National Assessment of Shoreline Change: Historical Shoreline Changes in the Hawaiian Islands



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National Assessment of Shoreline Change: Historical Shoreline Changes in the Hawaiian Islands

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


Tiffany R. Anderson2Anderson1, S. Chyn Lim1, Sean Vitousek1, Christopher Bochicchio1, and Bruce M. Richmond3Richmond2

Open-File Report 2011–1051



1 University of Hawaii, Department of Geology and Geophysics, Honolulu, HI 96822

2 University of Hawaii Sea College Program, Honolulu, HI 96822

32 USGS Pacific Coastal & Marine Science Center, Santa Cruz, CA 95060

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: 2011

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Fletcher, C.H., Romine, B.M., Genz, A.S., Barbee, M.M., Dyer, Matthew, Anderson, T.R., Lim, S. C.Chyn, Vitousek, Sean, Bochicchio, ChrisC, and Richmond, B.M., 2011, National assessment of shoreline change: Historical shoreline changes in the Hawaiian Islands: U.S. Geological Survey Open-File Report 2011–1051, xx81 p.

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COVER

The cover is a ground photo looking north from near Makapuu Point, Oahu, over Makapuu Beach (foreground) and toward the beaches of Waimanalo and Bellows.

The cover is a ground photo looking south along Kailua Beach, Oahu.


Contents


Executive Summary 5

National Assessment of Shoreline Change: Historical Shoreline Changes in the Hawaiian Islands 6

By Charles H. Fletcher, Bradley M. Romine, Ayesha S. Genz, Matthew M. Barbee, Matthew Dyer,
Tiffany R. Anderson, S. Chyn Lim, Sean Vitousek, Chris Bochicchio, and Bruce M. Richmond 6

Introduction 6

U.S. Geological Survey National Assessment of Shoreline Change 6

Acknowledgements 6

The Role of State and Federal Governments 7

Prior National and Hawaii ‘I Shoreline Assessments 7

Environmental Framework of the Hawaiian Shoreline 7

Table 1. Topographic maps showing theComputer-generated relief models of the Hawai‘i Island Archipelago and its northern arm, the Emperor Seamount Chain. 7

Carbonate Geology of Hawai’i 7

Table 2. Principal Diagram showing principal stratigraphic components of the Oahu carbonate shelf. (Modified from Fletcher and others, 2008). 7

Table 3. Aerial photograph showing Ccarbonate sand beaches in Hawai‘iHawaii areas the result of reef bioerosion and direct calcareous production of calcareous material among 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). 8

Hawaiian Beach Sediments 8

Table 4. Relationships of littoral sand grain size to shoreline aspect (wind and wave exposure). 8

[Modified from Moberly and Chamberlain, 1964; phi, phi units; mm, millimeters; -, no data] 8

exposure. Modified from Moberly and Chamberlain (1964). 8

Table 5. Graph showing Vvolume of sediment by depth zone in Kailua Bay, Oahu (Location shown in figure 26). Dark bar shows all sediment. Light bar excludes the Kailua sand channel (Modified from Bochicchio and others, 2009). These data are applicable to other coastal settings in Hawaii with similar oceanographic and geologic characteristics. 9

Table 6. Shaded-Computer-generated relief topography and bathymetrymodel of Kailua Bay, Oahu. Sand bodies on the sea floor are shown in black. on the seafloor (Modified from Conger and others, 2009). 9

Sea Level 9

Table 7. Graphs showing Mmean- sea- level trends in Hawaiiat (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, 2011http://tidesandcurrents.noaa.gov/index.shtml). 9

Table 8. Photograph showing Beaches and waterfront development (Waikiki, Oahu; location shown in figure 28) threatened by sea-level rise. Because the groundwater table rises and falls with sea level, drainage problems will likely increase in this and other coastal communities. sea-level rise threatens beaches and waterfront development. The groundwater table in the coastal plain moves with sea level; hence, drainage problems will grow into a major problem among coastal communities. (Photograph by C.L. Conger, University of Hawaii Sea Grant College Program) 10

The Hawaiian Waves Climate 10

Table 9. Diagram showing DHawai‘i dominant swell regimes after Moberly and Chamberlain (1964), and wave- monitoring buoy locations in Hawaii. (Modified from Moberly and Chamberlain, 1964 and Vitousek and Fletcher, 2008). 10

Table 10. Satellite- (JASON-1) derived average wave heights [m] over the north Pacific in the summer and winter (National Oceanic and Atmospheric Administration, 2010). 10

Table 11. Graph showing the Ddaily average significant wave heights from buoy 51001 (1981 to 2005, location shown in fig. 8). This plot outlines shows the seasonal variability of the northNorth Pacific Ocean swell, which begins to increase in October, reachesing a peak in winter, and subsequently decreases in March, and reachesing a trough minimum in summer. 11

Table 12. Bargraph showing Nthe number of days per season that the trade winds occur with a particular speed (data from bBuoy 51001, 1981 to 2005). The days per season are shown in red for winter months and blue for summer months. Noteice the persistence of typical trade winds around at a speed of about 25 kilometers per hour (16 mphmiles per hour) (~25 kph) during summer months. 11

Table 13. OThe 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 Hawai‘iHawaii. 12

[Modified from Vitousek and Fletcher, 2008; Window, degrees from true north] (Vitousek and Fletcher, 2008). 12

Tides 12


Shoreline Change 12

Table 14. Diagrams showing sSchematic diagrams showing seasonal beach- profile adjustments induced by seasonal swell variations and resulting cross-shore sediment transport. 12

Coastal property in many areas of Hawai‘i 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 there is chronic erosion, occurs as waves are preventeding waves from accessing the sand reservoirs impounded behind hard structures. Sandy shoreline adjacent to armoring experiences flanking, extending the erosion problem along the shoreline and subjecting adjacent properties to the challenges of managing erosion. Thereforeus, efforts to mitigate coastal erosion have created a serious problem of beach loss and flanking resulting fromdue to sand deficiency, and wave reflection fromoff hard structures along many shorelines in the state, particularly on the most populated and developed islands. The Sneed to address this issue is acknowledged by state of Hawai’i and local communities acknowledge the need to address this issue, andwith the hope that a broadly scoped management plan will keep the Hawaiian shorelines in balance between the natural coastal morphology of the coast withand human- resource needs (Hwang, 2005). 13

Effects of Beach Alterations onInfluence Rates of Shoreline Change 14

Rates of shoreline change can be influenced by shore- stabilization practices. Artificial beach replenishment and or 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 will bias the rates of observed shoreline change toward accretion or stability, even though the natural beach, in the absence of nourishment, would be eroding. 14

In Hawaii, nourishment has not played a major significant role in the management of beach resources around the state other than at Waikiki. The most common stabilization approach has been sShoreline hardening in the form of seawalls has been the most common stabilization approach. Nourishment has largely been restricted to sites and locations where erosion poses an significant immediate threat to development. Sites of beach nourishment include Sugar Cove on Maui, Waikiki, and Lanikai on Oahu, as well as other isolated locations. 15

On the island of Oahu, research conducted by Fletcher and others (1997) foundrevealed that about 25 percent of significant amount of sandy beach (about ~25 percent) has been narrowed or been completely lost since 1949 as a result ofdue to artificial hardening of the shoreline. Differentiating between natural rates of erosion and the influences of beach nourishment is difficult because no experiments have not been conducted to specifically address this issue. 15

Sand mining is aAnother factor that has influenced shoreline positions in Hawai‘i is sand mining. Although the practice is not well documented, residents ofthere are a number of beaches where residents report that sand was takenhas been removed from several beaches for use in construction materials and for useor as lime fertilizer by theused in agriculture industry . Sand mining operations are observed in a few historical aerial photographs from the 1940s to 1960s (fig. 13). Sand mining may cause a deficiency in the sediment budget that can leading to temporary or chronic erosion. 16

Shaded-relief topography showing eEvidence of sand mining in the a 1949 photo of Kahuku golf course. The dunes were flattened, plowed into the surf, and shoveled to the loading machine. The beach width decreased approximately 60 m from 1949 to 1967. 16

Methods of Analyzing Shoreline Change 16

Compilation of Historical Shorelines 16

Table 15. Aerial photograph showing hHistorical shorelines and shore-perpendicular transects (20-meter spacing) (measurement locations, 20 m 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) 17

Mapping Historical Shorelines 17

Uncertaintyies and Errors 17

Table 16. Range of errors in position of historical shorelines for Maui, Oahu, and KauaiKauai, Oahu, and Maui historical shorelines. 17

Calculation and Presentation of Rates of Change 18

Table 17. Graph and aerial photograph of Ccalculating shoreline change rate from a time series of shoreline positions using the Singlesingle-Transect transect (ST) method (Weighted Least Squares regression, WLS). The slope of the line is the annual shoreline change rate. (WLS, weighted least squares regression; see fig. 13 for explanation of photograph). 18

Historical Shoreline Change Analysis 20

Summary: Historical Shoreline Changes in the Hawaiian Islands 20

Erosion is the general long-term trend of Maui, Kauai, and Oahu, and Maui beaches (table 4). Twenty-two km or 9 percent of the total length of beach analyzed was lost to erosion n during the analysis periodin the time -span of analysis. Oahu lost the greatest highest total length of beach to erosion (8.7 km), whereasile Maui hads the highest percentage of beach loss (11 percent). The average of all long-term rates is -0.11 ± 0.01 m/yr. Erosion is also the short-term trend for the three islands, as a whole (-0.06 ± 0.01 m/yr). MostA majority of transects are erosional in both the long and short term (70 percent long term and 63 percent, respectively short term). The maximum long-term erosion rate (-1.8 ± 0.3 m/yr) is foundwas measured at Kualoa Point, Oahu; t. The maximum short-term erosion rate (-2.2 ± 1.1 m/yr) is foundwas measure at Baldwin Park, Maui. The maximum long-term accretion rate (1.7 ± 0.6 m/yr) is foundwas measured at Pokai Bay, Oahu;. tThe maximum short-term accretion rate (2.8 ± 6.2 m/yr) is foundwas measured at the northern end of Polihale Beach, Kauai,. aAlthough, this rate ihas high associated with a high degree of uncertainty caused bydue to seasonal variability. Of the three islands, Maui has the highest average long- and short-term erosion rates (-0.17 ± 0.01 and -0.15 ± 0.01 m/yr, respectively) of the three islands. Oahu has the least lowest erosional average long-term erosion rate (-0.06 ± 0.01 m/yr). Kauai is the only island whoseith average short-term changeaverage rate that is not erosional (0.02 ± 0.02 m/yr). 20

Shoreline change trends for Kauai, Oahu, and Maui. 20

Kauai Regional Setting 21

General Characteristics of Study Areas 21

Table 18. Map showing Ffour regions of Kauai: nNorth, eEast, sSouth, and wWest. 21

Table 19. Number and range in years of historical shorelines for long- and short-term shoreline change analysis on Kauai. 21

Table 20. Shoreline change trends for Kauai, Oahu, and Maui. 21

Table 21. MLocation of maximum and minimum shoreline -change rates on Kauai. 21

General Characteristics of Study Areas 21

North Kauai 21

Table 22. North Kauai: long-term and short-term shoreline change rates.Long-term (all available years) and short-term (1940s to present) shoreline change rates, north Kauai. (Location shown in figure 15) 21

Table 23. Shoreline-change trendsAverage shoreline change rates for Kauai subregions. 22

East Kauai 22

Table 26. Long-term (all available years) and short-term (1940s to present) shoreline change rates, east Kauai. (Location shown in figure 15) 22

Table 27. East Kauai: long-term and short-term shoreline change rates. 22

South Kauai 22

Table 28. Aerial photograph of Eoliaenite headland (lithified carbonate sand dunes), Mahaulepu, south Kauai. (Location shown in fig. 19. Photograph by Hawaii Aviation, Incorporated) 23

Table 29. Long-term (all available years) and short-term (1940s to present) shoreline change rates, south Kauai. (Location shown in figure 15) 23

Table 30. South Kauai: long-term and short-term shoreline change rates. 23

West Kauai 23

Table 31. Aerial photograph of dDunes at the west end of the Mana coastal plain, west Kauai. (Location shown in fig. 21. Photograph by Hawaii Aviation, Incorporated) 23

Table 32. Analysis of Kauai DataKauai Shoreline Change 23

Table 33. From 3 to 11There are between three and eleven high-quality historical shorelines with dates ranging from 1927 to 2008 are available for Kauai ranging from 1927 to 2008 (table 5). The 1927 shoreline from the first time period is derived from a T-sheet and t. The 1930 shoreline is from a hydrographic chart. All other shorelines are derived from vertical aerial photographs. 23

Table 34. Number and range in years of shorelines for long- and short-term analysis on Kauai. 24

Table 35. Erosion is the general long-term trend of Kauai beaches (table 4). Six km or 8 percent of the total extent of Kauai beaches was lost to erosion during the analysis periodin the time-span of analysis. The average of rates for all Kauai transects is -0.11 ± 0.01 m/yr. Kauai beaches are stable to accretional in the short term, with an average rate of 0.02 ± 0.02 m/yr. MostA majority of transects are erosional in both the long and short term (71 percent in the long term and 57 percent, respectively in the short term). The minimum and maximum long-term shoreline change rates on Kauai are found 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 found 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 ahas high degree of uncertainty because the beach was lost to erosion and a truncated data set wais used to calculate the rate up to the time the beach disappeared. The rate at Polihale ihas associated with a high degree of uncertainty as a result ofdue to seasonal variability. 24

Table 36. Location of maximum and minimum shoreline-change rates on Kauai. 24

Table 37. North Kauai 24

Table 38. The North region of Kauai is composed of three subregions (fig. 17). For the North region of Kauai Tthere are from 4 to 11between four and eleven shorelines, ranging in yearswith dates ranging from 1927 to 2008 (table 5). ForOf the 1,104 transects, 13 percent of short-term rates and 18 percent of long-term rates are statistically significant (fig. 19). 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. 24

Table 39. Map and plots of North Kauai: long-term and short-term shoreline change rates. 25

Table 40. The average long-term rate forof all transects in the North Kauai is -0.11 ± 0.02 m/yr (table 4). 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 or rates weare not determined as a result ofanalyzed due to limited data. The maximum long-term erosion rate (-0.7 ± 0.6 m/yr) wais 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) wais 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 the most 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, whereasile the Kilauea and Haena subregions are eroding at -0.13 ± 0.03 m/yr and -0.23 ± 0.03 m/yr, respectively (table 7). 25

Table 41. Shoreline-change trends for Kauai subregions. 25

Table 42. In North Kauai, tThe average short-term rate (-0.06 ± 0.02 m/yr) indicatess less erosionve than the average long-term rate in North Kauai. Sixty percent of transects are erosional in the short term—a 16- percent decrease from the long- term rate. As well asith the long-term erosionrates, Hanalei is the largest exception to the overall trend of short-term erosion. The maximum short-term erosion rate (-1.0 ± 2.6 m/yr) wais found at a rocky outcrop at Kauapea (table 6). This section of beach is susceptible to seasonal changes in shoreline position, as indicated by which is reflected in the high associated rate uncertainty. The maximum accretion rate (0.8 ± 1.5 m/yr) wais measured located at Kahili Beach near Kilauea Stream mouth. This beach is also highly unstable as a result ofrelated to seasonal fluctuations in shoreline position from large waves and stream flow. 25

Table 43. Along the North Kauai coast, short- and long-term rates follow similar trends (fig. 19). Predictably, the short-term rates have greaterare associated with a greater degree of uncertainty than the long-term rates (becausedue to 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 therelated to strong seasonal influence on the data. HenceTherefore, linear methods do not fit these data wellresult in a good fit for these data. Spikes in short-term uncertainty values at Moloaa, Mokolea, and Pali Ke Kua are the result ofdue to calculating rates fromcalculations with a truncated data set (few shorelines) where the beach has been completely lost to erosion. 26

Table 44. East Kauai 26

Table 45. East Kauai is the most erosional region of Kauai, as indicated bybased on average shoreline change rates and percentages of transects that are indicative of erosionding transects (table 4). The East region consists of three subregions (fig. 20). There are frombetween three toand nine shorelines that range, ranging in dateyears from 1927 to 2008 (table 5). ForOf the 867 transects, 34 percent of long-term rates and 16 percent of short-term rates are significant (fig. 20). The average long-term rate is -0.15 ± 0.02 m/yr, the most erosional erosive 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) is locatedwas measured at the western end of Anahola. Other areas of significant long-term erosion are found at Nukolii (up to -0.5 ± 0.3 m/yr), north of Waipouli (up to -0.3 ± 0.2 m/yr), and Kapaa (up to -0.7 ± 0.4). The maximum long-term accretion rate (0.7 ± 0.4 m/yr) is locatedwas measured at Anahola Beach, south of Anahola River (table 6). This area is affectedinfluenced 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. 26

Table 46. Map and plots of East Kauai: long-term and short-term shoreline change rates. 27

Table 47. The average short-term shoreline change rate for east Kauai is -0.06 ± 0.02 m/yr. Sixty-three percent of the short-term rates are erosional, the highest percentage of for the four Kauai regions (table 4). East Kauai has the lowest percentage of accretional rates (33 percent). The maximum short-term erosion rate (-1.6 ± 0.3 m/yr) is located 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) wais measured atfound in the same location as the maximum long-term accretion rate (south of Anahola River). 27

Table 48. Along the coast, long-term and short-term rates followed similar trends to each other (fig. 20). The long- and short-term confidence bands for Lae Lipoa are relatively wide because rates weare calculated with from only three to four shorelines. 27

Table 49. South Kauai 27

Table 50. Summary statistics for South Kauai conflict in that aare somewhat conflicting, Average long- and short-term rates indicatesuggesting approximately stable to accreting shorelines, whereas p. Percentages of erosional and accretional transects indicatesuggesting a predominance of erosion. The South region is made up of four subregions (fig. 21). From three to eight shorelines, ranging in date from 1926 to 2007, are available for tThe South region of Kauai has between three and eight shorelines (table 5), ranging in years from 1926 to 2007. ForOf the 790 transects, 28 percent of the short-term rates and 32 percent of the long-term rates are significant (fig. 21). 27

Table 51. Map and plots of South Kauai: long-term and short-term shoreline change rates. 28

Table 52. The average long-term shoreline change rate for South Kauai is approximately stable at -0.01 ± 0.02 m/yr. Sixty-three percent of transects are erosional in the long term. The maximum long-term erosion rate (-1.5 ± 0.4 m/yr) wais 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 completely 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) is locatedwas measured at Waimea, east of Kikiaola Small Boat Harbor (table 12, fig. 6). The beach on the western side of the harbor (Oomano) showedhas the highest erosion rate in the West Kauai region (see West Kauai). 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). 28

Table 53. Unlike the long-term average shoreline change rate, the short-term rate of 0.05 ± 0.01 m/yr indicatessuggests an overall trend of accretion along South Kauai (table 4);. hHowever, the beach is erosional at 57 percent of transects in the short term, indicatingsuggesting an overall trend of erosion. The maximum short-term erosion rate (-1.7 ± 9.9 m/yr) was found is located at the end of a pocket beach in Lawai Bay, 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 hHigh degree of uncertainty associated with this rate is a result of using truncated data (three3 shorelines) to calculate a rate in an area of beach loss. The maximum short-term accretion rate (1.7 ± 0.3 m/yr) is locatedwas measured at the same position as the maximum long-term rate (Waimea—east of Kikiaola Small Boat Harbor). 28

Table 54. Long-term and short-term rates follow similar trends along the South Kauai coast (fig. 21). The short-term uncertainty bands at Kipu Kai are especially large due to limited available shoreline data. Long-term rates at Kipu Kai weare calculated using four to five4–5 shorelines, whereasile short-term rates weare calculated using only three3 shorelines. A spike in the short-term confidence band for the short-term rates at Poipu (transect 586) is also a result of truncated (limited) data in an area of beach loss. 29

Table 55. Long-term (all available years) and short-term (1940s to present) shoreline change rates, west Kauai. (Location shown in figure 15) 29

Table 56. Map and plots of West Kauai: long-term and short-term shoreline change rates. 29

Oahu Regional Setting 29

Table 57. Map showing Ffour regions of Oahu: nNorth, eEast, sSouth, and wWest. 29

Table 58. Number and range in years of historical shorelines for long- and short-term shoreline change analysis on Oahu. 30

Table 59. MLocation of maximum and minimum shoreline -change rates on Oahu. 30

North Oahu 30

Table 60. Aerial photograph of Lfossil reef limestone headlands at Turtle Bay and Kawela BayKahuku Point and Kuilima (Turtle Bay), nNorth Oahu. (Locations shown in fig. 24. Photograph by Andrew D. Short, University of Sydney). 30

Table 61. Long-term (all available years) and short-term (1940s to present) shoreline change rates, north Oahu. (Location shown in figure 22)North Shore of Oahu: long-term and short-term shoreline change rates. 30

Table 63. Average sShoreline -change trendsrates for Oahu subregions. 31

East Oahu 31

Table 64. Aerial photograph of Lanikai (foreground) and Kailua Beaches, eEast Oahu. (Location shown in figure 26. Photograph by Andrew D. Short, University of Sydney) 31

Table 65. Long-term (all available years) and short-term (1940s to present) shoreline change rates, east Oahu. (Location shown in figure 22) 31

Table 66. East Oahu: long-term and short-term shoreline change rates. 31

Table 67. Photograph of 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) 31

South Oahu 32

Table 68. Aerial photograph of Ethe engineered shoreline at Waikiki, sSouth Oahu. (Location shown in figure 29. Photograph by Andrew D. Short, University of Sydney) 32

Table 69. Long-term (all available years) and short-term (1940s to present) shoreline change rates, south Oahu. (Location shown in figure 22) 32

Table 70. South Oahu: long-term and short-term shoreline change rates. 32

West Oahu 33

Table 71. Aerial photograph of Maili Beach, West Oahu. 33

Table 72. Analysis of Oahu DataOahu Shoreline Change 33

Table 73. A maximum of 12twelve high-quality historical shorelines, with a date range from 1910 to 2007, isare available for Oahu ranging from 1910 to 2007 (table 8). The earliest shoreline is derived from a 1910 or 1927 T-sheet or 1928 aerial photograph. A 1932–1933 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. 33

Table 74. Number and range in years of shorelines for long- and short-term analysis on Oahu. 33

Table 75. Erosion is the general long- and short-term trend of Oahu beaches (table 4). Nine km or 8 percent of the total length of beach analyzed was completely lost to erosion in the analysis periodtime -span of the study. The average of long-term rates for Oahu is erosional at -0.06 ± 0.01 m/yr. The average short-term rate is also erosional at -0.05 ± 0.01 m/yr (table 9). At mostA majority of transects, erosion is occurring are eroding in the long and short term (60 and 58 percent, respectively). The maximum long- and short-term erosion rates on Oahu weare found at Kualoa Point in East Oahu (-1.8 ± 0.3 m/yr and -1.9 ± 0.9 m/yr, respectively). The maximum long- and short-term accretion rates weare found at Pokai Bay in West Oahu (1.7 ± 0.6 m/yr). The long- and 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. 33

Table 76. Location of maximum and minimum shoreline-change rates on Oahu. 34

Table 77. North Oahu 34

Table 78. Twenty-fourOf the 1287 transects along North Oahu, 24 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 inof the four Oahu regions (fig. 28). The percentage of rates in this region that is significant rates in this region is low as a result ofdue to 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 ofdue to 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 monthsshorelines. 34

Table 79. Map and plots of North Shore of Oahu: long-term and short-term shoreline change rates. 34

Table 80. The overall trend of North Oahu beaches is erosion (table 4). The average long- and short-term rates on the northern shore are erosional at -0.11 ± 0.01 m/yr 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 on the basis ofbased on average rates (table 10). 34

Table 81. Shoreline-change trends for Oahu subregions. 34

Table 82. The maximum long-term erosion rate (-1.3 ± 0.8 m/yr) wais found at Haleiwa Beach Park at a segment of shoreline behind a small breakwater where the beach has been lost behind a small breakwater (table 9). This beach has undergone substantialignificant 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 ofdue to sand mining), and Mokuleia (up to -0.6 ± 0.1 m/yr). The maximum long-term accretion rate (0.8 ± 0.8 m/yr) wais found measured at Rocky Point in the Sunset subregion, though; this rate is likely affectedinfluenced by seasonal variability. The only significant notable exception to the overall trend of erosion along Mokuleia Beach wais found at an accreting cusp fronting along the beach at Waialua with rates up to 0.8 ± 0.8 2 m/yr (North Oahu maximum erosion rate). 34

Table 83. The maximum and minimum short-term change rates weare 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 as a result offrom a shortened data set (fewer shorelines) and high seasonal variability (fig. 28). 35

Table 84. East Oahu 35

Table 85. Overall, the beaches of East Oahu are approximately stable to slightly erosional as indicated by based on average long- and short-term average rate s and percentages of eroding and accreting transects indicating erosional or accretion. East Oahu beaches have frombetween five and twelve 5 to 12 shorelines with a ranging date range from 1910 to 2006 (table 8). Statistically significant shoreline change rates are found at thirty-five percent of the East Oahu transects in the long-term and twenty-four percent of the transects in the short-term Of the 2108 transects, Twenty-four24 percent of short-term rates and 35 percent of long-term rates at the 2,108 transects are significant (fig. 29). 35

Table 86. Map and plots of East Oahu: long-term and short-term shoreline change rates. 36

Table 87. The average long-term rate for East Oahu beaches is roughly stable at 0.01 ± 0.01 m/yr. Erosion is occurring at 50 Fifty percent of transects are eroding and accretion is occurring at 47 percent are accreting (table 4). The maximum and minimum erosion rates in the windward section weare 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 thanover 100 m, 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 up 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 (up to -1.2 ± 0.6 m/yr, as a result ofdue to sand mining), 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). 36

Table 88. Some of the longest extents of accreting shoreline in Hawaii weare found along East Oahu. Other 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;. hHowever, the beach along the adjacent shoreline to the north and south the beach has been completely lost its beach 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 ,m/yr and -0.09 ± 0.02 m/yr, respectively), whereasile the average long- and short-term rates for Southeast Oahu are accretional (0.12 ± 0.01 m/yr and 0.09 ± 0.02 m/yr, respectively) (table 10). 36

Table 89. The short-term rates follow similar trends similar to those of the long-term rates (fig. 29). Like the average long-term rate, the average short-term rate is approximately stable at -0.01 ± 0.01 m/yr. More transects are erosional in the short term than in the long term, with erosion occurring at 54 percent of transects eroding and accretion occurring at 44 percent accreting (table 15). The maximum short-term erosion and accretion rates weare also found at Kualoa (-1.9 ± 0.9 m/yr and 1.3 ± 1.8 m/yr, respectively;., table 9). 37

Table 90. South Oahu 37

Table 91. FAlong south Oahu there are rom 3 to 10between three and ten shorelines with a date rangeranging in years from 1927 to 2005 are available for the area along southern Oahu.. AtOf the 1,319 transects, 36 percent of long-term rates and 34 percent of long-term rates are significant (fig. 30). 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 itthe beach seaward (Miller and Fletcher, 2003; Wiegel, 2008). As a result ofDue to extensive shoreline reconstruction, only historical shorelines for the modern configuration of artificially altered beaches weare used to calculate change rates. 37

Table 92. Map and plots of South Oahu: long-term and short-term shoreline change rates. 37

Table 93. 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) indicatesuggest a slight overall prevalence of erosion (table 4). The Ewa subregion is the most erosional section of south Oahu, with an average long-term average rate of -0.06 ± 0.01 m/yr. The Honolulu subregion is also erodingsive 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) (table 10). 37

Table 94. The maximum long-term erosion rate (-1.6 ± 2.7 m/yr) wais found at Queens Beach, Waikiki (table 9) 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 study area 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 Ft 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) wais 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). 38

Table 95. The average short-term rate of -0.03 ± 0.02 m/yr is similar to the average long-term rate. For Like the long-term rates, as for the short-term rates, the percentages of eroding and accreting transects areis approximately equalabout even (table 15). The maximum short-term erosion and accretion rates and maximum accretion rate arewere measured at the same locations as the maximum long-term erosion and accretion rates, respectively (Kaimana and Queens, Waikiki) (table 9). 38

Table 96. The long-term and short-term rates follow similar trends (fig. 30). At the eastern end of Aina Haina, the short-term rates are associated with anhave exceptionally high degree of uncertainty as a result ofdue to low confidence in the model fit to the three available historical shorelines. 39

Table 97. West Oahu 39

Table 98. The three subregions in west Oahu have frombetween 6six to 12and twelve shorelines, with a date rangeing in years from 1910 to 2007 (table 8). Of the 628 transects, Forty-six46 and 26 percent of the rates at the 628 transects are significant in the long term and short term, respectively (fig. 31). 39

Table 99. Long-term (all available years) and short-term (1940s to present) shoreline change rates, west Oahu. (Location shown in figure 22) 39

Table 100. Map and plots of West Oahu: long-term and short-term shoreline change rates. 39

Table 101. Maili Beach, west Oahu. (Location shown in figure 30. Photograph by Andrew D. Short, University of Sydney) 39

Maui 39

Table 102. Map showing the Tthree distinct regions of Maui: nNorth, Kihei, and wWest. 40



Table 103. From 3 to 10 high-quality historical shorelines with dates ranging from 1899 to 2007 are available for Maui (table11). The shoreline from the earliest time period was derived from a T-sheet; all other shorelines were derived from vertical aerial photographs. 40

Table 104. Number and range in years of historical shorelines for long- and short-term change analysis on Maui. 40

Table 105. Average shoreline -change rates at each subregion on Maui (m/yr).for Maui subregions. 40

North Maui 40

Table 106. Long-term (all available years) and short-term (1940s to present) shoreline change rates, north Maui. (Location shown in figure 32) 40

Table 108. Aerial photograph of North Maui beaches, : looking west from Paia toward Baldwin Park. (Location shown in figure 33. Photograph by Andrew D. Short, University of Sydney) 40

Table 109. MLocation of maximum and minimum shoreline -change rates on Maui. 41

Kihei Maui 41

Table 110. Long-term (all available years) and short-term (1940s to present) shoreline change rates, Kihei, Maui. (Location shown in figure 32) 41

Table 111. Kihei coast, Maui: long-term and short-term shoreline change rates. 41

Table 113. Aerial photograph of Maalaea Bay Beach with dunes and wetlands, north Kihei coast, Maui. (Location shown in figure 35. Photograph by Andrew D. Short, University of Sydney) 41

Table 114. Aerial photograph of Makena Beach, southern Kihei coast, Maui. (Location shown in figure 35. Photograph by Andrew D. Short, University of Sydney) 41

West Maui 42

Table 115. Long-term (all available years) and short-term (1940s to present) shoreline change rates, west Maui. (Location shown in figure 32) 42

Table 117. Aerial photograph of Kaanapali Beach, wWest Maui. (Location shown in figure 38. Photograph by Andrew D. Short, University of Sydney) 42

Table 118. Map and plots of West Maui: long-term and short-term shoreline change rates. 43

Discussion and Additional Considerations 43

Summary of Shoreline Changes 43

Influences of Human Activities 44

Planned Updates and Related Research 44

Acknowledgments 44

References Cited 44


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