COASTAL MONITORING USING UAS TO TRACK CHANGES IN BEACH MORPHOLOGY: WAIKĪKĪ, HAWAIʻI

More than 70% of Hawaiian beaches are chronically eroding due to both natural and anthropogenic causes. Unmanned aerial systems (UAS) provide an efficient way to monitor these sandy shorelines so that coastal zone managers can more effectively manage them. One of Hawaiʻi’s most popular tourist destinations, Waikīkī’s Royal Hawaiian Beach, suffers from chronic erosion and requires regular replenishment to prevent complete beach loss. To evaluate the efficacy of using consumer-grade UAS in monitoring subaerial sand volume and processes that drive beach movement, we conducted weekly aerial and ground surveys from April 2018 to November 2018 from which high-resolution dense point clouds, digital elevation models, and orthomosaics were generated. Using a consumer-grade UAS, we conducted weekly aerial and ground surveys from April 2018 to November 2018. We developed high-resolution dense point clouds from which we generated digital elevation models and orthomosaics to monitor the subaerial sand volume and processes that drive beach movement. Various analyses were performed, including empirical orthogonal function analysis (EOF) and surface comparison. An “oscillating" effect was observed as the primary mode of variability as typical summer southerly and southwesterly swell angles result in erosion hotspots at the east end of the compartmentalized littoral cell, while the west and central areas of the beach accrete. More easterly swell angles, as occurring during storm events, resulted in a reversal of this pattern. Despite being characterized as a chronically eroding beach, an overall gain of surface area and sand volume was observed to be 617.11 m² and 1221.62 m³ over the course of the monitoring period, respectively, likely due to sediment additions from a relatively active hurricane season. Considering its economic value and the expected exacerbation of erosion as sea level rises, information provided through UAS surveys will likely be integral to coastal zone managers as they develop strategies to preserve Waikīkī’s Royal Hawaiian Beach.