Gilles Rixhon
Université de Strasbourg, France
Accurate dating of Quaternary fluvial archives is critical: disentangling the timing and drivers of river incision and landscape evolution across NW European river systems
This keynote highlights how robust chronologies of fluvial terraces are essential for directly linking phases of river incision to both climatic forcing and tectonic uplift. By combining cosmogenic nuclides, luminescence and electron spin resonance dating, it is now possible to establish consistent, high-resolution temporal frameworks across major European catchments. Key terrace records/staircases of the Rhine, Moselle and Meuse document successive incision phases throughout the Variscan Rhenish-Ardenne Massif. When accurately dated, these archives reveal both regionally coherent trends and significant time lags in incision between neighbouring basins, underscoring the complexity of large-scale controls on river response over Quaternary timescales. Comparable geochronological approaches applied to the Seine and Somme catchments in northern France extend this perspective to lowland environments draining the Paris Basin. Despite lower gradients, their terrace systems record similar patterns of incision and aggradation driven by climate variability and base-level fluctuations. Precise dating of fluvial archives thus (i) provides a unified framework for comparing fluvial responses across contrasting geomorphic settings and (ii) constitutes a critical tool for disentangling the respective roles of climate and tectonics in shaping European landscapes. It also provides essential chronological constraints for archaeological sites preserved within these fluvial archives, thereby strengthening interpretations of human occupation in relation to environmental change.
Biography
Gilles Rixhon is a specialist in physical geography, with a strong focus on geomorphology and the analysis of surface processes, primarily fluvial dynamics, while also addressing karst and coastal systems. His research places particular emphasis on the dating of fluvial terraces as key archives of landscape evolution, using cosmogenic nuclides, luminescence, and electron spin resonance, to establish robust chronologies of river incision and sedimentary sequences over Plio-Quaternary timescales. Through this work, he reconstructs long-term environmental changes and improves understanding of the coupling between climate, tectonics, and surface processes. His research also extends to palaeoenvironmental reconstruction, geoarchaeology, and sedimentology, contributing to broader insights into Earth surface dynamics and human-environment interactions. He is currently Professor of Physical Geography at the University of Strasbourg, within the LIVE laboratory, after holding positions at ENGEES in Strasbourg (associate lecturer) and at the University of Cologne (postdoc). He completed his academic training and doctoral research between the University of Liège and Aix-Marseille University, and obtained his habilitation at the University of Strasbourg.
Anne-Julia Rollet
Université Rennes 2
Restoration of low-enery rivers
The keynote will examine the specific characteristics of the hydromorphological functioning of low-energy watercourses, using examples from north-western France. The aim will be to draw operational implications regarding how to incorporate these specific characteristics into restoration projects. Several key areas will be explored: the specific challenges associated with continuity, the importance of biological monitoring, the enduring effects of human activities, and the nature of the technical choices involved in restoration work.
Biography
Having completed her PhD at Lyon 3 University, Anne Julia Rollet has been a Senior Lecturer at the University of Rennes 2 and a member of the UMR6554 – LETG laboratory since 2008. Her research focuses on the contemporary functioning of the hydrological, morphological and sedimentary components of anthropogenised river systems, and on the management and physical restoration of these environments. She is thus interested in the biophysical interactions between the main channel of the rivebed and its catchment area on the one hand, and its floodplain on the other, within complex systems where society-environment interactions are numerous and long-standing (changes in land use, fluvial works such as weirs, dams and river straightening, etc.). For the past two years, her research has also sought to re-examine the hierarchy of controlling factors in low-energy river systems by studying the relative importance of zoomorphological activity in the functioning of these systems.
David Sear
Southampton University
Structure and dynamics of chalk rivers
Chalk rivers are uniquely dependent on past processes and biological mediated processes for their ecological function. Decades of catchment modification and channel management have left a legacy of degraded river ecosystems that continue to be impacted by catchment scale delivery of sediments and other pollutants to the extent that we do not really know what a naturally functioning chalk looks like. Restoring chalk riverscapes therefore demands application of novel sources of evidence including paleoenvironmental analysis to support the development of restoration visions. An important element of restoration planning lies in understanding the diversity of chalk river types and their importance in delivering a range of ecosystem services, many moderated via biogeomorphic processes.
Biography
David Sear is Professor of Physical Geography at the University of Southampton. He is also Chair of the physical habitat and ecology advisory group which supports the UK’s national Chalk stream strategy. He is an applied fluvial geomorphologist with 35 years’ experience understanding and documenting sediment transport and the geomorphology of chalk rivers. In 1998 he convened the first workshop on Groundwater Dominated rivers, and has published widely on chalk river processes. He helped set up the UK River Restoration Centre and has been actively involved in developing tools for supporting process-based river restoration.
Ellen Wohl
Utah State University
Biophysical Interactions in Gravel-Bed River Corridors
Gravel-bed river floodplains have been described as an ecological nexus of regional biodiversity because of the many ecosystem services provided to freshwater and terrestrial environments. These services rest on continued maintenance of a patchy, spatially and temporally heterogeneous river corridor that ecologists describe as a shifting habitat mosaic. I review several years of research on biophysical interactions among flow, sediment, large wood, beaver, and living vegetation in the Swan River corridor of Montana, USA to illustrate the processes underlying the shifting habitat mosaic. I also consider the implications of these findings for management and restoration of lowland gravel-bed river corridors.
Biography
Ellen Wohl received a BS in geology from Arizona State University and a PhD in geosciences from the University of Arizona. She is a professor in the Department of Geosciences at Colorado State University and a University Distinguished Professor. Her research focuses on physical processes and forms in river channels and floodplains, and how these interact with biogeochemistry and ecological and human communities. She has conducted field research in diverse environments around the world.
