Nature-based flood mitigation using oxbow lakes as retention systems: hydrological routing and resilience assessment in a tropical watershed

ABSTRACT Graphical overview of an oxbow lake used as a Nature-based flood-retention system in a tropical watershed. The illustration shows floodwater entering the oxbow lake, temporary storage, controlled spillway release, and reduced downstream peak discharge. The system achieves approximately 11% peak-discharge reduction while supporting hydrological resilience and potential water-resource and ecosystem co-benefits. Flood mitigation in tropical watersheds increasingly requires sustainable approaches capable of maintaining effective flood-control functions under variable hydrological conditions. Although oxbow lakes possess considerable potential as Nature-based Solutions (NbS), their utilization as operational flood-retention systems remains insufficiently explored under tropical hydrological conditions. The study was conducted in the 931.11-km2 Krueng Keureuto watershed, where the evaluated oxbow lake has a maximum storage capacity of approximately 1.07 × 106 m3. This study evaluates the hydrological and hydraulic performance of the oxbow lake in Aceh, Indonesia, as a Nature-based retention system. An integrated hydrological-routing framework was developed to quantify flood-attenuation performance and storage effectiveness. The results demonstrate that the oxbow lake reduced peak flood discharge by 64.43 m3/s (approximately 11%) under the 2-year return-period flood scenario while maintaining safe storage operation without overtopping. The flood-attenuation mechanism was primarily influenced by temporary floodplain storage and controlled spillway release, which moderated downstream flow propagation. Hydraulic calibration and hydrological plausibility assessment showed reasonable consistency between simulated hydraulic responses and observed water levels and flood characteristics during the December 2023 event. In addition to flood mitigation, the oxbow lake may provide additional co-benefits, including seasonal irrigation storage, groundwater recharge, raw-water supply, and downstream flow regulation. Compared with conventional gray flood-control infrastructure, oxbow lake-based retention systems preserve natural hydrological connectivity while potentially reducing environmental disturbance. These findings demonstrate the potential of oxbow lakes as Nature-based retention systems that enhance hydrological resilience and support sustainable watershed management in tropical river basins.