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Hawaii Ratings
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Indicator Type |
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Info |
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Status |
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Beach Access |
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8 |
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7
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Water Quality |
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7
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6
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Beach Erosion |
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9
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- |
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Erosion Response |
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- |
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5
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Beach Fill |
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5 |
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- |
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Shoreline Structures |
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5 |
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3 |
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Beach Ecology |
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4 |
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- |
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Surfing Areas |
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10 |
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5*
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Website |
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5
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- |
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* Surfing areas on Oahu and Maui are threatened.
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Hawaii Beach Erosion
Erosion Data
Hawaii has a serious shoreline erosion problem and numerous studies have been
conducted to identify the affected areas, determine the causes, and recommend
solutions. Approximately 2% of Hawaii's shoreline is critically eroding, according
to the report "State Coastal Program Effectiveness in Protecting Natural Beaches,
Dunes, Bluffs, and Rock Shores" (T. Bernd-Cohen and M. Gordon) Coastal Management
27:187-217.
Beach loss because of seawall construction on eroding shorelines has been estimated to be 25% on Oahu and 20% on Maui.
On average, beaches are 50-75% narrower in front of seawalls in Hawaii.
Hawaii’s coastal erosion rates generally range from 0.5 to 1 ft/year. Nearly one-quarter of the Hawaiian Islands’ beaches have been significantly degraded over the last half-century. Studies have shown that 24% of Oahu’s sandy beaches have been significantly narrowed or lost. Eight miles of beach were likely lost due to shoreline hardening on Maui.
An important information resource is the Hawaii Coastal Erosion Website.
The Hawaii Shoreline Study provides shoreline change data to the public and government partners to assist in decision-making in the coastal zone. This site provides sets of historical maps and air photos, modern vertical and oblique air photos, and maps depicting rates of shoreline change spaced every 20 m on the sandy beaches of Maui, Oahu, and Kauai.
Coastal erosion data, in the form of erosion rate maps is available online for the island of Maui at http://www.soest.hawaii.edu/coasts/data/maui/index.html
The Maui Shoreline Atlas provides the most up to date erosion data for that island.
Shoreline profile data is available for Maui online at:
http://geopubs.wr.usgs.gov/open-file/of01-308/mauiindex.html
Shoreline profile data is available for Oahu online at:
http://geopubs.wr.usgs.gov/open-file/of01-308/oahuindex.html
Local sea-level rise is closely related to coastal erosion in Hawaii. The Hawaiian Islands are experiencing a sea-level rise of approximately 6 to 8 inches/century. Hawaii’s sea-level is likely to rise 10 inches by 2050 and 2 feet by 2100. This means that erosion is only going to get worse in Hawaii. Therefore, it is important that management precautions be established and put into effect as soon as possible.
Photos of beach erosion in Hawaii can be found at http://www.soest.hawaii.edu/seagrant/communication/kapilikai/main/photo.htm
According to the 1997 Assessment, Hawaii has many beach and low-lying shoreline
areas that have been heavily developed. In these areas, hurricanes, tsunami, and
storms create catastrophic risks to life and property. Hurricane Iniki caused
over $2 billion in damage (primarily on Kauai), and estimates of damage from a
direct hurricane hit on Oahu run as high as $17 billion. Chronic shoreline retreat
and episodic beach erosion have placed miles of public highway at risk, as well
as shorefront homes in some areas.
A recently completed Hawaii Beach Monitoring Program, a collaborative effort
conducted by USGS Coastal and Marine Geology Program and the University of Hawaii
Geology program, reports that 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). Recent studies on Oahu have
shown that nearly 24%, or 27.5 km (17.1 mi) of an original 115 km (71.6 mi)
of sandy shoreline (1940s) 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 lost on Maui, due at least in part, to shoreline armoring.
Causes of coastal erosion and beach loss in Hawaii are numerous but, unfortunately,
are poorly understood and are rarely quantified (see sites listed in remainder
of this section). Construction of shoreline protection structures limits localized
coastal land loss, but does not alleviate overall beach loss and may actually
accelerate the problem by prohibiting sediment deposition in front of the structures
and accelerating beach loss in areas adjacent to the shoreline protection structure.
Other factors contributing to beach loss include reduced sediment supply, large
storms, and sea level rise. Reduction in sand supply, either from landward or
seaward (primarily reef) sources, can have a myriad 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.
The Hawaii Beach Monitoring Program Web site allows you to view maps of profile locations on Oahu and Maui, provides
a detailed plan map for each profile site, access to site profile data, and
an image of profile envelopes for a given site. 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. The
home page for the USGS Coastal and Marine Geology Program is located at: http://walrus.wr.usgs.gov/
Additional background information on this collaborative effort can be found at:
http://gsa.confex.com/gsa/2001AM/finalprogram/abstract_17396.htm
A number of other studies have been completed on coastal hazards and beach erosion
in Hawaii. These include:
- The HCZM Program supported two phases of a coastal hazard mapping project.
These studies resulted in the Atlas of Natural Hazards in the Hawaiian
Coastal Zone. The Atlas identifies and ranks the severity of a range of coastal hazards for
the coastline of the main Hawaiian Islands, including tsunami, stream flooding,
high waves, storms, erosion, sea level rise, and volcanic and seismic hazards.
The Atlas does not define the inland boundary of the hazards. However, it is
useful to planners, developers, and regulators in determining if a particular
hazard needs to be assessed when planning development and reviewing permit applications
for a specific shoreline area.
- The University of Hawaii's School of Ocean and Earth Science and Technology
is mapping erosion trends for the city and county of Honolulu, and providing
interim guidance recommendations to DLNR. These new maps will be incorporated
into GIS systems for use by state and county agencies.
- As part of a FEMA pilot study, 60-year erosion hazard zones have been
calculated from aerial photography and mapping efforts, then overlaid
onto the Flood Insurance Rate Maps (FIRMs). FEMA used these maps in assessing
the economic impacts of erosion and coastal retreat strategies. For more
information on this work see: Coyne, Melanie A., C.H. Fletcher, and B.M.
Richmond. "Mapping Coastal Erosion Hazard Areas in Hawaii: Observations
and Errors." Journal of Coastal Research. Spring 1999. Special
Issue 28. pp. 171-184.
- The Hawaii Coastal Erosion Management Plan (COEMAP), prepared by a collaborative
effort between the University of Hawaii, School of Ocean Earth Science and Technology,
Department of Geology and Geophysics, and State Department of Land and Natural
Resources (DLNR) Land Division and Coastal Lands Program. The plan helps to
identify certain steps that will improve the current erosion management regime
in Hawaii.
- The Marine and Coastal Zone Management Advisory Group (MACZMAG) Coastal Erosion
Subcommittee provided guidance on the Shoreline Hazard Mitigation Project. The
Shoreline Mitigation Project is a multiyear project proposed to set strategies
to mitigate the damage caused by shoreline hazards, including shoreline erosion
and other shoreline events that affect public safety, economic viability, and/or
the natural resources of a community. This project developed a site-specific
plan for hazard mitigation through beach restoration instead of traditional
shoreline hardening. The plan provides recommendations on the most feasible
technical and engineering specifications and the most appropriate institutional
and administrative arrangements for successful erosion hazard mitigation at
an erosion "hotspot."
- The HCZMP notes the following reports: Oahu Shoreline Study; Kauai
Shoreline Erosion Management Study; Hawaii Shoreline Erosion Management
Study; Erosion Management Program Recommendations for Hawaii; and Aerial
Photograph Analysis of Coastal Erosion on the Islands of Kauai, Molokai,
Lanai, Maui and Hawaii; and the video Planning for the Inevitable.
These reports discuss beach management alternatives, generally and at
case study sites; identify critical erosion location; and provide a time-series
of shoreline position data for use in determining erosion trends. The
data also provide a baseline for monitoring future erosion in these areas.
- There is also the The Maui County Hazard Mitigation Plan,
prepared by Pamela Pogue.
In addition to coastal erosion, this document includes a discussion of
flooding, wind, and seismic hazards on Maui.
Waves and Coastal Erosion is a good general discussion of these subjects. Also see Strong Winds and Coastal Storms.
The Heinz Center's Evaluation of Erosion Hazards, conducted for the Federal
Emergency Management Agency, studied the causes of coastal erosion hazards and
proposed a variety of national and regional responses. The study, published
in April 2000, concentrates on the economic impacts of erosion response policies
as well as the cost of erosion itself to homeowners, business and governmental
entities. The study notes that coastal erosion is a widespread and locally severe
problem in the Hawaiian Islands, which have 500 miles of coastline (Federal
Emergency Management Agency, 1989), and elsewhere in the Pacific tropical region.
The Hawaiian coastline is susceptible to high waves associated with hurricanes,
tsunami, and large seasonal swells that can cause extensive short-term erosion.
The average long-term erosion rate in Hawaii is less than 1 foot per year (Coyne
et al., 1998). Human activities have aggravated coastal erosion problems on
the Hawaii coastline by restricting sediment supply and reducing beach width.
Erosion protection measures have focused on constructing shoreline-hardening
structures, such as revetments and seawalls (Coyne et al., 1998). Hardening
the shoreline restricts the transport of sand located landward of the vegetation
line, thus starving the beach of a sand supply and possibly leading to total
beach loss (Hanson and Kraus, 1986; Bush et al., 1986). The mean beach width
along armored shorelines is half of the mean beach width adjacent to unarmored,
freely migrating shorelines (Fletcher, 1997).
Also, check out Hawaii's Statewide Hazard Mitigation Forum Web site. It summarizes risks from a range of coastal hazards, including beach erosion,
on all of Hawaii's islands.
Other Web sites that provide information on beach erosion in Hawaii include University of Hawaii Sea Grant
and specifically, its coastal erosion and beach loss in Hawaii page.
An EPA Coastlines publication notes that many sandy beaches in Maui have narrowed or even disappeared as a result
of natural shoreline processes, development, hardening along the shoreline, and
other human activities. Studies have shown that 62% of Maui's sandy shoreline
is eroding at an average rate of 1.25 feet per year, and as much as 30% of Maui's
shoreline has experienced beach loss or significant narrowing of beaches.
A NOAA Web site that has graphs of sea level data for many coastal locations around the country over the last 40 to 50 years and projections into the future is http://tidesandcurrents.noaa.gov/sltrends/sltrends.shtml
NOAA recently launched the NOAA Shoreline Web site. The site is a comprehensive guide to
national shoreline data and terms and is the first site to allow vector
shoreline data from NOAA and other federal agencies to be conveniently
accessed and compared in one place. Supporting context is also included
via frequently asked questions, common uses of shoreline data, shoreline
terms, and references. Many NOAA branches and offices have a stake in
developing shoreline data, but this is the first-ever NOAA Web site to
provide access to all NOAA shorelines, plus data from other federal
agencies. The site is a culmination of efforts of NOAA and several
offices within NOS (including NOAA’s Coastal Services Center, National
Geodetic Survey, Office of Coast Survey, Special Projects Office, and
Office of Ocean and Coastal Resource Management) and other federal
agencies to provide coastal resource managers with accurate and useful
shoreline data. For more information, contact Tara Miller (tara.miller@noaa.gov).
Erosion Contact Info
Chip Fletcher
Professor and Chair
Department of Geology and Geophysics
School of Ocean and Earth Science and Technology (SOEST)
University of Hawaii at Manoa
1680 East-West Rd.
Honolulu, HI 96822
808-956-2582
Dolan Eversole
Coastal Geologist and Hawaii Sea Grant Extension Agent
Department of Land and Natural Resources
1151 PunchBowl St Rm 131
Honolulu Hawaii 96813
(808)587-0321
Hazard Avoidance Policies/Erosion Response
See Erosion Response section.
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