Assessing of topographic changes in the Fairy Stream, Phan Thiet by 3D topographic mapping method

Abstract

Currently, the Fairy Stream is a breathtaking tourist destination for domestic and foreign tourists due to the natural unspoiled beauty of the area. However, this landscape is vulnerable to human impacts such as littering, carving words on sand walls, climbing on sand walls causing slips and falls. Therefore, the requirements for management and monitoring of topographic changes are essential to preserving the beauty of this place. Unmanned aerial vehicle (UAV) technology is being widely applied in the world with much researches on applications in the fields of agriculture, mining, construction, etc. Thanks to the development of the "Structure from Motion" (SfM) method to generate a digital surface model (DSM) from UAV images and orthomosaic, which helps to accurately and quickly assess the topographic changes of the area. The author uses UAVs in landscape assessment, researches topographic changes in the Fairy Stream, Binh Thuan tourist, and 3D models at three different times about every 4 months. DEM of Difference (DoD) method is applied to analyze the change in elevation of the area and the Digital Shoreline Analysis System (DSAS) method to calculate the accretion and erosion interval over time. Flow velocity and material composition analysis demonstrate that the flow velocity exceeds the maximum erosion resistance velocities of fine and medium grain materials. Calculation by DSAS shows that erosion rate is 1.95m/8 months and accretion rate is 1.33m/8 months. After assessing, the author concludes that the fluctuation mechanism of the Fairy Stream is affected by the Northeast and Southwest monsoons, combined with the tourist factor. The study has demonstrated the potential of using UAVs in terrain change assessment to supports authorities in decision-making, provide better management measures such as zoning sensitive areas, placing signs, restricting visitors, etc.