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APPENDIX F Project Construction and Sediment Sources, Transfer, and Placement The construction of a beach nourishment project normally involves the search for sources of sediment that meet the criteria specified by the design, the removal and transfer of material to the nourishment site, and finally its placement on the beach. These components of a project are fundamental to its performance and often determine its feasibility by controlling costs. SEDIMENT SOURCES The search for viable sediment sources occurs at an early stage in the plan- ning because this controls, in part, project design and economics. Beach-quality sand and gravel can potentially be derived from a number of sources, which are summarized in this appendix in their order of importance as utilized in recent years in beach nourishment projects in the United States. Offshore Sources Over the past decade, the primary source of sand for beach nourishment has been "offshore" deposits on the continental shelf. One of the earliest beach nour- ishment projects using sand from offshore deposits was at Coney Island, New York, where over 1.3 million m3 of sand dredged from the seabed not closer than 500 m from shore was placed on the beach during 1922-1923; (Farley, 1923, Domurat, 1987; Dornhelm, 1995~. Many of the offshore deposits are relict beach sand that was initially depos ited in the littoral zone during the last 20,000 years when sea levels were lower 267
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268 BEACHNOURISHMENT AND PROTECTION than at present. This origin potentially makes the sand ideal for nourishment of the modern beach, although some fine-grained silts and clays may have been incorporated into the sand or may have partially covered desirable deposits. At the same time, the coastal processes that deposited these materials have shifted landward as sea level rose. Because the closure depth for measurable sand move- ment is well inshore of relict sand, offshore borrow sites tend to fill in with fine- grained material that is not suitable as beach fill. Therefore, it is unlikely that many deepwater borrow sites offshore will return to their predisturbed condition. Once the sand is used, other sources will have to be found (BEB, 1958; Gee, 1965; Watts, 19631. Locating and Assessing Offshore Sand Deposits The investigation generally begins with high-resolution seismic reflection profiling. The composition and thickness of the borrow sand are determined with a combination of grab samples of seafloor sediments and vibracore and jet-probe samples that can penetrate down into the sediment layers. Vibracore samples are relatively inexpensive to obtain and can recover the long and relatively undis- turbed cores required to assess the compositions and grain sizes of the materials, as well as to establish the stratigraphy of the deposits (Meisburger and Williams, 1981~. Cores as long as 6 m are routinely taken. Water jets are less expensive than cores, involving the waterjetted penetration of a pipe down through the sediment in order to determine the layering. An experienced operator can determine from the rate of penetration and "feel" of the probe whether it is passing through mud, clean sand, or sand containing some rock material. In general, jet probes are spaced between core borings in order to provide more documentation on sedi- ment thicknesses, while reducing the cost that would result from utilizing vibracore samples for complete coverage. Reconnaissance studies conducted to evaluate this resource and their overall findings are shown in Table 4-2. Use of Offshore Sand Deposits for Beach Fill Offshore sediments have been used as sand sources for many beach nourish- ment projects. In each case, the material was dredged from the seabed, trans- ported to the beach, and either dumped or pumped into the littoral zone. Sand and shell material derived from the shallow-water continental shelf served as the source for the Dade County, Florida (Miami Beach) nourishment and hurricane surge protection project (Wiegel, 1992) constructed between 1976 and 1981. This is the largest-scale nourishment project undertaken in the United States and involved the dredging of some 13 million m3 of sand in the offshore and its placement in the nearshore to produce a dry beach 55 m wide at an elevation of 3 m above mean low water (Egense and Sonu, 1987; Wiegel, 1992~. The sand for
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APPENDIX F 269 the fill was obtained from offshore dredging. The borrow area consisted of trenches that ran parallel to the shoreline 1.8 to 3.7 km offshore at water depths between 12 and 18 m. The nourishment sand from this source generally had a high carbonate content, consisting of shell and coral fragments. The more recent nourishment project at Ocean City, Maryland, also derived its sand from an offshore source (Grosskopf and Stauble, 1993) from two borrow areas 4 to 5 km offshore, which yielded grain sizes of 0.30 to 0.35 mm. Inlet Sources Tidal inlets, especially those used for navigation, are an historic source of nourishment material. For example, sand for the 1986 nourishment of Atlantic City, New Jersey, was obtained from the large subaqueous shoal that develops in Absecon Inlet at the north end of the jetty (Weggel and Sorensen, 1991~. Ap- proximately 800,000 m3 of sand was removed from the shoal by a hydraulic pipeline dredge and pumped directly to Atlantic City's beaches. In many cases, the sand dredged from inlets originally came from the beaches and accordingly should be returned rather than deposited offshore in deep water, where it may be permanently lost from the littoral zone. Dean (1987) documented that in the past 50 years more than 50 million m3 of good quality sand has been dredged from Florida's east coast inlets and dumped offshore. The calculations indicate that this volume would have been sufficient to advance the shoreline by more than 7 m over the entire 600-km sandy shoreline of the east coast of Florida. Inlet sources are increasingly being considered for nourishment projects in other states. One potential problem is that inlet shoals may be the source of sand to downdrift beaches. For example, Ocean City, Maryland, has considered the removal of sand from the inlet's ebb-tide shoal, in effect returning the sand to the updrift side in front of Ocean City. But sand was obtained from offshore borrow areas because use of the ebb-tide shoal has been objected to because the shoal is the source of sand for the downdrift beach along Assateague Island, which has suffered exten- sive erosion since jetties were constructed at the Ocean City inlet. Beach Sources Littoral Drift In some instances, accretional downdrift beaches have served as sources of sand for beach nourishment projects by "backpassing." An interesting example is the nourishment on Sandy Hook, New Jersey (Nordstrom et al., 19793. There is a significant northward alongshore transport of sediment along this spit. The con- struction of groins and other structures to the south has interrupted that transport and induced erosion, particularly at the South Recreational Beach. Sand eroded from South Recreational Beach moves north as littoral transport and has been
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270 BEACH NOURISHMENT AND PROTECTION deposited at the north end of the spit and within Sandy Hook Channel beyond the end of the spit. The beach nourishment project simply involves using the North Recreational Beach and channel as borrow areas and trucking the sand back to the South Recreational Beach, where it is recycled through the system. In another case, at Avalon, New Jersey, some of the sand eroded from the beach at the north end of town at Townsends Inlet that accretes on the beach at the south end of the town is excavated by construction equipment and transported back to the inlet area. The sand is placed back on the beach at the inlet to repeat the process. Sand Bypassing Bypassing of sand blocked by the construction of jetties or breakwaters is a special case of using an accretional beach as a sand source. There are a number of examples from Southern California (Wiegel, 1994) and from the Atlantic coast of the United States. The Santa Barbara breakwater was constructed on the Califor- nia coast beginning in 1927-1928 as a detached structure but was later extended and connected to the shoreline to prevent harbor shoaling (Wiegel, 1959, 1964~. It is estimated that the breakwater blocks some 200,000 m3 of sand per year. A dredge operates from within the protection of the harbor, using the accreted sand spit from the updrift side to nourish the deprived beach on the downdrift side of the harbor. Sand bypassing systems are also in operation at South Lake Worth Inlet in Florida, at the Indian River Inlet on the Delaware coast (see Figure F- 1), and at other locations on the Atlantic coast (USAGE, 1991, 1994~. Sand bypass- ing is discussed in more detail later in this appendix. Inland Sources Riverine Sources In some instances, an inland source of sediment can be identified. This could involve the mining of sand and gravel from the active bed of a river or from deposits within the flood plain of a river. For example, the primary source of sand for the nourishment of Doheny Beach State Park in California has been from mining within Capistrano Creek (Herron, 1987~. The potential impacts on the overall budget of sediments must be considered when drawing upon a river source; the operation could be self-defeating if the river is a natural contributor of sediments to the beach being nourished or it could induce erosion in another littoral compartment. Dunes Another potential inland source is dunes, particularly those found in the coastal zone. Dune sands, however, are typically finer "rained than beach sands,
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APPENDIX F 271 ..... .. ... > ..... , : ~ .............. ........ I ................. .................. ................. .................... $ . ~. ........... '.' " ...:. ~ I\. .. ~ i:: . ~ . ~ :: ::: i: :. $ ::::::::2'''.'. ' ,: :, ,' ' ', '' ' : :.:: ,~. .2~''.".'"'"'.' '.'' ' ,~, . ~ . ~ ............................ '.} ., ..' l .. $~$~$$ .'.'..'.'. E l it..... . ~ An. ~ 3 ~ . L_ ~ _~ ~ K;4 '\~$ ~;~ ~ ~-:,::: , , ... :.:.: :. ~ ~ ~ . ~,.,~ · ~ . $ ~::~ ::: ~ :. f ~ ~ :::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::: :::::::::::::: ~ ~ ~- FIGURE F-1 Sand bypassing at Indian River Inlet, Delaware. Jet pump positioned by crane (from Wayne Young, Marine Board, National Research Council). the smaller particles having been selectively removed by the winds from the beach and blown inland to form the dunes. This cycle would likely reoccur, potentially at an accelerated pace, if fine-grained sand were used as beach fill. Also, fine-grained sand is more susceptible to movement seaward than coarser- grained material. Use of dune sand for beach fill is generally not desirable be- cause of the natural shore protection that dunes provide. Furthermore, dunes provide unique fragile habitats. In the case of barrier islands, dune systems are fundamental to the natural stability of the islands themselves. Thus, dune sand is not normally a primary source of beach fill material, although recoverable dune sand moved landward by overwash during major storms has sometimes been relocated back to beach areas to restore some measure of natural protection. Overwash deposits tend to be coarser than dune sand, since beach face sediment is carried inland and deposits on and/or mixes with dune sand. Beach Ridge Deposits Another inland source is sand from "beach" ridges, which are ancient depos- its consisting of variable proportions of beach and dune sands. Beach ridge de- posits are often weakly cemented but can be crushed in order to return them to their original sand sizes. When Capistrano Creek has been an insufficient source
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272 BEACH NOURISHMENT AND PROTECTION for fill in Doheny Beach State Park, sand has been derived from ancient beach deposits located on a nearby marine terrace (Herron, 1987~. Glacial deposits composed of sand and gravel can also serve as ready sources in the northeastern and northwestern United States and in the Great Lakes region. As discussed previously, Ediz Hook, which projects into the Strait of Juan de Fuca at Port Angeles, Washington, has been nourished with gravel and cobbles derived from glacial outwash. This is the same type of sediment that was formerly delivered to the site by the Elwha River and alongshore transport and from sea cliff erosion before those sources were cut off by dam construction and the placement of a seawall (Galster and Schwartz, 1990~. Back Bay Sand Deposits Historically, the most important source of nourishment sands in many areas has been from bays and lagoons, often as a byproduct of harbor dredging. Sand derived from bays and harbors has been particularly important in California, where the wide beaches observed today are largely the product of nourishment by sand dredged from harbors such as San Diego (Herron, 1987; Flick, 1993; Wiegel, 1994~. During World War II, over 20 million m3 of sand was pumped from San Diego Bay onto Silver Strand Beach and Imperial Beach. Prior to that nourish- ment, those beaches had been deficient in sand owing to construction of the Rodriguez Dam on the Tijuana River and were frequently overtopped by storm waves. Similarly, the entire Santa Monica Bay beach has been widened by 60 to 100 m by a series of replenishment measures (Herron, 1987; Leidersdorf et al., 1994~. Activity of this type continues today. For example, the U.S. Army Corps of Engineers (USAGE) places beach-quality material from ship channel mainte- nance on a river beach in Oregon on the lower Columbia River. Placement of sand from channel maintenance dredging has also been conducted by the USACE in Florida at the St. Johns River and Pensacola Bay entrance. Under existing federal policy for channel maintenance and shore protection, such placements are a matter of convenience to the federal government in order to reduce transporta- tion costs for dredged material or as an alternative pending approval of cheaper rli~nn~1 ~rP.nc offshore. Alt~.rn~tivelv the local governmental entities can pay the Bard ,, ~ = additional cost for onshore placement. Herron (1987), Flick (1993), and Wiegel (1994) provide quantitative com- parisons of the volumes of sand supplied from nourishment projects to California beaches and the sand volumes derived from natural sources. In the 60 years prior to 1987, Herron estimates that within the 390 km of coast between Santa Barbara and the Mexican border some 70 million m3 of nourishment sand has been the byproduct of projects in coastal areas, such as excavations for harbors, power plants, sewage treatment plants, and highways. During that same period, the natural supply from local rivers and alongshore transport from beaches north of Santa Barbara amounted to some 115 million m3. About 70 million m3 of this
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APPENDIX F 273 "natural" supply was bypassed, naturally or by human activity, around breakwa- ters and jetties on this stretch of Southern California coastline. Flick (1993) provides similar assessments for the individual littoral cells from Santa Barbara to the Mexican border, reconfirming the past importance of nourishment sands derived from land sources. Of concern is that the importance of this source has diminished over the years, in part due to the reduced dredging of rivers, lagoons, bays, and estuaries, which are now recognized as important and fragile environ- ments. When those areas are dredged, however, they can be important sources of sand suitable for placement on beaches, and the sand should not be wastefully dumped offshore. Nonindigenous and Artificial Sand Sources Colitic Sands At times it is economical to utilize "exotic" sediments from more distant sources. Colitic aragonite sands, for example, have been imported from the Baha- mas for a nourishment project on Fisher Island, Florida, immediately south of Miami Beach (Bodge and Olsen, 1992~. The potential use of colitic sands for beach nourishment was initially explored in the 1960s, when laboratory wave- tank tests were undertaken to establish the properties of beaches composed of that sediment (Cunningham, 1966; Monroe, 1969~. The project at Fisher Island repre- sents its first full-scale use in the United States. This project was not large, however. It involved the barging of approximately 23,000 m3 of fill from the Bahamas and its placement on the beach within compartments between six T- head groins built along the 620-m-long fill area. The median diameter of the colitic sand is about 0.27 mm, which is estimated to be hydraulically equivalent (having the same fall velocity) to 0.36-mm quartz sand, as measured by sieving analyses (Bodge and Olsen, 1992~. No adverse environmental impacts have re- sulted from this nourishment project using colitic sand, and there has been no observed physical degradation of the aragonite grains owing to abrasion or disso- lution. The use of imported colitic sands was also considered as an option in the nourishment project undertaken at Hollywood and Hallandale to the north of Miami (Beachler and Higgins, 1992), which was a substantially larger fill (790,000 m3) than at Fisher Island. In this instance, the bids based on nearby sources of normal sand on the continental shelf were substantially lower than economically possible for the import of oolites from the Bahamas. This indicates that such imports will be limited to smaller projects and areas where the material has particularly desirable characteristics; in the Fisher Island project, the white colitic sand was used to blend with the Mediterranean architecture of the devel- opment (Bodge and Olsen, 1992~.
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274 Crushed Rock BEACH NOURISHMENT AND PROTECTION In a few instances, particularly for smaller projects, beaches have been con- structed of gravel made by crushing coral or rock. Wiegel (1993) documented crushed rock material usage at the following beach nourishment projects: · Smathers Beach, Key West, Florida; · Larvotto Bay Beach, Monte Carlo, Monaco; · "Marble Beach," Osaka Bay, Japan; · Maumee Bay State Park, Lake Erie, Ohio: and . Fort DeRussy, Waikiki Beach, Honolulu, Hawaii. There is little published information on the performance of projects that used crushed rock material. By visual inspection, they generally appear to be perform- ing as anticipated (Wiegel, 1993). The Monte Carlo beach in Monaco was constructed during 1965-1967 using 80,000 m3 of dolomite chippings, with a median diameter of 3-8 mm, from a local upland source (Tourman, 1968; Rouch and Bellessort, 1990~. The 400-m-long beach was contained within a system of groins and breakwaters. The gravel-sized chippings soon became rounded by abrasion within the surf as had been predicted by tests using a Los Angeles "rattler," which is a large rotating drum similar to a rock tumbler, to simulate the process in the laboratory. The 800-m-long beach fill at Maumee Bay State Park, Ohio, was constructed along its western part with 115,000 m3 of crushed Niagara limestone having a median diameter of 0.75 mm. After three and a half years, the beach has remained in good condition (Wiegel, 1993~. These placements suggest that nonindigenous materials can be used suc- cessfully in lieu of native sediments for beach fill purposes. TRANSPORT AND PLACEMENT Bridging the gap between the investigation and analysis of potential borrow sites and the design parameters attendant to the configuration of a renourished beach requires a basic understanding of dredging equipment, processes, capabili- ties, and limitations. Furthermore, various choices and trade-offs with respect to increased protection, recreational benefits, and maintenance savings that affect the cost of construction are presented for decision making during the design process. The designer and project decision makers must decide whether the cost of construction should be increased in order to reduce the overall lifetime cost of the project. Dredging Resources Generally, sand borrow is excavated and transported from a borrow site to a beach by one or more of three types of equipment: cutter-suction dredge, trailing
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APPENDIX F 275 suction hopper dredge, or dedicated sand bypass system. However, the vast ma- jority of beach projects have been accomplished either by using self-propelled hopper dredges with pumpout capability or by pumping the borrow material directly to the beach fill site via pipelines from cutter-suction dredges. Transport via trucks and placement directly onto the beach fill site have been used in some projects in which sand and gravel were obtained from upland sources. Transportation costs for a given material increase with distance. Although this is obvious whether a pipeline, hopper dredge, or truck is utilized, the effect on each varies and is not proportional to distance. Selection of a borrow site inherently restricts the range of suitable equipment for a project. Varying resources among contractors establish degrees of cost advantage or disadvantage. The ability to work offshore or, to meet high produc- tion capabilities, ownership of certain equipment such as hopper dredges or cer- tified dredges, and the financial resources to bond high-cost projects are all factors that tend to narrow the field of participants in large nourishment projects with offshore sources. Conversely, sources from inshore protected waters or closer borrow sites, including upland pits, allow a wider field of bidders. Existing Fleet At present, the U.S. marketplace for beach nourishment is served by the fleets of U.S. dredging companies utilizing equipment that is flexible and multi- purpose over a large range of dredging requirements and materials to include navigation channel maintenance, land reclamation, and construction dredging, as well as beach replenishment. Utilization of the fleets in this manner, combined with a substantial overcapacity in the U.S. industry, results in extreme competi- tion among the companies capable of nourishment projects, which in turn results in lower pricing to the marketplace. Although few large cutter-suction dredges or hopper dredges have been con- structed recently, the existing equipment is continually upgraded and is capable of meeting the requirements placed on it by the beach nourishment market at reasonable costs. As this market matures and greater offshore capabilities and higher productivity govern the pricing, the industry will respond with new ves- sels capable of earning favorable returns for their owners. Equipment Types and Capabilities/Limitations A cutter-suction dredge consists of one or more large pumps mounted on a barge with all the engines and drive mechanisms required to pump a slurry of sand and water to the beach through a pipeline without any double handling or intermediate processes. The material is excavated and introduced to the slurry by means of a cutterhead located on the end of an articulating ladder attached to the barge with a hinge mechanism. Figure F-2 shows schematically the layout of a
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276 _25.1 Landside FIGURE F-2 Layout of a typical offshore cutter dredge. BEACH NOURISHMENT AND PROTECTION ~ Swing Anchor Breast Anchor Breast Anchor \_ Swing Anchor I Stern Anchor Floating Pipeline jut Riser Connection Submerged Pipeline Beach Area "Y" Valve Distribution Pipeline typical offshore cutter dredge and its connected pipeline to the beach. The dredge is held in place on a system of cables, winches, and anchors. The stern of the dredge is moored in a single position with three anchors. On this pivot point the dredge and the submerged ladder swing through the width of a cut utilizing swing anchors set to each side. The dredge advances through the length of the cut by slacking the stern anchor and taking in on the two breast anchors after the mate- rial in each swing of the ladder is excavated. Connected to the dredge is a floating section of pipeline consisting of either steel pipe sections mounted on flotation tanks or flexible hose segments with their own integral flotation collars. Extending from the floating pipeline is a section of pipe placed on the bottom and leading to the shore landing. It is connected to the floating section with a ballpoint connection on some type of barge or flotation arrangement. The purpose of the floating segment is to allow flexibility to the dredge in movement and to allow disconnection from the pipe- line in cases where the dredge must be taken to safe harbor to escape bad weather conditions or for major repairs. The shore landing is typically located in the center of a length of beach to be replenished so as to minimize the total pipeline length on which the dredge is pumping. At the landing, a Y valve is installed to allow the shore crew to choose the direction and segment of pipeline on which to pump. As the fill advances down the beach, the shore crew adds sections of shorepipe on whichever line is
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APPENDIX F Borrow Area _~. 'f . Dredging ~_ ~ Dredging ~ Turning - Trailing Arms \ Beach Area Mooring Buoy or Barge for Pumpout Submerged Pipeline Hyt' Valve ~3 1~ Shorellne FIGURE F-3 Schematic of operation of a tra~ling-suction hopper dredge. 277 appropriate to control the distribution of the fill within the limits of the design template. The operation of a trailing-suction hopper dredge is illustrated schematically in Figure F-3. This dredge differs from a cutter-suction dredge in that it is a free- traveling vessel that is either a ship or a tug-propelled barge that sails back and forth over the area of the borrow site and that trails one or two arms on which are mounted dragheads that loosen the sand and deliver it to the suction pipe, which then loads the slurry into the hopper of the vessel. In order to deliver the sand to the beach, the hopper dredge must either (1) moor to a buoy or barge and pump the material through pipeline arrangements similar to that of a cutter-head dredge or (2) bottom dump the material directly in place through the use of doors in the bottom of the hull or via a split-hull arrange- ment where the ship divides itself into two halves hinged in the center on each end. Following are some characteristics of both types of dredges. Hopper Dredges U.S. vessels vary in size from about 700 to 12,000 m3 per load: . loaded drafts range from 4 to 9 m;
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APPENDIX F 283 to be sufficiently wide to accommodate the ideal swinging width of the dredge and needs to have as large an excavation depth as possible. The material must be available in sufficient quantity to supply the project after taking into account excess material placed beyond design templates, loss of finer-grained material placed under water, erosion of the beach during construc- tion, and rejection of material because of sand quality or environmental restraints. In a recent project in Manatee County, Florida, the principal sand source was initially identified as 18 million m3 but was reduced to 3 million m3 after analysis of limiting factors. In addition to the transport distance discussed above, the project length and its relation to the borrow sources often are factors in the cost of a project. Unim- peded access to the fill point from the borrow site will result in the lowest costs. Shoal waters that interrupt the line from borrow site to placement artificially extend the transportation distance, as do other natural or man-made structures that require rerouting of pipelines or transiting barges around an obstacle. Depth Constraints and Accessibility In marine borrow sites the navigational depths of the site and surrounding area are critically limiting to certain types or classes of dredging vessel. In addi- tion to hull clearance (loaded draft clearance for hoppers and scows), some opera- tional depth for maneuvering or operation of attendant plant is required. Very shallow borrow sites are restrictive to cutter- suction and hopper dredges, while very deep ones may exceed excavation depth limits and pump constraints. Pipe- line operations in deep areas are more difficult than those in shallower waters. Implications of Distant and Deepwater Sources In the future, near-term localized borrow shortages or environmental con- cerns may necessitate transportation of sand from sources far from the site of a constructed beach. In order to conserve transportation costs, this would necessi- tate the use of larger transport vessels and alternative methods of sand delivery to the beach from those presently in use. Vessels suited for this type of operation are generally not available in the U.S.-flag dredging fleet. Furthermore, the capabil- ity for deepwater mining of sand is constrained to depths of about 60 m by the limits of existing dredging technology and to depths of 30 m for the U.S.-flag dredging fleet. The increased costs of such operations might make nontraditional sources of material for fill, such as artificial sand, financially attractive or perhaps stimulate development of improved resource recovery technology. The develop- ment of deepwater mining technology and equipment, like the development of offshore oil production, will be a slow process that requires a profitable market- place for its product.
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284 Other Design Impacts on Construction Costs BEACHNOURISHMENT AND PROTECTION In any fill placement process involving slurry transport, the ability to ad- vance the pipeline along the project length without interrupting the production of the dredge is critical to the efficiency of the operation. High-productivity equip- ment is required for long transport distances or the ability to work offshore. If the fill quantities are limited (in terms of volume per unit length of beach), the dredging must be halted frequently to move the distribution pipeline or must be used at less than its minimum continuous production. This will result in a pre- mium unit price being paid without the full benefit of the equipment's capability. To avoid expensive special equipment or productivity delays, the berm width must provide an allowable working platform for the pipelines above the level of the wave runup at high water. Most design procedures recognize the inability of present dredging contrac- tors to grade or place material to close tolerances under water or within the wave- action zone without special equipment or procedures. These procedures limit well-defined templates to the dry beach and usually mandate volumetric require- ments and tolerances below the surf area in anticipation of natural shaping of the material through wave forces. Any requirement for design slopes that is contrary to natural processes, such as a steep slope requirement for fine material, will result in extra cost to the project without extra benefit. Projects that include an artificial dune should allow for shaping of the dune as a parallel effort to berm and slope construction. Insufficient berm width, unrealistic dune slopes, or a constricted construction area will result in inefficient and costly overfilling or production interruptions. Structures such as pedestrian and vehicular crossovers, seawalls, drainage outfalls, or sand-retaining fencing, as well as various dune grasses or plantings designed to stabilize the sand, add materials procurement time to a project that normally contains no scheduling for anything other than equipment time. These interfaces with the dredging schedule should be given considerable thought in planning. Local and Seasonal Weather Conditions Also of great effect on the dredging process are the weather conditions that may be encountered. For dredging sites in rivers or bays that are relatively pro- tected, the weather will have little effect except for cessations caused by short squalls or shutdowns caused by major hurricane events or flooding. The offshore borrow sites, however, will be subject to periods of reduced productivity as well as complete stoppages because of the effects of sea state and wind. Possible multiple interim local remobilizations because of the effects of major storms or hurricanes exacerbate the difficulties of accurate cost estimation. Unpredictable storms may cause 2 to 10 days of unproductive time when the
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APPENDIX F 285 payroll and other costs remain in place and no revenue is being generated. Addi- tionally, the potential for damage to equipment, injury to the contractor's person- nel, and third-party liability is great. These storms may also destroy work already in place, which may or may not be accepted depending on the contractual ar- rangements. Borrow Site Considerations Typical designs for borrow site use establish limits to excavation both hori- zontally and vertically. The dimensions are set to include sufficient borrow mate- rial for all facets of the project but to horizontally exclude proximate hard struc- ture, reefs, historical areas, nesting or spawning sites, and commercial- or recreational-use areas. Vertical dimensions exclude pockets or layers of unsuit- able material, as well as design dimensions, to eliminate holes that may trap fine- grained sediments or cause variations in wave energy at the shoreline. Design parameters for anchoring systems and turbidity generation must be considered in sites with closely adjacent sensitive areas. Limitations on equipment types or processes, such as on hopper dredging during turtle migrations, have an extreme impact on the cost of some projects. Construction Site Requirements Another area in which the designer must sometimes balance requirements of the project is in the fill itself. Typically, a construction contract has a requirement for the placement of material to a specific construction slope with a tolerance either above and below the construction template or only above the template. During construction, the actual slope is influenced by the material being pumped, the rate of pumping, the degree of effort used by the contractor to control the flow of material, and the effects of the surf conditions at the time. In some regions the need for beach nourishment has resulted from sand being trapped by a harbor being constructed (breakwaters) in the nearshore or by jetties built to fix the location of an entrance through a beach into a inland harbor. Net alongshore transport of sand can cause trapping of sand updrift of the structures, within the entrance, or add cost to the project without achieving any additional benefit. With the exception of the dry beach portion, which is easily controlled to a fairly tight tolerance, it is more cost effective to establish volumetric distribution parameters for the portions of the fill that are inaccessible by ordinary land equipment or by bottom dumping by hopper dredge. These areas can be allowed to fill at the natural angle of repose of the material being pumped at the time. Control of fill amounts and distribution may be done with specifications that require minimum amounts of fill within a certain reach of beach, maybe 150 m or so. Interim fill sections within this segment should be required to have similar amounts of fill within a reasonable tolerance to allow for variations in the filling process.
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286 BEACH NOURISHMENT AND PROTECTION In specific designs where the entire profile needs to be nourished during construction or particular placements of material are desired rather than hydraulic redistribution of the fill, these requirements may be met by utilizing bottom dumping by shallow-draft hopper dredges or by using a special-purpose spill barge or other pipeline handling arrangement. Contractual language that details the requirements for monitoring, habitat preservation, or relocation of identified plant and animal life is a requirement for each contract, along with provisions to preserve public and private property from damages due to construction operations. Access to the beach for contractor's operations is requisite for any project. Additionally, the construction operations must be controlled to prevent most interference with the tourist trade and beach use. This can be accomplished readily by securing an area at the immediate fill site with approximately 500 to 600 m of beachfront working area, providing pedestrian access over pipelines, and intensive public education. Public Access and Disturbance During Construction The primary solution to the aggravations of the impacts of construction on the use and enjoyment of a beach is the knowledge that they will pass any given area on the beach within a short period of time. To ensure the credibility of this remedy, the project management must require a sufficient rate of progress with the fill and limit the area on the beach accessible to the contractor for construction operations at any given time. The manner in which this is to be accomplished must be a requirement of the specifications and the subject of an understanding between the owner's representative and the contractor prior to the start of the project. Contractual Constraints Project Schedule Requirements The schedule for requirements on a beach nourishment project takes into account the protection offered (or recreation afforded) by the existing beach, construction interferences with the public during high-use periods, weather im- pacts on the cost of operations, impacts on the environment, and political timing with regard to funding cycles. Contractors choose equipment so as to produce the lowest unit cost and meet contractual requirements as defined economically. Low unit costs may be achieved with a costly daily expense over a short but highly productive period or a lower daily expense over a longer period. Payment Items Three items regarding pay structure are particularly important in beach re- plenishment projects. The first of these includes fair assessment and dealing with
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APPENDIX F 287 contractor risk due to weather impacts. Contractors have the ability to assess risk for average weather patterns but would be able to negotiate lower prices if some risk sharing with the owner is formulated. A second item relates to completed but unaccepted beach fill. Often requirements for acceptance of fill sections do not realistically evaluate contractor work in place prior to storm events. A third item is the designation of pay templates for the fill. Stringent requirements for slope dimensions in areas where the contractor cannot grade without specialized equip- ment on unrealistic slope designs lead to higher prices for "loss factor" contin- gencies or unfair payment for useful fill in place. Volumetric tolerances below the surf zone should be reasonable. Dredging Industry Considerations In addition to the effects of all these factors on the cost of a project from the contractor's viewpoint, there are some situations that may be more relevant to beach nourishment projects accomplished by dredging than to building or high- way construction. Dredging in most cases, and certainly in the case of offshore borrow sites, is accomplished by large individual pieces of equipment that each cost millions or tens of millions of dollars. Coupled with this high capital invest- ment is a relatively low yearly use, which may be on the order of 6 to 8 months for all types of navigation channel maintenance and construction dredging and generally 6 months or less for beach nourishment projects. This low utilization is a result of the construction issues discussed previously, as well as the number of available plants of these types in the United States today. There are at least nine major cutter-hydraulic dredges and eight major trailing-suction hopper dredges in the U.S. fleet today, as well as two barge-tug combinations that could perform offshore work. These two factors result in a high daily cost of equipment for beach nourishment projects. The cost of marine insurance for equipment, insur- ance requirements for dredging personnel, and recent increases in liability for environmentally sensitive situations further add to the cost of dredging opera- tions. The U.S. dredging industry has further experienced recent consolidation of existing companies and entrance into the beach nourishment area by companies that previously did not perform this type of work. Additionally, the continual retrofitting and construction of new plants have resulted in the possibility of four or more companies bidding in the beach nourishment marketplace for the various types of projects. This number could easily double if projects using material from protected waters are considered. Although this appears to present a favorable climate for the cost of beach projects, the general nature of these projects and their high cost force owners (who are generally public bodies) to look for areas in which to implement sav- ings. The greatest risks to contractors on these projects are the variable and somewhat unknown nature of the material being dredged and the unpredictable
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288 BEACH NOURISHMENT AND PROTECTION nature of the weather. Owners and engineers can mitigate the material factors by ensuring performance of a detailed and comprehensive prebid soils investigation. This could take the form of payment of a standby rate for periods of bad weather in which the plant could not work or payment for a portion or all of the costs associated with the interim demobilization and remobilization surrounding major storm events. To level the playing field and ensure a proper degree of effort on the contractor's part, these parameters would need to be expressed in terms of absolute sea conditions or wind forces rather than general terms describing the dredge's ability to work or its productive work hours. Another cost factor may be the volatility of costs for emergency work or cycles of maintenance conducted earlier than planned. It is obviously to the owner's advantage to be able to decline to contract the work if the prices at bid time are considered unreasonable. To protect this option, consideration should be given to the early performance of maintenance cycles before they become truly emergency in nature. Another possible solution to the increased cost of emer- gency work is a state, regional, or federal organization of contracts that provide for yearly maintenance work to be done. The specific assignment of work would be made according to the need at a time nearer to the time of dredging than is possible with the present lengthy prework planning period. Future Needs In order to serve the requirements of an expanding beach nourishment mar- ketplace, the following developments will be critical to the U.S. dredging indus- try. Greater Efficiency in Onshore Conditions As with the development of the offshore energy industry, the dredging mar- ket will demand greater productivity throughout larger ranges of weather condi- tions than at present. Development of more single-purpose offshore hull forms, more flexible and heavy-duty moorings, and more material delivery systems are presently evolving and will develop at a more rapid pace as the economics of beach material delivery grows. It is likely that much of this technology will evolve from offshore experience gained by energy companies and be adapted to dredging equipment. Ability to Mine Deeper Sand Deposits and Deliver Farther Larger equipment supporting longer dredge ladders or remote active drag- heads will be developed as borrowing of farther offshore deposits becomes eco- nomical. Higher-head pumping systems that use more sophisticated booster con- trol will enable delivery of sand from farther offshore borrow sites.
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APPENDIX F Long-Distar~ce Transport of Material 289 Although long-term source estimates of sand and gravel resources in the U.S. exclusive economic zone are in the billions of cubic meters, localized shortages (particularly in the Florida and Gulf coast regions) may make the importation of beach fill material from relatively long distances an economic feasibility. This concept may also see fruition if the public becomes willing to pay for this meth- odology as a compromise to environmental considerations in some regions. The transport distance for disposal of dredged material presently reaches roundtrips exceeding 160 km when carried to some U.S. Environmental Protec- tion Agency-designated ocean disposal sites. This is accomplished in the $9.00 / m3 range, including the dredging, albeit at small daily quantities of about 4,500 m3. This type of relatively local transport could be accommodated with large hopper barges or dump scows in today's beach nourishment market. Rehandling and placement costs would increase the cost. To become productive using this concept, bulk carriers of the type used to transport coal, ore, or grain internationally would be utilized. In addition to the freight charges, mining and loading costs, as well as unloading and placement costs on the receiving end, would be included. One concept would be to outfit the carriers so that the sand cargo could be deposited in underwater stockpiles strate- gically placed to allow redistribution via cutter-suction or hopper dredge as needed. Project Quality Control Having discussed the multitude of steps necessary to bring a beach nourish- ment project to construction, the owner must ensure proper construction tech- nique with the following quality control measures: · detailed pre- and postfill surveys, with sufficient extensions past closure depth; · daily samples of fill material and grain-size distribution analysis; · records of borrow site excavation coverage on a daily basis and calcula- tion of gross quantities removed; detailed calculations of fill volume within and without pay tolerances; and · records of contractor equipment used, hours worked, payrolls, and fuel consumption. Alternative Construction Concepts As additions to the presently considered beach nourishment concepts and techniques, the following ideas may have some merit.
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290 Regional Project Design BEACHNOURISHMENT AND PROTECTION Coastal segments, geological features, or other natural separations often fail to coincide with political boundaries. The concept of regionalization, although extremely difficult to implement, is as valid for beach replenishment as it is for water resource usage, infrastructure maintenance, and solid waste disposal. A larger coastline segment for a project may yield advantages in design, economies of scale, and savings in maintenance costs through contract efficiencies. Regional plans may also be more effective in attracting national funding sources. Stockpiling and Redistributing Navigation Dredging Material Present limitations on the use of navigation dredging for beach replenish- ment often require unwieldy coordination between the navigation project and the beach owner. An alternative way of assigning costs may be to allow navigation projects to stockpile material in close proximity to beach fill areas for later redistribution by the locality instead of mandating one continuous process from navigation project to beach fill. Storm Emergency Fleet Based loosely on other federal programs for private hopper dredges, it may be desirable that certain contract requirements be preprocessed for a core of emergency response equipment to facilitate protective rebuilding after natural disasters have decimated beaches and dune systems, and left people and property at risk. Sand Bypass Systems The use of sand bypassing systems was described in general terms in Chapter 4. The amount of sand to be bypassed is established by the natural coastal pro- cesses in the region. The quantity needed for beach nourishment may be greater than the amount trapped in the entrance channel and harbor, in which case by- passing only this amount will not be sufficient to adequately maintain the down- drift beaches. The system designed to bypass the sand depends upon the quantity to be bypassed, wave climate, tidal characteristics, the size and layout of the entrance channel and harbor, how often maintenance dredging is required, how often nourishment is needed, and the times of the year that bypassing will be permitted (due to environmental and multiple-use requirements). The system that is best for maintenance dredging may not be the optimum one for beach nourish- ment, and vice versa, but the system chosen must be adequate for both functions. Because of the complex relationships among wave dimensions and directional characteristics, water levels, and the transport and deposition of sand, a system
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APPENDIX F 291 that is optimum for normal use may be overwhelmed during some storms. The system used may well have to be modified based on experience. Several different systems have been designed and used that may be appropri- ate at a specific site: mobile dredges in the harbor entrance (Santa Cruz, Califor- nia); movable dredge in the lee of a detached breakwater forming the updrift sand trap (Channel Islands Harbor and Port Hueneme, California); movable dredge within an entrance using a weir jetty on the updrift side (Hillsborough Inlet, Florida); fixed pump with dredge mounted on a movable boom (South Lake Worth Inlet, Florida); a series of fixed jet pump-crater units mounted on a pier normal to the beach on the updrift side (Nerang River Entrance, Queensland, Australia); and a jet pump (eductor) mounted on a movable crane, with main water supply and booster pumps in a fixed building (Indian River Inlet, Dela- ware). These and other installations and their operational performance are de- scribed in Sand Bypassing System, Engineering and Design Manual (USAGE, 1991), which provides guidance for the design and evaluation of sand bypassing systems. The following information is needed to plan a project based on quantitative data: . · a statement of the problem; · sand sources and sinks and sand characteristics in the littoral cell; · background erosion and accretion rates and the reasons for them; · wave climate, including directions measured or hindcast; · tide data and calculations of flood- and ebb-tide sand transport character . . lStlCS; · calculations and observations of alongshore transport of sand; · cross-shore movement of sand by waves and tidal currents; · estimates of sand transport into the entrance or harbor, ebb-tide shoal, and external sand trap if one is a part of the project; · loss of sand to the offshore caused by structures; · sand budget, areal and temporal, based on calculations and observations of accretion at nearby structures, such as groins or jetties; storm surge climate; calculation of wave, water level, and sand movement during severe storms to evaluate system component safety; identification and mapping of habitats; effect of system on biological communities; effect of pumping and deposition of sand on biological communities, on other uses, and on public safety; and · calculation of downdrift changes with time for several scenarios of sand budget and placement schedules.
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292 BEACH NOURISHMENT AND PROTECTION After the above information has been obtained or estimated, a system may be designed. Some details on layouts, pumps, and other mechanical components are available in the USACE design manual (USAGE, l991J. REFERENCES BEB. 1958. Behavior of Beach Fill and Borrow Area at Harrison County, Mississippi. Technical Memorandum No. 107. Washington, D.C.: Beach Erosion Board' U.S. Army Corps of Engi neers. Beachler, K. E., and S. H. Higgins. 1992. Hollywood/Hallandale, building Florida's beaches in the 1990's. Shore and Beach 60(3):15-22. Bodge, K. R., and E. J. Olsen. 1992. Aragonite beachfill at Fisher Island, Florida. Shore and Beach 69(1):3-8. Cunningham, R. T. 1966. Evaluation of Bahamian colitic aragonite sand for Florida beach nourish- ment. Shore and Beach 34(1):18-21. Dean, R. G. 1987. Coastal sediment processes: toward engineering solutions. Pp. 1-24 in Proceed- ings of Coastal Sediments '87, Specialty Conference on Advances in Understanding of Coastal Sediment Processes, Vol. 1. New York: American Society of Civil Engineers. Domurat, G. W. 1987. Beach nourishment: a working solution. Shore and Beach 55(3-4):92-95. Dornhelm, R. B. 1995. The Coney Island public beach and boardwalk improvement of 1923. Shore and Beach 63(1):7-11. Egense, A. K., and C. J. Sonu. 1987. Assessment of beach nourishment methodologies. Pp. 4421- 4433 in Coastal Zone '87. New York: American Society of Civil Engineers. Farley, P. P. 1923. Coney Island public beach and boardwalk improvements. Paper 136. The Munici- pal Engineers Journal 9(4). Flick' R. E. 1993. The myth and reality of Southern California beaches. Shore and Beach 61(3):3-13. Galster, R. W., and M. L. Schwartz. 1990. Ediz Hook a case history of coastal erosion and rehabili- tation. Journal of Coastal Research, Artificial Beaches 6(Special Issue ):103-113. Gee, H. C. 1965. Beach nourishment from offshore sources. Journal of Waterways and Harbors Division 91(WW3):1-5. Grosskopf, W. G., and D. K. Stauble. 1993. Atlantic coast of Maryland (Ocean City) shoreline protection plan. Shore and Beach 61(1):3-7. Herron, W. J. 1987. Sand replenishment in Southern California. Shore and Beach 56(3-4):87-91. Leidersdorf, C. B., R. C. Hollar, and G. Woodell. 1994. Human intervention with the beaches of Santa Monica Bay, California. Shore and Beach 62(3):29-38. Meisburger, E. P., and S. J. Williams. 1981. Use of Vibratory Coring Samplers for Sediment Sur- veys. Coastal Engineering Technical Aid 81-9. Fort Belvoir, Va.: Coastal Engineering Re- search Center, U.S. Army Corps of Engineers. Monroe, F. F. 1969. Colitic Aragonite and Quartz Sand: Laboratory Comparison Under Wave Ac- tion. Miscellaneous Paper No. 1-69. Washington, D.C.: Coastal Engineering Research Center, U.S. Army Corps of Engineers. Nordstrom, K. F., J. R. Allen, D. J. Sherman, and N. P. Psuty. 1979. Management considerations for beach nourishment at Sandy Hook, New Jersey. Coastal Engineering 2:215-236. Rouch, F., and B. Bellessort. 1990. Man-made beaches more than 20 years on. Pp. 2394-2401 in Proceedings of the 22nd Coastal Engineering Conference, Vol. 3. New York: American Soci- ety of Civil Engineers. Tourman, L. 1968. The Creation of an Artificial Beach in Larvatto Bay-Monte Carlo, Principality of Monaco. Pp. 558-569 in Proceedings of the 11th Conference on Coastal Engineering. New York: American Society of Civil Engineers.
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APPENDIX F 293 USACE. 1991. Sand Bypassing System, Engineering and Design Manual. Engineering and Design Manual No. EM 1110-2-1616. Washington, D.C.: U.S. Army Corps of Engineers. USACE. 1994. Shoreline Protection and Beach Nourishment Projects of the U.S. Army Corps of Engineers. IWR Report 94-PS-1. Fort Belvoir, Va.: Institute of Water Resources, Water Re- sources Support Center, U.S. Army Corps of Engineers. Watts, G. M. 1963. Behavior of offshore borrow zones in beach fill operations. Pp. 17-24 in Interna- tional Association for Hydraulic Research Tenth Congress, Vol. 1. London: International Asso- ciation for Hydraulic Research. Weggel, J. R., and R. M. Sorensen. 1991. Performance of the 1986 Atlantic City, New Jersey, beach nourishment project. Shore and Beach 59(3):29-36. Wiegel, R. L. 1959. Sand bypassing at Santa Barbara, California. Journal of Waterways and Harbors Division 85(WW2):1-30. Wiegel, R. L. 1964. Oceanographical Engineering. Englewood Cliffs, N.J.: Prentice-Hall. Wiegel, R. L. 1992. Dade County, Florida, beach nourishment and hurricane surge protection. Shore and Beach 60(4):2-28. Wiegel, R. L. 1993. Artificial beach construction with sand/gravel made by crushing rock. Shore and Beach 61(4):28-29. Wiegel, R. L. 1994. Ocean beach nourishment on the USA Pacific coast. Shore and Beach 62(1):11- 36.
Representative terms from entire chapter: