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

Executive Summary 5

Introduction 6

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

Acknowledgements 6

The Role of State and Federal Governments 6

Prior National and Hawai‘I Shoreline Assessments 7

Environmental Framework of the Hawaiian Shoreline 7

Table 1. Topographic maps showing the Hawai‘i Island Archipelago and its northern arm, the Emperor Seamount Chain. 7

Carbonate Geology of Hawai’i 7

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

Table 3. Aerial photograph showing carbonate sand in Hawai‘i as the result of reef bioerosion and direct calcareous production among reef organisms. Reef morphology exerts strong control on shoreline sediment supply and dynamics. 8

Hawaiian Beach Sediments 8

Table 4. Relationships of littoral sand grain size to exposure. Modified from Moberly and Chamberlain (1964). 8

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

Table 6. Shaded-relief topography and bathymetry of Kailua Bay, Oahu. Sand bodies are shown in black on the seafloor (Conger and others, 2009). 9

Sea Level 9

Table 7. Graphs showing mean sea level trends in Hawaii (http://tidesandcurrents.noaa.gov/index.shtml). 9

Table 8. Photograph showing 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. Conger) 9

The Hawaiian Wave Climate 10

Table 9. Diagram showing Hawai‘i dominant swell regimes after Moberly and Chamberlain (1964), and wave monitoring buoy locations (Vitousek and Fletcher, 2008). 10

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

Table 11. Graph showing the daily average significant wave heights from buoy 51001. This plot outlines the seasonal variability of the north Pacific swell, which begins to increase in October, reaching a peak in winter and subsequently decreases in March reaching a trough in summer. 10

Table 12. Bargraph showing the number of days per season that the trade winds occur with a particular speed (data from Buoy 51001). The days per season are shown in red for winter months and blue for summer months. Notice the persistence of typical trade winds around 16 mph (~25 kph) during summer months. 10

Table 13. The 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‘i (Vitousek and Fletcher, 2008). 11

Tides 11

Shoreline Change 11

Table 14. Diagrams showing seasonal beach profile adjustments induced by seasonal swell variations and resulting cross-shore sediment transport. 11

Table 15. Shaded-relief topography showing evidence of sand mining in the 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. 12

Methods of Analyzing Shoreline Change 12

Compilation of Historical Shorelines 12

Table 16. Aerial photograph showing historical shorelines and shore-perpendicular transects (measurement locations, 20 m spacing) displayed on recent aerial photograph. 12

Mapping Historical Shorelines 13

Uncertainties and Errors 13

Table 17. Range of errors for Maui, Oahu, and Kauai historical shorelines. 13

Calculation and Presentation of Rates of Change 14

Table 18. Graph and aerial photograph of calculating shoreline change rate using the Single-Transect (ST) method (Weighted Least Squares regression, WLS). The slope of the line is the annual shoreline change rate. 14

Historical Shoreline Change Analysis 14

Summary: Historical Shoreline Changes in the Hawaiian Islands 14

Table 19. Shoreline change trends for Kauai, Oahu, and Maui. 15

Kauai 15

General Characteristics of Study Areas 15

Table 20. Map showing four regions of Kauai: North, East, South, and West. 15

Table 21. Aerial photograph of Eolienite headland (lithified carbonate sand dunes) Mahaulepu, south Kauai. 15

Table 22. Aerial photograph of dunes at the west end of the Mana coastal plain, west Kauai. 15

Analysis of Kauai Data 16

Table 23. Number and range in years of shorelines for long- and short-term analysis on Kauai. 16

Table 24. Location of maximum and minimum shoreline-change rates on Kauai. 16

Table 25. Map and plots of North Kauai: long-term and short-term shoreline change rates. 16

Table 26. Shoreline-change trends for Kauai subregions. 16

Table 27. Map and plots of East Kauai: long-term and short-term shoreline change rates. 16

Table 28. Map and plots of South Kauai: long-term and short-term shoreline change rates. 17

Table 29. Map and plots of West Kauai: long-term and short-term shoreline change rates. 17

Oahu 17

General Characteristics of Study Areas 17

Table 30. Map showing four regions of Oahu: North, East, South, and West. 17

Table 31. Aerial photograph of fossil reef limestone headlands at Turtle Bay and Kawela Bay, North Oahu. 18

Table 32. Aerial photograph of Lanikai (foreground) and Kailua Beaches, East Oahu. 18

Table 33. Aerial photograph of the engineered shoreline at Waikiki, South Oahu. 18

Table 34. Aerial photograph of Maili Beach, West Oahu. 18

Analysis of Oahu Data 18

Table 35. Number and range in years of shorelines for long- and short-term analysis on Oahu. 18

Table 36. Location of maximum and minimum shoreline-change rates on Oahu. 19

Table 37. Map and plots of North Shore of Oahu: long-term and short-term shoreline change rates. 19

Table 38. Shoreline-change trends for Oahu subregions. 19

Table 39. Map and plots of East Oahu: long-term and short-term shoreline change rates. 19

Table 40. Map and plots of South Oahu: long-term and short-term shoreline change rates. 19

Table 41. Map and plots of West Oahu: long-term and short-term shoreline change rates. 20

Maui 20

General Characteristics of Study Areas 20

Table 42. Map showing the three distinct regions of Maui: North, Kihei, and West. 20

Table 43. Aerial photograph of North Maui beaches: looking west from Paia toward Baldwin Park. 20

Table 44. Aerial photograph of Maalaea Bay Beach with dunes and wetlands, north Kihei coast, Maui. 21

Table 45. Aerial photograph of Makena Beach, southern Kihei coast, Maui. 21

Table 46. Aerial photograph of Kaanapali Beach, West Maui. 21

Analysis of Maui Data 21

Table 47. Number and range in years of shorelines on Maui. 21

Table 48. Average shoreline-change rates at each subregion on Maui (m/yr). 21

Table 49. Map and plots of North Maui: long-term and short-term shoreline change rates. 21

Table 50. Location of maximum and minimum shoreline-change rates on Maui. 21

Table 51. Map and plots of Kihei coast, Maui: long-term and short-term shoreline change rates. 22

Table 52. Map and plots of West Maui: long-term and short-term shoreline change rates. 22

References 22

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