Beach loss along armored shorelines on Oahu, Hawaiian Islands

Abstract

An analysis of an aerial photographic time series of Oahu's shoreline reveals that historical seawall and revetment construction (coastal armoring) to protect eroding lands has caused the narrowing of 17.3 ± 1.5 km and loss of 10.4 ± 0.9 km of sandy beach over the period 1928 or 1949 to 1995. This is ~24% of the 115.6 ± 9.8 km of originally sandy shoreline of Oahu. All narrowed and lost beaches occur in front of coastal armoring structures that fix the position of the shoreline. In addition, nearly all narrowed and lost beaches show a history of recent (5% of narrowed and lost beaches) or long-term (92% of narrowed and lost beaches) retreat. We conclude from this study that using a wail or revetment to fix the position of a shoreline undergoing retreat will cause the narrowing and eventual loss of the adjoining beach.