Geoheritage in lowland fluvial systems: preserving legacy landforms formed by natural and anthropogenic processes.

Fluvial systems in lowland environments in northwestern Europe have changed from nature to human-dominated systems. Climate change, as well as indirect and human activities such as land use change have an impact on the water and sediment balance, which may alter the river channel patterns, degree of sinuosity and channel dimensions. Direct human interventions such as levee construction and river straigthening may further change the morphological properties of river channels and their adjacent floodplain environment. In areas like lowland Belgium, the climatic transition from Late-Glacial to Holocene conditions resulted in a dramatic changes in river planform from braided to large meanders to small meandering channels. Next, these systems have experienced increasingly important human impact from the Neolithic to the present and rivers and floodplains have changed from anostomosing patterns in swampy floodplains to single-thread meandering channels with natural levees and backswamp areas to straighthened rivers disconnected from their floodplain. Depending on local conditions, channel patterns from all these time periods are still preserved in the landscape today and can increasingly be seen on high-resolution LIDAR elevation data. Also alluvial fans, crevasse splays and levees that are a testimony of increased sediment fluxes following human deforestation are preserved and represent a large variability in soil properties. All these subtle changes in topography and soil properties in these lowland environments that are related to millennia long changes in fluvial activity also lead to a high spatial variability in ecological conditions. With a renewed interest in river restoration projects (eg in line with the new EU nature restoration law), increasing biodiversity in floodplain environments through rewetting is often promoted. Whilst it is clear among geoscientists that the high biodiversity is strongly coupled to the large geodiversity in terms of topography, hydrology and soil properties, the geoheritage value coupled to this high geodiversity is not acknowledged by nature conservationists. Hence, many older channels may be dredged, enlarged, deepened to promote ecological conditions, however, withouth taking into account that geoheritage values may be destroyed. We encourage policy makers and nature conservationists to foster geoheritage in nature restoration projects. In this presentation, examples of highly geodiverse floodplains in northern Belgium will be shown and experiences with stakeholder interactions (river managers, nature conservationists, heritage agencies) and policy makers will be shared. I hope to stimulate discussion on how we as geoscientists can act best to promote the preservation of geoheritage in fluvial systems.