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CCES-APUNCH: Hydrological extremes and sediment transportBackground
APUNCH is a poly-project within the ETH Competence Centre for Environment and Sustainability; the project includes experts from 9 different institutes at EPF Lausanne, ETH Zürich, MeteoSwiss, and WSL. The goal of APUNCH is to gain a comprehensive and process chain based insight into the response of Alpine watersheds hit by storm rainfall events. These insights will allow the formulation of improved or new process models. Among others, some major challenges of the project are: (i) the investigation of the space-time structure of rainfall in mountainous regions; (ii) the laboratory and field experiments on initiation and evolution of sediment transport in steep channels and under rapidly varying flow conditions; (iii) the combination of physical modelling, field testing and numerical simulations to analyse and predict the conditions that lead to failure of dykes; (iv) the across-scales monitoring and modelling effort, which is expected to lead, on the long-term, on a process-based integrated watershed model system that can simulate the response of a watershed to set of complex hydrological hazards. ObjectivesWithin
APUNCH the Research Unit Mountain Hydrology and Massmovements focuses on the
assessment of flow conditions, on the initiation of sediment motion and on
sediment transport in steep channels with irregular bed morphology. The
objectives of this part are to perform measurements on bedload transport and flow
hydraulics in steep streams, and to develop a new theoretical approach to
describe initiation of particle motion and sediment transport in steep channels. Current IssuesAt the Riedbach, Ct. Valais, field investigations of channel morphology, flow conditions and bedload transport rates were conducted. Bedload transport was measured using so-called bedload traps, which consist of a nylon net attached to a aluminium frame (Figure 2). The bedload traps were mounted on the channel bed to collect bedload for about 1-60 minutes, depending on transport intensities. For further analysis, bedload transport measurements from the Erlenbach moving bedload baskets are used additionally. Measured transport rates were compared to calculated transport rates. As often observed in steep streams commonly used transport equations, developed either on lab data or on field data of lower gradient streams, overestimate transport rates. Within the APUNCH project, a sediment transport equation was re-analyzed (paper in preparation) based on field data of about 45 streams with channel gradients ranging from 0.05 to 17%. With this equation it is possible to significantly reduce the overestimation of sediment transport rates for the Riedbach (Figure 3). More informationParticipants
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