Molnar Peter
Sediment dynamics and morphological change in the braided Pfynwald reach of the Rhone River
Project Number: Parcs Data Center 9952 / 4D CH-4841
| Project Type: |
Master |
| Project Duration: |
12/01/2008 - 08/31/2010 project completed |
| Funding Source: |
other , |
| Leading Institution: |
ETH Zürich |
| Project Leader: |
Prof. Peter Molnar
Hydrologie und Wasserwirtschaft
Institut für Umweltingenieurwissenschaften (IfU)
ETH Zürich
HIL D 23.1
Stefano-Franscini-Platz 5
8093 Zürich
Phone: +41 (0) 44 633 29 58 ; +41 (0) 44 633 30 75
FAX: +41 (0) 44 633 10 61
e-Mail: molnar(at)ifu.baug.ethz.ch
https://hyd.ifu.ethz.ch/ |
Research Areas:
Disciplines:
Keywords:
Sediment, steep gravel-bed river, debris flow, model system BASEMENT
Abstract:
Steep gravel-bed rivers with high sediment supply and streamflow form a braided channel structure. The Pfynwald Rhone River reach between Susten and Sierre, located in the Rhone valley in the Central Alps of Switzerland, has kept its natural braided morphology. The nearby located Illgraben catchment, which is one oft he most active torrents in the Alps, has a large impact on the characteristics of the Pfynwald River section. There is large and instantaneous sediment supply to the Rhone River from the Illgraben through debris flows. The underlying research hypothesis of this study is that the interactions of flow regime, sediment supply and channel morphology are fundamental in order to quantify the sediment dynamics in braided rivers.
In this thesis the quantification of sediment transport is addressed by means of a numerical sediment transport model. The one dimensional as well as the two dimensional model of the numerical sediment transport model system BASEMENT are applied to the study reach. In the calibration process sensitive model parameters are identified.
The one dimensional model BASEchain is calibrated on the basis of annually surveyed topographic data for the period of 1995 to 2007. The adjusted 10 grain class model configuration is then used to investigate the sensitivity of the evolution of the longitudinal profile and of the mean annual sediment transport rate through the reach with respect to variable boundary conditions.
The two dimensional model BASEplane is calibrated just hydraulically due to a lack of data for a calibration of sediment transport. The spatial patterns of erosion and deposition in the channel bed for two different scenarios are addressed with the aid of the calibrated 2d-model using a mobile riverbed.
On the basis of a balance of observed and computed sediment volumes in the Pfynwald reach the mean annual sediment supply by the Illgraben and the mean annual bed load transport rate are estimated. For the period of 1995 to 2007 a sediment input of roughly 140’000m3/a results. The sediment transport rate in the Pfynwald reach decreases from 150’000m3/a at the confluence with the Illgraben to 30’000 m3/a at Sierre.
This study highlights that the application of numerical models to relatively steep alpine rivers with a braided morphology is a very difficult task and that current numerical models are not yet fully adequate to simulate satisfactorily sediment transport and erosion and deposition in such very dynamic river reaches. While the pure hydraulic simulations yield excellent results, the sediment transport computations need to be regarded with extra care, particularly concerning the one dimensional model, which appeared to suffer from many inconsistencies.
Leading questions:
How can sediment transport in the braided Pfynwald section of the Rhone River be modelled by means of the software system BASEMENT?
Publications:
Rüedlinger C. 2010. Sediment dynamics and morphological change in the braided Pfynwald reach of the Rhone River Institute of Environmental Engineering (IfU), Institute for Atmospheric and Climate Science (IAC), ETH Zurich.
PDF Masterarbeit
Last update: 4/5/22
Source of data: ProClim- Research InfoSystem (1993-2024)
Update the data of project: CH-4841
Go Back