SNF Projekt: Sediment transport measurements with geophone sensors

Background

Overview of the array of geophones in the Erlenbach with automated metal basket samplers (WSL archive).

Many formulas derived from a large range of different approaches have been created to predict sediment transport. In contrast to lowland gravel-bed rivers, a small number of studies have tried to predict sediment transport in torrents (stream gradients higher than about 5%). Bedload dynamics prediction in steep headwater channels is challenging mainly due to the interaction with active hillslope processes, the wide range of sediment sizes, discharge variance in time, the alternating bed roughness and the presence of steps and pools.

The Erlenbach stream in Alptal (Schwyz) is one of the Swiss Federal Research Institute WSL catchments were Bedload transport observations are available since 1982. In 1999 the piezoelectric bedload impact sensors (PBIS) were replaced by geophone sensors. Previous studies have demonstrated that the signal created by the kinetic impacts of bedload material registered by the geophone over an impact plate is a possible way to quantify bedload transport (The number of impulses per unit time being proportional to the total bedload volume of an event). The device calibration clearly depends on site specific variables such as the grain distribution, material density and discharge characteristics.

Objectives

The project aims to identify the main factors influencing the response of the geophone and to determine which aspects of calibration can be generalized in un-calibrated field sites. Further on, the possibility to extract grain size information from the geophone measurements will be explored (acoustic signal analysis).

Schematic illustration of experimental set up for laboratory experiments at VAW-ETHZ with bedload transport over geophone sensors system using particles from different streams where field measurements with geophone sensors and field calibration data are available.

Approach and methods

Bedload transport rates and grain sizes will be measured during short time intervals in the Erlenbach. Systematic flume experiments will be carried out using both uniform grain size classes and mixtures of different grain size classes to identify the relevant factors responsible for the variation of the different site calibrations. The laboratory setup includes the installation of a camera over a light table at the exit of the flume to determine instantaneous transport rates by tracking the particles. The new developed insights will be applied to other streams with geophone measurements in Switzerland, Austria and Israel for validation.

Projekt cooperation

• Volker Weitbrecht (VAW, ETH Zürich)
• Robert Boes (VAW, ETH Zürich)
  

Project team

• Carlos R. Wyss
• Jens M. Turowski
• Dieter Rickenmann
  

Project link

• Long-term bedload monitoring
  

Contact

• Dieter Rickenmann