The Effectiveness of Oxbow Lake Restoration as a Flood Reduction Nature-Based Solution (NbS) in the Kapuas River Basin, Indonesia

The frequency and severity of flooding in the Kapuas River Basin are increasing. One possible mitigation strategy is utilizing oxbow lakes as natural retention ponds, but sedimentation has reduced their storage capacity. Oxbow lake restoration is a part of Nature-based Solutions (NbS), aimed at restoring the natural functions of the floodplain ecosystem to reduce water runoff and create water reserves during dry seasons. This study offers a novel evaluation of oxbow lake restoration within a tropical floodplain system and provides a quantitative NbS assessment through integrated hydrological–hydraulic modeling. Hydrological modeling was performed using rainfall and field observation data to generate design rainfall and runoff. Hydraulic modeling was carried out with HEC-RAS 2D, utilizing terrain developed from a Digital Elevation Model (DEM) to simulate changes in storage capacity before and after restoration. The results demonstrate that reconnecting oxbow lakes to the main channel can reduce flood peaks by 12–18% and lower adjacent flood levels by up to 30 centimeters. The storage capacity of the Sinau, Jaras, and Selanyut oxbow lakes grew by 25–40% following dredging. Overall, incorporating NbS into river basin management offers an effective and sustainable way to reduce flood risk in the Kapuas River Basin. The findings provide valuable guidance for enhancing ecosystem-based flood resilience in this and other tropical regions.