Specific objectives include:
a) document the magnitude and extent of the erosion problem;
b) determine the individual causes for coastal erosion in the
Hawaiian Islands and establish their relative importance;
c) develop a coastal hazard database that can be applied to other
studies; and
d) provide input for predictive models on long-term coastal behavior.
The overall objectives of the Hawaii
Coastal Erosion Study are to document the recent history of shoreline
change in Hawaii and to determine the primary factor(s) responsible
for coastal erosion in low-latitude environments.
This project will integrate studies
of erosion history, large-scale coastal behavior, and the reef
record to develop a comprehensive model of coastal-systems evolution
with the goal of further enhancing our predictive capabilities
regarding shoreline stability in important low-latitude environments.
It is anticipated that results from this project can be applied
to low-latitude shorelines around the globe.
In an effort to establish baseline beach conditions, monitor
seasonal beach fluctuations, and understand the dynamics of beach
change in Hawaii, a program of beach and nearshore monitoring
was initiated in 1994 on the islands of Maui and Oahu. Five years
of biannual (approx. summer/winter) profiles on forty-two Oahu,
and thirty-seven Maui, beaches have been collected to date. In
order to address long-term change, we attempted to re-occupy
beach monitoring sites established by University of Hawaii
researchers
during the early 1960s (Moberly and Chamberlain, 1964). However,
determining the exact location of old profile sites proved difficult
because of development along the coast and loss of the 1960s
reference marks. All new sites are referenced to a common GPS
network for accurate horizontal and vertical positioning.
This data set is intended for scientific research of beach
Morphology and volume changes.
Location
North Kaanapali (2), Maui, Hawaii
Summary
Biannual beach profiles
were collected at 42 Oahu and 36 Maui
locations between August 1994 and August 1999. Surveys were
conducted at approximately summer-winter intervals and extend
from landward of the active beach to about -4 meters water depth.
Profile data on a CDROM are presented in both Microsoft EXCEL
97/98 & 5.0/95 Workbook (.xls) format and comma separated value
(.csv) format. Graphical representation of the surveys (x vs. z and
x vs. y) are presented in EXCEL format only. Site descriptions,
including beach location, directions to site, GPS information,
and a description of Reference Points used, are available in both
EXCEL and ADOBE ACROBAT .pdf format.
Coastal erosion is widespread and
locally severe in Hawaii and other low-latitude areas. Typical
erosion rates in Hawaii are in the range of 15 to 30 cm/yr (0.5
to 1 ft/yr; Hwang, 1981; Sea Engineering, Inc., 1988; Makai Ocean
Engineering, Inc. and Sea Engineering, Inc.,1991). Recent studies
on Oahu (Fletcher et al., 1997; Coyne et al., 1996) have shown
that nearly 24%, or 27.5 km (17.1 mi) of an original 115 km (71.6
mi) of sandy shoreline (1940's) has been either significantly
narrowed (17.2 km; 10.7 mi) or lost (10.3 km; 6.4 mi). Nearly
one-quarter of the islands' beaches have been significantly degraded
over the last half-century and all shorelines have been affected
to some degree. Oahu shorelines are by far the most studied,
however, beach loss has been identified on the other islands
as well, with nearly 13 km (8 mi) of beach likely lost due to
shoreline hardening on Maui (Makai Engineering, Inc. and Sea
Engineering, Inc., 1991).
Causes of coastal erosion and beach loss in Hawaii are numerous
but, unfortunately, poorly understood and rarely quantified.
Construction of shoreline protection structures limits coastal
land loss, but does not alleviate beach loss and may actually
accelerate the problem by prohibiting sediment deposition in
front of the structures. Other factors contributing to beach
loss include: a) reduced sediment supply; b) large storms; and,
c) sea-level rise. Reduction in sand supply, either from landward
or seaward (primarily reef) sources, can have a myriad of causes.
Obvious causes such as beach sand mining and emplacement of structures
that interrupt natural sediment transport pathways or prevent
access to backbeach sand deposits, remove sediment from the active
littoral system. More complex issues of sediment supply can be
related to reef health and carbonate production which, in turn,
may be linked to changes in water quality. Second, the accumulated
effect of large storms is to transport sediment beyond the littoral
system. Third, rising sea level leads to a natural landward
migration
of the shoreline.
Dramatic examples of coastal erosion, such as houses and roads
falling into the sea, are rare in Hawaii, but the impact of erosion
is still very serious. The signs of erosion are much more subtle
and typically start as a "temporary" hardening structure
designed to mitigate an immediate problem which, eventually,
results in a proliferation of structures along a stretch of coast.
The natural ability of the sandy shoreline to respond to changes
in wave climate is lost.
Info derived
The overall goals of this study are
to document the coastal erosion
history in Hawaii, determine the causal factors of that erosion,
provide high-quality data for other "end-users" in
applied studies (i.e. coastal engineers, planners, and managers),
and increase our general understanding of low-latitude coastal
geologic development. This project involves close cooperation
between the USGS Coastal and Marine Geology Program and the University
of Hawaii.
The data and results are presented as a web site (a separate
CDROM is also available). For the islands of Oahu and Maui,
Index maps show the location of the beach profile
monitoring sites. Each site is linked to a site map, photograph
of the area, collection of beach profiles, and the profile data.
Comments
Other field activities at North Kaanapali (2)
on Maui also have Activity IDs beginning with "N-2" and ending with "-MU"
Cross-shore beach profile data were collected as a component of
the Hawaii Coastal Erosion Study, a cooperative effort by U.S.
Geological Survey and University of Hawaii in order to document
seasonal and longer-term variations in beach volume and behavior.
The overall objectives of the Hawaii Coastal Erosion Study are to
document the recent history of shoreline change in Hawaii and to
determine the primary factor(s) responsible for coastal erosion
in low-latitude environments for the purpose of predicting future
changes and to provide quality scientific data that is useful to
other scientists, planners, engineers, and coastal managers.
The overall strategy consists of first quantifying the magnitude
and location of serious erosion problems followed by close monitoring
of coastal change in critical areas. Bi-annual beach profiles have
been collected at over 40 critical beach sites on the islands of Oahu
and Maui. Once sufficient background information is analyzed and key
problems are defined, field sites will be selected for detailed process-
oriented studies (both physical and biological) to gain an understanding
of the complex relationships between reef carbonate production, sediment
dispersal, and the interaction of man-made structures with sediment
movement along the shore.
Information derived from this project will be used to develop general
guidelines for sediment production, transport, and deposition of low-
latitude coasts. Planned major products include a comprehensive atlas of
coastal hazards, journal articles and reports presenting results of our
studies, and a "living" database of shoreline history and changes based
on results of the beach profile monitoring and softcopy photogrammetric
analysis.
Cross shore beach profiles were measured using a Geodimeter
464 total station and swimming rodman. The total station was
set up at a non-specific position on the beach. Up to five
permanent reference points were first surveyed in order to
establish the position of the station relative to the established
profile line. Beach profile measurements were then taken from
a point landward of the active beach to as far offshore as
conditions would allow (typically -4m water depth). Specific
morphologic features (high water, berm crest, top of beach toe,
etc.) were noted. Data were post-processed as follows Survey data
were downloaded from the Total Station memory, automatically
creating a RAW file and an associated JOB file. The RAW file
was used to generate a PTS file (UTM field coordinates are
extracted from the RAW file) Note: no recalculation is performed
on the original file). PFCODE.EXE was used on the JOB file to
generate an ED file. The ED file was edited to include necessary
Program 10 information, Points block listing, and INFO codes.
Field procedures were checked and corrected as necessary.
PFGD.EXE was used on the ED file to generate a PF file (Cartesian-
based, relative XYZ coordinates). Extraneous lines were removed
from the PF file to generate a DAT file (relative XYZ coordinates) DAT
files were compiled into a SUMMARY file (Excel) format, plotted,
and where necessary, corrected relative to a primary reference point.
Where GPS positions of the reference points were available, the entire
summary file was re-referenced to an absolute vertical elevation
(meters above the Local Hawaii Tidal datum).
