Selected Techniques 

in Water Resources 

Investigations

GEOLOGICAL SURVEY WATER-SUPPLY PAPER 1669-Z

Selected Techniques 

n Water Resources 

Investigations

'ompiled by GLENNON N. MESNIER and KATHLEEN T. ISERI

:ONTRIBUTIONS TO THE HYDROLOGY OF THE UNITED STATES 

jEOLOGICAL SURVEY WATER-SUPPLY PAPER 1669-Z

Articles on new techniques by E. G. 

Barron, ff^. L. Isherwood, F. C. Craig, 

P. M. Frye, IF. B. Mills, P. G. Drake, 

David McCartney, R. H. Musgrove, 

B. R. Colby, H. D. Brice, and Roy 

New come, Jr.

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1963
UNITED STATES DEPARTMENT OF THE INTERIOR 

STEWART L. UDALL, Secretary

GEOLOGICAL SURVEY 

Thomas B. Nolan, Director

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

Washington, D.G. 20402
FOREWORD

Increasing world activity in water-resources development has created an alert interest in techniques for conducting investigations in 

the field. In the United States, the Geological Survey has the responsibility for extensive and intensive hydrologic studies, and the 

Survey places considerable emphasis upon the development of better 

ways to carry out its responsibility. For many years, the dominant 

interest in field techniques has been "in house," but the emerging 

world interest has led to a need for a published account of this progress.

The papers contained in this report represent a sample of the new 

ideas being tested or applied in the hydrologic field program of the 

Geological Survey. Some of the techniques described, such as that 

for digital recording of water levels and machine processing of river 

records may, when perfected, influence the basic course of a major 

sector of water-resources investigations. Other techniques, less profound in their scope, can contribute significantly to the accuracy and 

ease of field operations.

Luna B. Leopold,

Chief Hydraulic Engineer,

U.S. Geological Survey

in

CONTENTS

Page

Foreword.-_________--_______---______--_---_-_______-___-------_- in

New instruments for surface-water investigations, by E. G. Barron______ Zl

Electromagnetic velocity meter..-_______-______-____-____-___-_- 1

Acoustic velocity meter. --___-______-__-__-_______-_-____-_---_ 2

Bubble gage __________________________________________________ 4

Surface follower_______________________________________________ 8

Sonic flood-measuring assembly_--___-_____----___-______---_--- 9

Velocity-azimuth-depth assembly (VADA)________________________ 10

Two-speed timer__--_-_-_-__-_________-____---_-___________-__ 12

Digital water-stage recorder, by W. L. Isherwood.__-__________---_____ 13

Introduction._________________________________________________ 13

Description of recorder__-_____________________________________- 13

Processing of records___________________________________________ 15

Variation in velocity distribution in a tide-affected stream, by Franklin C.

Craig-_______________________________________________. 17

Introduction._________________________________________________ 17

Procedure for determining variations in velocity distribution. _______ 17

Explanation of results..______-____________--____--_-____--__-__ 18

Location of index meter________________________________________ 21

Establishment of crest-stage gages at discontinued gaging stations, by

Prentis M. Frye_______________________________________________ 25

Use of plastic tubes for peak-stage gages on reservoirs, by Willard B. Mills__ 27

Field filtering unit for water samples, by Paul G. Drake______--__-.-__-- 29

Introduction._________________________________________________ 29

Description of filtering unit.____________________________________ 30

Operation of filtering unit-_____________________________________ 31

Test of a continuous dissolved-oxygen recorder, by David McCartney____ 33

Introduction._________________________________________________ 33

Principles of operation.________________________________________ 34

Choice of site _________________________________________________ 40

Results of test._____________________________________ 43

Maintenance of the instrument_________-____--___-__-___-------- 44

Accuracy of three nonstandard rain gages, by R. H. Musgrove__-------_ 45

Working graph for computing unmeasured sediment discharge, by Bruce R.

Colby_________._...___.__________..___.____..___________--_-._- 49

Limitation of depth-integrating samplers________________------_-- 49

Factors affecting the unmeasured sediment discharge.-.-.---------- 49

Computation procedures_______________________________------- 50

Tipping-bucket rain-gage attachment for a water-stage recorder, by H. D.

Brice___________________________________________----- 53

Development of the rain-gage and recorder attachments____-__-_-_- 53

Description of the attachments.-______-_______________----_---_- 53

Installation of the attachments___-____--_---____-----_---------- 55
VI CONTENTS

Simplified method of altimeter surveying, by Roy Newcome, Jr _________ Z59

Introduction. _________________________________________________ 59

Method. __________ _ ______ _ ____ _ ________________________ 59

Precautions to be observed in making altimeter surveys ____________ 64

ILLUSTRATIONS

FIGURES 1, 2. Electromagnetic velocity meter Page

1. Operating recorders.-___-_--_---_-_-___________ Z3

2. Rodmeter_--_-__-___-_-------_--_-_-__________ 3

3, 4. Acoustic velocity meter 

3. Continuous wave method_______________________ 5

4. Pulse-repetition-frequency method _______________ 5

5-7. Bubble gage 

5. Zero-displacement manometer-__________________ 6

6. Complete with recorder ______________________ 7

7. Differential type manometer-servo assembly_____ 8

8. Sonic flood-measuring equipment.____________________ 10

9, 10. Velocity-azimuth-depth assembly (VADA) 

9. Complete on crane and four-wheel base_________ 11

10. Sounding weight with sonic transducer and compass ready for insertion..____________________ 12

11. Digital water-stage recorder--------------_--____-__- 14

12. Relation between velocity at 0.2 depth and the average 

at 0.2 and 0.8 depths at station 225, Sacramento River 

at Sacramento, Calif., August 13-27, 1952. _______ 19

13. Time variation, in ratio of velocity at 0.8 depth to that 

at 0.2 depth, and stage hydrograph, station 225, Sacramento River at Sacramento, Calif., August 13-17, 

1952________________________________________.__. 20

14. Horizontal distribution of velocity during tidal-cycle 

measurement of June 27, 28, 1957, Sacramento River 

at Sacramento, Calif____________________________ 21

15. Hydrograph of stage and flow during tidal-cycle measurement of June 27, 28, 1957, Sacramento River at 

Sacramento, Calif-_______--------___-__-________- 22

16. Relations between mean velocity and index velocities 

at station 200 during tidal-cycle measurement of June 

27, 28, 1957, Sacramento River at Sacramento, Calif-- 23

17. Relations between mean velocity and selected index 

velocities during tidal-cycle measurement of June 

27, 28, 1957, Sacramento River at Sacramento, Calif- _ 24

18. Crest-gage mounting in stilling well__________________ 26

19. Peak-stage gage for reservoirs---.---.-.____________ 28

20. Filtering unit for water samples._____________________ 31

21. Relation of partial pressure to dissolved oxygen________ 35

22. Magnetic susceptibility of various gases_-__-__-_-_-__ 36
CONTENTS VH

FIGURE 23, 24. Contact sampler-analyzer Page

23. Front view...-...________________________ Z37

24. Back view_--_--_______-_.___------------------ 38

25. Continuous dissolved-oxygen recorder installation. _____ 39

26. Simplified circuit of dissolved-oxygen recorder. _______ 40

27. Analyzing cell of dissolved-oxygen recorder.___________ 41

28. Schematic diagram of operation of dissolved-oxygen

recording system___________________________._____ 42

29. Simultaneous rainfall catches in gages of various sizes. _ 46

30. Nomograph for computing unmeasured sediment discharge __________________________________________ 51

31-34. Rain-gage installation and equipment 

31. Tipping-bucket unit attached to rain-gage collar__ 54

32. Counter and marking-pen attachment....-.,... 55

33. Rain gage installed in recorder shelter..________ 56

34. Arrangement of instruments.___________________ 57

35. Chart for temperature correction of altimeter readings. _ 61

36. Barometric-correction graph.______________________ 62

37. Barometric curve. __________________________________ 63

TABLE

Fan 

TABLE!. Notes for graph in figure 36__ ______--__--______________ Z63

CONTRIBUTIONS TO THE HYDROLOGY OF THE UNITED STATES

SELECTED TECHNIQUES IN WATER RESOURCES 

INVESTIGATIONS

NEW INSTRUMENTS FOR SURFACE-WATER 

INVESTIGATIONS

By E. G. BARRON

ABSTRACT

An electromagnetic velocity meter and an acoustic velocity meter have been 

developed for continuously recording the velocity of water at a fixed location 

in open channels. The electromagnetic velocity meter records the velocity of 

water flowing past a streamlined probe, a rodmeter, mounted at a fixed point in 

the water. The acoustic velocity meter records the mean velocity on a line 

between transducers mounted in the water near both banks of a stream. These 

instruments have no moving parts in the water to be fouled by debris.

A bubble gage and a surface follower have been developed also. These 

instruments record continuously the stage of a stream or reservoir without need 

of costly and troublesome stilling wells and intakes. The bubble gage utilizes 

the gas-purge technique to transmit the pressure of the water to a specially 

designed servomanometer that operates a recorder. The surface follower, which 

also operates a recorder, follows the water level in a 2-inch or larger pipe that is 

mounted vertically in a stream.

A portable sonic sounder has been combined with a Price current meter for 

use in measuring fioodflows. In another instrument, the combination includes 

a remote-indicating compass for use in determining the velocity and direction 

of flow as well as the depth at any point in a river or a tidal estuary.

Also, a two-speed timer has been developed for use on small flashy streams, 

where it is desirable to automatically expand the time scale of the recording 

of high water to several times the low-water scale.

ELECTROMAGNETIC VELOCITY METER

The electromagnetic velocity meter measures the velocity of flowing 

water by a method based on Faraday's principle: an electrical conductor moving in a magnetic field generates an electrical voltage. As 

used in streamflow measurement, the meter continuously records the 

velocity of the water at a fixed point in a stream.

Zl
Z2 CONTRIBUTIONS TO THE HYDROLOGY OF THE UNITED STATES

The instrument was originally developed by the U.S. Navy as a 

ship's log for indicating both the speed of the vessel and the total 

distance traveled. Figure 1 shows the complete instrument as modified 

by the Survey for use in measuring streamflow. The rodmeter (fig. 2) 

is about 3 feet long and consists of a fiberglass-reinforced shell with 

an aluminum mounting plate at the top. An electromagnet and two 

terminals are mounted in the plastic shell. The terminals form part 

of an electrical pickup loop through the water. The rodmeter exciter 

coil is energized by an oscillator operating at a frequency of 65 to 70 

cycles to reduce the effect of 60-cycle currents that may be present in 

the water. The signal from the probe is amplified and recorded.

Laboratory tests indicate that the electromagnetic velocity meter 

is very sensitive to even slight changes in velocity and is capable of 

measuring velocity in either upstream or downstream directions with 

respect to the rodmeter. Tests also indicate freedom from long-term 

drift. Small percentage errors due to drift were present, however, 

when the velocity was changed suddenly. At all velocities, errors from 

drift average out in a relatively short time.

The first electromagnetic velocity meter was installed in November 

1957 on the St. John's Eiver at Jacksonville, Fla. Velocities during. 

the tidal cycle at this site range from about 6 feet per second in a 

downstream direction to about 4 feet per second in an upstream direction. The meter was calibrated at the site and has performed satisfactorily. Another assembly with more simplified circuits requiring 

less maintenance and producing a more desirable response to the probe 

signal will soon be installed near 'Columbus, Ohio, for field trial and 

calibration.

ACOUSTIC VELOCITY METER

The acoustic velocity meter uses ultrasonic waves for continuous 

recording of velocities of flow in open channels. The technique has 

been used successfully to measure velocities of fluids in closed conduits, 

and present efforts are directed to the more complicated task of applying the method to open channels of considerable width. The phenomenon involved in measuring water velocities by ultrasonic waves 

is analogous to the Doppler effect of sound in air the pitch of a 

constant sound source varies with both the speed and the direction of 

che sound source with reference to the receiver.

The principle can be illustrated by observing what happens when a 

stone is dropped in a quiet pool of water. The surface waves travel 

out from the source of the disturbance in uniformly spaced concentric 

circles. If the water is flowing, however, the waves moving against 

the direction of flow will condense that is, the wavelengths will 

shorten and those moving with the direction of flow will lengthen. 

Sound waves produced within the fluid behave in a similar manner.
TECHNIQUES, WATER RESOURCES INVESTIGATIONS Z3

FIGURE) 1. Electromagnetic velocity meter, operating recorders.

FIGURE 2. Electromagnetic velocity meter, rodmeter.
Z4 CONTRIBUTIONS TO THE HYDROLOGY OF THE UNITED STATES

Figure 3 illustrates a simple application of this principle to the 

measurement of flow velocity. If the reception is in phase without considering the velocity of flow, the reception considering the velocity of 

flow will be out of phase by a number of degrees proportional to the 

velocity of flow. However, the velocity of sound in the water varies 

about 6 feet per second per degree Fahrenheit change in temperature, 

which is more than enough to obscure the relatively small water velocities we wish to detect. It is therefore necessary to cancel the effect 

of sound-velocity variations by simultaneous sound transmissions, one 

angling upstream and one angling downstream.

The continuous-wave method was used successfully in closed conduits. However, tests in open channels indicated the presence of 

random deviations of the phase angle that were both meaningless and 

unstable. The instabilities were caused by multiple-path reception 

resulting from reflections of the sound waves from the water surface 

and refractions from thermoclines. The situation is analogous to 

the flutter on a television screen caused by multiple-path reception as 

an airplane passes overhead.

A pulse-repetition-frequency system was therefore developed as 

illustrated in figure 4. By this method a 135 kc (kilocycles) per second acoustic pulse is transmitted from the upstream transducer and received at the downstream transducer. The energy from this pulse 

activates a keying circuit, and another 135 kc pulse is transmitted. 

An 85 kc electroacoustic circuit operates simultaneously with, and in 

the same manner as, the 135 kc pulse, but in the upstream direction. 

The two pulse-repetition frequencies are fed into a computing circuit, 

the output of which is proportional to the water velocity. As installed 

in a river, the parallel acoustic paths are established in the water at 

approximately 45° to the flow so as to integrate with the width and 

eliminate the effect of variations in the water temperature.

A complete pulse-repetition-frequency system was installed on the 

Sacramento River at Sacramento, Calif., in July 1959. Performance 

of the meter was encouraging, but the results were not good enough 

for use in a standard streamflow computation, and the equipment is 

now undergoing modification.

BUBBLE GAGE

The bubble gage was developed to record river and reservoir levels 

without the use of stilling wells and intake pipes that are often expensive to construct and difficult to maintain. Installed in a prefabricated shelter at ground level at any convenient location above the 

reach of floodwaters, it can be used to take full advantage of existing 

natural or artificial controls, and the entire station can be readily dis-
Z5

TRANSMITTER

VELOCITY OF SOUND=5000 FT PER SEC

TRAVEL TIME = O.OI SEC

WAVELENGTH (A) = 4.17 FT

FREQUENCY=I200 CYCLES PER SEC

FLOW 

23456789 10

-DISTANCE =50 FT

FLOW VELOCITYHOFT PER SEC

 - IN 0.01 SEC 

SOUND WAVE IS MOVED 

DOWNSTREAM

TOTAL NUMBER OF DEGREES=4J320

4,320^ A° 

50 O.I

A°= 8.63°

FIGURE 3. Acoustic velocity meter, diagram of continuous-wave method of measuring

velocity of water.

FIGURE 4. Acoustic velocity meter, diagram of pulse-repetition-frequency method of

measuring velocity of water.
Z6 CONTRIBUTIONS TO THE HYDROLOGY OF THE UNITED STATES

mantled and relocated with practically no loss of investment. A description of the four major units that make up a bubble gage follows.

1. Gas-purge system. Provides a means of transmitting the pressure head of water in the stream to the manometer location. The following principle is applied: If a gas is bubbled slowly through a small 

tube and discharged freely at an orifice located at a fixed elevation in 

the stream, the pressure at the orifice, ;and hence at any point in the 

delving tube, is related to the head or depth of water over the orifice. 

This system consists of a cylinder of nitrogen and the polyethylene 

tubing necessary to convey the gas from the instrument shelter to the 

orifice. For most river installations, the required gas ((nitrogen) feed 

rate is so low that an ordinary cylinder of gas (112 cubic feet, costing 

about $4 per refill) will operate the equipment for a year or longer.

2. Servo-manometer assembly. Converts the pressure in the sensing 

element of the gas-purge system to a shaft rotation for driving a digital 

counter and a recording mechanism. The pressure from the gas-purge 

system, corresponding to the pressure in the water, is brought into the 

movable pressure cup through the bulkhead fitting in the manometer 

back plate (fig. 5). Mercury is used as the manometer liquid to keep 

the overall length to a minimum. The manometers have a sensitivity 

of ±0.005 foot and can be built to record ranges in stage in excess of 

120 feet. A unique feature of the manometer is that it is designed to 

operate at approximately 18° with the vertical. This angle allows 

the use of simple standard gears and threads and also provides an

FLOAT 

SWITCH

PRESSURE 

RESERVOIR

FIGURE 5. Bubble gage, illustration of zero-displacement manometer.
TECHNIQUES, WATER RESOURCES INVESTIGATIONS, Z7

exact means of adjusting for anything varying with stage (pressure) 

that would otherwise result in error. The river pressure in the movable cup acts on the mercury surface and causes enough movement of 

mercury through the flexible tube to sustain a stainless-steel float in 

the switch.

3. Transistor-control imit. Amplifies the small electric current in 

the float-switching circuit sufficiently to operate the servomotor and 

provide an appropriate time delay between the closing of the float 

switch and the starting of the motor. The transistor-control unit, 

used with the bubble gage, contains dual amplifiers and timing networks. It is necessary to amplify the extremely small current available 

from the light contacts in the float switch to drive the motor. The 

timing networks provide a delay of about 30 seconds to eliminate or 

appreciably dampen the reaction of the manometer to pressure surges. 

Use of the delay circuit eliminates undesirable "painting" of the 

recorder charts, lengthens battery life, and reduces wear on the motor 

and other components. A pair of the 7.5-volt dry batteries will operate 

the manometer for about a year in most installations.

4. Recorder. Converts the shaft rotation to a linear pin movement 

proportional to water stage and provides a continuous time scale for 

the recorded movements of the pen. Figure 6 shows the complete 

equipment for the bubble gage (35-foot range model).

The differential-type (dual pressure) manometer (fig. 7) which 

is similar in design to the single-pressure model, records directly the

FIGURE 6. Bubble gage, complete with recorder.
Z8 CONTRIBUTIONS TO THE HYDROLOGY OF THE UNITED STATES

slope in a relatively short reach of river channel. The differential 

pressure between two orifices, each at an extremity of the reach, is 

recorded by connecting the lower pressure to the float-switch chamber 

and allowing the higher pressure to act on the liquid level in the 

movable reservoir.

By using a nonf reezing solution of 60 percent glycerine and 40 percent water with a specific gravity of 1.17, the accuracy of the differential-type manometer is improved to about ±0.001 foot of water.

A differential-manometer assembly is now being used at the hydraulic laboratory at Colorado State University to record the fall in a 

100-foot reach of flume. A second assembly is being operated on the 

Olentangy Kiver near Columbus, Ohio, in an attempt to record the 

fall in a 500-foot reach.

FIGURE 7. Bubble gage, differential-type manometer-servo assembly. 

SURFACE FOLLOWEB

The surface follower was designed to follow the rise or fall of a liquid 

surface in a vertical 2-inch pipe. It is accurate to ±0.005 foot and 

has a maximum range of 45 feet. Two 7.5-volt dry batteries supply 

the necessary power for about a year to a small 6-volt reversible motor 

that in turn raises or lowers the float assembly in response to changes 

in the height of the surface of the liquid.

The instrument as designed is composed of a float assembly, a cable, 

a servocontrol unit, and a takeup-drum assembly. The float assembly
TECHNIQUES, WATER RESOURCES INVESTIGATIONS Z9

is mounted to an electrical switch with two fixed contacts and a movable center contact attached to a lighter-than-water float; the housing 

for the float assembly is plastic with a perforated brass shield over the 

float. The shield serves two purposes: it protects the delicate float, 

and it provides sufficient weight to keep the cable taut. The diameter 

of this assembly is 1% inches. A few thousandths of a foot change in 

the liquid level causes the float to tip until contact is made on the 

proper side, thus causing the cable drum to raise or lower the cable and 

float switch. The cable has two inner conductors and a braided outside 

shield that is used as a third conductor. The servocontrol unit is iden-^ 

tical with the one used with the bubble gage and thus provides a time 

delay to dampen surging. The takeup-drum assembly consists of a 

grooved cable drum driven by a 6-volt 4.58 rpm (revolutions per 

minute) reversible d-c motor through a mechanical linkage. The 

recorder drive is accomplished through a gear on the outboard end 

of the cable drum that meshes with a similar gear and replaces the 

float wheel of a Stevens A-35 water-stage recorder. Adjustable limit 

switches are provided so that the unit can be used in a stream that 

grK,& dry.

Sensing at the liquid surface rather than at the recorder has considerable advantage. Because friction along the cable or float does not 

affect the accuracy, the pipe installation need not be exactly plumb. 

The instrument shelter need not be supported directly over the pipe, as 

special elbows with internal sheaves can be used to bring the pipe 

horizontally to the instrument shelter.

SONIC FLOOD-MEASURING ASSEMBLY

A combination of a depth recorder (Fathometer) and a standard 

Price current meter (fig. 8) permits measurement of depths and 

velocities in stream channels without lowering the meter and weight 

assembly to the stream bottom. This is extremely advantageous in 

floodflows where relatively great depths are encountered and debris 

carried by the stream is a frequent menace to the equipment.

During floodflows it might be useful to submerge the weight perhaps 3 feet below the surface, thus placing the meter only 2 feet below 

the surface. Velocity and depth readings would be determined, and 

a coefficient applied to the velocity reading would reduce it to mean 

velocity for the vertical section. The coefficients could be determined 

quite accurately under less arduous conditions. This method would 

eliminate the risk involved in lowering measuring equipment to considerable depths, and it would also result in a savings of valuable 

time, which is especially short during floods. Furthermore, under 

severe flood conditions, the conventional method of observing velocity
Z10 CONTRIBUTIONS TO THE HYDROLOGY OF THE UNITED STATES

FIGURE 8. Sonic flood-measuring equipment, complete on crane and four-wheel base.

at the 0.2 and 0.8 depths probably would be less accurate than the 

near-surface observation because of the inherent errors in determining 

depth of water and in positioning the meter at the correct depths.

The Fathometer weighs 46 pounds and is completely portable. It 

operates on a frequency of 200 kilocycles, which does not penetrate 

the streambed; therefore, the depths recorded are to the top of the 

bed material of the channel. The transducer has a narrow 6° beam 

angle that minimizes errors on inclined streambeds and permits operation close to piers or other obstructions. The Fathometer can record 

depths to 240 feet in four depth ranges of 60 feet each. The effects 

of temperature and density give a possible error range of 4 percent 

under field conditions in fresh water, and even this can be reduced 

or eliminated by adjusting the sounder for the existing conditions. 

A 6-volt wet-cell battery will operate the Fathometer for about 10 

hours.

VELOCITY-AZIMUTH-DEPTH ASSEMBLY (VADA)

The velocity-azimuth-depth assembly is a combination of a sonic 

sounder with a remote-indicating compass and a Price current meter. 

This combined instrument records depths, indicates the direction of 

flow, and permits observations of velocity at any point in a stream or 

estuary.

Figure 9 shows the entire assembly mounted on a regular crane and 

four-wheel base. It shows a seven-conductor slip-ring assembly at
TECHNIQUES, WATER RESOURCES INVESTIGATIONS Zll

the top of the meter hanger. This assembly, with its radial and 

thrust bearings, frees the meter and weight so they can rotate independently of the supporting cable and face in the direction of flow 

at velocities as low as a tenth of a foot per second. The line from 

this seven-conductor slip-ring assembly is fed into a seven-conductor 

jack on the top of the weight and then to the transducer and remotecompass unit in the weight. Figure 10 shows the sonic transducer 

and compass ready for insertion in special brass sounding weight.

The quarter-inch seven-conductor reverse-lay stainless-steel supporting cable is wound on a sounding reel that has a capacity of about 90 

feet. A seven-conductor slip ring brings the circuits out of the reel.

The compass-indicating unit, shown mounted on the four-wheel 

base, utilizes 4 of the 7 leads and is operated by a 12-volt d-c to 400- 

cycle a-c inverter within the unit. Also incorporated within the 

remote-indicator box are the battery for the current-meter circuit, the 

earphone jacks, and the two-conductor jack for the sonic sounder. A 

switch allows the remote-indicating unit to be used separately or in 

conjunction with the sonic sounder.

The sonic recorder used with this assembly is the same as that described above.

FIGURE 9. Velocity-azimuth-depth assembly (VADA), complete on crane and four-wheel

base.
Z12 CONTRIBUTIONS TO THE HYDROLOGY OF THE UNITED STATES

FIGURE 10. Velocity-azimuth-depth assembly (VADA), sounding weight with sonic transducer and compass ready for insertion.

TWO-SPEED TIMER

This timer was devised for use on small flashy streams where it is 

desirable to automatically expand the time scale of the recording of 

the high-water scale to several times that at low water.

The clock of an A-35 recorder is replaced by a solenoid-ratchet 

device that advances the chart one-eightieth of an inch each time it 

is pulsed electrically. The Chelsea timer, driven by a Negator spring, 

rotates two timing cams at a rate of one revolution per hour. One of 

the cams actuates a microswitch eight .times per hour to pulse the 

solenoid-ratchet for a low-water scale of 2.4 inches per day. The 

other cam closes a pair of contacts 48 times per hour to pulse the 

solenoid-ratchet for a high-water scale of 14.4 inches per day.

A selector-switch device is connected to the recorder float-wheel 

shaft by sprockets and chain. This instrument can be set to switch the 

recorder from low to high drive at any selected stage as the water 

rises and back to low drive at a slightly lower stage on the recession.
DIGITAL WATER-STAGE RECORDER

By W. L. ISHEBWOOD

ABSTRACT

The digital water-stage recorder is a slow-speed battery-operated paper-tape 

punch designed to record river gage heights at remote field locations unattended 

for periods of at least 60 days. Its shaft-rotation input is sampled at intervals 

of 15, 30, or 60 minutes and recorded as four binary-coded decimal digits punched 

in parallel mode on 16-channel paper tape. The development of this recorder is 

part of the Geological Survey's program to increase the speed of computing and 

processing stream-gaging records.

INTRODUCTION

The digital water-stage recorder shown in figure 11 was developed 

to register river-gage heights at remote, unattended field installations. 

The data are collected on a tape directly readable by automatic equipment, and this tape record enables the use of a general-purpose digital 

computer to process the data very rapidly with a minimum of manual 

handling and interpretation.

The availability of a general-purpose degital computer in the 

Geological Survey encouraged a search for a digital water-stage 

recorder. An analog computer built to scan conventional, continuous 

water-stage-recorder charts did not operate satisfactorily; therefore, 

attention was focused on use of the digital computer and the digital 

water-stage recorder.

DESCRIPTION OF RECORDER

Input to the digital water-stage recorder is shaft rotation. At the 

usual gaging station a metal tape attached to a float in a stilling well 

turns a pulley mounted on the input shaft of the recorder. Any other 

water-level sensing element that results in a shaft rotation could be 

substituted for the tape and float input. The input shaft turns two 

mechanical coding disks, one directly connected to the input shaft 

and the other driven by the input shaft through a 100-to-l worm gear. 

The two coding disks have patterns of raised ridges along the outer 

1 inch of their front faces such that each one-hundredth of a rotation 

of the input shaft will result in a discrete reading. With a float

Z13
Z14 CONTRIBUTIONS TO THE HYDROLOGY OF THE UNITED STATES

FIGURE 11. Digital water-stage recorder.

wheel 1 foot in circumference mounted on the input shaft, the rivergage height can be recorded to the nearest 0.01 foot within the range 

from 0 to 99.99 feet. The position of the code disks at a particular instant is recorded by releasing a spring-loaded arm carrying a punch 

block threaded with paper tape against the front faces of the two code 

disks. Punch pins riding free in the punch block are struck against 

the patterns of ridges on the two code disks, so that the pins which 

hit the ridges are forced through the paper tape, whereas those that 

hit between the ridges do not go through.

The tape is punched in the binary decimal system, 4 binary bits for 

each of the 4 decimal digits are read, making a total of 16 information channels in parallel mode for each reading. Two fixed-position 

holes are also punched at each reading for later use as feed 'holes for 

the mechanical tape reader. Readings are made at regular intervals 

through use of a timing device. The timer consists of a clock with a 

cam mounted on the minute-hand shaft and a microswitch operated by 

an arm riding on the cam. As the cam turns one revolution an hour, 

a choice of cams with 1, 2, or 4 rises and dropoffs provides for read-
TECHNIQUES, WATER RESOURCES INVESTIGATIONS Z15

ings every 15, 30, or 60 minutes, as required, to produce the refinement desired at a particular gaging station. When the switching 

device triggers the recorder, a small battery-driven 6-volt motor turns 

a programing shaft that initiates punching, advances the paper tape, 

compresses a spring to store power to actuate the punch on the next 

cycle, and turns off the motor after the reading cycle has been completed. The battery will last about a year because it operates the 

motor for only about 12 seconds on each punching cycle.

PROCESSING OF RECORDS

Tapes are removed from the recorder about every 6 weeks, at the 

regular visits of a field engineer to the gaging stations. After identification and pertinent notes are written on the tapes by the engineer, 

they are sent to a processing center in Washington, D.C., where the 

computer facilities are located. At the processing center, the parallelcoded 16-channel paper tapes are translated automatically by special 

equipment onto serial-coded T-channel paper tapes readable by the 

computer, and the necessary fixed information identifying the stations 

and the starting dates are added. Shortly after this, the 7-channel 

tapes are read photoelectrically into the computer where the raw data 

are edited, arranged, and transferred onto a magnetic tape for later 

processing. While the transfer to the magnetic tape is being done, a 

simple summary of the raw data is printed out by the computer to 

help detect errors in any part of the data-collection system. These 

summary sheets are immediately sent to the field offices along with the 

original 16-channel tapes so that troubles with the field instruments 

can be detected, analyzed, and remedied at the earliest possible 

moment.

At the end of the period for which daily discharge records are to 

be computed (normally 6 months or a year), the field offices send to 

the processing center the supplemental data of datum corrections, 

shift corrections, and stage-discharge rating tables needed to complete 

the computations. The supplemental data are manually punched on 

T-channel tape for computer input. During computation, the gageheight data are read back from prepared magnetic tape, 1 day of 

record at a time, while the supplemental data are read in from paper 

tape as needed. The main output is a list of daily mean gage heights, 

daily shifts, and daily mean discharges with corresponding monthly 

summaries, 6 months to a sheet. One supplemental computer output 

is a small group of standard punch cards containing lists of peak discharges above a selected base. The list of peaks is prepared later 

from these cards as a separate operation by different equipment. Another supplemental output is a group of punch cards containing plotting positions for automatic plotting of a hydrograph on a semi-
Z16 CONTRIBUTIONS TO THE HYDROLOGY OF THE UNITED STATES

logarithmic chart. The automatic plotting is also done at a later 

time by equipment not attached to the computer.

The three items of output (list of mean daily gage heights with 

shifts and discharges, list of peak discharges, and plotted hydrograph) are sent to the field office, where they are examined for consistency, accuracy, and completeness. Any necessary corrections for 

special hydraulic conditions or the filling in of incomplete records are 

done at that time. Future plans call for corrected copies of the daily 

gage-height-and-discharge form to be returned to the processing center 

for transfer to magnetic tape and for printing the daily discharges for 

a year in a form suitable for direct camera copy for offset reproduction. All procedures except the latter have been put into test operation for a limited number of gaging stations, selected from a network 

of about 7,000 stations maintained by the Geological Survey.
VARIATION IN VELOCITY DISTRIBUTION IN A 

TIDE-AFFECTED STREAM

By FRANKLIN C. CBAIG

ABSTRACT

A study of changes in distribution of velocity as a result of unsteady flow is 

of consequence in selecting the location for installing an index velocity meter. 

Data are presented to show the kinds of variations that occur in tide-affected 

streams.

INTRODUCTION

Streams subject to rapidly changing discharge usually cannot be 

rated by a simple stage-discharge relation. Additional parameters 

are required. One such parameter that can be obtained is a continuous record of the velocity at an index point.

Common types of streams whose rapidly changing discharge complicates the discharge rating are streams subject to power regulations, 

tidal action, and sharp peaks from storm runoff. This report is a 

study of flow velocities.at an index point in a stream affected by tidal 

action. Unsteady flow causes variations in velocity which, if not 

taken into account, can negate the value of a record obtained from a 

velocity index point. The distribution of velocity in a cross section 

was found to vary both vertically and horizontally with the rate of 

flow. It is therefore necessary that a study be made of the variation 

in point velocities before an index point is selected for the continuous 

observation of velocity. A standard current meter, such as the one 

used in this study, is not well adapted to continuous operation for 

periods longer than a few days. A new instrument, the electromagnetic velocity meter, may prove to be more satisfactory.

PROCEDURE FOR DETERMINING VARIATIONS IN VELOCITY

DISTRIBUTION

Variations in velocity distribution can be noted in floodtime by 

the changing paths of drift movement or a change in the turbulence 

pattern before and after the crest is reached. Data are seldom available to judge the relative significance of these changes on a given 

stream. To get a complete picture of changes in velocity distribution

Z17
Z18 CONTRIBUTIONS TO THE HYDROLOGY OF THE UNITED STATES

would of course require the operation of many current meters distributed vertically and horizontally throughout the cross section and 

operated throughout a period of changing flow. Because this is seldom practical, an attempt was made to obtain the essential information 

using one current meter.

A series of discharge measurements was made by conventional methods throughout a period of changing flow in one cross section at the 

gaging station on the Sacramento River at Sacramento, Calif. At 

each of approximately 25 verticals (or stations) in this cross section, 

velocity was measured with a current meter at 0.2 of the depth and at 

0.8 of the depth this is a standard procedure in making a discharge 

measurement. The time of making each velocity observation was recorded. Time-sequence graphs (not shown) were made for each observation station in the cross section to show the velocity observed 

while making each discharge measurement in the series and to show 

the recorded time of the velocity observations. The velocity at any 

particular time for which a study of velocity distribution was to be 

made was picked from this graph. This is a method of obtaining 

simultaneous measurements of velocities for the purpose of comparison, even though the velocities are changing rapidly with time and the 

discharge measurement from which they are obtained takes appreciable time to complete.

Discharge measurements were made at 2-hour intervals throughout a 14-day tidal cycle, August 13-27,1952, and during a lunar day 

June 27, 28,1957.

EXPLANATION OF RESULTS

Figure 12 shows the relation between the 0.2-depth velocity and 

the average velocity in a selected vertical section. It shows the magnitude of the error that would result in determining the flow through 

the section if a velocity index point had been located at the 0.2-depth 

point in that section. Greater accuracy could probably be attained 

by locating the index meter at or near the 0.6-depth point. Automatic depth-positioning equipment is sometimes used to maintain 

the meter at a 0.6-depth point. Figure 13 shows that the variations 

in velocity distribution are not generally of a random nature, but that 

they follow a pattern which is related to changes in the rate of flow that 

are caused by changes in the tide phase.

Shown in figure 14 are mean vertical velocities at stations spaced 

25 feet apart across the stream. The observations were made throughout the lunar-day tidal cycle as shown in figure 15. During measurement 2, for example, there was far greater difference between the 

velocity at the center of the stream and that at the sides of the stream
TECHNIQUES, WATER RESOURCES INVESTIGATIONS Z19

than during measurement 16, yet both measurements were made at 

nearly the same stage. Under these conditions an index meter at 

the center of the stream or at either bank would not yield an index 

parameter that varied with stage alone or that maintained a constant 

relation to the mean velocity of the stream. A fairly good relation 

could be obtained by an index meter at about station 500, where the 

mean velocity would tend to approach the mean velocity of the stream 

during all phases of the tidal cycle. Because the stream is wide and 

there is probably some tendency for the flow to shift laterally, espe2.9

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AVERAGE OF VELOCITY, IN FEET PER SECOND, AT 0.2 AND 0.8 DEPTHS

FIGURE 12. Relation between velocity at 0.2 depth and the average at 0.2 and 0.8 depths 

at station 225, Sacramento River at Sacramento, Calif., August 13-27, 1952.
Z20 CONTRIBUTIONS TO THE HYDROLOGY OF THE UNITED STATES 

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FIGURE 13. Time variation in ratio of velodty at 0.8 depth to that at 0.2 depth, and stage 

hydrograph, station 225, Sacramento River at Sacramento, Calif., August 13-17,

cially when there is wind, the use of two index meters would be even 

better. The two index meters could be located perhaps at stations 

200 and 500 and averaged. Possible relations are shown in figures 16 

and 17. No attempt was made to determine the best possible indexpoint location or locations, but figures 15 and 16 show the improvement in relation that is possible by selecting the stationing and position 

in the vertical of velocity index points.
TECHNIQUES, WATER RESOURCES INVESTIGATIONS Z21

LEFT BANK RIGHT BANK

FIGURE 14. Horizontal distribution of velocity during tidal-cycle measurement of June 27, 

28, 1957, Sacramento River at Sacramento, Calif. Numerals on curves indicate measurement number.

LOCATION OF INDEX METER

The best location for a velocity index meter is that place at which 

the mean velocity in both the horizontal and vertical directions is approached. The location of the point or points at which the mean velocity in the horizontal direction occurs is not as well defined as it is in 

the vertical direction. According to data obtained by Pierce (1941), 

the mean velocity in a laboratory flume occurs at about two-tenths 

of the midstream distance from the sides. This flume presented an 

unnatural condition in that the walls were smooth and the bed was 

rough. In several large canals the mean tends to be at about fourtenths of the midstream distance from the sides. However, if there 

is any curvature in the channel this distance is subject to wide variation. In natural channels there are many factors that influence 

the location of the point of mean velocity. The point may have a tendency to move under the influence of changing flow, stage, wind, or 

salt or sediment loads.

It may not be possible to maintain a meter at the best possible indexpoint location. Errors introduced into the records as a result of 

unsteady flow and a meter location that is less than ideal tend to be 

compensating over periods of increasing and decreasing flow. Nevertheless, a study of variation in velocity distribution seems necessary in 

making such an installation.

REFERENCE

Pierce. C. H., 1941, Investigations of methods and equipment used in stream 

gaging: U.S. Geol. Survey Water-Supply Paper 868, 75 p.
Z22 CONTRIBUTIONS TO THE HYDROLOGY OF THE UNITED STATES

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INDEX VELOCITY, IN FEET PER SECOND

FIGURE 16. Relations between mean velocity and index velocities at station 200 

during tidal-cycle measurement of June 27, 28, 1957, Sacramento River at Sacramento, Calif. Numerals on curves indicate measurement number.
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CONTRIBUTIONS TO THE HYDROLOGY OF THE UNITED STATES

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INDEX VELOCITY, IN FEET PER SECOND

1.7

FIGURE 17. Relations between mean velocity and selected index velocities during tidalcycle measurement of June 27, 28, 1&57, Sacramento River at Sacramento, Calif. Numerals on curves indicate measurement number.
ESTABLISHMENT OF CREST-STAGE GAGES AT DISCONTINUED GAGING STATIONS

By PBENTIS M. FETE

ABSTRACT

Flood-frequency studies require a definition of the mean annual flood. Peakdischarge records may not cover a sufficient period of time to be used as a 

basis for defining the mean annual flood, but such records can be simply and 

inexpensively extended by using discontinued gaging stations.

A gaging station that is discontinued or relocated should be operated as a crest-stage gage if the station does not have sufficient record 

to define the mean annual flood needed in regional flood-frequency 

studies. To obtain a reliable record of the flood history, an accurate 

method of collecting peak-discharge data is necessary; and because of 

the increasing number of relocated stations, the technique should be 

economical. The methods commonly used when regular gaging structures have been left in place are to install regular crest-stage gages 

either inside or outside the gaging structure or to dump cork dust in 

the well. Because installation of the regular crest gage is somewhat 

costly and because the dumping of cork dust in the well has not 

proved to be entirely satisfactory, other methods have been tried. 

One of these methods, an economical and effective way of obtaining 

water levels was used at the gaging station, Garrison Fork at Fairfield, Tenn.

A redwood stick is secured to the existing instrument shelf or floor. 

A small can containing cork dust is then fastened to the bottom of 

the stick. Small holes are punched near the bottom of the can. The 

typical installation, shown in figure 18, is for a corrugated-pipe well 

with wooden lift-top shelter. For other structures the stick may be 

placed near the door or hinged to ensure accessibility. The length of 

the stick is determined by placing the bottom of the can at the stage 

that is normally exceeded about three times a year.

The gage heights of peaks are determined by measuring from the 

top of the withdrawn stick down to the high-water mark made by 

cork dust. Also the inside staff gage, if still in place, should be 

checked for high-water marks. Gage heights can be adjusted for 

surge to agree with previously published data on peaks by consideration of the amount of surge shown on the recorder charts for approximately equivalent peaks.

Some of the advantages of this type installation are as follows: (1) 

Excellent high-water marks, (2) economical cost, (3) ease of installation, and (4) ease of servicing. The results obtained from this particular installation have been very accurate.

Z25
Z26 CONTRIBUTIONS TO THE HYDROLOGY OF THE UNITED STATES

Bolt 

Mounting bracket

Instrument 

shelter

1-inch x 2-inch 

redwood stick

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24-inch

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pipe

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11 -Can

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FIGURE 18. Crest-gage mounting in stilling well, Garrison Fork at Fairfleld, Tenn.
USE OF PLASTIC TUBES FOR PEAK-STAGE GAGES ON

RESERVOIRS

By WIIXARD B. MILLS

ABSTRACT

A solution to the problem of obtaining peak stages at reservoirs equipped with 

staff gages is the use of a plastic tube. This tube, attached to an existing staff 

gage, provides a precise, easy-to-r.ead, and inexpensive peak-stage indicator.

In making special studies on reservoirs it is sometimes necessary 

to use a minimum of equipment. For some reservoirs, nonrecording 

staff gages read periodically are the only means of obtaining stage 

data. For water-budget studies, hydrologists must have not only 

periodic readings of stage and content but also readings of stage and 

content that may occur between the periodic readings. Most reservoirs have uncontrolled outlets to bring the reservoir to a fixed level 

after an influx of flood runoff; thus only by chance would a periodic 

reading of the staff gage reflect the peak stage.

The problem was to devise a peak-stage gage that would be precise, 

reliable, operative throughout the range in stage, easy to read, and 

inexpensive.

A solution to this problem is the use of a plastic tube installed on 

each staff-gage post, as shown in figure 19. All that is required is a 

clear plastic garden hose cut to the correct length. A small amount of 

cork dust is poured into the hose, both ends are stoppered, and breather 

holes are drilled near each end. One of these devices is then clipped 

to each staff gage. The clips used are standard pipe clips, and these 

are attached to the gage by using the screws that anchor the gage 

plates.

This type of installation has several advantages. It is inexpensive. 

No levels are required, as the gage height is read from the existing 

staff gage plates. The cost of the material required is inconsequential. 

A minimum of time and tools are needed for installation; the tube can 

be cut with a knife and installed with a screwdriver. Peak marks on 

the tube can be read as precisely as the staff gage permits, yet the gage 

requires no special setting. Although the tube must be firmly secured, 

it need not be exactly vertical, as the height of the water surface is all 

that is required. It can be adapted to any range in stage, an important factor when each staff gage is an individual installation. 

Peak marks are easily removed after reading. Regardless of aging 

and cracking, the tube will continue to operate.

There are some disadvantages. The tube can be moved or destroyed

Z27
Z28 CONTRIBUTIONS TO THE HYDROLOGY OF THE UNITED STATES

by vandals before a peak stage can be read. This is always a threat, 

but most reservoirs are built on farms that are fairly well guarded 

against trespassers by the farmers themselves. Also, the tube is subject to becoming soft and pliable in hot weather; tight hose clamps 

are required or the tube will slide out. Spiders build nests in the 

tubes, and the webs tend to strain the cork dust and prevent a distinct 

peak mark.

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r ;^-Existing gage plate

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SECTION A-A'

Notes:

1. Use small amount of fine cork in each 

section of hose

2. Use clear or green transparent plastic 

hose at least %-inch diameter

3. Erase peak marks by pulling a rag 

through hose with wire or rod or by 

flushing cork down with water

FIGURE 19. Peak stage gage for reservoirs.
FIELD FILTERING UNIT FOR WATER SAMPLES

By PAUL G. DRAKE

ABSTRACT

Separable material can be removed from a water sample at the time of collection by a simple filtration assembly. Precipitates of heavy-metal ions, particularly iron and manganese, which may form during the storage period before 

analysis, can be redissolved, and the analysis will then represent the sample 

concentration at the time of collection.

INTRODUCTION

The validity of the chemical analysis of a natural water sample is 

predicated upon the assumption that equilibrium between sediment 

and dissolved material exists in the water at the time of collection and 

that with certain precautions this equilibrium is sufficiently maintained until the time of analysis.

Among the factors that may affect this equilibrium are oxidation, 

reduction, absorption, ion exchange, precipitation, and solution of the 

sediment. These reactions particularly affect many of the heavymetal ions normally present in only trace amount to the extent that 

the collection of a separate sample filtered to remove the sediment 

and, in some instances, chemically fixed at the time of collection is 

advisable.

Iron and manganese are determined more frequently in water 

analysis than other heavy metals, and concentrations of iron and manganese are important parameters that affect a wide variety of municipal and industrial uses. Iron and manganese occur in water at two 

levels of oxidation. Iron, for example, occurs either in the bivalent 

ferrous or trivalent ferric state. The chemical behavior of the two 

forms is somewhat different, although both may be present in the same 

solution under certain circumstances. Under reducing conditions, 

iron in water will tend to be in the ferrous state. The ferrous salts, 

however, are unstable in the presence of oxygen or air and are changed 

to the ferric state through oxidation when natural water containing 

ferrous iron is exposed to the air.

In the pH range of 6 to 8, the solubility of feric iron in solution is 

limited by the solubility of ferric hydroxide, about 4X lO"10 to 5X 10~6 

mg (milligrams) of iron per liter, which is below the limit of detecZ29
Z30 CONTRIBUTIONS TO THE HYDROLOGY OF THE UNITED STATES

tion by methods ordinarily used in water analysis (Hem, 1959, p. 

58-66). The precipitatiQn of ferric hydroxide is frequently observed 

in stored samples that contain ferrous iron in solution.

In surface waters and in many ground waters the sediment normally present often includes some iron oxides that are formed in the 

process of weathering and are carried in colloidal suspension or as 

very small 'sediment particles. In water analysis, the determination 

of suspended iron is usually not desired; and because it is impossible 

to separate the soluble iron that has precipitated from the naturally 

occurring sediment after the sample has been collected and transported 

to the laboratory, the sample must be filtered at the time of collection. 

The filtration assembly here described is being used in the field by 

technical personnel engaged in water-resources investigations to obtain 

a sample that represents the iron or other heavy metal in solution at 

the time of collection. The sample can be chemically fixed after this 

separation process.

DESCBIPTION OF FILTEBING UNIT

The filtering unit consists of a two-piece polyethylene buchner funnel and a 6-ounce polyethylene bottle that serves both as the collecting 

vessel and as the source of suction. The buchner funnel is modified 

by inserting a perforated plastic disk between the two sections. This 

serves as a firm base for the filter paper that is placed between the 

two sections of the funnel. A rubber stopper fitted on the neck of the 

funnel and positioned in the polyethylene bottle provides an adequate 

seal to maintain sufficient vacuum for the system.

The grade of filter paper used depends upon the particle size to be 

retained. For most waters a filter paper of medium speed and high 

wet strength (Whatman No. 30 or equivalent) is satisfactory. However, a more retentive paper (Whatman No. 42 or equivalent) may 

be used where necessary.

The parts and the unit shown in figure 20 are identified as follows: 

A, Upper section of two-piece polyethylene buchner funnel, designed for 5 5-mm filter paper. 

B, Perforated plastic disk 2%2 -inch diameter, i£2 -incli 

thick, positioned in the lower section of the buchner funnel. 

C, Lower section of two-piece polyethylene buchner

funnel.

D, Polyethylene bottle, 6-ounce capacity. 

E, Filter paper, 90-mm diameter (oversize to form cup 

when placed between the two sections of the buchner funnel.) 

F, Filter unit assembled.
TECHNIQUES, WATER RESOURCES INVESTIGATIONS Z31

FIGURE 20. 'Filtering unit for water samples.

OPERATION OF FILTERING UNIT

In operation, the filter paper is placed between the two sections 

of the buchner funnel, and the two sections are pressed together. 

The polyethylene bottle is squeezed, and the neck is connected to the 

rubber stopper on the funnel stem. Sample is poured into the funnel, 

and the bottle tension is released. The resulting vacuum is sufficient 

to filter the sample effectively. One operation is usually sufficient to 

filter the reservoir capacity of the funnel.

The filtered sample may be left in the 6-ounce polyethylene bottle 

and capped for transport to the laboratory; or, preferably, the sample 

may be transferred to a clear glass bottle, thus enhancing visual 

inspection.

Two-piece polyethylene buchner funnels are available in 42.5-, 55-, 

70-, and 90-mm paper size. These may be combined with 6-ounce,
Z32 CONTRIBUTIONS TO THE HYDROLOGY OF THE UNITED STATES

8-ounce, or larger polyethylene bottles to provide larger units when 

desirable.

REFERENCE

Hem, John D., 1959, Study and interpretation of chemical characteristics of 

natural water: U.S. Geol. Survey Water-Supply Paper 1473, 264 p.
TEST OF A CONTINUOUS DISSOLVED-OXYGEN 

RECORDER

By DAVID MOCABTNEY

ABSTRACT

A dissolved-oxygen recorder was tested in the Delaware River near Philadelphia, Pa. The principles of operating the recorder are based on Henry's 

Law and the paramagnetic behavior of oxygen. The location for the test was 

determined by the convenience of the site and the fact that a wide variation 

in dissolved oxygen occurred there. Results of the test were based on 40 observations of dissolved-oxygen recorder values as compared to 40 simultaneous 

chemical determinations. Initially, observations were made twice daily, and 

finally, after reliability was established, about every 3 days. Total testing time 

was 59 days.

On the basis of specifications for accuracy of the dissolved-oxygen recorder 

and the accuracies of chemical tests, temperature, and oxygen-solubility tables*, 

a limit of a difference of 5 percent, saturation units is considered acceptable. 

This difference was exceeded only 5 times in 40 observations. The results 

of this test compare favorably with a previous test of this instrument by Macklin, 

Baumgartner, and Ettinger (1959).

INTRODUCTION

The absence, deficiency, or surplus of dissolved oxygen in water is 

closely related to management of water resources, particularly to disposal of sewage and industrial wastes. For proper classification and 

use of a stream it is helpful to understand the dissolved-oxygen 

characteristics of the water. The content of dissolved oxygen in water at equilibrium with normal atmospheric conditions is a function 

of the temperature and salinity of the water, because the ability of 

water to hold oxygen decreases with increasing temperature or dissolved solids.

The City of Philadelphia's Water Department is interested in additional information on the dissolved-oxygen content of Delaware 

River water. Continuous records of conductance, temperature, and 

dissolved oxygen are invaluable for describing the characteristics of 

Delaware River water and for identifying the factors that are responsible for changes in its quality.

The City of Philadelphia and the U.S. Geological Survey have been 

making monthly observations of the chemical quality of the DelaZ33
Z34 CONTRIBUTIONS TO THE HYDROLOGY OF THE UNITED STATES

ware River water between Trenton, N.J., and Marcus Hook, Pa., 

since August 1949 (Durf or and Keighton, 1954). Most of these observations have included the determinations of dissolved oxygen 

(D.O.) and biochemical oxygen demand (B.O.D.). Since 1955, periodic sampling has been supplemented by data from continuous conductivity and temperature recorders. The amount of dissolved solids 

can be estimated from the electrical conductivity of the sample; so 

these recorders supply a continuous estimate of the dissolved-solids 

concentration. In 1959 the use of a dissolved-oxygen recorder for analyzing the Delaware River water was begun, and in 1961 it was 

proposed to test another dissolved-oxygen recorder operating on a 

different principle. Such instrumentation facilitates studies of 

changes in dissolved-oxygen content as influenced by tidal flow, stream 

discharge, salinity, and other factors.

PRINCIPLES OE OPERATION

The dissolved-oxygen recorder operates on the principle of Henry's 

Law and the paramagnetic behavior of oxygen (oxygen is attracted 

by a magnetic field). As applied to water and oxygen, Henry's Law 

may be stated as follows: At equilibrium, the partial pressure of oxygen above a water surface is directly proportional to the concentration 

of dissolved oxygen in the water (fig. 21), or:

P=KN 

where

P=partial pressure above the water surface,

K=proportionality constant (Henry's Law constant), and

^^concentration of dissolved oxygen in water (ppm).

The proportionality constant, K, in this equation is for a given temperature. Variation in the partial pressure at a given temperature indicates variation in dissolved oxygen. Therefore, at a given temperature, the partial pressure due to the dissolved oxygen above the water 

surface is proportional to the percent saturation of dissolved oxygen 

in the water.

Oxygen is paramagnetic because it has two unpaired electrons. 

Most other gases (fig. 22) such as hydrogen sulfide, nitrogen, and carbon dioxide are diamagnetic (repelled by a magnetic field). Nitric 

oxide and nitrogen dioxide are paramagnetic, but their concentration 

in surface waters is extremely small. Their effect, therefore, is 

negligible.

The dissolved-oxygen recorder installation consists of three major 

units a pump, a contact sampler-analyzer (figs. 23,24), and a Wheatstone Bridge recorder (fig. 25). The entire system operates from a 

115-volt 60-cycle source and draws about 10 amperes. With the system 

in operation (fig. 26), the water sample is drawn through a 25-mesh
TECHNIQUES, WATER RESOURCES INVESTIGATIONS Z35

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DISSOLVED OXYGEN, IN PARTS PER MILLION

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FIGURE 21. Relation of partial pressure to dissolved oxygen at a given temperature.
Z36

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E

= 50

5LU

°= 30

02 N2 C02 H 2 S02 NH3 CH4 NO N02 

FIGURE 22. Magnetic susceptibility of various gases relative to oxygen.

screened intake that prevents debris from fouling the system. The 

sample is pumped at a constant, above atmospheric, pressure (3-5 

pounds-per-square-inch gage) into an aspirator where it mixes with 

the gases already in the system. (The exact system pressure is not 

important, but it must exceed the highest partial pressure exerted by 

the oxygen plus the nitrogen mixture. For example, at 200-percent 

saturation the system pressure would have to be 6 pounds-per-squareinch gage to maintain volume control.) The higher pressures of the 

system cause these gases to dissolve in the water.

Thorough mixing at the aspirator produces rapid equilibrium, in 

accordance with the principle of Henry's Law. The aspirated water 

sample is then forced into a water-gas separator, where the water is 

discharged. When the gases in the system dissolve in the water, the 

water level tends to rise in the water-gas separator. To prevent flooding of the system, a level-control electrode has been installed. When 

the water contacts this electrode a solenoid is actuated, and this allows 

the entry of about 1 cc of nitrogen gas, which forces the water level 

down. So that nitrogen may enter the system, the pressure of the gas 

is maintained at y2 to 1 pound per square-inch gage above the system 

pressure. An additional flood-prevention device has been installed in 

the base lines to and from the analyzing cell. Water passing these 

points completely shuts down the pumping unit, thus preventing damage to the analyzing cell. The undissolved gases above the water in
TECHNIQUES, WATER RESOURCES INVESTIGATIONS Z37

the water-gas separator now pass on to the analyzing cell. The analyzing cell (fig. 27) consists of two similarly heated resistance elements, one of which lies in a magnetic field. The oxygen-bearing gas 

is drawn into the magnetic field in the measuring cell, where it cools 

the heated resistor. In so doing, the oxygen loses its magnetism very 

rapidly (hi proportion to the square of its temperature rise). The 

heated demagnetized gas is forced out of the magnetic field and upward along the resistor by cooler and therefore more magnetic oxygenbearing gases from below. This magnetically induced flow of gas and 

resultant heat extraction produces a lower temperature in the measuring cell than in the comparison cell. As a result, the resistance of 

the measuring cell is less than that of the comparison cell. This resultant resistance differential is measured by a Wheatstone Bridge

FIGURE 23. 'Contact sampler-analyzer, front view.
Z38 CONTRIBUTIONS TO THE HYDROLOGY OF THE UNITED STATES

FIGURE 24. Contact sampler-analyzer, back view.

(fig. 28) and is proportional to the percent saturation of dissolved 

oxygen. The hot gases in the analyzing cell are now replaced by cooler incoming gases and move into the aspirator where they are mixed 

with fresh incoming water. Part of this gas will dissolve in the water 

and be discharged, and part will recirculate through the analyzing 

cell. This condition and the flow of water through the system produce the response time of the system. Initial response is 15 to 30 seconds, with a 90-percent response time of about 3.5 minutes for any 

arbitrary change in dissolved oxygen.

Calibration of the instrument is simple and rapid. If the magnet 

is moved away from the analyzing cell, equal cooling will take place. 

Essentially, the resistance of the measuring cell equals the resistance 

of the comparison cell. This becomes the 0-percent saturation adjust-
TECHNIQUES, WATER RESOURCES INVESTIGATIONS ZS9

FIGURE 25. Continuous dlssolved-oxygen recorder installation.

ment for the instrument. With the magnet in place and the system 

exposed to the atmospheric air, the instrument is adjusted to the 100- 

percent saturation. (Note: A 100-percent-saturated water in the system was originally in equilibrium with the atmosphere above it.)

When calibrating the instrument at the 100-percent saturation point 

on the recorder, corrections must be made. The range setting, therefore, may differ from 100 percent. The correct setting is found by 

the following formula:

Where

8= 100 percent PS -W

3

?= correct rainge setting,

PB= barometric pressure (in millimeters of mercury) , 

H = absolute humidity,

W= water vapor pressure at water temperature, and 

PR= standard barometric pressure (760 millimeters of mercury) .
Z40 CONTRIBUTIONS TO THE HYDROLOGY OF THE UNITED STATES

Example:

Pjs=750 mm Hg 

#=16 mm Hg

W=14 mm Hg 

P*=760 mm Hg

(760 14)

#=100 percent =98.4 percent 

(750-16)

The range setting in this example would be 98.4 percent. If parts 

per million dissolved oxygen is desired in place of percent saturation, 

temperature compensation can be added to the instrument.

CHOICE OF SITE

Regardless of what continuous physical or chemical measurement 

is made on a stream, it is important that one choose the right site. 

Temperature, conductivity, pH, and other factors require moving, 

nonsilting representative water conditions. These same requirements 

are especially applicable to the continuous measurement of dissolved 

oxygen. For example, if the intake is placed in shallow water where 

heavy algae growth predominates, the dissolved oxygen may be unusually high. If the intake is placed near the water surface in a turbulent area, again the results may be high and not representative. As 

with other continuous-recording instruments, the choice of site is based 

on reconnaissance.

ANALYZER RECORDER

CALIBRATION 

AIR

V

FIGURE 26. Simplified circuit of dissolved-oxygen recorder.
TECHNIQUES, WATER RESOURCES INVESTIGATIONS

CONNECTOR TO

MEASURING CIRCUIT

Z41

^RESISTORS 

CELL 

BLOCK

COMPARISON 

CELL

GAS OUTLETPIPE

XMOUNTING 

BLOCK

^GAS PASSAGE 

T^T BLOCK

FIGURE 27. Analyzing cell of dissolved-oxygen recorder.
Z42 CONTRIBUTIONS TO THE HYDROLOGY OF THE UNITED STATES

MEASURING 

CELL

COMPARISON 

CELL

MEASURING 

BRIDGE

SLIDEWIRE 

CONTACT

BALANCING 

SLIDE WIRE

PEN DRIVE 

MOTOR

AMPLIFIER AND

^UADT ' VOLTAGE REGULATOR 

CHART v_^

FIGURE 28. Schematic diagram of operation of dissolved-oxygen recording system.
TECHNIQUES, WATER RESOURCES INVESTIGATIONS Z43

The site for this first dissolved-oxygen test was the Delaware River 

Chestnut Street pier, Philadelphia, Pa. This location was convenient 

for daily observations and tests, and the river at this point has a wide 

range of percent-saturation dissolved-oxygen values. The suspended 

solids of the stream did not exceed 100 parts per million during the 

test. Previous work has indicated that this instrument will operate 

in activated sludges containing as much as 4,000 parts per million 

solids. No tests have been made to verify this. Power requirements 

for the instrument are such that battery operation would be very 

costly, so that it is desirable to select a site where power is readily 

available.

RESULTS OF TEST

At the beginning of the test, water samples were collected as frequentty as twice daily at the point of intake. With further testing, 

this time interval was extended. Collection, treatment, and determination of dissolved oxygen were carried out in accordance with recommended methods (American Public Health Assoc., 1955). The Alsterberg modification of the Winkler method (Alsterberg, 1925) was 

used for the laboratory dissolved-oxygen determination. The water 

temperature and barometric pressure were noted at the time of collection for conversion of parts per million to percent saturation of dissolved oxygen. The percent-saturation results of the chemical determinations were compared with the percent-saturation values of the 

recorder at the time of sampling.

During 59 days of testing, about 40 observations were made. The 

absolute difference between the analyzed percent saturation and the 

recorded percent saturation (dissolved oxygen) was noted. The 

average of these absolute differences was found to be 2.4-percent saturation units. These results compare favorably with the results of 

the initial field testing of the instrument by Macklin, Baumgartner, 

and Ettinger (1959). During their test, in which 21 samples of raw 

water from the Ohio River were analyzed, the absolute difference between recorded and analyzed values averaged 3.8-percent saturation 

units. It is difficult to place severe restrictions on the difference between the recorded and the analyzed oxygen concentrations because 

of the possible errors of both methods. However, the supplier of this 

test instrument has indicated an accuracy of ± 2 percent of full scale 

(0-100 percent saturation dissolved oxygen). On the other hand, it 

is not too difficult to realize ± 2-percent saturation variations in the 

analyzed results when considering temperature (± 1° F) or dissolved 

oxygen saturation tables (± 0.07 ppm) by the Alsterberg method 

(± 0.1 ppm). The previously mentioned investigators considered a 

limit of difference of 5-percent saturation as satisfactory. This figure
Z44 CONTRIBUTIONS TO THE HYDROLOGY OF THE UNITED STATES

is reasonable and has been used as the standard for this test. Of the 

40 observations, only 5 exceeded this acceptable difference limit.

MAINTENANCE OF THE INSTRUMENT

All recording instruments require careful maintenance. Maintenance checks were made every 3 days. At the test site the intake 

screen required cleaning from algae and sediment once each week. 

The instrument was calibrated once each week. The system pressure and nitrogen pressure were checked daily.

Breakdowns were few and usually minor. A broken intake screen, 

which caused fouling of the system; a loose motor wire; and a leak 

in the nitrogen supply accounted for all of the downtime. Failures 

of this type should be considered uncommon and unavoidable as recurrence is unlikely. With experience and a proper servicing schedule, loss of record would be minimized.

REFERENCES

Alsterberg, Gustof, 1925, Methods for the determination of elementary oxygen 

dissolved in water in the presence of nitrites: Biochem. Zeitschr, v. 159, 

no. 36.

American Public, Health Association, American Water Works Association, Federation of Sewage and Industrial Wastes Associations, 1955, Standard 

methods for the examination of water, sewage, and industrial wastes: New 

York, N.Y., American Public Health Assoc., 10th ed.

Durfor, C. N., and Keighton, W. B., 1954, Chemical characteristics of Delaware 

River water, Trenton, New Jersey, to Marcus Hook, Pennsylvania: U.S. 

Geol. Survey Water-Supply Paper 1262.

Macklin, M. O., Baumgartner, D. J., Ettinger, M. B., 1959, Performance test of 

continuous recording dissolved oxygen analyzer: Sewage and Indus. Wastes, 

v. 31, no. 7.
ACCURACY OF THREE NONSTANDARD RAIN GAGES

By R. H. MTJSGBOVE

ABSTRACT

Rainfall catches from three nonstandard gages of various sizes were compared with those from a standard U.S. Weather Bureau 8-inch gage. Results 

show catches in gages with thin walls or sharp-edge receiver rings are accurate 

regardless of the size of the gage.

Long-term rainfall records are usually the first hydrologic data to 

be compiled in water-resources investigations. It is often necessary to 

use rainfall records collected from nonstandard gages that have questionable accuracy. To make a study of the comparative accuracy of 

nonstandard gages, rainfall records were collected for 8 months in 

Ocala, Fla., from 4 nonrecording rain gages 3 were nonstandard tubes 

and 1 was a U.S. Weather Bureau standard 8-inch can.

The gages were installed in accordance with the U.S. Weather 

Bureau standards on exposure and location. The receiver rings of 

the gages were set at the same height and about 2 feet apart. The gages 

were all cylindrical and ranged from 0.65 inch to 8 inches in diameter.' 

They are described as follows:

1. A standard U.S. Weather Bureau 8-inch can with sharp-edge receiver ring.

2. A 2.8-inch aluminum can with 0.02-inch wall thickness and squareedge receiver ring.

3. A 0.85-inch glass tube with 0.06-inch wall thickness and round-edge 

receiver ring.

4. A 0.65-inch plastic tube with sharp-edge receiver ring.

Rainfall catches from the three nonstandard gages were compared 

with those from the U.S. Weather Bureau 8-inch gage, as shown in 

figure 29. The results point toward certain factors that can be applied 

to rainfall records if the type of gage is known. The thickness and 

cross-sectional shape of the receiver ring and the size of the receiving 

area, relative to the measuring area, are important factors.

The 2.8-inch aluminum gage underregistered by an average amount 

of 0.07 inch compared with the U.S. Weather Bureau 8-inch gage. 

Rainfall catches in this gage were measured by emptying them into 

a graduated cylinder. Water adhered to the walls of the gage, and

Z45
Z46 CONTRIBUTIONS TO THE HYDROLOGY OF THE UNITED STATES

S3HONI Nl '39V9 NIVH HONI-8 JO H01VO
TECHNIQUES, WATER RESOURCES INVESTIGATIONS Z47

consequently the total catch could not be measured. The 0.02-inch 

wall was thin enough to act as a sharp-edge receiver ring. A constant 

correction of +0.07 would be required when the aluminum gage is 

used.

The 0.85-inch glass gage overregistered all catches by an average of 

11 percent. This gage was made of relatively thick glass, and the 

receiver ring was rounded. Much of the rain falling on the receiver 

ring was caught in the gage, giving a funneling effect. A coefficient 

of 0.89 would be required for catches from this gage.

The 0.65-inch plastic gage is the type distributed by seed companies 

and is used as a "backyard" rain gage. The catches from this gage 

showed no constant source of error except the refinement to which it 

could be read. The scale was on the tube mounting and was graduated to 0.1 inch. The readings scattered considerably in comparison 

with readings of the U.S. Weather Bureau 8-inch gage, but the average of all readings was fairly accurate.

The principal conclusion drawn from the test is that if the receiver 

ring of the gage is thin or has a sharp edge, the rainfall catch is accurate regardless of the size of the gage.

WORKING GRAPH FOR COMPUTING UNMEASURED 

SEDIMENT DISCHARGE

By BBUCE R. COLBY

ABSTRACT

The part of the sediment discharge that is usually not determined at a river 

cross section can be quickly approximated on a nomograph from the mean velocity, the depth of flow, and the concentration of bed material in depth-integrated sediment samples.

LIMITATION OF DEPTH-INTEGRATING SAMPLERS

Depth-integrating samplers such as the U.S. DH-48, U.S. D-43, 

and U.S. D-49 models ([U.S.] Federal Inter-Agency River Basin 

Committee, 1952) are widely used to sample the suspended-sediment 

discharge of streams. However, they have an inherent limitation in 

that their intake nozzles are still a few inches above the streambed 

when the bottom of the sampler touches the bed. Thus, neither the 

bedload (the sediment that moves along very near the bed and is supported mainly by the bed rather than by the turbulence of the flow) 

nor the suspended sediment within a few inches of the bed is usually 

collected in depth-integrated samples. The concentration of the unsampled suspended sediment near the bed is normally greater than 

the concentration of sediment higher in the flow. Hence, sediment 

discharges computed from the samples and from the flow through 

the cross section at the time of sampling are generally less than the 

total discharge of sediment through the section by an appreciable 

amount, which is commonly called unmeasured sediment discharge. 

This unmeasured sediment discharge consists mainly of the material 

that is coarse enough to be significantly more concentrated near the 

bed than higher in the flow. In general, it is composed mainly of 

particles that are coarse enough to be found in appreciable quantities 

in the streambed and hence to be called bed material.

FACTORS AFFECTING THE UNMEASURED SEDIMENT DISCHARGE

Several factors have major effects on the unmeasured sediment discharge per foot of stream width. The bedload discharge depends

Z49
Z50 CONTRIBUTIONS TO THE HYDROLOGY OF THE UNITED STATES

mainly on the velocity of the water near the streambed and on the 

particle sizes of the bed sediment. The concentration of the suspended 

bed material both near the bed and higher in the flow is determined 

by such major factors as the velocity near the bed, particle size of the 

bed sediment, configuration of the bed, turbulence of the flow, and 

water temperature. All the major factors that control the unmeasured sediment discharge can be roughly represented by mean velocity 

and a ratio of bed-material concentration. The mean velocity is a 

measure of both velocity near the bed and turbulence of the flow. 

For a cross section, the ratio of the concentration of bed material in 

the depth-integrated samples to the concentration of bed material from 

a set of partly empirical and partly theoretical curves (fig. 30, auxiliary diagram) is a rough measure of the availability of bed material. 

That is, the concentration of bed material may be higher than the 

standard (the auxiliary diagram of fig. 30) because of fineness of the 

bed material, low water temperature, or abnormally high turbulence 

for the particular combination of velocity and depth. If the concentration is higher than the standard, the bed material seems to be more 

available than usual, and the unmeasured sediment discharge probably is also higher than the standard (the main curve of fig. 30).

COMPUTATION PROCEDURES

The definition of approximately the same curves as those of figure 

30 and the basic general approach to computing unmeasured sediment discharges have previously been explained in detail (Colby, 

1957).

Rough approximations of the unmeasured sediment discharge per 

foot of width of sand-bed streams can be taken directly from the 

main curve of the monograph. However, more accurate unmeasured sediment discharges usually can be determined by using the 

auxiliary diagram to adjust for the sampled concentration of bed material if the sampled concentration and depth of flow are known.

As an example of the use of figure 30, assume a depth of 5.0 feet, 

a mean velocity of 4.5 feet per x second, and a measured concentration 

of bed material of 620 parts per million. Place one leg of a pair 

of dividers on the intersection of the line for a depth of 5.0 feet and 

the vertical line for a mean velocity of 4.5 feet per second. (If the 

depth is between the depth lines, the interpolation is not a straight 

line but can be made so with a little practice.) Place the other leg 

of the dividers vertically below the first leg and on the line that represents 620 parts per million. From the curve of the main graph, 

measure this divider span downward along the line for a mean velocity of 4.5 feet per second. The indicated unmeasured sediment 

discharge per foot of width is 31 tons per day.
1

pUNMEASURED SEDIMENT DISCHARGE, IN TONS PE

5 

RELATIVE CONCENTRATION OF SUSPENDED BED MATERIAL, 

IN PARTS PER MILLION
Z52 CONTRIBUTIONS TO THE HYDROLOGY OF THE UNITED STATES

subtracted according to algebraic sign) by the distance between the 

horizontal lines that are marked 6.7 and 10 tons per day on the main 

graph. The new span is then measured downward from the main 

curve along the vertical line that represents a mean velocity of 4.5 

feet per second. The indicated unmeasured sediment discharge is 

20.5 tons per day for a width of 0.67 foot, or about 2,000 tons per day 

for the width of 67 feet.

REFERENCES

Colby, B. R., 1957, Relationship of unmeasured sediment discharge to mean 

velocity, Am. Geophys. Union Trans., v. 38, p. 708-717.

[U.S.] Federal Inter-Agency River Basin Committee, 1952, The design of improved types of suspended sediment samplers, in A study of methods used 

in measurement and analysis of sediment loads in streams: Minneapolis, 

Minn., St. Anthony Falls Hydraulic Lab. Rept. 6,103 p.
TIPPING-BUCKET RAIN-GAGE ATTACHMENT FOR A 

WATER-STAGE RECORDER

By H. D. BRICE

ABSTRACT

The desirability of registering rainfall directly on a water-stage recorder chart 

prompted the development of a tipping-bucket rain gage that could be operated 

in conjunction with a water-stage recorder. The rain gage can be simply and 

satisfactorily attached to a water-stage recorder housed in a shelter made from 

a 48-inch corrugated metal pipe.

DEVELOPMENT OF THE BAIN-GAGE AND RECORDER 

ATTACHMENTS

To meet a need for synchronized records of rainfall and reservoir 

stage, W. B. Langbein of the U.S. Geological Survey in 1953 devised 

experimental models of attachments for a nonrecording rain gage and 

a Stevens water-stage recorder, so that rainfall and reservoir stage 

could be recorded on the same chart. The rain-gage attachment is a 

tipping-bucket unit, and the water-stage recorder attachment is a 

counting and marking-pen unit. Their use for concurrent recording 

of rainfall and reservoir stage, or of rainfall and river stage, has become widespread in this country.

DESCRIPTION OF THE ATTACHMENTS

The tipping-bucket unit shown in figure 31 was designed for attachment to the collar on the underside of the collector-ring funnel of the 

nonrecording rain gage. If the standard 8-inch rain-gage receiver is 

used, the buckets tip after each 0.1-inch increment of precipitation, but 

the unit can be modified to tip for amounts as low as 0.05 inch. On 

the other hand, the unit will tip after each 0.05 inch of precipitation 

without the unit being modified, if a rain gage receiver 11.3 inches in 

diameter is used. During rainfall of high intensity, if each tip represents only 0.05 inch, the buckets tip so frequently that the recorder 

should be operated at a speed of at least 4.8 inches per day.

The counter and marking-pen unit shown in figure 32 is electrically 

operated and not only visually counts but graphically records the 

number of bucket tips. The counter shows only the accumulated numZ53
Z54 CONTRIBUTIONS TO THE HYDROLOGY OF THE UNITED STATES

FIGURE 31. Tlpping-bucket unit attached to rain-gage collar and 

supported by bracket assembly bolted to wall of recorder 

shelter.

her of tips, whereas the marking pen, which is simultaneously actuated, relates the tips to time and thereby provides a means for correlating rainfall and water stage.

To avoid the effects of excessive wind, rain gages ordinarily are 

placed on or near the ground. However, as most gaging stations are 

on river flood plains, a rain gage placed on the ground nearby must 

be securely anchored to prevent its being washed or floated away and 

the subsequent record for a critical event lost. Other hazards, such 

as damage by livestock or vandals, must be considered also.

In some locations the safest place for the tipp ing-bucket mechanism 

and the necessary wiring is inside the gaging-station shelter. In such 

situations the collector ring must be near enough to the tipping buckets so that not more than a negligible amount of water will adhere
TECHNIQUES, WATER RESOURCES INVESTIGATIONS Z55

FIGURE 32. Counter and marking-pen attachment, showing batteries, counter, and pen. 

Pen records rainfall along margin of chart.

to the inside of the tube that carries the water from the ring to the 

buckets during a period of operation. A roof installation meets this 

requirement adequately, provided the roof is out of the direct influence of any bridges, trees, or other large obstructions.

INSTALLATION OF THE ATTACHMENTS

Because recorder shelters built of 48-inch corrugated metal pipe 

(pipe commonly used for highway culverts) can be readily moved 

from site to site, they are especially well suited for use as gaging stations that are to be operated as secondary or short-term water-management stations. One of these installations is on Dee Creek at Greenwood, Nebr. The discharge records from this station, which represent 

runoff from a rural catchment area, are used in a comparative study 

of runoff from a nearby urban catchment area. To aid in the collection of concurrent records of rainfall and water stage at the gaging 

station on Dee Creek, a rain-gage attachment was installed in 1960. 

(See figs. 33, 34.)

An 8-inch nonrecording rain gage, a type used by the U.S. Weather 

Bureau, was modified for the Dee Creek recorder shelter by removing
Z56 CONTRIBUTIONS TO THE HYDROLOGY OF THE UNITED STATES

FIGURE 33. Rain gage installed in recorder shelter.

the collar from the underside of the collector-ring funnel and soldering a i/^j-inch garden-hose fitting to the bottom of the funnel. This 

assembly was placed in a hole cut in the peak of the roof and was 

bolted to the roof to prevent lifting of the funnel by sudden pressure changes in the shelter.

An 8- by 10-inch shelf bracket was then bolted to the shelter wall 

at the left end of the instrument shelf about 2% inches above the top 

of the receiving can. A piece of wood 10 inches long, 2i/2 inches wide, 

and 1% inches thick was attached to the horizontal arm of this 

bracket with wood screws, and the collar from the collector-ring funnel was fastened to the front face of this piece with a sheet-metal 

band about 2 inches wide.

The collector ring and funnel in the peak of the roof and the collar 

on the wall bracket then were connected by means of a short length
TECHNIQUES, WATER RESOURCES INVESTIGATIONS Z57

FIGTJBE 34. Arrangement of instruments at left end of shelf in recorder

shelter.

of transparent garden hose, and the tipping-bucket attachment was 

fastened to the collar. After the attachment was leveled, it was calibrated with the 8-inch receiving can in place on the instrument shelf. 

Then the counter and marking-pen unit was installed in the Stevens 

recorder, and wiring to the battery and tipping-bucket unit was completed.

SIMPLIFIED METHOD OF ALTIMETER SURVEYING

By ROY NEWCOME, JR.

ABSTRACT

Altimetry is an inexpensive and time-saving substitute for spirit-level surveys 

that do not require extreme accuracy. A one-instrument method, in which readings at successive stations are made within small intervals of time, has been 

observed to provide a general accuracy within 2 or 3 feet.

INTRODUCTION

Altimetry is a useful tool for hydrologists in regions lacking adequate topographic maps. In many investigations it is not expedient, 

financially or timewise, to make spirit-level traverses. Also, the great 

accuracy obtained in spirit leveling commonly is not required.

Several methods of altimeter surveying are in use, but most of them 

require two or more instruments, and tedious calculations and corrections. The purpose of this discussion is to describe a method of altimeter surveying that requires only one instrument and a minimum 

of calculation. Altitudes determined by this method approach in 

accuracy those provided by the more complicated procedures. An 

average error of only 2 to 3 feet and a maximum error of 6 feet were 

noted during use of the method for 5 years in gently rolling to rougji 

country in Tennessee.

METHOD

Following is the procedure found satisfactory by the writer. A calm 

clear day is chosen when possible. Gusty days or days when the sun 

is "in-and-out" and temperature changes are sudden should be avoided. 

Best results are obtained if the work is done between 9 a.m. and 4 p.m., 

as the effects of convection are least during that period of the day.

The altimeter is read at or near the bench mark, care being taken 

to place it in a level position in a shaded place. After allowing time 

for the altimeter to overcome any lag due to recent changes in altitude, 

the instrument is read 3 or 4 times at 3- or 4-minute intervals. During 

this period a thermometer is suspended in an open place out of the 

sun and some distance from the earth or any other 'body likely to 

interfere with the temperature and circulation of the air. A temperaZ59
Z60 CONTRIBUTIONS TO THE HYDROLOGY OF THE UNITED STATES

ture reading is taken and recorded, along with the time of the reading. 

Reliable air-temperature readings can be obtained while driving by 

holding the thermometer outside a window on the shady side of the car.

Not more than 10 minutes should elapse between readings at successive stations. If it is not possible to go from the base bench mark 

to the point for which the altitude is to be determined in 10 minutes, 

readings should be taken at an intermediate point. This has the effect of moving the bench mark nearer the unknown point. As many 

intermediate points as desired may be visited, provided they are revisited on the return leg of the traverse. The traverse may be terminated at a bench mark other than the one from which the traverse 

started. The readings at the termination must be adjusted for the difference in altitude between the two bench marks.

When a traverse is completed, two corrections must be applied to 

the altimeter readings in order to obtain the correct altitude. The first 

correction made is the temperature correction. As most altimeters 

are constructed to yield accurate pressure readings only when exposed 

to an air temperature of 50° F, it is necessary to make corrections 

when the air temperature is above or below 50° F. For this purpose, 

a temperature-correction chart (fig. 35) constructed by Rogers (1947) 

is used.

Vertically, the chart is divided equally into eight sections representing 100 feet each. These are in turn divided into 10 units representing 10 feet each. The altitude of the base bench mark is set 

opposite the middle horizontal line. Subsequent altimeter readings 

are marked on the vertical scale with relation to the first reading. A 

sliding scale may be constructed as an aid in this step.

Horizontally, the chart is divided equally into five sections, each 

representing 10° F. The curved lines on the chart are obtained by 

use of the formula xy=l, xy=%, 'xy=5, and so on. The spaces between the curved lines on each half of the chart are numbered consecutively from 1, away from the middle horizontal line. The lines 

representing an altimeter reading and the temperature of the air at 

the time of that reading intersect at a point on the chart. The number of the section in which the point falls is the number of feet to be 

applied to the altimeter reading to compensate for the difference between the air temperature and 50° F. For temperatures above 50° 

F the corrections are positive on the upper half of the chart and negative on the lower half. If the correction is positive it is added to the 

observed barometric reading; if negative, it is subtracted. For temperatures below 50° F the signs of the chart are reversed. For this 

reason, the temperature headings at the top are 50°, 40°, 30°, 20° F, 

and so on.
TECHNIQUES, WATER RESOURCES INVESTIGATIONS Z61 

60° 70° 80° 90° 100°

50° 60° 70° 80° 90° 100°

FIGURE 35. Chart for temperature correction of altimeter readings. From Rogers (1947).
Z62 CONTRIBUTIONS TO THE HYDROLOGY OF THE UNITED STATES

The chart in figure 35 shows that at a temperature of 50° F there is 

no correction regardless of differences in altitude and that for points 

having the same altitude as the bench mark, there is no correction 

regardless of the temperature.

After applying the temperature correction to the altimeter readings, 

the readings are plotted against time on graph paper in order to determine the barometric correction. Figure 36 is a typical traverse in 

which the altitude for only one well is determined.

CO

10:20 10:30 10:40 

TIME

10:50 11:00

FIGURE 36. Barometric-correction graph for one-well traverse.

In plotting the altitudes, the first reading taken at the bench mark 

is the datum for the other bench-mark readings. Thus it is assumed 

as the line of no correction and may be labeled "0." As subsequent 

bench-mark readings already have had temperature corrections applied to them, the amount that any reading lies above or below the 

"0" line is the barometric correction that must be applied to that reading to make it equal the known bench-mark altitude. The correction 

is negative if the reading is above the "0" line and positive if below it.

In plotting the well readings on the barometric-correction graph it 

is necessary only to locate the points on the proper time lines and in 

the correct relationship to one another, as they are moved arbitrarily 

up or down the time lines in order to fit into the barometric" curve of 

the traverse. It is upon the "fit" of the well-reading curve with the 

barometric curve that the accuracy of the traverse depends. The first 

step is to draw a smooth curve that passes through the bench-mark
TECHNIQUES, WATER RESOURCES INVESTIGATIONS Z63

readings. The slope of the curve between the two sets of bench-mark 

readings indicates the fluctuation of barometric pressure in that interval of time. It is then generally a simple matter to fit the well-reading 

curve into the barometric curve by sliding it up or down the time lines. 

At this point the barometric correction for any time on the traverse 

may be taken from the graph and applied to the altimeter readings 

already corrected for temperature deviation.

Each altimeter user will probably develop his own form of note 

keeping. The one shown as table 1 has proved convenient for this 

writer.

TABLE 1. Notes for graph in figure 86

Bench mark: U.S. Coast and Geodetic Survey, 

2327; altitude, 663.743 feet

February 14, 1952 

Weather clear

Station

BMi.. ..........

BM..............

BM..............

Woll

Well. ... ......

Well... ...... .

Well.. .... . _

BM..............

BM_..__._.__.__.

BM..............

BM..............

Time 

(a.m.)

10:15

10:19

10:23

10:32

10:36

10:40

10:44

10:53

10:57

11:01

11:05

Temperature (°F)

62

62

64

Altimeter 

reading 

(feet)

664

665

665

778

779

782

784

677

678

675

674

Temperature 

correction 

(feet)

0

0

0

-1-3

-1-3

-1-3

-1-3

0

0

0

0

Corrected 

altimeter 

reading - 

(feet)

664

665

665

781

782

785

787

677

678

675

674

Barometric 

correction 

(feet)

-0

-1

-1

-1

 2

-5

-7

-13

-14

-11

-10

Altitude 

(feet)

664

664

664

780

780

780

780

664

664

664

664

Bench mark.

Several altitudes can be determined in a single traverse if the points 

are visited in a sequence that permits for each point the drawing of 

a barometric curve that can be fitted logically into the curves for the 

other wells. This is illustrated in figure 37.

BM

BM

TIME 

FIGURE 37. Barometric curve for multiple-well traverse.
Z64 CONTRIBUTIONS TO THE HYDROLOGY OF THE UNITED STATES

PRECAUTIONS TO BE OBSERVED IN MAKING ALTIMETER SURVEYS

Not all barometric curves plot as smoothly as those shown in figures 36 and 37. It is not unusual to obtain erratic or inconsistent 

curves for one or more of the following reasons: Unfavorable weather 

conditions, sticking of the altimeter needle, local warm or cold air currents, vibrations, and haste by the operator in taking readings.

The following is a list of suggestions, or precautions, that should 

aid in obtaining a reasonable percentage of good altitude determinations.

1. Use an altimeter that is checked frequently for instrument errors; 

use the same instrument for all work, if possible.

2. Run altimeter surveys only during calm weather and not during 

hours when the earth and air are being heated or cooled rapidly.

3. Use care in taking temperature readings; the thermometer should 

be in the shade and where air can circulate freely around it.

4. Allow time for altimeter to settle down after reaching a new station ; be sure needle is free.

5. If readings at a station contradict one another, take a few more to 

define the trend.

6. The less time that elapses between visits to different stations, the

more accurate the survey. 

1. In plotting the barometric curve, discount points that are obviously

erratic and draw a logical curve through the consistent points. 

When starting an altimeter traverse, the instrument can be set to 

read the initial bench-mark altitude, or it can be locked in a permanent position and the difference between the first reading and the 

bench-mark altitude applied to all readings of that traverse. An advantage of the latter method is that it requires one less manipulation 

of the instrument.

SELECTED REFERENCES

Buckmaster, J. L., and Mears, A. H., 1958, Instrumental improvements in altimetry: U.S. Geol. Survey Circ. 405, 33 p.

Demler, L. E., 1950, Altimetry its present-day techniques: Belleville, N.J., Wallace and Tiernan Products, Inc., 10 p.

Hill, B. A., 1929, Preliminary survey procedure: Las Angeles, Calif., American 

Paulin System, Inc.

Lahee, F. H., 1941, Field Geology: 4th ed., New York, McGraw-Hill, 853 p.

Rich, J. L., 1934, Corrections for temperature in barometric surveying: Am. 

Assoc. Petroleum Geologists Bull., v. 18, no. 1, p. 133-138.

Rogers, J. K., 1947, Temperature corrections in altimeter surveying: Am. Assoc. 

Petroleum Geologists Bull., v. 31, no. 2, p. 370-374.

* U.S. GOVERNMENT PRINTING OFFICE : 1964 O 740-132