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OCR for page 267
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
OCR for page 268
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,
OCR for page 271
APPENDIX F
271
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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
OCR for page 273
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
OCR for page 275
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
OCR for page 277
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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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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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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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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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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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.
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Representative terms from entire chapter:
borrow site
