Sminaire GESTRANS Ancien Monastre de SainteCroix 26 3

Séminaire GESTRANS Ancien Monastère de Sainte-Croix (26), 3 November 2010 Bedload-transport measurements with geophones Dieter Rickenmann WSL - Swiss Federal Research Institute Mountain Hydrology and Torrents Birmensdorf, Switzerland

Content 1) Introduction 2) Measuring method and test sites 3) Calibration of bedload sensors 4) Results of additional investigations 5) Conclusions and outlook

Runoff and sediment measuring station array of PBIS or geophone sensors on check dam Erlenbach stream (Alptal, CH) A = 0. 7 km² S = 0. 17

measuring sites with PBIS or geophone sensor arrays Erlenbach stream (Alptal, CH): A = 0. 7 km², mean channel slope S = 0. 17

Erlenbach, PBIS measuring site at sediment retention basin array of PBIS or geophone sensors on check dam

PBIS: piezoelectric bedload impact sensor Threshold voltage for impulse counting = 0. 2 V sliding, right side voltage [V] rolling, center time [s] Example of original PBIS signal, for a 3. 8 kg particle passing over a sensor

piezoelectric / geophone bedload impact sensor fixing of PBIS or geophone sensors on a steel plate since the year 2000 we use geophone sensors (instead of the piezoelectric sensors)

Sediment transport measurements: Erlenbach (Alptal) Q = 15 l/s Q = 0. 7 m 3/s Q = 10 m 3/s

Erlenbach coarse sediment along channel bed

Erlenbach, Alptal (Switzerland): 14 July 1995 flood events 25 July 1984

Erlenbach, flood event of 25 July 1984: 2000 m 3 sediment deposition

Pitzbach (A): second test site for PBIS measurements

Pitzbach (A), test site for PBIS measurements Pitzbach water intake Austria

Grain size distributions of sediment at test sites range of estimated threshold size for detection with PBIS sensor

Content 1) Introduction 2) Measuring method and test sites 3) Calibration of bedload sensors 4) Results of additional investigations 5) Conclusions and outlook

Pitzbach (A): comparison of sediment transport measurements and bedload sensors (hydrophones)

PBIS calibration: Pitzbach (A) measurements PBIS sensor, no. of impulses sediment volume [m 3]

PBIS calibration: Pitzbach (A) measurements = sensor impulses / sediment volume

Moving basket system for bedload transport measurements Erlenbach, sediment retention basin, view upstream

New installations at Erlenbach bedload measuring site rotating crane geophone sensors supporting rail metal basket with wire mesh

Moving basket system for bedload transport measurements Sediment from flood of 4 July 2009

Erlenbach: Geophone calibration with moving basket samples

Drau river (Dellach, A): Geophone calibration with slot sampler

Geophone calibration from several field sites in CH and A

Content 1) Introduction 2) Measuring method and test sites 3) Calibration of bedload sensors 4) Results of additional investigations 5) Conclusions and outlook

Erlenbach (CH), second bedload measuring site Test of PBIS measurements with two successive rows of sensor arrays

Erlenbach (CH), second bedload measuring site bridge two successive rows with PBIS sensor arrays

Erlenbach (CH), second bedload measuring site Test of PBIS measurements with two successive rows of sensor arrays

Laboratory study: PBIS measurements with particles from Erlenbach No. of sensor impulses b-axis: 3. 5 - 4. 5 cm b-axis: 14 - 16 cm b-axis: 9 - 11 cm b-axis: 18 - 20 cm Sample weight of uniform grains [kg]

Laboratory study: PBIS measurements with particles from Erlenbach Normalized cummulative frequency curves. Top: uniform material (4 cm) with different sample weights. Bottom: 4 different grain sizes with 2 sample weights for each size class

Content 1) Introduction 2) Measuring method and test sites 3) Calibration of bedload sensors 4) Results of additional investigations 5) Conclusions and outlook

Advantages of PBIS measuring system - robust technique requiring only very few maintenance - continuous measurement of bedload transport intensities - detection of beginning and ceasing of bedload motion - relatively low costs for measuring equipment and necessary constructions at measuring site - for longer observation periods and larger bedload volumes a reasonable accuracy is obtained for the calibration relationships (considering natural variability of bedload transport in mountain streams)

Disadvantages of PBIS measuring system - calibration of the system is necessary - no information on particle sizes in transport can be obtained - there is a limit for the lower critical particle size which can be detected - influence of hydraulic conditions and sediment properties on calibration are almost unknown at present - changing flow intensities are likely to change the size distribution of transported bedload particles (resulting in non-linear calibration relations, if such effects are not averaged out)

Outlook: WSL – GESTRANS cooperation project Objective: Comparison of two complementary indirect bedload transport measuring approaches: - Geophone measurements as applied by WSL - Hydrophone measurements as applied by Université Joseph Fourier, LTHE, Grenoble Possible sites for comparative measurements: - Erlenbach stream (operated by WSL) - Draix experimental catchment (Cemagref) - Experimental flume (Cemagref, LTHE) Possible travel support: - Germaine de Staël program (submitted proposal)

Séminaire GESTRANS Ancien Monastère de Sainte-Croix (26), 3 November 2010 Bedload-transport measurements with geophones Thank you for the attention Dieter Rickenmann WSL - Swiss Federal Research Institute Mountain Hydrology and Torrents Birmensdorf, Switzerland

piezoelectric / geophone bedload impact sensor fixing of PBIS or geophone sensors on a steel plate