

A broad range of technology has been applied over a wide variety of habitat projects. Although there are some gaps in technical capabilities, they are not limiting factors for most projects. 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. Valuable lessons can be learned from both successful and unsuccessful projects when comprehensive monitoring is planned and executed. These lessons can be applied in subsequent project planning, design, and implementation. The major gaps in scientific knowledge and engineering practice and predictive capabilities are known. Research can be conducted to establish the informed basis needed to overcome scientific and technological impediments to marine habitat management projects. In the absence

Suggested Citation:"3 The State of Engineering Practice in Marine Habitat Management." National Research Council. 1994. Restoring and Protecting Marine Habitat: The Role of Engineering and Technology. Washington, DC: The National Academies Press. doi: 10.17226/2213.
×

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. Application of the technology is impeded by inadequate professional qualifications of some practitioners and regulators and by the regulatory process itself.

Suggested Citation:"3 The State of Engineering Practice in Marine Habitat Management." National Research Council. 1994. Restoring and Protecting Marine Habitat: The Role of Engineering and Technology. Washington, DC: The National Academies Press. doi: 10.17226/2213.
×
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Suggested Citation:"3 The State of Engineering Practice in Marine Habitat Management." National Research Council. 1994. Restoring and Protecting Marine Habitat: The Role of Engineering and Technology. Washington, DC: The National Academies Press. doi: 10.17226/2213.
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Suggested Citation:"3 The State of Engineering Practice in Marine Habitat Management." National Research Council. 1994. Restoring and Protecting Marine Habitat: The Role of Engineering and Technology. Washington, DC: The National Academies Press. doi: 10.17226/2213.
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Suggested Citation:"3 The State of Engineering Practice in Marine Habitat Management." National Research Council. 1994. Restoring and Protecting Marine Habitat: The Role of Engineering and Technology. Washington, DC: The National Academies Press. doi: 10.17226/2213.
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Suggested Citation:"3 The State of Engineering Practice in Marine Habitat Management." National Research Council. 1994. Restoring and Protecting Marine Habitat: The Role of Engineering and Technology. Washington, DC: The National Academies Press. doi: 10.17226/2213.
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Suggested Citation:"3 The State of Engineering Practice in Marine Habitat Management." National Research Council. 1994. Restoring and Protecting Marine Habitat: The Role of Engineering and Technology. Washington, DC: The National Academies Press. doi: 10.17226/2213.
×
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Suggested Citation:"3 The State of Engineering Practice in Marine Habitat Management." National Research Council. 1994. Restoring and Protecting Marine Habitat: The Role of Engineering and Technology. Washington, DC: The National Academies Press. doi: 10.17226/2213.
×
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Suggested Citation:"3 The State of Engineering Practice in Marine Habitat Management." National Research Council. 1994. Restoring and Protecting Marine Habitat: The Role of Engineering and Technology. Washington, DC: The National Academies Press. doi: 10.17226/2213.
×
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Suggested Citation:"3 The State of Engineering Practice in Marine Habitat Management." National Research Council. 1994. Restoring and Protecting Marine Habitat: The Role of Engineering and Technology. Washington, DC: The National Academies Press. doi: 10.17226/2213.
×
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Suggested Citation:"3 The State of Engineering Practice in Marine Habitat Management." National Research Council. 1994. Restoring and Protecting Marine Habitat: The Role of Engineering and Technology. Washington, DC: The National Academies Press. doi: 10.17226/2213.
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Suggested Citation:"3 The State of Engineering Practice in Marine Habitat Management." National Research Council. 1994. Restoring and Protecting Marine Habitat: The Role of Engineering and Technology. Washington, DC: The National Academies Press. doi: 10.17226/2213.
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Suggested Citation:"3 The State of Engineering Practice in Marine Habitat Management." National Research Council. 1994. Restoring and Protecting Marine Habitat: The Role of Engineering and Technology. Washington, DC: The National Academies Press. doi: 10.17226/2213.
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Suggested Citation:"3 The State of Engineering Practice in Marine Habitat Management." National Research Council. 1994. Restoring and Protecting Marine Habitat: The Role of Engineering and Technology. Washington, DC: The National Academies Press. doi: 10.17226/2213.
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Suggested Citation:"3 The State of Engineering Practice in Marine Habitat Management." National Research Council. 1994. Restoring and Protecting Marine Habitat: The Role of Engineering and Technology. Washington, DC: The National Academies Press. doi: 10.17226/2213.
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Tremendous changes have occurred this century in the nation's coastal habitats, in the way society views them, and in the way they are managed. This volume offers a complete, highly readable assessment of how scientific knowledge and coastal engineering capabilities can be more effectively used to protect and restore marine habitat. It addresses traditional and innovative uses of technology to protect remaining natural marine habitats, to enhance or restore those that have been altered, and to create marine habitat from lands used for other purposes. The use of dredged materials as a vital resource in protection and restoration work is explored. The book also explores organizational, management, and regulatory barriers to using the best available technology and engineering practice. Specific options for improvements are offered in each area.

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