Bedload-transportBedload-transport

measurementsmeasurements

with geophoneswith geophones

Dieter Rickenmann

WSL - Swiss Federal Research Institute

Mountain Hydrology and Torrents

Birmensdorf, Switzerland

Séminaire GESTRANS Ancien Monastère de Sainte-Croix (26), 3 November 2010

1) Introduction

2) Measuring method and test sites2) Measuring method and test sites

3) Calibration of bedload sensors

4) Results of additional investigations

5) Conclusions and outlook

ContentContent

Erlenbach stream (Alptal, CH)

A = 0.7 km²

S = 0.17

Runoff and sediment measuring station

array of PBIS or geophone sensors

on check dam

Erlenbach stream (Alptal, CH): A = 0.7 km², mean channel slope S = 0.17

measuring sites with PBIS or geophone sensor arrays

Erlenbach, PBIS measuring site at sediment retention basinErlenbach, PBIS measuring site at sediment retention basin

array of PBIS or geophone sensors

on check dam

PBIS: piezoelectric bedload impact sensor PBIS: piezoelectric bedload impact sensor

Example of original PBIS signal, for a 3.8 kg particle passing over a sensor

rolling, center sliding, right side

Threshold voltage for impulse counting = 0.2 V

time [s] time [s]

volta

ge [

V]

volta

ge [

V]

piezoelectric / geophone bedload impact 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)

Q = 10 m3/sQ = 0.7 m3/sQ = 15 l/s

Sediment transport measurements: Sediment transport measurements: Erlenbach (Alptal)Erlenbach (Alptal)

ErlenbachErlenbach

coarse sediment along channel bed

14 July 199514 July 1995

Erlenbach, Alptal (Switzerland):Erlenbach, Alptal (Switzerland): flood eventsflood events

25 July 198425 July 1984

Erlenbach, Erlenbach, flood event of 25 July 1984:flood event of 25 July 1984: 2000 m 2000 m33 sediment deposition sediment deposition

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

Pitzbach (A), test site for PBIS measurements Pitzbach (A), test site for PBIS measurements

Pitzbach

water intake

Austria

Grain size distributions of sediment at test sites Grain size distributions of sediment at test sites

0

10

20

30

40

50

60

70

80

90

100

0.1 1 10 100 1000

% finer by weight

grain size [mm]

0102030405060708090

100

0.1 1 10 100 1000

Pitzbach: settling basin

Pitzbach: bed materialupstream of intake

Erlenbach: retention basin(mean 1984-1987)

Erlenbach: surface bedmaterial (1993)

% finer by weight

grain size [mm]

range of estimated threshold size for detection with PBIS sensor

1) Introduction

2) Measuring method and test sites

3) Calibration of bedload sensors3) Calibration of bedload sensors

4) Results of additional investigations

5) Conclusions and outlook

ContentContent

10

100

1'000

10'000

100'000

1'000'000

10'000'000

100'000'000

20.06 05.07 21.07 06.08 21.08 07.09

sensor pulses

1

10

100

1'000

10'000

daily bedload [m3]1984

Pitzbach (A): comparison of sediment transport measurements Pitzbach (A): comparison of sediment transport measurements

and bedload sensors (hydrophones) and bedload sensors (hydrophones)

B: y = 4.326x1.228

R2 = 0.759

A: y = 5.321x0.995

R2 = 0.556

C: y = 2.258x1.264

R2 = 0.912

0.01

0.1

1

10

100

1000

10000

0.01 0.1 1 10 100 1000

data set A (15 min)

data set B (1hour)

data set C (1 day)

G [m3]

SP (sensor impulses)

PBIS sensor, no. of impulses

PBIS calibration: Pitzbach (A) measurements PBIS calibration: Pitzbach (A) measurements

sediment volume [m3]

0.01

0.1

1

10

100

1000

0 2 4 6 8 10

data set A (15 min)

data set B (1 hour)

data set C (1 day)

Logarithmisch (dataset C (1 day))Logarithmisch (dataset B (1 hour))Logarithmisch (dataset A (15 min))

SP/G

Qmax/Qc

PBIS calibration: Pitzbach (A) measurements PBIS calibration: Pitzbach (A) measurements

= sensor impulses / sediment volume

Erlenbach, Erlenbach, sediment sediment

retentionretention

basin,basin,

view upstream view upstream

Moving basket system for bedload transport measurements Moving basket system for bedload transport measurements

New installations at Erlenbach bedload measuring siteNew installations at Erlenbach bedload measuring site

rotating crane

metal basket with wire mesh

supporting rail

geophone sensors

Sediment from flood of 4 July 2009

Moving basket system for bedload transport measurements Moving basket system for bedload transport measurements

Erlenbach: Geophone calibration with moving basket samplesErlenbach: Geophone calibration with moving basket samples

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

Geophone calibration from several field sites in CH and AGeophone calibration from several field sites in CH and A

1) Introduction

2) Measuring method and test sites

3) Calibration of bedload sensors

4) Results of additional investigations 4) Results of additional investigations

5) Conclusions and outlook

ContentContent

Erlenbach (CH), second bedload measuring siteErlenbach (CH), second bedload measuring site

Test of PBIS measurements with two

successive rows of sensor arrays

Erlenbach (CH), second bedload measuring siteErlenbach (CH), second bedload measuring site

two successive rows with PBIS sensor arrays

bridge

Erlenbach (CH), second bedload measuring siteErlenbach (CH), second bedload measuring site

Test of PBIS measurements with two successive rows of sensor arrays

y = 0.7868x1.0128

R2 = 0.8639

0.01

0.1

1

10

100

1000

0.01 0.1 1 10 100 1000

sensor impulses downstream row, SPd

sensor impulses upstream row, SPu

er row

Laboratory study: PBIS measurements with particles from ErlenbachLaboratory study: PBIS measurements with particles from Erlenbach

b-axis: 3.5 - 4.5 cmb-axis: 9 - 11 cm

b-axis: 18 - 20 cmb-axis: 14 - 16 cm

Sample weight of uniform grains [kg]

No

. of s

en

sor

impu

lse

s

Laboratory study: PBIS measurements with particles from ErlenbachLaboratory 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

1) Introduction

2) Measuring method and test sites

3) Calibration of bedload sensors

4) Results of additional investigations

5) Conclusions and outlook 5) Conclusions and outlook

ContentContent

- 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)

Advantages of PBIS measuring systemAdvantages 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)

Disadvantages of PBIS measuring systemDisadvantages of PBIS measuring system

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)

Outlook: WSL – GESTRANS cooperation projectOutlook: WSL – GESTRANS cooperation project

Bedload-transport measurements with geophonesBedload-transport measurements with geophones

Dieter Rickenmann

WSL - Swiss Federal Research Institute

Mountain Hydrology and Torrents

Birmensdorf, Switzerland

Séminaire GESTRANS Ancien Monastère de Sainte-Croix (26), 3 November 2010

Thank you for the attentionThank you for the attention

piezoelectric / geophone bedload impact sensor piezoelectric / geophone bedload impact sensor

fixing of PBIS or geophone sensors

on a steel plate