2015 GSA Annual Meeting in Baltimore, Maryland, USA (1-4 November 2015)

Paper No. 207-13
Presentation Time: 9:00 AM-6:30 PM


HABEL, Shellie L., Geology and Geophysics, University of Hawaii at Manoa, 2500 Campus Rd, Honolulu, HI 96822, FLETCHER, Charles H., School of Ocean and Earth Science and Technology, University of Hawaii, 1680 East-West Rd, POST 802, Honolulu, HI 96822, BARBEE, Matthew M., Geology and Geophysics, University of Hawaii, 1680 East-West Rd, POST 723, Honolulu, HI 96822 and ANDERSON, Tiffany, Geology and Geophysics, University of Hawaii, 1680 East-West Road, POST 701, Honolulu, HI 96822, skey@hawaii.edu

Waikiki has long been touted for its world-class beaches, while in reality the region is incapable of retaining large amounts of sand in its natural state. Numerous engineering projects have been undertaken since the late 19th century to increase the recreational functionality of the beach for visitors and local beachgoers. In 2012, Royal Hawaiian Beach, located along central Waikiki, received a sand nourishment of 17,550 m3 from offshore carbonate sand fields. The project was the largest maintenance effort to take place in this region in 40 years. Beach monitoring was accomplished to quantify nourishment performance, and to obtain information for future maintenance efforts. Beach and offshore profile data were collected prior to sand placement and quarterly thereafter for a period of 2.7 years. The time-sequence of profile data was used to construct digital elevation models (DEMs); a method tailored for this study to achieve improved spatial accuracy relative to two-dimensional profile comparisons that often ignore measurement inconsistency. Various analyses were performed as part of this study and include empirical orthogonal function (EOF) analysis, surface comparison, and correlation to local swell conditions. Monitoring data confirm the placement of 12,700+/-3,700 m3 of sand within the beach region; a surprisingly low figure compared to volumes reported by contractors. A large part of the discrepancy likely resulted from the method of sand transport employed during nourishment; loaded dump trucks repeatedly traversed across the beach to reach placement locations which likely caused physical and chemical compaction of fragile carbonate sand, and produced a 0.3-1 m hardened berm along much of the project beach. By the end of monitoring, we find that the beach retained the majority of the total placed volume and approximately half of the original placed width.