Research on Alpine Sediment Processes, Morphodynamics and Ecosystem Behaviour Considering Extreme Events

Extreme floods of the recent 14 years in Austria demonstrate the vulnerability of mankind against such events. River geometry is not constant during flood events as an increase of their width by up to 14 times has been documented. Hence, morphodynamics is of central importance for flood risk management and therefore an improved understanding of the underlying sediment transport is fundamental.

On the other hand sediment transport and morphodynamics form the backbone for the ecosystem of rivers and thus determine the ecosystem services. Important shortcomings concerning this matter are the lack of field data, adapted calibrated and validated mathematical models for sediment transport and the relevant ecological processes. Thus, in Alpine rivers, changes of sediment transport processes like interruption of the sediment continuum are of great importance due to their ecological, energy and risk-related consequences.

Based on these knowledge gaps an integrating project called RAISE was outlined, aiming to combine longterm (e.g. geological setting) with shortterm (e.g. extreme floods) sediment research, including abiotic and biotic processes and particularly related socioeconomics.

The objectives are to link and integrate sediment data sampled over the last decade at various Austrian sites, study the interlinkages between sediment sources, erosion, transfer, deposition and remobilisation in relation to climate change (e.g. glacier retreat) for an integrated and sustainable sediment management.

First outcomes show the essential role of sediment supply on sediment transport processes, partly based on anthropogenic interference. Based on longterm bedload data, different process types were defined reflecting different bedload rates at comparable hydraulic conditions. Based on this conceptual model of bedload transport process types as a function of bedload transport efficiency and dimensionless stream power, sampled data, having order-of-magnitude variabilities, can now be categorized and described. A numerical sediment transport model was set up for a stretch where extensive bedload transport measurements took place over the last decade to establish interfaces between the different models and to increase process understanding. The sediment transport model was also applicable during flood events with an intra-event modification of the transport formula.