Annual and interannual changes on a reef-fringed pocket beach: Kailua Bay, Hawaii

Abstract Historical aerial photographs and topographic survey sheets are used to establish a 70-year shoreline history (1926–1996) for Kailua Beach, Oahu, Hawaiian Islands. The shoreline has migrated seaward over this period at an average rate of 0.5 m/yr, with a maximum net accretion along the beach of 58.7 m and a maximum net erosion of −13.2 m. Net accretion has taken place even while sea levels have risen on the order of 0.1 m. Semi-annual and monthly beach profile surveys (1995–1999) at seven transects reveal short-term variations of shoreline position, sand volume, and beach shape. A relationship between beach width and corresponding sand volume fluctuations, established from the beach profile data, is applied to the historical shoreline change data to establish a history of sand volume fluctuations. Results show that Kailua has experienced a net accretion of 673 000 m3 of sand over the period 1926–1996, with average annual rates of volume change varying between 6.8 m3/m/yr and −0.1 m3/m/yr. The most recent period (1989–1996) shows a net volume increase of 41 000 m3. Given the lack of sand inputs at the ends of the beach, exchange with offshore deposits is a likely mechanism for long-term accretional trends. Seasonal fluctuations in Kailua Beach morphology dominate the variability with a response to seasonal wave state that varies along the length of the beach in magnitude and sign. At least four alongshore zones are observed, with the first and third zones exhibiting high/low sand volumes during the summer/winter, and the second and fourth zones exhibiting opposite behavior with high/low volumes during the winter/summer. Although seasonal sand accumulation varies along the beach, the overall beach profile is largely maintained. Moreover, changes in sand volume occur in phase over the subaqueous and subaerial sections of the beach. This behavior suggests that longshore rather than cross-shore sand transport is important at annual time scales. A simple seasonal transport pattern is proposed to account for these observed fluctuations, which depends in part on the topography of the offshore reef.

[1]  Nicholas C. Kraus,et al.  GENESIS: Generalized Model for Simulating Shoreline Change. Report 1. Technical Reference , 1989 .

[2]  P. Bruun.  Coast Erosion and the Development of Beach Profiles , 1954 .

[3]  Jodi N. Harney,et al.  CARBONATE SEDIMENTOLOGY OF A WINDWARD SHOREFACE: KAILUA BAY, OAHU, HAWAIIAN ISLANDS , 1999 .

[4]  C. Fletcher,et al.  Beach Loss Along Armored Shorelines on Oahu, Hawaiian Islands , 1997 .

[5]  E. Thieler,et al.  Mar. geol.: Erratum to “Geology of the Wrightsville Beach, North Carolina shoreface: Implications for the concept of shoreface profile of equilibrium” [126 (1995) 271–287] , 1996 .

[6]  P. Bruun.  Sea-Level Rise as a Cause of Shore Erosion , 1962 .

[7]  R. Nicholls,et al.  Storm-driven variability of the beach-nearshore profile at Duck, North Carolina, USA, 1981-1991 , 1998 .

[8]  R. Nicholls,et al.  A Conceptual Fairweather-Storm Model of Beach Nearshore Profile Evolution at Duck, North Carolina, U.S.A. , 1995 .

[9]  Randall A. Wise,et al.  Sbeach: Numerical Model for Simulating Storm-Induced Beach Change, Report 3 : User's manual , 1989 .

[10]  David L. Kriebel,et al.  Engineering Methods for Predicting Beach Profile Response , 1991 .

[11]  C. Fletcher,et al.  A budget of marine and terrigenous sediments, Hanalei Bay, Kauai, Hawaiian Islands , 2002 .

[12]  Per Bruun,et al.  Review of conditions for uses of the Bruun rule of erosion , 1983 .

[13]  R. Nicholls,et al.  A conceptual fairweather-storm model of beach nearshore evolution applied at Duck, North Carolina, USA , 1995 .

[14]  César Vidal,et al.  Historical Evolution and Morphological Analysis of "EI Puntal" Spit, Santander (Spain) , 1991 .

[15]  J. Neter,et al.  Applied linear statistical models : regression, analysis of variance, and experimental designs , 1974 .

[16]  David G. Aubrey,et al.  Seasonal patterns of onshore/offshore sediment movement , 1979 .

[17]  Hilary F. Stockdon,et al.  Sea-cliff erosion as a function of beach changes and extreme wave runup during the 1997–1998 El Niño , 2002 .

[18]  Andrew D. Short,et al.  Short-term changes in the morphodynamic states of beaches and surf zones: An empirical predictive model☆ , 1985 .

[19]  George L. Smith,et al.  Calculating Long-Term Shoreline Recession Rates Using Aerial Photographic and Beach Profiling Techniques , 1990 .

[20]  R. Hallermeier.  USES FOR A CALCULATED LIMIT DEPTH TO BEACH EROSION , 1978 .

[21]  M. Merrifield,et al.  Steep beach morphology changes due to energetic wave forcing , 2000 .

[22]  Juan J. Muñoz-Perez,et al.  Equilibrium Beach Profile Model for Reef-Protected Beaches , 1999 .

[23]  R. Morton,et al.  Meso-scale transfer of sand during and after storms: implications for prediction of shoreline movement , 1995 .

[24]  D. J. Clarke,et al.  Low-frequency changes of sediment volume on the beachface at Warilla Beach, New South Wales, 1975–1985 , 1988 .

[25]  E. Thieler,et al.  Geology of the Wrightsville Beach, North Carolina shoreface: Implications for the concept of shoreface profile of equilibrium , 1995 .

[26]  D. Inman,et al.  Description of seasonal beach changes using empirical eigenfunctions , 1975 .

[27]  R. Hallermeier,et al.  A PROFILE ZONATION FOR SEASONAL SAND BEACHES FROM WAVE CLIMATE , 1980 .

[28]  W. Pilkey,et al.  The concept of shoreface profile of equilibrium: a critical review , 1993 .

[29]  J. Dingler,et al.  Changes to Monterey Bay beaches from the end of the 1982-83 El Niño through the 1997-98 El Niño , 2002 .