|
Items in cart [4] |
Questions? Call 888-624-8373 |
| Copyright © 2009. National Academy of Sciences. All rights reserved. Terms of Use and Privacy Statement |
Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter.
Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.
OCR for page 294
APPENDIX
G
Physical Processes Monitoring
Monitoring the physical elements of beach nourishment projects provides a
means for determining a project's actual performance versus its predicted perfor-
mance. Monitoring also provides data needed to identify and correct any prob-
lems associated with the project and to help guide future renourishment pro-
grams.
Physical processes monitoring is undertaken to determine whether a beach
nourishment project is performing successfully or whether it is time to renourish.
The monitoring of physical processes is undertaken more often than biological or
economic monitoring. The physical processes monitored are usually those that:
· move sand alongshore,
· move sand normal to the shore, or
.
cause elevated water levels.
Measurements may include both the forces that move sand and the response of
the beach to these forces. However, many physical processes monitoring pro-
grams address only the response of a beach to these forces for example, beach
profile changes and shoreline recession. Important forces include waves and
currents. Beach responses include the transport and redistribution of sand by
wave-induced alongshore currents and seasonal and storm-caused beach profile
changes that is, onshore and offshore sand movement.
The decision to reflourish a beach needs to be based on the occurrence of a
predefined set of site conditions that a monitoring program is capable of provid-
ing. These might include:
294
OCR for page 295
APPENDIX G
295
· recession of the "average" shoreline to a predefined line,
· loss of a specified fraction of the sand volume placed in an area.
· occurrence of local erosional hot spots that seriously jeopardize upland
development of the project itself, or
a combination of these conditions.
.
If shoreline recession is the trigger, normal seasonal beach profile variations
must be taken into account.
Renourishment criteria need to be chosen with a planned factor of safety, so
that upland development and the project do not become vulnerable to the effects
of storms of less-than-design criteria during the necessary planning, engineering,
and mobilization period that precedes construction. For example, renourishment
might be triggered when the shoreline recedes to the point where it is projected
that, on average, it will no longer provide adequate protection against the design
storm in the next year or two. This example presumes that the project includes
advanced fill to provide a cushion against loss of design integrity.
Designing a monitoring program that will meet the preceding objectives
requires the use of local physical conditions to characterize the range of condi-
tions that might be encountered at the project site. These local conditions would
include wave climate, currents, wind conditions, and other physical factors. Data
for these conditions are generally available as a result of the design process.
PURPOSES OF MONITORING
Monitoring can be undertaken for various purposes. These principally in-
clude operational and performance monitoring. Operational monitoring is under-
taken to implement and maintain a project. It can be as simple as a periodic site
inspection or can involve the collection of quantitative data on which to base
. .
decisions to
· renourish.
· repair structures, or
· take other remedial action to prevent economic loss or damage.
Operational monitoring includes both prestorm and poststorm monitoring. Per-
formance monitoring is undertaken to develop information and procedures for
design verification and for lessons that may be applied in the design of future
projects. It involves systematic data collection to develop information useful for
the design of future projects or to validate the design methodology used on a
given project. One purpose of performance monitoring is to understand funda-
mental coastal processes and how they influence beach nourishment project per-
formance for example, to understand how a project impacts adjacent areas as
sand is moved along and across the shore.
OCR for page 296
296
BEACH NOURISHMENT AND PROTECTION
Computer models and other analytical models used for beach nourishment
project design and sediment budget analyses form the framework for perfor-
mance monitoring programs. Monitoring must measure those forces included in
the models that move sediments as well as the beach's response to those forces-
that is, waves, currents, and beach profiles. Performance monitoring can provide
feedback to the design process by testing design assumptions. It can lead to the
development of new design procedures. Performance monitoring might also pro-
vide additional data on the physical environment at a project site that were not
available at the time of the design.
PHASES OF MONITORING
Monitoring has three basic phases: preconstruction, construction, and post-
construction monitoring.
Preconstruction monitoring acquires regional and site-specific data for de-
sign and for baseline data against which project-caused changes can be measured.
It involves the collection of data about the physical environment that describe
regional and site-specific processes and includes collecting data for design. The
physical data needed include measurement of waves, currents, water levels, beach
profiles, and meteorological conditions.
Construction monitoring might be undertaken to verify payment to a con-
tractor, to ensure quality control, to obtain as-built information or to document
construction practices and how they affect project performance. It involves col-
lecting data on how a project was actually built, how much sand was actually
placed, and where it was placed. Such monitoring is conducted in order to pay a
contractor or to ensure quality control and to keep track of what materials were
actually used (e.g., size characteristics of the sand actually placed on the beach).
The objectives of quality control during construction include ensuring that the
specified quantity of sand is received and that the sand meets the desired design-
size distribution.
Postconstruction monitoring involves the systematic collection of data after
construction is complete to study the project's performance. Data are gathered on
how a project is performing with respect to design objectives or to make opera-
tional decisions such as when to renourish or repair structures. Postconstruction
monitoring seeks to answer the basic question: Is the project functioning as
intended?
SCALE AND DURATION OF MONITORING PROGRAMS
A simple monitoring program might involve only periodic inspections to
determine the width of the protective beach at various locations within a project
to determine if renourishment or other corrective action is required. Profile sur-
veys determine the disposition of the sand placed in the project area and establish
OCR for page 297
APPENDIX G
297
the volume of sand remaining on the beach per unit length of beach. Hot spots-
areas of localized erosion can be identified from visual inspection and quanti-
fied from profile surveys.
Because of the dynamic nature of beach nourishment projects, both short-
and long-term monitoring programs are needed. Short-term impacts are defined
as those that occur during construction and those that persist for a few days or
weeks following construction, but that are not discernable after several months.
Long-term impacts are those that persist on the order of months to years. Short-
term monitoring is needed to assess near-term performance and any design and
placement adjustments that may be needed to accommodate site-specific condi-
tions that deviate from design parameters. Long-term monitoring consists of
systematic collection of physical data needed to support assessment of project
performance and to guide the renourishment program.
PHYSICAL PROCESSES MONITORING
Monitoring the physical processes and their effects relevant to a beach nour-
ishment project needs to be done within the framework of a sediment budget for
OCR for page 298
298
BEACH NOURISHMENT AND PROTECTION
· ......................... ................................................... . O
. ~h Noupph - ~ ~on'tonng Pe~ ~ I
:t ~ ~ ~ 1:=: _ =
............................................................... . - ~
I . . ~ . ~s ibis
1~ ~ =31=
............... ~ ~ 'g"'0"'-' i"
the project area and adjacent areas. A sediment budget expresses the principle of
conservation of sand: sand is neither created nor destroyed. Sand lost from one
area is gained by another. A sediment budget seeks to answer questions such as:
· What is the initial distribution of sediment within the project?
· Where is it going?
· At what rate?
· How much is being lost from the project?
· How is it redistributed within the project?
· What processes move the sand?
· What physical characteristics of the sand must be known to quantitatively
define the sediment budget?
· What have the historical rates of erosion been?
A sediment budget requires that all sediment sources and sinks in the study area
be identified. Regional sand sources, in addition to beach nourishment, might
include rivers, local bluff erosion, and sand transport into an area from adjacent
OCR for page 299
APPENDIX G
299
areas. Sinks include ebb- and flood-tide shoals associated with tidal inlets, wind
transport into back bay areas, losses to offshore canyons, and sand movement out
of an area by alongshore or offshore transport.
The spatial extent of the sediment budget and the time period for which it is
constructed determine the kind and amount of data to be collected. When the time
period for which the sediment budget is being developed (the averaging period) is
on the order of months or years, the sediment budget is generally based on long-
term data. The conservation of sand principle can also be applied to time periods
of several hours or days in order to develop numerical computer models of sand
transport, which can be used to predict shoreline changes and onshore-offshore
transport. Numerical models of coastal processes are, in fact, the limiting case of
sediment budget equations constructed for an infinitesimally small time interval
and subsequently integrated over time. Numerical models apply knowledge of
coastal processes to predicting sand movement within and out of a beach nourish-
ment project.
Previous History of a Project Area and Adjacent Areas
The history of events and coastal projects along a reach of beach may simply
be anecdotal or may involve quantitative documented data on earlier nourishment
projects and on other natural and man-made changes. Data can be regional or site
specific. Background information, among other things, needs to include:
historical erosion rates,
relative changes and trends in sea level,
astronomical tides,
· storm surges,
· local anthropogenic impacts,
· statistical descriptions of the wave environment and storm frequency, and
documented information on wave climate.
.
Beach Profiles
Beach profiles provide basic data on the volume and location of sand within
and adjacent to beach nourishment projects. Profiles are simply measurements of
elevation along a line across the subaerial and subaqueous beach extending from
the dune offshore into deep water. Profile lines along which elevations are mea-
sured are usually established perpendicular to the shoreline. As shoreline orienta-
tion changes, however, the relative alignment of profile lines may change. Profile
surveys spaced in time can be used to determine the movement of the sand along
the profile as well as along the shoreline. Also, beach nourishment projects often
benefit beaches outside the project area or are affected by conditions adjacent to
the project. It is often necessary to look outside the immediate project boundaries,
OCR for page 300
300
BEACH NOURISHMENT AND PROTECTION
and profile lines may need to be established on beaches adjacent to the project
area as well as on project beaches.
Factors to be considered in establishing profile survey lines include:
· profile spacing,
· profile length,
· frequency of surveys,
· surveying procedures available,
required accuracy, and
application of the data to make operational decisions or to develop a
sediment budget or mathematical model.
Spacing between adjacent profile lines is dictated by the expected changes
with distance along a beach. If changes occur over short distances, as they might
on beaches with structures, profiles must be spaced close together to accurately
define volumetric changes. If spaced too far apart, profiles will not accurately
define erosion or accretion on the beach. For example, between structures in a
groin field, at least two and preferably three profile lines are needed; on long
reaches of relatively straight beaches, profiles may be more widely spaced. Pro-
files also need to be spaced closer to each other near the ends of nourishment
projects to monitor end losses. Profiles outside of the project area need to be
located in a manner so as to permit determination of how much sand is gained by
adjacent beaches at the expense of the project.
OCR for page 301
APPENDIX G
301
The length and accuracy of a profile line determine whether cross-shore
coastal processes can be quantified. Ideally, profiles would start at the upper part
of the beach landward of where wave action and erosion occur (at the toe of the
dune) and extend offshore to at least the depth of closure. Profile changes occur
infrequently seaward of the depth of closure (Hallermeier, 1981~. (A fixed depth
of closure is difficult to define. It must be defined in a statistical sense given the
local wave climate and offshore profile. While phenomena other than large, long-
period waves might move sand seaward of the closure depth, for practical pur-
poses closure depth is determined by the wave environment.) Profiles can be
divided into subaerial and subaqueous components. Often the two components
are surveyed at different times, since different survey techniques are often used.
The problem is to match the two surveys where they traverse the same area across
the surf zone a region where bathymetric changes occur frequently and rapidly.
Subaerial profiles can be surveyed by using standard leveling techniques. Sub-
aqueous surveys can be obtained by lead-line sounding or by using an acoustic
fathometer. However, the best profiling systems can traverse the surf zone from
the subaerial beach to the closure depth without interruption. For example, a
survey sled with a graduated mast towed from offshore across the surf zone onto
the dry beach provides such a system (Langley, 1992~. Grosskopf and Kraus
( 1994) recommend that a system composed of a sea sled capable of traversing the
surf zone and a total-station surveying system be used wherever possible to
survey profiles (see Figure G-11. They show that errors in determining offshore
and surf-zone elevations are small using this technique and that measurements
are more reproducible. This in turn leads to better estimates of sand volumes lost
and gained across the profiles and to better determinations of the fate of nourish-
ment sand. C)ther systems capable of traversing the surf zone and producing
accurate surveys include sophisticated mobile survey stations like the "CRAB"
(see Figure G-2~.
Profile surveys must be spaced close enough in time to define seasonal
profile changes, beach response to storms, and long-term profile evolution. Sur-
vey frequency might also change during a monitoring program with more fre-
quent surveys taken shortly after construction when changes are rapid and less
frequent surveys taken later when changes are slower. Initially, profile surveys
need to be made at least quarterly to document typical seasonal variations. When
experience is gained, less frequent surveys might suffice.
In addition to scheduled profile surveys, the effects of storms on beach
profiles need to be monitored. This might require special mobilization after storms
to conduct beach surveys. Ideally both pre- and poststorm surveys need to be
obtained. However, prestorm surveys are difficult to obtain because sufficient
advance mobilization time often is not available. Poststorm surveys need to be
obtained as soon as is practical after each significant storm in order to record the
storm's effects. Changes following the first significant storm of a season will
bring about the most dramatic profile changes; subsequent storms, unless more
OCR for page 302
~2
~^ ~ r r~ ~~
SSSsSsSs
. .....
....
. .: ..~.~.: : : .. ...... . ... .... . ....... . . . ,., .... ..,: ~ . ................
FIGURE G- 1 Sea sled far measuring beach prohlos Tom the dry beach through [he surf
zone to depth of closure.
.........
.
. . .
.. ..
.......
......... .
. ... . .
.~.,~.,~
,..S
. ...
FIGURE G-2 Coastal Research Amphibious Buggy (CRAB), a sophisticated mobile
survey station used to profile the scud Mom the dune through the sum zone out to a
Parr dupe of 10 m.
OCR for page 303
APPENDIX G
..............
............
. ~. ~M Mo.~g tendon Roc" Beth FIor'da
.......................... ...... .... ....... ....... . .
I ~1 111 11~ resent me ~ p-In I learn ELocH;s Eat
~'"~'""'"''" ~'~'' = mu"" - ' ' ' ' ~-
' ' '"'"'''' '' ' ~'"~'' '' ' ' "em"
~ ~ ~r
..-. .
............ ~ ~.~
.............. ....................... - .......
=~5 ~ y 2 :~
it ''~'''I'~m''P''?~e p~ ~ ~ ?! ?~
i ~ ~'a~ ~
i ... .
~in
303
severe than preceding storms or preceded by an extended period of beach build-
ing, will cause less dramatic profile changes.
Beach profile data are usually analyzed by comparing two profiles taken at
the same location at different times to determine changes during the intervening
time. The area between the two profiles represents the volumetric change per unit
of shoreline length during that period. A similar analysis of a nearby profile line
allows the volume change between the two profile stations tome computed. The
volume lost or gained is the average of the two end-area changes multiplied by
the distance between the stations. The accuracy of the computed area change at a
given station depends on the accuracy of the profile data. The accuracy of volume
computations depends on the distance between the two stations, the accuracy of
the individual profiles, and whether the two profiles adequately characterize the
beach conditions between them. Beach profile errors are not cumulative, and an
error made during one survey affects only that survey and possibly only a portion
of the profile. Volume calculations made using erroneous profile data lead to
errors in estimating volume changes, but those errors can be corrected by subse-
quent surveys. Where shoreline orientation and processes do not change much
along a beach, profile lines can be spaced farther apart and still adequately de-
scribe beach conditions. For beaches that change their orientation with distance,
closely spaced profiles are necessary.
More detailed analyses can quantify changes above, below, or between given
contour lines. For example, subaerial beach changes can be quantified by com-
puting profile changes above the mean sea level (MSL) contour. In addition to
volume calculations, shoreline movement in the period between two surveys can
be determined from profile data. The distance from a fixed baseline to any given
OCR for page 304
304
BEACH NOURISHMENT AND PROTECTION
shoreline contour the mean high-water, mean sea-level, or mean low-water
contour-can be found from each survey.
Waves
Waves produce the most important forces that move sand in the littoral zone.
Consequently, wave data are important in any perfor~ance-type monitoring pro-
gram. Wave-induced alongshore currents move sand along shore. Changing wave
heights and periods continuously move sand onshore and offshore toward an
elusive equilibrium.
Data on wave height, period, and direction are needed in order to estimate
potential alongshore transport rates; heights and periods alone are insufficient.
Wave data can be obtained by direct measurement or by using mathematical
relationships that transform meteorological data such as atmospheric pressure
fields or wind data into wave heights, periods, and directions. The U.S. Army
Corps of Engineers (USAGE) Wave Information Study used atmospheric pres-
sure data and wind data to hindcast historical wave information, including heights,
periods, and directions, for the Atlantic, Gulf of Mexico, Pacific, and Great Lakes
coastal waters. (See, for example, Jensen, 1983, and Hubertz et al., 1993.) If wave
conditions are known at an offshore location, they must be transformed to the
project site by shoaling and refraction analyses. An advantage of direct wave
measurement is that its characteristics can be obtained in the vicinity of the
nourishment project and would require little or no transformation to obtain condi-
tions at the project site. A disadvantage is that local wave measurements may not
apply to distant parts of a project because of local bathymetric differences.
There are many types of wave gauges. They include surface-piercing gauges
(e.g., Baylor gauge), pressure gauges, combined pressure gauges with biaxial
current meters, accelerometer buoys, and inverted echo sounders. Each has inher-
ent advantages and disadvantages (NRC, 19891. Multiple-gauge arrays can be
used to measure wave direction. Direction can also be determined by slope arrays
of pressure gauges in shallow water and tilt buoys in deep water. Directional
wave gauge systems frequently experience operational problems and are gener-
ally expensive to operate and maintain. Their advantage is their ability to accu-
rately measure concurrent time histories of wave height, period, and direction
(and water level if so configured) and report the data in near real time when
cabled to shore. The USACE routinely uses directional wave gauges to collect
wave data for project studies. Another alternative is to couple a normal wave
gauge to obtain wave heights and periods with detailed hindcasts to obtain direc-
tion.
Visual wave and nearshore current observations can provide estimates of
nearshore wave height, period, and direction; however, data are often biased
toward low heights (observers do not want to visit the beach during storms), and
directional estimates are at best poor. An example of a visual wave observation
OCR for page 305
APPENDIX G
305
program is the Littoral Environmental Observation Program, which was operated
by the USACE for a number of years (Schneider, 1981~. Wave data are analyzed
to obtain significant wave height, period, and, when possible, direction.
Complex wave gauge arrays or other systems are usually necessary to deter-
mine wave direction; consequently, wave direction is not often obtained in beach
nourishment monitoring programs. Alternatively, wave direction may be inferred
from local wind direction for locally generated seas; however, distantly generated
swell may not be traveling in the same direction as local winds. If waves have not
been generated by local winds, wave direction and wind direction can differ
significantly.
Wave measurement systems need to be selected in view of any special con-
ditions that exist at monitoring sites, such as unusually long period wave compo-
nents, bimodal spectra, salinity, water depths, or tidal range.
Currents
Nearshore currents are not typically measured as part of beach nourishment
monitoring except for research purposes. If measured, nearshore currents are
likely to be used to estimate potential alongshore sand transport rates. For ex-
ample, alongshore current measurements obtained by using the USAGE's Lit-
toral Environmental Observation Program procedures (Schneider, 1981) can be
used to estimate alongshore sand transport rates (Walton, 19801. Usually, how-
ever, alongshore currents are computed from wave height, period, and direction.
In addition to alongshore currents caused by waves, other nearshore currents
can provide a mechanism for moving sand into, within, and out of beach nourish-
ment projects. Tidal currents might be important in causing end losses from a
nourishment project. Beach nourishment projects located near tidal inlets can be
affected by flood and ebb currents; however, tidal currents at inlets are rarely
measured during typical beach nourishment monitoring programs. For research
purposes, they might be measured to determine the tidal prism entering an inlet
and to estimate how much sand is removed from the littoral system and trapped
by the inlet. Wind-driven nearshore currents are generally less important.
Current speed and direction can be measured by deploying fixed recording
current meters; however, spatial variations in current speed and direction cannot
be obtained without installing an array of expensive meters. Other techniques for
measuring current speed and direction track floating drogues using standard sur-
veying techniques. Also, dye patches in the water can be tracked using Littoral
Environmental Observation-type procedures (Schneider, 1981) or photographed
to determine current speed and direction. This latter technique is not useful for
long-term or routine monitoring but provides data for only a limited space and
time.
OCR for page 306
306
BEACH NOURISHMENT AND PROTECTION
Water Levels
Information on water levels during storms is important for performance
monitoring to validate the design procedures used to predict dune erosion and
flood damage. Astronomical tides are predicted and water levels are measured
routinely by the National Oceanic and Atmospheric Administration's (NOAA)
National Ocean Survey at stations located around the U.S. coastline (NOAA,
1993~. Meteorological or storm tides constitute that portion of the measured
water-level record not explained by predicted astronomical tides. Generally, these
deviations from predicted tides are due mostly to wind stresses on the water
surface and to atmospheric pressure (including the "ship wave" effect in shallow
water caused by rapidly moving pressure systems) and Coriolis setup. Storm- and
astronomical-tide levels combine to allow waves to act higher up on a beach
profile and result in flooding and beach and dune erosion during storms. They
are, therefore, very important in evaluating the response of a beach nourishment
project to a given storm. At some tide-recording stations, periods of records
extend back more than 100 years. Water-level data are available from NOAA for
sites near most beach nourishment projects in the United States. For stations with
long records, data on relative sea-level changes can also be obtained (Hicks,
1983~. Water-level data are also a natural byproduct of using pressure gauges to
measure nearshore waves if care is taken to preserve the mean water-level data.
Sediment Characteristics
Important sediment characteristics include mineralogy, specific gravity, spe-
cific surface, mean grain size, grain size distribution, grain shape, and settling
velocity (Smith, 1992~. The primary parameter in determining the response of a
beach profile to waves and currents is the settling velocity. The effects of many of
the other parameters are included through their influence on the sand's settling
velocity. Information on these characteristics is needed for
· sand in borrow areas,
· sand on a beach prior to beach nourishment (native sand), and
· sand actually placed on a beach by truck or from a dredge's discharge
line.
Spatial differences in sediment characteristics may also be important. For
example, the distribution of mean grain size along the beach profile and along a
beach can be important, since different grain sizes are moved at different rates by
waves and currents. Coarser grains tend to accumulate in the surf zone.
Temporal changes in sediment characteristics may also occur on a beach as a
result of wave winnowing processes. Consequently, a sediment monitoring pro-
gram may require periodic resampling to determine such changes.
OCR for page 307
APPENDIX G
307
Structures
Coastal structures contribute to the performance of beach nourishment
projects by trapping sand in alongshore transport, reorienting the local shoreline
with respect to prevailing incident waves, sheltering the shoreline, and slowing
the loss of sand. Alternatively, some long structures can speed the offshore loss
of sand by altering local current patterns. The types of structures present in a
project area are important. They can include
. .
sing e groins,
multiple groins (a groin field),
. .
terminal groins,
seawalls,
bulkheads,
revetments, and
nearshore breakwaters.
In order to acquire sufficient data for analysis, monitoring programs must
identify
the types of structures present;
· how they are constructed;
· their planform, orientation, spacing, and height;
· their effect on waves and currents;
· their permeability to waves and sand; and
· their effect on the stability of the beach nourishment project.
The effects of structures on the stability of a beach nourishment project can
vary over the project's lifetime. As sand erodes, the structures may become more
and more exposed to waves and currents, and their beneficial or detrimental
effects may be enhanced. The location and spacing of structures dictate the spac-
ing of beach profiles needed to obtain accurate volumetric beach changes.
Borrow Areas
Borrow areas need to be monitored to quantify physical changes; however,
they are often not monitored at all. Prior to construction, borrow areas need to be
sampled to determine whether proper-sized sand is available. Following con-
struction, infilling of the borrow area needs to be monitored to determine the
characteristics of the material that accumulates and the rate of filling. If the same
borrow area is intended for reuse as a sand source, monitoring needs to establish
if there is sufficient sand available for future use.
OCR for page 308
308
BEACH NOURISHMENT AND PROTECTION
Special Studies
It may often be useful to conduct certain special studies in conjunction with
beach nourishment monitoring. Examples of special studies might include hy-
draulic or sedimentation measurements at tidal inlets; sand tracer studies to deter-
mine dispersal patterns for sediments along beaches, onshore and offshore, and
into inlets; dye studies to monitor unusual current patterns in the vicinity of
coastal structures; and evaluations of new dredging and nearshore disposal tech-
niques. For example, studies using naturally occurring materials as tracers as well
as dyed or radioactively tagged native sand have been used to identify the source
of sediments and to monitor their movement in the littoral zone. Other special
studies (perhaps more correctly classified as field experiments) might be con-
ceived and carried out to quantify unique conditions associated with specific
beach nourishment projects. Such special studies are usually in the realm of
research.
Global Positioning Systems
The establishment and availability of global positioning systems (GPSs) in
recent years have revolutionized terrestrial surveying. GPS systems use signals
from three or more satellites to determine the horizontal and vertical positions of
a point on the earth's surface to within about 4 in. Defense applications can
achieve such accuracy in real time; however, commercial applications must rely
on data available only after a survey has been conducted to correct readings if
such accuracy is desired. Lesser accuracy on the order of 5 to 10 m can be
obtained in real time, if needed, for commercial applications using differential
GPS (DGPS) equipment. Real-time measurements are generally not needed for
beach nourishment project monitoring, so GPS does not, at present, offer advan-
tages over standard surveying techniques for measurements like profile surveys.
In the future, however, as costs decline, accuracy improves, and DGPS is more
widely adopted, it may prove to be an economical system for surveying nourish-
ment projects.
DGPS has other applications, however, that impact the construction and
monitoring of beach nourishment projects. It can be used to locate equipment
such as wave gauge arrays installed on the ocean bottom and to position cutterhead
and hopper dredges to excavate in tightly defined borrow areas.
Geographical Information Systems
In recent years geographical information systems have come into promi-
nence for storing, displaying, and analyzing spatial data of all types. These sys-
tems have been used for marine resource management (Friel and Haddad, 1992)
OCR for page 309
APPENDIX G
309
and may provide a convenient way of storing and analyzing monitoring data
obtained from beach nourishment projects.
Photographic Documentation
Photographs can be used to graphically document the performance of a
beach nourishment project. Photographs are inexpensive, are easy to obtain, and
can be used to picture conditions in areas between profile lines and at times
between scheduled surveys. Ground-level photographs taken at the same loca-
tion, in the same direction, and at various times of the year provide a quick
indication of the changes within a project.
Time-lapse photography has been used to document beach changes. Depend-
ing on the time between photographs, time-lapse photography can document
changes over a tidal cycle, resulting from storms, or over a season. Periodic
controlled vertical aerial photography can provide data on changes in the location
of the shoreline and, using standard photogrammetric methods, can provide data
on changes in the topography of the subaerial beach.
Videotape can supplement regular photography and can also be used to
document project conditions and performance before, during, and after storms.
Prestorm video can be obtained quickly when a stow is predicted. A small
airplane or helicopter can be used as a platform from which to videotape condi-
tions over long stretches of coastline in a short period of time.
THIRD-PARTY MONITORING
in some instances, it may be advisable for monitoring to be done by a disin-
terested third party who can objectively evaluate the project's performance. This
might be done in cases where a project, or some element of a project, is contro-
versial and its sponsor or the public wants an independent evaluation of its
performance. However, the objectives, scope, required accuracy, frequency of
data collection, and how the data will be analyzed must be carefully defined in
view of the project's objectives and expectations. Definitions of what constitutes
successful performance need to be agreed upon prior to third-party monitoring of
controversial projects.
REFERENCES
Bodge, K. E., E. J. Olsen, and C. G. Creed. 1993. Performance of beach nourishment at Hilton Head
Island, South Carolina. In: Beach Nourishment Engineering and Management Considerations,
Coastal Zone '93, New Orleans, Louisiana. New York: American Society of Civil Engineers.
Creaser, G. J., R. A. Davis, Jr., and J. Haines. 1993. Relationship between wave climate and perfor-
mance of a recently nourished beach, Indian Rocks Beach, Pinellas County, Florida. In: Pro-
ceedings of Beach Nourishment Engineering and Management Considerations, Coastal Zone
'93, New Orleans, Louisiana. New York: American Society of Civil Engineers.
OCR for page 310
310
BEACHNOURISHMENT AND PROTECTION
Friel, C., and K. Haddad. 1992. GIS brings new outlook to Florida Keys marine resources manage-
ment. GIS World 5(9).
Grosskopf, W. G., and N. C. Kraus. 1994. Guidelines for surveying beach nourishment projects.
Shore and Beach 62(2):9-16.
Hallermeier, R. J. 1981. Seaward Limit of Significant Sand Transport by Waves: An Annual Zona-
tion for Seasonal Profiles. Coastal Engineering Technical Aid No. CETA 81-2. Fort Belvoir,
Va.: Coastal Engineering Research Center, U.S. Army Corps of Engineers.
Hicks, S. 1983. Sea Level Variations for the United States, 1855-1980. Washington, D.C.: National
Oceanic and Atmospheric Administration.
Hubertz, J. M., R. M. Brooks, W. A. Brandon, and B. A. Tracy. 1993. Hindcast Wave Information
for the U.S. Atlantic Coast. WIS Report 30. Vicksburg, Miss.: Coastal Engineering Research
Center, U.S. Army Waterways Experiment Station, U.S. Army Corps of Engineers.
Jensen, R. E. 1983. Atlantic Coast Hindcast, Shallow-Water Significant Wave Information. WIS
Report 9. Vicksburg, Miss.: Coastal Engineering Research Center U.S. Army Waterways Ex-
periment Station, U.S. Army Corps of Engineers.
Langley, T. 1992. Sea sled surveying through the surf zone. Shore and Beach 60(2):15-19.
NOAA. 1993. Tide Tables for the East Coast of North and South America. National Ocean Survey,
National Oceanic and Atmospheric Administration. Washington, D.C.: U.S. Department of
Commerce.
NRC. 1989. Measuring and Understanding Coastal Processes for Engineering Purposes. Marine
Board, Commission on Engineering and Technical Systems, National Research Council. Wash-
ington, D.C.: National Academy Press.
Schneider, C. 1981. The Littoral Environmental Observation (LEO) Data Collection Program. CETA
81-5. Fort Belvoir, Va.: Coastal Engineering Research Center, U.S. Army Corps of Engineers.
Smith, A. W. S. 1992. Description of beach sands. Shore and Beach 60(3):23-30.
Stauble, D. K., and N. C. Kraus. 1993. Project performance: Ocean City, Maryland, beach nourish-
ment. In: Proceedings of Beach Nourishment Engineering and Management Considerations,
Coastal Zone '93, New Orleans, Louisiana. New York: American Society of Civil Engineers.
Stauble, D. K., A. W. Garcia, N. C. Kraus, W. G. Grosskopf, and G. P. Bass. 1993. Beach Nourish-
ment Project Response and Design Evaluation: Ocean City, Maryland, Report 1, 1988-1992.
Technical Report CERC-93-13. Vicksburg, Miss.: Coastal Engineering Research Center, U.S.
Army Waterways Experiment Station, U.S. Army Corps of Engineers.
Walton, T. L. 1980. Computation of Longshore Energy Flux Using LEO Current Observations.
CETA 80-3. Fort Belvoir, Va.: Coastal Engineering Research Center, U.S. Army Waterways
Experiment Station, U.S. Army Corps of Engineers.
Work, P. A. 1993. Monitoring the evolution of a beach nourishment project. Pp. 57-70 in D. K.
Stauble and N. C. Kraus, eds., Proceedings of Beach Nourishment Engineering and Manage-
ment Considerations. New York: American Society of Civil Engineers.
Representative terms from entire chapter:
nourishment projects
