Sonic Depth Sounder for 

Laboratory and Field Use

GEOLOGICAL SURVEY 

CIRCULAR 450
Sonic Depth Sounder for Laboratory

and Field Use

By E. V. Richardson, D. B. Simons, and G. J. Posakony

GEOLOGICAL SURVEY CIRCULAR 450

Washington 1961
United States Department of the Interior

STEWART L. UDALL, SECRETARY

Geological Survey

THOMAS B. NOLAN, DIRECTOR

Free on application to the U: S. Geological Survey, Washington 25, D. C
CONTENTS

Page Page

Abstract ________________________ 1 Data obtained______ _ ____________ 5

Introduction.__ _________________ 1 Sonic depth sounder for field

Description and specifications ________ 3 use______________________________ 6

Operation____ ___________________ 5 References___________ - - ____ 7

ILLUSTRATIONS

Figure 1. Forms of bed roughness in allyvial channels _____ - - ___ --.

2 . Linearity of the sonic depth sounder ____________________-------.

3. Variation in elevation of an alluvial bed with distance - ______

4. Variation in elevation of an alluvial bed with time ________________

Page 

2

4

. _________ 5

. ______ __ 6

IE
Sonic Depth Sounder for Laboratory and Field Use

By E. V. Richardson, D. B. Simons, and G. J. Posakony1

ABSTRACT

The laboratory investigation of roughness in alluvial 

channels has led to the development of a special electronic 

device capable of mapping the streambed configuration under 

dynamic conditions. This electronic device employs an 

ultrasonic pulse-echo principle, similar to that of a fathometer, that utilizes microsecond techniques to give high accuracy in shallow depths. This instrument is known as the 

sonic depth sounder and was designed to cover a depth 

range of 0 to 4 feet with an accuracy of ± 0.5 percent. The 

sonic depth sounder is capable of operation at frequencies 

of 500, 1,000 and 2,000 kilocycles. The ultrasonic beam 

generated at the transducer is designed to give a minimumdiameter interrogating signal over the extended depth range. 

The information obtained from a sonic depth sounder is recorded on a strip-chart recorder. This permanent record 

allows an analysis to be made of the streambed configuration under different dynamic conditions.

The model 1024 sonic depth sounder was designed principally as a research instrument to meet laboratory needs. 

As such, it is somewhat limited in its application as a field 

instrument on large streams and rivers. The principles employed in this instrument, however, have many potentials 

for field applications such as the indirect measurement of 

bed load when the bed roughness is ripples and (or) dunes, 

depth measurement, determination of bed configuration, and 

determination of depth of scour around bridge piers and 

abutments. For field application a modification of the present system into a battery-operated lightweight instrument 

designed to operate at a depth range of 0 to 30 feet is possible and desirable..

INTRODUCTION

In September 1956 the U.S. Geological Survey established a research project at Colorado 

State University to investigate roughness in 

alluvial channels (Simons and Richardson, 

1960). In an alluvial channel the form of the 

bed can be a plane, ripples, dunes, transition, 

standing waves, or antidunes depending on 

flow and sediment characteristics as illustrated in figure 1 (Simons and others, 1961). 

A plane bed will have surface irregularities 

on the order of the grain size, whereas a dune 

bed is composed of approximately triangularshaped elements which, in the flume, are 2 to

1G.J. Posakony, Automation Industries, Inc., Research Division, 

Boulder, Colo.

10 feet long and 0.2 to 1.0 foot high. A ripple 

bed is composed of similar triangular-shaped 

elements which are less than 2 feet long and 

are 0.02 to 0.20 foot high and may compose 

the major element of bed form or be superimposed on the back of dunes. Antidunes are 

sinusoidal undulations which, in the flume, 

have amplitudes from 0.05 to 0.3 foot and 

wavelengths from 3 to 10 feet. In the field the 

wavelength and amplitude of dunes and antidunes may be much greater depending on 

depth of flow.

In the laboratory investigation it soon became apparent that measurement of the bed 

configuration should be made under dynamic 

conditions. Measurements of bed form that 

are made after an experiment has been concluded and the flume has been drained can be 

inaccurate and misleading. Because of the 

softness of the bed, measurements made by 

mechanical probing during the experiment 

were also inaccurate. Some method of obtaining the bed configuration, both areally and as 

it changed with time at a point, had to be 

developed.

Sonic depth sounders proved the most logical type of instrument for measuring the bed 

configuration under dynamic conditions. However, commercial instruments, designed to 

operate at great depths relative to those in a 

laboratory flume, were not accurate enough. 

These commercial instruments have a minimum-depth range of about 60 feet and their 

accuracy is + 0.5 percent of full scale. Since 

the propagated sound beam in most of these 

instruments is a cone which has a divergence 

of about 20°, the beam diameter at the bottom 

(or bed surface) is a function of depth. The 

normal frequency of most commercial instruments is 50 kilocycles and their pulse repetition rate is about 500 cycles per minute.
SONIC DEPTH SOUNDER FOR LABORATORY AND FIELD USE

A. Typical ripple pattern, F «l 

^ Weak boil

E. Plane bed, F <l and d i 0.4 mm

B. Dunes with ripples superposed F« I

Boil-^

F. Standing waves, F > I

Incipient breaking V 

and moving upstream11 '

C. Dunes,F <l 6. Antidunes , F > I

 ^^*SN^.

> 

Breaking antidune wave t-.

I*'1 *

, Washed out dunes or transition, F < 1 H. Antidunes, F >l

Figure 1. Forms of bed roughness in alluvial channels.

In contrast, an instrument was needed which, 

would operate in depths of water ranging from 

0.3 to 2.0 feet with an accuracy of 0.01 foot. 

The effective area of the bed which would 

reflect the sound waves should not be any 

greater than 1 square inch and smaller if 

possible; as there would be large quantities 

of suspended sediment, methods of minimizing 

its effect had to be developed; and the instrument would have to define the downstream 

face of the dunes which makes an angle with 

the horizontal of 25° to 40°. These requirements for a useful depth sounder were very 

stringent. The desired accuracy (small reflection area) required the use of highfrequency sound waves. However, the higher 

the frequency of the waves, the shorter is 

their wavelength. Any sediment particle in 

suspension with a diameter equal to or greater 

than the wavelength of the sound energy will 

readily reflect some of the sound wave. This

may, in some instances, help solve other 

problems but in this application it was a detriment. The steep downstream face of the 

dune did not present a problem because the 

granular surface of the streambed reflected 

enough acoustical energy in the plane of the 

transducer so that an amplifiable echo was 

always received.

In the development of the sonic depth 

sounder, the major accomplishments have 

included:

1. The design and development of transducers that have a nondiverging sound beam 

so as to define small changes in the streambed.

2. The development of a timing-circuit 

clock and a linear time-measuring circuit 

that can accurately (within 0.01 ft) determine 

the distance from the transducer face to the 

bed.
DESCRIPTION AND SPECIFICATIONS

DESCRIPTION AND SPECIFICATIONS

The basic elements of the sonic depth 

sounder and their functions are:

A. Pulser to provide timed pulses of high 

voltage at a given frequency. Pulses operating at three frequencies -500, 1,000,2,000 

kilocycles per second -are provided. Pulse - 

repetition rate is 400 cycles per second, the 

pulse duration is 1 microsecond, the pulse 

amplitude is 1,200 volts, and the duty cycle 

is 0.04 percent.

B. Transducers to convert the high-voltage 

pulses to acoustic energy. A lithium sulfate 

crystal was used in the transducer to make 

the conversion. This same crystal is used as 

a receiver to detect and change the echo from 

acoustical to electrical energy and feed it to 

the receiver. Crystals are frequency-sensitive so a transducer is provided for each 

frequency. However, a crystal tuned for one 

frequency (for example, 2,000 kilocycles) can 

be driven by pulses of a lower frequency (500 

kilocycles) but the returning echo is weaker, 

requiring greater amplification. The transducers are designed, using conventional 

acoustic theory (O'Neal, 1949; Posakony and 

McMasters, 1960), to maintain a nondivergent 

sound beam. This sound beam has very little 

divergence from the central axis. The area 

of the bed from which the sound wave is re - 

fleeted is a function of frequency and crystal 

diameter. The beam diameter of the transducers used ranged from half an inch at 2,000 

kilocycles per second to 1-3/4 inches at 500 

kilocycles per second. To maintain a nondiverging sound beam, the size of the transducer must vary with frequency. The lower 

the frequency, the larger must be the transducer. The 500 kilocycle transducer is 3 

inches in diameter and the 2,000 kilocycle 

transducer is 1 inch in diameter (Heuter and 

Bolt, 1955). Tomalntain anondiverging sound 

beam at a frequency of 60 kilocycles would 

require a transducer that has a diameter of 

about 18 inches.

C. Clock to provide atime base with which 

the other system modules are synchronized 

and which the linear time circuit uses as a 

base to compute the time between main pulse 

and echo.

D. Receiver to detect, shape, and amplify 

the small echo signals from the transducers 

for the linear-time-measuring circuit and 

display system. The receiver is provided 

with a variable gain so that amplification of

the echo canbe controlled. This is necessary 

to keep interference from suspended sediment 

to a minimum. Excessive amplification can 

cause spurious echoes from the suspended 

sediment. The linear-time-measuring circuit measures time from the initiating pulse 

to the first returning echo. Spurious echoes 

can cause the measurement of the wrong time 

interval. Amplification of the signal should 

be set at a level at which the echo from the 

bed surface is sufficient to trigger the lineartime-measuring circuit. By varying the gain 

and frequency, it was always possible to obtain excellent definition of the bed with little 

or no interference from suspended sediment.

E. Linear-time-measuring circuits which 

measure the time between the initial pulse 

and the echo from the bed. This time is then 

converted into voltage that is linearly proportional to the distance from the bed. This 

voltage actuates a strip-chart recorder. The 

linearity of the instrument is illustrated in 

figure 2. Here, the actual distance from the 

bed is compared with the strip-chart readings.

F. Visual display system, consisting of an 

oscilloscope where the initial pulse and returning echo are displayed on the time base, 

for monitoring the ultrasonic information.

The instrument is designed to operate at 

depths betweenO.2 and 4feet. Since the electronic responses of the transmitter-receiver 

system require a few microseconds to establish a quiescent level, the minimum depth is 

set at 0.2 foot. The maximum depth is limited to 4 feet to maintain the high accuracy of 

the linear-time-measuring circuit.

Physically, the pulse-repetition rate used 

limits the maximum depth of this instrument 

to 6 feet. That is, at depths in excess of 6 feet 

the echoes have not been received before another cycle starts. This 6 foot depth limit 

can be increased by decreasing the pulse 

rate, but at extended ranges time is more 

difficult to measure accurately. With this 

instrument deeper depths may be sounded by 

lowering the transducer, by rod or sounding 

weight, a predetermined distance below the 

water surface.

With the present unit the range scales are 

0-1, 0-2, 0-3, and 0-4 feet. To define small 

irregularities on the order of 0.01 and 0.02 

feet, an expanded scale is provided for range 

of 0 4 feet. This expanded scale takes the
SONIC DEPTH SOUNDER FOR LABORATORY AND FffilD USE

0-2ft 

Range

0-3ft 

Range

0-4ft 

Range

0.4 0.8 1.2 1.6 2.0 

Distance from bed, in feet

2.4 2.8 3.2

Figure 2. Linearity of the sonic depth sounder.

last 1 or 2 feet on the 0 4 scale and expands 

it to a scale of 0 1 or 0 2 feet.

Accuracy of the instrument is better than 1 

percent of full scale. Its accuracy ranges 

from 0.01 foot for the ranges of 0 1 and 0 2 

feet to 0.02 foot for those of 0-3 and 0-4 feet.

The controls for the instrument are a range 

selector, expanded range selector, frequency 

selector, variable gain, and variable damping. 

The variable-damping selector places capacitors across the output terminals to the stripchart recorder to further decrease any effeot 

of suspended sediment.

In addition two calibration controls, zero 

and range, are incorporated in the instrument. 

These controls are to adjust signal output to 

the strip-chart recorder so that their zeros 

coincide, and true change in depth will be reflected by a corresponding movement of the 

pen for each of the ranges selected. In 1

year's operation there has been no change in 

the range control since the initial calibration. 

However, the zero has drifted because of 

voltage fluctuations in the power supplied to 

the instrument. This can be corrected by an 

external voltage regulator.

The instrument operates on 120 volts., 60 

cycles alternating current, and requires 500 

watts power. It is 28 inches long, 18 inches 

high, and 16 inches wide and weighs about 140 

pounds.

Two types of recorders have been used satisfactorily with the instrument. One was a 

Texas Instrument milliamp recorder which 

operates on the current output. The other 

was a Leeds and Northrup null-balance recorder which operates by voltage differences. 

Using these recorders, the instrument hap 

given excellent performance with very little 

maintenance and, as stated before, has required no change in the range calibration.
DATA OBTAINED

OPERATION

In the laboratory, two methods have been 

used to measure depth and bed configuration 

with this instrument. One method is to take 

three or more profiles of bed configuration 

along a 70 -to 100 foot reach of the flume bed. 

.The other method is to set the transducer at 

a point in the cross section and record the 

changes in bed configuration with time.

dunes, although not to proper scale, appear 

as if they were. This results from selecting 

a chart speed based upon traverse speed. It 

is important in the interpretation of the profiles that dunes or ripples are in a suitable 

scale ratio of length to height. To accomplish 

this, recorders with high response and fast 

chart speeds are needed or the traverse must 

be made at too slow a speed to obtain a suitable scale ratio of dune length to height.

To obtain the bed configuration as it varied 

with distance the transducer was mounted on 

the instrument cart, which was supported by 

rails along the flume walls, a known distance 

below the water surface and moved downstream at about 1 foot per second. The sonic 

depth sounder can operate at even higher traverse speed but the recorders available have 

response times and chart speeds which are 

too slow. With the faster recorders now 

available, traverse velocities of at least 5 

feet per second should be possible.

DATA OBTAINED

In figure 3 a typical trace of a dune bed 

configuration obtained by longitudinally traversing the flume is presented. Note that the

The variation of the bed at a point as a function of time is illustrated in figure 4. This 

record graphically illustrates the changes of 

the bed with time. The depth of flow can vary 

200 or 300 percent of the average depth in the 

interval of a few minutes.

With the ability to evaluate the velocity and 

amplitude of tranquil -flow sand waves, a 

theoretical expression for bed -load transport 

was developed (Simons, D» B., Richardson, 

E.V., and Haushild, W. L., written communication, 1961). This equation for total load is

qb Vs h/2

in which

q. = volume rate of bed -load transport per

foot of width per unit of time 

A = porosity of sand bed

wa

* o"

O 

0.25 

0.50 

Q.75 

1.00

1 9«s

Wate

A

y

5

=-j-^==

r surfa

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2 5

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4

V

ce ^

k ^

Flow .

k 5

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8

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0

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7

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2

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Stations along the flume, in feet

wo

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tf

0.25

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0.75 

1.00 

1 9 R

r^

7

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6

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Bed configuration 

, 

7

 

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D= Chart reading +0.4 ft.

<?=I7. 2 cfs 5 = 0.0014 

/= 2.1 If ps ^=|==9.90

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.02ft

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0

Figure 3. Variation in elevation of an alluvial bed with distance.
SONIC DEPTH SOUNDER FOR LABORATORY AND FIELD USE

WS|

$

O

« 0 

.0

Time, in hours

0.45 -Transducer

i t 

0= Chart reading to.45 ft. rf = 0.68ft 

Q=9.66cfs S« 0.0014 

V« 1.78 fps

Figure 4, Variation in elevation

Vs = velocity of the sand waves in the direction of flow 

h = average amplitude of sand waves

The sediment load computed by.this equation is very closely related to total bedmaterial load under flume conditions because 

of relatively shallow depths. However, as 

demonstrated by Hubbell and others (written 

communication, 1960) the computed bed load 

correlates very well with actual bed load 

under field conditions.

As stated earlier, the form of the bed in an 

alluvial stream is variable and is a function 

of flow and the characteristics of the bed 

material. The bed surface may be plane 

without bed-material movement, or it may 

consist of ripples, dunes, a plane surface 

with bed-material movement, standing waves, 

or antidunes depending on depth of flow, 

slope, size and distribution of bed material, 

and a few other minor variables such as temperature and seepage forces. The sonic depth 

sounder, by giving a trace of the bed, will indicate which bed form-exists. This is important because resistance to flow and sediment transport are intimately related to the

of an alluvial bed with time.

form of the bed roughness. Knowledge of the 

bed form will greatly increase the accuracy 

of prediction of both flow-resistance coefficients and total bed-material load.

SONIC DEPTH SOUNDER FOR FIELD USE

The sonic depth sounder was primarily designed for laboratory use, however, it shows 

potential in many field applications. With a 

bed roughness consisting of ripples and (or) 

dunes, using this or a similar instrument, the 

velocity, length, and height of the sand waves 

can be determined and from these data the 

bed load can be estimated by applying the 

total-bed-load equation above.

In streams where the bed degrades, or it is 

believed that it does, this instrument used 

with the standard water-surface recorder will 

give a record of the depth of flow as it changes 

with time. With some modifications, the sonic 

depth sounder will record actual depth of flow. 

In most alluvial channels the depth-discharge 

rating curve is more stable than the stage - 

discharge relation. In addition, the sonic 

depth sounder will define the form of bed
REFERENCES

roughness as it changes with stage. Very little is known about this change where the instrument is used in the field.

In an alluvial channel one of the most diffi - 

cult and largest sources of error is in the 

determination of depth when making a discharge measurement. In the tranquil-flow 

regime with dunes the bed is exceedingly soft 

and a sounding weight may penetrate 1 foot or 

more. In the rapid-flow regime the highvelocity flow deflects the sounding weight 

downstream, also effecting depth measurement. In measuring flood flow, especially on 

the smaller streams, debris and rapidly 

changing stage are always a problem. Using 

the sonic depth sounder for determining depth 

and making velocity determinations just below the water surface would mitigate the effect of debris and rapidly changing stage. 

This procedure should result in more accurate flood-discharge measurements.

The instrument has been used as a scour 

meter in the laboratory in experiments to de - 

termine depth of scour around bridge piers.

With some modification, especially to increase 

maximum depth and decrease cost, a portable 

scour meter for field use could be developed. 

Thus, it should be possible to obtain records 

of depth of scour on the prototype where there 

is a serious lack of data.

REFERENCES

Heuter, T. F., and Bolt, R. H., 1955, Sonics: 

New York, John Wiley & Sons.

O'Neal,H.T., 1949, Theory of focusing radiators : Acoustical Soc. of America Jour., v. 21, 

p. 516-526.

Posakony, G. J. and McMasters, R. C., 1960, 

Analysis of ultrasonic test techniques: Automation Industries Tech. Paper 601.

Simons, D. B., Richardson, E. V., 1960, Resistance to flow in alluvial channels: Am. 

Soc. Civil Engineers Jour., v. 86, no. HY5.

Simons, D. B., Richardson, E. V.,and Albertson, M. L., 1961, Flume studies using medium sand: U.S. GeoL Survey Water-Supply 

Paper 1498-A (in press).

INT.DUP.,D.C.61-93&79