UAV SURVEYS TO MONITOR VOLUMETRIC BEACH CHANGES OVER AN EXTREME HIGH-TIDE EVENT: WAIKIKI, HAWAII

Currently, more than 70% of Hawaiian beaches are chronically eroding due to both natural and anthropogenic influences. As sea level rises, erosion is expected to accelerate, leaving coastal zone managers in a race to preserve those that are left. Chronic erosion and beach loss characterize Waikīkī’s Royal Hawaiian Beach, Hawaiʻi’s most popular tourist destination, accounting for approximately 46% of visitor industry revenue. The area’s economic importance, in addition to its cultural significance and ecosystem services, have prompted beach nourishment efforts since the 1950s and as recently as early 2012. Despite this, the beach continues to erode, leading to limited beach area and overcrowding. To better understand the influence of high water levels on the beach, we conducted aerial surveys using consumer-grade unmanned aerial vehicles (UAVs) paired with cross-shore profiles before and after the highest water levels documented in the century-long Honolulu tide gauge record. We developed high-resolution dense point clouds and digital elevation models to monitor subaerial volumetric changes and to further understand the processes that drive beach movement on shorter time scales. This event simulates the effect that future sea level rise may have on sediment transport and coastal processes along this highly engineered urban shoreline. It was found that these extreme high tide events result in significant beach movement between surveys, providing further indication regarding the possibility of accelerated erosion under elevated water levels and the need for more proactive management efforts to preserve the Royal Hawaiian Beach as sea levels rise.