3:30 PM - 3:45 PM
[HTT14-01] Watershed characteristics influencing volume changes in sandy coasts of Japan
★Invited Papers
Keywords:coastal dune, remote sensing, RTK-UAV, ecosystem
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. A Generalized Linear Mixed Model (GLMM) was performed with this amount of change as the objective variable and watershed characteristics (e.g., topography, forest vegetation, land use, etc.) as explanatory variables. The reason for this analysis is to understand the watershed characteristics that affect changes in sandy coasts.
The changes in sandy coasts were evaluated using both erosion and sedimentation as indicators. Many sandy coasts exhibited erosion trends, and the erosion amount tended to be higher in the dune areas than in the beach areas. On the other hand, some sandy coasts showed sedimentation trends, and there were variations in change patterns observed from coast to coast. These differences are believed to result from variations in the surrounding environment and watershed characteristics. In particular, the statistical analysis indicated that the magnitude of change in sandy coasts is 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. A Generalized Linear Mixed Model (GLMM) was performed with this amount of change as the objective variable and watershed characteristics (e.g., topography, forest vegetation, land use, etc.) as explanatory variables. The reason for this analysis is to understand the watershed characteristics that affect changes in sandy coasts.
The changes in sandy coasts were evaluated using both erosion and sedimentation as indicators. Many sandy coasts exhibited erosion trends, and the erosion amount tended to be higher in the dune areas than in the beach areas. On the other hand, some sandy coasts showed sedimentation trends, and there were variations in change patterns observed from coast to coast. These differences are believed to result from variations in the surrounding environment and watershed characteristics. In particular, the statistical analysis indicated that the magnitude of change in sandy coasts is likely influenced by population density as an environmental factor in the watershed.