State of the Beach/State Reports/HI/Beach Erosion
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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, beach profiles and shoreline imagery for all the Hawaiian Islands is available online.
University of Hawaii News reported in March 2015 the results of a coastal erosion study performed by Scientists at the University of Hawaii’s School of Ocean and Earth Sciences and Technology (SOEST) and published in the journal Natural Hazards. From the news report:
Like the majority of Hawaiʻi’s sandy beaches, most shorelines at the 10 study sites on Kauaʻi, Oʻahu and Maui are currently retreating. If these beaches were to follow current trends, an average 20 to 40 feet of shoreline recession would be expected by 2050 and 2100, respectively.
“When we modeled future shoreline change with the increased rates of sea level rise (SLR) projected under the IPCC’s “business as usual” scenario, we found that increased SLR causes an average 16–20 feet of additional shoreline retreat by 2050, and an average of nearly 60 feet of additional retreat by 2100,” said Tiffany Anderson, lead author and post-doctoral researcher at the UH Mānoa School of Ocean and Earth Science and Technology.
“This means that the average amount of shoreline recession roughly doubles by 2050 with increased SLR, compared to historical extrapolation alone. By 2100, it is nearly 2.5 times the historical extrapolation. Further, our results indicate that approximately 92 percent and 96 percent of the shorelines will be retreating by 2050 and 2100, respectively, except at Kailua, Oʻahu which is projected to begin retreating by mid-century.”
An article published in Science Daily in 2013 summarized the results of studies by researchers from the University of Hawaii -- Manoa (UHM), School of Ocean and Earth Science and Technology (SOEST) and the State of Hawaii, Department of Land and Natural Resources which indicated that sea level rise (SLR) is a primary factor driving historical shoreline changes in Hawaii and that historical rates of shoreline change are about two orders of magnitude greater than SLR. Results of island-wide historical trends indicate that Maui beaches are significantly more erosional than beaches on Oahu. On Maui, 78% of beaches eroded over the past century with an overall (island-wide) average shoreline change rate of 13 cm of erosion per year, while 52% of Oahu beaches eroded with an overall average shoreline change rate of 3 cm of erosion per year.
The Maui Shoreline Atlas provides the most up to date erosion data for that island.
Shoreline profile data is available from USGS for Maui and Oahu.
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.
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.
The report 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.
In May 2012 a report National Assessment of Shoreline Change: Historical Shoreline Change in the Hawaiian Islands, by scientists at University of Hawaii and U.S. Geological Survey was published. This report summarizes historical shoreline changes on the three most densely populated islands of the eight main Hawaiian Islands: Kauai, Oahu, and Maui. The report emphasizes the hazard from “chronic” (decades to centuries) erosion at regional scales and strives to relate this hazard to the body of knowledge regarding coastal geology of Hawaii because of its potential impact on natural resources, the economy, and society. Results are organized by coastal regions and sub-regions. Geographic information system (GIS) data used in the analyses are made available for download. The report shows that 70 percent of beaches on the islands of Oahu, Maui and Kauai are undergoing long-term beach erosion. The average rate of coastal change – taking into account beaches that are both eroding and accreting – was 0.4 feet of erosion per year from the early 1900s to 2000s. Of those beaches eroding, the most extreme case was nearly 6 feet per year near Kualoa Point on East Oahu. Of the three islands, Maui beaches experienced the highest rates and greatest extent of beach erosion with 85 percent of beaches eroding. Erosion is the dominant trend of coastal change on all three islands with 71 percent of beaches eroding on Kauai and 60 percent of beaches eroding on Oahu. A companion report is National Assessment of Shoreline Change: A GIS Compilation of Vector Shorelines and Associated Shoreline Change Data for the Sandy Shorelines of Kauai, Oahu, and Maui, Hawaii.
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. Serious erosion on the north shore of Oahu in the Rocky Point area occurred in late 2013 and early 2014, with several homes being threatened. An article Saving Waikiki Beach — At Least for Now which appeared in Honolulu Civil Beat in March 2015 discussed growing erosion problems at Waikiki Beach and the associated need to fund an ongoing beach fill program.
The Hawaii Beach Monitoring Program website 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. Also see the home page for the USGS Coastal and Marine Geology Program. Additional background information on this collaborative effort can be found here.
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 multi-year 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, studies and useful links: Kauai Shoreline Erosion Management Study; Historical Shoreline Change in the Hawaiian Islands; and Hawaii Coastal Erosion Website.
- There is also the Maui County Multi-Hazard Mitigation Plan, (May 2010). In addition to coastal erosion, this document includes a discussion of flooding, wind, and seismic hazards on Maui.
A May 2013 Doctoral dissertation is Historical Shoreline Changes on Beaches of the Hawaiian Islands with Relation to Human Impacts, Sea Level, and Other Influences on Beach Dynamics by Bradley M. Romine. The dissertation's abstract states:
- "Over the past century, erosion (recession) was the dominant trend of shoreline change in Hawaii with an overall average shoreline change rate of -0.11 m/yr and 70% of beaches eroding, including 21km of beach (9% of beaches studied) that completely disappeared. Maui beaches were the most erosional of the three islands (85% erosional, island-wide average rate of -0.17 m/yr). Seventy-one percent of Kauai beaches eroded (average rate -0.11 m/yr), including 8% that completely disappeared. Sixty percent of Oahu beaches eroded (average rate -0.06 m/yr), including 8% that completely disappeared."
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).
Additional information on beach erosion in Hawaii can be found through University of Hawaii Sea Grant.
An EPA Coastlines publication (December 1999) noted 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.
General Erosion Data References
The Heinz Center's Evaluation of Erosion Hazards, conducted for the Federal Emergency Management Agency (FEMA), 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, businesses, and governmental entities.
A NOAA website 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 Sea Levels Online.
NOAA Shoreline Website 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 Website 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.
A related site launched in 2008 is NOAA Coastal Services Center's Digital Coast, which can be used to address timely coastal issues, including land use, coastal conservation, hazards, marine spatial planning, and climate change. One of the goals behind the creation of the Digital Coast was to unify groups that might not otherwise work together. This partnership network is building not only a website, but also a strong collaboration of coastal professionals intent on addressing coastal resource management needs. Website content is provided by numerous organizations, but all must meet the site’s quality and applicability standards. More recently, NOAA Coastal Services Center has developed a Sea Level Rise and Coastal Flooding Impacts Viewer as part of its Digital Coast website. Being able to visualize potential impacts from sea level rise is a powerful teaching and planning tool, and the Sea Level Rise Viewer brings this capability to coastal communities. A slider bar is used to show how various levels of sea level rise will impact coastal communities. Completed areas include Mississippi, Alabama, Texas, Florida, and Georgia, with additional coastal counties to be added in the near future. Visuals and the accompanying data and information cover sea level rise inundation, uncertainty, flood frequency, marsh impacts, and socioeconomics.
Erosion Contact Info
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
NOAA Coastal Storms Program Coordinator, Pacific Region
University of Hawaii Sea Grant Program
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