Effect of Vertical Motion 

On Current Meters

GEOLOGICAL SURVEY WATER-SUPPLY PAPER 1869-B
Effect of Vertical Motion 

On Current Meters

By N. A. KALLIO

RIVER HYDRAULICS

GEOLOGICAL SURVEY WATER-SUPPLY PAPER 1869-B

A study of the effect of vertical 

movement on the registration of 

three types of current meters

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1966

213-882-1 nterior-1689
UNITED STATES DEPARTMENT OF THE INTERIOR 

STEWART L. UDALL, Secretary

GEOLOGICAL SURVEY 

WILLIAM T. PECORA, Director

For sale by the Superintendent of Documents, U.S. Government Printing Office 

Washington, D.C. 20402 - Price 15 cents (paper cover)

213-882-1 nterior-1689
CONTENTS

Page

Abstract .-.-.-... _-...._-.. ......-.......... . . ......... ... . .. . Bl

Introduction -...-..._. _....--.-.... -......-......-......-.... ......... .. . .- ....-.-..... . 1

Testing the effect of vertical motion .......--... ...... ....... ... . 3

Current meters tested .__. .._..-_._.__..__-__._.-_ . ___.. -.. __- .__ 3

Test procedure under simulated conditions __. -____ _ ____._____. 5

Test results for simulated conditions ___._ _.... _.--_ _ 7

Price meter .............-._...-.-... .... .- .........._..... ..... . .....-... _.... 7

Vane-type meter ._ .. __..... . . . ..... ... .... . 12

Ott meter _. . ._._._ ._._.._. ._. ._._._.._ __. ._.. ..._..._.__ 14

Test under actual conditions .... ._............... ...... . . . ... _- 16

Results of test under actual conditions... ......._. _... .- . - 17

Conclusions . _.. . ... .-... .. ....-__.. --.-. .- . . .. .... .. 18

Literature cited ..__... _. . -_..-..._....._ .__ . _ _____ ..__ ._.__. ._ -_- 20

ILLUSTRATIONS

Page

FIGURES 1-4. Photographs of 

1. Standard Price current meter .-......... ..._-._.....- B4

2. Vane-type current meter __._____.____ _..... ... . .. 4

3. Three adaptations of vane-type current meter .. 5

4. Ott current meter _ ...._ -- __.._.__.._ .__ _ __. _ 6

5-7. Graphs showing effect of vertical motion on 

5. Price current meter suspended by a cable ..... 9

6. Vane-type current meter supported by a rod __.. 10

7. Ott current meter suspended by a cable and 

equipped with a standard tailpiece without 

stabilizer ..... ...... ..- _.....-.... . .....-. ....-. 11

8. Graph of expanded test plot for Price current meter __... 12 

9-12. Graphs showing effect of vertical motion on 

9. Price current meter supported by a rod _..... .. 13

10. Vane-type current meter suspended by a cable .. 14

11. Ott current meter suspended by a cable ____________ 15

12. Ott current meter (rotor 8646-A) supported

by a rod __ _ __.... .. __..____._. ____ __..______._ 16

13. Photograph of Ott current meter with rotor 8406-1

and modified tailpiece .- . .- ...-..-.. ... ...-........ 16

ill

213-882-lnterior-1689
IV CONTENTS

Page

FIGURE 14. Graph showing effect of vertical motion on Ott current 

meter (rotor 8406-1) suspended by a cable and 

equipped with a short tailpiece __ _______-___ __ B17

15. Photograph of chronograph equipped for recording 

revolutions of two current meters and vertical 

movement of a boat... ._.... _.... .. ________________________ 18

16. Graphs showing comparison of registered velo"ities

by two Price current meters ___________________________________ 19

TABLE

Page

TABLE 1. Registration errors for Price, vane-type, and Ott current

meters -__ -___-__ __ _____ ____ ___-.-___ __ _____ _.____ __ B8

213-88 2-lnterior-1689
RIVER HYDRAULICS

EFFECT OF VERTICAL MOTION ON CURRENT METERS

By N. A. KALLIO

ABSTRACT

The effect of vertical motion on the performance of current meters at 

various stream velocities was evaluated to determine whether accurate discharge measurements can be made from a bobbing boat.

Three types of current meters Ott, Price, and vane types were tested 

under conditions simulating a bobbing boat. A known frequency and amplitude 

of vertical motion were imparted to the current meter, and the related effect on 

the measured stream velocity was determined. One test of the Price m^ter was 

made under actual conditions, using a boat and standard measuring gear. 

The results of the test under actual conditions verified those obtained by 

simulating the vertical movements of a boat.

The tests show that for stream velocities below 2.5 feet per second the 

accuracy of all three meters is significantly affected when the meters are 

subjected to certain conditions of vertical motion that can occur during actual 

field operations. Both the rate of vertical motion and the frequency of 

vertical oscillation affect the registration of the meter.

The results of these tests, presented in the form of graphs and tables, can 

be used as a guide to determine whether wind and stream flow are vithin an 

acceptable range for a reliable discharge measurement from a boat.

INTRODUCTION

Streamflow is usually measured by observing the depth and 

velocity at selected verticals in a cross section of a stream. The 

velocity is measured with a current meter attached to a rod or 

suspended on a cable from a bridge, cableway, or boat.

The accuracy of a steamflow measurement depends on the 

performance of the current meter, as well as on the number of 

observations of depth and velocity that are made in a given cross 

section. The performance of the common types of current meters 

has been thoroughly tested in various towing tanks, and Townsend

Bl

213-882-1 nterior-1689
B2 RIVER HYDRAULICS

and Blust (1960, p. 14) showed that comparative ireasurements 

of discharge with Price, Ott, and Neyrpic current meters in a 

turbulent stream agree within 0.2 percent of the mean. Similar 

comparisons of the performance of the Price and Ott meters for 

19 pairs of discharge measurements of the Mississippi River at 

Vicksburg by Carter and Anderson (1963, p. 108) showed a mean 

difference of 0.15 percent and a maximum difference of 2.76 percent. These tests and comparisons attest to the accuracy and 

reliability of discharge measurements made with current meters 

suspended from a stationary structure; however, the performance 

of current meters subjected to vertical motion, as where suspended 

from a bobbing boat, has not been thoroughly investigated.

The effect of vertical motion on velocity registration by the 

Price current meter, and thus on the accuracy of discharge measurements made from a boat on a windy day, has often been a 

subject of conjecture. Hydrographers have observed that the 

Price meter responds positively (same direction as if recording 

stream velocity) if moved vertically in still water, regardless of 

the direction, frequency, or rate of vertical movement.

C. J. Chappell (written commun., 1959) stated that several tests 

were conducted by U.S. Geological Survey personnel in August 

1939 to determine the effect of vertical motion on the F~ice current 

meter. The tests were limited to a single stream velocity of 2.5 

feet per second. The results of those tests indicated underregistration if the rate of vertical motion was less than 0.75 fps and increasing overregistration if the rate of vertical motion was more 

than 0.75 fps. These results led to the conclusion that the rate of 

vertical motion determines whether the Price meter overregisters 

or underregisters, but this conclusion is not in agreement with the 

observations mentioned previously that the meter always responds in a positive direction regardless of the directior, frequency, 

or rate of vertical movement in still water. One could assume, 

therefore, that in flowing water, some element of oscillatory motion 

must have a retarding effect on the registration of stream velocity 

by the Price meter, though the more significant effect is toward 

overregistration.

This report describes and presents the results of an investigation 

of the effect of vertical oscillation (simulated movement of a bobbing boat) on the performance of the Price, vane-type, and Ott 

current meters. The meters were tested within a range of frequency and amplitude of vertical oscillation that might be expected 

while measuring discharge from a boat. The effect of frequency 

of oscillation, as well as the rate of vertical motion, was evaluated.

Tests were conducted mostly in the rating flume at the Bonne213-882-lnterior-l 689
EFFECT OF VERTICAL MOTION ON CURRENT METERS B3

ville Hydraulic Laboratory of the Corps of Engineers U.S. Army. 

Several tests were also conducted in uniform streamflow from 

bridges spanning the Willamette and Columbia Rivers in Oregon. 

Some tests conducted in the Willamette River were later duplicated (same stream velocity) in the rating flume, and results were 

practically identical. All the tests, with the exception of one where 

a meter was suspended from a boat, were performed under simulated conditions of vertical motion.

The effect of moving a current meter up and down in uniform 

flow is not the same as holding a current meter motionless in turbulent flow. The assumption, therefore, should not be made that 

the effect of vertical motion on current meters, as presented herein, 

applies to current meters held motionless in turbulent flow.

For cable suspension, the meters were attached to a standard 

C-type sounding weight and suspended with a 0.10-inch sounding 

cable. For rod support, the meters were attached rigidly to a %- 

inch metal pipe.

TESTING THE EFFECT OF VERTICAL MOTION

CURRENT METERS TESTED

The Price standard and Pygmy current meters are commonly 

used by the U.S. Geological Survey in measuring streamflow. The 

meters function similarly to an anemometer and have six conical 

cups that form a wheel which has an axis of rotation normal to 

streamflow. The standard Price meter shown in figure 1 was used 

for testing.

The U.S. Geological Survey designed and built the vane-type 

meter (see fig. 2) for use in measuring streamflow under ice 

cover. This meter is the same as the Price meter except that in 

place of conical cups it has curved vanes that are not as easily 

clogged by snow and ice. Figure 3 shows three adaptations of the 

vane-type meter. Vertical-motion tests were conducted mainly 

with meter A. Meter B was also tested, but on a cable (same 

suspension as for Price and Ott) instead of on the rod shown. 

Meter C is identical to A but is equipped with specially designed 

weights and tailpiece to allow suspension by a cable through an 

augered hole in ice cover.

The Ott meter is a screw-type meter having its axis of rotation 

parallel to streamflow. Standard equipment for cable-suspension 

includes a buoyant 39-inch tailpiece having a detachable horizontal 

fin which serves as a vertical stabilizer and counterbalance. The 

meter can be attached to the hanger bar with one pin, which al213-882-lnterior-l 689
B4 RIVER HYDRAULICS

FIGURE 1. Standard Price current meter.

FIGURE 2. Vane-type current meter adapted for supporting by a rod. Photograph furnished by Plans and Operations Section of U.S. Geol. Survey, 

Columbus, Ohio.

213-882-lnterior-1689
EFFECT OF VERTICAL MOTION ON CURRENT METERS B5

FIGURE 3. Three adaptations of the vane-type meter: A, for supporting by a rod from ice cover or a boat; B, for supporting by a 

rod while wading or for suspending by a cable; C, for suspending 

by a cable through an augered hole in ice cover.

lows considerable pivot action about the pin, or it can be attached 

rigidly with two pins. Several types of rotors (propellers) are 

available for use with the Ott meter. Figure 4 shows an Ott meter 

with a cosine rotor (8646-A) and a standard tailpiece having a 

detachable stabilizer fin. This rotor is designed to register the 

cosine component of angular flow up to a 45° angle from the meter 

axis.

TEST PROCEDURE UNDER SIMULATED CONDITIONS

The vertical bobbing of a boat was simulated by the use of 

either a sounding reel (U.S. Geol. Survey type A) for cable 

suspension or a length of %-inch pipe provided with guides and 

adjustable stops for rod suspension.

The meter was raised and lowered manually with these devices, 

and the cycle period of the vertical movements was timed with a 

stopwatch. Various periods and amplitudes of vertical motion were 

used, each carefully controlled and recorded so that the vertical

213-882-lnterior-l 689
B6 RIVER HYDRAULICS

FIGURE 4. Ott current meter with rotor 8646-A and standard tailpiece with

stabilizer fin.

velocity of the meter could be computed. The amplitudes ranged 

from a minimum of +0.1 to 0.1 foot to a maximum of +2.0 to 

 2.0 feet. The cycle periods ranged from 1 to 30 seconds. Various 

combinations of periods and amplitudes were used in the tests to 

ensure that the simulated motion would encompass the unpredictable oscillations of a boat and to disclose any tendency of a meter 

to be affected by frequency of change in vertical direction as well 

as by the rate of vertical motion.

During tests conducted in the rating flume, the current meter 

was suspended near middepth from a tow cart, and the revolutions 

were counted electrically in a circuit synchronized with solenoids 

that expelled a dart at the beginning and at the termination of 

each run. The towing speed (control velocity) was determined 

from the time interval and distance between darts. During tests 

conducted from bridges, a stationary control meter was suspended 

at the same elevation (midpoint of vertical oscillation) and about 

2 feet laterally from the meter being tested. The registrations 

(revolutions) of both the test and control meters were recorded 

simultaneously on a chronograph.

Prior to each series of tests from bridges, the stream velocity 

was measured at various depths within the vertical range of test 

oscillations to assure that the vertical distribution of stream 

velocity was approximately uniform. The registered velocities of 

the control and test meters, both held stationary at the same depth,

213-882-lnterior-l 689
EFFECT OF VERTICAL MOTION ON CURRENT METERS B7

were then compared. If a disagreement was evident, the subsequent registrations were adjusted by the amount of the difference. 

Some disagreement in the registration of the two meters was noted 

during a few of the tests and presumably caused either by differing stream velocity within the lateral distance between meters or 

by calibration error. The test-meter registration was also adjusted 

for any variation in stream velocity as recorded continuously by 

the control meter during each series of tests.

TEST RESULTS FOR SIMULATED CONDITIONS

Figures 5, 6, and 7 show, in feet per second, the relation between the vertical motion (abscissa) and the stream velocity 

(ordinate). The intercept on the ordinate axis (where the plotted 

line for a given observed velocity intercepts the ordinate axis) 

for each curve represents the true stream velocity, and the difference between the dashed horizontal line through the intercept and 

any given point on the curve is the overregistration or under - 

registration caused by the indicated rate of vertical motior. Each 

test point, shown as a small dot, indicates the test-meter registration during an interval of time (40-60 seconds) when the meter 

was being moved up and down at a constant amplitude and cycle 

period (frequency). The amplitude and cycle period are not identified on these graphs because of lack of space. Data ertracted 

from these graphs, partly by interpolation, are shown in tabular 

form in table 1. The curves and the table indicate that each of 

the three meters tested is affected to some degree by vertical 

motion.

PRICE METER

Figure 8 shows an expanded plot of typical tests of tlXQ. Price 

meter at a stream velocity of 1.4 fps. Each test point represents 

a known cycle period and amplitude of vertical motion, as identified 

by numbers and symbols, at a constant stream velocity. The 

position of each test point on the plot indicates the effect of that 

vertical motion on the registered stream velocity. Note that the 

test points farthest on the negative side (less than control velocity 

as registered by control meter) represent oscillations of relatively 

small amplitude or high frequency, whereas those near control 

velocity or on the positive side represent relatively large amplitude 

or low frequency. This distribution of test points indicates that 

the frequency of oscillation and the rate of vertical motion affect 

the Price meter registration of stream velocity. Vertical movement 

causes a positive effect (overregistration), whereas changes in

213-882-1 nterior-1689
B8 RIVER HYDRAULICS

TABLE 1. Registration errors, in percentage of stream velocity

Vertical motion 

(ft per sec)

0.2 0.4 0.6 1.0 1.2 1.5

Price current meter

[Suspended by a cable]

0.5

1.0

1.5

2.0

2.6 

3.0

4.0

6.0___ .

7.0

10.0

-2.0

-3.0

-6.7

-2.5

0

0

0

+ -4

_ 7

- .5

+ 10

-1.0

-6.7

-2.5

0

0

0

+ 1.0

_ 4

- .3

+ 36

+ 10

-4.0

-2.5

0

0

0

+ -6

0

0

+ 72

+ 24

+ 1.3

-2.0

0

0

0

0

+ .1

0

+ 120

+ 40

+ 8.0

0

0

-2.3

-1.3

- .2

- .4

_ _g

+ 150

+ 50

+25

+ 4.0

+ -8

-2.0

-1.3

0

- .7

- .7

+ 210

+ 56

+ 27

+ 14.0

+ 4.0

0

0

+ -8

_ ^4

-1.3

Vane-type current meter

[Suspended by a rod]

0.5

1.0 

1.6 - - 

2.0

2.5 

3.0 - 

4.0

6.0 

7.0_ _ 

+ 4.0

+ 5.0

+ 3.3

+ 2.0

+ 2.0

-1.7

I 1 O

-1.0

- .7

+ 6.0

+ 10

+ 8.7

+ 6.5

+ 4.4

+ 3.7

+ -8

-2.6

- .7

+ 20

i 19

+ 10

+ 9.0

+ 6.4

+ 5.3

+ -3

-2.8

- .3

+ 44

+ 10

+ 6.7

+ 9.5

+ 7.6

+ 6.7

+ 1.0

-2.0

0

+ 72

+ 11

+ 3.3

+ 8.5

+ 8.0

+ 7.3

+2.5

- .4

0

+ 100

+ 15

+ 3.3

+ 6.0

+ 7.2

+ 7.7

+ 3.8

- .2

+ -3

+ 160

+ 26

+ 10

+ 7.5

+ 6.4

+ 6.7

+ 3.3

-2.0

- .4

Ott current meter

[Cosine rotor 8646-A, standard tailpiece without vertical stabilizer, and two-r'n attachment to

cable hanger]

0.5

1.0 - 

1.5 

2.0

2.5

3.0 

4.0 _ ---.._

6.0.. .

7.0 .

0

0

0

0

0

0

0

+ .4

0

+ 6.0

0

0

0

0

9

0

+ -6

0

+ 10

0

0

0

0

0

+ -5

+ .4

0

+ 20

+ 4.0

+ 1.3

+ -5

0

+ -3

+ 1.0

+ -6

0

+ 30

+ 9.0

+ 4.0

+2.0

+ 1.6

+ 1.0

J_1 0

+ 1.0

j_ q

+ 44

+ 15

+ 7.3

+ 4.5

+ 2.8

+2.3

+2.5

+ 1.4

+ -7

+ 70

+30

+ 17

+ 9.5

+ 6.4

+ 6.0

+3.8

+ 2.0

+ 1.4

213-882-lnterior-l 689
EFFECT OF VERTICAL MOTION ON CURRENT METERS B9

10

0.2 0.4 0.6 0.8 1.0 1.2 

VERTICAL MOTION, IN FEET PER SECOND

1.4

FIGURE 5. Effect of vertical motion on the Price current meter siispended 

by a cable. The vertical intercept is the true stream velocity, and the 

departure from the dashed line through the intercept is the error in 

registration caused by the rate of vertical motion (abscissa), ""he true 

stream velocity for the lowest curve is zero.

213-882-1 nterior-1689
BIO RIVER HYDRAULICS

0.2 0.4 0.6 0.8 1.0

VERTICAL MOTION, IN FEET PER SECOND

1.2 1.4

FIGURE 6. Effect of vertical motion on the vane-type current meter supported by a rod. The true stream velocity for the lowest curve is zero.

vertical direction cause a negative effect (underregistmtion). The 

negative effect varies directly with the frequency of changes in 

direction and probably has a retarding effect whenever the meter 

is oscillated up and down in flowing water, but it is the dominant 

factor only at small amplitude in stream velocities lietween 0.5 

and 2.4 fps.

Because of the horizontal fins on the sounding weight and the 

tailpiece of the current meter, the cable-suspended meter and 

sounding weight are poorly balanced hydrodynamically when 

moved vertically and they, therefore, tend to pivot about their 

hanger pins when moved up and down. Some freedom for pivoting

213-882-lnterior-l 689
EFFECT OF VERTICAL MOTION ON CURRENT METERS Bll

0.2 0.4 0.6 0.8 1.0 1.2 

VERTICAL MOTION, IN FEET PER SECOND

1.4

FIGURE 7. Effect of vertical motion on the Ott current meter suspended by 

a cable and equipped with rotor 8646-A and a standard tailpiece without 

stabilizer. The true stream velocity for the lowest curve is zero.

is provided in the hanger-bar attachment of both the meter and 

the weight, but during higher rates of vertical oscillation, the 

limits of that freedom are exceeded. As a result, the hanger bar 

begins to tilt forward on downward movement of the weight and 

meter and backward on upward movement. The combined pivoting 

and tilting tends to head the meter in the direction of vertical 

motion.

In an effort to evaluate the effect of pivoting and tilting' on the 

registration of the Price meter, several tests were conducted with 

the meter attached to a rod. Figure 9 shows the results of these 

tests. Comparison with test results for cable suspension (fig. 5)

213-8 82-1 nterior-1689
B12

2.0

1.6

1.2

RIVER HYDRAULICS

 I I 

X±o 

O±o.io

A±0.50

V±i.oo

D±1.50 

 ±2.00

__ _Control velocity __ 

1.40 feet per second

0.2 0.4 0.6 0.8 1.0 1.2 

VERTICAL MOTION, IN FEET PER SECOND

1.4

FIGURE 8. Expanded test plot for Price current meter in a stream velocity 

of 1.40 feet per second. The symbols show the various ampl: tudes in feet, 

of simulated wave motion for which the meter was tested. The numbers 

indicate cycle periods in seconds. Curve drawn through the points represents the average deviation from true velocity for various combinations of 

amplitude and cycle period.

indicates that the pivoting and tilting of the cable-suspended meter 

increase the registration at most of the stream velocities tested.

VANE-TYPE METER

The vane-type meter is used mostly for measuring streamflow 

under ice cover and in open water where slush ice is flowing. 

Figure 6 shows that the rod-suspended meter overregisters significantly from 0 to 4 fps and underregisters at 5 fps stream velocity 

if subjected to vertical motion. Meter-calibration tests at 5 fps 

stream velocity indicated some rating instability, which may 

account for part of the underregistration at this velocity.

The meter (meter B, fig. 3) was also tested while suspended by 

a cable. Figure 10 shows that the effect of vertical motion is very 

similar to the effect on the rod-supported meter except that the 

cable-suspended meter underregistered at 0.5 fps stream velocity 

if the vertical motion was between 0 and 0.6 fps. The pivoting 

and tilting observed during the tests of the Price m°.ter also occurred during these tests, but comparison of figures 6 and 10 does 

not indicate any overregistration from that cause.

213-882-lnterior-1689
EFFECT OF VERTICAL MOTION ON CURRENT METERS B13

4.2 

4.0 

3.8 

3.6 

3.4 

3.2 

3.0

2.6 

2.4

2.0 

1.8 

1.6 

1.4 

1.2 

1.0 

0.8 

0.6 

0.4 

0.2

0.2 0.4 0.6 0.8 1.0 1.2 

VERTICAL MOTION, IN FEET PER SECOND

1.4

FIGURE 9. Effect of vertical motion on the Price current meter supported 

by a rod. The true stream velocity for the lowest curve is zero.

213-882-lnterior-1689
B14 RIVER HYDRAULICS

0.4 0.6 0.8 1.0 

VERTICAL MOTION, IN FEET PER SECOND

1.2 1.4

FIGURE 10. Effect of vertical motion on the vane-type currert meter suspended by a cable. The true stream velocity for the lowest curve is zero.

OTT METER

Figure 7 shows that the Ott meter overregisters if subjected to 

vertical motion but to a lesser extent than the Price or vane-type 

meters. The cosine property of the rotor (8646-A) used in these 

tests has been tested, with favorable results, in the Bureau of 

Standard's rating flume. Vertical motion tests, therefore, were 

expected to show no overregistration at rates of vertical motion 

less than stream velocity (resultant angle of flow le?s than 45° 

from meter axis) because it was assumed that the cosine property 

would cancel any tendency of the meter to overre-dster. The 

curves shown in figure 7 tend to verify that assumption up to a 

stream velocity of about 1.0 fps. At higher stream velocities, however, the meter begins to overregister at less than a 45° angle 

of flow.

Because the Ott meter has such a long tailpiece, it is even less 

well balanced hydrodynamically than the Price meter in vertical 

movement; consequently, it tilts more if moved up and down. 

The two-pin attachment fixes the meter rigidly to the hanger bar 

and eliminates the possibility of pivoting, but, as explained for the 

Price meter, the hanger bar tilts forward and backward during 

higher rates of vertical oscillation. The Ott meter was tested 

mostly without the stabilizer fin because the fin would cause the 

meter to tilt even more. Because a hydrographer has the option of 

removing the fin, it probably would not be used when measuring

213-882-lnterior-l 689
EFFECT OF VERTICAL MOTION ON CURRENT METERS B15

5 1-5

5 D- 1.3

< hLiJ UJ

Cd LLJ

k ^ 1.2

1.1

-x Two hanger pins; no stabilizer fin

- Two hanger pins; stabilizer fin

-^ One hanger pin; stabilizer fin

0.2 0.4 0.6 0.8 1.0 1.2 

VERTICAL MOTION, IN FEET PER SECOND

1.4

FIGURE 11. Effect of vertical motion on the Ott current meter suspended by 

a cable. The curves show the comparative effect of one- and two-pin 

attachment to the hanger bar, and the effect of the stabilizer fin.

velocity from a bobbing boat; the two-pin attachment to the 

hanger bar would generally be used.

Figure 11 shows the results of vertical motion tests with and 

without the stabilizer fin and with one- and two-pin attachment to 

the hanger bar. The two-pin attachment without stabilizer fin 

caused the least amount of tilting, whereas the one-pin attachment 

with stabilizer fin caused the most. No significant increase in overregistration, however, is indicated by an increased amount of 

tilting.

To determine the effect of vertical motion when tilting is not 

a factor, the Ott meter was tested while attached to a rod. Figure 

12 shows that the meter still overregisters, and comparison with 

figure 7 indicates that overregistration was reduced slightly by 

elimination of the tilt factor.

Vertical-motion tests were also conducted with the Ott meter 

using rotor 8406-1 and a modified tailpiece. (See fig. 13.) The 

short tailpiece (not standard Ott equipment) was designed to improve the hydrodynamic balance of the meter and thereby reduce 

the tilting. The meter was tested from a suspended cable, and no 

tilting was observed except at rates of vertical motion exceeding 

1.0 fps. Rotor 8406-1 has considerably greater pitch than cosine 

rotor 8646-A and is apparently designed for low stream velocities. 

The results of these tests (fig. 14) show significant underregistration for the slow-velocity rotor at all stream velocities. Comparison of test data for the two Ott rotors shows that rotors of various 

pitch designs can vary considerably in their response to vertical 

motion, and this fact indicates that a rotor could possibly be 

designed which would not register vertical motion.

213-882-lnterior-1689
B16 RIVER HYDRAULICS

2.0

1.8

cr 1.4

LU

CL

LU 1.2

LU 

U_

? 1.0 >"

g o.s

LU

1 0.6

LU

CCL

& 0.4 

0.2

0.2 0.4 0.6 0.8 1.0 1.2 

VERTICAL MOTION, IN FEET PER SECOND

1.4

FIGURE 12. Effect of vertical motion on the Ott current meter supported by 

a rod and equipped with rotor 8646-A.

TEST UNDER ACTUAL CONDITIONS

Results of the foregoing tests represent the effect on registration of current meters when subjected to various combinations of 

man-induced wave motion in various stream velocities. To corroborate the results of these simulated studies, a Price meter 

was suspended from a 14-foot boat having standard U.S. Geol. 

Survey equipment and was tested under actual conditions.

FIGURE 13. Ott current meter with rotor 8406-1 and modified tailpiece.

213-882-1 nterior-1689
EFFECT OF VERTICAL MOTION ON CURRENT METERS BIT

0.2 0.4 0.6 0.8 1.0

VERTICAL MOTION, IN FEET PER SECOND

1.2 1.4

FIGURE 14. Effect of vertical motion on the Ott current meter suspended 

by a cable and equipped with rotor 8406-1 and a short tailpiece.

The boat, positioned beneath a bridge which spans the Columbia 

River at Hood River, Oreg., was restrained from horizontal movement by a cable attached to piers 200 feet apart but was free to 

move up and down. One Price meter (test meter) was suspended 

from a standard boat measuring boom which extended 2 feet over 

the bow of the boat, and a control meter (Price) was suspended 

from the bridge at the same elevation, but 3 feet laterally from 

the test meter. The revolutions of both meters and the vertical 

movements of the boat were simultaneously recorded on a chronograph, as shown in figure 15. The wind was variable and the 

velocity was estimated to be 5-30 miles per hour. There were no 

"white caps" thus wind conditions were relatively calm for the 

Columbia River gorge.

RESULTS OF TEST UNDER ACTUAL CONDITIONS

Figure 16 shows the chronological sequence of vertical motion 

of the test meter and the registration of stream velocity by both 

the test meter and the control meter. The data were computed 

and plotted for 10-second intervals by summing the number of 

revolutions of the rotor for each meter at 10-second intervals and 

converting that to velocity and by summing the vertical distances 

the meter traveled, as recorded on the chronograph (without regard to direction) for each 10-second interval, and dividing by 

10 to obtain the velocity of vertical motion. Even with a mild 

wind, which is common during many discharge measurements, the

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B18 RIVER HYDRAULICS

FIGURE 15. Chronograph equipped for recording revolutions of two current 

meters and the vertical movement of a boat.

Price meter overregistered nearly 8 percent on the average and 

more than 30 percent at times.

The results from the tests made from the boat agree very favorably with the results of tests from simulated wave motion. Underregistration began to occur when the vertical motion decreased to 

less than 0.5 fps, which agrees with the test results for 1.1 fps 

stream velocity shown in figure 5. The magnitude of overregistration and underregistration also agrees with the amounts shown 

in figure 5 for corresponding rates of vertical motion.

CONCLUSIONS

The results obtained from the tests during this study indicate 

that the performance of each of the three current meters tested 

is significantly affected by vertical motion in lower stream velocities. Discharge measurements made at low stream velocities, 

therefore, can be in error by a significant amount.

The results shown in figures 5, 6, and 7 and table 1 can be used 

as a guide in deciding whether wind and streamflow are within 

an acceptable range for a reliable discharge measurement from a 

boat. The rate of vertical motion of a boat can be approximated

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10

CO

00

00

10

I6* 

o

00

o uj

3 y> 1.4

tH o:

-> UJ

5^

< IL±J UJ

CC UJ

1.2

1.0

1.0

5 « 0.8

0.4

0.2

T t I 1 I I I I I I I I I | I I I 1 | I 1 I I | I 

---- Current meter suspended from a boat boom

Current meter suspended from a bridge

 Vertical motion (velocity) of boat boom

50 100 150 200 250 

TIME, IN SECONDS

FIGURE 16. Comparison of registered velocities by two Price current me

from a boat beneath the bridg
B20 RIVER HYDRAULICS

by measuring its vertical movement (twice the average distance 

from lowest to highest positions) with a sounding or anchor line 

and then multiplying by the number of cycles (frequency) per 

second. During the boat test performed for this study, the frequency of vertical motion remained relatively constant; only the 

amplitude varied.

In stream velocities above 2.5 fps, the effect of vertical motion 

on the Price meter becomes insignificant within the range of 

vertical motion tested in this study. The underregistration of the 

Price meter at low rates of vertical motion is caused by relatively 

high frequency of vertical oscillation rather than the rate of 

vertical motion. Measurement of velocities from a small boat in 

choppy water may result in underregistration in the velocity 

range from 0.5 to 2.4 fps.

The vane-type meter overregisters significantly in steram velocities up to 4 fps if subjected to vertical motion. Underregistration 

at 5 fps may have been caused partly by rating instability, which 

is suggested by a variation in several calibration checks made at 

this stream velocity.

The results shown for the Ott meter in figures 7,11, ?nd 12 and in 

table 1 apply only to rotor type 8646-A. The rotor overregisters 

significantly in stream velocities up to 4 fps if the rates of vertical 

motion exceed 0.8 fps. At stream velocities of 1.0 fps and less, 

however, it overregisters at lower rates of vertical motion. Where 

the meter is used with other types of rotors, the effect of vertical 

motion, as shown by the test results for rotor 8406-1 (fig. 14), is 

likely to be different. The variation in the effect on rotors of 

different design indicates that a rotor could be designed which 

would not be affected by vertical motion.

LITERATURE CITED

Carter, R. W., and Anderson, I. E., 1963, Accuracy of current r^eter measurements: Am. Soc. Civil Engineers, Jour. Hydraulics Div., v. 89, no HY 

4, Proc. Paper 3572, p. 105-115.

Townsend, F. W., and Blust, F. A., 1960, A comparison of stream velocity 

meters: Am Soc. Civil Engineers, Jour. Hydraulics Div., v. 89, no. HY 

4, Proc. Paper 2438, p. 11-19.

U. S. GOVERNMENT PRINTING OFFICE: 1966 O 213-882

213-882-lnterior-1689