Floodplain Inundation Mapping and Modelling: A Case Study for the Daly Catchment in Northern Australia

Floodplain inundation modelling is considered an essential part of river basin management for engineering, ecological and environmental perspectives. This study characterises inundation dynamics and quantifies river-wetland connectivity across the Daly River catchment using a two-dimensional hydrodynamic model (MIKE 21). The model was configured for the downstream reaches of the Daly River and its tributaries, focusing on floodplain regions subject to seasonal inundation. High resolution topographic data (1 m LiDAR) for the main river and 30 m FABDEM for surrounding areas) were used to construct the elevation model. A gridded land use and land cover (LULC) map was used to derive surface roughness in the model. We assessed inundation dynamics using five different high flood events from 2015 to 2024. To calibrate the MIKE 21 HD model, we analysed a representative flood event by benchmarking modelled water levels and extents against Sentinel-1–derived inundation maps and gauged water levels. Our results reveal spatial and temporal variability in floodplain inundation and highlight the influence of both seasonal and anthropogenic factors on inundation extent.