SNF project: Sediment transport in steep streams

Basket sampler for bedload transport measurements in the Erlenbach. The basket is moved into the flow automatically when bedload transport occurs (Picture: D. Rickenmann, WSL)

Background and aims

Accurate prediction of bedload transport is important for hazard assessment and in engineering applications. The main purpose of this proposed research project is to advance the understanding of bedload transport processes through detailed field observations. For more than 20 years discharge and bedload transport has been monitored in the Erlenbach. Deposited sediment volumes in the retention basin are surveyed regularly and geophone sensors measure the acoustic signals of moving particles.

Recently the bedload monitoring infrastructure in the Erlenbach has been upgraded, with two main aims: the improvement of the indirect measurement method using geophone sensors and the improvement of direct observation of sediment transport processes in steep streams.

Brief description of the sampling station

The core of the upgrade is the installation of basket samplers on the check dam upstream of the retention basin. The baskets are mounted on a rail on the dam and can be moved laterally using a winch system. Sampling occurs automatically once bedload transport is observed. The first basket was installed in autumn 2008. A crane can be used to lift the baskets with bedload samples of 50-200 kg to a working platform. There, the sample can be analysed for its grain size distribution with a mobile sieving station.

With the baskets samplers we are able to collect bedload samples at specific times of interest. In addition, the new infrastructure offers the advantage to compare the detailed geophone signals with short term measurements of bedload transport rates and grain size properties. To optimise the potential of the site, the full geophone signal will be recorded at 10 kHz in future.

Geophone sensors mounted at a check dam in the Vogelbach, Alptal (Picture: B. Reye)

Synergy with other projects

We will compare the detailed observations from the Erlenbach with measurements from other sites where geophones are employed. These are, amongst others, the Fischbach and the Ruetz in Austria and the Riedbach in southern Switzerland, where measurements have been made since 2008. In addition, geophones will be installed in the Nahal Eshtemoa in Israel, where long-term sediment transport observations allow an exact calibrations of the instruments.

Links

• Long-term bedload monitoring
• HYDRALP
  

Participants

• Jens Turowski
• Dieter Rickenmann

Contact

• Jens Martin Turowski