Hydrology, Cryosphere & Earth Surface Meeting Report

Braiding Rivers: State of the Art and Future Challenges

Braided Rivers Workshop 2014;
Le Domaine de Sainte Croix, France, 23–27 June 2014

By , Alain Recking, and Nicola Surian

Braided Rivers Workshop 2014;
Le Domaine de Sainte Croix, France, 23–27 June 2014

Eleven years after the last Braided Rivers Conference in Birmingham, England, a group of 47 scientists from 11 countries met at le Domaine de Sainte Croix, France, to discuss the current state of knowledge and future research directions for braided rivers. Several core themes and research challenges arose from the 5-day workshop.

First, there remains an inadequacy of tools and metrics to characterize the diversity of multichannel rivers. Open questions include the following: Is there a morphodynamic and sedimentological signature of braiding, and is it possible to identify a set of universal conditions that transcends scale (from laboratory models to proglacial gravel bed streams to large sand bed rivers like the Brahmaputra). Significant advances will be made by exploiting developments in Earth observation technologies, particularly airborne and terrestrial lidar, three-­dimensional image reconstruction, multibeam echo-sounding, and subsurface geophysics.

Second, measurements of flow and sediment transport are often more challenging than in other river systems, and comprehensive data sets remain scarce. Participants agreed that research focused on selected observatory sites, spanning temporal and spatial scales, would be an effective route for yielding such data sets.

Third, numerical modeling opens exciting opportunities for the study of braided rivers and can be used to guide future investigation, supported by field measurements and laboratory experiments, although existing models are challenged by the highly dynamic behavior and complexity of braided systems. Future models require improved methods for reproducing lateral channel migration and bar form morphodynamics, as bed and banks coevolve. Discussion also highlighted the questions of what aspects of braided river morphology can be inferred from the sedimentology and if numerical models can help answer this through long-term simulations.

Fourth, from a river management perspective, future research must focus on the parameters controlling braided river evolution, such as long- and short-term sediment supply. The case of the Drôme River is emblematic; it faces a long-term decline in braiding intensity, associated with changes in land use through reforestation in the upper catchment, climatic change since the end of the Little Ice Age, and more direct controls through embankments, drop structures, and gravel mining.

Fifth, participants also emphasized the need to define the ecological template of these heterogeneous environments, with an improved understanding of the interrelationship between the physical environment and ecological functioning. Links between physical complexity and habitat diversity appear to be key for more detailed investigation to quantify existing thresholds controlling riparian vegetation and fauna colonization.

Overall, the workshop highlighted the need for a multiscale approach to the study of braiding based on collaborative research that fosters data sharing and community-led model development and testing.

The meeting was organized as an “open space workshop,” where ad hoc working groups reviewed the different research themes. Summaries of these discussions were reported to the plenary assembly each day. More than half of the participants were Ph.D. candidates and postdoctoral scholars, who also presented research during a poster session. A field trip to the Drôme River illustrated its resilience to anthropogenic impacts and alternative solutions for restoration of river form and function.

Further information, including the list of participants, can be found at http://braidingriver.irstea.fr.

—Walter Bertoldi, University of Trento, Trento, Italy; email: [email protected]; Alain Recking, Institut national de recherche en sciences et technologies pour l’environnement et l’agriculture (IRSTEA), Saint Martin d’Hères, France; and Nicola Surian, University of Padova, Padua Italy

© 2014. American Geophysical Union. All rights reserved.