Grabow references for Hydrologic review2

©Garry Grabow, 2012 BAE 576 FLOW MEASUREMENT
Flow Measurement
Topics: Hydraulics of flow, flow measurement devices, streamgaging, rating curves
After completing this module and homework, you should be able to:
• Understand concept of open channel flow
• Identify appropriate water measurement devices for given situations
• Size water control structures for a given design discharge
• Understand how to current meter a stream (perform stream gaging)
• Construct rating curves
Measurement of flow in watershed monitoring is very important for a variety of reasons.
Flow measurement is critical in order to:
• Estimate loads which are a product of concentration and discharge
• Develop relationships between flow and concentration to use in estimating concentra-
tion when flow measurements exist and concentration data does not
• Trigger automated sampling events that are based on flow -paced or flow -proportional
sampling
• Assess changes in hydrology due to land use changes
Fundamentals of Open Channel Flow
Flow in open channel hydraulics can be categorized in terms of time and space. A flow
that does not change in depth over space (channel distance) is termed uniform flow. In
reality, uniform flow occurs rarely normally confined to well formed geometric channels
such as trapezoidal channels used in irrigation and drainage. Uniform flow requires not
only a uniform cross-section, but an absence of in -channel structures that could affect flow
depth. Flow that varies in depth over space is called varied flow. This type of flow is
further categorized into gradually varied flow and rapidly varied flow. As the names imply,
gradually varied flow varies in depth gradually over space while rapidly varied flow changes
depth suddenly. An example of rapidly varied flow is a hydraulic jump or a hydraulic drop.
Most flow in natural rivers is gradually varied flow. The hydraulic modeling computer
program HEC-RAS models gradually varied flow. Examples of gradually varied flow and
rapidly varied flow are shown in Figure 1.
Steady flow is flow that does not change in depth over time at a particular location,
while unsteady flow does. Examples of unsteady flow are flood waves and hydraulic bores
illustrated in Figure 1. Channel control locations may be defined as those locations with
features that control the depth of flow upstream in a sub -critical flow regime (downstream
control). In supercritical flow, the control or influence is upstream.
The location of flow depth control can vary with flow rate. Figure 2 illustrates this
concept. It is important to know where control point are when siting a flow control structure
or selecting a stream gaging location.
Water Measurement Structures
Flowing water can be measured in terms of energy and momentum. In open channel
hydraulics, much analysis is conducted in terms of energy rather than in terms of momen-
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©Garry Grabow, 2012 BAE 576 FLOW MEASUREMENT
Figure 1. Illustration of gradually varied and rapidly varied flow in a natural stream
Figure 2. Natural channel profile showing channel control locations under high and low flow con-
ditions
turn. Energy relates to the internal state of a volume of water while momentum involves
external forces.
The energy of water can be divided into potential energy (the depth of water or height
above a datum) and kinetic energy due to velocity (velocity head). Total energy in an open
channel is:
2
E=y+2(1)
9
where:
y = depth of flow measured from a datum, ft (m)
v2/2g = velocity head, ft (m)
For any flow and specific energy, there are 2 depths that can exist - one at subcritical
depth (slower flow) and one at supercritical depth (faster flow). The state of flow can be
found by calculation of the Froude number; the ratio of inertial to gravitational forces:
and
Fr = � (2)
2

©Garry Grabow, 2012 BAE 576 FLOW MEASUREMENT
v = average streamflow velocity, ft sec-1 (m sec—')
g = gravitational constant, ft sec-2 (m sec-2)
L = characteristic length, ft (m)
The characteristic length normally used is the hydraulic depth, D, which in a rectangular
section is equal to depth, y, and in a natural stream is equal to the cross-section area of
flow divided by the top width of flow at the water surface.
The depth of flow that produces the minimum energy is called the critical depth, and
that flow can only occur at one depth. The Froude number at critical depth is equal to 1.0.
Near critical depth, flow will look wavy and unstable since with a small change in energy, a
large change in depth occurs. When a number of these plots of flow depth, y, versus energy
(E) are done for different flow rates, a line can be drawn through the minimum energy
points, resulting in a line of the equation:
2
y, = 3 E,
where:
y, = critical depth of flow, ft (m)
(3)
Knowledge of this relationship is used in the derivation of equations used to predict flow
across critical flow devices. These devices force water to pass through critical depth (from
subcritical to critical) thereby producing a unique head -discharge relationship.
Selection of Water Measurement Devices
Selection of an appropriate water measurement device depends on many criteria, among
them:
1. Cost
2. Accuracy
3. Head loss
4. Ability to pass sediment
5. Calibration requirements
6. Installation requirements
7. Operational requirements
Item 3 refers to the fact that all measurement devices require a head loss (reduction
in combination of elevation and velocity [energy]) to measure flow. Sharp crested weirs in
general require more head loss then broad crested weirs or flumes. In fact, weirs normally
require some sort of drop, either produced by the weir bulkhead or natural drop, to function
well over a range of flows. This means that water will have to be backed up more for a weir
than a flume in most cases to pass the same discharge and accurately measure flow rate.
Flumes are able to pass sediment and trash more easily, since they do not have an bulkhead
set perpendicular to flow that can catch objects, and an upstream pool that slows water
and allows sediment to deposit. Weirs that are of standard geometry that are installed
correctly are less likely to require calibration than custom-made devices.
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©Garry Grabow, 2012 BAE 576 FLOW MEASUREMENT
Weirs
Weirs are simply overflow structures placed in open channels perpendicular to flow to
measure flow rate (discharge). They are generally categorized into two categories; broad -
crested and sharp crested. Flumes can be grouped within the broad -crested category,
but are separated for purposes of discussion here.
Another classification of weir types is suppressed or contracted. Suppressed weirs are
those in which the side walls of the channel form the edges of the weir, whereas contracted
weirs have sides that are offset from the channel walls. In natural channels, most weirs and
flume are contracted as an irregular natural channel section is not conducive to suppressed
types. Figure 3 illustrates different types of weirs.
Weirs operate on the principal that there is a unique relationship between upstream
water surface elevation (head) and discharge, i.e. for any given upstream depth, there will
be one and only one discharge. A unique head -discharge relationship does not always hold
true in natural channels since channel resistance may change over time or season, thereby
changing the relationship between depth and flow. Installing a weir alleviates this concern,
as the weir sill (bottom) becomes the constant control feature in the channel.
Figure 3. Various sharp -crested weirs (after USBR (2001))
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©Garry Grabow, 2012 BAE 576 FLOW MEASUREMENT
Broad Crested Weir
Broad Crested Weirs fall into a general category of weirs that do not have a bulkhead -
faceplate configuration such as a sharp crested weir. As with all types of weirs, they generate
a unique head -discharge relationship by forcing flow through critical depth. Using the
relationship shown in Equation 3, and the knowledge that the velocity head at the critical
state of flow is equal to half the hydraulic depth D, or alternately D,=2(v'/2g), an equation
for flow over a broad crested weir can be obtained. For a rectangular section D=y so the
equation above may be written y,=2(v2/2g). Setting the 2 equations equal gives:
_H'(4)2 (V2
2g) 1.5
where:
H is equal to E in Equations 1 and 3. Rearranging Equation 4 yields:
9Ho (5)
vc =
1.5
From continuity, unit discharge (q,)=v, x y, and using Equations 3 and 5 we obtain:
F�3q = vcyc = 2 3 Hc (6)
which upon further reduction yields
q = 3.09H,1.5 (7)
for U.S. customary units (cfs per foot of weir crest) and
q = 1.70H,'.5 (8)
for metric units (cros per m of weir crest) which are the theoretical equations for a broad -
crested weir. To determine total discharge the right hand side of equations 7 and 8 are mul-
tiplied by the crest length L, and the generic form of the weir equation becomes Q=CdLH1.5
where Cd is called the coefficient of discharge. In practice it is very difficult to determine the
location where critical depth develops, so measurement is taken upstream of the weir where
velocity is slow and therefore h,,, , H, where h,,, is the measured water depth above the
weir crest (see Figure 4). The coefficient of discharge takes into account drawdown (flow
contraction) across the weir, velocity head, and flow resistance in a broad crested weir.
Values of Cd are oftentimes derived from laboratory studies and for typical weirs may be
found in manufacturers tables or hydraulic reference manuals. The coefficient of discharge
may be found by back -solving in a calibration procedure in which discharge is measured:
__ Q
Cd 1.70Lhl*5
5
(9)

©Garry Grabow, 2012 BAE 576 FLOW MEASUREMENT
where
L = width of the weir, ft (m)
hti, =the head upstream of the weir as measured from the water surface to the weir crest.
A simple device that functions as a broad -crested weir is shown in Figure 4.
Figure 4. A broad -crested type weir shown in a laboratory setting
Sharp Crested Weir
Knowing that the sum of kinetic energy and potential energy at any 1 point (cross-
section) is a constant, and referring to Equation 1 we know that:
v = 2gH
(10)
Since the discharge (Q) is equal to vA, unit discharge (q), is vH. Integrating Equation
10 from H=H to H=0 (weir crest), and multiplying by the weir crest length, L, and by a
coefficient of discharge (Cd)to allow for flow contraction over the crest and the effects of the
boundary conditions at the weir, gives:
Q = 2CdLH2 2g
0

©Garry Grabow, 2012 BAE 576 FLOW MEASUREMENT
Rehbock found that the coefficient of discharge was related to the ratio of head on the
weir, H to the distance from the channel bottom to the weir crest (see Figure 5):
Cd = 0.062 + 0.083 P (12)
Equation 11 can be reduced to derive a sharp crested weir equation, similarly to the broad
crested weir equation as was done in Equations 7 and 8. For practical Purposes, weir
equations for common weirs including coefficients of discharge are shown in
the following sections.
H
P
Nappe
Figure 5. Sharp crested weir (longitudinal section) showing terms used in Equation 12 and the
overflowing jet called the nappe.
Rectangular Contracted Weir
Rectangular contracted weirs are popular in watershed monitoring of small watersheds
since they are relatively simple in concept and simple to construct. Figure 6 is an illustration
of such a weir. This type of weir is contracted on all sides (two sides and bottom). To be
fully contracted, the sides of the weir plates must be located at least twice the maximum
head from the channel boundaries.
The discharge equation for a rectangular contracted weir shown in Figure 6 is from
Francis (1883):
where
Q = discharge , cfs
H = head on the weir, ft
L=length of weir crest, ft
Q = 3.33H3/1 (L — 0.2H)
Q = 3.33 [(H + h)3/2] (L — 0.2H) 13
7

©Garry Grabow, 2012 BAE 576 FLOW MEASUREMENT
h= approach velocity head, v2/2g
The upper equation may be used when the velocity of approach is negligible (a Froude
number less than 0.5 is generally ok).
bwarr• Gv+t CM)
Figure 6. Rectangular Contracted Weir
If the channel is such that installing a fully contracted weir is not possible, e.g., a
short crest distance from channel bottom and/or small side contraction are used to reduce
head loss (reduce upstream backwater), then the Kindsvarter-Carter method (Kindsvater
& Carter, 1959) that also corrects for velocity of approach should be used:
Q = CeLeHie�2 (14)
where
Ce = effective coefficient of discharge
Le = L+kb, where kb is a correction factor to obtain the effective weir length
Hie= Hl+Kh where Hl is head above weir crest, ft, and Kh is a correction factor (0.003 ft).
The reader is referred to (USBR, 2001) for details on how to derive the coefficients and
factors involved with Equation 14.
The Kindsvater-Carter method may also be applied to fully suppressed weirs. The
Francis formula (U.S. customary units) for a fully suppressed rectangular weir is:
Q = 3.33LH3/2
Cipoletti Weir
(15)
A Cipoletti weir is a contracted weir with side slopes on the weir plate of 1HAV. This
design lessens the side contraction and thus lessens the reduction of cross -sectional flow area

©Garry Grabow, 2012
BAE 576 FLOW MEASUREMENT
found in contracted weirs with vertical sides. Most Cipoletti weirs are found in irrigation
system applications. The formula for a Cipoletti weir is (U.S.Customary units):
Q = 3.367LH3/2 (16)
An illustration of a Cipoletti weir is shown in 7.
V-Notch Weirs
!� elope rr
Pont to M"Kn depth (H)
a rrr �
fir, `•F��fy� �j-�i�fi �rf�rl�/ fiy' ,
Figure 7. Cipoletti Weir. Note 1H:4V slope on weir plate.
V-Notch weirs are suited for small flows being more accurate than rectangular weirs
in the low flow range. Although the standard v-notch weir is 90°, any angle can be used.
The degree stipulated is the angle formed by the notch in the weir plate/bulkhead. The
drawback of a v-notch weir is the head required to pass higher discharges, therefore requiring
impractical weir plate/bulkhead heights. The discharge equation for a 90' v-notch weir
(illustrated in Figure 8 is:
Q = 2.49H2.48 (17)
The formula for v-notch weirs of any angle is:
Q = 0.43,,,fg-tan 12 I H5/2 (18)
where
0 = notch angle, degrees
g = gravitational constant in U.S. customary units, (32 ft sec-2)
9

©Garry Grabow, 2012 BAE 576 FLOW MEASUREMENT
Figure 9 shows the head required to pass a given flow for a 90' v-notch weir and a 2-foot
fully contracted rectangular weir.
Figure 8. V-notch Weir (90 degree notch).
Compound Weirs
Compound weirs refer to types of measuring structures that have two or more types of
weir geometry. Probably the most common combination is a v-notch weir that graduates
to a rectangular weir. This allows for accurate low flow measurement, but allows higher
discharges to pass without an inordinate rise in head (and backwater). Another type of
compound weir is shown in Figure 10. A plot of head -discharge for a v-notch weir of 2 ft
height transitioning to a rectangular weir with a 5 ft crest length is shown in Figure 11.
Note the change in relationship at a head of 2 ft, the elevation at which the transition from
v-notch to v-notch with rectangular weir occurs.
Flumes
In general, a flume is an open channel flow section that accelerates flow. Normally
the intention is to accelerate the flow through a converging section so that the flow passes
through critical depth. In this case, only one measuring point is required. Some flumes can
also provide accurate flow measurements under less than ideal conditions (very low flow or
when downstream water level causes submergence) when flow does not pass through critical
depth. Some typically used flumes are discussed in the following sections. Broad -crested
weirs are also classified as long -throated flumes. Flumes require side walls of a constant
and known geometry, so have been used extensively in irrigation canals that may be lined
or easily fitted with headwalls. Flumes are less adaptable to natural streams, and if used
in such an application require that headwalls be constructed to force all flow through the
flume section.
10

©Garry Grabow, 2012 BAE 576 FLOW MEASUREMENT
4
4M
u'7
[ti
Q
N
� W'7
-0e r
O
LE
C
O
C
0 10 20 30
Discharge, cfs
Figure 9. Head discharge relationships for 90 v-notch weir and rectangular contracted weir with
crest length of 2 feet.
Parshall Flumes
Parshall flumes are able to measure accurately with relatively low head loss, and can be
measured under considerable submergence. The narrowest section of any flume is referred
to as the throat. The discharge equations for Parshall flumes are:
Q = Q =
4W Ha •522Wo. o2s
(19)
Q = (3.6875W + 2.5) H1
where
Q = discharge, cfs
W= flume throat width, ft
Ha=upstream head measured from flume floor (see Figure 12
The upper equation is for throat widths (W) of 1 to 8 feet, and the bottom equation is
for throat widths of 10-50 feet. Ha is the measurement location in the upstream section of
the flume shown as the upstream staff gage in Figure 12. The downstream measurement
point, Hb is used in conjunction with Ha under conditions of submergence that occur when
the ratio of Hb/Ha is 0.70 for flumes of throat width 1-4 feet and 0.80 for flumes of throat
width 10-50 feet. Table can be consulted to correct flow estimates for submerged conditions.
Parshall flumes have many sloping angles, so are not easily constructed. Usually smaller
flumes (Parshall and others) are made of prefabricated fiberglass or plastic and may be
purchased from vendors.
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©Garry Grabow, 2012 BAE 576 FLOW MEASUREMENT
Figure 10. Compound partially contracted rectangular weir
Other Flumes
Other flumes used in water measurement include Cutthroat flumes, H-flumes, and
Palmer -Bowles flumes. A cutthroat flume has a converging and diverging section like a
Parshall flume, but has a flat bottom so is easier to construct. H-flumes have a trapezoidal
section with converging side walls. H-flumes have been used on small watersheds and pass
sediment easily, however, they are limited to lower flow rates and require more head loss
than other flumes. Palmer -Bowles flumes have traditionally been used in municipal wastew-
ater applications since they are designed to be positioned inside a pipe flowing partially full.
If a steam has a culvert, it may be adapted to that application.
Siting Water Measurement Structures
For sharp -crested weirs, the following general rules should be observed during installing
and operation:
• Maximum downstream water surface elevation should be at least 0.2 feet below the
weir crest
• Head measurements below 0.2 feet should be treated with caution unless it can be
verified that the overpour is not clinging to the weir crest
• Head measurement should be taken a minimum of 4 times the distance of the maxi-
mum head (maximum distance from water surface to weir crest) on the weir
• Weir plates should be between 0.03 and 0.08 inches. This may be achieved by cham-
fering stock to the prescribed thickness.
• The distance from the bottom of the approach channel (weir pool) to the crest should
be at least twice the head on the weir and in most cases not less than 1 foot.
For all water measurement structures:
12

©Garry Grabow, 2012 BAE 576 FLOW MEASUREMENT
.V
C
C,
0 1 2 a
H" fi.
Figure 11. Head discharge relationship for a compound v-notch, rectangular weir.
• The site should have a stable channel bottom. This avoids undercutting of a structure
placed within the channel
• If possible, the Fronde number should not be above 0.5 for a distance of 30 times the
head measurement at maximum flow
Submergence
Submergence is a condition in which the downstream water level, also known as tail -
water, is too high relative to the upstream water level for the weir or flume to measure as
intended. In this case, head loss is not sufficient, and the stage -discharge relationship of the
measuring device is changed. For some types of flumes, notably flumes with downstream
stage, i.e., hb measuring capability, correction may be made knowing the relationship of
hb/ha,. Tables specific to a particular type of flume and submergence ratio (hb/hp,) are
available to make adjustments to flows.
It is important to locate weirs and flumes such that submergence does not occur. This
is normally achieved by placing weirs just upstream of drops or by raising the crest of the
weir by either building up its foundation (in the case of a flume) or otherwise making sure
the weir crest elevation is high enough. Raising the weir or flume higher than necessary
means that the upstream water surface is raised (backed up) higher than necessary. This
may retard passage up sediment and otherwise unduly change natural flow regimes.
13

©Garry Grabow, 2012 BAE 576 FLOW MEASUREMENT
M mm*-
Umm_ = NO =80. il
-VS f
C �r
/{aft ogwo
flM
lm wtar
Figure 12. Plan, Profile and Isometric view of Parshall Flume. The profile view shows free -flow
and submerged conditions
Velocity of Approach
Velocity of approach refers to the velocity, and consequently the velocity head, in the
section of stream upstream of a flume or weir. If the velocity of approach is too high,
the discharge rating will be inaccurate as elevation head (measurable head) is converted to
velocity head. The velocity of approach is determined by the channel conditions upstream
of the measuring device. For weirs, velocity of approach can be limited by an adequate
upstream pool that creates a larger cross-section and slows the water.
Stream Gaging
Stream gaging is used when flow measurement using an in -channel structure is imprac-
tical or cost prohibitive. The general concept is based upon the fact that the product of
velocity and cross -sectional flow area is equal to the discharge of that area. A current meter
is used to measure velocity at points along a stream section, and the flow for each sub -section
14

©Garry Grabow, 2012 BAE 576 FLOW MEASUREMENT
represented by each measurement point is added up to obtain the total stream discharge.
Velocity measurement may be made with meters that have cups that spin in proportion to
the flow velocity (like an anemometer cup), or more recently available transducers such as
Doppler meters.
Control Section
Often times erosion, deposition, or changing vegetation in a channel change the stage -
discharge relationship of a stream. In order to provide a constant stage -discharge relation-
ship, control sections are sometimes built at the location to be gaged, or just downstream
of the gaging station.
The easiest way to provide for a constant stage -discharge relationship in a natural stream
is to locate the gage upstream of a section not subject to erosion and deposition. Artificial
controls are sometimes built and resemble low weirs. Their function is to control the flow
over at least the low- to mid -range discharges and provide a unique stage -discharge rela-
tionship. It is often times impractical to build such a control for higher stages. The controls
are not meant to estimate flow like a weir, but simply to provide a control for the upstream
water surface.
Sometimes control sections are built to simplify a rating curve development and provide
a stable section. Such an example is shown in Figure 13.
Figure 13. Rated control section in a forested watershed, central coast of California
15

©Garry Grabow, 2012 BAE 576 FLOW MEASUREMENT
Stream Gaging Hardware
The most common way of stream gaging is to use a current meter. A Price Type
AA current meter is shown in Figure 14. These are used extensively by the United States
Geological Survey (USGS) in their stream gaging programs. Another commonly used meter
is a pygmy meter, which, as the name implies is smaller the the standard meter. It is suitable
for use in shallow depths.
Current meters are attached to wading rods for use directly in the stream, or may
be attached to cables suspended by reels on a bridge or other structure crossing a stream.
Cableways, that are cables stretched across a stream suspending a self-propelled seat (called
a cable car) are used by the USGS in rivers that are too deep and/or swift to use a wading
rod, and where a bridge does not exist. Weights are normally required when a meter is
attached to a cable to stabilize the meter and prevent it from deviating too far from a
vertical angle. Reels are anchored permanently on a bridge, supported by a crane assembly
with a movable base, or suspended with a bridge -board that may be re -positioned at each
measuring point along the cross-section. A bridge board is simply a plank with a sheave
that the cable passes through at one end, and the reel is placed at the other end. A bridge
board is normally extended and balanced over a bridge railing.
Figure 14. Price Type AA current meter with a top -set wading rod with USGS technician
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©Garry Grabow, 2012 BAE 576 FLOW MEASUREMENT
Calculation of Discharge
The Rantz method is normally used to calculate discharge using data obtained by a
current (velocity) meter. The equation for the discharge through any subsection x is:
qx = vx I bx — 2 bx-1 + bx+1 I
2 — bx dx (20)
Conceptually this is a mid -point integration method as illustrated in Figure 15. Total
discharge of the station is simply the summation of partial discharges:
n
Q = E qx
x=1
(21)
Velocity used in Equation 21 is the average of measurements taken at two depths, or
at one depth if the depth of flow is too shallow for the current meter. In the two -point
method velocities are taken at 0.2 and 0.8 of the depth below the surface. For shallow
depths a single reading at 0.6 of the depth below the surface is used (0.4 of the depth from
the bottom).
Top set wading rods can both measure the depth of flow, and help set the current meter
at desired fractions of the depth of flow through markings on the rod.
1, v' [az"
I
Figure 15. Rantz method applied at cross-section stations 1 and 4
Measurement of Stage
Whether a flow measurement device such as a weir of flume is used to measure flow, or
a current meter is used to estimate flow, depth of flow or stage will need to be measured.
Stage measurement is necessary to convert stage to head for a critical flow device or to
17

©Garry Grabow, 2012 BAE 576 References
estimate flow from a rating curve developed during a stream gaging campaign. Devices to
record stage range from manually read staff gages to various transducer -type methods that
measure stage indirectly.
The simplest and most direct method of measuring stage is by a manually read staff
gage. Such a gage is shown in Figure 12 and Figure 13. If used in conjunction with a weir
or flume, the elevation of the crest of the weir or flume must be tied into the staff gage so
that head (H in the appropriate equation) can be determined from the staff gage.
Some flumes and many gaging stations use stilling wells in which staff gages or other
water level recording devices are housed. Stilling wells help damp any waves in the water
surface. Float devices are well adapted to stilling wells, and when connected to a pully with
a counterweight can be used with a drum recorder (a pen records stage on a chart) or a
shaft encoder that provides an analog voltage or current that is logged in a datalogger and
converted to stage. Other indirect methods of measuring stage commonly used are pressure
transducers and bubbler systems.
Pressure transducers have a diaphragm that senses water pressure on one side through
strain. They are normally vented to the atmosphere to cancel out the atmospheric pressure,
thereby measuring only the piezometric (elevation and pressure head) of the water.
Rating Curves
Rating curves are primarily developed for use in streams that have been gaged, but may
also be developed and used for weirs and flumes that are calibrated. Several measurements
of discharge and the corresponding stage are required to develop a rating curve. The most
common form of a rating equation is of a power form as presented in Kennedy (1984) and
is illustrated in Figure 16. In the figure, e is called the zero stage offset or the stage below
which no flow occurs.
Summary
Measurement of flow may be one of the most difficult aspects of watershed monitoring,
yet arguably it may be one of the most important. Foresight and planning should take place
before selecting flow and stage measurement devices and site selection.
References
Rancis, J. (1883). Lowell hydraulics experiments (fourth ed.). New York: D. Van Nostrand.
Kennedy, J. (1984). Discharge ratings at gaging stations [Computer software manual].
Kindsvater, C., & Carter, R. (1959). Discharge characteristics of rectangular thin -plate weirs.
Transactions of the American Society of Civil Engineers, 124.
USBR. (2001). Water measurement manual (third ed.) [Computer software manual].
This document is written in LATE and converted to pdf
In

©Garry Grabow, 2012 BAE 576 References
Figure 16. Illustration of rating curve fit to measured data.
19

�-✓
I
i,mUSGS
science for a changing world
Techniques of Water -Resources Investigations
of the United States Geological Survey
•
Chapter A6
GENERAL PROCEDURE
FOR GAGING STREAMS
By R. W. Carter and Jacob Davidian
Book 3
APPLICATIONS OF HYDRAULICS
0

DEPARTMENT OF THE INTERIOR
❑ONALD PAUL HODEL, Secretary
U.S. GEOLOGICAL SURVEY
Dallas L. Peck., Director
First printing 1968
Second printing 1969
Third printing 1977
Fourth printing 1989
UNITED STATES GOVERNMENT PRINTING OFFICE : 1968
For sale by the
Books and Open. -File Reports Section
U.S. Geological Survey
Federal Center, Box 25425
Denver, CO 80225
•
•
0

•
PREFACE
The series of manuals on techniques describes procedures for planning
and executing specialized work in water -resources investigations. The
material is grouped under major subject headings called books and further
subdivided into sections and chapters; section A of book 3 is on surface -
water techniques.
The unit of publication, the chapter, is limited to a narrow field of
subject matter. This format permits flexibility in revision and publication
as the need arises.
Provisional drafts of chapters are distributed to field offices of the
U.S. Geological Survey for their use. These drafts are subject to revision
because of experience in use or because of advancement in knowledge,
techniques, or equipment. After the technique described in a chapter is
sufficiently developed, the chapter is published and is sold by the U.S.
Geological Survey Books and Open -File Reports Section, Federal Center, Box
25425, Denver, CO 80225 (authorized agent of Superintendent of Documents,
Government Printing Office). III
0

TECHNIQUES OF WATER -RESOURCES INVESTIGATIONS OF THE
UNITED STATES GEOLOGICAL SURVEY •
The U.S. Geological Survey publishes a series of manuals describing procedures for planning and conducting
specialized work in water -resources investigations. The manuals published to date are listed below and may be ordered
by mail from the U.S. Geological Survey, Books and Open -File Reports, Federal Center, Box 25425, Denver, Colorado
80225 (an authorized agent of the Superintendent of Documents, Government Printing Office).
Prepayment is required. Remittance should be sent by check or money order payable to U.S. Geological Survey.
Prices are not included in the listing below as they are subject to change. Current prices can be obtained by writing
to the USGS, Books and Open File Reports. Prices include cost of domestic surface transportation. For transmittal
outside the U.S.A. (except to Canada and Mexico) a surcharge of 25 percent of the net bill should be included to cover
surface transportation. When ordering any of these publications, please give the title, book number, chapter number,
and "U.S. Geological Survey Techniques of Water -Resources Investigations."
TWI I -DI. Water temperature -influential factors, field measurement, and data presentation, by HA1. Stevens, Jr., 3.F. Ficke, and G.F. Smoot.
1975. 65 pages.
TWI 1-132. Guidelines for colli.ction and field analysis of ground -water samples for se tee led unstable constituents, by W.W. Wood. 1976. 24
pages.
TWI 2-D1. Application of surface geophysics to ground water investigations, by A.A.R. 7ohdy, G.P. Eaton, and D.R. Mabey. 1974. 116 pages.
TWI 2-D2. Application of se is n ic -re frac t i on techniques to hydrologic studies, by F.P. Haeni. 1988. 86 p.
TWI 2-El. Application of borehole geophysics to water- resources investigations, by W.S. Keys and L.M. MaeCary. 1971. 126 pages.
TWI 3-Al. General field and c0ice procedures for indirect discharge measurement, by M.A. Benson and Tate Dalrymple. 1967. 30 pages.
TWI 3-A2. Measurement of peak discharge by the slope -area method, by Tate Dalrymple and M.A. Henson. 1967. 12 pages.
TWI 3-A3. Measurement of peak discharge at culverts by indirect methods, by G.L. Bodhaine. 1968. 60 pages.
TWI 3-A4. Measurement of peak discharge at width contractions by indirect methods, by H.F. Matthai. 1967. 44 pages.
TWI 3-A5. Measurement of pi;ak discharge at dams by indirect methods, by Marry Hulsing. 1967. 29 pages.
TWI 3-A6. General procedure for gaging streams, by R.W. Carter and Jacob Davidian. 1968. 13 pages.
TWI 3-A7. Stage measurements at gaging stations, by T.J. Buchanan and W.P. Somers. 1968. 28 pages.
TWI 3 A8. Discharge measurements at gaging stations, by T.J. Buchanan and W.P. Somers. 1969. 65 pages.
TWI 3-A9. Measurement of time of travel and dispersion in strea3ns by dye tracing, by E.F. Hubbard, F.A. Kilpatrick, L.A. Martens, and
J.P. Wilson, Jr. 1982. 44 pages.
TWI 3-A10. Discharge ratings at gaging stations, by E.J. Kennedy. 1984. 39 pages.
TWI 3-All. Measurement of discharge by moving -boat method, by G.F. Smoot and C.C. Novak. 1969. 22 pages.
TWI 3-Al2. Fluorometric procedures for dye tracing, Revised, by James F. Wilson, Jr., Ernest D. Cobb, and Frederick A. Kilpatrick. 1986. 41
pages.
TWI 3-A13. Computation of continuous records of stream flow, by Edward J. Kennedy. 1983. 53 pages.
TWI 3-A14. Use of Humes in measuring discharge, by F.A. Kilpatrick, and V.R. Schneider. 1983. 46 pages.
TWI 3-A15. Computation of water -surface profiles in open channels, by Jacob Davidian. 1984. 48 pages.
TWI 3-A16. Measurement of discharge using tracers, by F.A. Kilpatrick and E.D. Cobb. 1985. 52 pages.
TWI 3-A17. Acoustic vetoe ity ricter systems, by Antonius Lac nen. 1985. 38 pages.
TWI 3-Bl. Aquifer -test design, observation, and data analysis, by R.W. Stallman. 1971. 26 pages.
iWI 3-B2.= Introduction to ground -water hydraulics, a programmed text for self -instruction, by G.t7. Bennett, 1976. 172 pages.
TWI 3-B3_ Type curves for selected problems of flow to we [is in confined aquifers, by J.E. Reed. 1980. 106 pages_
TWI 3-B5. Definition of boundary and initial conditions in the analysis of saturated ground -water flow systems -an introduction, by 0. Lehn
Franke, Thomas E. Reilly, and Gordon D. Berndt. 1997. 15 pages.
TWI 3-B6. The principle of superposition and its application in ground -water hydraulics, by Thomas E. Reilly, O. Lchn Franke, and Gordon
D. Bennett. 1987. 28 pages.
TWI 3-Cl. Fluvial sediment concepts, by HY, Guy. 1970, 55 pages.
TWI 3-C2. Field methods of measurement of fluvial sediment, by H.P. Guy and V.W. Norman. 1974. 59 pages.
TWI 3-C3. Computation of fluvial -sediment discharge, by George Porterfield. 1972. 66 pages.
TWI 4-AL Some statistical tcois in hydrology, by H.C. Riggs. 1969. 39 pages.
TWI 4-A2. Frequency curves, by H- C. Riggs, 1968, 15 pages.
TWI 4-B1. Low -How investipitions, by H.C. Riggs. 1972. 18 pages.
TWI 4-B2. Storage analyses for water supply, by H.C. Riggs and C.H. Iiardison- 1973. 20 pages.
TWI 4-B3. Regional analyses of streamflow characteristics, by H.C. Riggs. 1973. 15 pages.
TWI 4-D1. Computation of rate and volume of stream depletion by wells, by C.T. Jenkins. 1970. 17 pages.
TWI 5-A1. Methods for determination of inorganic substances in water and fluvial sediments, by M.W. Skougstad and others, editors. 1979. 626
pages.
'Spanish translation also available.
tv

TWI 5-A2. Determination of minor elements in water by emission spectroscopy, by P.R. Barnett and E.C. Mallory, h. 197L 31 pages.
'1'WI 5-A3. Methods for the determination of organic substances in water and fluvial sediments, edited by A.L. Wershaw, M.J. Fishman, R.R.
Grabbe, and L.E. Lowe. 1987. 80 pages. This manual is a revision of "Methods for Analysis of Organic Substances in Water"
by Donald F. Goerlitz and Eugene Brown, Book 5, Chapter A3, published in 1972.
TWI 5-A4. Methods for collection and anaIysis of aquatic biological and microbiological samples, edited by P.E. Greeson, T.A. Cltlke, G.A.
Irwin, D.W. Liuu1, and K-V. Slack. 1977. 332 pages.
TWI 5-A5. Methods for determination of radioactive substances in water and fluvial sediments, by I—L. Thatcher, V.J. Janzer, and K.W.
Edwards. 1977. 95 pages.
TWI 5-A6. Quality assurance practices for the chemical and biological analyses of water and fluvial sediments, by L.C. Friedman and D.E.
Erdman n. 1932. 181 pages.
TWI 5-CL Laboratory theory and methods for sediment analysis, by H.P. Guy. 1969. 58 pages.
TWI 6-Al. A modular three-dimensional [mite-diHercnce ground -water Flow model, by MichateI G. McDonald and Arlen W. Harbaugh. 1988.
586 pages.
TWI 7-CL Finite difference model for aquifer simulation in two dimensions with results of numerical experiments, by P.C. Trescott, G.F.
Pinder, and S.P. Larson. 1976. 116 pages.
TWI 7-C2. Computer model of two-dimensiona] solute transport and dispersion in around water, by L.F. Konikow and J.D. Dredehoeft. 1978.
90 pages.
TWI 7-C3. A model For simulation of flow in sing Iar and interconnected channels, by R.W. Schaffranek, R.A. Dal tzer, and D.E. Goldberg.
1981. 110 pages.
TWI 8-A1. Methods of measuring water levels in deep wells, by M.S. Garber and F.C. Koopman. 1968. 23 pages.
TWI 8-A2. Installation and service manual for U.S, Geological Survey monometers, by J.D. Craig. 1983. 57 pages.
TWI 8.132. Calibration and maintenance of vertical -axis type current meters, by G.F. Smoot and C.E. Novak. 1968. 35 pages.
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CONTENTS
page
Preface------------------------------------
III
Discharge measurements —Continued
Abstract_ ---------------------
1
indirect discharge measurements--_----_-_
Introduction-------------------------------
I
Dilution method --------------
General objective4md procedures ------
I
Discharge ratings ---------------------------
Selection of gaging site -----------------------
2
Stage -discharge relations-------------
Artificial eonirols------------------------
3
Complex discharge ratings ---------------
- -
Measurement of stage------.-----------------
5
Computation and preparation of discharge
records
Methodsofsensingstage-----------------
o
-----_----------------------------
Station analysis ------------------------
Water-stage recorders _ - - - - - - - - - - -
6
Manual eomputations- - - - - - -------------
Reference gages ----------------
6
Automatic computations ----------------
Discharge measurements- - - - - . - - - - - - - - - - - - - - -
€i
Publication of records - - - - - - - - - - - - - - - - - - - - - - -
Current -meter measurements-------------
7
References ---------------------------------
FIGURES
1-10. Photographs: page
I. Gage and natural control, Little Spokane River at Elk, Wash _ - - _ -- _ 2
2. Gage, concrete control, outside gage on bridge, and an engineer making
a wading measurement, Kaskaskia. River at Bondviile, Ill--------- 4
3. Concrete artificial control on Mill Creek near Coshocton, Ohio ------ 5
4. Artificial control on Delaware River near Red Bluff, N. Mex., with
shallow V-notch in the broad -crested weir----------------------- 5
5. Bubble -gage digital -recorder arrangement. Gas tank on right-, digital -
punch recorder on left---------------------------------------- 6
G. Measuring discharge. with current meter by wading -- - -- - 8
7. Measuring discharge with current ineter from bridge over the. Hudson
River V Poughkeepsie, N.Y----------------------------..------ 9
S. VADA (velocity-aziiilutli-depth-assembly) equipment in use for meas-
urement from bridge ------------------------------------------ 9
D. Pressurized constant -rate injection tanks for injection of dye into
strnazns----------------------------------------------------- 10
10, Equipment for ftuorometer testing of water samples in the Field--- - - - 11
V11
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GENERA! PROCEDURE FOR GAGING STREAMS
By R. W. Carter and Jacob Dravidian
Abstract
This chapter briefly describes the objectives and pro-
cedures used in obtaining streamflow records. It is
considered are introduction to other chapters on sur-
face -water techniQues which treat individual proce-
dures in greater detail.
Introduction
Measurement of the flow of streams was be-
gun by the U.S. Geological Survey in 1888 as
part of special studies relating to the irrigation
of public lands. Since that time systematic
records of strearnflo►r have been obtained at
more than 16,000 places in the United States by
the Geological Survey. In 1967 the stream -
gaging network comprised about, 91000 continu-
ous -record. stations. In addition, there were
,t:bout 7,200 partial -record stations where data
on only fioodflow or low flow were obtained.
Stream gaging is the largest operation among
the various hydrologic networks. St rearnfio►w is
The only part of the hydrologic cycle in which
moisture is so confined as to permit reasona-
bly accurate measurements of t lie volumes in-
volved. All other measurements in the hydro-
logic cycle are at best only inadequate samples
of the whole.
Wafter in streatnis serves man in many ways;
it, provides water supply for man and aiiimaLls,
irrigation water for plants, dilution and trans-
port for removal of waste, energy for produc-
tion of power, channels for water transport,
and a. medium of recreation. Records of strearn-
flow are important in each of these uses.
Wa-ter 111 stt'eaerns caii also he a hazard. Floods
ca►u5e extensive (Innrige and harrrlship. Records
of flood events obtained act• gagin"r a-tattions serve
rl5 tl3e la,i5i7 for rile desigu of highway bridges
and ca31►erts, danis,:tiiFl flood -control reservoirs
and for flood -plain delineation and flood-
►eaLrning systems.
The network of stream -gaging stations is de-
signed to nieet, the various needs for informa-
tion on strew. rnflo►v. Many stations are operated
to provide current information for use in the
day-by-day management of water supplies or
for use in forecasting flood events. Most of the
stations, however, are operated as it part of the
hydrologic network. Records for these stations
reflect the natural hydrologic characteristics of
the basins and can thus be used as samples of the
variations of streamflow in time and space.
The design of streamflow networks is gov-
erned to some extent by the ability to nneasure
stage and discharge at aL givers site to the re-
quired degree of accuracy. The continued de-
velopment of new instrumentation and analyti-
cal techniques has improved the capability of
obtaining streamflow records under difficult
conditions.
This chapter describes in general terns the
techniques used in obtaining continuous stream -
flow records---froin,selection of site to publica-
tion of records. It is considered an introduction
to four other chapters in book 3, section A,
surface -water techniques, which describe in de-
ta.il t.lw instruments and techniques used in
making specific measurements. This series of
chapters im y be considered an updating of
Water -Supply Paper 888, "Stream Gaging
Procedure."
General 06jective and Procedures
The objective in operating a, gaging station
is to obtain a continuous record of stage and
discharge wit the site. The exact location of the
station is chosen to take advantage of the best

2 TECHNIQUES OF WATER -RESOURCES INVESTIGATIONS
available condition for stage and discharge
measurements and for developing discharge
ratings.
A continuous record of stare is obtained by
installing instruments that sense and record the
tvat.er-surface elevation in the stream_ Dis-
eifaarge ineasuremen`s care initially made at vari-
miu , stag-P-S to define. the relation between stage
<alul discharge. Discharge measurements are
their 111ade at. periodic intervals, t)su ally
monthly, to verify the stage -discharge relation
or to define any change in the relation owing
to chaaages in elaaaaaaasl geometry.
At many Sites the discharge i5 aaot as unique
function of stage; variables other than stage
,also must be continuously measured to obtain
:idischaar-e record. For example, stream slope
is pleasured by the installation of an auxilia-ry
stage gage downstream if variable backwater
occurs. At other sites as contit)tta11s aneasaire of
stream velocity at a point. in the cross section
is obtained and used as an additional variable
in the discharge rat-iug. The rate of change of
stage can be an important. variable at sites hav-
ing considerable tuisteadiness of flow.
.Tloty weirs and drap)s are constructed at some
stations to stabilize the stage -discharge rela-
tions 1n the, lots• -flow ran(re. These control struc-
1 ures are calibrated by stage and discharge
73)ensurem ents ill the field.
The data. obtained at the raging station .are
1*4?V letl ed 1and an alv-red by eltgineeriilg persoi)iiel
at the eaael of the tv:atet yeaar. Discirarre ratings
,area established, :and the gage -height record is
reduced to mean values for selected time peri-
ods. The mean discharge for each day :and ex-
tremes of discharge. -for the year are computed.
The data are then prepared for publication.
Selection of Gaging Site
The selection of gaging sites is dictated by
the needs of ,rater )nana.gement or by the re-
quireineuts of the hydrologic network. In ful-
tilling needs there i-, lit'tle
or no freedom of choice in selecting gaging
sites, and frequently records Imast be obtained
)order very aadverso hydraulic co3aditfons. For
example, Inany of t:be principal streanns in the
(;nited States have been converted into a series
of fools by tlae Construction of dawns; yet, very
precise records are needed for operation. Rec-
ords are also needed in tidal reaches of stream
channels in connection with water supply, salin-
ity contamination, or Waste disposal.
Hydrologic network requirements allow more
choice in selecting good sites for gaging, al-
though in some places gaging conditions are
poor throughout an. entire region. For example,
all strew in a given region ana,y have -unstable
beds and banks, which result in continually
changing stage -discharge relations. However,
before ra streaYnl-gaging station is constructed,
:a geaaeral reconnaissance is made in order that
the most suitable site for the gage may be se-
lected. This reconnaissance is facilitated by an
exam nation of geologic, topographic, and other
maps of the arena. Tentative sites for gaging sta-
tions nlay be indicated on the maps, each site
being subject to critical examination Of the phy-
sical characteristics of the stream channel. In
selecting <a, site consideration should be given to
the following items:
1. Cllaannel ehaaraaateristics relative to as fixed
rmd permanent relation between stage and
dischalrge at the gage. A rock riffle or falls,
as shown in figure 1, indicates an ideal site.
If aa, site on as stream with a movable bed
must be accepted -for example, a, sand -
channel stream -it is best to locate the
gage in as uniform :a. reach as possible,
:away from obstructions in the channel
with as bridges.
?. Opportaznity to install an artificial control.
i. Possibility of baackwat.ez• from downstream
tributaries or other sources. If a site
Figure 1. Gage and natural eonfrol, Little Spokane River
at Elk, Wash.
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GENERAL PROCEDURE FOR GAGING STREAMS
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where backwater occurs must be accepted,
a uniform reach for measurement of slope
should be sought, in addition to the proper
placement of an Auxiliary gage. Un-
steady flow such as occurs in tide -affected
stream channels requires similar considera-
tion but, in addition, line power must be
available to insure simultaneous record-
ing of stage at the two gages.
4. Availability of a nearby cross section where
good discharge measurements can be made.
5. Proper placement of it stage gage with re-
spect to the measuring sect -ion and to that
part. of the channel which controls the
stage -discharge relation.
6. Suitability of existing structures for use
in making high -flow discharge measure-
ments, or the proper placement- of a cable-
way for this purpose.
7. Possibility of flow bypassing the site in
ground water or in flood channels.
8. Availability of line power or telephone lines
where needed, for special instrumentation
or for Telemark units.
9. Accessibility of the site by roads, particu-
larly during flood periods.
The gage an Kaskaskia River at Bondville,
III., shown in figure 2, satisfies several of the
above requirements. Low -flow measurements
are made by wading upstrmam from the artifi-
cial control, and high -flow measurements are
made from the bridge. The bridge site provides
accessibility, convenience to power lines, and
a, good location for an outside gage, shown. on
the downstream handrail.
Artificial Controls
Artificial controls are structures built in a
stream channel to stabilize the stage -discharge
relation and thereby simplify the: procedure of
obtaining accurate records of discharge. They
may be low damns, broad -crested ►veirs con-
forming to the general shape and freight of the
strearnhed, or flumes similar in design to the
Parshall flume. The adverse effects of unstable
conditions due to shifting bed or banks, the
formation of ice in ►vinter, progressive growth
of aquatic vegetation clna•ing tl►e summer, and
other phenomena. which at times affect the
stage -discharge relation at low stages may gen-
erally be eliminated or alleviated by the con-
struction of an artificial control. The structure
is seldom designed to function as a complete
control throughout the entire range of stage.
Generally it is impracticable to build it high
enough to eliminate the effects of downstream
conditions at high stages unless there is a steep
fall below the gage. If the downstream slope is
flat, so that with an increase in discharge the
water below the control rises faster than the
water above it, the control may be completely
effective only for low and medium stages. Fig-
ure 3 shows the artficial control on Mill Creek
near Coshocton, Ohio. A differently shaped
artificial control is shown in figure 4, for the
gage on the Delaware River near Red Bluff, N.
Mex. Note the shallow V-notch in the broad -
crested weir, to improve sensitiveness.
Although the artificial control is usually con-
structed in the forrn of a darn or a weir, it is
seldom if ever desirable to attempt the use of a
weir formula as its rating. The rating for each
station should be determined by a current -
meter or other method of measuring discharge.
The conditions or facilities for the accurate
measurement of small streams and for the
measurement of the low-water flow of larger
streams commonly can be unproved by the use
of artifical controls.
In the design of artificial controls the follow-
ii►g four major points should be considered:
1. The shape of tho structure should permit the
the passage of water without creating u33-
desirable disturbances in the channel above
or below the control.
2The struoture must be of sufficient height to
eliminate the effects of variable down-
stream conditions.
3. The profile of the crest of the control should
be designed so that a small change in dis-
charge at low stages will cause it measura-
ble change in stage, and the relation of
changes in stage to changes in discharge
should produce a rating curve of a shape
that may be extended to peak stages with-
out serious error.
4. The control should have structural stability
and should be permanent.
The artificial control should beself-cleaning and

GENERAL PROCEDURE FOR GAGTATG STREAMS
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Figure 3—Concrete artificiol control on Mill Creek near
Coshocton, Ohio.
Figvre 4.—Artificial control on Delaware River near Red
Bluff, N. Mex., with shallow V-notch in the broad -crested
weir.
should not be si.tbject to obstruction by debris
and ice or to deposits of sand, gravel, or silt. in
its itnmediate vicinity, either upstrea.nr or down-
stream.
Measurement of Stage
The stage of as strwun is the lieight of :rdie
grater surface above aan estabIislied datnal. platze.
1lea.sureinents of streaani stage are used in de-
tenninino, records of streaun discharge. In ad-
ditiori, records of stream stage are useful in
theinselves, such is in the design of structures
a fleeted by stream elevation or 'In the planning
of t.Ile it se, of (load plains.
A record of stage can be obtained by system-
atic observations of a nonrecording gage. In the
early days of the Geological Surrey, this was
the. means generally used, but now •i lie water -
Stage recorder is used at, practically all gaging
stations. The advantages of the nourecording
gage are the low initial cost and the ease of in-
stallation. The disadvantages are the need for
ata observer quid the Iaek of amuraey of then esti-
inated continuous stage graph sketched through
the points of observation. For long-term opera-
I.ion the advantages of the recording gage far
outiveigh those of the nonrecording gage, and
f.htts t1le i:se of the zionrecording gage is no
longer considered a feasible method of obtain-
ing a stage. record.
Methods of sensing stage
Stage is usually sensed by a float in a stilling
well that is connected to the stret,ni by intake
pipes. The stilling well protects the float and
dampens the fluctuation in the stream caused by
wind and turbulence. Stilling wells, though
usually placed in the hank of the stream, are
often placed directly in tlae stream as in
figure 4, attached to a bridge pier or abutments.
The bottom of the stilling well should be below
tho minimum anticipated stage and its top
above the n-ia.ximum anticipated stage. 'riie in-
take to diewell must be of proper size and loca-
tion to prevent Iag during periods of rapid
change in stage and io prevent velocity -mead
effects at its end.
Stage inay also be sensed by a gas -purge sys-
tem known as a bubble gage. This system does
not require a stilling well. A gas is fed through
it tube acid bubbled freely through an orifice
that is permanently mounted in the stream. The
gas pressure in the. tube is equal to the pieio-
metric head on the bubble orifice at any gage
height. The pressure in t•he tube is measured by
it zero -displacement mercury anwometer with
the :assoajated electrical components to drive a
stage recorder.
The bubble gage is used primarily at sites
where it would be expensive to install as stilling
well. It is :also used on sand -channel streams be-
vautse the gas tends to keep the orifice front be-
ing covered with sand and the tube tray be
easily extended to follow a stream channel that
shifts its location. However, the float stilling -
well installation is elieaper to install at most
sites, and its performmicce is iriore reliable than
is that, of the bubble gage. The t o systems have
.�Ex»tt [lie satime accuracy—±4.01 foot. The

�] TECHNIQUES OF WATER -RESOURCES INVESTIGATIONS
choice of system thus depends on the charac-
teristics of the site.
Water -stage recorders
Both strip -chart aazA digital -tape n•;ater-level
recorders ,are in general use. Either recorder
may lie actuated by the float, or bubble -gage
system. Figure .1 shows a bubble. -gage digital -
Punch arrangement.
Figure 5.—Bubble-gage digital -recorder arrangement. Gas
tanf on right; digitzil-punch recorder on left.
A strip -chart recorder produces as graphic
record of ahe rise an(l fall of the water surface
wN la respect to mm,. A gage -height scale of
I : 6 and a time seale,of one clay being equal to
2.4 inches are coinmonly used. ContlllUoUs t•e-
oorders such as the Stevens A--35 Nvill operate
unattended for periods of 60-90 days and pro-
vide, a very saaisfaactory record of stage.
A digital stage recorder punches coded values
of stage on paper tape at preselected time. inter-
vals. A. time Interval of 15 aninutes is normally
used. The Fischer-Poz-ter recorder is battery
operated and ,Fill run unattended for periods
of 00-90 days. The code consists of four groups
of four punches eaac.."a: the foaar haunches repre-
sent 1, 21 -1, and H In each group. The punching
of a stage requires only a 0.1-inch advance of
paper tape. The recorder is actuated by a cam
on a battery -driven inechanical clock.
Digital recorders are gradually replacing
strip -chart recorders aat gaging stations in the
United States. The tivo recorders .are about
equal in accuracy, reliability, and cost, but the
digital recorder is compatible With the use of
electronic computers in computing discharge
records. This automated system as developed by
the Geological Survey offers greater economy
and flexibility in the computation -publication
process than do manual methods associated with
graphical recording. However, the use of
graphical recorders will be continued at those
sites where a graphical record is necessary to
detect ice effects, backwater, or frequent nial-
functions of the recording system.
Reference gages
Because of the possibility of plugged intakes
or other inalfunctions, a nonrecording gage is
installed so that the Water level in the stream
can he directly aneasured. Comparat-I've readings
on the inside and outside gages are taken dur-
Mg each visit to the station by engineering per-
sonnel. Datum of all gages is checked at peri-
odic intervals —casually every 2 or 3 years. In
figure 2, the outside gage is on the bridge. Out-
side staff gages are visible in figures 3 and 4
in the pools near the gage structures.
•
DISckarge Measurements 0
Discharge measurements are made at each
gaging station to define the discharge rating for
the site. The discharge rating may consist of a
simple relation between stage and discharge or
as more complex relation in which discharge is
a function of stage, slope, rate of change of
stage, or other factors.
Discharge measurements are normally made
by the current -meter method, Which consists of
detcrininations of velocity and area in the parts
of a stream cross sectinn. However, indirect
methods are frequently used in determining
flood peak discharges. These, methods utilize
hydraulic equations in conjiniction with the in-
formation on channel characteristics and flood -
marks obtained in aa, field survey after the flood
event.
Discharge measurements may also be made by
the dilution method. This method depends on
determination of the degree of dilution of an
added tracer solution by the flowing water.
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GENERAL PROCEDURE FOR GAGING STREAMS
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0
Current -meter measurements
In the making of a, discharge measurement
the cross section is divided into 20-30 partial
sections, and the area and mean velocity of each
is determined separately. A partial section is a
rectangle whose depth is equal to the sounded
depth apt a meter location (a vertical) and whose
width is equal to the suer of half the distances
to the adjacent verticals. At each vertical the
follow ing observations are made : (1) The dis-
tance to n reference point on the bank, (2) the
depth of flow, and (3) the velocity as indicated
by current teeter at one or two points in the
vertical. These points are at either the 0.2 and
0.9 depths (two -point Method) or the i1fi deptli
(ogre -point method) from the water surface.
The average of the two velocities, or the single
velocity at 0.6 depth, is taken to be the mean
velocity in the vertical. The discharge in each
partial section is computed as the product of
mean velocity times depth at the vertical times
the sun3 of half the distances to adjacent verti-
cals. The sum of thc; discharges in all the par-
t-l:al sections is the total discharge of the, str•eftni.
The measurement can be made by wading the
stream with it current teeter which slides on a
graduated depth rod as sho►vn in figures 2 and
6, or it can be made from a supporting structure
such as a bridge (see fig. 7), cableway, or boat,
the meter being suspended by a cable.
The Price current, meter is used to observe
velocity, except in shallow depths where the
pygmy current meter is used. The rotor on both
these meters has :a. vertical ;axis atad six cone -
shaped cups. Each meter is individually cah-
brated irr the rating flinne at the National Bu-
reau of Standards. Figure 8 shows a velocity-
azirnm-li-depth assembly, which has been in use
since 1558, primarily on large rivers and in
estuarine studies.
These nrethods anti the atssOciateal erlriip
ment have been developed by the Geological
Survey over a period of 60 years. Satisfactory
results have been obtained in measuring dis-
cliaarges ranging from the trickle of a small
stream to the 7,500,000-cfs flow of the Amazon
River. Methods and equipment used in making
discharge measitreinents by the current -meter
method are described in detail in book 3, chap-
ter AS, of this series, by Buchanan and Somers.,
Indirect discharge measurements
During floods, it is frequently impossible or
impractical to measure the peak discharges
►guest they occur, because of conditions beyond
control. Hoards may be impassable; structures
frosil ► shell e.ttr•rent- meter Measurements might,
have been made may be nonexistent, not suitably
located, or destroyed; knowledge of the flood
rise may not be available sufficiently in advance
to permit reaching the site near the time of the
peak; the peak may be so sharp that a satisfac-
tory eiirrent-meter measurement could not be
intade. even with aii engineer present -it the time;
the flow of debris or ice may be such as to pre-
vent use of z current meter; or limitations of
personnel inight make it impossible to obtain
direct measurements of high -stage discharge at
numerous locations during a short flood period.
Consequently, naatny peak discharges resist be
determined after the passage of the flood by
indirect method-, stick as slope -area, contracted -
opening, flow -over -dam, or flow -through -enl-
ver't, rather than by direct current-roeter me.as-
ur•eriient.
To evaluate the accuracy of indirect methods,
comparisons have been made at every opportu-
nity. When it has been possible to compare peak
discharge computed by indirect means with
peak discharge measured by current meter or
other direct means, the agreement, in general,
has supported confidence in the auxiliary
methods.
Indirect measurements make use of the
energy equation for computing discharge. The
specific equations differ for different types of
fio-w, such as open -channel flow, flow over darins,
and flow through culverts. These equations re-
late the discharge to the hater -surface profiile
and the geometry of the channel. A field srarvev
is made rafter the flood to determilie the location
and elevation of high-water marks and the
geometry of the channel.
' Buchanan. T, J.. and Somers, W. i'., FxL�eharge measure-
menix at gitging +stntlonr-.: aI.S- Geoi- survLy 'Fet!iinigues
►►'titer-rresnurr-es Icir.. hook ehaip. AR, tinpuh. data.

q,rCT31NIQUES Or' WATf:R-Rh:SOURCES IVVESTIG&TIONS
n �, ..•;fir`
Figure b.—Measuring discharge with current meter by wading.
•
C I
•

•
•
0
GENERAL PROCEDURE FOR GAGING STREAMS
Figure 7. --Measuring discharge with current meter Erom
bridge over the Hudson River at Poughkeepsie, N.Y
-Detailed descriptiw)s of the procedures used
hi eollectilig field data aix.l in computing the
dischrtrge are giveii in Betison aid Dalrymple
(1067), Dalrymple and Benson (1.967), Bocd-
haine (1968), lllattliai (1967), and Hidsilig
(1967), which are book 3, chapters AI--A5, of
M
this series. The use of electronic computers in
these computations is explained by Anderson
and Anderson 2 and by Somers and Selner."
Dilution method
Measurement of discharge by this method
depends oii determination of the degree of di-
Itition of in added tracer solution by the flowing
water. A solution of a stable or radioactive
chemical is injected into the stream as either a -
constant rate or all at once. The solution be-
comes diluteal by the discharge of the stream.
Measurement of the rate of injectioli, the coli-
ce.iitrgtion of the tracer in the injected solution,
and the collcent.ration of the tracer at a. cross
An Slen:on, 1). B.. and Ande.mon, N. I... Compittation of
«:i�er- rrria�c liratiirs in ❑pen chann(�N ; U.S. Geol. surety
Ti oinii)ncs Wa ter, Kfrsgm vee5 Ins'.. impub. data.
Boater , W. 1'.. and tieiriCr, a. L. computation of : tagu-
dkeliargr relationship" at etih-erN and Computer tee.hnigiw
for s3npe-area nie.,LStirk!nw ts: U.s$ Geol- Swr%(zy TCChllique�-
hater-Iirsoarces Inv., anpub. data.
Figure 8.—VADA (velocity -azimuth -depth -assembly) equipment in use for measurement From bridge.

10 TECILNIQUES OF WATER -RESOURCES INVESTIGATIONS
section downstream from the injection paint
permits the computation of stream discharge.
The accuracy of the method critically depends
upon complete mixing of the injected solution
through the stream cross section before the
sampling station is re4whed and upon no adsorp-
tion of the tracer on stream -bottom materials.
The method is recommended only for those sites
,where conventional methods cannot be em-
ployed owing to shallow depths, extremely high
velocities, or excessive turbulence. A detailed
description of the procedures and equipment
used in measuring discharge by a dye -dilution
method is given by Cobb sand Bailey,' Figure
9 shows the pressurized constant -rate tanks
used to inject fluorescent dye solutions into the
streams, and figure 10 shows collected sample
bottles ready for field testing with a fluorometer
on the tailgate of a vehicle.
Discharge Ratings
The computation of continuous records of
discharge at gaging stations depends on defini-
tion of the discharge rating for the channel.
Discharge ratings may be simple or complex.
The rating may consist of a simple relation be-
tween stage and discharge or of several rela-
tion curves which define discharge as a function
of stage., slope, rate of change of stage, or other•
variables. The expression "discharge rating" is
an all-inclusive ter;rn to describe the one or
more relations used to determine the discharge
from measured pararneters of flow.
Stage-dis+charge relations
Discharge ratings at a large majority of
gaging stations consist of relations between
stage and discharge. These stage -discharge re-
lations are rarely permanent, particularly at
low flow, because of changes in the stream chan-
nel such as scour and fill, aquatic growth, ice,
or debris or because of changes in bed rough-
ness. Frequent disclarge measurements are
necessary to define the stage -discharge relation
at any time.
4 Cobb, E. D., and i nffi-y, .1. F., Measurement of discharge
he dye-ilnutlon methods: ]_S. Geoi. Survey Technlquea Water-
Resourrws Ins-., unpub. data.
Figure 9.—Pressurized constanWate injection tanks for injec-
tion of dye into slrearns.
The relation of stage to discharge is gen-
erally controlled by a section or reach of eharr-
nel below the gage, known as the station con-
trol. Section controls may be either natural
or constructed, and may consist of a ledge of
rock across the channel, a boulder -covered
riffle, an overflow dani or any other physicaP/
feature capable of maintaining a fairly stable
relation between stage and discharge. Section
controls are commonly effective only at low dis-
charges, and are completely submerged by
channel control at medium and high discharges.
Channel control consists of all the physical
features of the channel .which determine the
stage of the river at a given point for a certain
rate of flow. These features include the size,
slope, roughness, alinement., constrictions and
expansions, and shape of the channel. The
reach of channel which acts as the control may
lengthen as the discharge increases; such
changes introduce new features which affect
the stage -discharge relation.
Knowledge of the channel features which
•
•
0

GENERAL PROCEDURE FOR GAGING STREAMS 11
•
•
Figure t Q.--Equipment for Fluorometer testing of water samples in the Field.
control the stage -discharge relation is ianpor-
tant. The development of stage -discharge
curves where more than one control is effective
and the number of measurements is limited
generally requires judgment in interpolating
between measurements and in extrapolating
beyond the highest measurements. This judg-
ment is particularly necessary where the controls
are not permanent and various discharge meas-
urements represent different positions of the
stage -discharge curve.
Stage -discharge relations aro developed from
a graphical analysis of the data, plotter. on either
rectrnngular-coordinatte or logarithmic plotting
paper. A good analysis of the data requires a
knowledge of the characteristics of the channel
and a knowledge of opera -channel hydraulics.
The discharge measurements available for the
analysis rarely define a unique stage -discharge
relation because of changes in the channel dur-
0
ing the period represented by the measure-
ments. The determination of the proper shape
of the rating curve and its position at various
times requires considerable engineering knowl-
edge, experience, and judgment. In general, a
base stage -discharge relation is used, and devia-
tions from this relation with time (shifts) are
determined by consideration of the plotting of
individual discharge measurements. These
shifts, in the form of a stage adjustment, are
then used with the base rating In computing
the discharge record.
The stability of the stage -discharge relation
governs the number of discharge measurements
that are necessary to define the relation at any
tirne. If the channel is stable, one measurement
a month is generally sullicieat; in sand -channel
streams, three measurements a week may be
required because of the random shifting of the
stream ehanrnel.

12 TFC_fJNIQUES OF WATER-HESOURCES INVESTIGATIONS
Complex disckarge ratings
ff variable backwater or highly unsteady
now exists at a gaffing station, the discharge
rating cannot be described by stage alone.
Variable backwatt.,r may be caused by a tribu-
tary stream that enters the control reach down-
stream from the gage, by ;;manipulation of gates
at a dam, or by flow of water into and from
overbank storage created by natural constric-
tions in the stream channel. The discharge un-
der these conditions is a function of both stage
and the slope of the energy gradient, which is
approximated by the slope of the water sur-
face between two stage gages. Stage -fall -dis-
charge ratings are usually determined empir-
ically from observations of (1) discharge, (2)
stage at the base gage, and (3) the fall of the
water surface betNreen the base gage and an
auxiliary stage gage downstream. The general
procedures used in developing these ratings are
described in book 3, chapter A9, of this series,
by Carter and Davidian."
If the flow is very unsteady, as in a tidal
reach, the acceleration head governs the energy
slope. Under this condition. unsteady -flow equa-
tions must be used to describe the variation of
discharge with time. This method is described
by Davidian s
A special type of unsteady flow is treated
under the Beading "Uniformly progressive
floe" in Carter Lind Davidian.' For such flow
the stage and rate of change of stage observed
at a single gage are used to establish the dis-
cliarge rating.
Computation and Preparation of
Discharge Records
A continuous record of flow at a gaging sta-
tion is computed f rorn records of stage and the
discharge rating for the station. The typo of
stage recorder used at the station determines
whether the. computations are done manually or
n Carter. R. IV., .and Davidian. JauOt3, Discharge ratings
.at gaging stations: U.S. Geoff- Survey Techniques Water-
iiesonrces Ins'., hok 3, elia1). X), )inpuh, data.
' Davidian, Jacob, Computation of discharge in ticaai
re:t(i:m : U.S. Gea1. Sar•rey Technique4 Rater -Resources Ina-,
nnl)vb. data.
by an electronic computer. In either system the
engineer must study the data and prepare what
is termed a station analysis before computations
are performed.
Station analysis
A station analysis, which documents the re-
stiltof the study of the data, is prepared for
each station at tiie end of each water year. The
study includes the following items:
I. A review of field surveys of gage datum and
a determination of the datum corrections, if
any, to be applied to gage readings taken
during the year.
?. :L review of discharge-measumment notes.
3. An analysis of the discharge rating and the
determination of the rating (or shifts) ap-
plicable during each period of the year.
4. The preparation of tables which express the
discharge rating.
Manual computations
if stage, is recorded at the station on a strip-
chartt recorder, all computations are performed
manually in the following order:
1. Determination and application of gage -
height and time corrections to Clio gage -
height chart..
2. Computattion of 'the mean gage height for
each day, or for shorter periods if the range,
in discharge during the day is large. Sub-
division is necessary because of curvature
in the discharge rating.
3. Computation of discharge for each period
from mean values of stage and the dis-
charge rating, including any shift correc-
tions.
4. Computation of peak values of gage height
and discharge.
5. Listing of the values of meal, daily gage
heights and discharge and momentary
peaks.
€i. Computation of mean flow for each month
and the year in cubic feet per second and
in inches.
i. Review and comparison of the record of dis-
charge with that of nearby streams.
•
•
0

GENERAL PROCEDURE FOR GAGING STREAMS
%3
•
•
Automatic computations
If stage is recorded on a digital tape at the
station, the computations just outlined are per-
formed by an electronic computer. The input
to the computer is the digital record of stage,
with a list of any datum corrections, and the
discharge rating, with a list of any necessary
shift, corrections. Far stations at which the
stage -fall -discharge tyl3e of rating is aapplica.-
ble, the digital -tape records of stage from both
the primary and the auxiliary gages are fur-
nished to the computer. In add ition to the stage -
discharge relation, supplementary information
such as the stage -fall rela.�tion and the relation
of fall ratio versus discharge ratio are supplied.
The output from the computer consists of two
forms_ The first includes a lasting of the maxi-
mum, the ininimum, and the mean gage height
for each day, bilaourly gage heights for each
city, and the mean discharge for each day. The
second form includes as listing of mean daily
discharges and the naont.hly and yearly sum-
maries in the same format as is -used for publi-
cation. 13esides being pa.ablished, the daily dis-
clia,rges and yearly summaries are stored on
magnetic. tape. Corrections are inaade on the tape
where necessary after the computed records are
reviewed by engineering; personnel in the dis-
trict offices.
Publication of Records
Through September 30, 1960, the records of
diseli arge of streams Mid contents of bikes or
reservoirs mercy piiblisiwd in an annual series
Q
0 * 118 [30VF.-MIXT 1'F MI HG0 VICE 1-tl - 111-111 - 111111171
of Geological Survey water -supply papers en-
titled "Surface Water Supply of the United
States." Each volume in the series covered an
area whose boundaries coincided with those of
certain natural drainage basins.
Beginning with the 1961 water year, stream -
flow records and related data have been released
by the Geological Surrey in annual reports on
a State -boundary basis. These reports are pre-
pared and released by the district offices soon
after the close of the water year.
Daily discharges and annual summaries are
also being published in water -supply papers at
intervals of 5 years. The first series to be pub-
lished covers the period 1961-65.
References
Benson, M. A., and Dalrymple, Tate, 1967, General
field and office procedures for indirect measure-
ments: U.S. Geol. Survey Techniques Water -Re-
sources Inv., book 3, chaps Al, 30 p.
Bodhaine, G. L., 1968, Measurement of peak discharge
at culverts by indirect methods: U.S. Geol. Survey
Techniques Water -Resources Inv., book 3, chap.
A3, 60 p.
Dalrymple, Tate, and Benson, M. A., 1967, Measure-
ment of peak discharge by the slope -area method:
U.S. Geol. Survey Techniques Water -Resources
Inv., book 3, chap. A2, 12 p.
Huasing, Harry, 1967, Measurement of peak discharge
at dams by indirect methods. U.S. Geol. Survey
Techniques Water -Resources Inv., book 3, chap. A5,
29 p.
3latthai, H. F., 19%7, Measerement of peak discharge
at width contractions by indirect methods. U.S.
Geol. Survey Techniques Water -Resources Inv.,
book 3, Chap. A4, 44 p.

•
11
•

^-J
imUSGS
science for a changing world
Techniques of Water -Resources Investigations
of the United States Geological Survey
Chapter A8
DISCHARGE MEASUREMENTS AT
CAGING STATIONS
By Thomas J. Buchanan and William P. Somers
$oo� 3
APPLICATIONS OF HYDRAULICS

UNITED STATES DEPARTMENT OF THE INTERIOR
THOMAS S. KLEPPE, Secretary
GEOLOGICAL SURVEY
V. E. McKelvey, Director
First printing 1969
Second printing 1976
UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON .1969
For sale by the Superintendent of Documents, U.S. Government Printing Office
Washington, D. C. 20402

PREFACE
The series of manuals on techniques describes procedures for planning and
executing specialized work in water -resources investigations. The material is
grouped under major subject headings called hooks and further subdivided
into sections and chapters; -Action A of book 3 is on surface -water techniques.
Provisional drafts of chapters are distributed to field offices of the. U.S.
Geological Survey for their itse. These drafts are subject to revision because.
of experience in use or becaiFse of advancement in knowledge, techniques, or
equipment. After the teahniclue deserilwd in a chapter is sufficiently developed,
the chapter is published and is sold by t:lie U.S. Geological Surrey, 120(} Soiit.h
Fads Street., Arlington, VA 22201 .(authorized agent. of Superintendent of
Documents, Government Printing Office).
III

CONTENTS
page
Current -meter measurements —Continued
Page
1'refaCf'_ -. - _ - _ _ _
3Lt
C U rre n t -M Oter m('fl.+lIreMe. nt i)FWed uIT' _ _ _ -
37
_ _ _ _ _ _ _ ..- . _
1
Current -meter rnelislFreFrl4'FltS by wad -
Introduction - --- - - - - -
1
___----
38
Current -meter rueasurenreiit.z _ _ __. _ -_
1
Current -meter measurements from
lns3[runlents and F'quijJrlent_ _
4
cablewavc--.-----._--
['LrrrE:FIL meters -.. _ .-. _
4
Current -meter measurements from
LF'i't cFirr��nt. meters -
4
brid-------
41
llorianntid-,axis current meters__ _
7
Current -meter measurements from
f3lF#ir.lt ciirrr•Iit. ini�tcr. -.. -- -.- _
7
ice
42
Cgire of the ,,Irtical-axis current
cover -------. -----
7
Current -meter measurements front
meter
[tasting of current rneurs
8
boats -------------------------------
44
tiolrndiliK equipment
3
?Moving-baat measurements of dis-
Wa.Firngrods _
rJ
charge ----------------------------
46
Sounding weights and accessones.
11
Networks of current meters_ _ _ _ _ - _ - _ _
4.6
Sounding rF'.!'.1S__ _ - - _
13
Measuremeut of deep, swFft streams__
47
Somiding, cable- _ _
14
Possible to sound; weight and
14
meter drift downstream_
47
Depth iildicat.ors-._ _ _- _ _
14
Not possible to sound; standard
Power F uii t _ _ _ - .
15
cross section available_ - - - - - - - -
52
11:i11dline.'__-.-- - _ _ - -
15
Not possible to sound; standard
Snirie sounder -. - _ _ - - _ _ _ . _ _ _ _ . - _
16
cross section not available----
52
Width-mea:;uring, ecluipmem _
17
Not possible to put meter in water_
53
3'.rguipaleFlt. ,ltiseFri tiile _
18
]Measurements during rapidly changing
Cableway !.quilmilclit_
18
stage -----------------------------
53
13ridgo e(plipinent .._ _ _ _ _
20
SerieG of measurements during a peak
Boat equipment. -- _ _ _ _ -- _ _
24
of short duration ----------- ------
ir3
Ice F:gii1p111r'nt.-
27
Mean gage height of discharge measure-
1-eloeity-,1.irnnt.Ii-de 1..etll-zssemltiy
27
ments----------------------------
54
lli�cell,irientis equipment -
34
Portable weir plateg---------------------------
57
M eatiurernF+nt of c ekrciuI
31
Portable Pars, halI fiumes, description and theory_
ii9
•F!i'ti Call r�'[' flletliod_ _ _
31
61
Two-point
'I't!•n-point Friethod _ _ . -.. _ - _ _ _ - _ -. _
eth
32
Volumetric measurements____________________
Six-to°nths-depth method-_
32
Floats -------------------------------------
63
Two -tenths -depth rtaethod -- -. _ _ -.... -.
33
Indirect discharge measurements_. _
64
Three-point method_ _ _ ..- _ - - _ _ - _
37
Bye -dilution method of measuring discharge__
64
Subsurface method__ _ -. _________
37
References----__ -_ -
fill
FIGURES
Page
1. Definition sketch of midsection method of computing cross-section area for
discharge measurements-------------------------------------------------- 2
2. Comoutation notes of a current -meter measurement by the midsection
method----------------.---------------------
3. Assembly drawing of small Price type AA current meter_ - _ _ _ _ _ - - 5
9

VI CONTENTS
4-7. Photographs: Page
4. Price type AA and Price pygmy meters--------------------------- 6
5. Vane ice meter, and vane meter with cable suspension yoke- _ _ _ _ _ _ _ _ 6
6. Magnetic switch contact chamber, shaft, and adapter bushing, and
cat's whisker contact chamber and shaft_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 6
7. Ott current meter - - - - - _ -. - _ _
8. Velocity components measured by Ott and Price current meters_ _ 7
9. Photograph of 11off current meter -------------------------------------- 7
W. Photograph of optical current meter _ _ _ _ _ _ . _ _ _ _ 8
11. Current -meter rating table --------------------------------------- 10
12-55. Photographs:
12. Top -setting wading rod with meter attached _ _ _ _ _ _ - _ --
11
13. Closeup view of setting scale on handle of top -setting rod- -_ _
11
14. Paris for round wading rod_ _ - _
12
15. Round wading rod with meter attached_ _ _ - _
12
16. Lower section of ice rod for use with vane ice meter
13
17. Lower section of ice rod for use with Price meter_ _ _ _ _ -
13
18. Columbus sounding weights------------------------------------
13
19. Sounding -weight hangers and hanger pins------------------------
14
20. A -pack reel -------------------------------------------- -----
14
21. Canfield reel- --.-.-----...------------------------------------
15
22. B-56 reel -------------------------------------------------------
Ifi
23. E-53 reel_ ----------------------------------------------------
16
24. Connectors ---------------------------------------------------
17
25. Computing depth indicator
17
26. Power unit for sounding reel___ -----------------------------------
IS
27. Handline----------------------------------------------------
19
28. Lee- Au and 'Xiorgan handline reels_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
19
29. Handline in use from a bridge - _ _ _ _ _ _
19
30. Sonic -sounding recorder_ _ _ _ _ _ _ _ _ _ _ - - _ _ - _ - _ _ _ _ _
19
31. Sounding weight with compass and sonic transducer-_ _ _ _ _ _ _ _ -. - _ _ _ _
20
32. Sonic measuring assembly --_---------__ _--____
21
33, Pakron, Lee -Au and Columbus type A tag -line reels_____ _ _ _ _ _ _ _ _ _ _
21
34. Sitdown cable car_ _ _ _ _ _ _ _ _ _ _ _ _ _
21
35. Standup cable car ---------------------------------------------
36. PortahIr. reel seat on sitdown type cable car__ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
22
37. Cagle -car pullers ---------------------------------------------------
22
38. Battery -powered cable car --------------------------------------
22
39. Gasoline -powered cable car_ -- _ _ . _ _ _ _
23
40. Sitdown cable car with Canfield reel clamped to side of car
24
41. Typc�--A crane with 3-wheel base _ _ - _
25
42. Type -A crane with 4-wheel base ---------------------------------
26
43. Bridge board in use_ _ _ _ _ _ _ _ _
44. Truck -mounted crane used on the Mississippi River ---------------
28
45. IIori7ontal-axis boat tag -line reel without a brake ------------------
29
46. JJoriaontal-axis boat tag -line rool with a brake_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
30
47. Vertical -axis boat tag -line reel _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ -.
31
48. Boom and crosspiece for use on moats_ ---------------------------
32
49. Measuring equipment set up in a boat
33
50. Gasoline -powered ice drill. .----------------------- ----
33
5L Collapsible reel support and ice -weight assembly _ _ -- _ _
34
52. Velocity -azimuth -depth assembly_________________________
35
53. Stopwatch------------ --------------------------------
35
54. Automatic counter and headphone_ _ _ - _ -• _ - _ _ _ _ _ _ _ _ _ _
35
55. Ice creapers for boots and wagers-------------------------------
36
56. Tpyical verical-velocity curvc------------------------------------------
36
57. Diagram showing measurement of horizontal angles _ _ _ _ _ _ _ _
39

CQNTENT8
VH
Paga
58.
Photograph showing wading measurement using top -setting rod _ _ _ _ _ _ - _ _ _ _
39
59.
Photograph showing ice rod being used to support current meter for a dis-
charge measurement and ice drill being used to cut holes _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
42
60.
Diagram showing method of computing meter settings for measurements
under ice--- --------------------- --------------------
43
61.
Typical vertical -velocity curve under ice cover_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
44
62.
Sample sheet of part of notes for discharge measurement under ice cover_ _ _ _
45
63-65.
Diagrams:
63. Determining position in the cross section section, stadia method_ _ _ _
46
64. Determining position in the cross section, angular method_ _ _ _ _ _ _ _ _
46
65. Position of sounding weight and Iine in deep, swift water_ _ _ _ _ - _ _ _ _
48
66.
Sketch of geometry of relationship of actual to measured vertical angle when
flow direction is not normal to measuring section _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
51
67-69.
Charts
67. Computation of weighted mean gage height----------------------
55
68. Discharge measurement notes with discharge adjusted for channel
storage effect - - - •------------------------------ ---
56
69. I?ischarge measurement notes with mean gage height adjusted for
time -of -travel of flood wave -------------------------------- --
58
70.
Expanded plot of gage -height graph during measurement 264 at Sig Creek
near Dogwood, Va------------------------------------------------
59
71.
Sketch showing portable weir plate sizes_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
60
72.
Photograph of modified 3-inch ParshalI flume made of sheet iron _ _ _ _ _ - _ _ _ _
61
73.
Working drawing of modified 3-inch ParshaII flume -----------------------
62
TABLES
Page
1. Sounding reel data --------------------------- -------------- 14
2. Current -meter and velocity -measurement method for various depths_ _ _ _ _ _ 39
3. Velocity-mcasurement method for various suspensions and depths _ _ _ _ _ _ _ _ _ _ _ _ _ _ 40
C Air -correction table, giving difference, in feet, between vertical length and slant
length of sounding line above water surface for selected vertical angles_ _ _ _ _ ___ 49
5. Wet -line table, giving difference, in feet, between wet -line Iength and vertical
depth for selected vertical angles ------------------------------------------ 50
6. Degrees to be added to observed angles to obtain actual vertical angles_ _ _ _ _ _ _ _ _ 50
7. Summary table for setting the meter at 0.8-depth position in deep, swift streams_ _ 52
8. Rating table for 3-inch modified ParshalI flume ------------------------------ 61

DISCHARGE MEASUREMENTS AT GAGING STATIONS
By Thomas J. Buchanan and William P. Somers
Abstract
The techniques used in making discharge
measurements at gaging stations are described
in this report. Most of the report deals with
the current -meter method of measuring dis-
charge, because this is the principal method
used in gaging streams. The use of portable
weirs and flumes, floats, and volumetric tanks
in -measuring discharge are briefly described.
Introduction
The U.S. Geological Survey makes thousands
of streamflow measurements each year. Dis-
charges measured range from a trickle in a
ditch to a flood on the Amazon. Several
methods are used, but the Geological Survey
makes most strearnflow measurements by
current meter. The purpose of this report is
to describe in detail the procedures used by
the Geological Survey for making current -
meter measurements and to describe briefly
several of the other methods of measuring
streamflow.
Streamflow, or discharge, is defined as the
volume rate of flow of the water including
any sediment or other solids that may be
dissolved or mixed with it. Dimensions are
usually expressed in cubic feet per second.
Other common units are million gallons per
day and acre-feet per day.
Current -Meter Measurements
A current -meter measurement is the sum-
mation of the products of the partial areas
326-263 0-69 2
of the stream cross section and their respective
average velocities. The formula
Q=Z(a v) (1)
represents the computation where Q is total
discharge, a is an individual partial cross-
section area, and v is the corresponding mean
velocity of the flow normal to the partial area.
In the midsection method of making a
current -meter measurement it is assumed that
the velocity sample at each location represents
the mean velocity in a partial rectangular
area. The area extends laterally from half the
distance from the preceding meter location to
half the distance to the next and vertically,
from the water surface to the sounded depth.
(See fig. 1.)
The cross section is defined by depths at
locations 1, 2, 3, 4, . . . n. At each location
the velocities are sampled by current meter to
obtain the mean of the vertical distribution of
velocity. The partial discharge is now computed
for any partial section at location x as
q==v=+ 1d.
L 2 2
1- 2
where
q==discharge through partial section x,
vx=mean velocity at location x,
bx=distance from initial point to location
x,
bt=_I) =distance from initial point to preced-
ing location,
b(y+l)=distance from initial point to next
location,
dx—depth of water at location x.
1

TECHNIQUES of WATER -RESOURCES INVESTIGATIONS
bn
h(n-r
jbS
Initial
point
f'a
bz
bi
I
1 � I
I I
I a I m
I I b
I
11-- -J
-3
b
4
I
I
I
I
I
I
I
I
I
i
I
I
y
M
EXPLANATION
Water surface
1, 2, 3.......
Observation points
b1, b2,b3..... ...bl
Distance, in feet, from the initial
paint to the observation point
di,d2,d3, ...... -dn
Depth of water, in feet, at the
obse vation point
Dashed lines
Boundary of partial sections; one
heavily outlined discussed in text
Figure 7 ,—Definition sketch of midsection method of computing cross-section area for discharge measurements.
Thus, for example, the discharge through
partial section 4 (heavily outlined in fig. 1) is
q4-N1 2b8]ds. r .{ z
The procedure is similar when x is at an end
section. The "preceding location" at the be-
ginning of the cross section is considered coinci-
dent with location 1; the "next location" at the
end of the cross section is considered coincident
with location n. Thus,
q1=v1[�2 dF, and
'� qm=v,� 2 d,�.
For the example shown in figure 1, qI is zero
because the depth at observation point 1 is
zero. However, when the cross-section boundary
is a vertical line at the edge of the water as at
location n, the depth is not zero and velocity
at the end section may or may not be zero. The
formula for q1 or q„ is used whenever there is
water only on one side of an observation point
such as at piers, abutments, and islands. It
usually is necessary to estimate the velocity at
an end section as some percentage of the adja-
cent section because it normally is impossible
to measure the velocity accurately with the
current meter close to a boundary. There also

DISCHARGE MEASUREMENTS AT GAGING STATION'S
is the possibility of damage to the equipment if The mean --section method used by the Survey
the flow is turbulent. prior to 1950 differs from the midsection method
The sumination of the discharges for all the in computation procedure. Partial discharges
Martial sections is the total discharge of the are computed for partial sections between suc:-
stream. An example of the measurement notes cessive locations. The velocities and depths at
is shown in figure 2. successive locations are each averaged, and
o y_ci•.. t .3iBy ...
-31
- I r
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UMNARSE PRAWREYEKF MOTE$ 4
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w.s,. T�fke.f wi LFi's' J`+.34
-
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�]
Figure 2,--Computation notes of a current -meter measurement by the midsection method.

4 TECHNIQUES OF WATER -RESOURCES ItiVESTIGATIONS
the section extends laterally from one observa-
tion point to the next. Discharge is the product
of the average of two mean velocities, the
average of two depths, and the distance between
locations. A study by Young (1950) concluded
that the midsection method is simpler to
compute and is a slightly more accurate pro-
cedure than the mean -section method.
Current -meter measurements usually are
classified in terms of the means used to cross
the streain during the measurement, such as
wading, cableway, bridge, boat, or ice.
Instruments and equipment
Current meters, timers, and -counting equip-
ment are used when making conventional
types of measurements. Additional equipment
used depends on the type of measurements
being made. Instruments and equipment used
in making current -meter measurements are
described in this section under the following
�mtegories: current meters, sounding equipment,
width -measuring equipment, equipment as-
sernblies, and miscellaneous equipment.
Current meters
A current meter is an instrument used to
measure the velocity of flowing water. The
principle of operation is based on the pro-
portionality between the velocity of the water
and the resulting angular velocity of the meter
rotor. By placing a current meter at a point
in a stream and counting the number of revolu-
tions of the rotor during a measured interval
of time, the velocity of water at that point is
determined.
The number of revolutions of the rotor is
obtained by an electrical circuit through the
contact chamber. Contact points in the chamber
are designed to complete an electrical circuit
at selected frequencies of revolution. Contact
chambers can be selected having contact
points that will complete the circuit twice per
revolution, once per revolution, or once per
five revolutions. The electrical impulse produces
an audible click in a headphone or registers a
unit on a counting device.
The counting intervals are measured by a
stopwateh.
Current meters generally can, be classified
into two main types, those meters having
vertical -axis rotors and those having horizontal -
axis rotors. The comparative characteristics of
these two types are summarized below:
1. Vertical -axis rotor with cups or vanes.
a. Operates in lower velocities than do
horizontal -axis meters.
b. Bearings are well -protected from silty
water.
c. Rotor is repairable in the field without
adversely affecting the rating.
d. Single rotor serves for the entire range
of velocities.
2. Horizontal -axis rotor with vanes.
a. Rotor disturbs flow less than d❑ verti-
cal -axis rotors because of axial sym-
metry with flow direction.
h. Rotor is less likely to be entangled by
debris than are vertical -axis rotors.
c. Bearing friction is less than for vertical -
axis rotors because bending mo-
ments on the rotor are eliminated.
Vertical -axis current rnefers
The most common type of vertical -axis
current meter is the Price meter, type AA.
(See fig. 3.) This meter is used extensively by
the Geological Survey. The standard Price
meter has a rotor 5 inches in diameter and 2
inches high with six cone -shaped cups mounted
on a stainless -steel shaft. A pivot bearing
supports the rotor shaft. The contact chamber
houses the upper part of the shaft and an
an eccentric contact that wipes a bead of
solder on a slender bronze wire (cat's whisker)
attached to the binding post. A separate
reduction gear (pentagear), wire, and binding
post provide a contact each time the rotor
makes five revolutions. A tailpiece keeps the
meter pointing into the current.
In addition to the standard type AA meter
for general use there is a type AA meter for
low velocities. No pentagear is provided.
This modification reduces friction. The shaft
usually has two eccentrics making two contacts
per revolution. The low -velocity meter nor-
mally is rated from 0.2 to 2.5 fps (feet per
second) and is recommended when the mean
velocity at a cross section is less than 1 fps.
In addition to the type AA meters, the
Geological Survey uses a Price pygmy meter

21---
I Cap for contact chamber
8
Yoke
16
Pivot bearing
2 Contact chamber
9
Hole for hanger screw
17
Pivot
3 insulating bushing for contact
10
Tailpiece
18
Pivot adjusting nut
binding post
11
Balance weight
19
Keeper screw for pivot
4 Single -contact binding post
12
Shaft
adjusting nut
5 Penta-contact binding post
13
Bucket -wheel hub
20
Bearing lug
6 Penta gear
14
Bucket -wheel hub nut
21
Bucket wheel
7 Set screws
15
Raising nut
Figure 3.—Assembly
drawing of small Price type
AA current meter,
J:

G TECHNIQUES OF WATER -RESOURCES INVESTIGATIONS
in shallow depths. (See fig. 4) The pyomy
meter is scaled two -fifths as large its the stand-
ard meter and has neither it tailpiece nor a.
pent:wear. The contact chamber is an integral
part of the yoke of the meter. The pygmy
meter snakes one contact each revolution and
i.s used only for rod suspension.
The Geological Survey has recently developed
a four -vane vertical -axis meter. (See fig. 5.)
IJiis meter is useful for measurements under
ice rover becFac3se the vanes are less likely to
fill with slush ice, and because it requires a
much smaller hole to pass through the ice. One
yoke of the vane meter Is made to be sus )ended
.at the end of 23. rod :and will fit holes made by an
ire drill. Another yoke is made for regular sits -
pensions. (See fig. 5.) The vane meter has .a
disadvantage of riot responding as well as the
Price type AA meter at velocities belong 0.5 fps.
A new contact charnber has been designed by
the Geological Survey to replace the wiper
Figure 4.--Price type AA meter, top; and Price pygmy
meter, bottom
Figure 5 —Vane ice meter, top; and vane meter with cable
suspension yoke, bottom.
contact of tine type AA and v€Erie naeters. The
new contact chamber contains as magnetic
switch, glass enclosed in a hydrogen atmosphere:
and hermetically sealed. Tlae switch assembly
is rigidly fixed in the top of the meter head
just above the tip of the shaft. The switch is
operated by a small permanent magnet rigidly
fastened to the shaft. The switch quickly doses
when the magnet is alined with it, and then
promptly opens when the magnet moves away.
The magnet is properly balanced on the shaft.
Any type AA meter can have a magnetic switch
added by replacing the shaft and the contact
chamber. (See fig. 6.) The magnetic switch is
placed in the special contact chamber through
the tapped hole for the binding post. The rating
of the meter is not faltered by the change. An
automatic counter (see p. 31) is used with the
magnetic -switch contract charnber. If a head-
phone is used, arcing can weld the contacts.
A Price meter accessory that indicates the
direction of flaw is described on page 27.
Figure 6—Magnetic switch contact chamber, shaft, and
adapter bushing, left; and cat's whisker contact chamber
and shaft, right.

DISCHARGE MEASUREMENTS AT GAGING STATIONS
7
The care and rating of vertical -axis meters is
described below and by Smoot and Novak
(19(s8).
Horizontal -axis current meters
The types of horizontal -axis meters in use are
the Ott, Noyrpic, Haskell, and Hoff. The Ott
ineter is made in Germany, the Veyrpic meter
in .France, and both are used extensively in
Europe. The Haskell and Hoff meters were
developed in the United States where they are
ttsed to a limited. extent.
The Ott meter is a precision instrument but
is not used extensively in this country because
It is not as durable as the Price meter under
extreme conditions. (See fig. 7.) The makers of
the Ott meter have developed a component
propeller which in oblique currents auto-
matically registers the velocity projection at
right angles to the measuring section for angles
as much as 45' and velocities as much as 8 fps.
For example, if this component propeller were
held in the position AB in figure 8 it would
Figure 8.—Velocity components me4svred by Ott and Price
Current meters.
register V cos a rather than V, which the Price
meter would register.
The hreyrpic meter is used rarely in this
country because it has the same disadvantages
as the Ott meter.
The Haskell meter has been used by the U.S.
Lake Survey, Corps of Engineers, in streams
that are deep, swift, and clear. By using
propellers with a variety of screw pitches, a
considerable range of velocity can be measured.
The meter is durable, but has most of the other
disadvantages of horizontal -axis meters.
The Hoff meter is used by the Geological
Survey, the Department of Agriculture, and
others, especially for measuring pipe flow. (See
fig. 9.) The lightweight propeller has three or
four vanes of hard rubber. The meter is suited
to measurement of low velocities, but not for
rugged use.
Optical current meter
The Geological Survey, in cooperation with
the California Department of Water Resources,
has developed an optical current meter. (See
fig. 10.) This meter is a stroboscopic device
designed to measure surface velocities in open
channels without immersing equipment in the
stream. The optical current meter will find its
principal use in measurements of surface
velocity during floods when it is impossible to
use conventional stream -gaging equipment be-
cause of extremely high velocities and a high
debris content in the stream.
Care of the YerticaI-axis current meter
The calibration and maintenance of vertical -
axis type current meters is presented in detail
Figure 9.---Hoff current meter.

S TECHNIQUES OF WATER -RESOURCES JNVESTIGATIONS
Figure IO.--Optical current meter.
by Smoot and -Novak (1968). A brief descrip-
tion of the checks of the condition of a meter
and the care and cleaning of it during daily
field use is preseaated in the next few paragraphs.
Before and after each discharge me:asnre-
rnent, examine the meter cups or vanes, pivot
and bearing, and shaft for damage, wear, or
faulty alinement.. Before using the meter, check
its balance if on a hanger, check the alinement
of the rotor axis with a hanger or wading rod,
and adjust the conductor wire to prevent inter-
ference with meter balance and rotor spin.
Clean and oil ureters daily when in use. If
measurements are made in water carrying
noticeable suspended sediment, clean the meter
immediately after each measurement. Surfaces
to be cleaned and oiled are the pivot bearing,
pentagear teeth and shaft, cylindrical shaft
bearing, and thrust bearing at the cap.
After orlrng, spin the rotor to make certain it
operates freely. If the rotor stops abruptly, find
(lie cause and correct the trouble before using
the metier. On notes for each measurement,
record the duration of spin. Obvious decrease
in spin duration indicates need for attention
to the bearings.
The pivot needs replacement more often than
ether meter parts. Examine the pivot after each
rnewsurement. Replace a fractured, rough, or
sworn pivot.
Beep the pivot and Divot bearing separated
e-xcept, during rneasurernents. Use the raisin=;
not if provided, or, for pygmy meters, replace.
the pivot by the brass plug.
Most minor repairs can be made in the field.
alepair attempts; however, should be limited
only to rninor damages. This is particularly
true of the rotor because minor dents in the
bucket wheel or caps can have a large influence
on the meter rating. Unless minor dents in the
cups can be straightened out to "like new"
condition. the entire rotor should be replaced
with a new one. Badly sprung yokes, bent yoke
stems, misalined bearings and tailpieces, should
be reconditioned in shops equipped with the
specialized facilities needed.
Racing of current meters
In order to determine the velocity of the
water from the revolutions of the rotor of a
current ureter, a relation must be established
between the angular velocity of the rotor and
the velocity of the water turning it. The estab-
lishment of this relation, known as "rating the
current meter," is done for the Geological
Survey by the National Bureau of Standards.
Because there is rigid control in the manu-
facturc of the small Price meter, virtually
identical meters are produced and, for all
practical purposes, their rating equations are
identical. Therefore there is no need to calibrate
the meters individually. Instead, a standard
rating is established by calibrating a large
number of meters that have been constructed
according to Survey specifications and this
rating is then supplied with each meter. Identi-
calness of meters is insured by supplying the
dies and fixtures for the construction of small
Price meters to the manufacturer who makes
the successful bid.
:Meters which have been rated by means of
rod suspension, and then by means of cable
suspension using Columbus -type weights and
hangers, have not shown significant differences
in rating. Therefore, no suspension coefficients
:are needed, and none should be used, if weights
and hangers are properly used.
The current -meter rating station operated by
the National Bureau of Standards in Washing-
tora, D.C., has a sheltered reinforced concrete
basin 400 feet long, fi feet wide, and 6 feet deep.
An electrically driven car rides on rails extend-
ing the length of the basin. The car carries the
current meter at a constant rate through the
still water in the basin. Although the rate of
travel can be accurately adjusted by means of
a hydraulic regulating gear, the average velocity

DISCHARGE MEASUREMENTS AT GAGING STATIONS
of the moving car is determined for each run by
making an independent measurement of the
distance it travels during the time that the
revolutions of the rotor are electrically counted.
A scale graduated in feet and tenths of a foot
is used for this purpose. Eight pairs of runs
are usually made for each current meter. A pair
of runs consists of two traverses of the basin, one
in each direction, at approximately the same
speed. Practical considerations usually limit the
ratings to velocities ranging from 0A fps to
about 15 fps, although the rating car can be
operated at lower speeds. Unless a special
request is made for a more extensive rating,
the lowest velocity used in the rating is about
0.2 fps, and the highest is about 8.0 fps.
For convenience in field use, the data from
the current -meter ratings are reproduced in
tables, a sample of which is shown in figure 11.
The velocities corresponding to a range of 3 to
350 revolutions of the rotor within a period of
40 to 70 seconds are listed in the tables. This
range in revolution and time has been found to
cover general field requirements. To provide the
necessary information for extending a table for
the few instances where extensions are required,
the equations of the rating table are shown
in the spaces provided in the heading. The
equation to the left of the figure in parentheses
(2.28 in fig. 11) is the equation for velocities
less than 2.28 fps and the equation to the right
is for velocities greater than 2.28 fps: The 2.28
fps is the velocity common to both equations.
It should be noted that the equations given
are those of the rating table, and not necessarily
those of the actual rating. If a rating table
already on file matches a rating within toler-
ances, that table is selected in preference to
preparing a new one. Those tolerances are listed
below.
Recoftaions of rotor Tolerance
Per second in Pereeni
0.4-------------------------------- 1.0
1.0 and above------ -- 5
Sounding equipment
Sounding (determination of depth) is com-
monly done mechanically, the equipment used
depending on the type of measurement being
made. Depth and position in the vertical are
measured by a rigid rod or by a sounding weight
3316 153 0 -69 3
suspended from a cable. The cable is controlled
either by a reel or by a handline. A sonic sounder
is also available, but it is usually used in con-
junction with a reel and a sounding weight.
Sounding equipment used by the Geological
Survey is described in the following categories:
wading rods, sounding weights, sounding reels,
handlines, and sonic sounder.
Wading rods
The two types of wading rods commonly used
are the top -setting rod and the round rod. The
top -setting rod is preferred because of the con-
venience in setting the meter at the proper depth
and because the hydrographer can keep his
hands dry. The round rod can be used in making
ice measurements as well as wading measure-
ments, and has the advantage that it can be
taken down to 1-foot lengths for storing and
transporting.
The top -setting wading rod has a %-inch
hexagonal main rod for measuring depth and a
%-inch diameter round rod for setting the posi-
tion of the current meter. (See fig. 12.)
The rod is placed in the stream so the base
plate rests on the streambed, and the depth of
water is read on the graduated main rod. When
the setting rod is adjusted to read the depth of
water, the meter is positioned automatically for
the 0.6-depth method. (See fig. 13 and p. 32.)
The 0.6-depth setting might also be described
as the 0.4-depth position up from the stream -
bed. When the depth of water is divided by 2
and this new value is set, the meter would be
at the 0.2-depth position up from the streambed.
When the depth of water is multiplied by 2 and
this value is set, the meter would be at the 0.8-
depth position up from the streambed. These
two positions represent the conventional 0.2-
and 0.8-depth positions in reverse. (See p. 32.)
The round wading rod consists of a base
plate, lower section, three or four intermediate
sections, sliding support, and a rod end (not
essential). (See fig. 14.) The parts are assembled
as shown in figure 15. The meter is mounted
on the sliding support and is set at the desired
position on the rod by sliding the support.
The round rod is also used in making ice
measurements. Intermediate sections of the
round rod are screwed together to make an ice
:rod of desired length. (See fig. 16.) The most
convenient length for an ice rod is about 3 feet

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10.97
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16.43
19.16
41
42
.191
.298
.405
.%6
.834
1.10
-.37
1.64
2.117
42
42
2.71
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4.31
5.37
8.04
10.71
11.37
16.04
18.71
42
43
•187
.2W
.396
.553
,815
1.08
1.34
1.60
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43
43
2.61;
3.17
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5.25
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7.85
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10.46
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15.67
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43
44
.183 .286 .388
,541 .797 i.CS
:.% 2.38
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44
.59 3.C9 4.LL
12.7y 15.31
1?.86
44
45
•186
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1.0'+
i.28
1.53
2.03
45
45
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7.51
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12.413
1t.97
17.46
45
46
.177
•275
,372
.519
.764
1.Oi
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1.50
1.99
46
46
2.47
2.96
3.94
4.91
7.34
9.78
12.21
11..65
17,08
46
47
.174
.269
•365
.509
.748
.987
1.23
1.47
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47
47
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3.95
4.81
7.19
9.57
11.95
I4.34
16.72
.171
.264
.358
.499
.'7338
_.2c
:.44
1.51
48
48
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.260
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49
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6.90
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13.75
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50
-165
.255
.345
.480
.705
.930
I.15
1.3E
i.8,
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60
2.28
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3.62
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.251
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.912
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E 51
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33
1.76
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15.12
92
53
.157
.242
.327
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53
64
.155
.238
.322
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t 1.07
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.439
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55
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55
56
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.231
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.622
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57
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68
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59
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.221
.297
.411
.602
.793
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59
59
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3.84
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59
60
.142
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.405
.592
.78C
.368
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1.53
60
60
1.91 2.26 1.03
3.77
5.64
7.51
9.37
11.24
13.11
60
61
.141
.214
.288
.399
'
.593
.76F
.952 i.11•
1.51
61
Sl
1.87
2.24
2.98
3.71
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7.38
1 9.22
11.06
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61
62
.139
.211
.284
.393
.574
.7%
.937
1.12
1.L8
6$
62
1.84
2,21
2.93
3.65
5.46
7.27
9•0f7
10.88
12.6g
62
63
.137
.209
.280
.387
.�6
.74L
.923
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63
63
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61
i4
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•733
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108
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64
64
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10.54
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64
65
.134
.203
.272
.376
.549
.-(22
.89"
1.o7
1.41
65
65
1-%
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5.21
6-93
8.66
10.38
12.10
65
66
.,32
.200
.269
.371
.541
.712
.882
1.05
1.39
66
67
66
67
1.73
1.71
2.08
2.0,L
2,76
2.71
3.45
?-38
5.13
5.05
0'.33
6.73
8.52
8.4D
10.22
to.o7
11.92
11.74
66
67
67
.131 .198 .265
.3<6 .534 .702
.870 1.04 1.37
66
.129
.195
.262
.361
,526
.692
.857
1.02
1.35
69
68
1.GP
2.02
2.68
3.55
4.98
6.63
8.28
9.92
11.57
68
69
.128
..193
•258
.356
•5'.5
.682
.845
1.01
i.33
69
69
1.66
1.99
2.64
3.29
4.91
6.53
8.16.
9.78
11.v0
fig
70
125
.191
.255
35=
•5><
-67.3
•83u
•504 1.32 1
70
70
1.64
1.96
2.60
3.24
4.t34
6.44
8.04
9.64
11.24
70
3
6
7
10
15
2D
25
30
40
50
60
80
100
150
200
250
$00
350
Figure I4.--Current-meter rating table.
P.

DISCHARGE MEASUREMENTS AT GAGING STATIONS
11
Figure 12.—Top-setting wading rod with meter attached,
longer than the maximum depth of water to be
found in a cross section. About 12 feet is the
maximum practical length for an lee rod;
depths greater than 10 feet are usually measured
with a sounding weight and reel. The base
plate, sliding support, and lower section are not
used on fin ice rod. lnstead a special lower see--
tion is screwed directly into the top of the
contact chamber of the vane ice meter. (See
fig. 16.) If it Prim meter is used under ice cover,
Sa'44IAy
= 3.77
ire et r h%
3.77x d.4
te.a d re by.(
4
Figure 13.—Closeup view of setting stale on handle of
top -setting rod.
another special lover section is used to hold the
meter by means of the hanger screw. (See fig.
17.) All lower sections for ice rods now are
made so that the center of the vanes or cups is
at the O-foot point on the rod.
Sounding weights and accessories
If a strearn is too deep or too swift to wade,
the current meter is suspended in the water
from a boat, bridge, or cableway. A sounding
weight is suspended below the current meter
to keep it stationary in the water. The weight
also prevents damage to the meter when the
assembly is lowered to the streambed.
The sounding weights now used are the
Columbus weights, commonly called the C
type. (See fig. IS.) The weights are streamlined
to offer minimum resistance to flowing water.
Each weight has a vertical slot and a drilled
horizontal hole to accommodate a weight hanger
and securing pin.
The weight hanger is attached to the end of
the sounding line by a connector. The current

12 TECHNIQUES OF WATER -RESOURCES INVESTIGATIONS
(D
Figure 14. —Pa rts For round wading rod.
ureter is attached beneath the connector, and
the sounding weight is attached to the lower
end of the hanger.
There tire three types of weight hangers (fig.
19):
1. The Columbus or C type, by % by 12
inches (for weights up to 150 pounds).
2. )leavy weight, % by "; by 18 inches (for
200- and 300-pound weights).
3. Heavy weight, s by 1;� by 18 inches (for
200- and 300-pound sounding weights
which have the slots properly extended to
accommodate a 1j4-in. hanger).
The Coliinnbus hanger has three holes in it in
order to properly position the meter. The
hanger screw of the current -meter yoke is
placed through the bottoin hole to support the
meter whets a. :30-pound sounding weight is
useti. The center of the ineter cups is then 0.5
foot above the bottom of the weight. This
arr€ingement is designated as 30 C .5, which
ttieans that a 30-pound Columbus weight is,
being, used and the center of the meter e€ips is
Figure 15.—Round wading rod with meter attached.
0.5 foot above the bottom of the weight. The
hanger screw goes through the middle hole
when 15- or 50-pound weights are used. The
designations for these arrangements are 15 C .5
and 50 C .55. The hanger screw goes through the
upper hoie when 50-, 75-, 100-, and 150-pound
weights are used. The designations for these
arrangements are 50 C .9, 75 C 1.0, 100 C 1.0,
a-t1d 150 C 1.0. Each of the two heavy -weight
hangers has only one hole for the hanger screw
of the meter. The designations for these
arrangements are 200 C 1.5 and 300 C 1.5.

DISCHARGE MFASUREMEA"rS AT GAGING STATIONS
13
Figure 16.—Lower section of ice rod for use with vane ice
meter.
Weight -hanger pins of various lengths are
avriilable for attaching the sounding weight to
the weight hanger. (See fig. 19.) The stainless
steel pins are threaded on one end to screw into
the weight hanger and slotted (in the other.
Sounding reels
A sounding reel has a drum for winding
the sounding cable, a crank and ratchet as-
sern•bl;y for raising and lowering the weight or
holding it in any desired position, and a depth
indicator. 'Fable 1 contains detailed informa-
tion on each of the five reels most commonly
used.
'.'I he A -pack reel is light, compact, and ideal
for use at cableway sites a considerable distance
from the highway. (See fig. 20.) It can also
be used on cranes, bridge boards, and boat
booms.
Figure 17. —Lower section of ice rod for use with Price
meter.
Figure 18 —15-, 30-, 50•, 75-, and 100-pound Columbus
sounding weights.
The Canfield reel is also compact with uses
similar to that of the A -pack reel. (See fig. 21.)
The A-55 reel is for general purpose use
with the lighter sounding weights.
The B-56 reel (a major modification of the
B-50 reel) can handle all but the heaviest
sounding weights and has the advantage that
it can be used with a handcrank or power
equipment. (See fig. 22.)

14 TECHNIQUES OF WATER -RESOURCES INVESTIGATIONS
i,-
is
C,
lY�
Figure 19 —Sounding-weight hangers and hanger pins.
The E--53 reel is the largest reel commonly
used for current -meter measurements. This reel.
will handle the heaviest sounding weights and
is designed exclusively for use with power
equipment. It has a handerank for emergency
use. (See fig. 23.)
Sounding cable
Ellsworth reverse -lay two -conductor cable is
normally used on all sounding reels except the
Figure 20 —A-pack reel.
single -conductor Canfield reel which uses gal-
vardzed steel aircraft cord. It is important that
the appropriate size cable -laying sheave be
used on the reels.
Connectors
A connector is used to join the end of the
reel cable to the sounding -weight hanger. The
three types of connectors generally used are
types B, Au, and pressed sleeve. (See fig. 24.)
The type-B connector is used with A-55, B-56 ,
and E-53 reels. The Au connector is used with
the A -pack and Canfield reels although the
pressed -sleeve connector can be used on, these
reels. The pressed -sleeve connector is used
mainly on handlines. (See p. 15.)
Depth indicators
A computing depth indicator is used on the
A--55, B--56, and E-53 reels. (See fig. 25.) The
Table 1.—Sounding reel data
r7rRm
Maximum
Cable
circum-
C:al71e
shoe weight
Type
rtcc•;
$011I1fJ1Fkg cable
diameter
rerenec
m acity
recom-
Depth indicator
Brake
operation
(inches}
(feet)
[feet]
mended
(pounds)
A -pack__
F11sworth
0.084
1
45
50
Counter --------
No ----
Hand.
Canfield- .._
_-- Single
062ri
1
4.5
50
-----do ---------
No----
Do.
conductor.]
----- -----
Eliswortll---------
084
1
95
50
Self
`o----
Do.
10
80
too
computing.
1;-56------
---- do --- ._... _--
to
1��
144
t50
----- do---------
Yes----
Hand or
125
115
200
power.
-do-------.---
to
2
206
150
----- do---------
Yes----
Power.
. 125
165
300
3 Some Canfield nwls ]lave been converted to rloubin-cnnductnr cable bat rnmxt or them art still used as single -conductor reels.

DISCHARGE _MEASUREMENTS AT GAGING: STATIONS
15
Figure 41—Canfteld reel. Photograph by permission of Leupold and Stevens Instruments, Inc.
stainless -steel indicator is less than 3 inches in
diameter and has nylon bushings which do not
require oil. The inrain dial is graduated in feet
and tenths of a foot from ii to 10 feet. The
depth is Indicated by :a pointer. Terns of feet
:are read on It numbered inner dial through an
aperture near the top of the main dial.
The main dial has a graduated spiral to indi--
efate directly the 0-8-depth position (see P.
32) for depths up to 30 feet.
The A -pack and Canfield reels are equipped
n•ith counters for indicating depths. (:gee figs.
20 and 21.}
Power unit
A power unit is available for the B -56 and
E-53 reels to raise and lower the sounding
iveij,, aA and meter. (See fig. 26.) The power
unit can be used with fi-, 12-, 18-, or 24-volt
batteries.
HandIines
Handlines are devices used for making dis-
charge measurements from bridges using a 15-
or 30-pound sounding weight. (See fig. 27.)
The advantages of the handline are that it is
easily set nap, that it eliminates the use of a
sounding reel and supporting equipment, and
that it reduces the difficulty in making measure-
ments from bridges which have interfering
members. The disadvantages of the handline
are that there is It greater possibility of making
errors in determining depth because of slippage
of the handline or measuring scale or tape and
that it requires more physical exertion especi-
ally in deep streams. Handlines can be used.

1.6 TECHNIQUES OF WATER -RESOURCES TWESTIGATIONS
1W
Figure 23—E-53 reel.
Figure 22.—E-56 reel.
from cable cars, but this is not recommended
because of the disadvantages mentioned above.
Two types of handline reels are the Lee -Au
ftild the 'Mogan. (See fig. 28.)
1111si orth cable Is recommended for handlines
be,(iaiise nl its flexibility and durability.
The pressed -sleeve connector or the Au con-
nector are used on handlines because they are
lighter in weight than the type-B connector, yet
strong enaugh for the sounding weights used
with. handlines.
Figure 29 shows a handline in use from a
bridge.
Sonic sounder
A commercial, compact, portable sonic sound-
er has been adapted to measure stream depth.
(See figs. ,30, 31, and 32.)
The sounder is powered by either a 6- or 12-
volt storage battery and will operate continu-
ously for I0 hours on a single battery charge.
Three recording speeds are .available, 36, 9o, or
180 inches per hour. Four operating ranges,
0-60, 60-120, 120--180, and 180-240 feet allow
intervals of 60 feet of depth. The sounder is
portable, weighing only 46 pounds. The depth

DISCHARGE MEASUREMENTS AT GAGING STATIONS
Figure 44.—Connectors: top IeFt, Au connector with plastic
sheave; top right, Au connector with metal sheave;
middle, type-B connector; and bottom, pressed -sleeve
connector.
Ff.
i 4 `v t
Figure 45 --Computing depth indicator.
recorded is that to the streambed. The trans-
ducer has a narrow bear, angle of V° which
minimizes errors on inclined streambeds and
allows the hydrogr•apher to work close to piers
or other obstructions.
,'—Nl ': , 0 69 -!
17
Measurements can be made with this equip-
ment without lowering the meter and weight
to the streambed. As soon as the weight is in
the water, the depth will be recorded. The
meter can then be set at the 0.2 depth (see 1).
31) or just below the water surface (see p. 37)
,-here a velocity reading is obtained. Then a
coefficient is applied to convert measured
velocity to the mean in the vertical. (See
p. 37.)
Temperature change affects the sound propa-
gation velocity, but this error is limited to
about f 2 percent in fresh water. This error
can be eliminated completely by adjusting the
sounder to read correctly at a particular average
depth determined by other means.
Width -measuring equipment
The distance to any point in a cross section
is measured from an initial point on the bank.
Cableways and bridges used regularly for
making discharge measurements are commonly
marked at 2-, 5-, 10-, or 20-foot intervals by
paint marks. Distance between markings is
estimated, or measured with a rule or pocket
tape.
For measurements made by wading, from
boats, or from unmarked bridges, steel or
metallic tapes or tag lines are used.
Tag lines are made of %2-, �s�-, %� or 3s-inch
diameter galvanized steel aircraft cord with
solder beads at measured intervals to indicate
distances. The standard arrangement of solder
beads or tags is:
lversvd
Number oflags (feel) Arraatgemexrl or sfction
1--------------- 2 0-50
1__________- 5 50-150
1--------------- 10 150 to end
2----------------------- 0, 10, 20, 30, 40, 50,
150, 250, 350, 450
3----------------------- 100, 200, 300,400, 500
The standard lengths of tag line are 300, 400,
and 500 feet, but other sizes are available.
Three types of tag -line reels in use (fig. 33)
are Lee -Au, Pakron, and Columbus type A.
Larger reels designed particularly for use with
boats are described on page 24.
It is practically impossible to siring a tag line
for discharge measurements from a boat when
the width of the stream is greater than 2,500
feet. The methods used to determine width at
such places are described on page 44.

l5 TI CII14IQtit,:S OF WATER -RESOURCES I_N'VESTIGATION6
Figure 26,—Power unit for sounding reel.
Equipment assemblies
Special equipment is necessary for each type:
of current -meter measurement. The meters,
weights, and reels used have already been
described. The additional equipment needed is
described in this section.
The special equipment assemblies have been
divided into fire basic groups: cableway, bridge,
boat, ire, and velocity-a.zimutlr-deptli-assembly
(VADA) equipment.
Cableway equipment
The cableway provides a tract: for the opera-
tion of €z cable ear from which the hydrog-
rapher makes a current -meter measurement.
('able cars also support the sounding reel and
otber necessary equipment. Both sitdown and
standup types of cable cars are used in stream
r;a.ging. (See figs.:34-36.} Pierce (1947) describes
plans for both types. -Normally, sitdown can,
are used for cableway spans less than 400 feet
and where lighter sounding weights are used.
The standup car is used on the longer spans and
where heavy sounding weights are needed.
The ear.3 are moved from one point to another
on the cableway by means of cable -car pullers.
(See fig. 37.) The standard car puller is a cast
aluminum Niece With a snub attached. The
snub, usually four -ply belting, is placed be-
tween one of the car sheaves and the cable to
prevent movement of the car along the cable.
A second --type puller is used when a car is
equipped with a follower brake. (See fig. 37.)
A third type, the Colorado River cable -car
puller, is the same in principle as the puller
used on cars equipped with a follower brake.
Power -operated cable cars are available for
extremely long spans or other special situations.
(See figs, 38-39.)

DJSCHAR(CF MEIAS"HI;MENTS AT GAGING STATIONS
19
ov
Figure 27—Hondiine.
Figure 28—Handline reels, Lee -Au (top) and Morgan
(bottom).
Sitdowir cable cars Dave a variety of mean,
of supporting the sounding reel. A -pack and
(..'.infield reels are designed to clamp on the side
of the car, (See fig. 40.) Permanent or portable
reel seats are attached to the cable cars for
Ittrger reels. (See figs. 34 and 36.)
Figure 29.—Handline in use From a bridge.
Figure 30 —Sonic-sounding recorder.

Z[l
TECH_NTQT ES DID WATT Fi--RFSOT?HCES INVESTIGATIONS
Figure 31 —Sounding weight with compass and sonic transducer ready for assembly.
Standup cable cars have reel seats attached
t❑ the structural members of the car. (See fig.
35.1 A sheave attached to the structural mere-•
Lers carries the sounding line so that the sound-
ing weight and current meter will clear the
bottom of the car. Power reels can also be used
011. standup cable ears.
Carrier cables are being used on deep, narrow
streams for measuriag, as well as for sediment
s litplittg. They are used in areas where it is
inipossible to wade, where no bridges are avail -
Able, and where it, has been impracti(, al to build
is coanplete cableway. The assembly is operated
from the shore.
Bridge equipment
When one measures froin a bridge, the meter
d.11d sounding weight cart be supported by a
handline or by :a sounding reel mounted on as
crane or bridge borard. The hardline has been
described on page I5i.
Two tnws of hula] -operated portable cranes
are the type A (see figs. 4}, 42) for weights tip
to 100 pounds, and the typo E for heavier
weights.
All cranes are designed so that the super-
structure can be tilted forward over the bridge
rail far enough for the meter and weight to
clear most rails. Where bridge members are
found along the bridge, the weight :and meter
can be brought tip, and the superstructure
can be tilted back to pass by the obstruction.
(See fig. 41.)
Cast-iron counterweights weighing 60 pounds
each are used with four-wheel base cranes.
(See fig. 12.) The number of such weights
needed depends upon the size of sounding
weight behig supported, the depth and velocity
of the stream, and the amount of debris being
carried by the stream.
A protractor is used on cranes to measure the
angle the sounding lime makes with the vertical
when the weight and meter are dragged down-
stream by the water. The protractor is a
graduated circle clamped to an aluminum

DISCHARGE _-MMEASUREMENTS AT GAGI-rG STATIONS 21
Figure 32 --Sonic measuring assembly,
Figure 33.—Tag-line reels: top I0t, Pakron; top right,
Lec-Au with removable 66 in front; and bottom, Co-
lurrbus type A,
Figure 34—Sitdown cable car,

TEC TLNIQLA OF AVA`1'ER-RE OURCES INVESTIGATIONS
Figure 35.—Standup cable car
Figure: 36.—Portgble reel seat on sitdown-type cable car.
Mole lags on sounding cable.
Figure 38 —Battery-powered cable car.

DISCHARGE -NIFASirREMENTS AT GAGING STATIONS
23
Figure 39.—Gasoline-powered cable car.
plate. A plastic tube partly filled with colored
ant.if:•ee-re fitted in as groove between the grad-
tiated circle: and the plate is the protractor
index. A SttianleSS-Steel rod is attached to the
lower, end of the plate to ride iagaainst the doL4n-
streain side of the sounding cable. The pro-
t i-,,wt or st ill meanu m vertical tangles froin -- 25°
to , 90D. The cranes shown in figures 41, 42
itre erluippPd with protractors at the meter end
of the boom.
Bridge boards inay be used with au A -pack
nr A -ri i snuaadirig reel and weights lip to 50
pounds. A bi-idge boitc•d is usually it plank about
6-8 feet lung with it sheave tit one end over
which the nieter cable passes and it reel seat
near the, other end. The iroiart.l is placed on the
bi-idgE, mil so that the farce exerted by tlae
sounding weight: suspended from the reel cable
is counterb.tlanced by the weight of the sound-
ing reel. (See fig. 43.) The bridge board inay be
hinged nbar the middle to let one end be placed
on the sidewalk or roadway.
Many special arrangements for measuring
from bridges have been devised to suit a par-
ticular purpose. Truck -mounted cranes are
often used for measuring from bridges over
larger- rivers (see fig. 44). Monorail stream -
gaging cars have been developed for large
rivers. The car is suspended from the sub-
structure of bridges by means of 1-beams. The
czar is attached to the I-beam tracks by trolleys
and is propelled by a forklift motor having a
,, heel in corztaart with the bottom of the beam.
The drive mecha.nisan and sounding equipment

24 TECHNIQUES OF WATER -RESOURCES INVESTIGATIONS
3:-14
:.:
Figure 40.-5itdown cable car with Canfield reel clamped
to side of car.
.are powered by a 430-:arrapere-ho€Ii, 450-pound
12-Volt battery.
Boat equipment
Measurements made from boats require
special equipment not used for other types of
measurements.
Extra large tag -line reels are used on wide
-t•s eazns. Thi ee different tag -line reels are
ar%ailable for boat measurements.
1. A. heavy-duty, horizontal -axis reel without
a brake and with a capacity of 2,000 feet
of ;'s-inch diameter cable. (See fig. 45.)
2. A. heavy-duty, horizontal -axis reel with a
brake and with a capacity of 3,000 feet
of s-inch diameter cable. (See fig. 46.)
3. A vertical -axis reel without a brake and with
a capacity of 800 feet of %-inch diameter
cxtble. (3ee fig. 47.)
A utility line consisting of 30 feet of '112-inch
diameter cable with a harness snap at one end
and a pelican hook at the other is connected to
the free end of the boat tag line :and fastened
around a tree or post, thereby preventing
damage to the tag line. After the tag line is
strung across the stream, the reel is usually
bolted to a plank and chained to a tree. The tag
line is stationed at appropriate, intervals.
Special equipment is necessary to suspend
the ;peter from the boat when the depths are
such that rod suspension cannot be used.
A crosspiece reaching across the boat is clamped
to the sides of the boat and a boom attached to
the center of the crosspiece extends out over
the. bow. (See fig. 48.) 'rhe crosspiece is equipped
with a guide sheave and clamp arrangement at
each end to attach the boat to the tag line and
make it possible to slide the boat along the tag
line from one station to the next. A small rope
can be attached to these clamps so that in an
emergency a tug on the rope will release the
boat from the tag line. The crosspiece also has
a clamp that prevents lateral movement of the
boat along the tag line when readings are being
made. The boom consists of two structural
aluminum channels, one telescoped within the
other to permit adjustments in length. The
boom is equipped with a reel plate on one end
and a sheave over which the meter cable passes
on the other. The sheave end of the boom is
designed so that by adding a cable clip to the
sounding cable, a short distance above the
connector, the sheave end of the boom can be
retracted when the meter is to be raised out of
the water. The raised meter is easy to clean and
is in a convenient position when not being
operated.
All sounding reels fit the boat boom except
the A -pack and the Canfield, which can be
made to fit by drilling additional holes in the
reel plate on the boom.
In addition to the equipment already men-
tioned, the following items are needed when
making boat measurements:
1. A stable boat big enough to support the
hydrographers and equipment.
2. A motor that can move the boat with ease
against the maximum current in the
stream.
3. A pair of oars for standby use.

DISCHARGE MEASUREMENTS AT GAGRTG STATIONS 25
Fic;vre 41 —Type-A crane with 3-wheel base. During soundings and velocity observations the crane is tilted against the
bridge rail. An A-55 reei is mounted on file crane.

2 1 6 TECITNTIQUES OF WATER -RESOURCE.; INVESTIGATIONS
Figure 42.—Type-A crane with 4-wheel base with boom in retracted position, A B-56 Teel is mounted on crane. Note fluid
protractor on outer end of boom,

DISCHARGE ,lit?ASITRETMENTS AT GAGING STATIONS
27
figure 43.-Sridge board in use.
4. A life preserver for each hydrographer.
ri. A bailing device.
Figure 49 shows the equipment assembled
in az boat.
Ice- equipment
Current -meter measurements under ice cover
require special equipment for cutting hales in
the ice through which to suspend the meter.
Cutting holes through the ice on streams
to make discharge measurements has long been
a laborious and time-consuming job. The
development: of power ice drills, however, has
eliminated many of the difficulties and has
reduced considerably the time required to cut:
the holes.
Doles are often cut with it commercial ice
drill that cuts a 0-inch-diameter hole. (See
fig. 50.) The drill weighs about 30 pounds. € nd
under good conditions will cut through 2 feet
of ice in about a minute.
Where it is unpractical to use the ice drill,
ice chisels are used to cut the holes. Ice chisels
used are usually 4 or 4Y2 feet tong and weigh
about 12 pounds. The ice chisel 19 used when
first crossing an ice -covered stream to deter-
mine whether the ice is strong enough to support
the hydrographer. If a solid blow of the chisel
blade does not penetrate the ice, it is safe to
walk on, providing the ice is in contact with
the water.
Same hydrographers supplement the ice
chisel with a Swedish ice auger. The cutting
blade of this auger is a spadelike tool of hard-
ened steel which cuts a hole 6-8 inches in
diameter, by turning a bracelike arrangement
on top of the shaft.
When holes in the ice are cut, the wafer is
usually under pressure owing to the weight of
the ice, and it conies up in the hole. In order to
determine the effective depth of the stream
(see p. 42), ice -measuring sticks are used to
measure the distance from the water surface
to the bottoni of the ice. This is done with a,
liar about 4 feet long, made of strap steel or
wood, graduated in feet and tenths of a Boot
and leaving an L-shaped projection at the lower
end. The horizontal part of the L is held on the
underside of the ice and the depth to that point
is read at the water surface on the graduated
part of the stick. The horizontal part of the L
is at least 4 inches long so that it may extend
beyond any irregularities on the underside of
the ice.
When the total depth of water under ice
cover is greater than 10 or 12 feet, a sounding
reel or hardline is usually used. The sounding
reel is mounted on a collapsible support set
on runners. (See fig. 51.)
A special ice -weight assembly is used for
sounding under ice because a rep
eilar sounding
weight will not fit through the hole cut by the
ice drill. (See fig. 51.) The weights and meter
are placed in it framework that will fit through
the drilled hole.
Velocity -azimuth -de pth-assembiy
The velocity-a.zimiith-deptli-assembly, com-
monly called tiADA, combines a sonic sounder
with a remote -indicating compass and Price
current meter to record depth, indicate the
direction of flow, and permit observations of
velocity at any point.
In figure 52, the azimuth -indicating unit is
shown mounted on the four-wheel crane.
Incorporated within the remote -indicator box

25 TECHtiTIauES OF WATER -RESOURCES 1NVESTIGA:i'IOINB
Figure 44 —Truck-mounted crane used on the Mississippi River.

DISCHARGE MEASUREISENTS AT GAGING STATIONS 29
Figure 45--HorixontaI-axis boat tag-Iine reel without a brake.

30 TECHNIQUES OF WA'ri•.R-RESOURCES INVESTIGATIONS
Figure 46—Horizontal-axis boat fag -line reel wifll a brake.
is the battery for the current-ineter circuit, the 1 fications of this equipment are timers, counting
headphone ,jacks, and the two -conductor jack equipment, and waders and boots.
fcr the sonic somider. A switch allows the T ri order to determine the velocity at it point
rernote-indicating unit to be used separately with a. Current meter, it is necessary to count.
or in conjunction i ith the sonic sounder. The the revolutions of the rotor in a ineasured in-
sc:riir sounder is inentioned on pace fti. This terval of time, usctally 40-70 seconds. The
asembly is usefal in tidal Investigations and 1 velocity is then obtained from the meter -rating
other special studies as well as at regular table. (See fig. 11-) The time interval is measured
g; ,.ging stations, where it is desirable to deter- to the nearest ,-,ccond with a stol. w0ch. (See
Enine the direction of flow beneath the surface fig. 53.)
wheu it may differ from that at the si.rrface. The revolutions of the meter rotor during the
Miscellaneous equipment observation of velocity are counted by an elec-
Several miscellaneous items which have not I trio circrtit that is closed each time the contact.
bfen described are necessary when current- , wire touches the single or penta eccentric of the
Ineter Ineasurernents are Iriade. Three c•.lassi- eurrent. meter. A b:attery ,nid headphone are.

DISCHARGE MEASI:I{i:_MENTS AT GAGING STATIONS
31
Figure 47.—Vertical,uxis boat tag -line reel. When in use
the axis of the reel is vertical.
parts of the electrical circuit, and a click is
heard in the headphone each time the contact
,vire touches. (See fig. 54.) In many cases, Com-
pazct., coinfortable hearing -aid phones have been
adapted to replace headphones.
A magneticswit•ch contact, chamber has been
developed to replace the contact -wire chamber.
(See p. 6.) An automatic electric counter has
been developed for use with the magnetic con-
t:a.ct chamber. (See fig. 54.) The counter can
register up to 999 and has a reset button. A
metal clip is attached to the counter so that it
may be easily carried on the belt. The electric
counter should not be used with the contact -Hire
charrrber because at low velocities the contact.,
Nvire � ipes ircegularly thereby sending several
signals to the counter for each revolution.
Waders or boots are needed when wa.dim,
ineasurements are made. Waders should[ be
loose f t.ting even after allowa.nee has been irzade
for }wavy winter clothing. Ice creepers strapped
on the shoe of boots or evaders should be used
on steep or icy stream banks and on rocky or
,iuooth and slippery st:rea.mbeds. (See fig. 55.)
Measurement of velocity
The current meter measures velocity at: a
point. The method of Inak-inn. discharge meas-
urement•s at a cross section requires determina-
tion of the mean velocity in each of the selected
verticals. The mean velocity in a vertical is
obtained from velocity observations at many
points in that vertical. The mean can be approx-
imated by making a few velocity observations
and using a knolvn relation between those
velocities and the mean in the vertical. The
various methods of measuring velocity are:
I. Vertical -velocity curve.
2. Two -point.
3. Six -tenths -depth.
4. Two -tenths -depth.
5. Three-point.
6. Subsurface.
Vertical -velocity curve method
In the vertical -velocity curve method a
series of velocity observations at points well
distributed between the water surface and the
streambed are made at each of the verticals.
If there is considerable curvature in the lower
part of the vertical -velocity curve, it as advis-
able to space the observations more closely in
that part of the depth. Normally, the observa-
tions are taken at a.X-depth increments be-
tween 9.1 and 0.9 of the depth. Observations
are always taken at 0.2, 0.6, and 0.8 of the
depth so that the results obtained by the
vertical-vel(wity curve method may be com-
pared with the commonly used methods of
velocity observation. Observations are made
at least 0.5 foot from the water surface and
from the streambed with the Price AA meter
or the vane meter and are made at least 0.3
foot from these boundaries with the Price
pygmy teeter.
The vertical -velocity curve for each vertical
is based on observed velocities plotted against
depth. (See fig. 56.) In order that vertical -
velocity curves at different verticals may be
readily compared, it is customary to plot
depth-; as proportional parts of the total depth.
The mean velocity in the vertical is obtained
by measuring the area between the curve and
the ordinate axis with a planimeter, or by
other means, and dividing the area by the
length of the, ordinate axis.
The vertical -velocity curve method is val-
unble in determining coefficients for applica-
tion to the results obtained by outer methods,

22
TECHNIQUES OF WATER -RESOURCES INVESTIGATIONS
Figure 48.—Boom and crosspiece for use on boats. A, retraclabie end of boom; S, guide sheave and clamp For attaching to
tag line; C, clamp to prevent movement of the boat along the tag line; 0, plate to accommodate tee]; E, rope to release
clamps (6) to Free boat From tag line; and F, clamps to attach crosspiece to boat,
but is not generally adapted to routine dis-
charge ineamtrements because of the extra
time required to colleat field data and to com-
pute tine mean velocity.
Two -point method
In the two -point method of measuring
velocities, observations are made in each
1ertical at 0.2 and 0.8 of the depth below the
surface. The average of these two observations
is taken as the mean velocity in the vertical.
'Phis method. is based on many studies of actual
observation and on mathematical theory. Ex-
perience has shown that this method gives
-norn consistent and accurate result,; than any
of the other methods except the vertical -
velocity curve method. (See p. 31.) The
two -point method is the one generally used by
the Geological Survey.
The two -point method is not used at depths
less than 2.5 feet because the current meter
would be too close to the water surface and to
the streambed to give dependable results.
Six -tenths -depth method
In the 0.6-depth method, an observation of
velocity made at 0.6 of the depth below the
surface in the vertical is used as the mean
velocity in the vertical. Actual observation and
mathematical theory has shown that the 0.6-

DISCHARGE MEASUREMENTS AT GAGING STATIONS
33
Figure 49—Meawring equipment set up in a boat.
depth method gives reliable results and is used
by the Geological Survey under the following
conditions:
1. Whenever the depth is between 0.3 foot and
and 2.5) feet.
2. IV -lien large €Lniounts of slush ice or debris
make it impossible to observe the velocity
accurately at the 0.2 depth. This condition
prevents the use of the two -point niethod.
:3. When the meter is placed a distance above
the sounding weight which in Ekes it
impossible to place the meter at the 0.8
depth. 'Phis circumstance prevents the use
of the two -point method.
4. When the stage in a stream is clianging
rapidly and a measurement must be made
quickly.
Two -tenths -depth method
The two -tenths -depth method consists of
observing the velocity at 0.2 of the depth below
the surface and applying a coefficient to this
observed velocity to obtain the mean in the
vertical. It is usP.d mainly during tntms of high
Figure 50.--Gasoline-powered ice drill. Photograph by
permission of General Equipment Co.
water when the velocities are great, making it
impossible to obtain soundings or to place the
meter at the O.S or the 0.6 depth.
A standard cross section or a general knowl-
edge of the cross section at €r, site is used to
Compute the 0.2 depth when it is impossible to
obtain soundings. A sizeable error in an as-
sumed 0.2 depth is not critical because the slope
of the vertical -velocity carve at this point is
usually nearly vertical. (See fig. 56.) The 0.2
depth is also used in conjunction with the sonic
sounder for flood measurements. (See p. lfi.)
The two -point method and the 0.6-depth
method are preferred over the 0.2-depth method
because of their greater accuracy.
The ineasarement is normally cornputed by
using the 0.2-depth velocity observations with-
out coefficients as though each were a mean in

34 TECHNIQUE'S OF WATER -RESOURCES INVESTIGATIONS
. ........
..
-- --------
t�4
So-
x, J��l
;&2
V.
Figure 51 —Collap6ble reel support and
ice -weight assembly,

DISCfIARGE -MEASUREMENTS AT GAGING STATIONS
35
MA
+'L4iF
wnsw
V. 40
Figure 52.---Veiocity-azimuth-depth assembly.
.. AV
'
55.: w 5
5 -y1
i
c - 20
z f 35 25 y;a
30 mod,
`:X,
Figure 53.—Stopwatch,
Figure 54r—Automat1c counter (ieff) and headphone (right).
the vertical. The approximate discharge thus
obtained divided by the area of the measuring
section gives the weighted mean value of the
0.2-depth velocity. Studies of many measure-
ments made by the two -point method show
that for a. ;riven measuring section the relation

36
TEC= IQUES OF WATER-HFSOURCES INVESTIGATIONS
w 4 £ -
Figure 55.—Ice creepers for boots and waders.
0
1f,
LLj
U 2
w
7 J
N Q
{t �
w 0 4❑
¢ w
w
OCD
m W 60
00
Z rr
as
N_ z
0
80
tool_
0.20
between the mean 0.2-depth velocity and the
true mean velocity either remains constant or
varies uniformly with stage. In either circum-
stance, this relation may be determined for a
particular 0.2-depth measurement by recom-
puting measurements made at the site by the
two -point method using only the 0.2-depth
velocity observation as the mean in the vertical.
The plotting of the true mean velocity versus
the mean 0.2-depth velocity for each measure-
ment will give a velocity -relation curve for use
in adjusting the mean velocity for measurements
made by the 0.2-depth method.
If at a site enough measurements have not
been made by the two -point method to establish
a velocity --relation curve, vertical -velocity
curves are needed to establish a relationship
between the mean velocity and the 0.2-depth
WATER SURFACE
0.40 0-50 0-80 1-00
VELOCITY, IN FEET PER SECOND
Figure 56.—Typical vetficai-velocity curve.
1.20

DISCHARGE MEASUREMENTS AT GAGING STATIONS
37
velocity, The usual coefficient to adjust the 0.2-
depth velocity to the mean velocity is about
0,88.
Three-point method
The three-point method consists of observing
the velocity at 0.2, 0.6, and 0.8 of the depth,
thereby combining the two -point and 0.6-depth
methods. The mean velocity is computed by
averaging the 0.2- and 0.8-depth observations
and then averaging the result with the 0.6-depth
observation. When more weight to the 0.2- and
0.8-depth observations is desired, the arith-
metical mean of the three observations may be
used. The first procedure is usually followed,
however.
The three-point method is used when the
velocities in the vertical are abnormally dis-
tributed. It is also used when the 0.8-depth
observation is made where the velocity is
seriously affected by friction or by turbulance
produced by the streambed or an obstruction in
the stream. The depths must be greater than
2.5 feet before this method can be used.
Subsurface method
The subsurface method consists of observing
the velocity at some distance below the water
surface. This distance should be at least 2 feet
and preferably more for deep swift streams to
avoid the effect of surface disturbances.
The subsurface method is used when it is
impossible to obtain soundings and the depths
cannot be estimated with enough reliability
to even approximate a 0.2-depth setting.
Coefficients are necessary to convert the
velocities observed by the subsurface method to
the mean velocity in the vertical. Vertical -
velocity curves obtained at the particular site
are used to compute these coefficients. The
coefficients are generally difficult to determine
reliably because they may vary with stage,
depth, and position in the measuring cross
section.
Current -meter measurement procedure
The first step in making a current -meter
measurement is to select a reach of stream
containing the following characteristics:
1. A straight reach with the threads of velocity
parallel to each other.
2. Stable streambed free of large rocks, weeds,
and protruding obstructions such as piers,
which would create turbulence.
3. A flat streambed profile to eliminate vertical
components of velocity.
It is usually not possible to satisfy all of these
conditions. Select the best possible reach using
these criteria and then select a cross section.
After the cross section has been selected,
determine the width of the stream. String a tag
line or measuring tape for measurements made
by wading, from a boat, from ice cover, or
from an unmarked bridge. String the line at
right angles to the direction of flow to avoid
horizontal angles in the cross section. For cable-
way or bridge measurements, use the gradua-
tions painted on the cable or bridge rail as de-
scribed on page 17. Next determine the spacing
of the verticals, generally using about 25 to 30
partial sections. With a smooth cross section
and good velocity distribution, fewer sections
may be used. Space the partial sections so that
no partial section has more than 10 percent of
the total discharge in it. The ideal measure-
ment is one in which no partial section has more
than 5 percent of the total discharge in it, but
this is very seldom accomplished when 25 partial
sections are used. The discharge measurement "
shown in figure 2 had 6.2 percent of the total
discharge in the partial section with the greatest
discharge. Equal widths of partial sections
across the entire cross section are not recom-
mended unless the discharge is well distributed.
Make the width of the partial sections less as
depths and velocities become greater. Usually
an approximate discharge can be obtained from
the stage -discharge curve. Space the verticals
so the discharge in each vertical is about 5 per-
cent of tha d tscharga frem the ra. ing curve.
After the cross section has been selected and
the stationing determined, assemble the appro-
priate equipment for the current -meter meas-
urement and prepare the measurement note
sheets to record the observations. (See fig. 2.)
For each discharge measurement record the
following information:
1. Name of stream and location to correctly
identify the established gaging station; or
name of stream and exact location of site
for a miscellaneous measurement.

3$ TECHNIQUES OF WATER -RESOURCES INVESTIGATION15
2. Date, party, type of meter suspension, and
meter number.
3. Time measurement was started using mili-
tary time.
4. Bank of stream that was the starting point.
5. Control conditions.
S. Gage heights and corresponding times.
7. Water temperature.
S. Other pertinent information regarding the
accuracy of the discharge measurement
and conditions which might affect the
stage -discharge relation.
Identify the stream bank by either LEVY or
R.EW (left edge of water or right edge of water,
respectively, when facing downstream). Re-
cord the time in the notes periodically, during
the course of the measurement. This time usu-
alzy should be synchronized with the time of
pvnch on the digital recorder. (See fig. 2.) This
is important because if there is any appreciable
change in stage during the measurement, the
time is needed to determine the mean gage
height for the measurement. (See p. 53.) When
the measurement is completed, record the time
and the bank of the stream where the section
ends.
After the equipment and the note sheet have
been readied, begin the measurement. Indicate
on the note sheet the distance from the initial
point to the edge of the water. pleasure and
record the depth at the edge of water.
After the depth is known and recorded,
determine the method of velocity measure-
ment. Normally the two -point method or the
0.6-depth method is used. Compute the setting
of the meter for the particular method to be
used at that depth. Record the meter position
(as 0.8, 0.6, 0.2, . . .). After the meter is
placed at the proper depth, permit it to become
adjusted to the current before starting the
velocity observation. The time required for
such adjustment is usually only a few seconds
if the velocities are greater than I fps, but
for lower velocities, particularly if the current
meter is suspended by a cable, a long period
of adjustment is needed. After the meter has
become adjusted to the current, count the
number of revolutions made by the rotor for a
period of 40-70 se d� Start the stopwatch
`giff Ta,neously with the first signal or click,
counting "zero," not "one." End the count on
a convenient number given in the meter rating
table column heading. Stop the stopwatch on
that count and read the time to the nearest
second, or to the nearest even second if the
hand is on a half -second mark. Record the
number of revolutions and the time interval.
If the velocity is to be observed at more
than one point in the vertical, determine the
meter setting for the additional observation,
time the revolutions, and record the data.
Move to each of the verticals and repeat this
procedure; record the distance from initial
point, depth, meter -position depth, revolu-
tions, and time interval, until the entire cross
section has been traversed. (See fig. 2.)
If the direction of flow is not at right angles
to the cross section, find the velocity vector
normal to the section. Measure the cosine of
the horizontal angle (fig. 57) by holding the
note sheet in a horizontal position with the
point of origin (0) on the left edge of the note
sheet (fig. 2) over the tag line, bridge rail, or
any other feature parallel to the cross section.
With the long side of the note sheet parallel
to the direction of flow, the tag line or bridge
rail will intersect the value of the cosine of
the angle a on the top, bottom, or right edge
of the note sheet. Multiply the measured
velocity by the cosine of the angle to determine
the velocity component normal to the measur-
ing section.
Details peculiar to specific types of current -
meter measurements are described in the
following sections.
Current -meter measurements by wading
Current -meter measurements by wading are
preferred, if conditions permit. (See fig. 58).
Wading measurements offer the advantage over
measurements from bridges and cableways in
that it is usually possible to select the best of
several available cross sections for the measure-
ment.
Use the type AA or the pygmy meter for
wading measurements. Table 2 lists the type
of meter and velocity method to use for wading
measurements for various depths.
If a type AA meter is being used in a cross
section with an average depth greater than 1.5
feet, do not change to the pygmy meter for a
few depths less than 1.5 feet or vice versa. Use

D1SCHARGF MEAStiHEMENTS AT GAGING STATIONS
39
Meter in stream
,rm 9 V 5
Tag line, edge Of cable
Point of car, or badge rail
origin
Read anple .coefficient here
Figure 57--Measuremenf of horizontal angles.
Fable 2.—Current-meter and velocity -measurement method
for carious depths
7)4mh Velocity
(feet) _Veler rseehod
2.5 and above-- --- Type AA {or Type 0. 2 and 0. 8
A).
l.g-2.5 --- --------- do ---------- --- -6
.3--1.5----------- Pygmy i--------- -- .6
1 Used when wlocities are less than 2.5 fps.
the type AA meter at depths as shallow as 0.5
foot, l.ts use is not recommended below depths
of 1.0 foot because the registration of the meter
is affected by its proximity to the water surface
and to the streambed. Do not use the type AA
meter or the pygmy meter in velocities less
than 0.2 fps unless absolutely necessary.
Coeflicients given ley Pierre (1941.) for the
perforimir ce of em-rem. lneters in n:tter of
shttllmr del)tll alld Ion- Ve10cit.ie5 aIT'e no longer
t-igure 58:--wading measurement using top -setting rod
recommended for use, at. least. until further
1Flt'estio-ation.
When natural conditions for measuring are
in the range considered undependable, modify
the measuring cross section, if practical, to
provide acceptable conditions. Often it is pos-
sible to build dikes to cut off dead water and
shallow flows in a cross section, or to improve
the cross section by removing the rocks and
debris within the section and from the reach of
stream immediately upstream from it. .After
modifying a cross section, allow the flow to
stabilize before starting the discharge measure-
ment.
Stand in a position that least affects the
velocity of the water passing the current meter.
This position is usually obtained by facing the
bank, with the water flowing against the side
of the Ieg. Holding the wading rod at the tag
line, stand from 1 to 3 inches downstream from
the tag line and 18 inches or more from the
wading rod. Avoid standing in the water if
feet and legs would occupy a considerable per-
centage of the crass section of a narrow stream.
In small streams where the width permits, stand
on a plank or other support rather than in
the water.
Keep the wading rod in a vertical position
and the ineter parallel to the direction of flow
while observing the velocity. If the flow is not
at right angles to the tag line, measure the
angle coefficient carefully.

40 TECHNIQUES OF WATER -RESOURCES INTESTIGATIONFS
During measurements of streams with shift-
ing beds, the scoured depressions left by the
hydrogra.pher's feet can affect soundings or
velocities. Generally, place the meter ahead of
and upstream from the feet. Record an accu-
rate description of streambed and water -surface
configuration each time a discharge measure-
ment is made in a sand -channel stream.
For discharge measurements of flow too small
to measure with a current meter use a volu-
metric method, Parshall flume, or weir plate.
Current -meter measurements from ca6leways
The equipment assemblies for use on cable-
ways are described on page 18.
The size of the sounding weight used in
current -meter measurements depends on the
depth and velocity to be found in a cross sec-
tion. A rule of thumb is that the size of the
weight in pounds should be greater than the:
maximum product of velocity and depth in
44 the cross section. If insufficient weight is used,
1--the sounding line will be dragged at an angle
downstream. If debris or ice is flowing or if the
stream is shallow and swift, use a heavier weight
than the rule designates. The rule is not rigid
but does provide a starting point for deciding
or the size weight necessary. Examine notes of
previous measurements at a site to help deter-
mine the size weight needed at various stages.
The Price type --AA current meter is generally
used when making discharge measurements
from a cableway. The depth is measured by
using a sounding reel and the velocity is
measured by setting the meter at the proper
position in the vertical. (See table 3.) Table 3
is designed so that no velocity observations will
be made with the meter closer than 0.5 foot to
the water surface. In the zone from the water
surface to a depth of 9.5 foot, the current
meter is known to give erratic results.
ToWe 3. VeIocity-measurement method for Yariovs
suspensions and depths
Min ivmumdepth (fed)
01 and 0.8
smpensiora 0.6 method mdhod
15C.5,30C.5------------------ I.2 2.5
50 C JS5------------------------- 1.4 2.8
50 C .9-------------------------- 2.2 4.5
75 C 1.0, 100 C 1.0, 150 C 1.0_ _ - •• - - 2.5 5.0
200 C! 1.5, 300 C 1.53.8 7.5
Use 0.2 methr3d for depths 15-3-7 feet with appropriate meiiicient
[esr:iin:ited 0.88)-
Some sounding reels are equipped with a
computing depth indicator. To use the comput-
ing spiral, set the indicator at zero when the
center of the current -meter rotor is at the water
surface. Lower the sounding weight and meter
until the weight touches the streambed. If a 3€1
C .5 suspension is used and the indicator reads
18.5 feet when the sounding weight touches
the bottom, the depth would be 19.0 feet. To
move the meter to the 0.8-depth position,
merely raise the weight and the meter until the
hand on the indicator is over the 19-foot mark
on the graduated spiral (fig. 25) ; the hand will
then be pointing to 15.2 feet on the main dial.
To set the meter at the 0.2-depth position,
raise the weight and meter until the hand on the
indicator is pointing to 3.8 feet on the main
dial.
One problem found while observing velocities
from a cableway is that the movement of the
cable car from one station to the next makes
the car oscillate for a short time after coming
to a shop. Wait until this oscillation has
dampened to a negligible amount before
counting the revolutions.
Tags can be placed on the sounding line a
known distance above the center• of the meter
cups as an aid in determining depth. (See
fig. 36.) The tags, which are usually streamers
of different colored binding tape, are fastened
to the sounding line by solder beads or by
small cable clips. Tags are used for determining
depth in two ways:
Set the tag at the water surface and then
set on the depth indicator the distance
which that particular tag is above the
center of the meter cups. Then continue
as if the meter cups themselves had
been set at the water surface. This is the
preferred procedure. If debris or ice is
flowing, this method prevents damage
to the meter.
With the sounding weight on the stream -
bed, determine the depth by raising the
weight until the first tag below the water
surface appears at the surface. The total
depth is then the sum of (a) the distance
the weight was raised to bring the tag
to the water surface, (b) the distance the
tag is above the center of the meter
cups, and (c) the distance from the

DISCHARGE PASUREMENTS AT GAGING STATIONS
41
bottom of the weight to the center of
the caps. This method is sometimes used
with handlines.
By using tags, the meter can be kept under
water at all tunes to prevent freezing the meter
in cold air. Tags are also used in measurements
of deep, swift streams. (See 1). 47.)
If large amounts of debris are flowing in the
stream, raise the meter up to the cable car
several times during the measurement to be
certain the pivot and rotor of the meter are
free of debris. However, keep the meter in the
water during the measurement if the air tem-
perature is considerably below freezing. Carry
a pair of lineman's side -cutter pliers when
making measurements from a cableway. If the
weight. and meter become caught on a sub-
merged object or on flouting debris and it is
impossible to release them, cut the sounding
line to insure safety. Sometimes the cable car
can be pulled to the edge of the water and the
debris can be released.
When measurements are made from cable-
ways where the stream is deep and swift,
measure the angle that the meter suspension
cable makes with the vertical due to the drag.
The vertical angle, measured by protractor
p. 47), is needed to correct the soundings to
obtain the actual vertical depth. (See p. 49.)
Current -meter measurements from bridges
When a stream cannot be waded, bridges may
be used to obtain current -meter measurements.
Many measuring sections under bridges are
satisfactory for current -meter measurements,
but cableway sections are usually better.
No set rule can be given for choosing between
the upstream or downstream side of the bridge
when making a discharge measurement.
The advantages of using the upstream side
of the bridge are:
1. Hydraulic characteristics at the upstream
side of bridge openings usually are more
f avorable.
2. Approaching drift can be seen and be more
easily avoided.
3. The streambed at the upstream side of the
bridge is not likely to scour as badly as at
the downstream side.
The advantages of using the downstream
side of the bridge are:
1. Vertical angles are more easily measured
because the sounding Iine will move away
from the bridge.
2. The flow Iines of the stream may be straight-
ened out by passing through a bridge
opening with. piers.
Whether to use the upstream side or the down-
stream side of a bridge for a current -meter
measurement should be decided individually
for each 'bridge after considering the factors
mentioned. above and the physical conditions
at the bridge, such as location of the walkway,
traffic hazards, and accumulation of trash on
piles and piers.
Use either a handline, or a sounding reel
supported by a bridge board or a portable
crane to suspend the current meter and sound-
ing weight from bridges.
Measure the velocity by setting the meter at
the position in the vertical as indicated in table
3. Keep equipment several feet from piers and
abutments if velocities are high. Estimate the
depth and velocity next to the pier or abutment
on the basis of the observations at the vertical
nearest the pier.
If there are piers in the cross section, it is
usually necessary to use more than 25-30 partial
sections to get results as reliable as those from
a similar section without piers. Piers will often
cause horizontal angles that must be carefully
measured. Piers also cause rapid changes in the
horizontal velocity distribution in the section.
Footbridges are sometimes used for measuring
canals, tailraces, and small streams. Rod
suspension can be used from many footbridges.
The procedure for determining depth in low
velocities is the same as for wading measure-
ments. For higher velocities obtain the depth
by the difference in readings at an index point
on the bridge when the base plate of the rod
is at the water surface and on the streambed.
Measuring the depth in this manner will elim-
inate errors caused by the water piling up
on the upstream face of the rod. Handlines,
bridge cranes, and bridge boards are also used
from footbridges.
When using a sounding reel measure the
depth by methods described on page 44. To

42 TECHNIQUES of WATER -RESOURCES INVESTIGATIONS
dcternmic depth when using a handline, lower
the sounding weight to the streambed, then
raise the weight until one of the tags is at the
water surface. Measure along the rubber -
covered service cord with a steel or metallic
tape or is graduated rod to deterinine the dis-
tance the weight is raised. The total depth
of Water is then 'the sumnitatlon of (1) the
distance the litart.icultar ttsg is above the meter
(,ills, (2) the nw asured distance the meter
and weight was raised and (3) file distance
frorn the bottoni of the sleight to the meter
culls.
Another method of determining depths is
to set the meter cups at the water surface and
then lower the soundim weight to the stream -
bed while measurimg the amount of line that
luis been let out by one of the methods men-
tioned previously. This ineasured distance,
Alas the distance from the bottom of the sound-
ing sveiAit to the meter culls, is the depth of
wiateI•. When using it handline, unwind enough
cable from the handline reel to keep the reel
out of water when the sounding weight is on
the strearnbed tit the deepest part of the cross
section. If the bridge is high enough above the
water surface, raise and lower the weight and
meter by the rubber -covered cable rather than
by the bare cable. When the ineter is set for the
velocity observation, stand on the rubber -
covered (,table or tie it to the handrail to hold
the meter in place. This arriingem.ent frees
the Bands to record the data.
The handline can be disconnected from the
headphone mire and passed around to truss
member with the sounding weight on the
bottom. This eliminates the need for raising
the, weir lit and meter to the bridge each time a
move is made from one vertical to another, and
is the principal advantage of a handline.
Current -meter measurements from ice cover
Discharge measurements under ice cover tare
made tinder the most severe conditions (fig. 59)
but are. extremely important because a Marge
part of the discharge record during a winter
pez•iod may depend on one measurement.
Select the possible locutions of the cross
section to be used for a measirrentent from ice
cover during the open -water season when
channel conditions can be evaluated.
Ilk
Figure 59.--[ce rod being used to support current meter For
a discharge measurement, top; and ice drill being used to
cut holes, bottom;
The equipment used for cutting or drilling
the hales in the ice is described on page 27.
ever underestimate the danger of working
on ice -covered streams. When crossing, test

DISCHARGE MEASUREMENTS AT GAGING STATIONS
GR1
the strength of the ice with solid blows using a
sharp ice chisel. Ice thickness may be irregular,
especially late in the season when a thick snow
cover may act as an insulator. Water just
above freezing can slowly melt the underside of
the ice, creating thin spots. Ice bridged above
the water may be weak, although thick.
Cut the first three holes in the selected cross
section at the quarter points to detect the
presence of slush ice or poor distribution of the
flow in the measuring section. If poor conditions
are found, investigate other sections to find one
that is free of slush ice and that has good dis-
tribution of flow. Blake at least 20 holes in
the ice for a current -meter measurement.
Space the holes so that no partial section has
rnore than 10 percent of the total discharge in it.
The effective depth of the water (fig. 60) is the
total depth of water minus the distance from
the .eater surface to the bottom of the ice.
The vertical pulsation of water in the holes in
the ice sometimes causes difficulty in deter-
mining the depths. The total depth of water is
usually measured with an ice rod or with a
sounding weight and reel, depending on the
depth.
Measure the distance from the water surface
to the bottom of the ice with an ice -measuring
stick. (See p. 27) If there is slush under the
solid ice at a hole, the ice -measuring stick is
not used. To find the depth at which the
slush ice ends, suspend the current meter
below the slush ice. with the meter rotor
turning freely. Raise the meter slowly until
the rotor stops. This point is used as the depth
of the interface between water and slush.
After the effective depth of the water has been
determined, compute the proper position of the
meter in the vertical as shown in, figure 60.
The vane ice meter is recommended for use
under ice cover because the vanes do not be-
come filled with slush ice as the cups of the
Price meter often do, because the yoke of the
vane meter will fit in the hole made by the ice
drill, and because the yoke and ice rod can
serve as an ice -measuring stick. The contact
chamber of the vane meter can be rotated to
any position, so the binding post is placed per-
pendicular to the axis of the yoke to avoid inter-
ference when using the top of the yoke to deter-
mine the underside of the ice.
The velocity distribution under ice cover is
similar to that in a pipe with a lower velocity
nearer the underside of the ice. (See fig. 61.)
The 0.2- and 0.8- depth method is recommended
for effective depths 2.5 feet or greater and the
0.6-depth method is recommended for effective
depths less than 2.5 feet. It is recommended
4F.}ITTTf�rLTS.�
a=Water surface to bottom of ice 0.2-depth sett ing = G + 0. 2c
b= Total depth of water ❑.8-depth setting= b-0.2c
c=Effective depth (s=b—a) 0.5-depth setting=6-0.4c
Figure 60.--Method of computing meter settings for measurements
under ice cover.

111
TECHNIQUES OF WATER -RESOURCES INVESTIGATIONS
3l
ME
100
ICE
x
x
1
x
x
x
1
x
I
x
x
_ x
0 0.2 0.4 0.6 03
VELOCITY, IN FEET PER SECOND
Figure 61 Typical vertical -velocity curve under ice cover.
that two vertical -velocity curves be defined
when ice measurements are made to determine
whether any coefficients are necessary to con-
vert the velocity obtained by the 0.2- and 0.8-
depth method or the 0.6-depth method to the
mean velocity. Normally the average of the
velocities obtained by the 0.2- and 0.8-depth
method gives the mean velocity, but a coeffi-
cient of about 0.92 usually is applicable to the
velocity obtained by the 0.6-depth method.
When measuring the velocity, keep the meter
as far upstream as possible to avoid any effect
that the vertical pulsation of water in the hole
might have on the meter. Eliminate as much as
possible the exposure of the meter to the cold
air during the measurement. The meter must
be free of ice when the velocity is being
observed.
If there is partial ice cover at a cross section,
use the procedure described above where there
is ice cover, and use open -water methods
elsewhere.
A sample sheet of discharge -measurement
notes under ice cover is shown in figure 62. In
this measurement the vertical -velocity curves
indicate that the 0.2- and 0.8-depth method
gives the mean velocity and that the 0.6-depth
method requires a coefficient of 0.92.
Current -meter measurements From boats
Discharge measurements are made from
boats where no cableways or suitable bridges
are available and where the stream is too deep
to wade. Personal safety is the limiting factor
in the use of boats on streams having high
velocity of flow.
String the tag line at the measuring section
by unreeling the line as the boat moves across
the stream. Some tag -line reels are equipped
with brakes to control the line tension while

DISCHA13GE MEASUREMENTS AT GAGING STATIONS
45
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Figure 62,—Part of notes for discharge measurement under ice cover,
unreeling. (See p. 24.) After a tag line without
a brake has been stretched across the stream,
take up the slack by means of a block and
tackle attached to the reel and to an anchored
support on the bank- If there is traffic on the
river one man must be stationed on the bank to
lower and raise the tag line to allow the river
traffic to pass. Place streamers on the tag line
so that it may be seen by boat pilots. If there
is a continual flow of traffic on the river, or if
the width of the river is too great to stretch a
tag line, other means will be needed to position
the boat.
When no tag line is used, the boat can be
kept in the cross section by Iining up with flags
positioned on each end of the cross section.
(Seefig. 63.) Flags on one bank would suffice
but it is better to have them on both banks.
The position of the boat in the cross section can
be determined by a transit on the shore and a
stadia rod held in the boat. (See fig. 63.)
Another method of determining the position

46 TECHNIQUES OF WATER -RESOURCES INVESTIGATIONS
Transit
Stadia rod
held in boat
Fkjure 63 ^Determining position in the cross section, stadia
method.
of the boat is by setting a transit on one bank:
some convenient known distance from and at
right angles to the cross-section line. The
position of the boat is computed by measuring
the angle a to the boat. (See fig. 64.) A third.
method of determining the position of the boat
is done with a sextant read from the boat.
Position a flag on the cross-section line and
another at a known distance perpendicular to
the line. The boat position can be computed
by measuring the angle A with the sextant.
Unless anchoring is more convenient, the
nrotor must hold the boat stationary when
readings are being taken.
If the maximum depth in the cross section is
less than 10 feet and the velocity is low, use a
rod for measuring the depth and supporting
the current meter. For greater depths, use a
cable suspension with a reel and sounding
weight.
Boat measurements are not recommended at
velocities less than 1 fps when the boat is subject
to wave action. The up-and-down movement of
the boat (and the meter) seriously affects the
velocity observations.
X
Transit
MC CE tan a (transit)
MC -tanE(sextant)
Figure 64.—Determining position in the cross section,
angular method.
The procedure for measuring from a. boat
using the boat boom and crosspiece is the same
as that for measuring from a bridge or a cable-
way, once the special equipment has been set
up and the method of positioning the boat has
been. established.
Moving -boat measurements of Jisckarge
On large streams and estuaries the conven-
tional methods of measuring discharge are fre-
quently unpractical and involve costly and
tedious procedures. There may be no facilities
at remote sites. Where facilities do exist, they
may be inundated or inaccessible during floods.
At some sites, unsteady flow conditions require
that measurements be made as rapidly as possi-
ble. Measurements on tide -affected rivers must
not only be made frequently but continually
throughout a tidal cycle, The moving -goat
technique is a method of measuring rapidly on
large streams. It requires no fixed facilities,
and it lends itself to the use of alternate sites
if conditions make this desirable.
The moving -boat technique is described in
detail by Smoot and Novak (1968). It is similar
to the conventional current -meter measurement
in that the velocity -area approach to determine
discharge is used; the total discharge is the
summation of the products of the partial areas
of the stream cross section and their respective
average velocities. During the traverse of a boat
across a stream, a sonic sounder records the
geometry of the cross section, and a continu-
ously operating current meter senses the com-
bined stream and boat velocities. Three men are
required to operate the boat and equipment.
The data they collect are converted to discharge
quickly, efficiently, and inexpensively. Experi-
ence has shown that measurements obtained by
the moving -boat technique compare within 5
percent of measurements obtained by conven-
tional means.
Networks of current meters
Occasional special measurements require
simultaneous velocities at several points in a
cross section, distributed either laterally or
vertically. For example, it may be necessary to
measure a vertical -velocity profile quickly in
unsteady flows and to check it frequently in

DISCHARGE MEASUREMENTS AT GAGING STATIONS
47
order to determine the changes in shape of the
vertical profile as well as the rates of these
changes. In another example, for the measure-
ment of tide -affected streams, it is desirable to
measure the total discharge continuously dur-
ing at least a full tidal cycle, approximately 13
hours. The need for so many simultaneous
velocity determinations (one at each vertical
in the cross section) for so long a period could
be an expensive and laborious process using
conventional techniques of discharge measurement.
A grouping of 21 current meters and special
instrumentation has been devised by the Water
Resources Division to facilitate measurements
of the types just described. Only a few persons
are required. The 21 meters are connected
together so that the spacing between any
two adjacent meters can be varied up to 200
feet. Furthermore, each meter has sufficient
hardline cable to be suspended vertically from
a bridge as much as 200 feet. The ineters have
a uniform calibration. Revolutions of the rotors
are recorded by electronic counters which are
grouped compactly in one box at the center
of the bank of meters. The operator, by flipping
one switch, starts all 21 counters simultaneously.,
and after an interval of several minutes, stops
all counters. The indicated number of revolu-
tions for the elapsed time interval is converted
to a velocity for each meter. The distance be-
tween meters is known; a record of stage is
maintained to evaluate depth; prior informa-
tion at the site is obtained to convert point
velocities in the verticals to mean velocities in
those verticals. All of the information necessary
to compute discharge in the cross section is
therefore available, and is tabulated for easy
conversion to discharge.
Measurement of deep, swift streams
Discharge measurements of deep, swift
streams present no serious problems when
adequate sounding weights are used and when
floating drift or ice is not excessive. Normal
procedures must sometimes be altered, however,
when measuring these streams. The four most
common circumstances are:
1. Possible to sound, but weight and meter
drift downstream,
2. Not possible to sound, but a standard
cross section is available.
3. Not possible to sound, and a standard
crass section is not available.
4. Not possible to put the meter in the water.
Procedures are described below for use during
measurements made under these conditions.
The procedures for items 2, 3, and 4 are
used where there is a stable cross section.
The procedure to be used in unstable channels
must be determined by conditions at each
location.
Possible to sound; weight and meter drift downstream
Where it is possible to sound but the weight
and meter drift downstream, the depths
measured by the usual methods are too
large. (See fig. 65.) The correction for this
error has two parts, the air correction and the
wet -line correction. The air correction is shown
in figure 65 as the distance ed. The wet -line
correction in figure 65 is shown as the difference
between the wet -line depth de and the vertical
depth dg.
As shown in figure 65, the air correction
depends on the vertical angle P and the
distance ab. The correction is computed as
follows:
ab-ac
cos P=ad ac+cd ab+cd
ub +cb ^ab
cos P
cd=co .- ab=ab[co P-lj (3)
The air correction for even -numbered angles
between 4° and 36' and, vertical lengths be-
tween 10 and 100 feet is shown in table 4. The
correction is applied to the nearest tenth of a
foot; hundredths are given to aid in inter-
polation.
The air correction may be nearly eliminated
by using tags at selected intervals on the
sounding line and using the tags to refer to
the water surface. This practice is almost
equivalent to moving the reel to a position
just above the water surface.

48 TECHNIQUES OF WATER -RESOURCES INVESTIGATIONS
Apex of vertical angte
I in sounding line
I
l
1 -
i
I
I
I
I _ c
I d Water surface
Flow _
Figure 65: Position of sounding weight and line in deep,
swift water.
The correction for excess length of line below
the water surface is obtained by using an ele-
mentary principle of mechanics. If a known
horizontal force is applied to a weight sus-
pended on a cord, the cord takes a position of
rest at some angle with the vertical, and the
tangent of the vertical angle of the cord is
equal to the horizontal force divided by the
vertical force owing to the weight. If several
additional horizontal and vertical forces are
applied to the cord, the tangent of the angle in
the cord above any point is equal to a summa-
tion of the horizontal forces below that point,
divided by the summation of the vertical
forces below the point.
The distribution of total horizontal drag on
the sounding line is in accordance with the
variation of velocity with depth. The excess in
length of the curved line over the vertical
depth is the sum of the products of each tenth of
depth and the function (cos P----1 ) of the cor-
responding angles derived for each tenth of
depth by means of the tangent relation of the
forces acting below any point.
The wet -line correction for even -numbered
angles between 4' and 360 and wet -line depths
between 10 and 100 feet is shown in table 5.
The correction is applied to the nearest tenth of
a foot. The wet -line correction cannot be
determined until the air correction has been
deducted from the observed depth.
The following points concerning the wet -line
correction should be kept in mind:
1. The weight will go to the bottom despite the
force of the current.
2. The sounding is made when the weight is at
the bottom but entirely supported by the
line.

DISCHARGE MEASUREMENTS AT GAGING STATIONS 49
Tcsbie 4.--Air-correction table, giving difference, in feet, between vertical length and slant length of sounding line above water
surface for selected vertical angles
Vertical
Vertical angle of sounding tins at protractor
Vertical
length
(feet)
4°
6°
8°
10,
12'
14°
IV
IV
W
22'
24'
26°
28°
30"
32.
34°
3W
length
(feet)
10
- .
0- 02
0. 06
0,10
0.15
O. 22
0.31
140
0,51
0.64
1.79
0.95
1.13
1.33
1.55
1,79
106
Z 36
10
12. - _.
-_ _ _ _ _ _ _ _ _ _ _ _
.03
.07
.12
.19
.27
.37
.48
.62
.77
.94
1.14
1.35
1.59
1,86
2.15
2.47
2. 83
12
14------------------
-03
.08
.14
.22
Al
.43
.56
.72
,90
1.10
L32
1,58
1.86
2,17
2,61
2.89
330
14
16_ _ _
_ _ _ - _ - - _ -
.09
- 16
. 25
.36
.49
.64
.82
I.03
t, 26
1. 5I
1. $0
2.12
2.48
2,87
3,30
3:78
16
18_...-..-.-._____
.04
.10
.18
AS
'40
.65
.73
.93
1.16
1.41
1.70
2.03
2.39
178
&23
&71
4,26
18
20------
_ _________
_05
.11
.20
-31
.45
.61
.81
1,03
1.28
1.57
1.89
2.25
Z65
3.09
&58
4.12
4.72
20
22-----------------
-05
.12
.22
.34
.49
. 67
.89
1.13
1.41
1.73
2.08
2,48
2.92
3,40
3.94
4.54
5.19
22
24-- -
- - - - - - - - - - - - - - -
.06
.13
.24
.37
.54
.73
.97
1.24
1.54
1.88
2,27
2.70
3.19
3.71
4.30
4.95
5.67
24
26-..
- ---- - - - - - - -
- 0
. 14
.26
A0
.58
.80
1.05
1,34
1,67
2.04
2.46
2.93
& 45
4.02
4.66
5.36
6.14
26
28 --------------
.
.07
.15
-29
.43
.63
.86
1.13
1.44
1.80
2,20
2.65
& 15
3.71
4.33
5.02
5,77
6.61
28
30- - -
- - - - - - - - - - - ____
OT
.17
. 29
A6
.67
.92
1.21
1-54
1.93
2.36
2. 84
3.38
3.99
& 64
5. 38
6,19
7.09
30
32__________________
'08
.18
.31
.49
.71
.98
1,29
1.65
2.05
2,51
3.03
&60
4.24
4,96
6.73
&Go
7.55
32
34__-____----_---
.03
.19
.33
.52
_76
1.04
1.37
1,75
2.18
2.67
3.22
&83
4,51
&26
6.09
7.01
8,03
34
36------
..----------
.20
.35
.66
.80
1.10
1.45
1.85
2,31
2.83
&41
4.05
C77
6.57
6.45
7142
&50
36
38-------
.. ------
.09
-21
.37
.59
_85
1.16
1.53
1,96
2.44
2A9
3,60
4,28
5.04
5,89
6.81
7.84
8.97
38
40------------
_ --
10
-22
.39
.62
.89
1.22
1.61
2,06
2.57
3.14
3.79
4,60
6.30
6.19
7.17
8.26
9.44
40
42------------------
.10
.23
.41
.66
.94
L29
1.69
2.16
2-70
3,30
3.97
4.73
5,57
6.60
7,63
8.66
9.91
42
44.. _ ..
_ - _ _ _ - .
-24
.43
.fib
.98
1.35
1.77
2.26
2.82
3,48
4,16
4,95
6.83
& 81
7. 88
9.07
10.39
44
4fi-------------------
.11
.25
A5
.71
1.03
1.4I
1.85
2.37
2,85
& 61
4.35
5.18
6.10
7.12
9,24
9A9
10.86
46
48 ------------------
.12
-26
.47
.74
1.07
1.47
1.93
2-47
3.08
3,77
4,64
6.40
6.36
7.43
& 60
9.90
11.33
48
50---------------
--
.12
.28
.49
.77
1,12
1.63
2.02
157
3.21
3.93
4.73
6.63
&63
7.74
8.96
10.31
11.80
50
52_...,_____--------
_13
.29
.51
.80
1.16
1.59
2,10
2.68
3,34
4.08
4.0
5.86
6.89
&04
9,32
10.72
12.28
52
54--- .----------
.---
.13
.30
,53
.83
L21
1.65
2.18
2.78
3.47
4.24
5.11
&08
Z18
8,35
9.68
11,14
12,75
54
56__________________
_14
.31
A3
.86
1.25
L71
2.26
2.88
3,59
4,40
6.30
6.31
7.42
&66
10.03
11.55
13,22
56
58_ _ _ _
_ _ _ _ _ _ _ _ _ _ . - .
.14
-32
.67
.89
1,30
1.78
2,34
2,99
3.72
4.55
5, 49
6,63
7.69
& 97
10.39
11.96
1& 69
58
60- - -
- - - - - - - - - -
i5
.33
.59
93
1.34
1.84
2.42
3.09
3.95
4.71
& 69
6.76
7.95
9.28
10,75
12,37
14.16
60
62----------------
.15
.34
'61
A6
1,39
1.90
2.50
&19
3.98
4.87
&87
6.98
8.22
9.59
11.11
12.79
14.64
62
64__________________
_16
.35
.63
.99
1.43
L96
2,58
3.29
4.11
5,03
&06
7.21
8.48
9.90
11.47
13.20
15.11
04
66 _ _ _ -
- _ _ . - _ _
. 16
.36
.65
1,02
1.47
2,02
2. M
3,40
4. A
5.18
6,25
7,43
8.75
10.21
I L 83
13.61
16.68
86
68____
____________
.17
A7
.67
1.05
1.52
2.08
2.74
3.50
4-36
5.34
6.44
Z66
9.01
10.62
12,18
14,02
16.05
68
90----------------
-
.17
.39
.69
1.08
1-56
2,14
2,82
3.60
4,49
&50
6.62
7,98
9.28
10.83
12.54
14.44
J&52
70
72__________________
_18
.40
.71
1,11
L61
420
2.90
&71
4.62
5,66
6.91
&11
9,55
11,14
12.90
14.85
17,00
72
74
- _ _ _ _
.18
Al
.73
1.14
1.0
2.27
2.98
3.91
4.75
5.81
7.00
8.33
9AI
1 L 45
13,26
15.26
17.47
74
76------------------
.19
A2
.75
1.17
L70
2.33
3.06
&91
4,88
5.97
7.19
&66
10.09
11.76
1& 62
I&V
17,94
76
79 ------------------
19
.43
.77
1,20
I.74
2,39
3,14
4.01
5.01
6,13
7,38
8.78
M34
12,07
1& 98
16.09
18,41
78
80---------.
-
.44
.79
L23
I.70
2.46
&22
4.12
5.13
&28
7.67
9.01
10AI
12,38
14.33
16.50
19.89
80
82_ . _
_ _ _ - - _ _ _ . _ - _
-20
.45
.91
1,27
1.93
2,51
& 30
4.22
5_ 26
6.44
7.76
9,23
10.87
12.69
14.69
16.91
19.36
82
84--------------
_ . ,
.20
A6
.83
2.30
1,89
2.57
3.39
4.32
6.39
6,60
7.95
9,46
11.14
12- 99
15.05
17A2
19.83
84
86__________________
_21
A7
.85
1.33
1.92
163
& 47
4.43
5,52
6,75
8.14
9.68
11,40
1& 30
15.41
17.73
20,30
86
88__________________
_21
.48
.87
1.36
1,97
2,69
3.55
4,53
5.65
&91
8.33
9.91
11,67
1& 61
15.77
18.16
20.77
88
90-- • -
- - - - _
.22
.50
.89
1.39
2. 01
2.75
3.63
4.63
6,78
7.07
8.52
10.13
11.93
1& 92
16,13
18.56
21.25
90
92-- - -
- - - - - - - - - - - -
- 22
.51
.40
1,42
2.06
2, 82
3.71
4.73
5,90
7.22
9.71
10A6
12,20
14.23
16.48
19.97
21,72
92
94_ _ _ _
. - - - _ - - _ _ _ _ . -
.23
.52
.92
L 45
2.10
2,88
3. 79
4,84
6.03
7. 38
& 90
10. 58
12.46
14, 54
16.84
19.38
22.19
94
96------------------
-23
.53
.94
1.48
114
2.94
&87
4A4
6,16
7.54
9.09
10.81
12.73
14.85
17.20
19,80
22.66
96
98.----
.--------- _
.24
.64
.96
1,51
2.I9
&00
3,95
5.04
6,29
7,70
9,27
IL03
12.99
I6.16
17.56
20.21
23.13
98
100---------
. _ _ - _
.24
, 55
.98
1.54
2.23
3,06
4,03
5,15
6.42
7.85
9.46
11.26
13.26
15.47
17.92
M 62
23.61
100
3. Brag on the streamlined weight in the
sounding position is negleeted.
4. The table is general and can be used for any
size sounding weight or line, provided
they are designed to offer little resistance
to the current.
If the direction of flow is not perpendicular
to the measuring section, the angle in the
measuring line as indicated by the protractor
will be less than the actual angle in the line.
The air correction and wet -line correction will
then be too small. To correct for this the
horizontal angle between the direction of
flow and a perpendicular to the measuring
section is measured by using a protractor or by
determining the horizontal angle coefficient as
described mn page 39.
If the horizontal angle of the direction of
How may be called H, the measured vertical
angle P, and the actual vertical angle X, the
relation between the angles is expressed by the
formula
tart X=tan P (fig. 66). (4)
cos H
Table 6 gives the amounts in tenths of degrees
to be added to observed vertical angles to
obtain the actual vertical angles for a range of
horizontal angles between 8" and 28°.
The conditions that cause error in sounding
the depth also cause error in placing of the
meter at selected depths.
The correction tables are not strictly ap-
plicable to the problem of placing the meter

50 TECHN Q1 ES OF WATER -RESOURCES 1NVESTIGATIONS
Table 5.---Wet-fine table, giving difference, in feet, between wet -line length and vertical depth for selected vertical angles
Wet -line
VertScal angle of sounding line at protractor
Wet -line
length, in feet
4°
6°
8°
I0'
I2°
I4°
1B°
IS-
�o
tea°
�a
�°
30°
32°°°
length, 1n
feet
I0---------- --------
0.O1
0.02
0.03
0.05
0.07
0.10
0.13
0.16
0.20
0.25
0.30
0.35
a41
0.41
0.54
0.62
0.70
10
12___.-
.01
.02
.04
.06
.00
.12
.15
.20
.24
.30
.36
.42
.49
.57
.65
.74
.84
12
14 . ..-
.01
.02
.04
.07
.10
.14
I8
.23
.29
.35
.41
.49
.57
.66
.76
.87
.98
14
I6------------------
-0I
.03
A5
AS
.12
.16
.20
.26
.33
.40
.47
.56
.65
.76
.87
.99
1.12
16
i8_..
.01
.03
.06
.09
.13
.18
.23
.30
.37
.45
.63
.63
.73
.85
.98
1.I2
1.26
18
?a------------------
-III
.03
.06
.10
.I4
.20
.26
.33
.41
.50
.a
.70
.82
.94
1.09
1.24
1.40
20
22..................
.01
.04
.07
.11
.16
.22
.28
.86
.45
.55
.65
.77
.90
I.04
1.20
1.36
1.54
22
24•----------
AI
.04
AS
.12
.17
.24
.31
.39
.49
.60
.71
.84
.98
1.13
1.31
1.49
1.68
24
-------
26------------------
•02
.04
.08
.13
.19
.25
.33
-43
.53
.64
.77
.91
1.06
1.23
1.41
1.61
1.81
26
28----------- .--- ..-
.02
.04
.09
I4
.20
.27
.36
.46
.67
.69
.83
.98
1.14
1.32
1.52
L74
1.95
ffi
30------------------
-02
.05
.10
.15
.22
.29
.38
.49
.61
.74
.89
L05
1.22
1.42
1.63
1.96
2.09
30
32__________________
02
.05
.10
.16
.23
.31
.41
.52
.65
.79
.95
1.12
1.31
1.51
1.74
I.98
123
32
34_________
.02
.05
.1I
.17
.24
.33
.44
.56
rR
.84
1,01
1.19
1,39
1-60
I.M
2.11
2.37
34
.-------------
.02
.06
.12
.18
.26
.35
.46
.69
.73
.89
1.07
1.26
1.47
1.70
1.96
2.28
2.51
36
38--•--------- ....
-02
.06
.12
.19
.27
.37
.49
.82
.78
.%
1.12
1.33
1.55
1.79
107
2.36
2.6b
38
4p------------------
-02
.06
.13
.20
.29
.39
.51
.69
.82
.99
),IS
I.40
1.£3
1.89
2.18
Z 48
2.79
40
42------
-03
.07
.13
.21
.30
.41
.54
.69
.86
1.04
1.24
1.47
1.71
1.98
2.35
2.60
2.93
42
------------
44 ------- ----------
-03
.07
.14
.22
.32
.43
.56
.72
.90
1.09
1.30
L54
1.80
2.05
2.39
2.73
3.07
44
46____
• a
•07
.15
.23
.33
.45
.59
.75
.94
1.14
1.36
1-61
I,89
2.17
2.50
2.85
3.21
46
..........
48------..,
.03
.0S
.15
.24
.35
.47
.61
.79
.98
1,19
1.42
1.68
1.96
2.27
2.61
2.98
3.35
48
50--------------•---
.03
.08
.16
-25
.36
.49
.64
.92
1.02
L24
1.48
I-75
2.04
2.36
2.72
3.10
3.49
50
52------------------
-03
.08
.17
.26
.37
.51
.67
.85
1.06
1.29
1.54
1.82
2.12
2.45
2,83
3.22
3.63
52
54------------------
-03
.09
.17
.27
.39
.53
.69
.89
1.10
I.34
1.60
1.89
2.20
2.55
2.94
3.36
3.77
%
p6------------------
.03
.09
.IS
.28
.40
..,5
.72
.92
1.14
1.39
1.66
1.96
128
2.64
3.05
3.47
3.91
66
58--._______-__ -__
.03
.09
.19
.29
.42
.57
.74
.95
I. 18
1.44
1.72
2.03
2.3I
2.74
3.16
3.60
4.05
68
00. ...... .......
. .04
.10
.19
.30
.43
.59
.77
.98
1.22
1. 49
1.78
2. 10
2,45
2. 83
3. 26
3,72
4.19
69
..
62_..______-_..-.---
.04
.I0
.20
.3I
.45
.61
.79
1.02
1.26
1.54
1-94
117
2.53
2.93
3.37
3.84
4,33
62
64......... • • - • _ _ _ -
- US
10
.20
.32
.46
.63
.82
1,05
1.31
1.50
1.99
2.24
2.61
3. 02
3,48
3.97
4.47
64
.04
.11
.21
.33
.48
.65
.94
1.08
1.35
1.64
1.95
2.31
2.69
3.12
3.59
4.09
4.61
68
fi8___---------------
_04
.11
.22
.34
.49
.67
.87
1.12
1.39
1.09
2.01
138
2.77
3.21
3.70
4.22
C75
68
70..........
.04
.11
.-a
35
.50
.fig
90
1.15
1.43
1.74
2.07
145
2.86
3.30
3.91
4.34
4.89
70
72__________________
_04
.12
.23
.36
.62
.71
.92
1.18
1.47
1.79
2.13
2.52
2.94
3.40
3.92
4.46
5.03
72
74. . . . . . . .
. .04
.12
.24
.87
.53
.73
.95
1.21
1. 51
1.84
2.19
2.59
3.02
3.49
4,03
4. 59
0.17
74
.........
78.------ •--
.05
.12
.24
.38
.55
.74
.97
1.25
1,55
1.88
2.25
2.66
3.10
3.50
4.13
4.71
5.30
78
--------
73------------------
-05
.12
.25
.39
.58
.76
1.00
1,29
1.59
1.93
2.91
173
3.18
3.68
4.24
C84
5.44
78
So •------
.os
.13
A5
.40
.58
.79
1.02
I.31
1.63
1.99
2.37
2.80
3.26
3.78
4.35
4.96
5.58
80
-----------
82............
.05
.13
.26
.41
.59
.$0
1.05
1.34
1.67
2.03
2,43
187
3.35
3.87
4.46
5.08
5.72
82
......
94__________________
_05
.13
.27
.42
.60
.82
1.08
1.38
1.71
2.08
2.49
2.94
3.43
3.96
4.57
5.21
5.86
84
86___________
.05
.14
.28
.43
.62
.84
1.10
1.41
1.75
113
2.55
3.01
3.51
4.06
4.68
6.33
6.00
86
88__......... _____
_05
.14
.28
.44
.63
.96
1.13
1.44
1.80
2.18
2.60
3.09
8.59
4.15
4,79
5.48
6.14
89
g0------------------
.06
.14
.29
.45
AS
.89
1.15
1.48
1.84
2.23
2,66
3.15
3. 67
4.25
4.90
5. 58
& 28
90
92.... ........... -
- .06
.15
.20
.46
.66
.90
1.18
1,51
I.88
2,29
172
3,22
3. 75
C 34
5. 00
5.70
6,42
92
-
94--.---------------
06
.15
.30
.47
.68
.92
1.20
1.54
1.92
133
2.78
3.29
3.84
4.44
5.11
5.83
6.56
94
96
06
.15
.31
AS
.69
.94
1.23
1.57
1.96
2.39
2.84
3.36
&92
4.53
5.22
6.95
6.70
96
98........ ...-------
.06
.18
.31
.40
.71
.96
I.25
1.61
2.00
2.43
2.90
3.43
4. cc
4.63
b.33
6.09
6.81
98
.......
.06
.16
.32
.50
.72
.98
1.28
1.64
2.04
% 48
2,96
3. 50
4. 08
4.72
5.44
6.20
& 98
100
Table 6.-Degrees to be added to observed angles to obtain actual vertical angles
Observed vertical angle
3,
cos=0.99
I2°
zw=0.98
Horizontal angle
46° 20°
cAs=0.96 cos=0.94
u°
oos=0.91
2b°
cos=0.88
8--------------------------------
0.1
0.2
0.3
0.5
0.8
1.0
12'------------------------------
1
.3
.5
.8
1.1
1.5
160------------------------------
1
.4
.6
1.0
1.4
2.0
20°------------------------------
.2
.4
.7
1.2
1.7
2.4
24'------------------------------
.2
.5
.8
1.4
2.0
2.8
28* ------------------------------
.2
.5
1.0
1.5
2.2
3.0
32`-----------------------------
.2
.6
1.0
1.6
2.4
3.3
36°------------------------------
.2
.6
1.1
1.7
2.5
3.4
because of the increased pressure placed on the tables 4 and 5 will tend to eliminate this error
sounding weight by higher velocities when it is in placement of the meter, and although not
raised from the streambed. A meter placed in strictly applicable, their use for this purpose
deep, swift water by the ordinary methods for has become general.
observations at selected percentages of the For the 0.2-depth position, the curvature
depth will be too high in the water. The use of of the wet line is assumed to be negligible and

DISCHARGE MEASUREMENTS AT GAGING STATIONS
W
PLAN
c
0
yV
N
------------
_ Plane at protractor
c �f�oh
ELEVATION
n
fi
tan ,1f H=horizontal angle cosH=—Fh
P=measured vertical angle
x=actual vertical angle
bta = 90'
W0-90°
fih =90°
oih= 90°
tan P _ b X fh _ fh
Cos H of fi of
tan X= lb tan P
of Cos H
Figure fib. —Sketch of geometry of relationship of actual to measured
Yettical angle when Flow direction is not normal to measuring section.
the length of sounding line from the apex of the 1. Compute the 0.2 value of the vertica
vertical angle to the weight is considered a depth.
straight line. The method used to place the 2. Lower the meter this depth into the water
meter at the 0.2-depth position is: and read the vertical angle.

52 TECHNIQUES OF WATER -RESOURCES INVESTIGATIONS
3. Obtain the air correction from table 4.
The vertical length used to obtain the
air correction is the sum of 0.2 of the
vertical depth, of the distance the apex
of the angle is above water, and of the
distance the meter is above the bottom
of the weight.
4. Let out an additional amount of line equal
to the air correction.
5. If the angle increases appreciably when the
additional line is let out, let out more
Iine until the total additional line, the
angle, and the vertical distance are in
agreement with figures in the air -correction
table.
To place the meter at the 0.8-depth position,
a correction to the amount of line reeled in
must be made for the difference, if any, between
the air correction for the sounding position
and that for the 0.8-depth position. This
difference is designated as m in table 7. f
the angle increases for the 0.8-depth position,
the meter must be lowered- if it decreases,
the meter must be raised.
For the 0.8-depth position of the meter, the
wet -line correction may require consideration if,
the depths are more than 40 feet and if the
change in vertical angle is more than 5 percent.
If the vertical angle remains the same or de-
creases, the wet -line correction (table 5) for the
0.8-depth position is less than the wet -line cor-
rection for the sounding position by some differ-
ence designated as n in table 7. If the vertical
angle increases, the difference in correction n
diminishes until the increase in angle is about
10 percent; for greater increases in angle, the
difference between corrections increases also.
Table 7 summarizes the effect on air and wet -
line corrections caused by raising the meter
from the sounding position to the 0.8-depth
position.
For slight changes in the vertical angle,
because of the differences m and n in the air
and wet -line corrections, the adjustments to
the wet -line length of the 0.8-depth position are
small and usually can be ignored. Table 7
indicates that the meter may be placed a little
too deep if the adjustments are not made.
Because of this possibility, the wet -line depth
instead of the vertical depth is sometimes used
as the basis for computing the 0.8-depth position
with no adjustments for the differences m and n.
Not possible to sound; standard cross section available
When it is not possible to sound the bottom
but a standard cross section is available, the
procedure to follow is:
1. Determine the depths from the standard
cross section.
2. Measure the velocity at 0.2 of the depth.
3. Determine coefficients to adjust the 0.2-
depth velocity to mean velocity oil the
basis of previous measurements at the
site by the two -paint method.
4. Compute the measurement in the normal
manner using the depths from the standard
cross section and the velocities measured.
The coefficient is then applied to the com-
puted discharge.
Not possible to sound; standard cross section not available
When if, is not possible to sound and a
standard cross section is not available, the
procedure to follow is:
1. Refer the water -surface elevation before
and after the measurement to an elevation
reference point on a bridge, on a driven
stake, or on a tree at the water's edge.
Table 7.—Summary table for setting the meter at 0.8-depth position in deep, swift streams
Change in vertical angle
Air correction
Wet -line correction
Direction of change Correction to meter position Direction of change Correction to meter position
None-- ---------------- None -------------- None-------------- Decrease_____ Raise meter the
distance n.
Decrease ------------- Decrease ----------- Raise meter the -----do ------------- Do.
distance m.
Increase ------------- Increase___ Lower meter the Decrease, then {'}
distance m. increase.
= Raise meter the distance n nnlem the Increase in angle is greater than about 10 percent, then it is necessary to lower the meter the distance n.

DISCHARGE IIIEASUREMENTS AT GAGING STATIONS
53
2. Estimate the depth and observe the velocity
at 0.2 of the estimated depth. The meter
should be at least 2.0 feet below the water
surface. Record in the notes the actual
depth the meter was placed below the
water surface. If an estimate of the depth is
impossible, place the meter 2.0 feet below
the water surface and observe the velocity
there.
3. Make a complete measurement at a lower
stage, including some vertical -velocity
curves.
4. Use the complete measurement and differ-
ence in stage between the two measure-
ments to determine the cross section of the
first measurement. To determine whether
the streambed has shifted, the cross section
should be compared with one taken for a
previous measurement at that site.
5. Use vertical -velocity curves or the relation-
ship between mean velocity and 0.2-depth
velocity to adjust the velocities observed
in step 2 to mean velocity.
6. Compute the measurement in the normal
manner using the depths from step 4 and
the velocities from step 5.
Not possible to put meter in water
If it is impossible to keep the weight and
meter in the water, the procedure to follow is:
1. Repeat step 1 for conditions when it is not
possible to sound the bottom and a
standard cross section is not available.
2. Measure surface velocities by timing floating
drift, or by use of an optical flowrneter.
3. Repeat steps 3-6 for conditions when it is
not possible to sound the bottom and a
standard cross section is not available.
An optical flowzneter has been described by
Smith (1961). It is portable, battery operated,
and requires no great skill for quick and ac-
curate readings of the surface rate of flow. It is
not immersed, so it does not disturb the flow,
and it is in no danger of damage from floating
debris or ice.
It is well to note that just after the crest,
the amount ❑f floating drift or ice is usually
greatly reduced, and it may be possible to
obtain velocity observations with a current
muter.
Measurements during rapidly changing stage
During periods of rapidly changing stage,
measurements should be made as quickly as
possible to keep the change in stage to a mini-
mum. This speed will minimize errors caused
by shifting of flow patterns as the stage changes.
The procedure to foIIow to speed up a measure-
ment is:
1. Use the 0.6-depth method. The 0.2-depth
method or the subsurface method could
be used if placing the meter at the 0.6
depth creates vertical angles requiring
time consuming corrections, or if the
vertical angle increases because of drift
collecting on the sounding line.
2. Reduce the velocity observation time to
about 2G--30 seconds.
3. Reduce the number of sections taken to
about 15-18.
By incorporating all three of the above
practices a measurement can be made in 15-20
minutes. If the subsurface method for observing
velocities is used, then some vertical -velocity
curves will be needed later to establish co-
efficients to convert observed velocity to mean
velocity.
Carter and Anderson (1963) have shown that
discharge measurements having 30 sections and
using the two -point method of observation
with a 45-second period of observation will have
a standard error of 2.2 percent. This means that
two-thirds of the measurements made using
this procedure would be in error by 2.2 percent
or less. They have also shown that the standard
error for a 25-second period of observation and
using the 0.6-depth method of velocity obser-
vations with depth and velocity observed at
16 sections is 4.2 percent. The error caused by
using the shortcut method is generally less
than the error that can be expected by shifting
of flow patterns during periods of rapidly
changing stage.
Series ❑f measurements during a peak of short
duration
The procedure to follow if a series of meas-
urements is wanted during a peak of short
duration is:
1. Take about 10 sections.
2. Take velocity observations at 0.6 depth.

54 TECHNIQUES OF WATER -RESOURCES INVESTIGATIONS
3. Repeat velocity and depth observations at
the same 10 sections with corresponding
stages as often as possible throughout the
period of the flood wave.
4. Develop stage -velocity and stage -area curves
for each of the 10 sections.
5. Compute the discharge corresponding to
selected stages by summation of the
partial discharges from the curves thus
defined.
Mean sage heiglit of discharge measurements
The mean gage height of a discharge measure-
ment represents the mean height of the stream
during the period the measurement was made
and is referred to the datum of the gaging
station.
The mean gage height for a discharge
measurement is one of the coordinates used in
plotting the measurements to establish the
stage -discharge relation, often called the rating
curve. An accurate determination of the mean
gage height is therefore as important as an
accurate measurement of the discharge to
define the stage -discharge relationship.
The computation of the mean gage height
presents no problem when the change in stage
is 0.1 foot or less, for then the mean may be
obtained by inspection. However, measure-
ments must sometimes be made during floods
or regulation regardless of how rapidly stage
changes.
To obtain an accurate mean gage height, the
gage must be read before and after the dis-
charge measurement, and the recorder chart
must be read at breaks in the slope of the gage -
height graph during the measurement. If the
station is equipped with a digital recorder, the
gage -height readings punched during the
measurement are to be read. At nonrecording
stations the only way to obtain intermediate
readings is for the stream gager to stop during
the measurement once or twice to read the
gage, or to have someone else do this for him.
If the change in stage is greater than 0.1
foot, the mean is obtained by weighting the
gage -height readings rather than by inspection
of the available readings.
The mean gage heights during periods of
constant slope of the gage -height graph and
the corresponding measured partial discharges
are used to compute the mean gage height of
the measurement. The formula used is:
H _ q iAF T g2h2+gah,3 . . . . . . . . . +griAR
(5)
in which
H=mean gage height, in feet,
Q=total discharge measured, in
cubic feet per second
q1+q2+q3 . . . . . . +qn,
q,, q2, qa, . q.amount of discharged meas-
ured during time interval
1, 2, 3, . . . n, in cubic
feet per second,
Af, A2, A,,. A.=average gage height during
time interval 1, 2, 3,
. . . n, in feet.
Figure 67 shows the computation of a
weighted mean gage height. The graph at the
bottom is a reproduction of the gage -height
graph during the discharge measurement. The
discharges are taken from the current -meter
measurement shown in figure 2. The upper
computation of the mean gage height in figure
67 shows the computation using the given
formula. The lower computation has been done
by a shortcut method to eliminate the multi
plicatiori of large numbers. In this method.,
after the average gage height for each time
interval has been computed, a base gage height,
which is usually equal to the lowest average
gage height, is chosen. Then, the difference
between the base gage height and the average
gage heights is used to weight the discharges.
When the mean difference has been computed,
the base gage height is added to it.
If a discharge measurement is made at a
distance from the gage during a change in
stage, the discharge passing the gage during
the measurement will not be the same as the
discharge at the measuring section because of
the effects of channel storage between the
measuring section and the gage.
Adjustment is made for channel storage by
applying to the measured discharge a quantity
obtained by multiplying the channel surface
area by the average rate of change in stage in
the reach. The formula is:
Q, =Q, ±WL Di , (6)

DISCHARGE MEASUREMENTS AT GAGING STATIONS Jr rJ
.o .Ia .zc 1W .40 .To eo .70 W .85
E
D
W
�'�6
D`#I'
S
�F
Rt.-
0E1-
Tin
VELOCITY
1101- i
fa hu.
wal. or
Arcs
�4.v
Aa
P.m
'San
IT
Ave.-
C.
1.94
—..fir
It, G.
-
t i
7 _
-
----
+ -iD
j H Doll.
I�1
j
s H+
IQ
I
nr
*, zit-
!
11 Q
_
-
2
n
A
X
9�
JA
.o .10 .20 .30 to so .40 .ra .au .89 40
F330 )400 I1930
Figure 67,—Computation of weighted mean gage height.
in which ❑ =elapsed time during measurement, iri
Q,=discharge going over the control, in cubic seconds.
feet per second, A reference point (RP) or a temporary gage is
Q =-rnerecon rl discharge, ire cubic feel per 3et at the measuring section if channel storage
W= average xvidth vidth of stream betNveen measur- might be significant. The water-stirf ace eleva-
ing section and control, in feet, tion at the section is determined before and
L—length of reach between measuring section after the measurement to compute oh. If the
and control, in feet, measurement is made above the control, the
Ak=average change in stage in the reach L adjustment will be plus for falling stages and
during the measurement, in feet, and minus for rising stages; if made below the con-

56 TECHNIQUES OF WATER -RESOURCES INVESTIGATIONS
trot, it will be minus for failing stages and plus
for rising stages.
Figure 68 shows the front sheet of a measure-
ment that has been made at a distance from the
control during a period of changing stage.
The computation of the adjustment for storage
for the measurement shown in figure 68 follows:
Adjustment for measurement 264 on Big
Creek near Dogwood, Va.
Measurement made 0.6 mile upstream
3,170 feet.
Average width between measuring section
and control=150 feet,
Change in stage at control, 5.84--6.74
feet= +4-09 foot. ..1*-
Change in stage at measuring section.,
12.72-•13.74 feet=.+1.02 feet. Readings
taken at measuring section from a
reference point before and after measure-
ment.
Average change in stage= (0.901-1.02)
2=0.96 foot.
M� UN11- STATE'[: !
DEPART h1 ENT OF THE tNTEM.R[OR M. N. -Lv-'----
GEOLOGICAL SURVEY
14
WATM RIMOURCES DIVISION Cam -- -----
DISCHARGE MEASUREMENT NOTES cti.rwabr ------- ---_-
StL N.
DL.
width_...�____-• 19_t2_7. Party-___.:.-J�StQIlSS.!]--------------------
width A. 1.0.4.0 Yei 13-07 G. a _6. A
Melhod Na. aec. 3 Q_____ G. K change-129-0-- in hta. Suapb
Method cod. _ -_-.._- Hor. angle eoefVftr• 2A SosP. eoef. _f�_QO+ hitter No. .Is6.9_q---
EST GALE READINGS _ Date rated ____U.cd rating
'Fier ]Et. -r RxaAu I-i& Ouui&
�— for rnd _______-.. waP. Meter __�� Q.. ft.
14 1S _-'r---`t�- y- Jr-['$a,� "�-5 "��''S above bottom of wt. T&V checked -A- 4 -
_ ----- _____ __________ spin before meal. x'' ,s ... afltr _7.c-, 50_
---------- ------ p------------- ---
-�... V- ------• -• - Meaa. plots ------7, &ff.from------------ntir4
...- ._ Wading, table. ice. `boat, + pstr., dowrAtr-. rIs
t.�r-;3_ ----____--- ------------------- bridge ----- Q_'__Gl... feet. In above, below
---------- --------•' ----.....- ---------- ----- Me, and --------- .....----------------- •--------
�.rt,JS F�(f 6.Z4 --------- ------•--- Check bar. chain found -------------- --
t�3a -7� r--I-7L6 _7.1.6_ 11'J.
rhaKed to at --------------
Wr;se:ea rs G- H ---- _
. - ...-.-
Correct ______________
C. H. eerrali. .....
Corr�+ Nr. c-[i. _--- - Lavcla obtained _- ----- ----------
Measurement rated excellent (2%), oa {$°fo fair (8%), Poor {over 8%p). bued fallow}'U19
wnditions: Cron aectian t Al-1 i---3ti►C4r1�--S brtt...aAJ___SjrAVt ___bAILQi'►►-
Flow Glla�---dl'3QSl�a�1-'.F_Qrl� Weather .-R_Si1.Y�Jn pJ-------------------
Other hf >z�lrii ASsL{1iJre:._._..---------------------•---
GageSI.........................................
--------------- --............. Record removed . Y15_.---------- . intairc 0uahrd to `-__............
Oharrver __�.A�---Vd-i- 1 l-------------------------------- ---------------- .--- --------
Centro] __C__[Jar_....... .-
� tt--------------------------}y .-------------------
Remarks�-__Qi - Yam+- S
...............= -$4 ` `1 `-------------------------------------- ---------------
G. K of rnv &w---------------------------- ------ ft. Elev. R P = 3O.00
f? P r. W.5 6 1,41ib = f 7f. Zg; 30.0a —,7. 2.$; 12-.7 X se --taut-=
KPt-.WS SL,5"--16.Z4; 30.00-10-L6* 13•?+4
Figure 68.—D"tschwSe measurement notes with discharge adjusted for channel
storage effect.

DISCHARGE: MEASUREMENTS AT GAGING STATIONS
57
Elapsed time during measurement=ly4
hours=4,500 seconds.
Measured discharge=8,494 cfs (cubic feet
per second).
Qc= 8,494 — 150 (3,170) 0.96
=8,494-101=8,393 efs. Use 8,390 cfs.
It is also possible to approximate the effect
of storage by computing the time of travel of
the flood wave between the measuring section
and the control and then adjusting the gage
height for the traveltime to correspond to the
measured discharge. The flood -wave velocity is
generally assumed to be 1.3 times the mean
velocity for the measurement.
The traveltime is computed by the following
formula:
t 1.3V� (7)
in which
t=time of travel of the flood wave between
the measuring section and the control,
in seconds,
I = length of reach between measuring section
and control in feet and
V=mean velocity of measurement, in feet
per second.
1n applying the time adjustment, the time -of -
travel adjustment is subtracted from the ob-
served time at
s abav tl gage -orr 4al4iriglie
time-cif-#xav�l- j�r��-is armed o the--ab"
served --time- at -tiTe _gage -if- i-fre- nCstfeR=eft+--iS
either---belew-the—gage-•$n a ,—or
- - ;'_�iseve-th-e--gage max- �risirrg serge ��
+p Figure fig shows the front sheet for the same
j measurement used in figure 68, but this time
the storage adjustment has been made by
adjusting the gage height. The computation of
the traveltime is shown on the bottom of the
front sheet. Figure 70 is an expanded plot of
the gage -height graph during the time of the
measurement. By applying the traveltime to the
starting and finishing times of the measurement,
the adjusted gage heights of 5.90 feet and 6.80
feet are obtained from figure 70. The mean gage
height is obtained by weighting as described
previously,
�r
Ic mac. 3 , : s i7/?c tic � • �' i G ... _ rLd e �-•� S' �� _
$ .1 1�1__
The relationship between mean velocity and
the velocity of the flood wave is uncertain in
many instances. For this reason the adjustment
method using change in channel storage is
usually preferred.
The proper coordination of the gage height
and the discharge because of the amount of
change in stage is a separate and distinct
problem from that of making adjustments owing
to variable slopes caused by changing discharge.
Therefore the relation of stage to discharge at
the time a measurement is made should be
determined before adjustments owing to vari-
able slopes are made.
Portable Weir Plates
Current meter measurements made. in shallow
depths and low velocities are usually inaccurate,
if not impossible to obtain. Under these condi-
tions a portable weir plate is a useful device for
measuring the discharge.
A 90' V-notch weir is suitable because of its
favorable accuracy at low flows. A weir made
of 10- to 16-gage galvanized sheet iron ,vill
produce a free -flowing nappe having the effect
of a sharp -crested weir and will give satisfactory
performance. The thickness of the plate should
vary with the size of the weir. Refer to figure 71
for recommended proportions. Decreasing the
plate thickness on larger weirs will help maintain
portability. The notch is cut, without sharpen-
ing, leaving a flat, even edge. Framing, in the
form of small angle irons, is required for medium
and large sizes. Canvas attached on the down-
stream or upstream side prevents leakage under
or around the weir. Eyebolts, properly placed,
,trill secure rods driven in earth channels to
stabilize the plate.
A staff gage should be placed far enough
upstream from the weir opening so that it is
not in the drawdown region and it should be
related to the weir gage by means of a car-
penter's level. At a distance greater than twice
the head, the drawdown effect is negligible.
The staff gage is used to obtain head on the
weir.
Flows from 0.02 to 2.0 cfs are measured with
the large weir of figure 71. Discharges can be
measured within 3 percent accuracy if the weir

j$ TECHNIQUES OF WATER -RESOURCES INVESTIGATIONS
s-szse
[Auawt LUO UNITED YTATR$ X..
DEPARTMENT OF THE I14TERIOR
6L 0 tCAL i RVTY Carry. b7 - ---
r.•xw nxwlncca ~@n V
DISCRARGE MEASUREMENT NOTES �'W b' " —
i_-__-cr-eu-k---- nzar....DO- -........................
nate_MA.r. ---- 'b-------i9_62- Party
Width -_� `t_Q__ Area _ iQ.`.-? O VeS. $__t.b G. A 6. 3 S niarh. 8. 41 a --
Method _x'f:-8 No. secs. _ Q_ G. H. changet:I.Q in 1If hrs. Susp. Z5_5; __.
Method coef. �-_.._ Hor. angle coef.VArx4s Susp. coef. _I _Da Dieter No.4_9q
Bate rated z - �_�2_' 47 Z__ iised rating
$p GACR HEA DINGS
Ti— Ill T Refor rod ____..._ sosp. Maier __f__4_ ft.
`�? r�=_ z``1-r__- _�`i__ above bottom of wi. Tags checked ---------
1 `( `{ p ` o.t .9Q ---- Spin before mess. _ Zn.A5.. afterZ.'_50
----- ----••----•--- - - Mess. plots _.....1% dill, from ---- _rating
1� ----------
Wading, cable, ice, boat, M11—tr.1 downstr.,
L side bridge ---Q__ ___ feet, mile above
❑ - below ao, and -------------------------- ------
i_�5•_nis�s _4J:.i2... ---•_--.•.- Check -bar, chain found -------------------
changed to . ------ ---------- at _._......
---------- --------- Correct---------------------------------------------
G- H- correction_-..---------- __________ __________I
; Levels obtained ------------------- -----------
CarrccL M. G-H___ _-._________________ __________
Measurement rated excellent (2%), good (5%) fair {8%a =,poor (over 8%), based
on following conditions-. Cross section
Flaw Goa _c�il ri�_•�12I? ?Rn_i_ 9m4.-- Weather _ - n.j- - --------------------
-
Other ° F. @ __i_16-35---
Gage_ K------------------------------------ ------ Water-32
r_______________________ Record removed-_/Q.!.--------- Intake Bushed �
•��^^ ky L------------
observer__l_Qf_>•F.�----r'`'•h��......_...-----•---------------- -
-
Control __C.f.fiR.r---------- - ----------- . .----.----
---------------------- _... r.._..
Remarks __--Gn�tt-..._y]�i.y�,rt]---a�4StS 8�__..-F0,r..t'.r,,�..-----Q-S----
i.i
---------------• t>rA_Y_i.-j-----51..__aQ4----- Wa-V_3°A------------------------- ..... ....__.
G. H. of zero flow --- --------- ------ ----------------- ft. Sheet No. of. -Li.- Sheets.
L 3110
t _ _ - Z49 sacs. - 5 r•,=n.
Figure 69,—discharge measurement notes with mean gage height adjusted for
time of travel of flood wave.
is not submerged. A weir is not submerged when
there is free circulation of air on all sides of the
nappe.
The general equation for flow over a sharp -
edged triangular weir with a 94° notch is
Q= ChS12, (8)
where Q is the discharge, h is the static head,
and C is the coefficient of discharge. Each weir
should be rated by determining the flow
volumetrically. In the absence of such a rating
a value of C of 2.47 may be used.
To place the plate in a sand or silt channel,
the only tools required are a carpenter's level
and a shovel. The level is used to make the top
of the plate horizontal and the plate plumb.
Another way to level the plate is by fastening
a staff gage or level bubble to each end of the
weir. The staff gages are set at the same

DISCHARGE MEASUREML•'I`T5 AT GAGING STATIONS
59
Figure 70—Expanded plot of gage -height graph during measurement 264 at Big Creek near Dogwood, Va.,
March 26, 1962.
elevation. The plate is leveled by making the
staff -gage readings identical or by using the
level bubbles. The flow should be allowed to
stabilize before making <a measurement. The
gage height should be read five or six times
during a 3-minute interval and it inean value
should be used. Ordinarily a lone man can
measure with a weir of this type.
Portable Parsha[[ Flumes,
Description and Tkeory
A portable Parsh:ill measuring flume is
useful for measuring discharge when the depths
are shallow and the velocities are low. The
flume has a converging section, a throat., and a
diverging section. The floor of the converging,
or upstream section is level bath longitudinally
and transversely when in place. The floor of
the threat section slopes downward and the
floor of the diverging or downstream section
slopes upward.
'I he flume may be operated as a free -flow,
single -head measuring device, or operated under
submerged -How conditions where two heads are
measured. The head in the converging section
and the head near the downstream end of the
throat section are read on staff gages or in
stilling wells, Both gages have their datum at
the elevation of the floor of the converging
section.
Tree flow occurs when the ratio of the lower
gage reading to the upper gage is less than 0.6.
The discharge under this condition defends
only on the length of crest [width of throat

�1
A"
90' h
d
nn
m
Corners may be
trimmed if desired
)�T
Weir 7 h S 1 A T Weight(lb)
Large
Medium
Small
1.75
1.00
0.75
4.0
1.0
15 ga.
24
1.25
.80
.45
3.0
_7
14 ga.
17
.75
.47
.28
2.0
_53
10 ga.
8
Figure 71 .---Portable Weir plate sizes.
0

DISCIiARGE MEASUREMENTS AT GAGING STATIONS
61
section) and depth of water at the upper gage.
Submerged flow occurs when the ratio of the
Iower gage reading to the upper gage reading
ex(eeds 0.6. When this occurs, a reduction
adjustment to the free -flow rating of the
flume is needed.
A flume that is properly constructed has an
accuracy of 2-3 percent under free -flow con-
ditions, but is less accurate during submerged
flow.
A modified Parshall flume was designed by
C. A. Taylor and H. C. Troxell in 1931 (fig. 72)
and is virtually the same as the Parshall flume
Figure 72-Modified 3-inch Parshall Hume made of sheet
iron.
except that it does not have a diverging section
and is used only under free -flow conditions.
The plans are shown in figure 73 and the rating
is given in table 8.
The modified Parshall flume is recommended
for general use because of its simplicity, light
weight, :and ease of installation. However, the
regular Parshall flume is also satisfactory.
The flume is installed by placing it in a hole
dug in the channel and by filling in around it
to prevent any water from bypassing it. A
carpenter's level is used to set the floor of the
converging section level. Some flumes are
equipped with levels attached to the braces
on the Hume. After the flume is in place, the
streiamflow is allowed to stabilize before reading
the gages. Gage readings indicate flow condi-
tions. The discharge is determined by means
of the flume rating.
Volumetric Measurements
The most accurate method of measuring
small discharges is by observing the time
required to fill it container of known capacity,
or the time required to partly fill a calibrated
container to a known volume. The basic
equipment needed is a calibrated container
and a stopwatch.
Calibration is done by weighing the con-
tainer with varying amounts of water in it,
Table 8.--Ratin9 table for 3-inch modified Parshall flume as designed by C. A. Taylor and H. C. Troxell 0 93 1)
(,age height (it)
llisCliarge {efs}
Gage height (It)
Discharge W-9) t3age heght ((o Discharge {eIs}
0.01
0.0008
0.21
0.097
0.41
0.280
.02
.0024
. 22
104
42
.290
03
.0045
.23
.III
43
.301
04
.0070
.24
.119
44
.312
05
.010
.25
127
45
. 323
.06
.013
. 26
I35
.46
.334
. 07
.017
.27
M4
47
.345
.08
.021
. 28
.153
.48
.357
.09
. 025
.29
162
.49
368
10
.030
.30
170
50
380
11
.035
.31
179
51
.392
12
. 040
.32
188
52
.404
13
.045
.33
.198
53
.417
14
051
. 34
.208
. 54
.430
15
057
.35
218
55
.443
16
.063
.26
228
.56
.456
17
.069
.37
238
.57
.470
18
.076
.38
.248
.58
.483
19
.083
.39
259
.59
.497
.20
.090
.40
269

62 TECHNIQUES OF WATER -RESOURCES Y-WESTIGATIONS
Material: I/a-in. aluminum
Welded construction
Note: This stilling well can accommodate
a 3-in. float and be used with a recorder
if continuous measurement is desired for a
period.
Figure 73; Working drawing of modified 3-inch Paishall flume.
noting the depth of water in the container,
and then using the following formula:
V_W2—WIC (p)
w
in which
V=volume of water in container, in
cubic feet,
t
Wz—weight of container with water, in
pounds.,
WI = weight of container empty, in pounds,
w=unit weight of water, 62.4 lb per cu ft
{pounds per cubic foot}.
Another way to calibrate a container is to add
known volumes of water by increments and
note the depth of water in the container.

DISCHARGE MEASUREMENTS AT GAGING STATIONS
DR]
Volumetric ineasnrerr eats are made under
two types of conditions.
1. When the flow is concentrated or can be
concentrated so that all of it may be
diverted into a container.
2. When the depth of water flowing over
broad -crested weirs and dams is small
and volumetric -increment samples can
be obtained.
Measurements are made under the first
condition at V-notch weirs, at artificial controls
where all the flow is in a notch or catenary,
and at places where an earth dam can be built
and all the water can be diverted through a
pipe of small diameter. Sometimes it is necessary
to plane a trough against the artificial control
to carry the water from the control to the
calibrated container. If a small dam is built,
the stage behind the dann is allowed to stabilize
before the measurement is begun. The measure-
ment is made three or four tines to be certain
no errors have been made and to be sure the
results are consistent.
Volumetric measurements are made under
the second condition by catching a. segment
of the streamflow with a container having a
known width of opening, Samples are taken
at a m.mber of locations across the dam or
weir similar to procedures used for current -
meter measurements. The flow rate of each
sample is increased by the ratio of the sub-
section width to the saml,led width to obtain
a discharge rate for each subsection. The
total discharge of the stream is the summation
of the discharge rates of each subsection.
Floats
Floats have very limited use in stream gaging,
but there are two occasions when they prove
useful. A float can be used where the velocity
is too logs- to obtain reliable measurements with
the current meter. They are also used where
flood measurements are needed and the meas-
tiring structure has been destroyed or it is
impossible to use a meter.
Both surface floats and rod floats are used.
Surface floats may be almost anything that
floats, such as wooden disks, bottles partly
filled, or oranges. Rod floats are wooden rods
weighted on one end so they will float upright
in the stream. Rod floats must not touch the
streambed. Floating debris or ice cakes may
serve as natural floats.
Two cross sections are selected along a reach
of straight channel for a float measurement.
The cross sections should be far enough apart
so that the time the float takes to pass from
one cross section to the other can be measured
accurately. A traveltime of at least 20 seconds
is recommended, but a shorter time can be used
on small streams with high velocities, where it is
impossible to select an adequate length of
straight channel.
The procedure for a float measurement is to
distribute a number of floats uniformly over
the stream width, nesting the position of each.
They should be allowed to reach a constant
velocity before timing by stopwatch the interval
each takes to travel between two cross sections.
The distance of each float from the bank as it
passes each cross section should also be noted.
The velocity of the float is equal to the
distance between the cross sections divided by
the time of travel. Care must be taken when
measuring low velocities, that the floats are not
being affected by wind. The mean velocity of
flow in the vertical is equal to the float velocity
multiplied by a coefficient which is based on
the shape of the vertical -velocity profile and
relative depth of immersion of the float. A
coefficient of about 0.85 is commonly used to
convert surface velocity to mean velocity. The
coefficient for rod floats varies from 0.85 to
1.00 depending on the shape of the cross section
and the velocity distribution.
The discharge in each partial section is com-
puted by multiplying the average area of the
partial section by the mean velocity in the
vertical for that partial section. The total dis-
charge is equal to the sum of the discharges
for all the partial sections.
Float measurements can be made with an
accuracy within 10 percent under good condi-
tions and when a certain amount of care is
exercised. If a poor reach is selected and not
enough float runs are made, the results can be
as much as 25 percent in error.

64 TECTINIQUES OF WATER -RESOURCES INVESTIGATIONS
Indirect Discharge Measurements
During floods, it is frequently impossible or
impractical to measure the peak discharges
when they occur, because of conditions beyond
control. Roads may be impassable; structures
from which current -meter measurements might
have been made may be nonexistent, not suita-
bly located, or destroyed; knowledge of the
flood rise may not be available sufficiently in
advance to permit reaching the site near the
time of the peak; the peak may be so sharp
that a satisfactory current -meter measurement
could not be made even with an engineer present
at the time; the flow of debris or ice may be
such as to prevent use of a current meter; or
limitations of personnel might make it impossi-
ble to obtain direct measurements of high -stage
discharge at numerous locations during a short
flood period. Consequently, many peak dis-
charges must be determined after the passage
of the flood by indirect methods such as slope -
area, contracted -opening, flow -over -dam, or
flow -through -culvert, rather than by direct
current -meter measurement.
Detailed descriptions of the procedures. used
in collecting field data and in computing the
discharge are given in Benson and Dalrymple
(1967), Dalrymple and $enson (1967), Bod-
haine (1968), Ma.tthai (1967), and Hulsing
(1967), which are book 3, chapters AI-A5, of
this series. The use of electronic computers in
these computations is explained by Anderson
and Anderson I and by Somers and Selner.2
Dye -Dilution Method of Measuring
Disckarge
Measurement of discharge by this method
depends on determination of the degree of dilu-
tion of an added tracer solution by the flowing
water. A solution of a stable or radioactive
chemical is Mier Led Into ۥhe stream at either a
constant rate or all at once. The solution be-
9 Anderson, Y7. 13., and Anderson, W. I,., Computation of water -surface
profiles in open channels: U.S. 'leol. Survby Techniques Water -Re-
sources Inv., unpub, data.
2 Somers, W. P., and Seiner, 0. I., Computation of stage -discharge
relationships at culverts and Computer techn}quo for slope -area meas-
urements: U - & neol. SurveY T chniques Water -Resources Inv., unSsub.
data.
comes diluted by the discharge of the stream.
Measurement of the rate of injection, the con-
centration of the tracer in the injected solution,
and the concentration of the tracer at a cross
section downstream from the injection point
permits the computation of stream discharge.
The accuracy of the method critically depends
upon complete mixing of the injected solution
through the stream cross section before the
sampling station is reached and upon no ad-
sorption of the tracer on stream -bottom mate-
rials. The method is recommended only for those
sites where conventional methods cannot be
employed owing to shallow depths, extremely
high velocities, or excessive turbulence. A de-
tailed description of the procedures and equip -
meet used in measuring discharge by a dye -
dilution :method is given by Cobb and Bailey.'
References
Benson, M. A., and Dalrymple, Tate, 1967, General
field and office procedures for indirect measure-
ments: U.S. Geol. Survey Techniques Water -
Resources Inv., book 3, chap. Al, 30 p.
Bodhasne, G. L., 1968, Measurement of peak discharge
at culverts by indirect methods: U.S. Geol.
Survey Techniques Water -Resources Inv., book
3, chap. A3, 60 p.
Carter, R. W., and Anderson, 1. E., 1963, Accuracy
of current -meter measurements: Am. Soc. Civil
Engineers Jour., v. 89, no. HY 4, p. 105-115.
Dalrymple, Tate, and Benson, M. A., 1967, Measure-
ment of peak discharge by the slope -area method:
U.S. Geol. Survey Techniques Water -Resources
Inv., book 3, chap. A2, 12 p.
Hulsing, Barry, 1967, Measurement of peak discharge
at dawns by indirect methods: U.S. Geoff. Survey
Techniques Water -Resources Inv., hook 3, chap.
A5, 29 p.
Matthai, H. F., 1967, 'Measurement of peak discharge
at width contractions by indirect methods:
U.S. Geol. Survey Techniques Water -Resources
Inv., book 3, chap. A4, 44p.
Pierce, C. IL, 1941, Investigations of methods and
equipment used in stream gaging, part 1, Per-
formance of current meters in water of shallow
depth: U.S. Geol. Survey Water -Supply Paper
868-A, 35 p.
1947, Structure for cablE'%i %V4: T.S. Geci1.
Survey Circular 1i, 38 p., 25 pl.
Rouse, Hunter, 1950, Engineering Hydraulics: New
York, John Wiley and Snns, p. 222, 223.
= Cobb, E. D., and Bailey, 3, F., Measurement of discharge by dye-
d.lution methods: u.s. Cwoi. SurvAy Techniques Water-Ilesnurcez; Inv.,
uapub. data.

DISCHARGE MEASUREMENTS AT GAGING STATIONS
65
Schubauer, G. B., and Mason, M. A., 1937, Per-
formance characteristics of a water current, meter
in water and air: Natl. Bur. Standards Research
Paper, ItP 981,
Smith, Winchell, 1961, Optical current meter in
Short papers in the geologic and hydrologic
sciences: U.S. Geol. Survey Prof. Paper 424-B,
Art. 424, p. D383-D384.
Smoot, G. F., and Novak, C. E., 1968, Calibration and
maintenance of vertical -axis type current meters:
U.S. Geol. Survey Techniques Water -Resources
Inv., book 8, chap, B2, 23 p.
1968, Measurement of discharge by the moving -
boat method: U.S. GeoI. Survey Techniques of
Water -Resources Inv., book 3, chap. A11, 22 p.
Townsend, F. W., and Blust, F. A., 1960, A comparison
of stream velocity meters: Am. Soc. Civil Engi-
neers .lour., v. SS, no. HY 4, p. 11-19.
Young, K. B., 1950, A comparative study of mean -
section and mid -section methods for computation
of discharge measurements: U.S. Geol. Survey
open -file report, 52 p.
U.S. GOVERN VENT PRINTING OMM! I969 0-328-25a

EARTMENT OF THE
INT
MiSGS U.S. DUPS. GEOLOGICAL URVEYERIOR
science for a changing world
78°52'30"
39720i
50,
47'
730
F
35°45'
%k5"bL'3U"
Produced by the Urljted States Geological Survey
North American Datum of 1983 (NAD83)
World Geodetic System of 1984 (WGS84). Projection and
1 000-meter grid: Universal Transverse Mercator, Zone 17S
10 000-foot ticks: North Carolina Coordinate System of 1983
Imagery.......................................................NAIP, July 2008
Roads..............................................02006-2010 Tele Atlas
Names...............................................................GNIS, 2008
Hydrography .................National Hydrography Dataset, 2008
Contours............................National Elevation Dataset, 2008
N.
8° 46'
156 MILS N
1° 1T
23 MILS
UTM GRID AND 2010 MAGNETIC NORTH
DECLINATION AT CENTER OF SHEET
U.S. National Grid
100,000-m Square ID
r o0
PV I QV
Grid Zone Designation
17S
The National Map
==j USTopo
50'
47'30"
PV QV
bU' 4/'3U" PV QV
SCALE 1:24 000
1 0.5 0 KILOMETERS 1 2
1000 500 0 METERS 1000 2000
1 0.5 0 1
MILES
1000 0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000
FEET
CONTOUR INTERVAL 10 FEET
NORTH AMERICAN VERTICAL DATUM OF 1988
This map was produced to conform with version 0.5.10 of the
draft USGS Standards for 7.5-Minute Quadrangle Maps.
A metadata file associated with this product is draft version 0.5.11
O H CAROILINA
01IAnRANf,1 F 1 OCATInN
Southwest
Southeast
Durham
Durham
Bayleaf
Green
Cary
Raleigh
Level
West
New Hill
Apex
Lake
Wheeler
CARY QUADRANGLE
NORTH CAROLINA
7.5-MINUTE SERIES
78°45'
35°52'30"
72
70 000
=ET
71
70
69
68
50'
67
66
65
64
47'30"
63
62
61
60
59000"N
35°45'
/ 6-4b'
ROAD CLASSIFICATION
Interstate Route State Route
US Route Local Road
Ramp 4WD
WInterstate Route 0 US Route �—� State Route
CARY, NC
2010
ADJOINING 7.5' QUADRANGLES