The geomorphology of a lowland river and its relevance to environmental management (Lys River, Belgium)

Abstract

Lowland rivers with minimal topographic demarcation present significant challenges for geomorphological mapping. This study developed a detailed 1:50,000 geomorphological map of the Lys Valley (Belgium) by generating a relative elevation topographic surface from a high-resolution LiDAR-based 1-m Digital Elevation Model (DEM). This surface visualises topography as elevation relative to the local river level, revealing subtle landforms that are otherwise difficult to detect. Combined with thematic datasets and targeted field validation, the method identifies four geomorphological sections, characterised by features such as natural levees, point bars, flood basins, paleo-channels, oxbow lakes, and aeolian dunes. By moving beyond traditional reliance on soil maps, this integrated approach offers a more accurate basis for flood risk assessment, river restoration, and geoarchaeological research. As the Lys River is a restoration priority under the Seine–Scheldt waterway project, the map provides a high-resolution resource for planning and stakeholder engagement. Key policy highlights Utilising a relative elevation topographic surface enables accurate large-scale mapping of lowland environments (here the Lys Valley in Belgium), supporting environmental management; of floodplains in particular The map holds broader significance for studying human-environmental histories over longer time periods.