3:45 PM - 4:00 PM
[HTT14-02] Relationship between watershed characteristics and sandy coast erosion using UAV-SfM-MVS and ALS data in Japan
Keywords:Coastal erosion, Coastal sand dune, RTK-UAV, Ecosystem, Land use, Vegetation
Sandy coast is one of the most important ecosystems because it has developed a unique ecosystem and has multilateral functions. Sandy coast is the boundary between the sea and land, where water and wind forces move sand back and forth, and are dynamically maintained systems. This system is called the Beach Dune System. Many plants and animals adapted to the dynamic environment live and grow here. In addition, coastal dunes that develop on sandy coasts have attracted attention as protective barriers and buffer zones that prevent seawater from entering inland due to tsunamis and storm surges. Therefore, it has been conserved in countries with large areas of land with low elevation, such as the Netherlands.
Since the late 20th century, increased development and recreational use near the coast have caused ecological destruction and landscape degradation. Furthermore, there is concern that rising sea levels due to climate change will accelerate coastal erosion. Progressive coastal erosion worldwide not only means a decrease in land area but also directly leads to the loss of habitat for a variety of marine and terrestrial ecotone-dependent organisms. Therefore, coastal erosion is an urgent issue for both human society and marine and terrestrial ecosystems.
Most studies of beach erosion on sandy beaches have used changes in the sandy beach shoreline as an indicator, and few have targeted changes in the dunes behind the beach. There are also scattered studies that have measured dunes in three dimensions and measured the changing, but none have focused on multiple sandy coasts. To clarify the reality of coastal erosion more realistically, it is necessary to understand and evaluate the topographic changes of multiple sandy coasts in three dimensions. For this purpose, it is necessary to analyze multiple sandy coasts, but until now, the difficulty of obtaining 3D data from multiple locations at multiple times for analysis has been one of the limiting factors in advancing the study.
This study will overcome the above issues by measuring and utilizing high-definition spatial information from UAVs (Unmanned Aerial Vehicles) and ALS (Airborne Laser Scanning). The accuracy of UAV-SfM (Structure-from-Motion) in reconstructing 3D structures of terrain and vegetation has improved remarkably. With conventional UAV-SfM, multiple ground reference points need to be surveyed and established separately due to the low accuracy (error: several meters) of the aircraft's positioning information. In recent years, RTK (Real-Time Kinematic) -GNSS (Global Navigation Satellite System), which enables highly accurate position acquisition, and UAVs have been integrated to dramatically improve positional accuracy (error: several centimeters). As a result, ground control points, which required a great deal of labor to install, are no longer necessary. The use of RTK-UAVs not only improves accuracy but also enables the acquisition of topographic information at multiple locations. This allows us to grasp the topographic changes of sandy coasts in three dimensions and a wide area, and we believe that this will lead to the clarification of the actual state of coastal erosion.
In this presentation, the amount of change (erosion and sedimentation) was calculated from the difference analysis between the DSM created by RTK-UAV-SfM and ALS to clarify the actual erosion of coastal dunes on the sandy coasts of Hokkaido, Honshu, Shikoku and Kyushu in Japan. Further, The analysis is carried out to clarify the relationship between watershed characteristics and sandy coast erosion, and the results will be presented.
The actual erosion of sandy coasts was evaluated using both erosion and sedimentation as indicators. There were many sandy coasts with erosion trends, and the erosion amount tended to be higher in the dune areas than in the beach areas. On the other hand, there are several sandy coasts with sedimentation trends, and there are differences in the trends of change from coast to coast. These differences were thought to be due to differences in the environment around the sandy coasts and the watershed characteristics. In particular, the amount of change in sandy coasts was statistically shown to be likely influenced by population density as an environmental factor in the watershed.
Since the late 20th century, increased development and recreational use near the coast have caused ecological destruction and landscape degradation. Furthermore, there is concern that rising sea levels due to climate change will accelerate coastal erosion. Progressive coastal erosion worldwide not only means a decrease in land area but also directly leads to the loss of habitat for a variety of marine and terrestrial ecotone-dependent organisms. Therefore, coastal erosion is an urgent issue for both human society and marine and terrestrial ecosystems.
Most studies of beach erosion on sandy beaches have used changes in the sandy beach shoreline as an indicator, and few have targeted changes in the dunes behind the beach. There are also scattered studies that have measured dunes in three dimensions and measured the changing, but none have focused on multiple sandy coasts. To clarify the reality of coastal erosion more realistically, it is necessary to understand and evaluate the topographic changes of multiple sandy coasts in three dimensions. For this purpose, it is necessary to analyze multiple sandy coasts, but until now, the difficulty of obtaining 3D data from multiple locations at multiple times for analysis has been one of the limiting factors in advancing the study.
This study will overcome the above issues by measuring and utilizing high-definition spatial information from UAVs (Unmanned Aerial Vehicles) and ALS (Airborne Laser Scanning). The accuracy of UAV-SfM (Structure-from-Motion) in reconstructing 3D structures of terrain and vegetation has improved remarkably. With conventional UAV-SfM, multiple ground reference points need to be surveyed and established separately due to the low accuracy (error: several meters) of the aircraft's positioning information. In recent years, RTK (Real-Time Kinematic) -GNSS (Global Navigation Satellite System), which enables highly accurate position acquisition, and UAVs have been integrated to dramatically improve positional accuracy (error: several centimeters). As a result, ground control points, which required a great deal of labor to install, are no longer necessary. The use of RTK-UAVs not only improves accuracy but also enables the acquisition of topographic information at multiple locations. This allows us to grasp the topographic changes of sandy coasts in three dimensions and a wide area, and we believe that this will lead to the clarification of the actual state of coastal erosion.
In this presentation, the amount of change (erosion and sedimentation) was calculated from the difference analysis between the DSM created by RTK-UAV-SfM and ALS to clarify the actual erosion of coastal dunes on the sandy coasts of Hokkaido, Honshu, Shikoku and Kyushu in Japan. Further, The analysis is carried out to clarify the relationship between watershed characteristics and sandy coast erosion, and the results will be presented.
The actual erosion of sandy coasts was evaluated using both erosion and sedimentation as indicators. There were many sandy coasts with erosion trends, and the erosion amount tended to be higher in the dune areas than in the beach areas. On the other hand, there are several sandy coasts with sedimentation trends, and there are differences in the trends of change from coast to coast. These differences were thought to be due to differences in the environment around the sandy coasts and the watershed characteristics. In particular, the amount of change in sandy coasts was statistically shown to be likely influenced by population density as an environmental factor in the watershed.