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MS Plan A Defense: Seasonal wave climate anomalies on the North Shore indicative of erosion conditions
29 April 2022 @ 1:00 pm - 2:00 pm
Department of Ocean and Resources Engineering
University of Hawaiʻi at Mānoa
Zoom Meeting Link
Meeting ID: 986 0663 8344
Sea level rise and seasonal wave climate have beset the Sunset Beach shoreline community with several episodic erosion events that have impacted local infrastructure. In support of the local community, the US Army Corps of Engineers (USACE) Honolulu District has employed a series of remote sensing technologies at Sunset Beach to generate a regional sediment budget to better inform the community of their situation. The objective of this study is to explain the more frequent erosion events that have occurred in the last decade. Given a lack of significant long-term observations of the area of interest, this study uses a combination of numerical modeling, buoy observations, sediment characteristics, USACE’s remote sensing observations, and anecdotal evidence from local community observers. The seasonal cycle of Sunset Beach is dramatic, with large waves in December through March and small waves in May through August which corresponds to a strong seasonal cycle of the measured median sand grain size. This study relates seasonal wind, wave, and water level anomalies to the recent erosion and non-erosion years using offshore buoy records, a 41-year wave hindcast, recorded water levels, and wind observations. The wave and wind fields have the largest deviations from the average year in the May-August preceding the dramatic erosion observed during September-December. The largest and most significant changes are related to the change in the wind seas generated by the deviation of summer local trade winds (+14% to -23%) from the average year. The work also demonstrates that the interannual variability associated with the El Nino Southern Oscillation likely has a considerable impact on the longshore sediment transport capacity with El Nino explaining up to 29% of the variability. These findings suggest the summer conditions help (or hinder) the beach recovery to endure (or suffer) the average erosive wave conditions experienced in the winter months.