Identifying Vegetation Succession Sites to Repurpose as Storage Spaces in the Alluvial Plain of the Lower Tone River Basin, Japan

Abstract The loss of potential storage space due to vegetation succession is a significant issue, particularly in unmanaged farmlands connected to drainage channels, reducing the effectiveness of the land in mitigating flood risk. This study aimed to discover unmanaged spaces within the alluvial plain of the Lower Tone River Basin, Japan, that have undergone vegetation succession. By monitoring the distribution of vegetation succession, the aim was to develop a technical method to identify and repurpose vegetation succession sites as storage spaces through proposed interventions to mitigate inland flooding within the alluvial plain of the Lower Tone River Basin. The analytical framework involved extracting alluvial plain areas, monitoring vegetation succession by integrating optical and synthetic aperture radar satellite images over the 2017–2024 period, analyzing the relationship between land-use types and vegetation succession patterns, extracting targeted vegetation succession sites, and classifying targeted vegetation succession patches based on height above the nearest drainage, distance to the nearest drainage channel, and other parameters. The classification resulted in three functional classes. Class 1 spaces were closely linked to water channels, making them critical areas for immediate floodwater storage. Class 2 spaces served as intermediate storage areas, situated at moderate distances from the water channels. Class 3 spaces provided final storage spaces for dispersed floodwater at the highest elevation and the furthest distance from the drainage channels. The sequential impact of inland flooding characterizes the functional hierarchy among Classes 1, 2, and 3, considering the on-site conditions. Overflowing from the drainage channels first impacts the Class 1 spaces. As the floodwater dispersed, it reached Class 2 spaces. Finally, Class 3 spaces served as the last line of mitigation, storing floodwater spread widely across the landscape. By identifying and categorizing vegetation succession patches for conversion into storage spaces, this study provides a basis for prioritizing areas for intervention and developing targeted flood mitigation strategies.