Coastal hazards mapping using high-resolution UAV image and DEM. A Case study in Siung Beach, Gunungkidul, Indonesia

Abstract

The southern coast of Gunungkidul, which is adjacent to the subduction zone, is prone to various coastal hazards. The increasing number of visitors to the beach leads to more exposure and increases the risks. This study aims to determine the coastal hazards in Siung Beach, Gunungkidul, Yogyakarta. A high-resolution aerial image and DEM were acquired using a low-cost Unmanned Aerial Vehicle. The acquired images were processed using Structure from Motion (SfM) photogrammetry to generate an orthomosaic image with 5cm spatial resolution. A worst-case tsunami hazard scenario (12 m) was executed using raster filtering on the generated UAV-DEM. Based on the tsunami inundation model, most of the buildings are affected by the worst-case tsunami scenario. According to orthomosaic interpretation, rip current hazard is also spotted on the eastern part of the beach. The rip current is considered a channel rip, a stationary rip current affected by the bathymetric condition. Potential rockfall due to slope instability might be occurred on the southern part of the beach, as a former enormous mass movement can be delineated from the orthomosaic image. Siung Beach is formed by the combination of volcanic origin and karst process, resulting in undulating topography. Due to various coastal hazards in Siung beach, disaster management planning should be established to reduce the risks.