U.S. Department of the Interior

U.S. Geological Survey

Open-File Report 2011–1051

National Assessment of Shoreline Change: 

Historical Shoreline Change in the Hawaiian Islands
Cover. View looking northwest of Makapuu Beach Park (foreground) and Waimanalo Bay in the distance, southeast Oahu, Hawaii.
National Assessment of Shoreline Change: 

Historical Shoreline Change in the 

Hawaiian Islands

By Charles H. Fletcher, Bradley M. Romine, Ayesha S. Genz, Matthew M. Barbee, 

Matthew Dyer, Tiffany R. Anderson, S. Chyn Lim, Sean Vitousek, Christopher 

Bochicchio, and Bruce M. Richmond

Open-File Report 2011–1051

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

KEN SALAZAR, Secretary

U.S. Geological Survey

Marcia K. McNutt, Director

U.S. Geological Survey, Reston, Virginia: 2012

For more information on the USGS—the Federal source for science about the Earth, its natural and living 

resources, natural hazards, and the environment, visit http://www.usgs.gov or call 1–888–ASK–USGS.

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U.S. Government.

Although this report is in the public domain, permission must be secured from the individual copyright owners to 

reproduce any copyrighted materials contained within this report.

Suggested citation:

Fletcher, C.H., Romine, B.M., Genz, A.S., Barbee, M.M., Dyer, Matthew, Anderson, T.R., Lim, S.C., Vitousek, Sean, 

Bochicchio, Christopher, and Richmond, B.M., 2012, National assessment of shoreline change: Historical shoreline 

change in the Hawaiian Islands: U.S. Geological Survey Open-File Report 2011–1051, 55 p. (Also available at http://

pubs.usgs.gov/of/2011/1051.)
iii

Executive Summary

Beach erosion is a chronic problem along most open-ocean shores of the United States. As 

coastal populations expand and community infrastructure comes under increasing threat from 

erosion, there is a demand for accurate information about trends and rates of shoreline movement, as well as a need for a comprehensive analysis of shoreline movement that is consistent 

from one coastal region to another. To meet these national needs, the U.S. Geological Survey 

began an analysis to document historical shoreline change along open-ocean sandy shores of 

the conterminous United States and parts of Hawaii and Alaska. An additional purpose of this 

work is to develop systematic methodology for mapping and analyzing shoreline movement so 

that consistent periodic updates regarding coastal erosion can be made nationally. 

This report on shoreline change on three of the eight main Hawaii islands (Kauai, Oahu, and 

Maui) is one in a series of reports on shoreline change in coastal regions of the United States 

that currently include California, the Gulf of Mexico region, the Southeast Atlantic Coast, and 

the Northeast Atlantic Coast. The report summarizes the methods of analysis, documents and 

interprets the results, explains historical trends and rates of change, and describes the response 

of various communities to coastal erosion. Shoreline change in Hawaii was evaluated by 

comparing historical shorelines derived from topographic surveys and processed vertical aerial 

photography over time. The historical shorelines generally represent the past century (early 

1900s–2000s). Linear regression was used to calculate rates of change with the single-transect 

method: long-term rates were calculated from all shorelines (from the early 1900s to the most 

recent), whereas short-term rates were calculated from post-World War II shorelines only.

Beach erosion is the dominant trend of shoreline change in Hawaii. However, shoreline change 

is highly variable along Hawaii beaches with cells of erosion and accretion typically separated 

by only a few hundred meters on continuous beaches or by short headlands that divide the coast 

into many small embayments. The beaches of Kauai, Oahu, and Maui are eroding at an average 

long-term rate for all transects (shoreline measurement locations) of -0.11 ± 0.01 m/yr (meters 

per year) and an average short-term rate of -0.06 ± 0.01 m/yr. The majority, or 70 percent, 

of transects on the three islands indicate a trend of erosion in the long term and 63 percent 

indicate a trend of erosion in the short term. A total of 22 kilometers of beach, or 9 percent of 

the total length of beach studied, was completely lost to erosion over the past century. Annual 

erosion is greatest on Maui with an average long-term shoreline change rate of -0.17 ± 

0.01 m/yr and erosion at 85 percent of transects. Short-term analysis for Maui indicates a 

similar erosional trend with an average rate of -0.15 ± 0.01 m/yr and erosion at 76 percent 

of transects. Nearly 7 kilometers (11 percent) of beach was completely lost to erosion in the 

analysis period on Maui. Annual erosion for all transects on Kauai is intermediate in the long 

term, with an average rate of -0.11 ± 0.01 m/yr and erosion at 71 percent of transects. The 

short-term average rate for Kauai (0.02 ± 0.02 m/yr) suggests stable or accreting beaches; 

though, the majority (57 percent) of transects indicate a trend of erosion. Six kilometers or 

8 percent of Kauai beaches were completely lost to erosion in the analysis period. Oahu 

beaches are the least erosional of the three islands in the long term; though, erosion is still the 

dominant trend of shoreline change with an average long-term rate of -0.06 ± 0.01 m/yr and 

erosion at 60 percent of transects. Shoreline change trends on Oahu beaches are roughly the 

same in the short term as in the long term with an average rate of -0.05 ± 0.01 m/yr and erosion 

at 58 percent of transects. The single-transect method of rate calculation indicates that erosion 

rates are statistically significant (95-percent confidence interval) at 30 percent of transects in 

the long term and 22 percent of transects in the short term. 
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v

Contents

Introduction.....................................................................................................................................................1

U.S. Geological Survey National Assessment of Shoreline Change............................................1

The Role of State and Federal Governments ............................................................................................2

Prior National and Hawaii Shoreline Assessments.................................................................................2

Environmental Framework of the Hawaiian Shoreline............................................................................3

Carbonate Geology...............................................................................................................................3

Beach Sediments..................................................................................................................................6

Sea Level................................................................................................................................................8

Waves ....................................................................................................................................................9

Tides ..................................................................................................................................................15

Shoreline Change................................................................................................................................15

Methods of Analyzing Shoreline Change ................................................................................................16

Compilation of Historical Shorelines ...............................................................................................16

Mapping Historical Shorelines.........................................................................................................17

Uncertainty and Error.........................................................................................................................18

Calculation and Presentation of Rates of Change ........................................................................19

Historical Shoreline Change Analysis......................................................................................................20

Kauai ..................................................................................................................................................20

North Kauai.................................................................................................................................23

East Kauai....................................................................................................................................25

South Kauai.................................................................................................................................25

West Kauai..................................................................................................................................29

Oahu ..................................................................................................................................................31

North Oahu..................................................................................................................................33

East Oahu ....................................................................................................................................33

South Oahu..................................................................................................................................35

West Oahu...................................................................................................................................39

Maui ..................................................................................................................................................39

North Maui..................................................................................................................................42

Kihei Maui ...................................................................................................................................44

West Maui...................................................................................................................................47

Discussion and Additional Considerations..............................................................................................49

Summary of Shoreline Changes.......................................................................................................49

Influences of Human Activities ........................................................................................................50

Planned Updates and Related Research........................................................................................50

Acknowledgments.......................................................................................................................................50

References Cited..........................................................................................................................................50
vi

Figures

1. Computer-generated relief models of the Hawaii Island Archipelago and its 

northern arm, the Emperor Seamount Chain ...........................................................................4

2. Schematic diagram showing principal stratigraphic components of the Oahu 

carbonate shelf.............................................................................................................................5

3. Aerial photograph showing carbonate sand beaches in Hawaii are the result of reef 

bioerosion and direct production of calcareous material by reef organisms....................5

4. Bar graph showing volume of sediment by depth zone in Kailua Bay, Oahu .....................8

5. Computer-generated relief model of Kailua Bay, Oahu..........................................................9

6. Graphs showing mean-sea-level trends at A, Hilo, 1927–2010; B, Kahului 1947–2010; 

C, Honolulu 1905–2010; and D, Nawiliwili, 1955–2010, Hawaii.............................................10

7. Ground photograph showing beaches and waterfront development (Waikiki, Oahu)

threatened by sea-level rise .....................................................................................................12

8. Schematic diagram showing dominant swell regimes and wave-monitoring buoy 

locations in Hawaii .....................................................................................................................12

9. Satellite images (JASON-1) showing derived average wave height over the North 

Pacific in summer and winter...................................................................................................13

10. Graph showing daily average significant wave height from buoy 51001 (1981 to 2005).14

11. Bar graph showing number of days per season that trade winds occur with a 

particular speed (data from buoy 51001, 1981 to 2005).........................................................14

12. Schematic diagrams showing seasonal beach-profile adjustments induced by 

seasonal swell variations and resulting cross-shore sediment transport........................16

13. Aerial photograph showing historical shorelines and shore-perpendicular transects 

(20-meter spacing) displayed on a portion of a recent (2006) aerial photograph of 

Mokuleia Beach, North Oahu ...................................................................................................17

14. Graph showing calculation of shoreline change rate from a time series of shoreline 

positions using the single-transect method...........................................................................20

15. Index map showing four regions of Kauai: north, east, south, and west..........................21

16. Graphs showing long-term (all available years) and short-term (1940s to present) 

shoreline change rates, North Kauai ......................................................................................24

17. Graphs showing long-term (all available years) and short-term (1940s to present) 

shoreline change rates, East Kauai.........................................................................................26

18. Oblique aerial photograph of eolianite headland (lithified carbonate sand dunes), 

Mahaulepu, South Kauai ...........................................................................................................27

19. Graphs showing long-term (all available years) and short-term (1940s to present) 

shoreline change rates, South Kauai ......................................................................................28

20. Oblique aerial photograph of dunes at the west end of the Mana coastal plain, 

West Kauai...................................................................................................................................29

21. Graphs showing long-term (all available years) and short-term (1940s to present) 

shoreline change rates, West Kauai .......................................................................................30

22. Index map showing four regions of Oahu: north, east, south, and west...........................31

23. Oblique aerial photograph of limestone headlands at Kahuku Point and Kuilima 

(Turtle Bay), North Oahu............................................................................................................33

24. Graphs showing long-term (all available years) and short-term (1940s to present) 

shoreline change rates, North Oahu .......................................................................................34

25. Oblique aerial photograph of Lanikai and Kailua Beaches, East Oahu.............................35

26. Graphs showing long-term (all available years) and short-term (1940s to present) 

shoreline change rates, East Oahu..........................................................................................36
vii

27. Aerial photograph of the south end of Kahuku Beach, northeast Oahu, 1949, 

showing evidence of sand mining ...........................................................................................37

28. Oblique aerial photograph of engineered shoreline at Waikiki, South Oahu...................37

29. Graphs showing long-term (all available years) and short-term (1940s to present) 

shoreline change rates, South Oahu.......................................................................................38

30. Graphs showing long-term (all available years) and short-term (1940s to present) 

shoreline change rates, West Oahu........................................................................................40

31. Oblique aerial photograph of Maili Beach, West Oahu .......................................................41

32. Index map showing three regions of Maui: north, Kihei, and west ...................................41

33. Graphs showing long-term (all available years) and short-term (1940s to present) 

shoreline change rates, North Maui .......................................................................................43

34. Oblique aerial photograph of North Maui beaches, looking west from Paia toward 

Baldwin Park ...............................................................................................................................44

35. Graphs showing long-term (all available years) and short-term (1940s to present) 

shoreline change rates, Kihei, Maui........................................................................................45

36. Oblique aerial photograph of Maalaea Bay Beach with dunes and wetlands, 

north Kihei coast, Maui..............................................................................................................46

37. Oblique aerial photograph of Makena Beach, southern Kihei coast, Maui .....................46

38. Graphs showing long-term (all available years) and short-term (1940s to present) 

shoreline change rates, West Maui ........................................................................................48

39. Oblique aerial photograph of Kaanapali Beach, West Maui...............................................49

Tables

1. Relation of littoral sand grain size to shoreline aspect (wind and wave exposure) 

in Hawaii ........................................................................................................................................6

2. Observed maximum annually recurring significant wave heights (Hs) and the 

largest 10-percent (H1/10) and 1-percent (H1/100) wave heights for various 

directions around Hawaii ..........................................................................................................15

3. Range of errors in position of historical shorelines for Kauai, Oahu, and Maui..............18

4. Number and range in years of historical shorelines for long- and short-term 

shoreline change analysis on Kauai........................................................................................22

5. Shoreline change trends for Kauai, Oahu, and Maui ...........................................................22

6. Maximum shoreline change rates on Kauai ..........................................................................23

7. Average shoreline change rates for Kauai subregions .......................................................25

8. Number and range in years of historical shorelines for long- and short-term 

shoreline change analysis on Oahu ........................................................................................32

9. Maximum shoreline change rates on Oahu...........................................................................32

10. Average shoreline change rates for Oahu subregions ........................................................35

11. Number and range in years of historical shorelines for long- and short-term 

shoreline change analysis on Maui.........................................................................................42

12. Average shoreline change rates for Maui subregions ........................................................42

13. Maximum shoreline change rates on Maui ...........................................................................44
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Introduction

U.S. Geological Survey National Assessment of 

Shoreline Change

Sandy beaches of the United States are some of the most 

popular tourist and recreational destinations. Coastal property 

constitutes some of the most valuable real estate in the country. Beaches are an ephemeral environment between water 

and land with unique and fragile natural ecosystems that have 

evolved in equilibrium with the ever-changing winds, waves, 

and water levels. Beachfront lands are the site of intense 

residential and commercial development even though they are 

highly vulnerable to several natural hazards, including marine 

inundation, flooding and drainage problems, effects of storms, 

sea-level rise, and coastal erosion. Because the U.S. population continues to shift toward the coast where valuable coastal 

property is vulnerable to erosion, the U.S. Geological Survey 

(USGS) is conducting a national assessment of coastal change. 

One aspect of this effort, the National Assessment of Shoreline 

Change, uses shoreline position as a proxy for coastal change 

because shoreline position is one of the most commonly 

monitored indicators of environmental change (for example, 

Fletcher, 1992; Dolan and others, 1991; Douglas and others, 

1998; Galgano and others, 1998). Additionally, the National 

Research Council (1990) recommended the use of historical 

shoreline analysis in the absence of a widely accepted model 

of shoreline change.

A principal purpose of the USGS shoreline change 

research is to develop a common methodology so that shoreline change analyses for the continental U.S., portions of 

Hawaii, and Alaska can be updated periodically in a consistent and systematic manner. The primary objectives of this 

study were to (1) develop and implement improved methods of assessing and monitoring shoreline movement, and 

(2) improve current understanding of the processes controlling 

shoreline movement.

Achieving these ongoing long-term objectives requires 

research that (1) examines the original sources of shoreline 

data (for example, maps, air photos, global positioning system 

(GPS), Light Detection and Ranging (lidar)); (2) evaluates the 

utility of different shoreline proxies (for example, geomorphic 

feature, water mark, tidal datum, elevation), including the 

errors associated with each; (3) investigates bias and potential 

errors associated with integrating different shoreline proxies 

from different sources; (4) develops standard, uniform methods of shoreline change analysis; (5) examines the effects of 

human activities on shoreline movement and rates of change; 

and (6) investigates alternative mathematical methods for calculating historical rates of change and uncertainties associated 

with them.

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 (island side) 

and sub-regions (common littoral characteristics). This report 

of Hawaii coasts is part of a series of reports that include text 

summarizing methods, results, and implications of the results. 

In addition, geographic information system (GIS) data used 

in the analyses are made available for download (Romine and 

others, 2012). The rates of shoreline change and products presented in this report are not intended for site-specific analysis 

of shoreline movement, nor are they intended to replace any 

official source of shoreline change information identified by 

local or State government agencies, or other Federal entities 

that are used for regulatory purposes.

Rates of shoreline change presented herein may differ 

from other published rates, and differences do not necessarily 

indicate that the other rates are inaccurate. Some discrepancies are to be expected, considering the many possible ways 

of determining shoreline positions and rates of change, and 

the inherent uncertainty in calculating these rates. Rates of 

shoreline change presented in this report represent shoreline 

movement under past conditions and are not intended for 

use in predicting future shoreline positions or future rates of 

shoreline change. 

National Assessment of Shoreline Change: 

Historical Shoreline Change in the Hawaiian Islands

By Charles H. Fletcher1, Bradley M. Romine1, Ayesha S. Genz1, Matthew M. Barbee1, Matthew Dyer1, 

Tiffany R. Anderson1, S. Chyn Lim1, Sean Vitousek1, Christopher Bochicchio1, and Bruce M. Richmond2

1

University of Hawaii.

2

U.S. Geological Survey Pacific Coastal & Marine Science Center.
2 National Assessment of Shoreline Change: Historical Shoreline Change in the Hawaiian Islands

The Role of State and Federal 

Governments

One reason for conducting this national assessment 

of shoreline change is that there is no widely accepted, 

standardized method of analyzing shoreline change. Each 

state has its own data needs and coastal-zone management 

responsibilities (for example, construction set-back lines, dune 

protection zones, and public access) and, therefore, each state 

uses a different technique and standard to compile shorelines 

and calculate rates of shoreline movement. Consequently, 

calculated rates of shoreline change and projected erosion 

hazard zones are inconsistent from state to state and often 

cannot be compared directly. These inconsistencies were 

clearly demonstrated by the FEMA-sponsored erosion studies 

(Crowell and Leatherman, 1999) that were used as the basis 

for evaluating erosion hazards (The H. John Heinz III Center 

for Science, Economics, and the Environment, 2000).

Several Federal agencies (U.S. Geological Survey, 

USGS; Federal Emergency Management Agency, FEMA; 

National Oceanic and Atmospheric Administration, NOAA; 

and U.S. Army Corps of Engineers, USACE) have regulatory or administrative responsibilities pertaining to shorelines. 

These responsibilities are different, however, and require 

different approaches. They also offer substantial opportunities 

for cooperation. For example, the USACE is authorized and 

funded by Congress to report on the economic and environmental implications of shoreline change and the costs of 

erosion mitigation. Its National Shoreline Management Study 

(Stauble and Brumbaugh, 2003) is being conducted using 

existing shoreline data. The USGS shares data and information, such as the lidar-derived shoreline and rates of change, 

in support of that effort. NOAA has a mandate to establish the 

official shoreline boundary for the nation using tidal datums. 

Its emphasis is on safe navigation and using the shoreline to 

generate nautical charts. NOAA also conducts the VDatum 

program, which assists agencies in delineating shorelines for 

a variety of purposes. Congress authorized and funded FEMA 

to report on the economic impact of erosion hazards on coastal 

communities, and on claims to the National Flood Insurance 

Fund. To accomplish this goal, FEMA contracted with state 

agencies and academic researchers to conduct a pilot study 

of erosion hazards that included shoreline change data for 

limited geographic areas (Coyne and others, 1999). The USGS 

is responsible for conducting research pertaining to coastal 

change hazards, understanding the processes that cause coastal 

change, and developing models to predict future change. The 

USGS is the only government agency that has a dedicated program to monitor coastal change into the future using consistent 

methods nationwide. This program is critically important for 

the assessment of national issues such as the coastal impacts 

of sea-level rise. 

Prior National and Hawaii Shoreline 

Assessments

The U.S. Army Corps of Engineers (1971) conducted 

the first national assessment of coastal erosion. That study 

identified areas of critical and non-critical erosion on the basis 

of economic development and potential for property loss, but 

rates of shoreline movement were not evaluated. Dolan and 

others (1985) conducted a comprehensive analysis of shoreline change for the mainland U.S. Their analysis was based 

on compilation of rates of shoreline change contributed by 

other investigators and derived from their own studies. Rates 

of change were presented and long-term trends of erosion and 

accretion were summarized.

In the State of Hawaii, process-oriented research 

exploring the dynamic and unique nature of Hawaiian 

beach morphology was first conducted by Moberly (1963). 

Hwang (1981) published a methodology incorporating aerial 

photographs to determine vegetation-line position changes 

since 1928 for the island of Oahu. That methodology was 

continued by Makai Ocean Engineering and Sea Engineering 

(1991), who expanded it to neighboring islands and updated 

the database to include aerial photography up to 1988. Sea 

Engineering (1988) completed a shoreline-change study of 

Oahu for the City and County of Honolulu based on updates 

to Hwang (1981). With this report, the University of Hawaii 

updated the database for the islands of Kauai, Oahu, and 

Maui with aerial photography from 2005, 2006, 2007, and 

2008. This study also augmented past studies with additional 

photographs and maps of historical shorelines. 

The County of Maui contracted with the University of 

Hawaii to develop a methodology for a parcel resolution 

(20-meter (m)) shoreline study of the Maui sandy shoreline. 

In 2005, the Maui Planning Commission incorporated the 

university study methodology and initial results into a revision 

of setback guidelines for beachfront property development. In 

2003, the County of Maui contracted with the University of 

Hawaii to update the shoreline study with 2007 aerial photography. The City and County of Honolulu contracted with the 

University of Hawaii to use aerial photography to develop a 

database of shoreline change rates for sandy beaches on the 

island of Oahu. The County of Kauai also contracted with 

the University of Hawaii to conduct a similar study of all 

sandy beaches on the island of Kauai other than along the Na 

Pali coastline. In 2008, the Kauai County Council adopted a 

new setback law that included rates of coastal erosion. The 

university has published several reports documenting the 

results of its studies of shoreline change: Coyne and others 

(1996; 1999), Fletcher and others (1997), Fletcher and Lemmo 

(1999), Harney and others (2000), Rooney and Fletcher 

(2000; 2005), Richmond and others (2001), Norcross and 

others (2002; 2003), Miller and Fletcher (2003), Eversole and 

Fletcher (2003), Rooney and others (2003), Fletcher and others (2003), Genz and others (2007a, 2007b, 2009), Vitousek 
Environmental Framework of the Hawaiian Shoreline 3

and others (2007), Frazer and others (2009), Romine and others (2009), and Anderson and others (2009). Additionally, the 

University maintains a Web site (http://www.soest.hawaii.edu/

asp/coasts/index.asp) that serves shoreline change data to the 

public and partnering agencies.

Since the work of Dolan and others (1985), methods of 

obtaining, analyzing, displaying, and storing shoreline data 

have improved substantially, and coastal change has continued. Furthermore, coastal scientists have not agreed on standard methods for analyzing and reporting shoreline change, 

nor have they identified rigorous mathematical tests that are 

widely accepted for quantifying the change and associated 

errors. Consequently, there are critical needs for (1) a nationwide compilation of reliable shoreline data, including the most 

recent shoreline position; and (2) an improvement in methods 

for obtaining and comparing shoreline positions and mathematically analyzing trends in shoreline movement.

Environmental Framework of the 

Hawaiian Shoreline

The Hawaii hotspot lies in the mantle under, or just south 

of, the “Big Island” of Hawaii where it feeds magma to two 

active subaerial volcanoes (Mauna Loa and Kilauea) and one 

active submarine volcano (Loihi). Centrally located on the 

Pacific plate, the hotspot is the source of the Hawaii Island 

Archipelago and its northern arm, the Emperor Seamount 

Chain (fig. 1).

The main Hawaiian Islands are built of shield volcanoes 

composed of basaltic lavas, intrusive dike complexes, and 

tephra deposits. Valley floors between volcanoes and coastal 

plains surrounding them consist of alluvial sediments eroded 

from the interior and carbonate deposits around the shoreline. 

The geology of most coastlines in Hawaii is characterized by 

outcropping volcanic bedrock, lithified tephra, and carbonate 

deposits (eolianite, beach rock, unconsolidated carbonate sand, 

and reef rock). Unconsolidated calcareous and clastic sediment, eroded from either the offshore reef or upland sources 

or directly produced by calcareous marine organisms, collects 

along the shore to form narrow beaches relative to continental 

siliciclastic beaches. 

Carbonate Geology

Because Hawaii’s white sand beaches are derived from 

fringing reefs, beach origin and history are intimately connected to the geologic framework of reefs. The fossil reefs of 

Oahu have been the subject of several studies (for example, 

Dollar, 1982; Grigg, 1983) that are reviewed by Fletcher 

and others (2008). Offshore of island beaches, the insular 

shelf typically dips gently seaward to near the -20-m contour. There, a limestone dropoff marks the end of the shallow 

portion of the shelf in most places. The base of this wall is 

typically found at a depth near -30 m, where a deeper, partially sand-covered terrace extends seaward to approximately 

-50 m. Below -50 m, a second wall and third terrace are found 

(Fletcher and Sherman, 1995). 

The past half-million years of geologic history has 

been characterized by the occurrence of dramatic swings in 

global climate approximately every 100,000 years. Oscillating between cold episodes (glacial periods, or ice ages) and 

warm intervals (interglacial periods), climate changes have 

caused global sea level to rise and fall over a range of approximately 130 m. During interglacial periods, sea level is high 

and reefs are constructed on the island margins. Because sea 

level reaches different heights in successive glacial cycles, the 

carbonate history of Hawaii is complex.

The insular shelf is constructed from multiple carbonate units representing reef accretion and erosion over recent 

glacial cycles (fig. 2). Specifically, the shallow shelf is a fossil 

reef complex dating from Marine Isotope Stage (MIS) 7 

(about 190,000–210,000 years ago; Sherman and others, 1999; 

Grossman and Fletcher, 2004). The front of this shelf accreted 

separately during MIS 5a–d (about 80,000–110,000 years 

ago). Eolianites (lithified dunes) of late last interglacial (about 

80,000 years ago) and Holocene (about 10,000 years ago to 

present) age (Fletcher and others, 2005) are found in the nearshore and coastal plain regions of most of the islands. Most 

modern Holocene reef accretion is limited to environments 

on the deeper front of the reef, where wave energy is not 

destructive. Grossman and Fletcher (2004), Conger and others 

(2006a), and Bochicchio and others (2009) infer that rugosity 

in depths less than 10 m atop the fringing reef is largely the 

result of karstification of limestone, not reef accretion, during 

times of lower sea level, most recently since the last interglacial period. Modern wave scour has prevented accretion in this 

zone. At depths greater than 10 m, the karst surface may be 

overgrown by Holocene accretion where wave energy permits 

(Conger and others, 2006b).

Hawaiian reef morphology (fig. 3) exerts a strong control 

on shoreline sediment supply and dynamics. Dollar (1982) and 

Dollar and Tribble (1993) identified physical disturbance from 

waves as the most important factor determining the structure of Hawaiian coral reef communities. Expanding on this 

work, Grigg (1983) articulated the “intermediate disturbance 

hypothesis” and presented two models of coral community 

succession: (1) an undisturbed (lack of wave impact) community that reaches peak diversity as a result of recruitment followed by a reduction due to competition; and (2) a disturbed 

community where diversity is set back to zero in the case of 

a large disturbance, or diversity is ultimately increased in the 

case of intermediate disturbance (substrate is opened for new 

recruitment). In the case of geological studies, interpretation of 

paleocommunities and their role in sediment production must 

be grounded in an understanding of the roles of succession and 

disturbance. Therefore, community assemblage models related 

to wave energy are commonly developed during studies of 

Hawaiian reef stratigraphy (Engels and others, 2004).
4 National Assessment of Shoreline Change: Historical Shoreline Change in the Hawaiian Islands

Figure 1. Computer-generated relief models of the Hawaii Island Archipelago and its northern arm, the Emperor Seamount Chain.

Maui

Molokai

Lanai

Kahoolawe

Niihau

Kauai

Oahu

Hawaii

Elevation, in kilometers

0

-1

-2

-3

-4

-5

-6

1

2

3

4

EXPLANATION

Emperor

Seamounts

Hawaii

Archipelago

60° N

40° N

20° N

120° E 140° E 160° E 180° 160° W 140° W 120° W 100° W

0 1,000 Miles

0 1,000 Kilometers

Base (top) from ETOPO2v2 computer‐generated global relief model

(2‐minute latitude/longitude grid, Cylindrical Equidistant projection):

National Oceanic and Atmospheric Administration,

2006 (http://www.ngdc.noaa.gov/mgg/image/2minrelief.html);

(bottom) from Hawaiian multibeam bathymetry synthesis

computer‐generated relief model

(version 18, 0.0005‐degree latitude/longitude grid, WGS 1984),

Hawaii Mapping Research Group, 2011

(http://www.soest.hawaii.edu/HMRG/multibeam/index.php).

0

-3

-5

-7

-9

-11

1

3

5

9

Elevation, in kilometers

EXPLANATION
Environmental Framework of the Hawaiian Shoreline 5

Figure 2. Principal stratigraphic components of the Oahu carbonate shelf. (Modified from Fletcher and others, 2008)

Figure 3. Carbonate sand 

beaches in Hawaii are the 

result of reef bioerosion and 

direct production of calcareous 

material by reef organisms. Reef 

morphology exerts strong control 

on shoreline sediment supply and 

dynamics. (Kaaawa, Oahu, location 

shown in figure 26) (Photograph by 

Hawaii Aviation, Inc., 2005)

EXPLANATION

Beach

Dune

Marine isotopic

stage numbers Fossil reef

Modern reef

1

Kapapa highstand

(+ 2 meters)

Modern sea level

Leahi

reef

Holocene

reef

Waianae reef

Waimanalo reef

Leahi

dune

Holocene

dune and beach

5a-d

5a-d

5a-d

5e

7

1

Holocene veneer

Kaneohe

0 shoreline

-120

50 100 150 200

Depth, in meters

Time, in thousands of years

1

2 3

4 5 6

a

b

c

d 7

e Modern sea level

0 250

Paleochannel

Reef flat

Reef crest

Fore-reef
6 National Assessment of Shoreline Change: Historical Shoreline Change in the Hawaiian Islands

To improve understanding of reef community assemblage in the Hawaiian Islands, Harney and others (2000), 

Harney and Fletcher (2003), Grossman and Fletcher (2004), 

Engels and others (2004), and Grossman and others (2006) 

surveyed benthic communities to develop coral assemblage 

models marking distinct environments. In their work along 

the south shore of the island of Molokai, Engels and others 

(2004) developed a community zonation model related to 

wave-generated bed shear stress as modeled by Storlazzi and 

others (2002). Engels and others (2004) define three assemblages: low, mid, and high energy. The zonation model relates 

bed shear stress to percent living coral cover, relative percent 

coralline algae cover, dominant coral species, dominant coral 

morphologies, and water depth. Each assemblage is divided 

into three depth zones: less than 5 m, 5 to 10 m, and greater 

than 10 m. All observed coral types that account for at least 

10 percent of living coral cover are represented in the model.

Modern reef communities in wave-exposed settings are 

suppressed to a veneer (Grigg, 1998). North Pacific winter 

swell produces the largest and most frequently damaging 

energy, yet waves of greatest magnitude and impact are likely 

to occur only rarely and are associated most often with strong 

El Niño years (for example, 1998) perhaps a decade or more 

apart (Rooney and others, 2004). Intervening coral growth 

able to survive the strong annual pounding by waves may 

be wiped out by these interannual waves of extraordinary 

size and energy. Radiocarbon dates of fossil corals show that 

coral growth in wave-exposed settings has been continually 

suppressed since about 5,000 years ago on northern exposed 

coasts (Rooney and others, 2004) and about 3,000 years ago 

on southern shorelines (Grossman and others, 2006).

Beach Sediments

Effective, sustainable management of Hawaiian beach 

systems requires an understanding of sediment production, 

as many beaches are losing sediment with time (eroding). 

Hawaiian beach sands are derived primarily from calcareous 

debris eroded from the insular reef shelf, which is reworked 

into sand-size grains by breaking waves on the reef shelf 

and at the shoreline. Hawaiian beach sands are, on average, 

medium in size (classification of Wentworth (1922)) (Inman, 

1952; Dunbar and Rodger, 1957), though the sediment on 

individual beaches can range in size from coarse to fine 

sand. Moberly and Chamberlain’s (1964) analysis of littoral 

sediment grain size around the Hawaiian Islands shows that 

grain size is closely related to wave and current energy, which 

in Hawaii is strongly related to shoreline aspect (table 1). 

Beach sediments on these islands generally are finest on the 

windward or northeastern-facing coasts as a result of the 

persistent working of the sediment by trade wind waves with 

fairly consistent heights and periods that rapidly sorts the 

sediment and reduces its size. 

Table 1. Relation of littoral sand grain size to shoreline aspect (wind and wave exposure) in Hawaii. 

[Modified from Moberly and Chamberlain, 1964; phi, phi units; mm, millimeters; --, no data]

Sample characteristics Shoreline aspect

Windward Southeastern Leeward Northeastern All

Kauai

Number of samples 58 54 70 92 274

Median size (phi) 1.17 1.82 1.50 1.26 1.41

Median size (mm) 0.47 0.27 0.35 0.42 0.38

Oahu

Number of samples 224 77 107 133 521

Median size (phi) 1.52 0.73 0.89 0.66 1.09

Median size (mm) 0.35 0.60 0.54 0.63 0.47

Maui

Number of samples 35 0 258 81 374

Median size (phi) 2.42 -- 1.79 1.21 1.72

Median size (mm) 0.18 -- 0.29 0.43 0.30

All

Number of samples 317 131 435 306 1,169

Median size (phi) 1.52 1.28 1.50 1.21 1.41

Median size (mm) 0.35 0.44 0.35 0.43 0.38
Environmental Framework of the Hawaiian Shoreline 7

Sediments on south shore beaches tend to be coarse and 

poorly sorted, as runoff from strong but infrequent southerly 

“Kona” storms washes coastal plain sediments back into the 

littoral system and high wave energy fragments the nearshore 

reef. These high-energy wave conditions are short lived so 

that new sediments are not highly abraded or sorted. Strong 

surf generated on western and northern coasts by winter North 

Pacific swell leads to coarse-grained beaches, as sediments 

are abraded only during a portion of the year. In general, the 

grain-size diameter of sand on all beaches tends to be finer in 

the summer months (June to September) and coarser in the 

winter months (November to March). 

Beach and reef morphology is similarly dependent on 

shoreline aspect (Moberly and Chamberlain, 1964; Grigg, 

1998). Beaches on north- and west-facing shorelines tend to 

be the longest and widest, whereas reefs tend to be narrower, 

deeper, and more irregular. North- and west-facing beaches 

transition from wide and gently sloping in summer to steep 

and narrow in winter, as sand is moved seaward. 

Lacking a continental source, sand in the Hawaiian 

Islands is often highly calcareous with a smaller contribution 

from eroded volcanic rock. The volcanic component of beach 

sediments is typically controlled by the bedrock geology adjacent to the shoreline (Stearns and Vaksvik, 1935; Macdonald 

and others, 1960). The light color of most Hawaiian beaches 

results from the dominance of grains from fragmented marine 

invertebrate animals and algae. Moberly and Chamberlain 

(1964) show that the composition of many Hawaiian beaches 

is dominated by larger (approaching 1 mm in diameter) species of foraminifera (27 percent, 80 percent of which was 

Amphistegina), followed by mollusks, red algae, and echinoids. Coral fragments constitute only the fifth largest fraction. 

Halimeda, sponge spicules, crab fragments, and similar rare 

components are less abundant. The predominance of foraminifera in beach sand is thought to result more from their relative 

durability in wave action rather than from their ecological 

abundance (Moberly, 1968). 

In contrast to the island-wide surveys of beach sands 

mentioned above, Harney and others (2000) performed a 

more detailed study of sand composition in Kailua Bay, 

windward Oahu (beach face to a depth of -20 m). They 

found that more than 90 percent of sand grains were biogenic 

carbonate dominated by skeletal fragments of coralline algae 

(for example, Porolithon—up to 50 percent) followed by the 

calcareous green algae Halimeda, coral fragments, mollusk 

fragments, and benthic foraminifera. Results of this work 

indicate that sand composition and age can vary considerably 

across the sea floor. These results also indicate a relatively low 

percentage of foraminifera in benthic sands, whereas Moberly 

and Chamberlain (1964) show substantially higher percentages 

in beach sand.

Radiocarbon age of carbonate sands has been used as an 

indicator of longevity, production rate, and transport of coastal 

sediments (Kench, 1997; Gischler and Lomando, 1999). 

Dates measured for Hawaiian coral and skeletal fragments 

show that sediment is produced, transported, and lost from 

the coastal system on a millennial scale. Dates measured for 

Kailua beach and offshore sediment bodies range from 500 to 

2,000 years before present (BP) (Harney and others, 2000). 

Similarly, radiocarbon dates for Amphistegina in surface beach 

sands of Oahu show ages of more than 1,500 years (Resig, 

2004). The dominance of older sediment grains may reflect 

changes in carbonate productivity during the Holocene Epoch. 

As an example, Kailua’s broad, flat coastal plain was flooded 

during a +1 to 2-m, mid- to late Holocene sea level high stand 

(Stearns, 1935; Fletcher and Jones, 1996; Grossman and 

Fletcher, 1998). A substantial portion of sediment volume in 

Hawaiian beaches could result from a past period of higher 

productivity related to higher sea levels (Calhoun and Fletcher, 

1996; Harney and others, 2000) if such an expanded shallow 

nearshore environment resulted in a proliferation of calcareous 

algae and their detritus (Kraft, 1982; Athens and Ward, 1991).

Sediment storage in Hawaiian beach systems occurs as 

either beach reservoirs or nearshore bodies of sediment. Beach 

reservoirs in the Hawaiian Islands are low relative to those 

in continental settings. According to the most comprehensive 

study of Hawaiian beach volume, (Moberly and Chamberlain, 

1964), a total of 39.56 × 106 m3 (cubic meters) of sand was 

stored in beaches as of 1964. More than one-third of all beach 

sand in the Hawaiian Islands is found on the beaches of Kauai 

and more than one-fourth is found on the beaches of Oahu. 

The two islands together hold 61.4 percent of the total beach 

sand found in the State of Hawaii.

Nearshore sediment reservoirs have gained considerable 

attention from researchers as they may contain sands that may 

still be part of the active sand exchange system. A comparison 

of beach volume and reef-top sediment volume in Kailua Bay 

showed that more than 106 m3 of sediment is stored in the 

nearshore sand bodies other than the beach (Bochicchio and 

others, 2009).

Reef karstification is an important aspect of sediment 

storage in sediment budgets for Hawaii (Conger, 2005; 

Bochicchio and others, 2009). Unconsolidated sediment accumulates on the reef surface either by erosion of reef framework or by direct production as skeletal components (Harney 

and Fletcher, 2003). In many cases this sediment fills reef-top 

depressions, creating discrete, isolated sediment deposits. Sediment deposits on reef flats are conspicuous and display large 

variations in size, shape, and location, but are easily recognized in remotely sensed imagery (Conger and others, 2006). 

Sediment deposits also represent a prominent component of 

the geologic framework of insular shelves and potentially are 

an active component of littoral sediment budgets. Sediment 

exchange between sand deposits and the beach face could be 

an important component of shoreline stability and in some 

cases could provide substantial quantities of affordable sand 

for beach replenishment (Moberly and Chamberlain, 1964; 

Casciano and Palmer, 1969; Moberly and others, 1975). 

Most reef-top sand bodies are in water less than 10 m deep 

(Conger, 2005). Detailed volume analysis of sand bodies in 

Kailua Bay, windward Oahu, shows a similar relation of sediment volume to depth if the contribution from large sand channels is excluded (fig. 4) (Bochicchio and others, 2009). 
8 National Assessment of Shoreline Change: Historical Shoreline Change in the Hawaiian Islands

Sediment trapping on the reef surface keeps sand potentially available for circulation within a littoral cell rather than 

allowing it to be lost to offshore sites (Grossman and others, 2006). Most sediment in reef systems is produced on the 

shallow nearshore platform, where carbonate productivity and 

erosion are highest. Sediment remains on the reef platform 

in storage or as part of the active littoral system unless it is 

transported seaward of the reef crest and insular shelf (Harney 

and Fletcher, 2003). Once sediment crosses this threshold, the 

comparatively steep angle of the forereef slope likely prevents 

most shoreward transport, effectively removing sediment from 

littoral circulation unless it moves back into shallow water 

through paleochannels cut into the reef (Grossman and others, 

2006). On many islands, steep submarine terraces more than 

20 m deep exacerbate sediment loss by presenting a seawardfacing sharp break in topography (Coulbourn and others, 

1974). In some cases, large channels are incised perpendicular 

to the shoreline and through the reef crest, creating a potential 

pathway for sediment exchange between inner and outer portions of the reef platform (Grossman and others, 2006). 

The majority of reef-top depressions are relict features 

incised into the surface of Hawaiian reef platforms through 

dissolution or fluvial erosion during periods of lower sea 

level, when subaerially exposed limestone is in contact with 

meteoric waters (Purdy, 1974). The resulting channel and 

doline karst landscape is drowned by rising sea level and 

subsequently filled with sediment, unless depressions are filled 

by new reef accretion (Grigg, 1998; Grossman and Fletcher, 

2004; Rooney and others, 2004; Conger, 2005; Grossman and 

others, 2006). Most shallow reef-top sediment storage (deposition) occurs in depressions (fig. 5) that likely are eroded during periodic subaerial exposures of fossilized reefal limestone. 

Therefore, the potential for modern sediment storage is, to 

some degree, a function of pre-Holocene erosion (increasing 

storage space) and post-Holocene reef accretion infilling the 

eroded features (reducing storage space). 

A study of sediment-body distribution on the reef of 

southeastern Oahu (Bochicchio and others, 2009) indicates 

that two factors control the pre-Holocene karst and fluvial 

erosion that formed the reef-top depressions: (1) availability 

of freshwater drainage and (2) topographic slope of the reef. 

Meteoric runoff from onshore watersheds is a major contributor to erosion of the exposed limestone reef. It follows 

that proximity to an onshore watershed is a major control on 

depression formation and, consequently, offshore sand storage. 

Similarly, complexes of sand bodies are observed more commonly on low reef slopes than high on the southeast Oahu reef 

(Bochicchio and others, 2009).

Sea Level

Local relative sea level around Hawaii (fig. 6) is not 

only dependent on the global eustatic average trend (a rise of 

about 3 mm/yr (millimeters per year); Merrifield and others, 

2009) but also is affected by local oceanographic patterns, 

basin-scale meteorology, and localized flexure of the oceanic 

lithosphere, which responds elastically to the heavy load of 

volcanic rocks over the Hawaiian hotspot. It is estimated that 

one half of the upward construction of Hawaiian volcanoes is 

lost to subsidence and that most of the volcanoes have subsided 2 to 4 kilometers (km) since emerging above sea level 

(Moore, 1987). Subsidence associated with active volcanism 

causes upward plate flexure at a radius that correlates to the 

modern-day position of Oahu. Oahu, as evidenced by the presence of emerged fossil reefs, is undergoing long-term geologic 

uplift; however, the rate of uplift is less than 1 percent of the 

rate of sea-level rise.

Sea level has risen around Hawaii approximately 

1.5 mm/yr over the past century. Although this rate may seem 

small, long-term sea-level rise can lead to chronic coastal 

erosion, coastal flooding, and drainage problems, all of which 

2,919

3,819

53,042

1,482

119

42

1 10 100 1,000 10,000 100,000

0-10

10-20

20-30

Depth range, in meters

All sediment

Excluding Kailua

channel sediment

Log sediment volume, in thousands of cubic meters

EXPLANATION

Figure 4. Volume of sediment by depth 

zone in Kailua Bay, Oahu. (Location shown 

in figure 26) (Modified from Bochicchio and 

others, 2009)
Environmental Framework of the Hawaiian Shoreline 9

are experienced in Hawaii. This long-term trend also increases 

the impact of short-term fluctuations when extreme tides cause 

episodic flooding and erosion along the coast (Firing and 

Merrifield, 2004; Fletcher and others, 2010). 

Coastal erosion, although not solely tied to climate 

change, is an important factor in managing the problem of 

rising sea level. Sea-level rise accelerates and expands erosion, potentially affecting beaches that previously were stable. 

Chronic erosion seaward of developed lands has historically 

led to seawall construction, resulting in beach loss (Fletcher 

and others, 1997).

Although the rate of global mean sea-level rise has 

approximately doubled since 1990, sea level not only did not 

rise everywhere, but actually declined in some large areas 

(National Aeronautics and Space Administration, 2011). The 

pattern of global sea-level change is complex because sea 

level is affected by winds and ocean currents, which also are 

changing. In Hawaii, improving our understanding of the 

effects of sea-level change requires attention to local variability with careful monitoring and improved modeling efforts. 

Climate change is expected to cause sea-level rise to continue, 

and accelerate, for several centuries; and may exceed 1 m 

above the 1990 level by the end of the 21st century (Fletcher, 

2009b; Vermeer and Rahmstorf, 2009). Continued sea-level 

rise will increase marine inundation of coastal roads and communities. Saltwater intrusion will intensify in coastal wetlands, 

groundwater systems, estuaries, and elsewhere. Extreme tides 

already (2012) cause drainage problems in developed areas. 

Sea-level rise threatens Hawaiian beaches (fig. 7), tourism, quality of life, and infrastructure. Hawaiian communities 

located at the intersection of intensifying storm runoff and 

rising ocean waters will likely experience increased flooding.

Waves

The four dominant regimes responsible for large swells in 

Hawaii are the North Pacific swell, trade wind swell, southern swell, and Kona storm waves (including hurricanes). The 

regions of influence of these regimes, outlined by Moberly and 

Chamberlain (1964), are shown in figure 8. A rose diagram 

depicting annual swell heights and directions (Vitousek and 

Fletcher, 2008) has been added to the original illustration. 

The average directional wave spectrum in Hawaiian waters is 

bimodal and is dominated by the North Pacific and trade wind 

swell regimes (Aucan, 2006). Although important to describe 

the complete Hawaiian wave climate, southern swell and 

Kona storm regimes do not occur with the high magnitude and 

frequency that characterize North Pacific and trade wind swell 

regimes. The buoy network around Hawaii is managed by the 

NOAA National Data Buoy Center (NDBC) (fig. 8). These 

sensors provide the local wave-climate data. Buoy reports are 

available at http://www.ndbc.noaa.gov/maps/Hawaii.shtml.

Interannual and decadal cycles, including El Niño 

Southern Oscillation (ENSO; Goddard and Graham, 1997) 

and Pacific Decadal Oscillation (PDO; Mantua and others, 

1997; Zhang and others, 1997), are important contributors to 

the variability of the Hawaiian wave climate. These largescale oceanic and atmospheric phenomena are thought to 

control the number and extent of extreme swell events; for 

example, strong ENSO events are thought to increase the 

size and frequency of swell events, relative to non-ENSO 

years (Seymour and others, 1984; Caldwell, 1992; Seymour, 

1998; Allan and Komar, 2000; Graham and Diaz, 2001; 

Wang and Swail, 2001; Aucan, 2006). The magnitude and 

frequency of extreme wave events may control processes 

N

0 0.5 MILES

0 0.5 KILOMETERS

Kailua Bay

(no data)

EXPLANATION

Depth, in meters

0

35

Sand

(no data)

Kailua

(land)

Sand-filled paleochannel

Oahu

21°

45' N

21°

30'

21°

15'

158°15' W 158°00' 157°45'

Kailua

Bay

Oahu

Figure 5. Computer-generated 

relief model of Kailua Bay, Oahu. 

Sand bodies on the sea floor are 

shown in black. (Modified from 

Conger and others, 2009)
10 National Assessment of Shoreline Change: Historical Shoreline Change in the Hawaiian Islands

1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010

EXPLANATION

EXPLANATION

Monthly mean sea level with the average 

 seasonal cycle removed 

Upper 95-percent confidence interval

Linear sea level trend

Lower 95-percent confidence interval

Monthly mean sea level with the average 

 seasonal cycle removed 

Upper 95-percent confidence interval

Linear sea level trend

Lower 95-percent confidence interval

0.60

0.45

0.30

0.15

0

0

-0.15

-0.30

-0.45

-0.60

1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010

-0.60

0.60

0.45

0.30

0.15

-0.15

-0.30

-0.45

A. Hilo, Hawaii 3.27 +/- 0.35 millimeters per year 

B. Kahului, Hawaii 2.32 +/- 0.53 millimeters per year

Meters Meters

Figure 6. Mean-sea-level trends at A, Hilo, 1927–2010; B, Kahului 1947–2010; C, Honolulu 1905–2010; and D, Nawiliwili, 1955–2010, 

Hawaii. (Data from National Oceanic and Atmospheric Administration, 2011)
Environmental Framework of the Hawaiian Shoreline 11

Data with the average seasonal cycle removed 

Upper 95-percent confidence interval

Linear mean sea level trend

Lower 95-percent confidence interval

EXPLANATION

0.60

0.45

0.30

0.15

-0.15

-0.30

-0.45

-0.60

-0.60

0.60

0.45

0.30

0.15

-0.15

-0.30

-0.45

Meters Meters

0

0

1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010

1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010

D. Nawiliwili, Hawaii 1.53 +/- 0.59 millimeters per year

C. Honolulu, Hawaii 1.50 +/- 0.25 millimeters per year

EXPLANATION

Data with the average seasonal cycle removed 

Higher 95-percent confidence interval

Linear mean sea level trend

Lower 95-percent confidence interval

Figure 6. —Continued
12 National Assessment of Shoreline Change: Historical Shoreline Change in the Hawaiian Islands

Annual significant wave height,

in meters

6

4

2

0

0 100 KILOMETERS 

0 100 MILES

45°

282°

0°

123°

SOUTHERN SWELL

147°

147° 210°

KONA STORM WAVES

258° 51003

51002

51004

51001

51201

51202

Wave buoy and

identification number

NORTH PACIFIC SWELL

NORTHEAST

TRADE

WAVES

From Vitousek and Fletcher, 2008

51002

EXPLANATION

Figure 7. Beaches and 

waterfront development 

(Waikiki, Oahu; location 

shown in figure 29) threatened 

by sea-level rise. Because the 

groundwater table rises and 

falls with sea level, drainage 

problems likely will become 

a major problem in this and 

other coastal communities. 

(Photograph by C.L. Conger, 

University of Hawaii Sea Grant 

College Program)

Figure 8. Dominant swell regimes and wave-monitoring buoy locations in Hawaii. (Modified from Moberly and Chamberlain, 1964, 

and Vitousek and Fletcher, 2008).
Environmental Framework of the Hawaiian Shoreline 13

such as coral development (Dollar and Tribble, 1993; Rooney 

and others, 2004) and beach morphology changes in Hawaii 

and elsewhere (Moberly and Chamberlain, 1964; Ruggiero 

and others, 1997; Kaminsky and others, 1998; Storlazzi and 

Griggs, 2000; Rooney and Fletcher, 2005; Ruggiero and 

others, 2005).

Located in the middle of the large swell-generating basin 

of the North Pacific, Hawaii receives large ocean swell from 

extratropical storms that track predominantly eastward from 

origins in the Northwest Pacific. The storminess of the North 

Pacific reaches a peak in the boreal winter, as the Aleutian 

low intensifies and the North Pacific high moves southward. 

Strong winds associated with these storms produce large 

swells, which can travel for thousands of miles until reaching 

the shores of Hawaii. In summer months, the North Pacific 

high moves northward and storms in the North Pacific become 

infrequent (Flament and others, 1996). Satellite-derived average wave heights over the North Pacific in winter and summer 

are shown in figure 9. The average winter wave heights in the 

North Pacific are about 3 m or greater, whereas summer wave 

heights are about 2 m or less. Although figure 9 gives the average state of the North Pacific, individual storm events in this 

dynamic system typically track eastward with wave heights 

on the order of 5 to 10 m. These swell-producing storms occur 

during winter months with typical reoccurrence intervals of 

1 to 1.5 weeks (for 5- to 7-m swells), 2 to 3 weeks (for 7- to 

9-m swells), and 1 month (for swells 9 m high or greater). 

Many North Pacific storms do not produce swells that reach 

Hawaii. Storms that originate in high latitudes and those that 

track to the northeast send swells to the Aleutian Islands and 

the Pacific Northwest. Swells that originate from storms in 

lower latitudes and those that track slightly to the southeast 

reach Hawaii with the largest wave heights.

Hawaii receives its largest swell from the North Pacific, 

with an annually recurring maximum deep-water significant 

(average of the highest third of the waves) wave height of 

7.7 m (Vitousek and Fletcher, 2008) with peak periods of 14 to 

18 seconds. However, the size and number of swell events in 

Hawaii vary each year by a factor of 2 (Caldwell, 2005). The 

annual maximum wave height recorded at buoy 51001 (fig. 8) 

ranges from about 6.8 m (in 1994, 1997, and 2001) to 12.3 m 

(in 1988). 

The seasonal cycle of North Pacific swell peaks in winter 

with a daily average wave height about 4 m (fig. 10) (Vitousek 

and Fletcher, 2008). Aucan (2006) depicted the monthly 

average directional spectra from buoy data at Waimea (buoy 

51201) and Mokapu (buoy 510202) that showed the dominance of North Pacific swell out of the northwest in winter 

months, and relatively persistent energy out of the northeast in 

higher frequency bands associated with trade wind swell.

Summer Winter

0

0.5

1

1.5

2

2.5

3

3.5

Average wave height,

in meters

EXPLANATION

Figure 9. Satellite images (JASON-1) showing derived average wave height over the North Pacific in summer and winter. (National 

Oceanic and Atmospheric Administration, 2010)
14 National Assessment of Shoreline Change: Historical Shoreline Change in the Hawaiian Islands

Occurring about 75 percent of the year, the trade winds 

are northeasterly (average, 73°) winds with an average speed 

of 25 kilometers per hour (16 miles per hour). Anticyclonic 

(clockwise) flow around the North Pacific high bolsters the 

trade winds in Hawaii in summer months, increasing their persistence. In winter months, the North Pacific high flattens and 

moves closer to the islands, decreasing the trade wind persistence (fig. 11). Although the number of days characterized by 

trade winds is greater in summer than in winter months, mean 

trade wind speed in summer and winter months is similar.

The persistent trade winds generate limited-fetch swell on 

north-, northeast-, east-, and southeast-facing coasts (fig. 8). 

Trade wind waves in Hawaii are characterized by choppy 

seas with average wave heights of 2 m and peak periods of 

9 seconds from the northeast. These are nominal conditions, 

however, and trade wind waves can exceed 5 m in height and 

have periods of 15 to 20 seconds.

Southern swell arriving in Hawaii is typically generated farther away from the islands than North Pacific swell. 

These swells are generated by storms south of the equator 

0 10 20 30 40 50 60

0

1

2

3

4

5

Wind speed, in kilometers per hour

Number of days

Summer (June, July, Aug)

Winter (Dec, Jan, Feb)

EXPLANATION

Figure 10. Daily average significant wave height from buoy 51001 (1981 to 2005, location shown in figure 8). This plot shows the 

seasonal variability of North Pacific Ocean swell, which begins to increase in October, reaches a peak in winter, decreases in March, 

and reaches a minimum in summer.

Figure 11. Number of days per 

season that trade winds occur 

with a particular speed (data from 

buoy 51001, 1981 to 2005). Note the 

persistence of typical trade winds 

at a speed of about 25 kilometers 

per hour (16 miles per hour) during 

summer months.

July Aug. Sept. Oct. Nov. Dec. Jan. Feb. Mar. Apr. May June

1.5

2.0

2.5

3.0

3.5

4.0

4.5

Month

Daily average significant height, in meters 

Observed

Smoothed

EXPLANATION
Environmental Framework of the Hawaiian Shoreline 15

near Australia, New Zealand, and as far as Antarctic waters. 

Southern swell occurs in summer months (winter months in 

the southern hemisphere) and reaches Hawaii with an annual 

significant wave height of 2.5 to 3 m and peak periods of 

14 to 22 seconds, which is a smaller but slightly longer period 

than North Pacific swell (Armstrong, 1983; Vitousek and 

Fletcher, 2008).

Kona storms generally refer to low-pressure areas 

(cyclones) of subtropical origin that usually develop northwest 

of Hawaii in winter and move slowly eastward, accompanied 

by southerly winds (from whose direction the storm derives 

its name) and by the clouds and rain that have made these 

storms synonymous with bad weather in Hawaii (Giambelluca 

and Schroeder, 1998). Strong Kona storms generate wave 

heights of 3 to 4 m with periods of 8 to 11 seconds, along with 

wind and rain, and can cause extensive damage to south- and 

west-facing shores (Rooney and Fletcher, 2005). Minor Kona 

storms occur nearly every year in Hawaii, however, major 

Kona storms resulting in substantial shoreline change tend 

to occur every 5 to 10 years, during the negative PDO cycle 

(Rooney and Fletcher, 2005). Consequently, positive (warm) 

PDO and El Niño phases tend to suppress Kona storm activity 

(Rooney and Fletcher, 2005).

Although each wave regime (trade wind swell, North 

Pacific swell, southern swell, and Kona storms) has its own 

underlying processes and mechanics, the sum of all of these 

regimes contributes to the wave heights and shoreline change 

in Hawaii. Breaking waves at the shoreline are composed of 

swell sources from many different storms and swell regimes. 

The most common combination of swell modes for northfacing shores is North Pacific swell and trade wind swell. The 

most common combination of swell modes for south-facing 

shores is southern swell and trade wind swell. Thus, the 

spectral approach to swell and surf patterns following Aucan 

(2006) is an informative way of depicting the Hawaiian 

wave climate. 

The maximum annually recurring significant wave 

heights (Hs) and the largest 10-percent (H1/10) and 1-percent 

(H1/100) wave heights for various directions in 30 degree 

windows around Hawaii are given in table 2 (Vitousek and 

Fletcher, 2008); annual wave heights are also depicted in 

figure 8.

Tides

The tide range in Hawaii is comparatively small, typically 0.58 m (Mean Higher High Water (MHHW)—Mean 

Lower Low Water (MLLW)), and the spring tide range is 

about 1 m. Although the astronomic tide typically represents 

the largest water-level variability at a particular location, 

other factors such as atmospheric pressure, wind setup, ENSO 

cycles, and oceanic disturbances can produce water-level 

variability on the order of tens of centimeters. One important 

process influencing extreme sea-level events in Hawaii is the 

occurrence of mesoscale eddies, which are large (greater than 

100 km) oceanic disturbances with elevated sea levels of about 

15 cm (Firing and Merrifield, 2004). 

As discussed previously, many sources contribute to the 

maximum water level on a beach, including tide, wave setup, 

wave run-up, and other sources of water-level variability. 

Coincidence of large swell and tide events can cause severe 

coastal flooding and overtopping in Hawaii, whereas swell 

events that occur at low tides or neap cycles typically are less 

severe (Caldwell and others, 2009). 

Shoreline Change

All the processes considered thus far influence beach 

morphology in Hawaii. Morphologic changes include seasonal 

beach profile changes, extreme events, and chronic trends. 

Seasonal beach-profile changes result from the seasonal 

variability of the Hawaiian wave cycle (see the Hawaii beach 

profile Web site at http://geopubs.wr.usgs.gov/open-file/

of01-308/). In winter months, north-facing shorelines are 

exposed to increased wave activity from the North Pacific 

swell. In summer months, south-facing shorelines are exposed 

to increased wave activity from the southern swell. This wave 

activity is associated with increased run-up and increased 

impacts to the beach and coastal dunes. Elevated energy at 

the shoreline transports sand offshore or alongshore with 

dominant currents. The beach profile remains in an adjusted 

state until wave heights decrease or swell patterns change to 

allow the displaced volume of sand to return. A conceptual 

example of cross-shore sand transport and profile change is 

shown in figure 12.

Table 2. Observed maximum annually recurring significant 

wave heights (Hs) and the largest 10-percent (H1/10) and 1-percent 

(H1/100) wave heights for various directions around Hawaii. 

[Modified from Vitousek and Fletcher, 2008; Window, degrees from true 

north; m, meters]

Window (degrees) Annually recurring wave heights (m)

Hs H1/10 H1/100

0 30 5.9 7.4 9.8

30 60 6.0 7.6 10.0

60 90 5.1 6.5 8.5

90 120 4.3 5.5 7.2

120 150 2.8 3.5 4.6

150 180 3.0 3.8 5.0

180 210 2.4 3.0 3.9

210 240 1.6 2.0 2.7

240 270 1.5 1.9 2.5

270 300 3.7 4.7 6.2

300 330 5.9 7.5 9.9

330 360 5.8 7.4 9.7
16 National Assessment of Shoreline Change: Historical Shoreline Change in the Hawaiian Islands

Extreme beach profile changes, whose magnitude exceeds 

typical seasonal levels, result from extreme swell, storm, 

and sea-level events often associated with a corresponding 

ENSO or PDO cycle. Examples of extreme beach changes in 

Hawaii include the erosion that has occurred (2005–present) 

at Kailua Beach Park near the boat ramp during persistent 

windy conditions (La Niña), followed by the short-lived return 

of sand associated with the low wind (El Niño) conditions of 

winter 2009/2010. As the El Niño ended and La Niña winds 

returned, the sand at Kailua again disappeared, and erosion 

has dominated since. Another example of extreme beach 

fluctuations occurred in 2003 at Kaanapali Beach, Maui, as 

a result of the combination of high water levels caused by a 

mesoscale eddy juxtaposed with spring high tide, late summer 

heating, and a modest southern-swell event (Vitousek and 

others, 2007). 

One of the main goals of this study was to quantify the 

extent of long-term or “chronic” erosion on Hawaiian shorelines. Chronic changes are long-term (decades to centuries) 

changes that do not show a cyclical pattern. Chronic beach 

changes or chronic erosion in Hawaii can result from longterm sea-level rise and sediment budget deficiency (often 

related to human activities). 

Methods of Analyzing Shoreline 

Change

Coastal scientists have been quantifying rates of shoreline movement and studying coastal change for decades. Time 

series of shoreline positions can be used to document coastal 

change and are interpreted to improve our understanding of 

shoreline stability.

Compilation of Historical Shorelines

The most commonly used sources of historical shoreline 

data have traditionally been NOAA’s National Ocean Service 

(NOS) Topographic sheets (T-sheets; Shalowitz, 1964) and 

vertical aerial photographs. Ideally, extraction of past shoreline positions from these data sources involves georeferencing 

and removing distortions from maps and aerial photographs, 

followed by digitizing the shoreline position. 

Depending on location, data source, and scientific preference, different proxies are used to represent the position of the 

shoreline. Common shoreline proxies include the high water 

line (HWL) (Shalowitz, 1964); a wet-dry line (maximum runup; Moore and others, 2006); the first line of vegetation (for 

example, Hwang, 1981); the toe or crest of the abutting dune 

(Moore and Griggs, 2002); a low water line such as the toe of 

the beach (for example, Fletcher and others, 2003); a cliff base 

or top (for example, Hapke and Reid, 2007); and a tidal datum 

or elevation—typically the location where the plane of mean 

high water (MHW) intersects the beach face (for example, 

Morton and others, 2004).

In this study, the methods of Fletcher and others (2003) 

and Romine and others (2009) for mapping historical shorelines were followed closely. Historical shorelines were 

digitized from NOS T-sheets and orthorectified aerial photo 

mosaics with spatial resolution (pixel size) of 0.5 m (fig. 13). 

Aerial photographs were orthorectified and mosaicked in 

PCI Geomatics, Inc., Geomatica Orthoengine software 

(http://www.pcigeomatics.com/) to reduce displacements 

caused by lens distortion, Earth curvature, refraction, camera 

tilt, and terrain relief. A Root Mean Square (RMS) positional 

error less than 2 m is commonly achieved. T-sheets are 

georeferenced using polynomial mathematical models in 

PCI with RMS errors typically less than 4 m. Rectification 

of T-sheets is also verified by overlaying them on aerial 

photomosaics to compare their fit to unchanged features. 

Previous workers (Shalowitz, 1964; Crowell and others, 1991; 

Daniels and Huxford, 2001) who addressed the accuracy of 

T-sheets found that they meet national map accuracy standards 

Beach

Dunes Normal beach profile

New dunes Recovery

Adjustment for large waves

Dunes

and beach

release sand

Coastal dunes and

beach store sand until

next large wave event

Sand moves

offshore

Sand moves

onshore

NOT TO SCALE

Figure 12. Seasonal beach-profile adjustments induced by 

seasonal swell variations and resulting cross-shore sediment 

transport.
Methods of Analyzing Shoreline Change 17

(Ellis, 1978) and recommended them for use in shoreline 

change studies as a valuable source of data needed to extend 

the time series of historical shoreline positions (National 

Academy of Sciences, 1990). 

T-sheets were rectified using ERDAS, Inc., Imagine 

geographic imaging software (http://www.erdas.com/

Homepage.aspx) by placing a minimum of six ground control 

points (GCPs) distributed throughout the image on the T-sheet 

graticule. For some T-sheets produced before 1930 additional 

coordinate transformation information from NOAA was 

required to convert the data from the United States Standard 

Datum (USSD) to the North American Datum of 1927 (NAD 

27). The datum transformation was applied to T-sheet graticule 

coordinates prior to rectification. Total RMS error for the 

rectification process was maintained below 1 pixel, which is 

approximately 4 m at a scale of 1:20,000 and approximately 

1.5 m at a scale of 1:10,000. The resulting RMS error typically 

was much lower than 1 pixel. 

To verify T-sheets and datum transformations, shoreline 

features that change little over the period of study (for example, rock headlands and engineered structures) were used. In 

the Hawaiian Islands, the adoption of the NAD 27 datum for 

mapping and the emergence of several unsupported local and 

island-specific datums have led to confusion among cartographers and surveyors. Many T-sheet products used in this study 

were re-rectified to correct substantial errors associated with 

incorrect projection datum definitions. Such errors otherwise 

would have rendered the sheets unusable. 

Newly georeferenced T-sheets were loaded in ESRI 

(http://www.esri.com/) ArcGIS software and ArcToolBox was 

used to transform the T-sheets into the Universal Transverse 

Mercator (UTM) projection on the North American Datum of 

1983 (NAD 83) prior to shoreline digitization. A verification 

of the T-sheet shoreline was carried out where possible using 

control marks or physical shoreline features that are present on 

the T-sheet by comparing them with a reliable current image. 

Where verification failed, T-sheets were re-rectified using 

ground control points on existing control stations and identifiable shoreline features. In all cases, shoreline-feature verification produced a high-quality data product. 

Mapping Historical Shorelines

In Hawaii, the high reflectivity of Hawaiian white carbonate beaches reduces the visibility of the HWL on historical 

aerial photographs (Fletcher and others, 2003). Norcross and 

others (2002) and Eversole and Fletcher (2003) found that the 

low water mark (LWM) or toe of the beach was important as a 

pivot point for cross-shore and alongshore sediment-transport 

processes at their study sites at Kailua Beach, Oahu, and 

Kaanapali Beach, Maui, respectively. Excellent water clarity 

September, 1949

April, 1967

Transect, 20-meter spacing

March, 1971

March, 1975

February, 1988

July, 1996

June, 2006

January, 1928

October, 1958

Topographic sheet,1932

Historical shoreline

EXPLANATION

Figure 13. Historical 

shorelines and shoreperpendicular transects 

(20-meter spacing) displayed 

on a portion of a recent 

(2006) aerial photograph 

of Mokuleia Beach, North 

Oahu. (Location shown in 

figure 24) (Photograph by 

Hawaii Aviation, Inc.)
18 National Assessment of Shoreline Change: Historical Shoreline Change in the Hawaiian Islands

relative to most continental beaches allows the delineation of 

the LWM on historical aerial photomosaics, which is distinguished by a black and white or color tonal change at the base 

of the foreshore, most easily identified by the relative position 

of wave run-up on the beach. 

A LWM was digitized from aerial photomosaics as the 

shoreline proxy. The beach toe, or base of the foreshore, 

is a geomorphic representation of the LWM. Removing 

or quantifying sources of uncertainty related to temporary 

changes in shoreline position is necessary to achieve the 

goal of identifying chronic long-term trends in shoreline 

movement. Using a LWM as a shoreline proxy on Hawaiian 

carbonate beaches offers several advantages toward the goal of 

limiting uncertainty. Studies from beach-profile surveys have 

shown that the LWM is less prone to geomorphic changes 

typical of other shoreline proxies (for example, wet-dry 

line and high water mark) on the landward portions of the 

beach (Norcross and others, 2002). The vegetation line was 

used as the shoreline proxy in some previous Oahu studies 

(Hwang, 1981; Sea Engineering, Inc., 1988). However, on 

many Hawaiian beaches the vegetation line is cultivated, 

fixed by shoreline revetments, obscured by overhanging trees, 

or dominated by aggressive species, and therefore may not 

represent natural erosion and accretion patterns. 

The original surveyors working on T-sheets mapped the 

HWL as a shoreline proxy. To include T-sheet shorelines in the 

time series of historical shorelines, the HWL is migrated to a 

LWM in our study using an offset calculated from measurements in beach profile surveys at the study beach or a similar 

nearby location. To determine patterns of historical shoreline 

movement, changes in shoreline position were measured relative to an offshore baseline along shore-perpendicular transects spaced 20 m apart. 

The migration of the HWL to the LWM was possible 

using topographic beach profiles. The USGS, in coordination 

with the University of Hawaii, conducted a 5-year beach 

profile study at beaches on the islands of Oahu and Maui 

(Gibbs and others, 2001). University researchers have 

extended this survey to include the period 2006–08 on Oahu 

(35 locations; C.H. Fletcher, B.M. Romine, and M. Dyer, 

unpub. data, 2008) and on Kauai (27 locations; C.H. Fletcher, 

T.R. Anderson, and M. Dyer, unpub. data, 2008). Distances 

between the two shoreline features are calculated at the nearest 

representative beach profile location, and an average offset 

distance was calculated.

Additional details on the dates of specific shorelines and 

their spatial coverage are available in the companion online 

data report by Romine and others (2011).

Uncertainty and Error

Several sources of error affect the accuracy of historical 

shoreline positions and final shoreline change rates. In 

this report, two types of uncertainty are defined: positional 

uncertainty and measurement uncertainty. Following methods 

of Romine and others (2009), and building on work by 

Fletcher and others (2003), Genz and others (2007a), Morton 

and others (2004), and Rooney and others (2003), seven 

different sources of error in identifying shoreline positions 

on aerial photographs and T-sheets (three positional and four 

measurement errors) were quantified. The seven sources of 

error are summed in quadrature (the square root of the sum of 

the squares) to arrive at a total positional uncertainty (Ut). The 

range of values of each type of error for each island are listed 

in table 3.

Positional uncertainties, including errors related to 

seasons, tides, and T-sheet HWL-to-LWM shoreline conversions, are related to all phenomena that reduce the precision 

and accuracy of defining a shoreline position in a given year. 

These uncertainties center mostly on the nature of the shoreline position at the time an aerial photo is taken. 

Seasonal error (Es) is the error associated with movements in shoreline position from waves and storms. In Hawaii, 

this movement is largely a seasonal process, with swell from 

the North Pacific in winter and South Pacific in summer (see 

Waves). Some beaches (or sections of beach) tend to accrete 

in summer and erode in winter, whereas other beaches tend 

to do the opposite as a result of seasonal shifts in predominant swell direction. Because seasonal change is cyclical, the 

probability of a photograph depicting a summer shoreline is 

equal to the probability of a photograph depicting a winter 

shoreline. Therefore, a uniform distribution is an adequate 

approximation of seasonal uncertainty. Seasonal differences in 

shoreline position (LWM) were quantified from summer and 

winter beach profile measurements at a study beach or nearby 

beach with similar littoral characteristics. If available, seasonal 

shoreline positions from aerial photographs taken in adjacent 

seasons can be used in place of beach profile data. The mean 

and standard deviation of seasonal changes were calculated 

from the absolute values of differences between summer 

Table 3. Range of errors in position of historical shorelines for 

Kauai, Oahu, and Maui.

[m, meters; ±, plus or minus]

Source of error Magnitude range (m)

Maui Oahu Kauai

Seasonal error (Es) ± 1.2–7.1 ± 3.6–6.2 ± 2.5–19.9

Tidal error (Etd) ± 1.4 ± 2.5–3.4 ± 2–6

T-sheet conversion error (Ec) ± 1.9–7.5 ± 3.4–5.7 ± 1.0–13.8

Digitizing error (Ed) ± 0.8–5.1 ± 0.5–5.7 ± 0.8–9.7

Pixel error (Ep) ± 0.5 ± 0.5 ± 0.5–3.41

Rectification error (Er) ± 0.1–6.1 ± 0.6–3.0 ± 0.0–7.3

T-sheet plotting error (Ets) ± 5.1 ± 5.1 ± 5.1
Methods of Analyzing Shoreline Change 19

and winter shoreline positions. A uniform distribution was 

generated (with MatLab rand function) that incorporates the 

mean and two times the standard deviation as minimum and 

maximum values. The standard deviation of the distribution is 

the seasonal error. 

Tidal fluctuation error (Etd) is the error from horizontal 

movement in shoreline position along a beach profile due 

to vertical tides. Aerial photographs were obtained without 

regard to tidal cycles, which can influence the position of the 

digitized shoreline. The horizontal movement of the LWM 

during a spring tidal cycle was monitored on several beaches 

to assess this error. Because the tides cyclically fluctuate 

between low and high, a photograph can capture the shoreline 

at any tidal stage. Therefore, like seasonal error, a uniform 

distribution is an adequate approximation of tidal uncertainty. 

A uniform distribution is generated that incorporates the 

mean and two times the standard deviation as minimum and 

maximum values. The tidal error is the standard deviation of 

the distribution. 

Conversion error (Ec) is calculated only for T-sheets and 

is the error associated with migration of T-sheet HWL shorelines to a LWM position. The error is the standard deviation of 

the differences between the offset and HWL-to-LWM beach 

profile measurements.

Measurement uncertainties, including errors related to 

shoreline digitization, image resolution, image rectification, 

and T-sheet plotting, are related to analyst manipulation of the 

map and photo products. For T-sheets, National Map Accuracy 

Standards (U.S. Bureau of the Budget, 1947) were adopted 

that provide a measure of both position and measurement 

uncertainties. For photos, measurement uncertainty is related 

to the orthorectification process and onscreen delineation of 

the shoreline. 

Digitizing error (Ed) is the error associated with digitizing 

the shoreline. One analyst digitizes the shorelines for all photographs and T-sheets to eliminate the possibility of different 

interpretations by multiple analysts. The error is the standard 

deviation of the differences (distances) between repeated 

digitizations by several analysts. The error is calculated for 

photos/T-sheets at different resolutions.

Pixel error (Ep) is the pixel size of the image. The pixel 

size in orthorectified images is 0.5 m, which means that any 

feature smaller than 0.5 m cannot be resolved. The pixel size 

in T-sheets is 1.0 to 3.0 m.

Rectification error (Er) is calculated from the orthorectification process. Aerial photographs are corrected, or rectified, 

to reduce displacements caused by lens distortions, refraction, 

camera tilt, and terrain relief using PCI Orthoengine. The 

RMS values calculated by the software are measures of the 

offset between points on a photo and established GCPs. The 

rectification error is the RMS value.

T-sheet plotting error (Ets) is calculated only for T-sheets. 

The error is based on the analysis of topographic surveys by 

Shalowitz (1964). Three major errors are involved in the following accuracy of T-sheet surveys: (1) measured distance has 

an accuracy of 1 m, (2) planetable plotting has an accuracy 

of 3 m, and (3) delineation of the HWL on the beach has an 

accuracy of 4 m. The three errors are summed in quadrature to 

obtain the T-sheet plotting error. 

These errors are random and uncorrelated and can be 

represented by a single measure calculated by summing in 

quadrature, (equation 1). The total positional uncertainty (Ut) 

is

U E t s = ± + Etd +++ EEE c d p r + + E Ets 2 2 222 2 2 (1)

For aerial photographs, Ec and Ets are omitted. For T-sheets, 

Etd is omitted. Ut is used as the accuracy attribute field for each 

shoreline year. These uncertainty values can be propagated 

into the shoreline change result using weighted linear 

regression (or weighted least squares, WLS) in the Digital 

Shoreline Analysis System (DSAS) (Thieler and others, 

2009). The resulting uncertainty in the rate incorporates the 

uncertainty in each shoreline and the uncertainty in the ratedetermining model.

Calculation and Presentation of Rates of Change

Rates of shoreline change were generated in ArcGIS 

with DSAS version 4, an ArcMap extension developed by the 

USGS (Thieler and others, 2009). DSAS employs the singletransect method (ST) to calculate change rates and rate uncertainties at regularly spaced transects (measurement locations) 

alongshore. ST uses various methods (for example, end point 

rate, least squares, weighted least squares) to fit a trend line to 

the time series of historical shoreline positions at a transect. 

ST is the most commonly utilized method for calculating 

shoreline change (for example, see Fletcher and others, 2003; 

Morton and others, 2004; Morton and Miller, 2005; Hapke and 

others, 2006; Hapke and Reid, 2007). 

Transects were spaced approximately at 20-m intervals 

alongshore, roughly perpendicular to the trend of the shoreline. Hawaiian beaches are typically narrower and shorter 

than mainland beaches. To adequately characterize change on 

Hawaiian beaches, the transect spacing used was narrower 

than that typically employed in studies of mainland U.S. 

beaches (for example, 50 m; Morton and others, 2004; Morton 

and Miller, 2005).

Shoreline change rates were calculated with ST using 

WLS regression, which accounts for uncertainty in each 

shoreline position when calculating a trend line. The weight 

for each shoreline position is the inverse of the uncertainty 

squared (for example, wi = 1/Ut

2

). Shoreline positions with 

higher uncertainty have less influence on the trend line than 

data points with smaller uncertainty. The slope of the line is 

the shoreline change rate (fig. 14). 

Rates were calculated for long- and short-term shoreline 

data. All shorelines were used for long-term rate calculations, 

and post-WWII shorelines were used for short-term rate 

calculations. A minimum of three historical shoreline positions 
20 National Assessment of Shoreline Change: Historical Shoreline Change in the Hawaiian Islands

is required when calculating a shoreline change rate with 

WLS. Transects with less than three shoreline intersections 

are given a ‘null’ rate and are not included in calculating 

regionally averaged rates. In some instances, the beach 

disappeared over the course of the study period. In these cases, 

rates were calculated using only shorelines up to and including 

the first shoreline indicating no beach. The total extent of 

beach lost in a region is estimated by multiplying the number 

of transects where the beach was lost times 20 m (20-m 

transect spacing). The percent of beach lost in a region is the 

number of transects where the beach was lost divided by the 

total number of transects. 

Historical shoreline data typically are sparse (commonly 

less than 10 shorelines) and noisy (high positional uncertainty). Consequently, shoreline change rates tend to have high 

uncertainty, resulting in many rates that are not statistically 

significant. For this study, an insignificant rate was defined as 

a rate that is indistinguishable from a rate of 0 m/yr; in other 

words, the calculated ± rate uncertainty overlaps 0 m/yr. Rates 

that are statistically insignificant still provide coastal managers with a most likely scenario of shoreline change—valuable 

information for assessing the risk of future shoreline erosion. 

Reducing the uncertainty in shoreline change rates using 

improved statistical methods will assist coastal managers in 

making more informed, science-based decisions when planning for future erosion hazards.

Regionally averaged shoreline change rates are the 

average of rates from all transects in a coastal region. The 

95-percent confidence interval on the linear regression at each 

transect is assumed to be random and independent. Therefore, 

the uncertainty of an average rate (Uavg) can be calculated as 

the root sum of squares of rate uncertainties (Ui) at all transects divided by n:

U

n avg

Ui i

n

= ∑ =

2

1 (2)

The resulting average rate and uncertainty are often 

small relative to rates from individual transects. The greater 

the number of transects over which the uncertainty is averaged, the smaller the uncertainty of the average rate. To avoid 

reporting statistically significant average rates as indicating no 

change or having zero uncertainty, average rates were reported 

at higher precision (centimeters per year, 0.00 m/yr) than rates 

from individual transects (decimeters per year, 0.0 m/yr).

Historical Shoreline Change Analysis

Kauai

Kauai, is the northernmost populated island in the state. 

Kauai is more than 5 million years old and has a roughly circular shape as a result of at least one, and perhaps two, shield 

volcanoes. More than 1.5 million years after the primary 

shield-building stage had ceased, rejuvenated volcanism (the 

Figure 14. Calculation of shoreline change rate from a time series of shoreline positions using the single-transect method. The slope 

of the line is the annual shoreline change rate. (See figure 13 for explanation of photograph)

1920 1940 1960 1980 2000

−50

0

50

Year

Shoreline position,

in meters

2010

Rate = −0.4 ± 0.1 meters per year

Shoreline position with 

95-percent confidence interval

Regression line

EXPLANATION
Historical Shoreline Change Analysis 21

Koloa Volcanic Series) began resurfacing two thirds of the 

eastern side of the island. Kauai has approximately 75 km of 

sandy beach that is separated into four regions: north, east, 

south, and west (fig. 15). 

From 3 to 11 historical shorelines with dates ranging 

from 1926 to 2008 are available for Kauai (table 4). The 1927 

shoreline is derived from a T-sheet and the 1930 shoreline is 

from a hydrographic chart. All other shorelines are derived 

from vertical aerial photographs. 

Erosion is the general long-term trend of Kauai beaches 

(table 5). During the analysis period, 6.1 km or 8 percent of 

the total extent of Kauai beaches was lost to erosion. The 

average of long-term rates for all Kauai transects is -0.11 

± 0.01 m/yr and 71 percent of transects indicate a trend of 

erosion. The short-term average rate for Kauai suggests 

stable or accreting beaches at 0.02 ± 0.02 m/yr. However, 

the majority (57 percent) of transects still indicate a trend of 

erosion in the short term. Overall reduced erosion in the short 

term for Kauai beaches is due largely to a change in average 

rates along West Kauai from erosion in the long term to 

accretion in the short term. The minimum and maximum longterm shoreline change rates on Kauai are measured near Koki 

Point in South Kauai (erosion, -1.5 ± 0.4 m/yr) and at Major’s 

Bay in West Kauai (accretion, 1.6 ± 1.8 m/yr) (table 6). The 

maximum short-term change rates are measured at Lawai 

Bay in South Kauai (erosion, -1.7 ± 9.9 m/yr) and at Polihale 

in West Kauai (accretion, 2.8 ± 6.2 m/yr). The rate at Lawai 

is associated with a high degree of uncertainty because the 

beach was lost to erosion and a truncated data set was used to 

calculate the rate up to the time the beach disappeared. The 

rate at Polihale is associated with a high degree of uncertainty 

as a result of seasonal variability. 

Figure 15. Four regions of Kauai: north, east, south, and west.

South 

West 

North

East

Kauai

N

21°

45'

N

22°

00'

159°45' W 159°30' 159°15'

Hawaiian

Islands

22 °

N

20 °

160 °W 158 ° 156 °

Kauai

Oahu

Maui

0 100 MILES

0 100 KILOMETERS

Pacific Ocean

Pacific Ocean

Base from National Elevation Dataset

(1/3 arc-second grid, NAD83),

U.S. Geological Survey, 2009. 0 2.5 5 MILES

0 2.5 5 KILOMETERS
22 National Assessment of Shoreline Change: Historical Shoreline Change in the Hawaiian Islands

Table 4. Number and range in years of historical shorelines for long- and short-term shoreline change 

analysis on Kauai.

Region

Shoreline change

Long-term Short-term

Number of shorelines1 Range in years1 Number of shorelines1 Range in years1

North 4–11 1927–2008 3–10 1950–2008

East 3–9 1927–2008 3–8 1950–2008

South 3–8 1926–2008 3–7 1950–2008

West 3–9 1926–2006 3–8 1950–2006

1

Number of shorelines and range in years vary in each region.

Table 5. Shoreline change trends for Kauai, Oahu, and Maui.

[km, kilometers; m/yr, meters per year; LT, long-term; ST, short-term]

Region Number of 

transects

Beach loss 

(km)

Beach loss 

(percent)

Average rate (m/yr) Percent eroding Percent accreting

LT ST LT ST LT ST

Kauai

North 1,104 1.7 8 -0.11 ± 0.02 -0.06 ± 0.02 76 60 23 38

East 867 1.0 6 -0.15 ± 0.02 -0.06 ± 0.02 78 63 19 33

South 790 1.9 14 -0.01 ± 0.02 0.05 ± 0.04 63 57 34 39

West 962 1.5 7 -0.13 ± 0.04 0.16 ± 0.08 64 48 33 49

Total 3,723 6.1 8 -0.11 ± 0.01 0.02 ± 0.02 71 57 27 40

Oahu

North 1,287 0.2 1 -0.11 ± 0.01 -0.07 ± 0.01 73 68 25 30

East 2,108 5.5 13 0.01 ± 0.01 -0.01 ± 0.01 50 54 47 44

South 1,319 3.0 11 -0.04 ± 0.01 -0.03 ± 0.02 50 47 48 50

West 628 0.0 0 -0.25 ± 0.01 -0.13 ± 0.02 83 71 16 27

Total 5,342 8.7 8 -0.06 ± 0.01 -0.05 ± 0.01 60 58 38 40

Maui

North 903 0.9 6 -0.26 ± 0.02 -0.22 ± 0.03 87 74 12 16

Kihei 1,011 2.1 11 -0.13 ± 0.01 -0.12 ± 0.02 83 77 16 20

West 1,519 3.8 14 -0.15 ± 0.01 -0.13 ± 0.01 85 77 14 18

Total 3,433 6.8 11 -0.17 ± 0.01 -0.15 ± 0.01 85 76 14 18

Hawaii (all beaches studied)

Total 12,498 21.5 9 -0.11 ± 0.01 -0.06 ± 0.01 70 63 28 34
Historical Shoreline Change Analysis 23

North Kauai

The backshore of Kauai’s north coast is composed of 

rejuvenated volcanic basalt. The shoreline is characterized 

mostly by embayments and fringing reef systems. The shore 

is exposed to large North Pacific swell in winter and northeast 

trade wind waves throughout the year. The beaches tend to 

be steep and are composed of coarse-grained calcareous sand 

(Fierstein and Fletcher, 2004). 

The eastern end contains extensive fringing reef systems 

and pocket beaches between volcanic headlands. The beach at 

Hanalei Bay, the largest bay on Kauai, is composed of a mix 

of calcareous and terrigenous sand. The Na Pali cliffs are west 

of Haena and contain intermittent calcareous pocket beaches 

(Fierstein and Fletcher, 2004). The beaches of the Na Pali 

region were not analyzed in this study.

The North region of Kauai is composed of three subregions (fig. 16). There are from 4 to 11 shorelines, with dates 

ranging from 1927 to 2008 (table 4). For the 1,104 transects, 

13 percent of short-term rates and 18 percent of long-term 

rates are statistically significant (fig. 16). Low rate significance 

on North Kauai beaches may be attributed, in part, to high 

seasonal variability (noise) from short-term erosion during 

large winter waves. 

The average long-term rate for all transects in North 

Kauai is -0.11 ± 0.02 m/yr (table 5). Seventy-six percent of 

transects are erosional in the long term and 23 percent are 

accretional. The remaining 1 percent of transects have rates 

of 0 m/yr or rates were not determined as a result of limited 

data. The maximum long-term erosion rate (-0.7 ± 0.6 m/yr) 

was found immediately west of Haena Point. Other locations 

with significant long-term erosion rates include Moloaa (up to 

-0.4 ± 0.2 m/yr) and Anini (up to -0.4 ± 0.1 m/yr). The maximum long-term accretion rate (0.7 ± 0.7 m/yr) was found near 

the middle of the 3.5-km-long crescent-shaped beach at 

Hanalei, which is accreting along most of its length. The 

Hanalei subregion is a notable exception to the predominant 

trend of erosion along North Kauai. The beach at Hanalei 

Bay is accreting at an average long-term rate of 0.11 ± 

0.03 m/yr, whereas the Kilauea and Haena subregions are 

eroding at -0.13 ± 0.03 m/yr and -0.23 ± 0.03 m/yr, respectively (table 7). 

In North Kauai, the average short-term rate (-0.06 ± 

0.02 m/yr) indicates less erosion than the average long-term 

rate. Sixty percent of transects are erosional in the short 

term—a 16-percent decrease from the long-term rate. As with 

the long-term analysis, Hanalei is the largest exception to the 

overall trend of short-term erosion along North Kauai. The 

maximum short-term erosion rate (-1.0 ± 2.6 m/yr) was found 

at a rocky outcrop at Kauapea (table 6). This section of beach 

is susceptible to seasonal changes in shoreline position, as 

indicated by the high associated uncertainty. The maximum 

accretion rate (0.8 ± 1.5 m/yr) was measured at Kahili Beach 

near Kilauea Stream mouth. This beach is also highly unstable 

as a result of seasonal fluctuations in shoreline position from 

large waves and stream flow. Higher short-term accretion rates 

Table 6. Maximum shoreline change rates on Kauai.

[m/yr, meters per year; max., maximum; ±, plus or minus]

Region Long-term rate 

(m/yr) Location1 Short-term rate (m/yr) Location1

North

Max. erosion -0.7 ± 0.6 Haena Point -1.0 ± 2.6 Kauapea, seasonal variability

Max. accretion 0.7 ± 0.7 Hanalei Bay, near middle 0.8 ± 1.5 Kahili Beach, near Kilauea Stream

East

Max. erosion -0.7 ± 0.4 Aliomanu Beach, west end -1.6 ± 0.3 Anahola, Kuaehu Point

Max. accretion 0.7 ± 0.4 Anahola Stream mouth 1.1 ± 0.6 Anahola Stream mouth

South

Max. erosion -1.5 ± 0.4 Pocket Beach near Koki Point2 -1.7 ± 9.9 Lawai Bay, east end, beach lost2

Max. accretion 1.4 ± 0.7 Waimea, east side Kikiaola Harbor 1.7 ± 0.3 Waimea, east side Kikiaola Harbor

West

Max. erosion -1.4 ± 0.2 Oomano, west side Kikiaola Harbor -1.5 ± 0.3 Oomano, west side Kikiaola Harbor

Max. accretion 1.6 ± 1.8 Majors Bay, seasonal variability2 2.8 ± 6.2 Polihale, seasonal variability3

1

Locations shown in figures 16, 17, 19, and 21.

2

Maximum erosion or accretion for Kauai.

3

Maximum erosion or accretion for all three islands (Kauai, Oahu, and Maui).
24 National Assessment of Shoreline Change: Historical Shoreline Change in the Hawaiian Islands

North Kauai

1 Moloaa

2 Kahili

3 Kauapea

4 Anini

5 Hanalei

6 Lumahai

7 Haena Point

1

2

3

4

5

6

Kilauea Subregion

1

2

3

4

5

6

Hanalei

Subregion

Haena Subregion

1

2

3

4

5

6

Pacific Ocean

7 7

7

95-percent confidence interval Rate Beach

2 MILES

2 KILOMETERS

0

0

EXPLANATION

Long-term rates,

in meters per year

200

0

400

600

800

1,000

2 1 0 -1 -2 2 1 0 -1 -2

Transect number

Short-term rates,

in meters per year

Accretion Erosion Accretion Erosion

N

Figure 16. Long-term (all available years) and short-term (1940s to present) shoreline change rates, North Kauai. 

(Location shown in figure 15)
Historical Shoreline Change Analysis 25

were found at transects 2 (0.9 ± 29.4 m/yr) and 567 (1.0 ± 

13.0 m/yr). Neither rate is reported as the maximum accretion 

rate due to low confidence in these results (high rate uncertainty) where the beach was completely lost to erosion and 

only one historical shoreline indicated a beach present (the 

remainder were rocky shoreline).

Along the North Kauai coast, short- and long-term rates 

follow similar trends (fig. 16). Predictably, the short-term rates 

are associated with a greater degree of uncertainty than the 

long-term rates (because fewer shorelines were measured for 

short-term rates). Kauapea and Lumahai have high uncertainty 

bands for both short-term and long-term trends, likely because 

of the strong seasonal influence on the data. Therefore, linear 

methods do not result in a good fit for these data. Spikes in 

short-term uncertainty values at Moloaa, and Kahili are the 

result of calculating rates from a truncated data set (few shorelines) where the beach has been completely lost to erosion. 

East Kauai

Kauai’s eastern coast is characterized by embayments 

and fringing reef systems. The shore is exposed to northeast 

trade winds. Streams and rivers flow into the embayments, 

sometimes causing coastal flooding (Fierstein and Fletcher, 

2004). The Kapaa region of this coast was once a series of 

embayments, but has been straightened as a result of sediment infilling (Moberly and Chamberlain, 1964; Fierstein and 

Fletcher, 2004). 

East Kauai is the most erosional region of Kauai, as 

indicated by average shoreline change rates and percentages 

of transects that are indicative of erosion (table 5). The East 

region consists of three subregions (fig. 17). There are from 

three to nine shorelines that range in date from 1927 to 2008 

(table 4). For the 867 transects, 34 percent of long-term rates 

and 16 percent of short-term rates are significant (fig. 17). 

The average long-term rate is -0.15 ± 0.02 m/yr, the most 

erosional rate of the four Kauai regions. Seventy-eight percent 

of transects are erosional in the long term. East Kauai has 

the lowest percentage of accreting transects (19 percent) of 

the four Kauai regions. The maximum long-term erosion 

rate (-0.7 ± 0.4 m/yr) was measured at the western end 

of Aliomanu Beach. Other areas of significant long-term 

erosion are found at Nukolii (up to -0.5 ± 0.3 m/yr) and 

north of Waipouli (up to -0.3 ± 0.2 m/yr). At Kapaa, erosion 

rates as high as -0.9 m/yr were found along a short extent 

(transects 493–500) where beach appeared intermittently 

and was ultimately lost to erosion (coastal armoring). A rate 

from this area is not reported as a regional maximum due 

to low confidence (high uncertainty) with these results. The 

maximum long-term accretion rate (0.7 ± 0.4 m/yr) was 

measured at Anahola Beach, south of Anahola River (table 6). 

This area is affected by the river discharge and is dynamic 

(Makai Ocean Engineering and Sea Engineering, 1991). All 

subregions of East Kauai are erosional in the long and short 

term (table 7). The Kapaa subregion is the most erosional of 

the three, with an average long-term rate of -0.17 ± 0.02 and 

an average short-term rate of -0.08 ± 0.02 m/yr. 

The average short-term shoreline change rate for East 

Kauai is -0.06 ± 0.02 m/yr. Sixty-three percent of the shortterm rates are erosional, the highest percentage for the four 

Kauai regions (table 5). East Kauai has the lowest percentage 

of accretional rates in the short term (33 percent) among the 

four Kauai regions. The maximum short-term erosion rate 

(-1.6 ± 0.3 m/yr) was measured in Anahola, north of Kuaehu 

Point (table 6), adjacent to a stone revetment. The maximum 

short-term accretion rate (1.1 ± 0.6 m/yr) was measured at the 

same location as the maximum long-term accretion rate (south 

of Anahola River).

Along the coast, long-term and short-term rates followed 

similar trends to each other (fig. 17). The long- and short-term 

confidence bands for Lae Lipoa are relatively wide because 

rates were calculated from only three to four shorelines. 

South Kauai

Kauai’s southern coast is exposed to Kona storm waves, 

trade wind waves, and southern swell. Longshore currents 

transport sediment westward from the mouths of large rivers (for example, Hanapepe Stream) (Fierstein and Fletcher, 

2004). Hurricane Iwa (1982) and Hurricane Iniki (1992) devastated this area, which was inundated as far as 300 m inland 

at Poipu (Fletcher and others, 2002). 

The Waimea subregion lacks a shallow near-shore 

reef and has a wide, steep beach with a high proportion 

Table 7. Average shoreline change rates for Kauai subregions.

[m/yr, meters per year; ±, plus or minus]

Region Subregion Number of 

transects

Average rate (m/yr)

Long-term Short-term

North

Kilauea 546 -0.13 ± 0.03 -0.09 ± 0.04

Hanalei 212 0.11 ± 0.03 0.10 ± 0.03

Haena 346 -0.23 ± 0.03 -0.12 ± 0.03

East

Lihue 267 -0.15 ± 0.02 -0.02 ± 0.03

Kapaa 315 -0.17 ± 0.02 -0.08 ± 0.02

Anahola 285 -0.13 ± 0.04 -0.07 ± 0.05

South

Waimea 128 0.74 ± 0.05 0.95 ± 0.04

Hanapepe 360 -0.16 ± 0.03 -0.15 ± 0.04

Poipu 123 -0.15 ± 0.04 -0.12 ± 0.05

Mahaulepu 179 -0.15 ± 0.03 -0.08 ± 0.13

West

Polihale 272 -0.14 ± 0.07 0.37 ± 0.11

Barking Sands 585 -0.04 ± 0.06 0.18 ± 0.11

Oomano 105 -0.64 ± 0.03 -0.44 ± 0.02
26 National Assessment of Shoreline Change: Historical Shoreline Change in the Hawaiian Islands

East Kauai

1 Nukolii

2 Waipouli

3 Kapaa

4 Lae Lipoa

5 Anahola

6 Kuaehu Point

7 Aliomanu

1

2

3

4

5

Lihue Subregion

1

2

3

4

Anahola Subregion

1

4

Kapaa Subregion

5 5

6

7 6

7

6

7

2

3

Pacific

Ocean

95-percent confidence interval Rate Beach

EXPLANATION

0 2 MILES

0 2 KILOMETERS

N

0

100

200

300

400

500

600

700

800

1 0 -1 1 0 -1

Transect number

Long-term rates,

in meters per year

Short-term rates,

in meters per year

Accretion Erosion Accretion Erosion

Figure 17. Long-term (all available years) and short-term (1940s to present) shoreline change rates, East Kauai. 

(Location shown in figure 15)
Historical Shoreline Change Analysis 27

of terrigenous sediment (relative to typical calcareous 

Hawaiian beaches) from the Waimea River. The west end 

of the Hanapepe subregion is composed of narrow, gently 

sloping, calcareous beach. The remainder of the Hanapepe 

and the Poipu subregions is composed of rejuvenated volcanic 

basalt with calcareous pocket beaches and fringing reef. The 

Mahaulepu subregion contains lithified sand dunes (fig. 18) 

(Makai Ocean Engineering and Sea Engineering, 1991; 

Fierstein and Fletcher, 2004).

Summary statistics for South Kauai conflict in that average long- and short-term rates indicate approximately stable 

to accreting shorelines, whereas percentages of erosional and 

accretional transects indicate a predominance of erosion. The 

South region is made up of four subregions (fig. 19). From 

three to eight shorelines, ranging in date from 1926 to 2007, 

are available for the South region of Kauai (table 4). For the 

790 transects, 28 percent of the short-term rates and 32 percent 

of the long-term rates are significant (fig. 19).

The average long-term shoreline change rate for South 

Kauai is approximately stable at -0.01 ± 0.02 m/yr (table 5). 

Sixty-three percent of transects are erosional in the long term. 

The maximum long-term erosion rate (-1.5 ± 0.4 m/yr) was 

found at a small pocket beach north of Koki Point (table 6) 

where most of the remaining beach is now perched on a rock 

bench or has disappeared. Other locations with significant 

long-term erosion rates include Salt Pond (up to -0.8 ± 

0.5 m/yr), Poipu (up to -0.3 ± 0.1), Shipwreck (up to -0.7 ± 

0.4 m/yr), and Mahaulepu (up to -0.5 ± 0.4). The maximum 

long-term accretion rate (1.4 ± 0.7 m/yr) was measured 

at Waimea, east of Kikiaola Harbor (table 6, fig. 19). The 

beach on the western side of the harbor (Oomano) showed 

the highest erosion rate in the West Kauai region (see West 

Kauai, fig. 21). The harbor, built in 1959, disrupts alongshore 

transport of sand and acts as a groin, impounding sand on the 

Waimea (eastern) side and preventing sand from nourishing 

the beach at Oomano (Makai Ocean Engineering and Sea 

Engineering, 1991).

Unlike the long-term average shoreline change rate, the 

short-term rate of 0.05 ± 0.04 m/yr suggests an overall trend 

of accretion along South Kauai (table 5). However, the beach 

is erosional at 57 percent of transects in the short term, suggesting an overall trend of erosion. The maximum short-term 

erosion rate (-1.7 ± 9.9 m/yr) was found at the end of a pocket 

beach in Lawai Bay (table 6, fig. 19), where an overall trend 

of erosion in the bay has resulted in loss of the beach at the 

eastern end of the bay prior to 1984. The high degree of uncertainty associated with this rate is a result of using truncated 

data (three shorelines) to calculate a rate in an area of beach 

loss. The maximum short-term accretion rate (1.7 ± 0.3 m/yr) 

was measured at the same position as the maximum long-term 

rate (Waimea—east of Kikiaola Small Boat Harbor). Longterm and short-term rates follow similar trends along the South 

Kauai coast (fig. 19), though, rates are less erosive in the short 

term as indicated by average rates and percentages of eroding 

and accreting transects (table 5).

Figure 18. Eolianite headland 

(lithified carbonate sand dunes), 

Mahaulepu, South Kauai. (Location 

shown in figure 19) (Photograph by 

Hawaii Aviation, Inc.)
28 National Assessment of Shoreline Change: Historical Shoreline Change in the Hawaiian Islands

Figure 19. Long-term (all available years) and short-term (1940s to present) shoreline change rates, South Kauai. (Location 

shown in figure 15)

N

0

100

200

300

400

500

600

700

2 1 0 -1 -2 2 1 0 -1 -2

Transect number

Long-term rates,

in meters per year

Short-term rates,

in meters per year

Accretion Erosion Accretion Erosion

South Kauai

1 Kikaola Small 

 Boat Harbor

2 Waimea

3 Koki Point

4 Salt Pond

5 Lawai

6 Poipu

7 Shipwreck

8 Mahaulepu Bay

3

4

5

6

Hanapepe Subregion

5

Poipu

6

Subregion

Mahaulepu Subregion

3

4

5

6

Waimea

Subregion

3

4

7

8

Pacific Ocean

7 7

8 8

1

2

1 1

2 2

95-percent confidence interval Rate Beach

0 2 MILES

0 2 KILOMETERS

EXPLANATION
Historical Shoreline Change Analysis 29

West Kauai

Kauai’s western coast is located on the Mana coastal 

plain, and is characterized by gently sloping beaches. The 

Mana Plain extends 5 km inland and is the product of 

converging longshore sediment transport from the north and 

southeast. The sediment transport from the north is driven by 

North Pacific swell and trade winds in winter; the transport 

from the southeast is driven by summer southern swell and 

trade winds (Moberly, 1968). The shoreline is composed of 

calcareous sand with outcrops of beach rock. Most of the 

beaches in this area are wide and backed by an extensive sand 

dune system (fig. 20).

As a whole, West Kauai is erosional in the long term 

and accretional in the short term (table 5). The West region is 

divided into three subregions (fig. 21). Shoreline change analysis for West Kauai was based on from three to nine shorelines 

ranging from 1926 to 2006 (table 4). Only 12 and 13 percent 

of transects indicate significant rates in the long term and short 

term, respectively (fig. 21). Rates are significant for only a few 

isolated transects outside the Oomano subregion. West Kauai 

is exposed to refracted swells from the north in winter and 

from the south in summer. The seasonal shift in predominant 

wave direction results in high seasonal variability in shoreline 

position (noise), which is likely responsible for the low percentage of significant rates along West Kauai. 

The average long-term rate in this region is erosional at 

-0.13 ± 0.04 m/yr, and 64 percent of transects are erosional 

in the long term (table 5). Average long-term rates in all 

subregions are erosional (table 7). The Oomano subregion 

is the most erosional, with an average rate of -0.64 ± 

0.03 m/yr. The maximum long-term erosion rate (-1.4 ± 

0.2 m/yr) was measured at Oomano, just west of Kikiaola 

Small Boat Harbor (table 6, fig. 21). As discussed in the 

section on the South Kauai region, the harbor blocks sediment 

transport from Waimea to the east that otherwise would 

nourish Oomano Beach. The maximum accretion rate (1.6 ± 

1.8 m/yr) was found in Majors Bay at the shorefront of the 

Pacific Missile Range. This segment of beach experiences 

large seasonal fluctuations in shoreline position, resulting in 

high rate uncertainty. 

In contrast to long-term shoreline change analysis, 

short-term analysis at West Kauai indicates an overall trend 

of accretion. The average of all short-term rates is accretional 

at 0.16 ± 0.08 m/yr (table 5). Roughly the same percentage of 

transects is accretional (49 percent) as erosional (48 percent). 

The maximum short-term erosion rate (-1.5 ± 0.3 m/yr) was 

measured at the same transect as the maximum long-term 

Figure 20. Dunes at the west end 

of the Mana coastal plain, West 

Kauai. (Location shown in figure 21) 

(Photograph by Hawaii Aviation, Inc.)
30 National Assessment of Shoreline Change: Historical Shoreline Change in the Hawaiian Islands

Figure 21. Long-term (all available years) and short-term (1940s to present) shoreline change rates, West Kauai. (Location 

shown in figure 15)

0 2 MILES

0 2 KILOMETERS

EXPLANATION

Transect number

N

0

100

200

300

400

500

600

700

800

900

2 0 -2 2 0 -2

Long-term rates,

in meters per year

Short-term rates,

in meters per year

Accretion Erosion Accretion Erosion

West Kauai

1 Polihale

2 Majors Bay

3 Oomano

4 Kikialoa Small 

 Boat Harbor

1

3

2

Polihale Subregion

1

2

1

2

3 3

Pacific

Ocean

Mana Coastal Plain

Barking sands Subregion Oomano

Subregion

4

4 4

95-percent confidence interval Rate Beach
Historical Shoreline Change Analysis 31

erosion rate (Oomano, just west of the harbor). The maximum 

short-term accretion rate (2.8 ± 6.2 m/yr) was measured at the 

northern end of Polihale (table 6), which is exposed to the full 

energy of large winter waves, resulting in seasonal fluctuations 

in shoreline position.

The alongshore pattern of variability of short-term shoreline change rates is similar to the pattern of long-term rates 

throughout most of West Kauai, with the exception of 

the north half of the Polihale subregion (fig. 21). However, 

the three subregions are significantly less erosional between 

the long term and short-term rates (table 7). The Polihale 

subregion is erosional in the long term with an average rate 

-0.14 ± 0.07 m/yr but accretional in the short term at 0.37 ± 

0.11 m/yr. Similarly, Barking Sands is stable to erosional 

in the long term with an average rate -0.04 ± 0.06 m/yr but 

accretional in the short term at 0.18 ± 0.11 m/yr. Oomano is 

significantly erosional in the long and short-term shoreline 

change. Though, the average rate is somewhat reduced in 

the short term compared to the long term (-0.44 ± 0.02 m/yr 

compared to -0.64 ± 0.03 m/yr). Other than those at Oomano, 

few rates at individual transects along West Kauai are significant due to high short-term (seasonal to decadal) variability in 

shoreline position.

Oahu

Oahu is the third largest and most populated island of the 

Hawaiian chain. Oahu is made up of eroded remnants of two 

shield volcanoes (Waianae Range and Koolau Range, fig. 22) 

separated by the central Schofield Plateau (Macdonald and 

others, 1986). Explosive eruptions from the Honolulu 

Volcanic Series created several of the headlands on the 

southern-southeastern side of the island, including Diamond 

Head, Koko Head, and Mokapu Point. Emerged carbonate 

reefs formed under higher sea levels in the late Pleistocene 

Epoch compose many of the smaller headlands and underlie 

much of the coastal plain around the island. Oahu has 

approximately 107 km of sandy beach that is separated into 

four regions: north, east, south, and west.

West 

South 

North

Oahu

East

Kaena

Point

Barbers

Point

Makapuu

Point

N

Koolau Range

Waianae Range

21°

45'

N

21°

30'

21°

15'

158°15' W 158°00' 157°45'

Hawaiian

22 ° Islands N

20 °

160 °W 158 ° 156 °

Kauai

Oahu

Maui

0 100 MILES

0 100 KILOMETERS

Pacific Ocean

Pacific Ocean

Kahuku

Point

Base from National Elevation Dataset

(1/3 arc-second grid, NAD83),

U.S. Geological Survey, 2009. 0 2.5 5 MILES

0 2.5 5 KILOMETERS

Figure 22. Four regions of Oahu: north, east, south, and west.
32 National Assessment of Shoreline Change: Historical Shoreline Change in the Hawaiian Islands

A maximum of 12 high-quality historical shorelines, 

ranging from 1910 to 2007, are available for Oahu (table 8). 

The earliest shoreline is derived from a 1910 or 1927 T-sheet 

or 1928 aerial photograph. A 1932–33 shoreline from a T-sheet 

is also included for some study areas. All other shorelines are 

derived from vertical aerial photographs taken from 1928 

to 2007. 

Erosion is the general long- and short-term trend of Oahu 

beaches (table 5). Approximately 9 km or 8 percent of the total 

length of beach analyzed was completely lost to erosion in 

the analysis period. The average of long-term rates for Oahu 

is erosional at -0.06 ± 0.01 m/yr. The average short-term rate 

is roughly the same as the long-term average rate at -0.05 ± 

0.01 m/yr (table 5). Erosion is occurring in the long and 

short term at the majority of transects (60 and 58 percent, 

respectively). The maximum long- and short-term erosion 

rates on Oahu were found at Kualoa Point in East Oahu 

(-1.8 ± 0.3 and -1.9 ± 0.9 m/yr, respectively; table 9). The 

maximum long- and short-term accretion rates were found 

at Pokai Bay in West Oahu (1.7 ± 0.6 m/yr). The longand short-term rates at Pokai are equal because they were 

calculated using a truncated data set (1967–2007) following 

the construction of harbor breakwalls. The long-term rates at 

Kualoa and Pokai are the highest in the three islands. 

Table 8. Number and range in years of historical shorelines for long- and short-term shoreline change 

analysis on Oahu.

Region

Shoreline change

Long-term Short-term

Number of shorelines1 Range in years1 Number of shorelines1 Range in years1

North 5–11 1910–2007 5–8 1949–2007

East 4–12 1910–2006 3–10 1949–2006

South 3–10 1927–2005 3–9 1949–2005

West 6–12 1910–2007 5–9 1949–2007

1

Number of shorelines and range in years vary in each region.

Table 9. Maximum shoreline change rates on Oahu.

[m/yr, meters per year; max., maximum; ±, plus or minus]

Region Long-term rate 

(m/yr) Location1 Short-term rate (m/yr) Location1

North

Max. erosion -1.3 ± 0.8 Haleiwa Beach Park, beach lost -1.3 ± 0.8 Haleiwa Beach Park, beach lost

Max. accretion 0.8 ± 0.8 Rocky Point, high seasonal change 1.1 ± 0.9 Rocky Point, high seasonal change

East

Max. erosion -1.8 ± 0.3 Kualoa Point2 -1.9 ± 0.9 Kualoa Point3

Max. accretion 1.5 ± 0.4 Kaneohe Bay, west of Kualoa Point 1.3 ± 1.8 Kaneohe Bay, west of Kualoa Point

South

Max. erosion -1.6 ± 2.7 West side Natatorium, beach lost -1.6 ± 2.7 West side Natatorium, beach lost

Max. accretion 0.8 ± 0.2 Kaimana, south side Natatorium 0.9 ± 0.3 Kaimana, east side Natatorium

West

Max. erosion -1.2 ± 0.5 Maili, sand mining -1.0 ± 0.3 Yokohama, sand mining

Max. accretion 1.7 ± 0.6 Pokai Bay, north of harbor breakwall2 1.7 ± 0.6 Pokai Bay, north of harbor breakwall3

1

Locations shown in figures 24, 26, 29, and 30.

2

Maximum erosion or accretion for all three islands (Kauai, Oahu, and Maui).

3

Maximum erosion or accretion for Oahu.
Historical Shoreline Change Analysis 33

Figure 23. Limestone headlands at Kahuku Point and Kuilima 

(Turtle Bay), North Oahu. (Locations shown in figure 24) 

(Photograph by Andrew D. Short, University of Sydney)

North Oahu

Oahu’s north shore is seasonally dynamic. This region is 

exposed to the strong winter North Pacific swell that causes 

steepening of the foreshore and narrowing of the beaches. 

During relatively calm summer conditions, the beaches are flat 

and wide (Hwang, 1981). A fringing reef of variable width and 

depth is present offshore. The coastal plain is variable in width 

and is composed largely of fossiliferous limestone and unconsolidated sand. Outcrops of calcareous eolianite and reefrock 

form many of the short headlands in this region, including 

those at Puaena Point, Sharks Cove, Kawela Bay, Kuilima 

(Turtle Bay), and Kahuku Point (fig. 23). 

The North region is divided into two subregions: Sunset 

and Mokuleia (fig. 24). The Sunset subregion extends from 

Kahuku Point at the northern tip of the island to Haleiwa. A 

continuous 6-km-long beach extends from Waialee to Ke Iki. 

The remainder of the beaches in the Sunset subregion are in 

pockets between rocky headlands. The Mokuleia subregion 

is between Kaiaka Bay and Camp Erdman. Mokuleia Beach 

is a continuous 12-km-long beach extending from Waialua to 

Camp Erdman. 

Twenty-four percent of the short-term rates and 31 percent of the long-term rates at the 1,287 transects along North 

Oahu are significant—the lowest percentages in the four Oahu 

regions (fig. 24). The percentage of rates in this region that is 

significant is low as a result of high seasonal variability (noise) 

in shoreline position. Large winter swells cause variations 

in beach width by up to two thirds. The rates at some North 

Oahu beaches are also unreliable as a result of poor seasonal 

distribution of the available aerial photographs. For example, 

along much of the Sunset subregion the most recent historical 

shorelines (1996 and 2005) are from summer months, whereas 

earlier air photo shorelines are from winter or spring months. 

The overall trend of North Oahu beaches is erosion (table 5). 

The average long- and short-term rates on the northern shore 

are erosional at -0.11 ± 0.01 and -0.07 ± 0.01 m/yr, respectively. Seventy-three percent of the total extent of North Oahu 

beaches is eroding in the long term and 68 percent is eroding 

in the short term. The two subregions of North Oahu (Sunset 

and Mokuleia) have an overall trend of long- and short-term 

erosion, as indicated by average rates (table 10). 

The maximum long-term erosion rate (-1.3 ± 

0.8 m/yr, table 9) was found at Haleiwa Beach Park at a 

segment of shoreline behind a small breakwater where the 

beach has been lost. This beach has undergone substantial 

modification throughout its history, including construction of 

a groin, breakwater, and sea wall and two beach nourishment 

projects (Hwang, 1981; Sea Engineering, Inc., 1988). Other 

areas with significant erosion rates include Kuilima (up to 

-0.4 ± 0.2 m/yr), Waimea (up to -0.8 ± 0.4 m/yr, as a result 

of sand mining), and Mokuleia (up to -0.6 ± 0.1 m/yr). The 

maximum long-term accretion rate (0.8 ± 0.8 m/yr) was 

measured at Rocky Point in the Sunset subregion, though 

this rate is likely affected by seasonal variability and/or bias 

toward two summer shorelines at the end of the analysis 

period. The only notable exception to the overall trend of 

erosion along Mokuleia Beach was found at an accreting cusp 

along the beach at Waialua with rates up to 0.8 ± 0.2 m/yr. 

The maximum and minimum short-term change rates 

were found at the same locations as the long-term maximum 

and minimum. Long- and short-term rates follow similar 

trends, with increasing uncertainty in the short-term rates as 

a result of a shortened data set (fewer shorelines) and high 

seasonal variability (fig. 24). 

East Oahu

Oahu’s eastern coast faces into the predominant easterly 

trade winds. As a result, the shoreline is exposed to shortperiod trade wind waves year round. Large refracted North 

Pacific swells also affect this coast on occasion in winter. The 

coast is mostly a low-lying plain and is moderately to highly 

developed, with the densest development in the southeast, 

around Kailua and Lanikai (fig. 25). 

Shallow fringing reef that lines much of East Oahu 

protects the shoreline from the full energy of large waves. 

However, beaches that back shallow protective reefs are typically low and narrow and are prone to inundation during large 

waves and storms. Even low rates of chronic erosion have led 

to beach loss along portions of these narrow beaches. Seawalls 

have been constructed along much of the coast to protect 

homes and the coastal highway, and contribute to beach loss in 

many areas. East Oahu is divided into two subregions, Northeast and Southeast, separated by Kaneohe Bay. The back-bay 

shoreline of Kaneohe Bay was not included in this study.
34 National Assessment of Shoreline Change: Historical Shoreline Change in the Hawaiian Islands

Figure 24. Long-term (all available years) and short-term (1940s to present) shoreline change rates, North Oahu. 

(Location shown in figure 22)

0 2 MILES

0 2 KILOMETERS

EXPLANATION

0

200

400

600

800

1,000

1,200

1 0 -1 1 0 -1

Long-term rates,

in meters per year

Transect number

Short-term rates,

in meters per year

Accretion Erosion Accretion Erosion

N

North Oahu

1 Kahuku Point

2 Kuilima

3 Turtle Bay

4 Kawela Bay

5 Waialee

6 Rocky Point

7 Ke Iki

8 Sharks Cove

9 Waimea Bay

10 Puaena Point

11 Haleiwa

12 Kaiaka Bay

13 Waialua

14 Mokuleia

15 Camp Erdman

2

Sunset Subregion

Pacific

Ocean

Mokuleia Subregion

3

4

5

6

7

8

9

10 11

12

13

14

15

2,3

4

5

6

7 8

9

10

11

12

13

14

2,3

4

5

6

7 8

9

10

11

12

13

14

15 15

1

1 1

95-percent confidence interval Rate Beach
Historical Shoreline Change Analysis 35

Overall, the beaches of East Oahu are approximately 

stable to slightly erosional as indicated by average long- and 

short-term rates and percentages of transects indicating erosion 

or accretion. East Oahu beaches have from 5 to 12 shorelines 

with a date range from 1910 to 2006 (table 8). Statistically 

significant shoreline change rates are found at 35 percent of 

the East Oahu transects in the long-term rates and 24 percent 

of the transects in the short-term rates (fig. 26). 

The average long-term rate for East Oahu beaches 

is roughly stable at 0.01 ± 0.01 m/yr (table 5). Erosion is 

occurring at 50 percent of transects and accretion is occurring 

at 47 percent. The maximum and minimum erosion rates were 

found within a few hundred meters of each other at Kualoa 

at the northern end of Kaneohe Bay (table 9). The shoreline 

at Kualoa Point has retreated more than 100 m since 1928, 

with rates as high -1.8 ± 0.3 m/yr. Eroded sand is transported 

around Kualoa Point to the west, where it is deposited inside 

the bay, forming a spit that is accreting at 1.5 ± 0.4 m/yr—the 

maximum long-term accretion rate in the East Oahu region. 

Other locations with significant erosion rates include Kahuku 

Beach (up to -1.2 ± 0.6 m/yr, as a result of sand mining, 

fig. 27), Laniloa (up to -0.7 ± 0.2 m/yr), Hauula (up to -0.3 ± 

0.1 m/yr), Makalii Point (up to -0.3 ± 0.2 m/yr, beach lost to 

erosion), Kaaawa (up to -0.3 ± 0.1 m/yr), and Bellows (up to 

-0.6 ± 0.3 m/yr). 

Some of the longest extents of accreting shoreline in 

Hawaii were found along East Oahu. Areas of significant 

accretion in East Oahu include Laie (up to 0.4 ± 0.2 m/yr), 

Kahana (up to 0.7 ± 0.3 m/yr), Mokapu (up to 0.6 ± 

0.5 m/yr), and Kailua (up to 0.7 ± 0.2 m/yr). The beach at 

central Lanikai is accreting at up to 0.8 ± 0.3 m/yr; however, 

the beach along the adjacent shoreline to the north and south 

has been lost to erosion (seawalls) in the last few decades. 

Most of the accretion along East Oahu is concentrated in the 

Southeast subregion. The average long- and short-term rates 

for Northeast Oahu are erosional (-0.07 ± 0.01 and -0.09 ± 

0.02 m/yr, respectively), whereas the average long- and shortterm rates for Southeast Oahu are accretional (0.12 ± 0.01 and 

0.09 ± 0.02 m/yr, respectively) (table 10). 

The short-term rates follow trends similar to those of 

the long-term rates (fig. 26). Like the average long-term rate, 

the average short-term rate is approximately stable at -0.01 ± 

0.01 m/yr. However, more transects are erosional in the short 

term than in the long-term rates, with erosion occurring at 

54 percent of transects and accretion occurring at 44 percent 

(table 5). The maximum short-term erosion and accretion 

rates were also found at Kualoa (-1.9 ± 0.9 and 1.3 ± 1.8 m/yr, 

respectively; table 9). 

South Oahu

Oahu’s southern shore is heavily developed on a predominantly low-lying coast, with much of the shoreline lined 

with hardened structures such as seawalls, revetments, and 

groins. This shore is exposed to strong trade winds that tend to 

blow alongshore, and southerly waves from the South Pacific 

and occasional Kona storms. Tsunamis and hurricanes pose a 

potential threat to the low-lying coastal plain and dense urban 

development (Fletcher and others, 2002). With the exception 

of Diamond Head and Koko Head, the coast is gently sloping 

with a wide, shallow fringing reef. 

Table 10. Average shoreline change rates for Oahu subregions.

[m/yr, meters per year; ±, plus or minus]

Region Subregion Number of 

transects

Average rate (m/yr)

Long-term Short-term

North

Sunset 673 -0.10 ± 0.02 -0.04 ± 0.02

Mokuleia 614 -0.12 ± 0.01 -0.11 ± 0.01

East

Northeast 1,245 -0.07 ± 0.01 -0.09 ± 0.02

Southeast 863 0.12 ± 0.01 0.09 ± 0.02

South

Ewa 499 -0.06 ± 0.01 -0.03 ± 0.01

Honolulu 376 -0.05 ± 0.02 -0.05 ± 0.02

Maunalua 394 -0.02 ± 0.02 -0.01 ± 0.05

Kaiwi 50 -0.02 ± 0.03 -0.06 ± 0.04

West

Makua 174 -0.28 ± 0.03 -0.08 ± 0.06

Waianae 264 -0.25 ± 0.02 -0.09 ± 0.02

Nanakuli 190 -0.21 ± 0.02 -0.24 ± 0.02

Figure 25. Lanikai (foreground) and Kailua Beaches, East Oahu. 

(Location shown in figure 26) (Photograph by Andrew D. Short, 

University of Sydney)
36 National Assessment of Shoreline Change: Historical Shoreline Change in the Hawaiian Islands

0 4 MILES

0 4 KILOMETERS

EXPLANATION

1245

1246

N

0

200

400

600

800

1,000

1,200

1,400

1,600

1,800

2,000

−1 0 1 −1 0 1

Long-term rates,

in meters per year

Short-term rates,

in meters per year

Accretion Erosion

Transect number

Accretion Erosion

95-percent confidence interval Rate Beach

East Oahu

1 Kahuku

2 Laie

3 Laniloa

4 Hauula

5 Makalii Point

6 Kahana

7 Kaaawa

8 Kualoa

9 Mokapu

10 Kailua

11 Lanikai

12 Bellows 

3

2

1

Kaneohe

Bay

Pacific Ocean

4

5

6

7

8

9

10

11

12

3

2

1

4

5

6

7

8

9

10

11

12

1

2

3

4

6

5

7

8

9

10

11

12

Northeast Subregion Northeast Subregion

Figure 26. Long-term (all available years) and short-term (1940s to present) shoreline 

change rates, East Oahu. (Location shown in figure 22)
Historical Shoreline Change Analysis 37

Waikiki is the hub of Hawaii’s tourist economy and the 

health of its beaches is critical to the state economy (Miller 

and Fletcher, 2003) (fig. 28). Waikiki was originally a wetland with a narrow strip of sandy beach. Development in this 

region started in the late 1800s, and the construction of a canal 

was proposed to divert streams from Waikiki, facilitating 

additional development. As development increased in the early 

20th century, beach erosion became an increasing problem. 

Seawalls and groins were constructed and beach nourishment 

projects were pursued to maintain a healthy beach. Beach 

nourishment has continued into the 21st century, with the 

most recent nourishment project occurring in early 2012 

(24,000 square yards). There are four subregions along South 

Oahu: Ewa, Honolulu, Maunalua, and Kaiwi. 

From 3 to 10 shorelines from 1927 to 2005 are available for analysis of South Oahu beaches (table 8). At the 

1,319 transects, 36 percent of long-term rates and 34 percent 

of short-term rates are significant (fig. 29). The modern shoreline from Sand Island to Diamond Head (Honolulu subregion) 

bears little resemblance to the shoreline in its natural condition 

and is largely the result of engineering efforts (for example, 

groins, sand fill, and seawalls) intended to widen the beach 

and move it seaward (Miller and Fletcher, 2003; Wiegel, 

2008). As a result of extensive shoreline reconstruction, only 

historical shorelines for the modern configuration of artificially altered beaches were used to calculate change rates.

The average long-term shoreline change rate in the south 

(-0.04 ± 0.01 m/yr) and the percentage of eroding transects 

(50 percent) and accreting transects (48 percent) indicate 

a slight overall prevalence of erosion (table 5). The Ewa 

subregion is the most erosional section of South Oahu, with 

an average long-term rate of -0.06 ± 0.01 m/yr (table 10). The 

Honolulu subregion is also eroding in the long term (-0.05 

± 0.02 m/yr). The average long-term rate for the Maunalua 

subregion is slightly erosional to stable (-0.02 ± 0.02 m/yr). 

The maximum long-term erosion rate (-1.6 ± 2.7 m/yr) 

was found at Queens Beach, Waikiki where the shoreline is 

hardened and much of the beach disappeared prior to 1975. 

Erosion up to -1.6 ± 0.4 m/yr is also occurring at the eastern 

end of the Ewa subregion near the Pearl Harbor entrance 

channel (Keahi Point), where erosion of a sandy headland 

has forced the removal of several homes and prompted 

construction of a boulder revetment. Other areas with 

significant long-term erosion rates include Nimitz Beach (up 

to -0.3 ± 0.1 m/yr), Oneula (up to -0.3 ± 0.2 m/yr), Sand Island 

(up to -0.3 ± 0.2 m/yr), Ala Moana (up to -0.8 ± 0.3 m/yr), 

Fort DeRussy (up to -0.8 ± 0.4 m/yr), and Kahala (-0.8 ± 

0.7 m/yr, beach lost). The maximum long-term accretion rate 

(0.8 ± 0.2 m/yr) was found at Kaimana Beach in Waikiki, on 

the eastern side of the natatorium. The natatorium walls act 

as a groin, disrupting the westerly longshore transport 

of sediment and resulting in accretion on the eastern side of 

the natatorium (Kaimana) and erosion on the western 

side (Queens).

Figure 27. The south end of Kahuku Beach, northeast 

Oahu, 1949, showing evidence of sand mining. The dunes 

were flattened, plowed into the surf, and shoveled to the 

loading machine. The beach width decreased approximately 

60 meters from 1949 to 1967. (Location shown in figure 26) 

(Photograph by R.M. Towill Corporation)

Figure 28. Engineered shoreline at Waikiki, South Oahu. 

(Location shown in figure 29) (Photograph by Andrew D. Short, 

University of Sydney)

Loader 

machine

Sand plowed to loader Flattened

dunes

N

0 100 METERS

0 400 FEET
38 National Assessment of Shoreline Change: Historical Shoreline Change in the Hawaiian Islands

0 2 MILES

0 2 KILOMETERS

EXPLANATION

N

0

200

400

600

800

1,000

1,200

−1 0 1 −1 0 1

Long-term rates,

in meters per year

Transect number

Short-term rates,

in meters per year

Accretion Erosion Accretion Erosion

95-percent confidence interval Rate Beach

South Oahu

1 Nimitz

2 Oneula

3 Keahi Point

4 Pearl Harbor

5 Sand Island

6 Ala Moana

7 Ft DeRussy

8 Waikiki

9 Queens

10 Natatorium

11 Kaimana

12 Diamond Head

13 Kahala

14 Koko Head

1

Pacific

Ocean

2

3 4

5

6

7

8 9

10

11

12

13

Ewa Subregion Honlulu Subregion Maunalua Subregion

Kaiwi

Subregion

1 1

2 2

3 3

5 5

6 6

7 7

8 8

9 9 11 11

12 12

13 13

14

14

14

Figure 29. Long-term (all available years) and short-term (1940s to present) shoreline change rates, 

South Oahu. (Location shown in figure 22)
Historical Shoreline Change Analysis 39

The average short-term rate of -0.03 ± 0.02 m/yr is 

similar to the average long-term rate. For the long-term 

rates, as for the short-term rates, the percentages of eroding 

and accreting transects are approximately equal (table 5). 

The maximum short-term erosion and accretion rates were 

measured at the same locations as the maximum long-term 

erosion and accretion rates, respectively (Kaimana and 

Queens, Waikiki). 

The long-term and short-term rates follow similar trends 

(fig. 29) along the shore and average rates and percentages of 

eroding and accreting transects are similar in the long- and 

short-term shoreline changes. Similarities between long- and 

short-term trends along South Oahu may be a result of extensive use of truncated data sets for rate calculation in areas with 

engineered shoreline (only recent shorelines used for longand short-term analysis) and limited availability of pre-WWII 

shorelines for many areas (for example, only one shoreline 

removed from the data set for short-term rate calculation). 

West Oahu

Oahu’s leeward western coast consists of sandy beach 

embayments and basaltic and limestone headlands. The 

shore is exposed to refracted North Pacific swells in winter 

and southerly swells in summer. Easterly trade winds blow 

offshore along most of this coastline. Southerly Kona storm 

winds blow onshore and can cause temporary beach erosion. 

Shoreline position is highly variable at many beaches in this 

region, as sand shifts alongshore with alternating wave direction between the North Pacific and southern swell seasons. 

There is a moderate risk of coastal flooding from large winter 

waves and when tropical storms pass near this region (Fletcher 

and others, 2002).

Most of the coast is gently sloping. The coast becomes 

more rocky and narrow near Kaena Point (northwestern point 

of Oahu). The shoreline is composed of carbonate sand and 

limestone rock, and beach rock is prevalent (Fletcher, 2010). 

The West region is made up of three subregions: Makua, 

Waianae, and Nanakuli. The three subregions in West Oahu 

have from 6 to 12 shorelines, with a date range from 1910 

to 2007 (table 8). Forty-six and 26 percent of the rates at 

the 628 transects are significant in the long- and short-term, 

respectively (fig. 30). 

West Oahu is the most erosional region of the island, with 

an average long-term rate of -0.25 ± 0.01 m/yr and 83 percent 

of transects indicating erosion in the long term (table 5). All 

three subregions are erosional in the long term, with average 

rates of at least -0.20 m/yr (table 10). The maximum long-term 

erosion rate (-1.2 ± 0.5 m/yr) was found in the northern part 

of Maili Beach (table 9, fig. 31) and is at least partly the result 

of removal of sand by mining operations in the mid-1900s 

(Hwang, 1981; Sea Engineering, Inc., 1988). Sand mining was 

widespread along western Oahu beaches and also likely affects 

shoreline change rates at Makua and Yokohama (Campbell 

and Moberly, 1978; Hwang, 1981). Other areas with significant erosion rates include Makua (up to -0.4 ± 0.3 m/yr, as 

a result of sand mining), Keaau (up to -1.0 ± 0.3 m/yr), 

Mauna Lahilahi (up to -0.3 ± 0.1 m/yr), Pokai (up to -0.4 ± 

0.3 m/yr), Nanakuli (up to -0.3 ± 0.1 m/yr), and Tracks (up to 

-0.5 ± 0.2 m/yr). The maximum accretion rate (1.7 ± 0.6 m/yr) 

was found in the southern part of Pokai Bay. This section of 

beach has been accreting since the construction of a breakwater in the 1950s. 

The average short-term rate of -0.13 ± 0.02 m/yr is less 

erosive than the average long-term rate (table 5). Seventy-one 

percent of transects indicate erosion in the short term, compared to 83 percent in the long term. The maximum short-term 

erosion rate (-1.0 ± 0.3 m/yr) is at the southern end of Yokohama Beach (table 9), where sand mining occurred from 1949 

to 1972 (Hwang, 1981). The maximum short-term accretion 

rate (1.7 ± 0.6 m/yr) was found at Pokai Bay, the same location at which the maximum long-term rate was measured. 

Rates at this location were calculated with a truncated data set 

following construction of the breakwater. 

The long-term and short-term shoreline change rates 

follow similar trends (fig. 30). Short-term rates typically 

have a higher associated uncertainty as a result of a shortened 

data set. The short-term rates at Yokohama, Keaau, and 

Maili are less erosive than the long-term rates, indicating 

that shoreline recession may have slowed since sand-mining 

operations ceased.

Maui

Maui is the third largest of the Hawaiian Islands. It is 

composed of two shield volcanoes, West Maui and Haleakala, 

with a low-lying isthmus separating them. The approximately 

90 km of sandy beach on Maui is separated into three 

subregions for analysis: North Maui, Kihei, and West Maui 

(fig. 32). From 3 to 10 high-quality historical shorelines 

with dates ranging from 1899 to 2007 are available for Maui 

(table 11). The shoreline from the earliest time period was 

derived from a T-sheet; all other shorelines were derived from 

vertical aerial photographs. 

Maui’s beaches are the most erosional among the three 

islands (table 5). Average shoreline change rates for all analysis regions and subregions are erosional (tables 5 and 12). The 

average long-term rate for all transects is -0.17 ± 0.01 m/yr 

and the average short-term rate is -0.15 ± 0.01 m/yr. A majority of the Maui transects indicate erosion with 85 percent of 

the long-term rates erosional and 76 percent of the short-term 

rates erosional. Eleven percent (6.8 km) of the total extent of 

Maui beaches studied was lost to erosion during the analysis 

period—the highest percentage of the three islands. 
40 National Assessment of Shoreline Change: Historical Shoreline Change in the Hawaiian Islands

0 2 MILES

0 2 KILOMETERS

EXPLANATION

N

0

100

200

300

400

500

600

2 1 0 −1 2 1 0 −1

Transect number

Long-term rates,

in meters per year

Short-term rates,

in meters per year

Accretion Erosion Accretion Erosion

95-percent confidence interval Rate Beach

West Oahu

1 Yokohama

2 Makua

3 Keaau

4 M. Lahilahi

5 Pokai

6 Maili

7 Nanakuli

8 Tracks

1

Pacific

Ocean

2

3

4

5

6

7

8

Makua Subregion Waianae Subregion Nanakuli Subregion

1 1

2 2

3 3

5 5

6 6

7 7

8 8

4 4

Figure 30. Long-term (all available years) and short-term (1940s to present) shoreline change rates, West Oahu. (Location 

shown in figure 22)
Historical Shoreline Change Analysis 41

Figure 31. Maili Beach, West Oahu. 

(Location shown in figure 30) (Photograph 

by Andrew D. Short, University of Sydney)

West 

Kihei 

North

Maui

N

West

Maui

Haleakala

21°

00’

N

20°

45’

156°30’ W 156°15’ 156°00’

Hawaiian

22 ° Islands N

20 °

160 °W 158 ° 156 °

Kauai

Oahu

Maui

0 100 MILES

0 100 KILOMETERS

Pacific Ocean

Pacific Ocean

Base from National Elevation Dataset

(1/3 arc-second grid, NAD83),

U.S. Geological Survey, 2009. 0 2.5 5 MILES

0 2.5 5 KILOMETERS

Figure 32. Three regions of Maui: north, Kihei, and west.
42 National Assessment of Shoreline Change: Historical Shoreline Change in the Hawaiian Islands

North Maui

The northern shore of Maui (fig. 33) is a gently embayed 

coastal system exposed to wind and waves from the northeast, 

north, and northwest. The shore experiences large swell during 

winter months and short-period trade wind waves throughout 

the year. The area also has a history of tsunami inundation. 

The North Maui region was divided into three subregions for 

additional analysis. The eastern Waihee–Waiehu subregion 

is affected by heavy rainfall and runoff from the dissected 

watersheds of the West Maui highlands and is dominated by 

cobble and sand beaches. The central study beaches, from 

Kahului Harbor to Baldwin Park (Kahului and Kanaha–Paia 

subregions) have low-lying hinterlands and a sand-rich coastal 

plain. A fringing reef is found along both the central and 

eastern study areas. The eastern study beaches, beginning 

at Paia, have a narrow, rocky coastal plain at the base of 

Haleakala volcano. This subregion contains short, embayed 

pocket beaches and narrow perched beaches located on lowelevation rocky terraces (fig. 34). 

Along North Maui, the number of historical shorelines 

ranges from four to eight, with dates ranging from 1899 to 

2002 (table 11). Of the 903 transects, 38 percent of the longterm rates and 27 percent of the short-term rates are statistically significant (fig. 33). Despite seasonal variability in 

shoreline position caused by large winter waves, the percentage of rates that are significant is higher for North Maui than 

for the other two Maui regions—resulting in an overall trend 

of chronic erosion. 

The average long-term rate for all North Maui beaches, 

-0.26 ± 0.02 m/yr, is the most erosional average rate of any 

region on the three islands (table 5; approximately the same 

as West Oahu: -0.25 ± 0.01 m/yr). Average long-term rates for 

each of the North Shore subregions are erosional (table 12). 

Eighty-seven percent of the transects along North Maui 

indicate a trend of erosion in the long term and 74 percent 

indicate a trend of erosion in the short term. The maximum 

erosion rate (-1.5 ± 1.1 m/yr) was found in front of an offshore 

rock bench at Baldwin Park (table 13). Shoreline recession at 

Baldwin is, in part, the result of sand-mining operations for a 

now-defunct lime kiln. A bench of beach rock was previously 

linked to the beach by a tombolo, but is now isolated offshore 

(Genz and others, 2009). Other areas of significant erosion 

were found at Waiehu Beach Park (up to -0.5 ± 0.3 m/yr, long 

term) and Kanaha Beach Park (up to -1.5 ± 0.7 m/yr, long 

term). The maximum long-term accretion rate (1.5 ± 1.3 m/yr) 

was measured between two groins at Kanaha Beach Park. 

The average short-term shoreline change rate for North 

Shore beaches, -0.22 ± 0.03 m/yr, is roughly the same as the 

average long-term rate (table 5). Seventy-four percent of the 

beach is erosional in the short term. The maximum short-term 

erosion rate (-2.2 ± 1.1 m/yr) was found in the same location as the maximum long-term erosion rate—Baldwin Park 

(table 13). The maximum short-term accretion rate (2.1 ± 

0.2 m/yr), like the maximum long-term accretion rate, was 

found in Kanaha Beach Park. Short-term and long-term rates 

follow a similar pattern, though uncertainty is higher in the 

short-term rate because of the truncated data set.

Table 11. Number and range in years of historical shorelines for long- and short-term shoreline change 

analysis on Maui.

Region

Shoreline change

Long-term Short-term

Number of shorelines1 Range in years1 Number of shorelines1 Range in years1

North 4–8 1899–2002 3–5 1960–2002

Kihei 3–9 1900–2007 3–8 1949–2007

West 5–10 1912–1997 3–8 1949–1997

1

Number of shorelines and range in years vary in each region.

Table 12. Average shoreline change rates for Maui subregions.

[m/yr, meters per year; ±, plus or minus]

Region Subregion

Number 

of transects

Average rate (m/yr)

Long-term Short-term

North

Waihee-Waiehu 277 -0.12 ± 0.02 -0.17 ± 0.02

Kahului Harbor 63 -0.05 ± 0.03 -0.06 ± 0.08

Kanaha-Paia 563 -0.35 ± 0.02 -0.26 ± 0.04

Kihei

Makena-Wailea 335 -0.13 ± 0.02 -0.13 ± 0.02

Central Kihei 283 -0.07 ± 0.03 -0.12 ± 0.03

Maalaea Bay 393 -0.17 ± 0.02 -0.10 ± 0.04

West

Lahaina 986 -0.15 ± 0.01 -0.11 ± 0.01

Kaanapali 228 -0.08 ± 0.02 -0.13 ± 0.03

Napili-Kapalua 305 -0.22 ± 0.02 -0.19 ± 0.03
Historical Shoreline Change Analysis 43

EXPLANATION

2 MILES

2 KILOMETERS

0

0

N

0

100

200

300

400

500

600

700

800

900

−2 0 2 −2 0 2

Long-term rates,

in meters per year

Transect number

Short-term rates,

in meters per year

Accretion Erosion Accretion Erosion

95-percent confidence interval Rate Beach

North Maui

1 Waihee

2 Waiehu

3 Kahului Harbor

4 Kanaha Beach 

 Park

5 Baldwin Park

6 Paia

1

Pacific

Ocean

2

3

4

5

6

Waihee-Waiehu Subregion Kanaha-Paia Subregion

1 1

2 2

3 3

5 5

6 6

4 4

Kahului

Subregion

Figure 33. Long-term (all available years) and short-term (1940s to present) shoreline change rates, North Maui. (Location 

shown in figure 32)
44 National Assessment of Shoreline Change: Historical Shoreline Change in the Hawaiian Islands

Kihei Maui

The Kihei coast (fig. 35) is a deeply-embayed shoreline in the north (Maalaea Bay) and partially embayed series 

of pocket beaches in the south along the southwest flank of 

Haleakala Volcano. The coast is mostly shadowed from large 

ocean swell by the islands of Molokai, Lanai, and Kahoolawe. 

Refracted winter North Pacific swells affect the southern portion of the coast. Southern swell can affect the entire coastline 

in summer months causing substantial seasonal shifts in shoreline position. Kona storms also cause short-term erosion along 

this south- to west-facing coast.

The Kihei coast is divided into three subregions for 

further analysis: Makena–Wailea, Central Kihei, and Maalaea 

Bay (fig. 35). The coastal plain in the north, along Maalaea 

Bay, is a flat, sand-rich terrace with barrier beaches, dunes, 

and wetlands that have been greatly affected by development 

(fig. 36). The coastal plain becomes progressively narrower to 

the south with basalt headlands marking boundaries between 

watersheds lacking dissected valleys. The fringing reef along 

the Kihei coast is generally narrower and deeper than along 

North and West Maui. The beaches in the northern and southern sections of Kihei are generally wider than those in the 

central portion (fig. 37).

Figure 34. North Maui 

beaches, looking west from 

Paia toward Baldwin Park. 

(Location shown in figure 33) 

(Photograph by Andrew D. 

Short, University of Sydney)

Table 13. Maximum shoreline change rates on Maui.

[m/yr, meters per year; max., maximum; ±, plus or minus]

Region Long-term rate 

(m/yr) Location1 Short-term rate (m/yr) Location1

North

Max. erosion -1.5 ± 1.1 Baldwin Park, sand mining2 -2.2 ± 1.1 Baldwin Park, sand mining3

Max. accretion 1.5 ± 1.3 Kanaha Beach Park, groins 2.1 ± 0.2 Kanaha, groins2

Kihei

Max. erosion -1.1 ± 0.6 Kawililipoa, within fishpond remains -1.8 ± 7.5 Kalepolepo Beach Park, beach lost

Max. accretion 1.6 ± 0.4 Kawililipoa, accretional cusp2 1.8 ± 0.5 Kawililipoa, accretional cusp

West

Max. erosion -0.9 ± 0.6 Ukumehame, coastal road revetment -0.7 ± 1.7 Kapalua, Mokuleia Beach, variable

Max. accretion 0.6 ± 0.2 Lahaina, Puunoa Point 0.7 ± 0.2 Lahaina, Puunoa Point

1

Locations shown in figures 33, 35, and 38.

2

Maximum erosion or accretion for Maui.

3

Maximum erosion or accretion for all three islands (Kauai, Oahu, and Maui).
Historical Shoreline Change Analysis 45

N

0

100

200

300

400

500

600

700

800

900

1,000

−1 0 1 −1 0 1

EXPLANATION

2 MILES

2 KILOMETERS

0

0

Long-term rates,

in meters per year

Transect number

Short-term rates,

in meters per year

Accretion Erosion Accretion Erosion

95-percent confidence interval Rate Beach

Kihei Maui

1 Makena

2 South Wailea

3 North Wailea

4 Kihei

5 Kalama

6 Kawililipoa

7 Kalepolepo

8 Maalaea Bay

1

Pacific

Ocean

2

3

4

5

6

Makena-Wailea Subregion Maalaea Bay Subregion

1 1

2 2

3 3

5 5

6 6

4 4

Central Kihei Subregion

Maalaea

Bay

7

8

7 7

8 8

Figure 35. Long-term (all available years) and short-term (1940s to present) shoreline change rates, Kihei, 

Maui. (Location shown in figure 32)
46 National Assessment of Shoreline Change: Historical Shoreline Change in the Hawaiian Islands

Figure 36. Maalaea Bay 

Beach with dunes and 

wetlands, north Kihei coast, 

Maui. (Location shown in 

figure 35) (Photograph by 

Andrew D. Short, University 

of Sydney)

Figure 37. Makena Beach, 

southern Kihei coast, Maui. 

(Location shown in figure 35) 

(Photograph by Andrew D. 

Short, University of Sydney)
Historical Shoreline Change Analysis 47

Kihei is highly erosional compared to study regions of 

Kauai and Oahu, based on average rates and percentages of 

transects indicating erosion (table 5). However, rates along 

Kihei are lower than along the highly erosional beaches of 

North Maui. Of the 1,011 transects in Kihei, statistically 

significant change rates were found at 22 percent of transects 

in the long term and 19 percent of transects in the short term—

the lowest percentages in the three Maui regions (fig. 35). The 

low proportion of significant rates at Kihei relative to the other 

Maui regions may be a result of high short-term variability in 

shoreline position (noise), as the number and range of dates of 

historical shorelines available (3 to 9 shorelines, 1900 to 2007) 

are similar to those in other Maui regions (table 11). Two km, 

or 11 percent, of the total length of Kihei beaches analyzed in 

this study was completely lost to erosion. The average longterm rate of shoreline change at Kihei is -0.13 ± 0.01 m/yr. 

Eighty-three percent of transects are erosional in the long term 

and 77 percent are erosional in the short term. The maximum 

long-term erosion rate (-1.1 ± 0.6 m/yr) was found at 

Kawililipoa, in the remains of a fish pond (table 13). Other 

areas with substantial long-term erosion include South Wailea 

(up to -0.5 ± 0.2 m/yr), North Wailea (up to -0.4 ± 0.2 m/yr), 

Kalama Park (up to -0.8 ± 0.5 m/yr; beach lost), and Maalaea 

(up to -0.6 ± 0.2 m/yr). The maximum long-term accretion 

rate (1.6 ± 0.4 m/yr) was also found at Kawililipoa, along an 

accretional cusp. 

The average short-term rate is -0.12 ± 0.02 m/yr, and 

77 percent of the short-term rates are erosional (table 5). The 

maximum short-term erosion rate (-1.8 ± 7.5 m/yr) was found 

at Kalepolepo Beach Park, where the beach has been completely lost to erosion. The maximum short-term accretion rate 

was found at the same location as the maximum long-term 

accretion rate (Kawililipoa; 1.8 ± 0.8 m/yr). Long- and shortterm rates have similar overall trends. 

West Maui

West Maui (fig. 38) has a gently arcing convex coast. 

From south to north, the shoreline changes orientation from 

southwest-, to west-, to northwest-facing. The shoreline is 

generally characterized by lengths of sandy beach interrupted by rocky headlands and engineered structures (fig. 39). 

The islands of Molokai, Lanai, and Kahoolawe offer partial 

protection from swells. The region is affected by alternating 

summer southern swell and the winter North Pacific swell that 

causes substantial changes in the beach profile and shifts in 

sediment along the coast. This region is heavily dissected by 

watersheds that produce large alluvial fans during low sealevel stands. Shallow fringing reefs line much of this coast, 

especially in the central and southern portions. Most beaches 

are narrow and often sand depleted. West Maui is divided into 

three subregions for further analysis: Lahaina, Kaanapali, and 

Napili–Kapalua.

West Maui has from 5 to 10 historical shorelines, with 

dates ranging from 1912 to 1997 (table 11). Of the 1,519 transects, 27 percent of long-term rates and 18 percent of shortterm rates are significant (fig. 38). Roughly 4 km, or 14 percent, of the total length of beach analyzed was completely lost 

to erosion during the study period—the highest percentage of 

beach loss of any region on the three islands (tied with South 

Kauai, table 5).

The average of all long-term rates for West Maui is 

-0.15 ± 0.01 m/yr and 85 percent of transects are erosional in 

the long term. All subregions in West Maui are erosional in 

the long and short term based on average rates. The NapiliKapalua subregion has the highest average erosion rates, 

-0.22 ± 0.02 m/yr in the long term and -0.19 ± 0.03 m/yr in 

the short term (table 12). The maximum erosion rate (-0.9 ± 

0.6 m/yr) was found at Ukumehame adjacent to a boulder 

revetment installed to protect the coastal highway (table 13). 

Other areas of significant long-term erosion include Hekili 

Point (up to -0.3 ± 0.2 m/yr), Olowalu (up to -0.3 ± 0.2 m/yr), 

Launiupoko (up to -0.5 ± 0.3 m/yr), Puamana (up to -0.5 ± 

0.2 m/yr), Mala Wharf (up to -0.5 ± 0.4 m/yr), Honokowai 

(up to -0.5 ± 0.4 m/yr), Kahana (up to -0.4 ± 0.1 m/yr), and 

Napili Bay (up to -0.4 ± 0.2 m/yr) The maximum long-term 

accretion rate (0.6 ± 0.2 m/yr) was measured at Puunoa Point. 

The accretional cell at Puunoa Point is flanked by erosion 

at the Lahaina and Mala Wharf shorefronts, suggesting that 

eroded sediment is transported from the adjacent beaches and 

deposited at Puunoa Point.

Erosion at West Maui is slightly lower in the short-term 

than in the long-term rate, with an average short-term rate of 

-0.13 ± 0.01 m/yr, and 77 percent of transects are erosional 

(table 5). The maximum short-term erosion rate (-0.7 ± 

1.7 m/yr) was found at Mokuleia Beach (table 13). The percentage of accretion increased from 14 (for long-term rates) to 

18 (for short-term rates). The maximum short-term accretion 

rate was found at the same location as the maximum rate in the 

long-term analysis (Puunoa Point at Lahaina). 
48 National Assessment of Shoreline Change: Historical Shoreline Change in the Hawaiian Islands

EXPLANATION

2 MILES

2 KILOMETERS

0

0

N

0

500

1,000

1,500

−0.5 0 0.5 −0.5 0 0.5

Long-term rates,

in meters per year

Transect number

Short-term rates,

in meters per year

Accretion Erosion Accretion Erosion

95-percent confidence interval Rate Beach

West Maui

1 Ukumehame

2 Hekili Point

3 Olowalu

4 Launiupoko

5 Puamana

6 Lahaina

7 Puunoa Point

8 Mala Wharf

9 Kaanapali

10 Honokowai

11 Kahana Beach Park

12 Napili

13 Kapalua

14 Mokuleia Beach

1

Pacific

Ocean

2

3

4

5

6

Lahaina Subregion

1 1

2 2

3 3

5 5

4 4 Kaanapali Subregion Napili-Kapalua Subregion

7

8 7 7 8 8

6 6

9

9 9

10

10 10

11 11 11

13 12

13 13

12 12

14 14 14

Figure 38. Long-term (all available years) and short-term (1940s to preset) shoreline change rates, West Maui. 

(Location shown in figure 32)
Discussion and Additional Considerations 49

Discussion and Additional 

Considerations

Summary of Shoreline Changes

Shoreline change along Kauai, Oahu, and Maui beaches 

is dominated by erosion. However, shoreline change is highly 

variable along Hawaii beaches with cells of erosion and 

accretion typically separated by only a few hundred meters on 

continuous beaches or by short headlands that divide the coast 

into many small embayments. Twenty-two km or 9 percent of 

the total length of beach analyzed was completely lost to erosion during the analysis period (table 5). Oahu lost the greatest 

total length of beach to erosion (8.7 km), whereas Maui had 

the highest percentage of beach loss (11 percent). The average of long-term rates from all transects on the three islands is 

-0.11 ± 0.01 m/yr and the majority, or 70 percent, of the transects indicate a trend of erosion in the long term. Erosion is 

also the short-term trend for the three islands, with an average 

rate of -0.06 ± 0.01 m/yr and 63 percent of transects indicating 

beach erosion. The maximum long-term erosion rate (-1.8 ± 

0.3 m/yr) was measured at Kualoa Point, Oahu. The maximum 

short-term erosion rate (-2.2 ± 1.1 m/yr) was measured at 

Baldwin Park, Maui. The maximum long-term accretion rate 

(1.7 ± 0.6 m/yr) was measured at Pokai Bay, Oahu. The maximum short-term accretion rate (2.8 ± 6.2 m/yr) was measured 

at the northern end of Polihale Beach, Kauai, although this 

rate is associated with a high degree of uncertainty caused by 

seasonal variability. 

Maui beaches are clearly the most erosional of the three 

islands with average long- and short-term erosion rates of 

-0.17 ± 0.01 and -0.15 ± 0.01 m/yr, respectively. Eighty-five 

percent of Maui transects indicate a trend of erosion in the 

long term and 76 percent indicate erosion in the short-term 

rates. Long-term trends for Kauai beaches are intermediate with an average rate -0.11 ± 0.01 m/yr and 71 percent of 

transects indicating a trend of erosion. Kauai is the only island 

whose average short-term change rate is not erosional (0.02 ± 

0.02 m/yr) due largely to increased beach accretion along West 

Kauai in the short term. Though, the majority (57 percent) of 

transects on Kauai beaches indicate a trend of erosion. Oahu 

has the lowest average long-term erosion rate of the three 

islands at -0.06 ± 0.01 m/yr. However, erosion is still the 

dominant trend of shoreline change on Oahu with 60 percent 

of transects indicating a trend of erosion in the long term. 

Short-term analysis for Oahu signifies a similar trend of erosion as the long-term analysis with an average rate of -0.05 ± 

0.01 m/yr and 58 percent of transects indicating erosion.

Figure 39. Kaanapali 

Beach, West Maui. 

(Location shown in figure 38) 

(Photograph by Andrew D. 

Short, University of Sydney)
50 National Assessment of Shoreline Change: Historical Shoreline Change in the Hawaiian Islands

Influences of Human Activities

Coastal property in many areas of Hawaii is at a premium, and the encroachment of the Pacific Ocean onto 

multimillion-dollar residential and commercial lands and 

development has not gone unnoticed by landowners. In many 

cases, the response is to armor the shoreline with seawalls, 

revetments, sand bags, and other structures and devices. 

Artificial hardening of the shoreline protects coastal land at the 

expense of the beach where chronic erosion occurs as waves 

are prevented from accessing the sand reservoirs impounded 

behind hard structures. Sandy shoreline adjacent to armoring 

experiences flanking erosion, extending the erosion problem 

along the shoreline and subjecting adjacent properties to the 

challenges of managing erosion. Therefore, efforts to mitigate coastal erosion have created a serious problem of beach 

loss and flanking erosion resulting from sand deficiency and 

wave reflection from hard structures along many shorelines 

in the state, particularly on the most populated and developed 

islands. The State of Hawaii and local communities acknowledge the need to address this issue, and hope that a broadly 

scoped management plan will balance the natural morphology 

of the coast with human-resource needs (Hwang, 2005).

Rates of shoreline change can be influenced by shorestabilization practices. Artificial beach replenishment and 

engineering structures tend to alter coastal processes, sediment 

availability, and shoreline position. For example, beach nourishment artificially causes rapid, temporary shoreline accretion. Depending on the frequency of beach nourishment, the 

placement of large volumes of sand on the beach may bias the 

rates of observed shoreline change toward accretion or stability, even though the natural beach, in the absence of nourishment, would be eroding.

In Hawaii, nourishment has not played a major role in the 

management of beach resources around the state other than at 

Waikiki. The most common stabilization approach has been 

shoreline hardening in the form of seawalls. Nourishment has 

largely been restricted to locations where erosion poses an 

immediate threat to development. Sites of beach nourishment 

include Sugar Cove on Maui, Waikiki, and Lanikai on Oahu, 

as well as other isolated locations.

On the island of Oahu, Fletcher and others (1997) found 

that about 25 percent of sandy beach has narrowed or been 

completely lost since 1949 as a result of artificial hardening of 

the shoreline. Differentiating between natural rates of erosion 

and the influences of beach nourishment is difficult because no 

experiments have been conducted to address this issue. 

Sand mining is another factor that has influenced shoreline positions in Hawaii. Although the practice is not well 

documented, residents report that sand has been removed 

from several beaches for use in construction materials or as 

lime fertilizer used in agriculture. Sand mining operations are 

observed in a few historical aerial photographs from the 1940s 

to 1960s. Sand mining may cause a deficiency in the sediment 

budget that can lead to temporary or chronic erosion. 

Planned Updates and Related Research

The USGS plans to revise and update rates of shoreline 

change every 5 to 10 years. Therefore, this report and 

associated data are a work in progress. The revision interval 

will depend on the availability of new shoreline data and 

technological advances. Continued monitoring of shoreline 

change is vital in the coming decades as the dynamics of the 

coastal environment that lead to beach erosion (for example, 

sea-level rise, storms, and waves) are likely to change with 

changing climate. 

Acknowledgments

The authors thank Michael Rink and David Doyle of 

the National Oceanic and Atmospheric Administration. The 

authors also thank Jennifer Wozencraft and Thomas Smith 

of the U.S. Army Corps of Engineers and U.S. Geological 

Survey (USGS) personnel Ann Gibbs, Thomas Reiss, and 

Cheryl Hapke. The authors acknowledge Matthew Niles, 

Daren Suzuki, and Thorne Abbott of the Maui Planning 

Department for their support of erosion studies on Maui and 

Sam Lemmo of the Hawaii Department of Land and Natural 

Resources. The University of Hawaii Sea Grant extension 

faculty members have been a valuable asset in coastal studies 

and policy development. The authors also appreciate Kauai 

County Planning Department, City and County of Honolulu 

Department of Planning and Permitting, Hawaii Coastal Zone 

Management, the Hawaii Department of Land and Natural 

Resources, and the Harold K.L. Castle Foundation for funding 

erosion studies on Kauai and Oahu.

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