Fluvial sediment budget out of balance. An effect of climate change and anthropogenic influence on rivers

SUPERVISOR: Christoph HAUER

PROJECT ASSIGNED TO: Michael PASTER 

It is predicted that global warming generates sediment surplus in high alpine areas. Triggered by the temperature increase, deglaciation and permafrost degradation create (fluvial) transport-limited conditions by the storage of big quantity of meta- and unstable sediment within glacier forelands (proglacial areas). This very high sediment supply in the mid- to high-latitudes will become the most significant process in high-alpine areas for the next few hundred years.[1] Fluvial sediment reworking, one of the predominant processes in proglacial areas[2], leads to a continuous switch between transport and supply-limited conditions in catchment as well as on the reach scale as a consequence of permanent altered sediment availability. However, the sensitivity of (proglacial) fluvial systems to global warming is generally not yet fully understood. Predictions of the future morphological development and sediment transport are uncertain up to date, but will become even more important in future (e.g., reservoir management or natural hazards assessment). In contrast to the natural sediment surplus in high-alpine proglacial areas, the sediment continuum of lowland rivers is interrupted by anthropogenic interventions (e.g., transversal structures). As a consequence, they prevent a natural dynamic sediment regime where erosion is balanced by deposition.[3] This results in sediment surplus above and sediment deficit downstream of such anthropogenic obstructions, with consequences like cost-intensive sediment removal (upstream) or channel incision and habitat degradation downstream (e.g., riverbed clogging by fine sediment). In addition to human activities (e.g., reservoir flushing), climate change by e.g., erosive precipitation events is a key parameter for increasing (fine) sediment input in lowland rivers.

The main objective of this project is to make morphological assessments of high-alpine to lowland rivers (holistic view of the sediment dynamics) in terms of changing fluvial processes, triggered by global warming as well as anthropogenic influence. For this purpose, improved process understanding of fluvial river morphology in proglacial high-alpine rivers is targeted, since such fluvial processes can be investigated from the sources in high altitudes due to recently deglaciated areas and the absence of human interventions. This improved process understanding should in turn help to optimize river continuum measures in lowland rivers. Changing sediment input and composition, as well as altered hydrology, require adjustments in the measurements, assessments and evaluations of sediment regimes and the sediment continuum. This is an important task to improve the reservoir and ecological functionality of (high-alpine and lowland) rivers to meet the major future challenges of 21^st century.[4] Thus, this project can primarily be associated to the HR21 Research Cluster II (connectivity), as it relates to improved process understanding of changing fluvial sediment dynamics.