SAR Change Detection to Evaluate Flood Event Characteristics, Pre- and Post-Restoration of a Floodplain

A method using Sentinel-1 synthetic aperture radar (SAR) data to evidence flood changes after floodplain restoration is proposed. A Natural Flood Management (NFM) project on the Ouse river in southern England, undertaken by the Sussex Flow Initiative, was analysed to ascertain any reduction of previous flood risk. GIS operations were conducted on the results of the change detection analysis to identify how flood area, form and compactness were affected after the NFM installation, and how these changes relate to the project aims. Flood records based on internet-published drone footage verified the change detection methodology. A scorecard was developed to evaluate the benefits and disadvantages of spatial changes seen in post-restoration floods in comparison to inundation before the measures were installed. Evaluation results were used in the annual report of the SFI project to demonstrate the attenuation of floodwaters in accordance with the aims of the project.