Flood risk reduction through nature-based diversion solutions: an integrated design framework leveraging palaeochannels at the floodplain scale

Abstract This study presents an integrated framework for identifying, designing, and evaluating palaeochannels as a nature-based solution for flood mitigation at the floodplain scale. The framework combines field observations, GIS analysis, high-resolution two-dimensional hydrodynamic modelling, and flood hazard and damage assessment. Palaeochannels are first identified using aerial imagery and digital elevation data, then incorporated into hydrodynamic simulations to assess their role in improving floodplain connectivity and reducing peak flood levels. The framework is applied to the Moree Plains in New South Wales, Australia. Results show that reconnected and modified palaeochannels can reduce flood extent and associated impacts, particularly during moderate flood events (≥ 5% annual exceedance probability), where reductions in peak water levels and hazard intensity are observed. The effectiveness of these interventions depends on maintaining hydraulic connectivity with the main river and appropriately adjusting channel dimensions to increase conveyance capacity. However, results also indicate that small-scale palaeochannel modifications provide limited flood mitigation benefits and may not justify implementation costs. In addition to flood risk reduction, palaeochannel restoration offers ecological co-benefits, including improved habitat diversity and enhanced environmental water distribution across the floodplain. Overall, the study demonstrates that palaeochannel-based interventions provide a practical, scalable, and locally adaptable approach to integrated floodplain management, supporting both flood mitigation and environmental sustainability under changing hydrological conditions.