Bedload -transport measurements with geophones

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

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

3. 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

4. measuring sites with PBIS or geophone sensor arrays Erlenbach stream (Alptal, CH): A = 0.7 km², mean channel slope S = 0.17

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

6. PBIS: piezoelectric bedload impact sensor Threshold voltage for impulse counting = 0.2 V rolling, center sliding, right side voltage [V] voltage [V] time [s] time [s] Example of original PBIS signal, for a 3.8 kg particle passing over a sensor

7. 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)

8. Sediment transport measurements: Erlenbach (Alptal) Q = 15 l/s Q = 0.7 m3/s Q = 10 m3/s

9. Erlenbach coarse sediment along channel bed

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

11. Erlenbach, flood event of 25 July 1984: 2000 m3 sediment deposition

12. Pitzbach (A): second test site for PBIS measurements

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

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

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

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

17. PBIS calibration: Pitzbach (A) measurements PBIS sensor, no. of impulses sediment volume [m3]

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

19. Movingbasketsystemforbedloadtransportmeasurements Erlenbach, sediment retention basin, viewupstream

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

21. Movingbasketsystemforbedloadtransportmeasurements Sediment from flood of 4 July 2009

22. Erlenbach: Geophonecalibrationwithmovingbasketsamples

23. Drauriver (Dellach, A): Geophonecalibrationwithslotsampler

24. Geophonecalibrationfromseveralfieldsites in CH and A

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

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

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

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

29. Laboratory study: PBIS measurements with particles from Erlenbach b-axis: 3.5 - 4.5 cm b-axis: 9 - 11 cm b-axis: 14 - 16 cm b-axis: 18 - 20 cm No. of sensorimpulses Sample weight of uniform grains [kg]

30. Laboratory study: PBIS measurements with particles from Erlenbach Normalizedcummulativefrequencycurves. Top: uniform material (4 cm) with different sampleweights. Bottom: 4 different grainsizeswith 2 sampleweightsforeachsizeclass

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

32. 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)

33. 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)

34. Outlook: WSL – GESTRANS cooperationproject 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)

35. 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 HydrologyandTorrentsBirmensdorf, Switzerland

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