Conferences - Seminars
EESS talk on "Sediment Supply: The Underrated Ruler in Bedload Transport"
By Dr Francesco Comiti, Associate professor, River Basin Group, Faculty of Science and Technology, Free University of Bozen-Bolzano (Italy)
Dr. Francesco Comiti (born in Venezia, Italy, in 1975) is associate professor at the Free University of Bozen-Bolzano (Faculty of Science and Technology) since 2015. He obtained his PhD at the University of Padova in 2004, and later in 2007 he was Fulbright Visiting Scholar at Colorado State University (U.S.A.). Current teaching activities include rural hydrology and hydraulics, management of natural hazards, hydromorphology and sediment transport in mountain rivers. His research focuses on the monitoring of water, sediment and wood fluxes in mountain basins, including ecohydrological dynamics, long-term river changes and geomorphic response to flood and debris flow events. He is currently associate editor for “Water Resources Research” and member of the Editorial board of “Geomorphology”.
High-elevation catchments are highly dynamic systems which are undergoing rapid hydrological changes. Seasonally, headwaters are responsible for the transport of large volumes of runoff and sediment (fine and coarse) to the downstream channel network, which tend to adjust to the upstream-imposed liquid and solid fluxes. Predicting how mountain rivers will change under different future climatic scenarios is key for their sound management. But, do we know enough on how bedload transport works to aim at such an ambitious goal ?
The presentation will focus on recent results obtained in two glacierized basin of the Eastern Italian Alps, where runoff and sediment transport have been monitored since 2011. An array of different methodologies to measure sediment transport (both suspended and bedload) have been deployed. In parallel, hydrologic tracers were used to understand timing and relative contribution to runoff of different water sources. Additionally, morphological monitoring of the main channel was carried out. Results indicate that the relationship between sediment transport and water discharge is strongly season-dependent, with bedload rates and suspended sediment concentrations consistently much higher (1-2 orders of magnitude) during glacier melt than during snowmelt flows, for identical water discharges. Contrasting hysteresis loops were found for bedload and suspended transport in relation with snow- vs. ice melt flows, highlighting the complexity of sediment supply mechanisms in mountain basins. In contrast, the inclusion of sediment supply variations – which require the identification of time-varying sediment sources and of their connectivity to the channel network – in bedload transport predictions for both scientific and practical purposes is widely neglected. Indeed, the traditional application of transport capacity-based estimations may lead to highly erroneous bedload yields, and in turn to wrong forecast on the expected morphological changes in river systems.
Accessibility General public
This event is internal