Reef platform sediment storage and long-term littoral sediment transport patterns along a windward shoreline

Beach loss is significant to the economy, environment, and quality of life of many coastal regions, particularly in Hawaii. In an effort to better understand and mitigate beach loss this thesis examines patterns of and factors effecting beach loss along a section of the Oahu shoreline. The southeastern shore of Oahu consists of Kailua and Waimanalo bays, separated by the broad slightly embayed Lanikai headland, totaling 22 kilometers of shoreline. This littoral system is well confined by bordering volcanic headlands making it an excellent opportunity to study sedimentation processes on a reef-fringed sandy shoreline. This thesis is comprised of two studies: (1) a survey and analysis of reef-top sediment storage and (2) examination of transport processes controlling multi-decadal shoreline changes along the Lanikai-Waimanalo shoreline in the area of Bellows Beach.Sediment bodies are classified into three dominate morphologies: channel, field, and karst depression. The volume of sediment stored in channels is 58,253 +/- 618 x 103 m3 fields contain 171 +/- 6 x 103 m3, and karst depressions contain 1332 +/- 248 x 103 m3. Correlation of sediment body distribution with reef and coastal plain morphology reveals potential geologic controls on sand body formation in this region. Meteoric runoff and reef slope are important controls on the spatial distribution of sand bodies.Three commonly used techniques are integrated for studying shoreline change: (1) grain-size sediment trend analysis (GSTA), (2) hydrodynamic computer modeling (Delft 3D), and (3) historical aerial photoanalysis. Results of GSTA and hydrodynamic modeling are generally consistent with shoreline change observed in historical aerial photographs. It is shown that sediment has been shared between Lanikai and Bellows and that decadal-scale changes in the dominant trade wind direction are closely tied to shoreline change.