Real-Time Ultrasonic Measurement Technique for Monitoring Suspended
Sediment Concentration in Reservoirs

Tetsuya Sumi
University of Kyoto, Kyoto, Japan

Yu-Jun Huang, Chia-Chi Sung, Jihn-Sung Lai, Fong-Zuo Lee, Yih-Chi Tan
Hydrotech Research Institute, NTU, Taipei City, Taiwan
adamhuang@ntu.edu.tw
ABSTRACT:During typhoon flood or rainstorm seasons, rivers usually carry great amount of suspended sediment flowing into reservoir. Highconcentration of sediment current spread out in all directions in the reservoir, which not only reduces reservoir's life span but also
creates treatment problems in the water supply plant. For reservoir operation, real-time monitoring of sediment concentration in theturbidity current has received significant attention from reservoir desiltation operations in Taiwan. Ultrasonic spectroscopy is highly
suitable for real-time measurement, in particular for dense particle systems. In the present study, an automatic ultrasonicmeasurement system is designed and fabricated for measuring solid suspension concentration with respect to the propagation ofultrasound waves in solid-liquid mixture in sites. The measurements obtained by ultrasonic measurement technique for sedimentconcentration in turbidity currents during 2009 typhoon floods in the reservoir show good agreement with the sampled data. It has
been demonstrated that the ultrasonic measurement technique is operative and trustworthy in site with harsh working environments.
In the future, the sediment yield in the reservoir watershed may be affected by global climate change in the long term. The ultrasonicdevice develop has taken the high suspended sediment concentration measurement into account.
Keywords: sediment concentration, ultrasonic, attenuation, real-time

1.

INTRODUCTION

based

on

attenuation

spectrometry.

Sound

wave

attenuation through dispersed phase suspensions of aDuring typhoon floods or torrential rain seasons, rivers

continuous second phase material could be used tousually carry great amount of suspended sedimentcharacterize suspensions. The concentration measuringflowing into reservoir from its watershed. Highrange of commercial instruments using traditional light

concentration of sediment-laden may form a turbidity

scattering methods is usually only up to 30,000 ppm.

current in the reservoir, which not only reduces reservoir

Ultrasonic methods advantageously penetrate optically

capacity but also creates water treatment problems for

opaque mixtures. Spectrometer result errors, caused by

the water supply plant. For instance, it was observed thatparticle size, temperature, and trapped air bubbles,

the sediment concentration sampled near the intake

strongly affect ultrasonic signals, but can be overcome

entrance in the Shihmen reservoir, Taiwan, was recorded

by good measuring system design. Urick first considered

5

up to 2.42 x 10 ppm during Typhoon Aere (2004).

the sound absorption problem in suspensions of one

Recent growing interest in sediment concentrationmaterial or another. McClements solved ultrasonicmonitoring by using ultrasonic diagnostic methods is

attenuation with a stress-strain relation and equations ofstate using a boundary condition series expansion at themodel assumes no gravitational field, nor heat or mass

single particle surface, reviewed by Allegra and Hawley.

transfer

The Harker and Temple coupled-phase suspension model

define   2 /  f , in which δ is the viscous skincalculated ultrasonic attenuation in suspensions. All

betweenphases.

For

brevity,weflow

depth, η is viscosity, ω is the angular frequency of themeasurements include several processes: transmission,

oscillation, and uf denotes fluid local velocity. In a solid

propagation and reception of ultrasonic waves, signal

particle suspension, each particle of density s is
assumed to be uniform, spherical, and of radius a.

ultrasonicmethods

intendedforliquidconditioning, and data processing. During the processes,
determining ultrasonic velocity in a movable liquid is theultimate goal. Relative velocity is mostly measured.
Ultrasonic methods can be successfully implemented in aliquid flow measurement because they have satisfactorystability, a wide dynamic range, and allow velocity
measurementofelectricalconductive

and

non-

conductive liquids both in clean and impure liquids.
Although an ultrasonic system has a concentration
measurement advantage, it provides only transmitting
and receiving signals. In the present study, a novel
portableultrasonicdevicewasdesignedandmanufactured for real-time sediment concentration and

The continuity equations are written as( s )  ( s u s )  0
t
z

(1)



[(1   )  s ]  [(1   )  s us ]  0
t
z

(2)

Equating the sum of related forces to the particle
momentum change rate gives
1  2
9 dur( s u s )  u s ( s u s )   f (

)
t
z
2(1   ) 4a dt
flow velocity measurements in the field. A series ofexperiments were conducted using kaolin and reservoir
sediment within a wide range of concentrations up to
300,000 ppm at various temperatures. The experimental
data were compared with the numerical results calculatedby the coupled-phase model proposed by Harker andTempleto examine the effect of the particle size

9
 2
p
 f  [  2 ]ur  ( )
4
a a
z

(3)



1  2
9 du[(1   )  f u f ]  u f[(1   )  f u f ]   f (
 ) r
t
z
2(1   ) 4a dt


9
 2
p
 f [  2 ]u r  ( )(  1)
4
a a
z

(4)

were also constructed as a function of attenuation andwhere us is the moving particle velocity, f is the fluid
density, and ur = uf - us denotes relative velocity is thetemperature. Through laboratory tests for calibration andparticle volume fraction, and p denotes fluid pressure.

validation and had been successfully employed to

We assume variations only in the z direction, and ameasure sediment concentration and flow velocity (time-suspension sufficiently dense to be treated as a volume-

difference method by ultrasonic probes) along water

averaged continuum.

column during typhoon floods in the Shihmen reservoir,

Equations 1 to 4 can be solved using a wave-like

Taiwan.

solution. The complex ultrasonic wave number k derived

distribution. Regressed relationships of concentration

is expressed as follows [7]:2.

THEORYThe coupled-phase model was proposed by Harker andTemple [7] to analyze wave propagation in a two-phasemixture. The model is constructed by four governing
differential equations in a system consisting of two
continuity equations, Eqs. 1 and 2, the drag on one phaseby the other in Eq. 3, and the momentum equationconservation for a solid-liquid mixture in Eq. 4. The

k 2   2 [(1   )  f   s ]{

 f [  s (1    S )   f S (1   )]
 s (1   ) 2   f [ S   (1   )]}(5)
Where f is fluid phase compressibility, and s is solid
phase compressibility. S is a complex quantity given byS

1 1  29
9  2()i (  2 )
2 1
4a
4 a a

(6)

Once the complex wave number k is obtained,
attenuation α and velocity c can be calculated fromkc

 i .

3.

MEASUREMENTSYSTEMS

AND

EXPERIMENTS
Two measurement systems, a model-typed device and a

Apparently, attenuation depends on the particle volume
fraction  , the fluid viscosity  , the particle radius a

portable ultrasonic device (PUD), are introduced in thisand the frequency  . The coupled-phase model in Eqs. 1

concentration measurement in the laboratory, while theto 4 is idealized in a form containing only particles of a

PUD is a prototype designed for measuring both

single size in the solid-liquid mixture. Experimental

concentration and velocity in the field. For measuring

verification of this theory requires monodisperse

concentration, both of them have the same designed

sediments that are difficult to use commercial products insystem keeping the same distance between probes.

preparation processes. Additionally, sediments sampled

The model-typed device is designed for real-timefrom the field contain naturally varying sizes of particles.

measurement of solid suspension concentration in the

Therefore, it is necessary to extend the applicability oflaboratory. Figure 1 illustrates the main parts of athis model by taking the distribution of particle sizes into

standard

account. Thus, attenuation for sediments with various

longitudinal ultrasound. When it is being used as aparticle sizes obtained by the laser size analyzer

transmitter, a suitably varying voltage causes the(Mastersizer 2000, Malvern Instruments Limited, UK) is

piezoelectric disc to behave as a piston radiator andapproximated by dividing equally the size distribution

generate a sound wave in the ‘load’, i.e., the medium in

into i fractions, and obtaining its corresponding

the front of the face of the transducer. The model-typed

percentage of weight from the distribution curve. The

device is basically used for calibrating the temperature

resulting attenuation with various particle sizes isand pressure sensor, estimating the effect of air bubbles,

expressed as

regulating the speed of the stirring machine, testing the   i Zi(7)i

section.

The

model-typed

piezoelectric

devicetransducer

designedforforgenerating

performance of the piezoelectric transducer, andobtaining the regression function for specific sediments

where index i denotes the set of particle radius by thesize analyzer, αi is the attenuation of set i, and Zi is thein the laboratory. With a probe holder keeping theweight percentage of set i. The weight percentage for i

device shown in Fig. 3 is calibrated by using various

set is defined asconcentration samples to obtain the regression functions

Zi 

mi
W

(8)

distance of 0.16m between probes, the model-typed

for different sediments. The operating concentration
range is from 1,000 to 300,000 ppm with resolution ofwhere mi is the particle weight of set i, and W is the total

200 ppm. Measurement accuracy is ±2% and ±5% atweight of the mixture. The particle weight and volume ofconcentration ranges less than 50,000 ppm and greater

set i are written, respectively, as

than 50,000 ppm, respectively.

4mi  ai 3  s ni
3

mi

4
vi 
 ai 3ni
s 3

(9)
;
where ai is the size of set i, and ni is the particle

The prototype device, was designed and manufactured

numbers of set i. Finally, we obtain the modified

concentration and flow velocity in the field. All theexpression for attenuation as follows.
n3 iW mi   i i  3Ni
i 4Nai  selectronic circuits and transducers in the portable
(10)

for

real-time

monitoring

of

solid

suspension

ultrasonic device have the same elements as those in themodel-typed device. As shown in Fig. 3, the PUD is 0.75

where N is the total number of particles in the solid

m in length and 0.25 m in diameter with two pairs ofsuspension.

probes. The distances between probes are 0.16 m (i.e.
same as that of the model-typed device) and 0.46m forconcentration

and

flow

velocity

measurements,

respectively. The flow velocity measurement range is ±3

m/sec with a resolution of 0.01 m/sec, and its accuracy is

rpm to ensure well-mixed suspension without deposition.

±0.01 m/sec and ±2% for velocity ranges < 0.5 m/sec

It was found that there was no difference in attenuationand 0.5 ~ 3 m/sec, respectively.

measurement by operating the stirrer at various speeds,
and this was also reported by James and Richard (1999).

Case

Piezoelectric disc

The temperature was decreased from ambient to 15 oC

Cable
Front face (impedance
matching layer)(the lowest temperature recorded during typhoon floodsin the Shihmen reservoir) by circulating Freon through aElectrodes on faces of
piezoelectric disccoil installed near the cell bottom. A 1 MHz and 30cycle tone burst was generated as an ultrasonic signal.

Backing (damping)

The energy loss between transmitter and receiver wasmeasured to obtain ultrasonic attenuation.

Figure 1. The design of a standard probe.

Measurement
systemCooling system

Stirrer

Stirrer

0.16m

LaptopTransmitter
ReceiverFigure 2. The model-typed device and its probe holder forconcentration measurement in the laboratory.
Flowmeter
probesFigure 4. Experimental setup

Rear fin4.
0.4

SELF-CONFIRMATION

6m
0.7

TESTS

FOR

MEASUREMENT SYSTEM
5m

Cable

The entire components of measuring concentration in the
PUD are the same as there in the model-type device,

0.1

except the packing. In order to verify the accuracy of

6m

concentration measurements by adopting the regression

Concentration
probesfunction in the PUD, a circular tank with a high power

Figure 3. The PUD for both concentration and flow velocity

stirrer was set up. Figure 5 shows the experimental

measurements in the field.

configuration and the sampling positions in the tank. The
PUD was placed at the location between pt. A2 and pt.

The layout of the experimental setup is shown in Fig. 4.

B2 during experiment.

The central frequency of probe was 1MHz, and the

1.2 m

distance between transmitter and receiver was 0.16m.

variable-speed

mechanicalstirrerstomaintainahomogeneous particle suspension in the liquid. A four-

1.5 mwide and 0.5 m tall plexiglas cell equipped with two

0.2m 0.2m 0.2m

0.2m 0.2m

The experiments were conducted in a 0.6 m long, 0.5 m

B1 A1
B2 A2
B3 A3

B

blade propeller (45° pitch) of 0.2 m diameter provided
agitation and was placed at 0.05 m above the cell bottom.
The stirrer rotation rate was operated from 500 to 1000

Stirrer
(a)

(b)

A

Figure 5. Configuration of the circular tank and sampling
positions seen as (a) side view (b) top view

Table 1 shows the results of concentration measurement
by PUD in the circular tank, compared with sampling
results after extraction and oven drying. For each run, thedata obtained from different sampling positions byextraction using a siphon were very close. It indicatesthat the solution was well-mixed in the tank. The
averaged error between measurement and extraction
results was 5%, which would be attributable to thesystem error and could be offset.
Table 1. Concentration measurements by PUD compared withthose of extraction samples at 25 oC
Run
No.

1

2

3

4

Sampling
Position

Extraction
samples
(ppm)

A1
A2
A3
B1
B2
B3
A1
A2
A3
B1
B2
B3
A1
A2
A3
B1
B2
B3
A1
A2
A3
B1
B2
B3

10054
10070
10063
10061
10088
10044
54353
54327
54310
54367
54295
54245
99735
99785
99573
99773
99640
99792
200467
199369199445
199685
199380200282

Measurement
by PUD (ppm)

9515

51907

95620

191049

Error
5.4%
5.5%
5.4%
5.4%
5.7%
5.3%
4.5%
4.5%
4.4%
4.5%
4.4%
4.3%
4.1%
4.2%
4.0%
4.2%
4.0%
4.2%
4.7%
4.2%
4.2%
4.3%
4.2%
4.6%

Figure 6. Photo of the (a) PUD mounted on the carriage (b) the
towing tank
Table 2. Flow velocity measurements by PUD, compared withstandard speeds
Run No.

1

2

3

4

5

6

7

Standard speed (m/sec)

0.00

0.50

1.00

1.50

2.00

2.50

3.00

Measurement (m/sec)

0.00

0.49

1.01

1.50

1.96

2.48

2.97

Error

0.0%

-2.0%

1.0%

0.0%

-2.0%

-0.8%

-1.0%

Figure 6 shows the photo of the 150 m long, 10 m wide
and 6 m deep towing tank with a carriage. In theexperiments, the speed of the carriage was controlled as
the standard speed and varied from 0 to 3 m/sec in steps

5.

FIELD MEASUREMENT RESULTS

of 0.5 m/sec. The PUD was mounted on the carriage andimmersed in water, 1 m deep, to measure flow velocity.

Due to dangerous working conditions, it is usually
impossible to conduct measurement on ship during

Table 2 lists the comparison of flow velocity by PUD

typhoon flood in a reservoir. Fortunately, we had theand the standard speed by carriage to present very good

opportunity to perform real-time field measurements byagreement. The errors in all test runs are less than 2%.

PUD in the Shihmen reservoir during Typhoon Jangmi
on September 30 in 2008, while winds and flows wererelatively slow. The Shihmen reservoir is one of the two
major multipurpose reservoirs in northern Taiwan, which
serves purposes including flood control, water supply,
immigration and power generation. Figure 7 shows that
the PUD was operated by a motor-driven crane mounted
on the ship. The PUD was first lowered into the waterand near to the bottom; afterward, the PUD was lifted
gradually. As the PUD was continuously lifted up frombottom to surface, the samples of reservoir sediment
solutions were collected at several specific positions forvalidation of the measured data. The sampling time of
the PUD was 2 sec to obtain time-averaged concentrationand velocity, while the pressure (in terms of depth) andtemperature

were

simultaneously

recordedwithconcentration. The sediment solution samples were taken
by a sediment sampler controlled by an electromagnetic
valve, and the concentration of each sample wasobtained later by oven drying in laboratory.

Figure 8. Measured data (2008/9/28/1pm) by PUD andsampled data at the floating barrier in the Shihmen reservoir

Figure 7. Operation of PUD in the Shihmen reservoir

The data taken were collected by PUD at Lungchu Bay
and the floating barrier, located 4 km and 7 km from thedam, respectively, in the Shihmen reservoir during
Typhoon Jangmi. As shown in Fig. 8, the measured
sediment concentrations show very good agreement withsampled ones. The vertical profile of sedimentconcentrations indicates that the turbidity current body(inner region) had about 5 m deep above the bottom andFigure 9. Velocity profile data (2008/9/28/1pm) by PUD at thethe highest concentration was recorded near the bottom

floating barrier in the Shihmen reservoirof the reservoir. The flow velocities measured are plotted
together with the data taken by a 2D electronic current

6.

CONCLUSIONS

meter (ACM2-RS, ALEC CO., LTD.). In Fig. 9, thevertical velocity profile of turbidity current has a

In summary, the modified coupled phase model

maximum velocity in its inner region (inside the body of(ultrasound propagation in particulate mixtures model) is

the turbidity current), directed downstream; in the outerused in this research. The theoretical attenuation byregion the upstream velocity reflects the backflow ofweightambient fluid in still reservoir water.

experiment results. The particle size radius dominates thepercentage

hasbetterconsistency

withattenuation slope, causing a slight difference between
prediction results and measurement results. Attenuation
for both theoretical results increases with increasing
concentration and decreasing particle size.The goodexperimental results were found by employing PUD for
sediment concentration and flow velocity measurements
in turbidity currents during Typhoons Sinlaku andJangmi floods in Shihmen reservoir, which demonstrates
that the PUD is operative and trustworthy on site.

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