SNF project: Field measurements of sediment-flux-driven bedload erosion

Bedrock reach shaped by bedload transport at the Gornera glacial stream, Zermatt. Alexander Beer (WSL)

Photogrammetric surveying of erosion slabs installed in the streambed. Erlenbach stream, Alptal. Alexander Beer (WSL)

Erosion of bedrock and concrete structures is crucial for the evolution of river cross sections and hydraulic engineering. Sediment particles promote erosion by impacting rock surfaces and plucking out small splints. So far there are few field studies worldwide of detailed erosion measurements parallel to discharge and sediment transport data over short timescales. That is due to difficulties in measuring in natural streams, unknown timing of sufficient discharge events and hardly constrainable sediment transport rates.

In this project erosion rates are measured on exposed bedrock surfaces and on stones equipped with erosion sensors. Highly accurate laser scanning and photogrammetry is used to measure erosion rates in the field at different spatial and time scales. Sediment load passing the measuring sites will be investigated to bring up relationships between sediment transport and erosion.

Field work is conducted at two mountain streams where long-time hydrological data exists. At the hydrological test site at the Erlenbach, Alptal, Canton Schwyz instrumented stone slabs were installed in the bed and their surface is surveyed regularly. Passing bedload can be estimated by volume calculations of sediments in the retention basin, geophone impulses and bedload samples during transport events taken by so called basket samplers. The second field site is below the Gorner glacier in the matter valley, Canton Valais. There several bedrock surfaces are surveyed that are overflown during flushings of settling basins from the glacial stream captured for hydropower procdution. Here bedload volumes are derived from the filling of these basins.

Gained data and calculations shall be used for further development and improvement of existing erosion and landscape evolution models. They shall serve to validate formulas for bedload transport calculations in steep mountain streams and can help for a better evaluation of sediment volumes in hydropower facilities.

Participants

• Alexander Beer
• Jens Turowski
• James Kirchner

Contact

• Alexander Beer