A one-dimensional bedload transport model for steep slopes

Abstract

A sediment routing model called SETRAC has been developed to simulate bedload transport in torrents and mountain streams. SETRAC is the acronym for Sediment Transport in Alpine Catchments. Flow resistance is modelled using an approach proposed by Smart and Jäggi, and bedload transport is predicted with an equation by Rickenmann. Form roughness losses are accounted for by an empirical approach which is based on flow resistance observations in mountain streams. It is possible to compute fractional bedload transport taking grain sorting effects into account. Flow hydrographs are routed through the channel network by using the kinematic wave approach. An application of the model is discussed for an extreme flood event of August 2005 in the Chiene catchment, Switzerland, which mobilized 120,000 m³ of bedload along the mountain stream. The simulation results underline the importance of form resistance when modelling bedload transport in steep and rough channels.

Keywords:

• Bedload transport
• form resistance
• numerical model
• simulation
• steep slope

Acknowledgements

The project has been funded by the Austrian Science Fund (FWF) through the Translational Research Program L147 on “Sediment routing model for steep torrent channels”. The Swiss Federal Office for the Environment (BAFU) supported the Chiene case study and provided the LiDAR DTM for the situation after the event 2005. The LiDAR DTM before the event 2005 was provided by the Swiss Federal Office of Topography (swisstopo). All figures showing LiDAR analysed results are based on “DTMAV DOM-AV ©2008 BAFU” and “DTM-AV DOM-AV ©2008 swisstopo” (DV033492.2). We thank Jörg Häberle and the Forest Department of Berne Canton for organising the past event LiDAR measurements, and Martin Hägeli and Christian Ginzler, both at WSL, for their support.

Notes

SETRAC, as well as a user guide, a technical manual and tutorials will soon be available as free downloads at www.bedload.at.