Quantifying the Lifespan of 3D Flood Structures: Unlocking the Potential of Flood Detention Areas for Enhanced Flood Control in China

Abstract The escalating frequency and magnitude of floods pose significant challenges to traditional flood control measures with fixed defense capacities, such as levees, dams, and reservoirs. Flood Detention Areas (FDAs) have been widely implemented in many countries as solutions to extreme flood events, functioning by temporarily holding excess floodwaters and serving as farmland and residential zones during periods of inactivity. However, uncertainties regarding their flood control effectiveness, concerns over post‐activation livelihood recovery, and the lack of management guidelines have limited their broader adoption and effective utilization. Here we proposed an innovative remote sensing and AI based framework to derive the lifespan of 3D flood structure incorporating flood extent and depth. Taking the once‐in‐a‐century flood in China's Hai River Basin (HRB) in 2023 as example, the thrived two‐month‐long catchment‐scale 229,000‐km 2 3D flood structure enabled the first quantitative evaluation to the flood control and drainage capacities of FDAs. The results revealed that eight activated FDAs detained 2.7 billion m 3 of floodwaters, with most of the water drained within two weeks. River conveyance capacity was identified as a pivotal factor in the flood drainage process. The 3D flood structure further highlights disparities in detention processes between upstream and downstream FDAs due to cascade effects, providing valuable guidance for their management. These findings resolve the key uncertainties and debates regarding FDAs, providing insights to enhance FDA management, and supporting their broader implementation in flood‐prone regions with extensive agricultural land use and dense populations, thereby mitigating future flood risks and minimizing associated losses.