Stream-Gaging Stations

For Research on Small

Watersheds

U.S. DEPARTMENT OF AGRICULTURE AGRICULTURE HANDBOOK NO. 268

FOREST SERVICE MAY 1964
Stream-Gaging Stations

For Research on Small

Watersheds

Kenneth G. Reinhart and Robert S. Pierce

Northeastern Forest Experiment Station

Forest Service, U.S. Department of Agriculture

AGRICULTURE HANDBOOK NO. 268 MAY 1964
Contents

Page

Introduction 1

Choosing the stream-gaging site 2

Types of stream-gaging stations 3

Weirs 3

Flumes 8

Choosing the stream-gaging station design 10

A sharp-crested 120° V-notch weir 12

Design 13

Cutoff wall 13

Watertight box 15

Construction 15

Layout 15

Excavation 16

Cutoff wall 16

Sidewalls 19

Floor 20

Weir blade 20

Drainpipes 21

Debris dam and baffles 21

Gagehouse and well 22

Intake pipes 23

Cost of construction 24

Instrumentation 24

Water-level recorder 24

Hook gage 25

Reference tape 25

Staff and crest gages 26

Operating procedures and maintenance 27

Rating the weir 27

Periodic chart changing 28

Checking water levels 28

Instrument and basin 28

Trash screens 28

Cold weather maintenance 29

Enclosure of well 29

Subfloor 29

Oil cyhnder 29

Heating appliances 29

Ice in the weir basin 30

Bibliography 31

Appendix 33

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

Washington, D.C., 20402-Price 30 cents.
Introduction

With an increasing population and percapita consumption of water, nationwide

concern has arisen about the adequacy of

our water supplies. Some regions suffer

acute shortages. Yet many areas sometimes

sustain major damage from great floods.

Watershed research has shown that land

use and treatment affect both water yield

and peak flows. Under certain situations

yield may be increased by vegetation management and other land practices; in other

circumstances, peak flows may be reduced.

This research is just being started in some

parts of the country.

One of the accepted research techniques in

watershed management is the measurement

of streamflow from small experimental

watersheds. Such measurement permits

evaluation of the effect that manipulation

of cover has on water-yield characteristics

for fairly homogeneous areas.

During the past several years (since 1955),

the authors have been responsible, or have

had close contact with those responsible,

for building 21 stream-gaging stations in

small experimental watersheds in the Northeast, particularly on the Fernow Experimental Forest in West Virginia and the

Hubbard Brook Experimental Forest in New

Hampshire. This experience, a review of the

literature, and information from several

other workers in the field provide the basis

for this handbook. It is prepared especially

for researchers who have little experience

in water measurement but are responsible

for the construction and operation of streamgaging stations.

Details of all aspects of stream gaging will

not be discussed. This report is only a general guide on the design and construction

of small stream-gaging stations. Additional

details should be sought from the literature

and from geologists, engineers, and hydraulic

experts.

Stream gaging, as used here, is the measurement of the water leaving a watershed as

flow in a natural stream channel. Water lost

to deep seepage and not appearing as streamflow at the point of measurement cannot be

measured by the stream-gaging station.

Therefore, watersheds with minimum deep

seepage are best for research.

Small watersheds include those of about 20

to 1,500 acres. Such watersheds are large

enough —in the Northeast at least —to provide flow all or most of the time, but they

are small enough so that construction of an

artificial control is not impractical. On

larger streams, gaging is usually done by

using natural controls; such measurement is

generally less precise than that with artificial controls on smaller streams.

A control is a natural constriction of the

channel, a long reach of the channel, a

stretch of rapids, or an artificial structure

downstream from a gaging station that determines the stage-discharge relation at the

gage (Langbein and Iseri 1960).^

There are many objectives of stream gaging in watershed research. In some cases

one objective may be paramount; in others

several may be about equally important.

A common objective is a continuous record

of streamflow. To attain this goal, recording

instruments that give a round-the-clock record are required. Usually yearlong records

are obtained, but records for the growing

season or some other short period may

suffice. Measurements may be made to determine maximum flows and runoff" volumes

for major storm periods, low flows, or all

flow leaving the watershed.

The research program will specify the number of stream-gaging stations required.

Ordinarily two or more watersheds, as nearly

identical as possible, are chosen. This permits the development during the pretreatment period of an expression for predicting

flow of one watershed from that of the other;

after treating one of the watersheds, differences between predicted and measured flow

indicate the effect of treatment.

Sometimes only one watershed is used, and

flows before and after treatment are compared to determine treatment effects. In

this case, equations for predicting flow must

be developed from climatic measurements in

the calibration period.^ Comparison through

a control watershed partly counteracts the

difficulties experienced because of differences

in climate from year to year or before and

after treatment (Reinhart 1958).

In this handbook, the types of gaging stations with which the authors have had personal experience will be discussed in some

detail. Other types of stations will be considered in a more general way to provide an

overall treatment of the subject.

^ Names and dates in parentheses refer to Bibliography, p. 31.

2 Reigner, Irvin C. CaUbrating a watershed by using

chmatic data. U.S. Forest Serv. Res. Paper NE-15, 45

pp., illus. Northeast. Forest Expt. Sta., Upper Darby, Pa.

1964.
Choosing the Stream-Gaging Site

Selection of a stream-gaging site depends

mainly on two factors: The objectives of the

research program and the physical land features necessary to meet these goals.

For example, if the objective is to measure

total streamflow, the site must be one where

all streamflow can be channeled through the

measuring device. Limestone, permeable

gravel beds, or other soil or bedrock conditions may make it virtually impossible to

measure all or even almost all of the outflow

from a watershed. However, if measurement of stormflow is the objective, primary

consideration should be given to a site suitable to handle large flows, and low or subsurface flows can be disregarded. And where

the measurement of flows in sluggish, lowgradient streams with porous channels is the

aim, a totally different set of gaging-site

requirements must be met.

Because technical requirements are perhaps more rigid for measurement of total

flows than for other types of flow, primary

consideration will be given to the selection

of sites for this purpose.

First, to find the best location on the

stream, it should be determined whether the

watershed above the site is suitable in regard to cover type, acreage, anticipated flows,

uniform terrain, elevation differences, soils,

geology, etc.

Factors influencing the choice of the site

include: (1) Presence of impermeable material, (2) stream gradient, (3) stream alinement, (4) character of streambanks, (5) depth

of channel, (6) topography and drainage at

site, (7) gaging-station design, and (8)

accessibility.

Impermeable material (soil or bedrock) in

the stream channel over which all streamflow must pass may be the primary requisite

for site location. The depth to such impermeable material may determine the feasibility of the site. Depth to bedrock or

impermeable material may be determined

by observation of outcrops in the vicinity,

by digging of preliminary pits, or by use of

a soil tube or auger.

The gradient of the stream channel must

be considered. If the gradient is too steep

or too low, it may be impossible, difficult,

or costly to meet certain hydraulic requirements for the gaging station (these will be

described later). Stream-gaging stations

such as V-notch weirs require sufficient

elevation to create a ponding basin in the

channel. But some flumes can be installed

in streams with as little as 3-percent

gradient.

Straight and uniform stretches of the

stream are generally the best approaches to

the gaging site. However, such stretches

are not required if a gaging-station design

that eliminates the influence of upstream

flow characteristics is selected.

The width between banks will greatly

govern the size of the installation, the

excavation necessary, and the type of station; that is, a simple cutoff wall is usually

needed if the streambed is narrow, but a

more elaborate structure is generally needed

if it is wide.

The depth of channel and width between

banks at the site approach will partly determine whether the site is suitable for

funneling all flow through the gaging station during peak runoff periods.

V-shaped stream channels of impermeable

subsoil or bedrock are very desirable for

stream-gaging sites because low flows may

be easily led from the confining natural channel through the measuring device, and construction of the gaging station may be less

costly. Where such ideal stream channels

may not exist —for example, in glaciated

terrain—compromises in site selection will

be necessary.

Determining the drainage area above the

gaging station is often a problem. The

topography and drainage characteristics in

the vicinity of a proposed site, such as the

presence of springs, should be studied. Often, selecting a site a short distance upstream or downstream may permit a better

determination of watershed boundaries.

In selecting gaging sites, consideration

should be given to the gaging-station design

most suitable for that site. However, modifications of standard stream-gaging designs

may be needed to fit local site conditions.

Inspection of the stream during extremely

low flow will often indicate the reaches where
flow is restricted to the surface because of

soil or geologic conditions and those where

flow is below the surface. The stream should

be inspected during high-flow periods to estimate maximum discharge and to see if the

banks at the site can carry the flow.

An additional consideration is accessibility.

Gaging sites that meet the technical requirements may be impractical because of excessive traveltime to the site, difficulty of

hauling in construction materials and equipment, lack of workspace, and inaccessibility

in certain seasons.

Types of Stream-Gaging Stations

The basic components of a stream-gaging

station are the control and the water-stage

recorder. The control and the volume of flow

determine the elevation of the water surface

at the recorder location. The relation between height of the water at the gaging point

and rate of flow over the control is called the

stage-discharge relationship or rating.

Generally artificial controls are used for

research on small watersheds, so only those

controls will be considered in this handbook.

For most measurements, the control must

be constructed so that nearly all outflow from

the watershed goes over it; flow under it or

around it will escape measurement.

The most common types of stream-gaging

stations are weirs and flumes. With weirs,

water is ponded above the control, and

changes in the elevation are related to discharge. Weirs have often been preferred for

gaging of small watersheds. The weir, when

properly set and maintained, is considered

one of the most accurate means of measuring

flowing water (Parshall 1950). Where heavy

sediment-laden flows are common, particularly as bedload movement, flumes should be

used; a flume is a stabilized channel (without

an impoundment) with access to a stilhng

well. Flumes also must be used where the

gradient of the stream is particularly low.

The various objectives for which streamgaging stations have been built, and the related conditions, have resulted in many

different types of weirs and flumes.

Weirs or flumes are constructed of various

materials. Concrete, because of its strength

and permanence, probably is used the most.

Treated wood, concrete blocks, metal, and

many other materials are also used. The

weir notch is often a steel blade set into concrete, and flumes are often lined with steel

for permanence.

WEIRS

Weir may denote a notch of regular form

(rectangular, triangular, trapezoidal, circular, or parabolic) through which water flows,

or it may mean the structure containing the

notch. As used in this handbook, weir includes all components of a stream-gaging

station that incorporates a notch control.

An impoundment of water (the weir basin)

is formed upstream from the wall or dam containing the notch. A stilling well with

water-level recorder is connected to the weir

basin. A gagehouse or some other type of

shelter is provided to protect the recorder.

The cutoff wall or dam is used to divert

through the notch all water (above or below

the streambed) moving down the channel.

Where possible, the cutoff wall is tied into

bedrock or other impermeable material so

that no water can flow under or around it.

But where leakage is apt to occur the weir

basin is sometimes constructed as a watertight box (see p. 15).

The edge or surface over which the water

flows is called the crest. Weirs can be either

sharp crested or broad crested. A sharpcrested weir has a blade with a sharp upstream edge so that the passing water

touches only a thin edge and springs clear of

the rest of the crest. The blades of the 90°

and 120° V-notch weirs installed by the authors are of M-inch angle iron or ^-inch
steelplate ground to a sharp edge at a 45-

degree-angle.

A broad-crested weir has a flat or broad surface over which the discharge flows. There

is a large variety of broad-crested weirs.

Some have sharp right-angle corners with

vertical sides and horizontal crests; some

have rounded corners; some have sloping

crests; and some have rectangular, triangular, or trapezoidal cross sections. Broadcrested weirs are generally used where

sensitivity to low flows is not critical and

where sharp crests would be dulled or

damaged by sediment or debris. A broadcrested weir is shown in figure 1. Tracy

(1957) discusses discharge characteristics of

broad-crested weirs.

The sheet of water flowing over the weir is

the nappe. The weir has free discharge if

the nappe discharges into the air: air circulates freely on all sides of the flow issuing

from the weir notch. Adherence of the

nappe to' the weir blade or cutoif wall can

cause an appreciable increase in the rate of

flow for a given head (Thomas 1957). If the

SURFACE CONTRACTION

\ , I \X(AERATED BELOW)

SHARP CREST AND

CREST CONTRACTION

NAPPE

BROAD CREST

FIGURE 1. —Schematic diagrams of general hydraulic

relationships for weirs, based on King (1954): A, Flow

characteristics over a sharp-crested weir; H is the

depth of water producing the discharge; B, minimum

requirements for proper discharge when H equals

greatest expected depth for a sharp-crested V-notch

weir with end and crest contractions; C, flow characteristics over a broad-crested weir of rectangular

cross section.

discharge is partially underwater, the weir is

submerged or drowned (King 1954). This

happens if there is insufficient fall below the

weir crest or when the channel below the

weir cannot carry the flow off rapidly enough.

Submerged flow is at best relatively unstable,

and measurements made by a submerged

weir should be considered approximate only

(Thomas 1957). When positioning the notch

during construction, consideration should be

given to maximum expected flows and likelihood of submergence.

As the nappe flows through the notch, the

velocity of flow increases, and the nappe

cross section is reduced or contracted. This

contraction is aff'ected by the shape of the

notch and basin characteristics immediately

upstream from the notch.

Where the depth of water from the crest

to the basin floor is less than 2.5 times the

head of water over the crest, the crest contraction of the nappe is partially suppressed.

Velocity of approach will increase, and actual

discharge will be greater than that shown by

the normally used formulas and tables (fig. 1).

If the basin is the same width as the crest,

the weir has its end contractions suppressed.

For complete end contractions, the distance

from the edge of the notch to the side of the

weir basin or channel should be at least 2.5

times the head being measured (King 1954).

A narrower weir basin or channel results in

increased velocity of approach and increased

flow for a given head.

For best results, the velocity of approach

should be held to a maximum of 0.5 foot per

second (Thomas 1957). Where velocities of

approach are appreciable, the discharge

should be corrected (U.S. Bureau of Reclamation 1953).

Water discharging over the crest of a weir

drops slightly in elevation immediately upstream from the crest. This decrease is

caused by the water's acceleration in velocity

as it approaches the crest. Such a drop is

called surface contraction or drop-down.

In sharp-crested weirs the effect of this surface contraction extends upstream from the

crest a distance twice the head of water flowing over the crest (King 1954). Therefore,

the intake to the stilling well should be

located upstream from the crest a distance

equal to or greater than twice the head of

the maximum anticipated flow (fig. 1).

Fully contracted weirs are generally preferred in research; however, site characteristics sometimes dictate suppression of end

contractions.

These factors are particularly important if

laboratory determinations of the stage-discharge relationship are to be used. A discussion of the conditions of flow over a weir
can be found in King's Handbook of Hydraulics (1954).

The rectangular weir has vertical sides and

a horizontal crest (fig. 2). Its height and

width can be varied considerably, depending

on the anticipated flow. The ratio of height

to width is usually about 1:3 or 1:4. Its

major advantage is its capacity to handle

large flows. However, the rectangular weir

cannot provide for precise measurement of

the low flows of small experimental watersheds—a small increase in head will give a

greatly increased discharge. Therefore,

small errors in measurement of head produce relatively large errors in discharge.

An example of a broad-crested rectangular

weir is the Trenton type of control, developed

by the U.S. Geological Survey (Corbett and

others 1943).

The trapezoidal weir is similar to the rectangular weir. Its sides, of course, are inclined from the vertical (fig. 3). It has a

larger capacity than a rectangular weir of

the same crest length; the discharge is ap1-440615

FIGURE 2. —A 6-foot rectangular weir with angle-iron

knife-edge blade is used on watersheds where flow

ranges from 0.70 to 90 cubic feet per second. Coweeta

Hydrologie Laboratory, Franklin, N.C.

proximately the sum of discharges from the

rectangular and triangular sections.

^^ ^

I - 4öy7J-l

FIGURE 3. —An 8-foot CipoUetti trapezoidal weir with knife-edge blade is used on watersheds of approximately 2,000

acres. Coweeta Hydrologie Laboratory, Franklin, N.C.
The Cipolletti weir is a special trapezoidal

weir that does not require a correction for

end contractions. Sides are sloped one unit

away from the vertical for each four units

of rise. The flow (with end contractions) is

about equal to the flow of a rectangular weir

of equal crest length that has a channel width

the same as the crest (weir with end contractions suppressed).

Sharp-crested V-notch or triangular weirs

are often used where accurate measurements

of low flows are important. In the V-notch

weir, a small increase in flow during low flow

will produce a relatively large increase in

head and a good sensitivity of measurement.

A V-notch weir may have a rectangular section above to accommodate infrequent high

flows.

The two most common sharp-crested Vnotch weirs are the 90° notch (fig. 4) and the

120° notch (fig. 5), with metal blades ground

to a sharp edge and built into a concrete

cutoff wall. The 90° type gives greater sensitivity at low flows; the 120° type covers a

wider range of flows. V-notch weirs are

usually constructed to accommodate heads

up to 2 feet; however, both in the United

States and elsewhere V-notch weirs capable

of handling gage heights in excess of 2 feet

are in use.

Broad-crested triangular weirs with 2:1,

3:1, and 5 :1 (fig. 6) side slopes (with notches

approximately 127°, 143°, and 157°, respectively) were developed and rated by the Soil

Conservation Service for measuring flows up

to about 1,000 c.f.s. (Harrold and Krimgold 1943). The shape and thickness of the

K-503I3I

FIGURE 5.-A 120° v-notch weir similar to the 90° Vnotch weir, but capable of handling flows almost twice

as large. This 2-foot-high notch has a capacity of

about 24 c.f.s. Fernow Experimental Forest, Parsons,

W. Va.

FIGURE 4.-A 90° v-notch weir with sharp-edge blade is

designed for great sensitivity at low flows. It is used

on watersheds of 5 to 50 acres. The 2-foot-high notch

has a capacity of about 14 c.f.s. Hubbard Brook Experimental Forest, West Thornton, N.H.

U1S-R.S-I9

FIGURE 6. —A triangular weir with 5:1 side slopes, recorder shelter, and stilling well on the 330-acre watershed operated by the Agricultural Research Service

near Fennimore, Wis.

crest permits comparatively free passage of

debris and minimizes the effect on the stagedischarge relationship of small irregularities

of the crest and of trash temporarily lodged

on the crest. A reasonably straight and practically level channel for 50 feet above the

weir, with the notch 6 inches above the bottom of the approach channel, is essential for

accuracy. Rating tables have been developed which give discharges corresponding to

heads up to 6 feet and also for cross-sectional areas of the channel 10 feet upstream

from the center of the crest (U.S. Agricultural Research Service 1962).
The Columbus deep-notch weir has a paraboHc notch and is designed to give accurate

measurement of a wide range of flows. The

notch, often lined with bronze for permanence, accommodates low flows; a larger,

nearly rectangular section, with crest sloping very gently toward the notch, accommodates high flows. The throat of the notch is

convex (along the axis of flow) to permit passage of debris. A modified Columbus deepnotch weir, with shortened sloping crest

and a rectangular section directly above, is

in use in several U.S. Forest Service installations (fig. 7).

r-469491

FIGURE 7.— A modified Columbus deep-notch weir with

a bronze liner in the notch is used for a wide range

of flows, especially where extreme sensitivity at low

flows is required. Coweeta Hydrologie Laboratory,

Franklin, N.C.

In one modification (fig. 8), the Trenton

weir is converted from rectangular to triangular by constructing it with slopes

upward away from the center at a rate of

1 :10 (notch is approximately 169°). It may

have vertical wingwalls at the side to accommodate high flows.

PF.NN STAiK rM\i:Ksri\ PIIOIO

FIGURE 8.-Trenton weir above a 90° v-notch. The slope

above the notch has a ratio of 1:10. Leading Ridge

Watershed near State College, Pa. A Pennsylvania

State University School of Forestry photo.

Economical stream gages using weir principles are sometimes placed in existing structures such as highway culverts and bridges.

Examples of these are the Villemonte weir

sill and the Virginia V-notch weir (U.S.

Agricultural Research Service 1962).

Abbreviated rating tables for several types

of weirs are given in table 1. Because all

necessary conditions of flow are not detailed,

this table should be used only for comparison

of weir types and not for determining actual

flows.

TABLE 1.-Comparative discharges for several types of weirs at various heads, in cubic feet

per second

Head ffppt)

Rectangular

(sharp-crested);

crest length,

1 foot'

Cipolletti

(sharp-crested

trapezoidal);

crest length,

1 foot'

v-notch (sharp-crested) Triangular (broad-crested); side slopes ofColumbus

deep notch

(broadcrested)«

Trenton

(broad-crested

rectangular);

90" 120°' 2:1" 3:1> 5:1'

discharge per

foot of length'

0.1 0.113 0.107 0.008 0.016 0.017 0.025 0.037 0.026 0.079

.2 .314 .301 .047 .086 .094 .132 .215 .055 .245

.3 .569 .553 .129 .232 .252 .364 .590 .085 .470

.4 .868 .852 .262 .470 .514 .757 1.23 .145 .752

.5 1.206 1.190 .455 .811 .903 1.35 2.15 .280 1.080

.6 1.576 1.565 .714 1.268 1.44 2.16 3.45 .530 1.450

.7 1.977 1.972 1.044 1.850 2.16 3.21 5.18 .935 1.87

.8 2.406 2.409 1.452 2.565 1.54 2.32

.9 2.861 2.875 1.943 3.423 2.49 2.80

1.0 3.340 3.367 2.520 4.430 3.89 3.31

2 0 9.252 9.522 13.96 24.19 62.30 10.15

By Formula: Q = 3.34H' " (King 1954).

' By Formula: Q = 3.367 LH« (King 1954).

» By Formula: Q = 2.52H' " (King 1954).

• By Formula: Q = 4.43H' "• (Hertzler 1938).

' (Harrold and Krimgold 1943).

«Northeastern Forest Experimental Station files; rating made by U.S. Geological Survey.

' Rating table furnished by U.S. Geological Survey, Trenton, N.J.

Note: In these formulas, Q is discharge in c.f.s., H is head in feet, and L is length of crest in feet.

717-764 0-64-2
FLUMES

A flume is an artificial open channel built

to contain flow within a designed crosssection and length. The types of flumes that

have been used on small watersheds are

described here.

HS, H, and HL flumes developed and rated

by the Soil Conservation Service have converging vertical sidewalls cut back on a slope

at the outlet to give them a trapezoidal projection (Harrold and Krimgold 1943) (fig. 9).

These have been used largely to measure intermittent runoff. Maximum depths of

waterflow are 1 foot for the HS type, 4.5 feet

for the H type, and 4 feet for the HL type.

Maximum flows are 0.8, 84, and 117 c.f.s.,

respectively. These flumes are in use at

many Agricultural Research Service installations (U.S. Agricultural Research Service

1962) and a number of other locations. The

above-cited publications give details of construction and ratings for these flumes.

'^^^^

fO.

^"^^

r!ç!.Ta'T(ti-;j

ratr=-

"Ä-'l^-^l^

CHANNEL GRADIENT

C

DIRECTION OF FLOW

ARS-20315

FIGURE 9.— An H-type flume. View looking upstream at

flume and recorder house on small watershed operated

by Agricultural Research Service near Riesel, Tex.

The Venturi flume (fig. 10) has a gradually

contracting section leading to a constricted

throat and an expanding section immediately

downstream (King 1954; Parshall and Rowher

1921). The floor of the Venturi flume is the

same grade as the stream channel, whereas

that of the Parshall flume (described below)

is depressed in the throat section. Stilling

wells for measuring the head are at the entrance and at the throat; the difference in

head at the two wells is related to discharge.

Venturi flumes are rectangular, trapezoidal,

triangular, or any other regular shape.

They are widely used in measurement of

irrigation water.

FIGURE lO.-Schematic diagram of Venturi flume. It

requires measurement of stage at two points. Floor

is same grade as stream channel: A, Plan view of

Venturi flume; B, cross sectiorr of Parshall flume; C,

cross section of Venturi flume.

The Parshall flume, a modification of the

Venturi flume, measures water in open conduits and is widely used, especially for

measuring irrigation water (Parshall 1950).

It consists essentially of a contracting inlet,

a parallel-sided throat, and an expanding

outlet, all of which have vertical sidewalls.

It can measure flows under submerged conditions. Two water-level recorders are used

when measuring submerged flow, one in the

sidewall of the contracting inlet and the

other slightly upstream from the lowest

point of the flow in the throat. When measuring free flow, only the upper measuring

point is used.

An inexpensive trapezoidal flume for gaging hard-to-reach locations in mountain

streams (fig. 11) was developed for the

Rocky Mountain Forest and Range Experiment Station (Goodell 1950; Robinson 1960).

This flume could be rated with a velocity

head rod (Wilm and Storey 1944).

The San Dimas flume (figs. 12-14) was designed on the San Dimas Experimental Forest of the U.S. Forest Service to measure

debris-laden flows in mountain streams

(Wilm et al. 1938). It is rectangular and

has a sloping floor (3-percent gradient) that

functions as a broad-crested weir except

that the contraction is from the sides rather

than the bottom; therefore, there is no bar-
rier to cause sediment deposition. Depth

measurements are made in the parallelwalled section at about the midpoint. Rapid

flow keeps the flume scoured clean. ,

FIGURE 11.-Trapezoidal flume used to gage streamflow

of Upper Fool Creek, Fraser Experimental Forest,

Fraser, Colo. The man in the picture is holding a

velocity head rod that has been used to rate this

flume.

FIGURE 13.-A l-foot San Dimas flume (on left) and

broad-crested weir used to gage streamflow of Fool

Creek, Fraser Experimental Forest, Fraser, Colo.

TRANSITION, PARALLEL WALL

-SECTION —t~ SECTION

UPSTREAM

END SLOT

I

-lé^W-

-w—J—w—

-Lp=2W —

DOWNSTREAM

END

SILT TRAPSECTION A-A

-L=3^WPLAN

W= WIDTH OF FLUME

Lp= LENGTH OF PARALLEL FLUME SECTION

L= TOTAL LENGTH OF FLUME

R= RADIUS OF TRANSITION

SILT TRAP

^

PIPE TO

STILLWELL

SECTION B-B

FIGURE 12. —Generalized drawing of San Dimas flume. This design has been used for flumes with widths of 0.5, 1.0,

2.0, 3.0, 4.0, 6.0, and 10.0 feet.
FIGURE 14.-A 3-foot San Dimas flume in lower center.

Note larger 10-foot-wide flume upstream and 90° Vnotch weir to left. The 3-foot flume can accommodate

flows up to 77 cubic feet per second, whereas the 10-

foot flume can handle flows to 1,000 cubic feet per

second. San Dimas Experimental Forest, Glendora,

Cahf.

The types of weirs and flumes that have

been discussed are those most used in research. In some cases, structures have been

built to incorporate features of more than

one type; for example, a 90° V-notch recently

built into a Trenton-type weir at The Pennsylvania State University. When a wide

range in flow or sediment load is anticipated,

it may be advantageous to install more than

one device at the same site. On several

watersheds at the San Dimas Experimental

Forest in California, stormflows are measured with a 3-foot San Dimas flume and low

flows are diverted to a 90° V-notch weir (fig.

14). A somewhat similar arrangement was

constructed for several watersheds on the

Hubbard Brook Experimental Forest in New

Hampshire. On the Sierra Ancha Experimental Watersheds in Arizona, a 90° V-notch

weir for low flows and a Cipolletti weir for

high flows are in use.

Choosing the

Stream-Gaging Station Design

The type of gaging station to be used depends upon many factors: Maximum and

minimum flows; accuracy needed in determining total discharge, high flows, and low

flows; amount of sediment or debris that is

expected, and whether it is suspended or

bedload; channel gradient; channel cross

section; underlying material; accessibility of

site; financial hmitations; and length of study.

Maximum and minimum flows likely to be

encountered must be estimated before construction. Such estimates can be made from

observation of high and low flows and high

watermarks (Johnstone and Cross 1949) and

from information given by local residents,

or they might be based on the area of the

watershed and records from other gaging

stations in the region. Maximum expected

flood peaks can also be estimated from rainfall, soil, and cover data, using a method

developed by the U.S. Soil Conservation Service (U.S. Bureau of Reclamation 1960). Assistance should be sought from the U.S.

Geological Survey and U.S. Soil Conservation

Service.

The maximum and minimum flows to be

measured at any degree of precision depend

upon the objectives of the study and the

extremes that might occur. In some cases, a

gage will be adequate if it will measure, with

acceptable accuracy, 90 to 95 percent of the

flow. These limits exclude extreme peaks

and very low flows. However, the structure

must be strong enough to withstand the

highest flow expected.

Once maximum and minimum estimates

are made, reference to rating tables for

various structures or to formulas for computing flow (King 1954) will show the types

and sizes of installations that can be used.

Maximum and minimum discharges for

several types of weirs and flumes are given

in table 2.

Rating tables will also show the relationship between the increase in discharge and

the corresponding rise in head at various

stage heights. This association indicates

the sensitivity of the gaging station at different levels of discharge.

10
TABLE 2,—Maximum and m^inimum. discharges for several types of weirs and

flumes in cubicfeet per second (approximate)

WEIRS

Type Minimum

Maximum

Sharp-crested weirs:

2 feet high, 90° V-notch <0.001

<.001

1 .24

1.30

1.46

2.017

2.025

2.037

.026

14

2 feet high, 120° V-notch 24

2 feet high, 6 feet wide rectangular...

2.75 feet high, 8 feet wide Cipolletti...

4 feet high, 12 feet wide Cipolletti

Broad-crested weirs:

Triangular 2 :1 side slopes

56

123

323

3 510

Triangular 3 :1 side slopes 3 803

Triangular 5 :1 side slopes 3 1 440

2 feet high Columbus deep notch 62

FLUMES

HS type:

0.4 foot hie-h. 1 0.001 0 1

LO foot hio-h ' .002 8

H type:

1.0 foot hiP-h ' 004 2

2.0 feet high 1 .007 11

4.5 feet hie-h 1 .015 84

HL type:

4.0 feet high. ' .03 117

San Dimas:

1 foot WIHP .1

2

10

36

6

3 feet wide 77

6 feet wide 318

10 feet WIHP 1,000

Trapezoidal:

1-foot-wide throat, 4 feet high, 30° 1.15 350

side slopes.

Parshall:

1 foot wide, 2 5 feet high .4 16

2 feet wide, 2 5 feet high .7 33

4 feet wide, 2.5 feet high 1.3 68

8 feet wide, 2.5 feet high. 4.6 140

' Flow at 0.05-foot head.

•^ Flow at 0.1-foot head.

3 Flow at 6-foot head with cross-sectional area of 300

square feet in the channel of approach 10 feet upstream

from center of crest.

Rating" can be simplified by choosing a

design for which a stage-discharge relationship has been determined in the laboratory.

Before construction, the conditions under

which the design was tested should be carefully studied. After construction, the laboratory rating should be checked at various

stage heights by direct measurement with

a current meter, velocity head rod, or another

instrument for determining velocity, or by

volumetric measurements. Rating-table discharges of sharp-crested V-notch weirs for

heads of less than 0.2 foot can be expected to

be inaccurate (Thomas 1957). For heads below 0.2 foot, the weir can be rated in the field,

as will be described later.

If a design is used for which a rating has

not been determined, the installation is rated

by making measurements at various stages,

using a current meter (Pierce 1941a; Corbett

and others 1943) or other means. Peak ñows

may be difficult to measure.

Where excessive amounts of suspended

sediment, bedload, and floating debris are encountered, flumes are preferable. Weirs

would be unsatisfactory because the basin

would trap this material, which would alter

the weir rating, and debris would clog the

crest of the weir, giving grossly inaccurate

measurements. Broad-crested weirs are

often used on agricultural watersheds where

grass and other debris would lodge on a

sharp-crested weir and invalidate the rating

curve (U.S. Agricultural Research Service

1962).

The gradient of the stream channel may

aff'ect choice of design. If the gradient is too

low, it may be impossible to install a weir

that will meet the requirements of a standard rating (depth of water below crest equal

to at least 2.5 times the maximum head to be

measured). A control with less elevation

may have to be built, and the station will

then have to be rated by current meter or

other means. It was largely because of the

low channel gradient that the combination

90° V-notch and Trenton weir was installed

at the Pennsylvania State University. Low

flows through the 90° V-notch correspond to

the standard rating, but higher flows are

rated with a pygmy meter.

The channel cross section and streambanks

may dictate design. Under some conditions,

a cutoff wall high enough to satisfy rating requirements would have to be of considerable

length to tie into solid material at the sides.

The cost of such a wall might rule out this

type of installation.

Underlying material must be considered.

If permeability is a problem, either a watertight-box weir design, which can support an

artificial head of water, or a flume will be

necessary.

The type of weir or flume and the material

used in its construction may be influenced

by the accessibility of the site. For example,

though ready-mix concrete is often the best

material, it cannot be used on forested watersheds where the terrain is so rugged that it

would not be practicable to build access roads

capable of accommodating ready-mix trucks.

The trapezoidal flume of the Rocky Mountain

Forest and Range Experiment Station was

designed for sites of poor accessibility,

some reached only by packhorse.

717-764 0-64-3 11
Length of study and financial limitations

inñuence the choice of construction materials. For a long-term study, concrete is

best. It should be of the best grade in order

to prevent leakage, reduce erosion, and insure maximum strength. Weir crests of

concrete may be eroded, with resultant

change in rating. Crest erosion may be excessive where water is especially acid —a

notch of brass or some other noncorrosive

material should be installed. Concrete

blocks were used in recent weir construction

by personnel of the Rocky Mountain Forest

and Range Experiment Station and on the

Baltimore City Watershed in Maryland.

Wood, preferably treated for decay resistance, is often used for economy in structures

that will be in service for a limited time

(Whipkey 1961). The H-type flumes, which

have been described, are constructed of sheet

brass or galvanized iron.

A satisfactory but inexpensive weir-basin

liner of 8-mil black vinyl plastic has been used

at experimental watersheds in Baltimore,

Md. The liner was placed inside a weir box

10 feet wide and 20 feet long built of 2-inch

oak planks. A V-notch blade was bolted, over

the plastic, to the box. The vinyl was cemented to the box and plate with asphaltasbestos roofing cement. Cost figures for

this weir are given in the appendix.

With weirs, sharp crests give greater accuracy than broad crests. Blades of sharpcrested weirs are constructed of angle iron

or steelplate, ground to a sharp edge or to a

flat edge one-sixteenth inch wide, and set into

concrete cutoff walls or dams. Blades may

be dented, bent, rusted, and clogged with

debris. In many locations they must be

screened to prevent clogging, and care should

be exercised when working near them; some

maintenance, such as annual painting, is

required.

At the Coweeta Hydrologie Laboratory in

North Carolina the following criteria were

used in selecting weir designs: ^

1. Sharp-crested weirs were used where

sediment production would not exceed that

from protected watersheds.

2. 90° V-notch weirs were used where discharge 95 percent of the time was expected

to be 0,01 to 8 c.f.s.

3. 120° V-notch weirs were used where flow

95 percent of the time was expected to be

between 0.10 and 20 c.f.s.

4. Rectangular and Cipolletti weirs were

used where flows less than 2 c.f.s. would seldom occur and where there was frequent

need to measure discharges greater than 30

c.f.s. Rectangular weirs less than 5 feet long

are so restricted in the range of flows measured as compared with the 120° V-notch that

they were never used.

Flumes are often satisfactory where weirs

are impracticable. They can handle debrisladen flows better; even so, such flows may

be difficult to measure. With flumes, velocity

of approach is less of a problem than with

weirs. There is less loss in head with flumes

than with weirs; thus, they can be used in

channels with low gradients; this is one of

the main reasons why flumes are used in

measurement of water for irrigation. And

flumes, requiring no excavation for ponding,

may be easier and cheaper to install.

^ Personal correspondence with Marvin D. Hoover,

June 6, 1961.

A Sharp-Crested 120° V-Notch Weir

A sharp-crested V-notch weir is excellent

for measuring streamflow in small mountain streams. Under certain conditions,

highly accurate measurements can be taken

of both high and low flows. For example, a

2-foot-high 120'' V-notch weir can be used

to accurately measure flows approaching 25

c.f.s. and those 0.086 c.f.s. or less. This type

of weir has been used since the 1930's at the

Coweeta Hydrologie Laboratory of the U.S.

Forest Service, where a stage-discharge formula was developed (Hertzler 1938). The

formula is: Q = 4.43 W^^^, in which Q is the

discharge in cubic feet per second and H

is the head in feet (measured 6 feet upstream from the blade). The stilling basin

of the weir on which this formula was determined was large enough to obtain a minimum

side contraction 2.5 times the head, with a

bottom contraction of 2.5 feet.

The following section presents the design

and method for constructing a sharp-crested

120° V-notch weir 2 feet high. Detailed descriptions of other types of stream-gaging

12
stations are not given. Except for their

blade design, rectangular, trapezoidal, and

Cipolletti weirs are similar in design and

function to sharp-crested V-notch weirs.

Sharp-crested 120° V-notch weirs are illustrated in figures 5 and 15.

F-503138

FIGURE 15.-A 2-foot, 120° v-notch weir with blade of

3/8-inch galvanized metal plate. Hubbard Brook Experimental Forest, West Thornton, N.H.

DESIGN

The simplest weir in design and construction consists of a watertight cutoff wall that

spans the stream channel, creating a pond or

stiUing basin upstream. The ends and base

of the cutoff wall are tied into bedrock or

other impermeable material.

A tighter container is required where the

channel bottom is permeable, where bedrock

is cracked or irregular, or where the stream

channel does not follow naturally worn Vshaped bedrock; such conditions are common

in glaciated areas. Here a watertight box

is required-a box that is open at the top

and upstream end. The box may be equipped

on the upstream end with wingwalls that extend into the sides of the streambank.

These walls will funnel the streamflow into

the box and thus serve in part as a cutoff

wall. This design makes it possible to intercept all of the surface flow at the upstream

edge of the box; the artificial head created

to satisfy weir requirements does not result in increased leakage through a permeable channel bottom as it would with the

simpler cutoff wall design.

Where the stream gradient is low and the

geology permits, a four-sided box may be

sunk in the stream channel. Streamflow

enters the box by dropping down a vertical

wall on the upstream side.

The three types of weir basins described

here are shown in figure 16. All of them

have a blade mounted in a notch on the downstream wall, drain and intake pipes, instrument shelter or gagehouse, and stilling well.

The watertight box is more compUcated, and

construction is more costly than for the cutoff wall type.

-STREAM CHANNEL CONCRETE

CUTOFF WALLEXCAVATED BASIN

IN IMPERMEABLE MATERIAL

DIRECTION OF FLOW-t=^

FIGURE 16.-Three types of weir basins: A, Weir basin

formed by simple cutoff wall spanning stream channel;

B, weir basin formed by watertight box with front wall,

two sidewalls, and floor with open upstream end; C,

weir basin formed by sunken watertight box with four

sides and floor.

Cutoff Wall

A cutoff wall was constructed on the Fernow Experimental Forest, near Parsons,

W. Va. The concrete wall was built across

the stream channel, with its base firmly imbedded in the impermeable bedrock. Structural views of this cutoff wall are given in

figure 17.

13
SECTION A-A SECTION B-B

FIGURE 17.-Plans for concrete cutoff wall constructed at Fernow Experimental Forest, Parsons, W. Va.

WATER-STAGE

RECORDER

|j^ir;v^^:f • .- : .f.^t:.^^-:v^

/::;/:•-• L AJÍ _ _'_ \ J.-^ :;j "^^^^"^-^^"^W^^^i^:^^^^

FIGURE 18. —Schematic diagram of 120° V-notch weir, watertight-box design.

14
The top of the cutoff wall is level with the

top of the V-notch. At the streambanks, the

cutoff wall projects 2 feet higher to provide a

rectangular section above the V to accommodate flows that exceed the V-notch capacity.

The width of this rectangular section is 12

feet.

Watertight Box

The watertight-box type is an elaboration

of the cutoff-wall design. Instead of spanning the width between natural streambanks, the cutoff wall is joined on both ends

by sidewalls (ñg. 18). A concrete floor forms

the bottom of the basin if the natural floor is

permeable.

A watertight box was constructed at the

Hubbard Brook Experimental Forest, West

Thornton, N.H. Component parts are the

same as in the cutoff-wall design; that is, a

concrete front wall, two sidewalls (watertight

concrete for the watertight box), blade, and

drainpipe. A concrete foundation (poured

first) served as a watertight floor and as a

base for the walls. Plans are shown in

figure 19.

The wall design (shape, thickness, foundation, reinforcement, concrete mix, etc.) for

the cutoff wall or watertight-box design

should be carefully chosen. Selection should

be based on soil, bedrock, or impermeable material conditions, possible ice pressures,

anticipated flood peaks, and other factors

that might influence the reliability of the

walls. Here again engineering advice should

be sought.

CONSTRUCTION

Layout

Before construction, the site should be surveyed, and stakes should be carefully placed

to guide operations. Channel alinement in

relation to the position of the weir must be

considered. Generally, straight flow is desirable through the weir and through a reach

above the weir.

The vertical position of the structure is

very inriportant. Where the simple cutoffwall

HORIZONTAL

REINFORCING

BARS

|"(D(q)l2"0.C.

VERTICAL BARS

I" 0(0)12" o.e.

4" DRAINHOLE

SECTION B-B

CONSTRUCTION JOINT

2Í-DIA

6x6 MESH

CONTINUOUS COPPER SHIELD

SECTION A-A

GALVANIZED BOLTS TO

SECURE BLADE TO WALL

BOLTS IMBEDDED IN WALL

8-DIAMETER GALVANIZED

IRON PIPE WITH THREADED

CAP

CVJ

-BUTTRESS T<Mr/--rir%M /- I-

(BASE IMBEDDED IN WALL) SECTION C-C

FRONT WALL VIEW

FIGURE 19.-Plans for concrete weir of watertight-box design constructed at Hubbard Brook Experimental Forest,

West Thornton, N.H.

15
is used, one guideline is to maintain the original stream gradient above the weir basin.

The vertex of the notch should ordinarily be

at the elevation of the original streambed or

somewhat lower. Thus, the impounded

water will be contained in the basin and will

not back up into the natural stream channel.

The dimensions of the basin must be determined and staked out. The width should be

at least the width of the notch plus a distance

on each side of the notch equal to 2.5 times

the maximum head. Thus, for the 120° Vnotch for an expected head of 2 feet, the

width should be at least 17 feet.

Determining the length of the basin is

often more difficult. One objective in operating a weir is to spread the flow evenly over

the whole cross section at the upstream edge

of the basin. Where this can be done, a

short weir basin suffices. Generally, the flow

does not enter uniformly even if efforts are

made to spread it; therefore, the weir basin

should be long enough to even out the flow

before it reaches the stilling well intake pipes

and the notch. Basins are often constructed

20 to 30 feet long for weirs with notches 2

feet high.

Where it is not feasible to dig a basin below

the normal stream channel —for example,

where hard bedrock forms the channel —the

length of the basin will be governed by the

slope of the stream channel. A channel with

a gradient of one vertical unit to three horizontal units is almost ideal; it would require

a basin about 25 feet long. If the stream

gradient is very low, it may be impractical

to use the watertight-box stream-gaging design because the length of the basin walls

necessary to fulfill the hydraulic requirement

would be prohibitive.

The recommended depth of the weir pond

at the notch (at least 2.5 times the head below

the vertex of the V), the stream gradient, and

the material underlying the stream channel

should also be considered in determining the

length of the basin. In some cases, setting

the elevation of the notch as previously described would require considerable excavation below the level of the streambed if the

basin were short. One answer might be to

lengthen the basin.

Besides consideration of the layout of the

stream-gaging site, provision should be made

for sufficient workspace around the site for

workers, tools, equipment, and forms, and for

unloading and storing materials. If concrete is to be used, the operation should be

planned so that the materials and mixer or

ready-mix trucks are above the highest point

in the structure. This will ease the job of

transporting the concrete to the forms.

Excavation

The first phase in the construction of a

stream-gaging station is excavation. It is

undertaken for one, two, or all three of the

following reasons: (1) To reach impervious

material to restrict water loss around the

control; (2) to secure a firm foundation for the

structure; and (3) to provide a pond in the

channel above the control.

The type and size of the stream-gaging station and the characteristics of the soil and

underlying strata will determine the dimensions of the excavation.

Unnecessary excavation should be avoided.

Excavation increases the possibility of the

streambanks becoming unstable and eroding.

Also, unconsolidated fill material may permit

seepage loss. The material removed in excavating should be piled away from the channel

to prevent it from washing into the stream.

Excavation may be done by mechanical

equipment such as a bulldozer, backhoe, or

shovel. Handwork will be necessary to complete the operation where the bedrock is

fissured or uneven, or where mechanized

equipment cannot operate. In some cases

dynamite may be used to blast trenches, remove uneven rock ledge, or make depressions

for stilling basins. However, it should be

used sparingly and carefully, for the explosions may shatter the bedrock or create cleavages that could result in serious leakage.

If a simple cutoff wall will be a satisfactory

control, excavation will only involve the digging of a trench across the streambed and

into the banks on both sides, and hollowing

a cavity for a stilling basin.

Cutoff Wall

Because one of the prime functions of the

cutoff wall is to force all water within the

basin to flow over the control notch, the cutoff

wall must make a watertight junction with

underlying natural material.

If the wall is to rest on bedrock, the stability of the wall and watertightness of the

wall-bedrock junction may be achieved in one

of several ways. Keys, IJ^ to 2 inches wide

and deep, may be drilled in the bedrock (fig.

20). This key will add to the watertightness

by creating a larger surface area at the joint;

it will also secure the concrete wall to the

bedrock, preventing sliding of the structure.

Steel anchor pins, imbedded in both the rock

ledge and the concrete wall, also secure the

walls. Footings of poured concrete perhaps 3

feet wide may provide both stability and

watertightness.

If the wall is to be built on tight subsoil,

it may be well to cut trenches or keys. Care

should be taken so cracks do not form and so

16
REINFORCING STEEL

CONCRETE

KEY FORMED

IN CONCRETE

CONCRETE

HOLES

EVERY 12"

CONTINUOUS KEY

1^' X 1^' IN

LEDGE

A. WALL KEYED TO BEDROCK B. WALL WITH CONCRETE

FOUNDATION

C. WALL WITH WIDE BASE

FIGURE 20. —Methods used to secure concrete walls to rock ledge.

the material is not shattered during excavation. With some subsoils, it may be advisable

to pour a concrete footing considerably wider

than the wall proper. The width of the footing- depends on the bearing strength of the

soil. Engineering advice should be sought if

there is any question on this point.

A simple cutoff wall is not suitable where

the substratum is permeable or where impermeable material does not form a confining

channel; for example, an impermeable substratum may be present on one bank but may

dip away from the other bank. Then a new

site must be found, or a watertight weir box

must be built on the one excavated.

Even though the weirs described in this report do not impound so much water that their

failure would endanger life and property, the

simple cutoff wall and the front or downstream wall in the watertight-box design

must be built according to sound engineering

principles. It is more practicable to provide

a large safety factor than to determine precise strength requirements. Sliding, overturning, and uplift forces should be calculated. Engineering assistance may be

needed. Forces affecting concrete gravity

dams and requirements for stability are

given in **Design of Small Dams" (U.S.

Bureau of Reclamation 1960).

As noted in figures 17 and 19, the concrete

cutoff wall and front wall have a vertical

upstream face and a battered or gently

sloping downstream face, which makes the

wall thicker at the bottom than at the top.

The battered wall is more stable than a vertical wall; it can withstand greater pressures

resulting from high flows, ice pressure within

the basin, or frost action from soil around the

basin. The larger basal surface area in the

battered wall also helps maintain a watertight joint. Slopes for the battered face may

vary from 4 to 12 vertical units to 1 horizontal

unit. The steeper slopes (such as 12:1) are

recommended only when reinforced concrete

is used.

Where freezing temperatures are persistent, reinforced concrete should be used. Reinforcing steel in concrete permits the use

of considerably less concrete for equal

strength and also lessens the possibility of

wall cracks resulting from the expansion and

contraction of the concrete with temperature

changes. An example of the amount of reinforcing steel required for a 12:1 battered wall

is given in figure 19.

Upstream and downstream forms are

needed for constructing the walls. Form

material usually consists of horizontal

sheathing (1-inch tongue-and-groove boards

or ^-inch plywood) with vertical 2- by 4-

inch studs for support. The vertical studs

should be spaced 12 inches on centers. If

tongue-and-groove boards are used, they

should be fastened to the 2- by 4-inch studs

with a single six-penny nail at each stud.

Figures 21, 22, and 23 illustrate one method

of form construction.

17
WOOD BRACE

SPIRIT LEVEL

ADJUSTED

TO DESIRED

SLOPE

•2x4 STUDS EXTERIOR FORM

INTERIOR FORM

B

INTERIOR FORM

-ANGLE

EXTERIOR FORM EXTERIOR FORM INTERIOR FORM

WOOD WEDGE

ROD CLAMP,

BRACES

2x4 WALE

^;2x4

HEATHIN6'

TIE ROD,

I" WATER

PROOF

SEALER I" WOOD

CONE

WASHER

FIGURE 21. —Plans for constucting forms for concrete walls for weir at Hubbard Brook Experimental Forest, West

Thornton, N.H.: A, cross section of wall forms; B, top view of corner arrangement of wall forms; C, cross section of

wall at the sloping section where blade is attached; D, details of tie-rod arrangement for bracing wall forms.

F-ÍJ03139

FIGURE 22. —Downstream view of forms for concrete

basin walls. Most of the interior form is complete.

Note vertical iron reinforcing rods in place, exposed

bedrock foundation, and flaring upstream wingwalls.

Weir constructed at Hubbard Brook Experimental

Forest, West Thornton, N.H.

F-503140

FIGURE 23.— Front corner view of weir shown in figure

22. Interior form is complete, and exterior form is

almost complete. Note position of blade, reinforcing

iron, tie rods passing between both forms, and horizontal wales for bracing.

t#
Although plywood is commonly used for

sheathing in the building trades (because it

can be used repeatedly), matched boards are

generally preferred for weir construction because they can be more easily fitted to the

rough surface upon which the structure will

rest. A poured concrete footing will eliminate much of the rough surface and speed up

form construction; bolts placed in the concrete can be used to anchor the forms.

Because a tremendous amount of pressure

develops against the forms when the concrete

is poured, the forms should be rigidly braced

to prevent their shifting out of position.

Several methods may be used to keep the

forms separated and braced. Wire (No. 9,

A.W.G.) may be strung and tied between the

two forms at 2-foot intervals, both horizontally and vertically. Tie rods (M-inch

steel rods and fittings) can keep the forms

properly separated and can reduce considerably the additional bracing needed. Where

small sections of wall are involved, the

separate walls may be braced independently

of each other by external wood braces. If

wires or tie rods are used, they should pass

through the entire form and be tightly secured at each end to horizontally placed

braces or wales set perpendicular to the vertical studs. To be effective the wales should

span four or more studs, and wale junctions

should overlap two studs. Figures 21, 22,

and 23 illustrate a method of bracing forms

with tie rods.

In constructing the forms, provision should

be made for placement of the weir blade and

drainpipes.

The weir blade or a template of it should be

mounted temporarily in its proper location

on the wall forms. Bolts that will ultimately

hold the blade in place should be positioned

and secured to the forms so that they will not

move during the concrete pouring. This may

be done by inserting them through accommodating holes in the template or blade and

by wiring them to the forms.

Where angle iron is used for the weir blade,

the portion of the concrete directly below the

V should be sloped sufficiently to prevent obstruction of the free-falling water. Construction of forms for these sloping walls

requires considerable time and eifort.

Building the forms requires some skill and

careful planning. No attempt will be made

to discuss all construction details; however,

figures 21, 22, and 23 illustrate some of the

techniques. To maintain the same slope for

all battered surfaces, a carpenter's level

should be used —one whose spirit level can be

adjusted to any 360° position. The desired

slope, for example 6:1, can be made by fastening a board to form the hypotenuse to a

1-foot horizontally placed board and a 6-foot

vertically placed board. When the carpenter's level is placed on the board forming the

hypotenuse, the spirit level should be adjusted to the level position. The carpenter's

level may then be used to set all studs to the

proper battered slope.

Where concrete walls are designed to jut

into the streambank, the earth sides of the

trench dug into the bank may be satisfactory

form walls. This obviates the need for backfill and helps reduce the chance of seepage

between streambanks and wall. Where backfilling is done, the choice of material is

important. Backfill consisting of four parts

loam soil and one part Bentonite clay mixed

dry in a cement mixer has been used successfully at the Fraser Experimental Forest in

Colorado.

The best time for constructing the cutoff

wall is during periods of low flow. The

stream may be diverted around the construction by a flume or ditch along the bank. Or

it may be passed over the cutoff wall or

through the notch by a flume or pipe.

Another alternative is to route it through the

drainpipe in the base of the cutoff wall. A

moderate amount of ponded or still water in

the excavation is permissible; the concrete

when poured will displace it. But even a

small amount of flow or seepage of moving

water through the concrete before it has set

will be disastrous; it will carry the cement

away from the mix, and leaks will result.

Sidewalls

Watertight sidewalls used in the watertight-box design are constructed similarly to

the front or cutoff walls. Intake pipes to the

well under the gagehouse have to pass

through one sidewall, and they should be provided for in the forms.

Where the cutoff wall alone is relied upon

to control streamflow, construction requirements for sidewalls are not exacting, for

their purpose is merely to prevent slumping

of the banks and erosion by water. These

sidewalls should not be watertight because

water held back would exert pressures that

might cause damage. A porous dry-built

stone wall is satisfactory (fig. 24). Concrete

blocks, without mortar, can be used. Wood

planks or logs, preferably treated for decay

resistance, will also be suitable. They should

be supported by posts securely tied into the

banks; for example, by use of buried anchor

logs. A pole across the basin above the high

water level may also be used to keep the sides

vertical. Under some conditions, the sides

of the basin can be sloped so that building

of a wall is not necessary. Planting grass

on the banks will help control erosion.

19
. - ' '• .^M^:^

9^^'T^'-^'

^^^^^D^K~"~

^^^^^^^ 4-

^m^ ^^^^Ê

"HH^^^^|HpP r^w F-503132

FIGURE 24.— Dry-built stone wall serving as a side of the

basin. Note low wall at upstream end of pond. The

horizontal angle iron at middle far right is a mount for

the hook gage.

control of concrete mixes and the construction of forms.

Weir Blade

Angle iron, 3^ by 3J4 by 33^ inches, has

been most commonly used in constructing

weir blades. More recently, steelplates have

been used because of their several advantages. The angle-iron blade is mounted on

a concrete cutoff or front wall by means of

bolts partially buried in the concrete. Somewhat similar techniques could be used for

other weir shapes —for instance, trapezoidal

or rectangular ones. The upper edge is

ground to a flat or sharp edge and should

have a 45-degree bevel below the edge. For

a 2-foot 120° V-notch blade, two sections of

angle iron are cut and welded to form a 120°

angle between the edges. The length of each

section along the edge is 4 feet (fig. 25).

In a sunken weir the basin is dug in the

natural stream channel. Water entering the

basin must fall from the channel to the water

surface below. A low soil-retaining wall,

composed of the same materials used in the

sidewalls, can be constructed between the

floor of the basin and the natural stream

channel. The top of this wall should be level,

and the streambed above it should be shaped

so that flow will enter the weir pond more

or less uniformly over the entire cross section. Spreading the flow lowers the velocity

of approach in the weir basin.

Floor

The concrete floor for the watertight-box

design may be poured within the confines of

the previously constructed walls. Or, a complete concrete floor can be poured before

pouring the concrete for the walls; the floor

then serves as a foundation for the walls

(fig. 19). The first type of floor should be 2

to 6 inches thick, whereas the second type

should be thicker, 4 to 12 inches. In both

types reinforcing steel mesh is added for

support.

The quality of the concrete used is very important. Watertight concrete should be used

throughout the structure. Thus, the water

should be carefully measured, and the mix

should be composed of the best available

sand, aggregate, and cement. Advice of an

engineer familiar with local materials should

be sought. Where frost damage is possible,

air entrainment is desirable. Use of a vibrator to settle concrete into forms is recommended. Several references listed in the

bibliography describe in detail the design and

6.928' 1

1 ,

3.464-

spv^^i**'

\^^ ! 2.000 ^"^^

H_^60q^ U ^45° BEVEL

^^^^ ~ /-BOLT

ADE ^

^ •• •• \ •. .\ \ \ •! ANGLE IRON BL *. .'^ ; Í V.

] " X 3 j" X 3 i" Ï: ^^ %

DIRECTION OF FLOW _«=> CONCRETE WALL

FIGURE 25.-Detailed plans for a 2-foot 120° angle-iron

weir blade.

Slots are made in the base section of the

angle iron to accommodate the bolts and to

facilitate placement of the blade. The upstream face of the angle iron should be placed

as vertical as possible and flush with the concrete wall. Also, a vertical line through the

bottom of the V should bisect the angle. To

do this, shims are inserted between the blade

and concrete, or the blade is adjusted by

threading leveling screws through the base

of the angle iron so they extend below the

base. By turning the screws the position of

the blade can be adjusted quite rapidly. A

layer of asphalt roofing cement, or some

other nonhardening cement, is placed between the blade and concrete to assure a

watertight juction.

The basal section of the angle iron and the

concrete wall below may obstruct the free fall

of the nappe at very low flows. The situation

is aggravated in winter if ice develops on

the angle iron and concrete surfaces.

20
The steelplate blade is made by cutting a

notch in a rectangular section. It is bolted

to the concrete flush with the upstream face

of the wall over a rectangular or U-shaped

opening in the wall. For a ^-inch metal

plate, as shown in figures 15 and 19, buttresses of yi- by 3- by 3-inch angle iron, 2.5

feet long, are set into the concrete and bear

against the plate to provide rigidity. This

type of blade allows unobstructed free fall of

water from the notch. It is easier to fabricate than the angle-iron blade, and its use

simplifies construction of the cutoff wall and

placement of the blade in the wall. On the

other hand, the plate is more expensive than

the angle iron.

The blade, whether angle iron or sheet

metal, should be treated with a primary coat

of rust-preventive paint and then a coat of

aluminum paint. Galvanizing the entire

blade provides longer protection. Although

galvanizing assures rust-free service, the upstream surface and edge of the blade may not

be smooth and uniform unless galvanizing is

done with care.

To accommodate flows that exceed the capacity of a 2-foot V-notch weir, rectangular

sections of varying length and height are

commonly added above the V-section (fig. 5).

When flows exceed the V-notch capacity, the

horizontal section above the notch assumes

in part the characteristics of a broad-crested

rectangular weir. Rating of these flows is

very difficult, and discharge measurements

are usually less accurate.

It is probably better to extend the V-notch

higher than 2 feet than to rely on a rectangular section above the V to accommodate high

flows. As a large V would be difficult to install properly, a 2-foot V-notch should probably be fabricated and precisely positioned,

and the additional height should be added

later. If possible, for rating purposes,

current-meter measurements should be made

during high flows.

Drainpipes

A drainpipe should be set in the cutoff wall

to drain the basin for cleaning. It should be

large enough to accommodate the highest

flow expected during maintenance. A 6- or

8-inch inside-diameter pipe is usually satisfactory. Its length depends on the thickness

of the wall. It should be located so that the

bottom of the pipe is at the low point on the

floor of the channel along the cutoff wall.

The drain should not be placed directly under

the notch.

The pipe should be tilted slightly downstream. The downstream end of the pipe

should extend about 4 inches beyond the surface of the wall and should be fitted with a

screw-on cap. Iron lugs about 4 inches long

and 1 inch in diameter should be welded to

the side of the pipe to prevent the pipe from

turning in the concrete when the cap is

screwed on and off. A stout, short section of

Wi- to 2-inch pipe welded across the cap will

provide a mechanical hold for a steel lever

for turning the cap.

Sometimes a second drainpipe is installed

at a higher elevation. Such an arrangement

permits draining most of the water and yet

retention of accumulated debris in the basin

for measurement. It will also facilitate

draining the weir when a large accumulation

of sediment blocks the lower pipe.

Debris Dam and Baffles

To minimize the debris that enters the weir

basin and to help distribute flow evenly

through the cross section, a dam can be built

upstream across the channel. It can be

made of rock, logs, timber, concrete, or other

substantial construction; otherwise, it might

wash out during high flow and do more harm

than good. The top of the dam should be

about 2 feet higher than the bottom of the

notch. In the watertight basin the dam

should be placed so that the water that is

ponded upstream from the dam is within the

conflnes of the walls and floor of the weir

basin.

In cold climates where much ice develops,

the debris dam should have a sloping surface

on the downstream side to relieve ice pressure that may develop in the basin. Figure

26 gives an example of a debris dam.

Baffles of various designs are sometimes

used in weir ponds to reduce velocity and

distribute the flow uniformly across the pond.

F-503141

FIGURE 26.-Debris dam in basin of watertight box.

21
Captive floating baffles can relieve ice pressure. Baffles should be firmly secured to

prevent them from becoming flotsam during

floods.

In the stilling well under the gagehouse,

the recorder float rises and falls as the water

stage fluctuates. The stilling well, as its

name implies, reduces wave action from the

Gagehouse and Well

Many shapes, sizes, and materials have

been used for gagehouses. These vary from

simple wooden box shelters just large enough

to house the recording instrument to large

concrete structures equipped with recorder,

heater, telephone relay systems, and other

apparatus (figs. 5, 8, 9, 11-13, and 27-29).

The design depends on factors such as building and maintenance costs, accessibility of

materials, duration of installation, and susceptibility to vandalism.

The most common type of gagehouse is like

a telephone booth, 3 to 4 feet square, and constructed of wood or concrete blocks. It

shelters both the recording instrument and

anyone servicing the instrument.

Screened openings or other ventilating devices should be provided in the walls. A

barrier should be placed over the well to

prevent water vapor from entering the waterlevel recorder or condensing on the tape.

The instrument should rest on an immovable

base. Plans for a gagehouse at the Hubbard

Brook Experimental Forest are given in

figure 30.

Concrete-block gagehouses (fig. 30) are more

expensive than other types, but they are exceedingly durable and weathertight, maintenance is negligible, accessibility to the well

is good, movement of reference points or instrument is practically nil, and they are

virtually vandalproof. FIGURE 28. —Corrugated cylinder instrument shelter,

Onion Creek Experimental Watersheds, Calif.

WlS-RS-22

FIGURE 27.-Box-type instrument shelter with weir,

stilling well, and observation platform on 330-acre

watershed operated by the Agricultural Research

Service near Fennimore, Wis.

FIGURE 29.—Wood-frame gagehouse at Fernow Experimental Forest, Parsons, W. Va.

22
INDUSTRIAL-TYPE"

GALVANIZED

STEEL DOOR

REINFORCED

CONCRETE ^x

FOUNDATION

\ REINFORCED

CONCRETE ROOF

^INSTRUMENT

BENCH

WATERTIGHT

KEY JOINT

FIGURE 30. —Cutaway section for concrete-block gagehouse for stream-gaging station at Hubbard Brook

Experimental Forest, West Thornton, N.H.

weir basin, thereby lessening fluctuation of

the hydrograph trace on the record chart.

Wells may be enclosed with corrugated

steel cylinders, poured concrete, or concrete

blocks. A firm foundation should be provided for the walls, especially when they

support the gagehouse.

The well should have adequate height to

permit the recorder and floats to operate

properly at the full capacity of the weir.

Some wells, principally those of corrugated

cylinders, can accommodate only the float

and counterweight. In cold regions, additional space may be required for placing an

oil cylinder in the well to prevent freezing.

In some cases it is desirable to construct

wells large enough to permit a man to enter

to adjust floats, clean, make hook-gage readings, and break up ice.

The location of the gagehouse and stilling

well in relation to that of the weir basin is not

critical if the relative positions of the intake

pipes and weir blade are satisfactory. For

cold regions, some people advocate that there

be 1 to several feet of earth between the weir

basin and stilling well because of the possibility of ice formation in the well. Sometimes the stilling well is placed within the

weir basin; however, unless the basin is

much larger than usually necessary to meet

hydraulic requirements, this may interfere

with even flow through the basin. When the

well is placed outside a basin of watertightbox design, intake pipes and connections

between weir basin and stilling well, and the

stilling well itself, must be watertight.

Intake Pipes

The gage well is connected to the weir

basin or stream channel by intake pipes.

Two or more intake pipes are used, one placed

higher than the other, to reduce the lag in

well elevation during rapid changes of water

stage in the basin, and to reduce the risk of

an obstructed pipe and thus lost records.

The pipes should be level.

Intake pipes also function as drainpipes

when the pond is drained for cleaning.

In the watertight-box design, the intakepipe opening to the basin may be set flush

with the basin wall. In a simple cutoff wall,

where the natural streambanks form the

sides, the intake pipes should extend into the

stream channel or basin, but not farther

than the middle of the stream. A complete

discussion of the design and construction of

intake pipes is given by Pierce (1941b).

Metal pipes of wrought iron, steel, or galvanized iron are most commonly used. Inexpensive asphalt-impregnated composition

pipe may be satisfactory where freezing is

not prevalent or for short-term installation.

Where freezing is a problem, intake pipes

should be insulated.

In the watertight-box design at the Hubbard Brook Experimental Forest, two 2J^-

inch inside-diameter galvanized iron pipes

were placed 12 inches apart (one above the

other), with their basin or stream ends flush

with the inside of the basin wall, oriented at

right angles to the stream channel, and with

the openings located approximately 6 feet

upstream from the blade.

The vertical placement of the pipes will depend on the location of the bottom of the Vnotch and the position of the gagehouse. A

feasible arrangement might be as follows:

The upper pipe located 1 foot below the notch

and the lower pipe about 1 foot above the

basin floor or bed of the stream channel.

Two additional pipes may be advantageous

for handling stormflows: one located 1 inch

below the V-notch and another 1 foot above

the V-notch. If the weir will be subject to

sediment deposition or thick ice layers, the

number and location of pipes must be adequate to permit free flow of water between

the basin and the well even though some of

the pipes may become blocked.

Because it is essential to maintain the

same water level in the well and basin dur23
ing all stages of flow, the ratio of the total

cross-sectional area of the intake pipes to the

stilling well should be at least 1:500, and

preferably 1:100.

The basin ends of the intake pipes should

be threaded, and a coupling should be attached. This will allow installation of reducers or baffles if necessary to assure equal

levels in both the basin and the well during

periods of high flow.

Placing the well directly in the weir basin

eliminates the need for intake pipes. For

example, a corrugated cylinder can be placed

in or immediately adjacent to the basin, and

a hydraulic connection between the basin

and well can be obtained by cutting openings

in the cylinder.

Cost of Construction

The cost of weir construction depends

primarily on the type and size of the weir

and expected duration of its use. Weirs

made of a simple concrete cutoff" wall and

wooden frame gagehouse with corrugated

steel well will probably cost between $2,000

and $3,000. More elaborate weirs of the

watertight-box design may cost between

$4,000 and $10,000.

The appendix contains time, material, and

cost figures for constructing weirs at the

Fernow Experimental Forest near Parsons,

W. Va.; the Hubbard Brook Experimental

Forest in West Thornton, N.H.; the Leading

Ridge Watersheds near State College, Pa.;

and the Baltimore, Md., Watersheds.

Instrumentation

WATER-LEVEL RECORDER

The purpose of a stream-gaging station is

to measure the water that passes through it.

Most stream-gaging stations do this indirectly. What is actually measured is the

level of the water surface, either the height

of the water ponded upstream from the control and influencing the amount of water

passing over the control, or the actual height

of water passing over the control. This

height of water may be converted to quantity if the control section has been rated

(stage-discharge relations derived).

When continuous records of streamflow

are desired, a water-level recorder is employed. The recorder makes a continuous

or staccato trace of the water stage on a time

chart. Where the installation is serviced

infrequently (at intervals of more than 1

week but less than 6 months), a recorder

employing a weight-driven continuous-roll

chart is used (fig. 31). If the site can be

visited frequently (once a week), a springdriven drum-type weekly chart is satisfactory (fig. 32).

Water stage is conveyed to the recorder

by a flexible tape or cable with an attached

float. For the recorders shown in figures

31 and 32, a metal tape or cable rides over a

pulley attached to the recorder. A counterweight is affixed to the other end of the tape

or cable to balance the float. The counterF-503134

FIGURE 31. —Stevens type A-35 water-level recorder for

continuous roll chart. Note reference tape on right.

weight should be placed on the tape so that

at zero flow (at the counterweight's highest

point of travel) it is barely below the pulley.

No obstructions should be met by the float

or its counterweight throughout their travel

from the highest to lowest position. Relative sizes of floats and float wells are discussed in the Hydraulic Data Book (Stevens

n. d.).

For gaging stations where streamflow is

intermittent, an automatic trigger device

has been developed for FW-1 water-level re24
FIGURE 32.-FW-l-type water-level recorder.

corders to set the recorder in operation when

flow commences (Curtis 1960).

Recent advances in instrumentation have

aided in the development of several promising water-measuring instruments that may

eventually replace those in use today. One

of these, the bubbler gage, ehminates the

need for a stilling well and float. The bubbler gage operates by releasing a given rate

of gas at a fixed point below zero flow over

the control. When the water stage changes,

the water pressure at the gas release point

will also change. A device for relating gas

pressure to stage height is attached to a

regular water-stage recorder (Barron 1960).

Another apparatus has been developed

that tape punches, in binary code, stageheights at predetermined time intervals.

The data on this tape can be translated onto

punchcards, and these cards and those with a

punched rating curve can be run through

electronic computers to get the discharge

for days or other time periods. Both of

these instruments are being tested by the

U.S. Geological Survey.

HOOK GAGE

A hook gage is used to accurately measure

the stage height of water above zero elevation in the control section. The gage consists of a pointed hook attached to a calibrated

FIGURE 33. - Hook gage on mounting post.

rod (fig. 33). The hook-gage point is placed

beneath the water surface and raised slowly

until the point (pointing upwards) just

touches the liquid surface. A vernier on

the gage is then read. The elevation of the

water can be determined by comparing the

hook-gage reading to the surveyed relationship between the zero elevation in the control section and the base setting on the hook

gage. Hook gages are available commercially.

The hook gage can be used in the weir basin

or within the stilling well. When hook gaging is done in the stilling well, clogging of

intake pipes, if it occurs, may not be discovered. The well is a better location because there is minimum disturbance to the

water surface. In either location the mount

for the hook gage should be firmly fixed to a

permanent, immovable base. In the weir

basin the hook-gage mount may be fastened

to a sidewall of the basin (if it is sufficiently

firm and not subject to settling) or to a concrete pier made for that purpose. In the well

the mount can be fastened to the inside of

the well wall.

One type of mount consists of a support

made from a piece of 3J^ by 33^ by J^-inch

angle iron, and a mounting plate. Figure 34

shows a suggested design for the hook-gage

mount.

Where the hook-gage point cannot be

readily seen, a portable, electric water-depth

gage may be used (Wilm and Collet 1941).

REFERENCE TAPE

Frequent water-level measurements can

be taken with a calibrated reference tape

equipped with float. A hook gage is needed

25
I -i;x -I LEVELING

I SCREW

^

^--0

SCREWS PROVIDED i

WITH WINGNUTS

SCREW MOUNTED

PERMANENTLY

IN PLATE

3^"x34x^ <

T ^"x l|'SECURING

BOLT

HOOK GAGE

MOUNTING BRACKET

ASSEMBLY

P 3^'x3-^'x^*ANGLE IRON

FIGURE 34.-Plans for hook-gage mount.

occasionally to establish or check the elevation of the reference float.

The tape rides on a pulley mounted on the

instrument bench, and it has a counterweight. A pointer, also mounted on the

bench, can be adjusted and set at a given

point on the tape. Once the relationship

between the zero elevation in the control

section and the base setting on the hook

gage is known, any water level can be determined by the hook gage, and the referencetape pointer can be adjusted to the corresponding level on the reference tape. The

water-stage height for the instrument chart

is taken from the reference tape.

Water levels obtained with the reference

tape or hook gage are referenced to zero

level on the control section by running levels

from the control section to a reference point

or hook gage. References should be checked

periodically.

STAFF AND CREST GAGES

Stage height can be read directly with a

staff gage, a metal plate marked in easily

read divisions and mounted on an immovable

base. If it is mounted at the proper elevation (by surveying levels from the control to

the staff gage), the head of water flowing

over the control may be read directly.

Crest gages are simple devices that record

high watermarks. They insure against the

loss of peak-flow records during flood discharges. A variety of these gages are

available (Collet 1942; Ferguson 1942; U.S.

Agricultural Research Service 1962). Most

use a floating device or material (cork or

wood chips) that is deposited at the high

water stage.

A crest gage may be made from a 1-inchdiameter pipe capped on the bottom. Several 3^-inch holes are provided in the pipe

near the cap. The pipe is fastened in an upright position in the basin so that the holes

are well below minimum flow. Finely ground

cork is placed on the water surface in the

pipe. A wood dowel or stick as long as the

inside length of pipe is inserted in the pipe,

a top cap is screwed on, and 3^-inchdiameter holes are drilled in the pipe next to

this cap. When high water occurs, the cork

will rise and leave a ring on the stick at the

water's maximum elevation.

26
Operating Procedures and Maintenance

Although the discussion in this section

deals principally with weirs, it also is generally applicable to flumes.

The major chores after installation of the

water-level recorder and associated instruments are rating the weir, periodic chart

changing, checking water levels with the

hook gage or reference tape, cleaning and

care of the instruments, and cleaning of the

basin or channel.

RATING THE WEIR

Check measurements of the stagedischarge relationships (rating curve) should

be made after the stream-gaging station has

been built. The control section of the station

should be built, if possible, according to the

specifications of a model that has been rated

under laboratory conditions. If this has

been done, the rating curve of the laboratory

model can be used unless there are differences between the two —for example, upstream approach conditions or weir blade

surfaces or edges.

If the field model does not conform exactly

to the specifications of the laboratory model,

or if the field-control section has no laboratory model, the control must be rated by

measuring water flowing over it throughout

the range of stage heights. In any case,

some check measurements should be made

after the station has been constructed.

Flows over a 120° V-notch weir up to 0.6-

foot head may be measured by collecting in

buckets or tanks the water passing over the

weir in a selected time. At 0.6-foot head, use

of a 400-gallon tank is advisable. A V-shaped

trough of sheet metal can be used to direct

the flow into the container. The position of

the trough must not prevent aeration of the

nappe.

The flow in cubic feet per second is computed from the time it takes to collect a container full of water; this is related to the

stage height at the time. Eight to 10 stage

heights well distributed between 0- and 0.6-

foot head, with 2 to 4 replicates at each stage,

are sufficient for this portion of the curve.

Stages are seldom at the proper height

when it is convenient to test them. If flow

is higher than the stage at which a test is

desired, part of the flow may be diverted

around the weir basin by a flume or a pipe

(2- to 4-inch aluminum irrigation tubing is

lightweight and convenient). Using this procedure, two different low-flow stages can be

rated during one visit to the installation.

Usually it is between 0- to 0.6-foot head that

the measured flow varies appreciably from

the laboratory rating. Slight variations in

the structure of the blade will influence the

discharge characteristics much more at low

flows than at high flows.

Flows greater than 0.6 foot (approximately

1.27 cubic feet per second for a 120° V-notch

weir) become unwieldy to measure by containers and are measured with a current

meter. Generally, velocities in the weir

basin are too low to permit use of the current

meter there.

Therefore, a natural nonturbulent section

of the stream channel, directly above or

below the artificial control, is used. A temporary flume made of boards, concrete, or

other materials will provide a suitable measuring section. If the flume is constructed

with sides of uniform width or regular geometric shape, the cross-sectional area may be

readily computed.

The pygmy current meter with wading rod,

a modification of the Price current meter, is

used to rate field installations. A measuring tape is first stretched across a straight

section of the stream. Measurements are

made along the cross section so that each

segment between the points of measurement

accounts for about 5 percent of the total

flow. At each point, total water depth is

measured with a rule, and velocity of flow

is determined with the meter and stopwatch. The meter has an earphone, and

the number of clicks in the measuring period

(usually 1 minute) indicates the velocity.

When water depth is 0.5 foot or less, the

meter is lowered halfway between the surface and the bottom; for depths between

27
0.5 and 2.0 feet, measurement is made at a

point 0.6 of the depth from the surface; for

depths over 2.0 feet, measurements are made

at 0.2 and 0.8 of the depth and averaged.

The area and velocity of flow in each section are determined by averaging measurements of depth and velocity made at each

side of the section; flow through the section

is determined by multiplying area in square

feet by velocity in feet per second. Total

discharge is determined by adding the flow

of the separate sections. Detailed instructions for making current-meter measurements have been given (Pierce 1941a and

1941b; Corbett et al. 1943).

Flow through a rectangular section above

a V-notch weir (fig. 5) creates a rating problem. If the flow has not been rated by a

current meter or by laboratory tests, a crude

estimate of flow can be made by summing

(1) the discharge of the V-notch weir at full

capacity, and (2) the discharge of a broadcrested rectangular weir of the given width

and a head measured from the base of the

rectangular section.

PERIODIC CHART CHANGING

The time between chart changes depends

on the instrument used, accessibility of the

gaging station, and chart interval suitable

for office handling. Although some recorders will run for 6 months unattended, it

is advisable, if possible, to visit the gages

weekly or at other frequent intervals to check

for malfunctions.

CHECKING WATER LEVELS

Each time the chart is changed or the installation is serviced, the water level should

be measured by hook gage or reference tape

and recorded, along with the date and time

of observation, both on the chart removed

and on the new chart. This level indicates

whether the instrument has been keeping

an accurate account of the water stage and,

if not, the corrections of the instrument or

chart that should be made.

INSTRUMENT AND BASIN

A regularly scheduled instrument checkup

and cleaning program is good practice.

Where several gages are operated, it is advisable to have an extra instrument or spare

parts, particularly clocks, ready as immediate replacements.

Maintenance checks should also be made of

the weir basin, walls, and weir blade. As

necessary, the blade should be repainted and

the nicks mended, and debris should be removed from the basin. Basin leaks can be

reduced or stopped by coating the walls and

floor with asphalt cement, bentonite, or vinyl

plastic, depending on the structural material.

The weir basin should be drained and

cleaned before accumulation of sediment and

other debris (such as leaves) reduces water

depth beyond the point necessary to meet

hydraulic requirements. It may also be

necessary to clean out the stilling well. The

frequency of draining and cleaning the weir

basin will vary with the amount of sedimentation and basin size; it is often done

annually.

TRASH SCREENS

Leaves, twigs, or other material lodged in

the notch can cause considerable error in the

stream-discharge record. To reduce this

error, trees should be removed from the

immediate vicinity of the gaging station (perhaps for a distance equal to the height of the

trees), and a trash screen should be placed in

the notch (fig. 35).

Trash screens are usually needed only

during low flows, because high flows have

sufficient volume and velocity to flush most

floating debris through the notch. At high

flows the screen should be removed, because

debris adhering to the screen may alter the

discharge characteristics of the weir.

Small screens —18 to 24 inches long, 12

inches wide, and 8 to 12 inches high —are

being used at both the Fernow and Hubbard

Brook Experimental Forests (Reinhart et al.

1961). Iron rods, one-fourth inch in diameter

and welded together, support the 1-inch-mesh

poultry netting or \i- to ^-inch-mesh hardware cloth. The screens have a trigger,

pulley, and weight device designed to raise

them automatically out of the notch section

when a predetermined stage height is

reached.

FIGURE 35.— Trash screen used to prevent floating debris

from clogging the notch.

28
i

Cold Weather Maintenance

In winter gaging, the well must be kept

free of ice because the formation of even a

thin layer in the stilling well would disrupt

the rise and fall of the float. Equipment

used to prevent ice formation in the well

includes well enclosures, subfloors, oil cylinders, and heating appliances.

ENCLOSURE OF WELL

Ice will form more quickly in a well in an

enclosure that is completely exposed to the

atmosphere than in one that has its lower section surrounded by earth. Surrounding soil

supplies heat to the well walls and provides

insulation against heat loss to the atmosphere. The more the well structure is

enclosed in earth, the higher the water temperature in the well, and the less chance for

ice to develop.

SUBFLOOR

A subfloor between the main floor and the

water reduces heat loss from the well and

prevents condensation of water vapor from

the well on the recording instrument. The

subfloor should be built well below ground

line but high enough so that it will not interfere with the float at maximum flood stages.

It should be constructed of light material

such as plywood or tongue-and-groove

boards, and be made in sections to facilitate

easy removal. It should have a minimum

area of openings for the float tape and counterweights. A blanket of insulating material over the subfloor will further retard heat

loss.

OIL CYLINDER

A cylinder can be used to confine a layer

of oil, such as kerosene or fuel oil, on the

water. The float is then placed on the oil

surface. From 5 to 20 gallons^ of oil will

^ Amount depends on diameter of oil tube and the occurrence of subfreezing temperatures. For conditions

at Hubbard Brook, 15 gallons of kerosene is sufficient

to prevent freezing in a 19-inch cylinder.

prevent freezing. The oil cylinder may be

made of galvanized sheet metal; it should

be about 3 inches larger than the diameter

of the float, open at both ends, and with perforations in the lower part (well below the

lowest possible flow) to allow free access to

water. The sides of the cylinder above the

perforated section should be watertight.

In position the top of the cylinder should

be slightly higher than the maximum expected stage. (An extra length should be

allowed for the oil layer above the water.)

The cylinder can rest on the stilling-well

floor or can be hung from the wellsides or

gagehouse floor; if the cylinder does not rest

on the bottom, perforations are not necessary. When winter ends, the oil is drained

from the cylinder.

Although the layer of oil may prevent the

formation of ice in the tube, ice may develop

in the unprotected parts of the gage well,

and it must be removed to permit operation

of the hook gage, reference float, or other

measuring devices. Reference floats should

be kept out of the water except when measurements are being made. Permanently

installed hook gages must also be raised

above the water level when not in use.

Use of oil causes the float to rest above the

true water level. Therefore, if hook-gage

measurements used to set and adjust the

recorder pen are made at an oil-covered point,

a correction for oil depth must be made.

HEATING APPLIANCES

For very low temperatures, portable space

heaters may be necessary. The most common heater uses bottled gas. Other heaters

operate on electricity, kerosene, or gasoline.

A small gasoline lantern may provide enough

heat to prevent freezing in the well. Most

heaters require frequent attention, and

unless they are controlled by a thermostat,

they waste heat.

A simple heater used at the Hubbard Brook

Experimental Forest consists of a single gaspilot burner (similar to pilots for hot-water

29
heaters) mounted on an empty airtight

1-gallon can that serves as a float to keep the

heat close to the water surface (fig. 36). A

piece of sheet zinc is fastened in a semicircle

(Quonset-hut style) to the can and over the

burner. One end of a short section of copper

tubing is connected to the burner, and the

other end to plastic tubing which leads to a

tank of bottled gas (propane). One 20-pound

tank of gas will keep the well free of ice for

about 2 months.

F-503136

FIGURE 36.-Portable space heater used for eliminating

ice in wells: Pilot burner (used for hot water heaters)

mounted on an airtight 1-gallon can which serves

as a float; 'A-inch plastic tubing connects burner to

regulator on bottled gastank; hood (sheet zinc) fastened

to float reflects heat to float and water surface.

ICE IN THE WEIR BASIN

During extremely cold weather a considerable depth of ice may develop in the weir

basin. However, this ice usually does not

greatly interfere with the normal discharge

of water over the control. Ice may develop

around the control at all points where the

water is not constantly moving, and it may

also form on surfaces immediately downstream from the control (fig. 37). To obtain

an accurate stage reading, the ice must be

removed several feet above and below the

notch or control section. Ice should also be

removed periodically around the notch to prevent excessive ice pressure, which might

spring the metal blade out of line. This ice

removal is usually done when the station is

visited for chart changing, or during other

regularly scheduled maintenance visits.

The stage height prior to ice removal and

15 minutes after such removal should be

noted on the chart. Ice should also be removed at the reference point so that a hook

gage or reference tape and fioat may be used

to determine the actual water level. The

correct water level should be noted on the

chart and, if necessary, the recorder should

be adjusted.

During extremely cold periods, ice may

build up on the downstream side of the blade

so that an ice siphon tube forms. This malfunction is indicated by sharp fluctuations in

the trace on the recorder chart. When this

occurs, water is siphoned from the basin

down to zero stage or lower. At this point

the siphoning action is broken, the stage rises

to normal flow, and the process is repeated.

An antifreezing hood for retarding or eliminating freezing in the discharge section of

V-notch weirs has been described by Johannessen (1957). The hood resembles a gabled

roof and is made of aluminum-foil-lined plywood. It is supported by rods attached to a

swinging beam at the side of the weir, and is

designed so that high flows will force the hood

clear of the notch so it will not interfere with

discharge.

Reduction or elimination of ice in the weir

basin may be possible if the basin can be completely covered with insulating material to

restrict heat loss from the water surface.

Such a covering, however, should be capable

of withstanding the weight of accumulating

snow and should not interfere with discharge.

F-503145

FIGURE 37.-Ice and snow accumulation in basin and

below sharp-crested 90° V-notch weir.

m
Bibliography

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1960. New instruments of the Surface Water Branch,

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1942. Crest-stage meter for measuring static heads.

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illus.

Curtis, Willie R.

1960. An automatic trigger device for use on FW-1

water level recorders. Jour. Forestry 58: 819-821.

Dils, Robert E.

1957. A guide to the Coweeta Hydrologie Laboratory.*

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Ferguson, G. E.

1942. Gage to measure crest stages of streams. Civil

Engin. 12: 570-571.

Goodell, B. C.

1950. A trapezoidal flume for gaging mountain

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Grover, C. N. and Harrington, A. W.

1943. Streamflow—measurements, records, and their

uses. 363 pp., illus. New York: John Wiley and

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Harrold, L. L., and Krimgold, D. B.

1943. Devices for measuring rates and amounts of

runoff employed in soil conservation research.*

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Hertzler, R. A.

1938. Determination of a formula for the 120° V-notch

weir. Civil Engin. 8: 756-757.

Johannessen, C. L.

1957. Anti-freezing hoods for V-notch weirs. Jour.

Forestry 55: 590.

Johnstone, Don, and Cross, William P.

1949. Elements of applied hydrology. 276 pp., illus.

New York: Ronald Press Co.

King, H. W.

1954. Handbook of hydrauHcs. Ed. 4, 556 pp., illus.

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1956. Hydraulics. Ed. 5, 351 pp., illus. New York:

John Wiley and Sons, Inc.

Langbein, W. B., and Iseri, Kathleen T.

1960. General introduction and hydrologie definitions. Manual of Hydrology: Part I. General surface-water techniques. U.S. Geol. Survey WaterSupply Paper 1541-A, 29 pp., illus.

Love, L. D.

1958. The Manitou Experimental Forest —its work

and aims. U.S. Forest Serv., Rocky Mountain

Forest and Range Expt. Sta., Sta. Paper 7, 21 pp.

1960. The Fraser Experimental Forest-its work

and aims. U.S. Forest Serv. Rocky Mountain Forest

and Range Expt. Sta., Sta. Paper 8, 16 pp., illus.

Marvis, F. T.

1949. There's no mystery in weir-flow calculations.

Engin. News Rec: 76-78.

Moore, A. M.

1957. Measuring streamflow under ice conditions.

Amer. Soc. Civil Engin. Jour. HydrauHcs 83 (HYI):

1-12 (Proc. Paper 1162).

Parshall, Ralph L., and Rowher, Carl.

1921. The Venturi flume. Colo. Agr. Expt. Sta. Bui.

265, 28 pp.

1950. Measuring water in irrigation channels with

Parshall flumes and small weirs.* U.S. Soil Conserv.

Serv. Cir. 843, 62 pp., illus.

Pierce, C. H.

1941a. Investigations of methods and equipment used

in stream gaging. Part 1. Performance of current

meters in water of shallow depth. U.S. Geol. Survey

Water-Supply Paper 868-A, 35 pp., illus.

1941b. Investigations of methods and equipment used

in stream gaging. Part 2. Intakes for gage wells.

U.S. Geol. Survey Water-Supply Paper 868-B, 75

pp., illus.

Portland Cement Association.

1951. Ultimate design of reinforced concrete. 18 pp.

Chicago.

1952. Concreting in cold weather. 5 pp., illus.

Chicago.

1952. Design and control of concrete mixture. Ed.

10, 68 pp., illus. Chicago.

1952. Watertight concrete. 2 pp. Chicago.

1954. Basic principles of air-entrained concrete.

21 pp. Chicago.

* Address requests for copies to the originating office. 1954. Concrete swimming pool. 27 pp. Chicago.

31
Ree, W. O., and Crow, F. R.

1954. Measuring runoff rates with rectangular highway culverts. Okla. Agr. Expt. Sta. Tech. Bui.

T-51, 19 pp., illus.

Reinhart, K. G.

1958. Calibration of five small forested watersheds.

Amer. Geophys. Union Trans. 38: 933-936.

Leonard, R. E., and Hart, G. E.

1961. Automatic devices to take water samples and to

raise trash screens at weirs. U.S. Forest Serv.

Northeast. Forest Expt. Sta., Forest Res. Note 112,

7 pp., illus.

Robinson, A. R.

1960. Report on model study of a trapezoidal flume

for measurement of stream discharge.* Colo. State

Univ. Res. Found. Civil Engin. Sect. Mimeo CER59ARR57. 14 pp. Fort ColHns, Colo.

Schoder, E. W., and Dawson, F. M.

1934. Hydraulics. Ed. 2, 429 pp., illus. New York:

McGraw-Hill Book Co., Inc.

and Turner, K. B.

1929. Precise weir measurements. Trans. Amer.

Soc. Civil Engin. 93: 99-110.

Sinclair, J. D., Hamilton, E. L., and Waite, M. N.

1956. A guide to the San Dimas Experimental Forest.

U.S. Forest Serv. California Forest and Range

Expt. Sta. Misc. Paper 11, 19 pp.

Staif, C. E.

1956. Plastic films in farm applications. Agr. Engin. 37: 741-746.

Stevens, J. C.

(n.d.) Hydraulic data book. Leupold and Stevens

instruments. Ed. 5, 144 pp., illus. Portland, Oreg.

Subcommittee on Small Water Storage Projects.

1939. Low dams. A manual of design for small water storage projects. Water Resource Com. of

Nat. Resources Com. 431 pp., illus. Washington.

Thomas, C. W.

1957. Common errors in measurement of irrigation

water. Amer. Soc. Civil Engin. Jour. Irrigation

and Drainage Div. 83 (RS2) Proc. Paper 1362, 24 pp.

Tracy, H. J.

1957. Discharge characteristics of broad-crested

weirs. U.S. Geol. Survey Cir. 397, 15 pp., illus.

United States Agricultural Research Service.

1962. Field manual for research in agricultural

hydrology. U.S. Dept. Agr., Agr. Handb. 224, 215

pp., illus.

United States Bureau of Reclamation.

1953. Water measurement manual. 271 pp., illus.

Washington: U.S. Govt. Printing Off.

1960. Design of small dams. 611 pp., illus. Washington: U.S. Govt. Printing Off.

Urquhart, L. C. (editor).

1959. Civil engineering handbook. Ed. 4, 1184 pp.,

illus. New York: McGraw-Hill Book Co.

Whipkey, Ronald Z.

1961. Plywood cutoff walls for temporary weirs.

U.S. Forest Serv. Central States Forest Expt. Sta.,

Sta. Note 150, 2 pp., illus.

Wilm, H. G.

1942. New gaging station for mountain streams.

Civil Engin. 12: 548-549.

Cotton, J. S., and Storey, H. C.

1938. Measurement of debris-laden streamflow with

critical depth flumes. Amer. Soc. Civil Engin.

Trans. 103: 1237-1278.

and Collet, M. H.

1941. A portable electric water-depth gage. Civil

Engin. 11: 305.

and Storey, H. C.

1944. Velocity head rod calibrated for measuring

stream flow. Civil Engin. 14: 475-476.

32
Appendix

COSTS FOR CONSTRUCTING STREAM-GAGING STATIONS

A. One 2-foot 120° sharp-crested V-notch

weir of the cutoff-wall design at the Fernow

Experimental Forest near Parsons, W. Va.,

in 1956.

Figures for this weir are based on the average cost of Fernow weirs 8 and 9. The average volume of concrete in the cutoff wall was

14 cubic yards, and the average area of the

watersheds was 37 acres. The cost per

weir—they were one-fourth mile apart —was

probably less than the cost of building a

single weir. The cost of building an access

road is not included.

Cutoff wall and weir basin:

Labor, general (544 hours) $680.00

Labor, carpenter, who also assisted in pouring and dressing concrete (70 hours) 156.00

Bulldozing basin, TD-9 bulldozer (4 hours)... 32.00

Lumber, for forms and sidewalls (2,000 board

feet) 170.00

Cement (95 bags) 116.00

Crushed stone (14 tons) 32.00

Sand (13 tons) 33.00

Hauling cement (12-mile haul) 20.00

Hauling stone (35-mile haul) 80.00

Hauling sand (30-mile haul) 70.00

Cement mixer, rental (2 days) 10.00

Air compressor, rental (9 operating hours)... 25.00

Transporting mixer and air compressor to

site (33-mile truck haul on hard road,

1-mile tractor tow on access road) 48.00

V-notch form, fabrication in woodworking

shop 11.00

Blade, VA- X 3V2- x 3V2-inch angle iron, contracted to machine shop 50.00

Drainpipe with cap, 8-inch diameter, 3 feet

long, secondhand 11.00

Bolts, tie wires, nails, miscellaneous 25.00

1,569.00

Gagehouse (wood frame) and stilling well:

Labor (32 hours) 48.00

Lumber (600 board feet) 100.00

Culvert pipe, steel (2-foot diameter, 10 feet

long) 60.00

Miscellaneous 10.00

218.00

Instruments:

Water-level recorder, Stevens A-35 360.00

Hook gage (assuming gage used for one weir

only) 80.00

Mount for hook gage 15.00

Installation (8 hours) 15.00

470.00

Total, complete installation $2,257.00

B. Two-foot 120° sharp-crested V-notch

weir of the watertight-box design with concrete-block gagehouse (weir No. 2, Hubbard

Brook Experimental Forest, West Thornton,

N.H., built in 1956).

La6or (1,616 man-hours) $2,477.00

Equipment rental:

D-7 caterpillar tractor (4 hours) 48.00

Compressor and jackhammer (11 hours) 88.00

Materials:

Cement (187 bags) 300.00

Reinforcing steel, H-inch diameter (880

feet) 70.00

Crushed rock, washed (26 tons) 98.00

Sand, washed (18 tons) 37.00

Concrete blocks (300) 86.00

Glass blocks (4) 4.00

Lumber (2,200 board feet) 220.00

Nails (23 pounds) 3.00

Pipe, 2 feet of 6-inch pipe and 10 feet of 2V2-

inch pipe 24.00

Blade, H- x SH- x 3>^ inch angle iron 114.00

Form ties (100) 15.00

Hook-gage support 10.00

Steel door, frame, ladder, floor, and supports 167.00

Miscellaneous hardware 12.00

Instrumentation: (Stevens A-35 water-level

recorder and reference gage, hook gage) 482.00

Total cost $4,255.00

C. Combination 90° (18-inch deep) V-notch

and Trenton weir with concrete-block gagehouse built at Leading Ridge Watershed near

Pennsylvania State University, University

Park, Pa., in 1958.

Materials:

Ready-mix concrete (22 cubic yards) $366.00

90° V-notch (1) 22.00

Lumber (850 board feet) 77.00

2 drainpipes, 6 inches x 2 J^feet, with cap 21.00

Nails (32 pounds); reinforcing steel (63 feet of

J^-inch-diameter steel) and reinforcing

wire mesh (5 x 23 feet) 29.00

Tie wire (1 roll) 4.00

Miscellaneous materials and services 44.00

Concrete blocks (310) 64.00

2 pipes, 2 inches x 16 feet 18.00

Five pieces of angle iron (J^x 2 inches x IJ^

inches x 5 feet) to support gagehouse floor

and recorder table 13.00

Wood door (1) 24.00

Glass blocks (4) 4.00

2 pipes, 4 inches x 9 feet 21.00

Culvert (15 inches x 5 feet) 20.00

Steel ladder 1.00

Cement (3 bags) 4.00

Equipment rental: John Deere tractor (22

hours) 121.00

Labor: (656 man-hours) 1,048.00

Instrumentation: FW-1 water-level recorder,

staff gage, hook gage 285.00

Total cost $2,186.00

D. One-foot 120° sharp-crested V-notch

weir of watertight-box design. Wooden box

built of 2 by 8-inch planks, no floor, platesteel weir blade, interior of box lined with

vinyl plastic. Built on Baltimore City

Watershed.

Lumber for box and gagehouse (about 1,000

board feet) $100.00

Vinyl plastic liner (22 x 40 feet) 40.00

Instrumentation, FW-1 recorder and hook

gage 285.00

Labor (18 man-days) 225.00

Weir blade (Ji-inch plate steel, 2x7 feet) 216.00

Total cost $866.00

33
PARTIAL LIST OF STREAM-GAGING STATIONS BEING USED FOR RESEARCH ON

SMALL WATERSHEDS IN THE UNITED STATES

Operating

agency

Northeastern Forest

périment Station

(Upper Darby, Pa.).

ExSoutheastern Forest Experiment Station (Asheville, N.C.).

Central States Forest

Experiment Station (Columbus, Ohio).

Lake States Forest Experiment Station (St.

Paul, Minn.).

Southern Forest & Range

Experiment Station (New

Orleans, La.).

Rocky Mountain Forest &

Range Experiment Station (Fort Collins, Colo.).

Location

Hubbard Brook Experimental Forest, West Thornton, N.H.

Fernow Experimental Forest, Parsons, W. Va.

Pocono Experimental Forest, Gouldsboro, Pa.

Dilldown watershed, Blakeslee. Pa.

Baltimore (Md.) municipal

watershed.

Newark (N.J.) municipal

watershed.

Coweeta Hydrologie Laboratory, Franklin, N.C.

Piedmont Research Center,

Union, S.C.

Dover, Ohio

LaCrosse, Wis.

Tallahatchie Research

Center, Oxford, Miss.

Fraser Experimental Forest, Fraser, Colo.

Prescott National Forest,

Arizona.

Front Range, near Fort

Collins, Colo.

Type of gaging station

90° and 120° V-notch weirs,

watertight-box design;

combined 3-foot San

Dimas flume and 90° Vnotch.

120° V-notch weirs, cutoñ"-

wall design.

Columbus deep-notch weir..

Columbus deep-notch weir..

120° V-notch weirs, concrete-block walls, watertight-box design.

120° V-notch weir, wooden

box with vinyl plastic

liner.

120° V-notch weirs, watertight box.

90° V-notch weirs

120° V-notch weirs.

Rectangular weirs, crest

length, 5-6 feet.

Cipolletti weirs, crest

length, 6-8 feet.

Cipolletti weirs, crest

length, 12 feet.

Columbus deep-notch weirs..

90° V-notch weirs

90° V-notch weir and 2-foot

San Dimas flume in

tandem.

90° V-notch weirs, temporary).

90° V-notch weirs, concrete-box type.

2-foot San Dimas flumes,

fabricated steel.

H-type trapezoidal flumes,

fabricated steel.

H-type flume, galvanized

iron construction.

Combination San Dimas

flume and rectangular

weir with oriñce plate for

low winter flows; combination broad-crested trapezoidal weir with rectangular flume notched into

center; 120° V-notch weir.

1-foot 120° V-notch weirs in

series with San Dimas

flumes; San Dimas flume.

2-foot San Dimas flume and

30-inch, 90° V-notch weirs.

Remarks

6 watersheds, 30 to 104 acres.

9 watersheds, 29 to 96 acres.

1 watershed, 560 acres.

1 watershed, 1,530 acres; in

cooperation with Pa. Dept.

of Forests and Waters and

U.S. Geol. Survey.

3 watersheds, 26 to 48 acres;

in cooperation with City of

Baltimore.

3 watersheds, 24 to 68 acres;

in cooperation with City of

Newark.

5 watersheds, 22 to 50 acres.

11 watersheds, 31 to 212

acres.

4 watersheds, 350 to 943

acres; not currently in

operation.

2 watersheds, 501 and 940

acres; not currently in

operation.

2 watersheds, 1,788 and

1,877 acres.

2 watersheds, , 23 and 145

acres; weir on larger

watershed not currently

in operation.

3 watersheds, 15 to 22 acres.

1 watershed, 13 acres.

2 watersheds, 18 and 23

acres; on land of Muskingum Conserv. Dist.

Spring-fed stream.

Storm runoff" only.

Do.

Mostly for storm runoff".

Velocity head rod used to

check rating.

34
PARTIAL LIST OF STREAM-GAGING STATIONS BEING USED FOR RESEARCH ON

SMALL WATERSHEDS IN THE UNITED STATES—Continued

Operating

agency

Location Type of gaging station Remarks

Rocky Mountain Forest &

Range Experiment Station (Fort Collins, Colo.)

(Continued).

Intermountain Forest &

Range Experiment Station (Ogden, Utah).

Pacific Northwest Forest &

Range Experiment Station (Portland, Oreg.).

Pacific Southwest Forest &

Range Experiment Station (Berkeley, Calif.).

Castle Creek, Willow Creek,

and Thomas Creek, near

Beaverhead, Ariz.

Campbell Blue, near Apline,

Ariz.

Sage Brush watersheds,

near Dubois, Wyo.

3-Bar watersheds, near

Roosevelt, Ariz.

Natural drainages. Sierra

Ancha Experimental Forest, Ariz.

Parker & Pocket Creeks,

Sierra Ancha Experimental Forest, Ariz.

Workman Creek, Sierra

Ancha Experimental Forest, Ariz.

Black Mesa, Near Grand

Junction, Colo.

Beaver Creek, near Prescott, Ariz.

Dog Creek Watersheds,

near Reno, Nev.

Davis County Experimental

Watershed, near Farmington, Utah.

Parrish Creek, near Farmington, Utah.

Great Basin Research Center, near Ephraim, Utah.

Tailholt Creek, Payette National Forest, Idaho.

Benton Creek, Priest River

Experimental Forest,

near Priest River, Idaho.

H. J. Andrews Experimental Forest, near McKenzie

Bridge, Oreg. (Corvallis

Research Center).

Bull Run watershed, near

Portland, Oreg.

South Umpqua Experimental Forest, near Tiller,

Oreg.

Entiat Watersheds, near

Portland, Oreg.

San Dimas Experimental

Forest, Glendora, Calif.

Teakettle Experimental

Forest, near Fresno, Calif.

Onion Creek Experimental

Forest,near Soda Springs,

Cahf.

5 weirs, 120° V-notch, 3-foot

head.

Villemonte Sill in culvert—

3 V-notch weirs, 120°

4 V-notch weirs, 90° and 120°

4 V-notch weirs, 90°

Wooden cutoff walls..

Concrete-block dams.

Combination Cipolletti and

90° V-notch weirs.

2 V-notch weirs, 1 trapezoidal flume, 1 combination Cipolletti and V-notch

weir.

3 V-notch weirs, 120°

14 modified trapezoidal

flumes.

Combination broad-crested

120° V-notch weirs.

Modified Venturi trapezoidal flumes.

0-Gee control section

Self-cleaning flumes

90° and 120° V-notch weirs.

120° V-notch weir

Self-cleaning flume; 120° Vnotch weirs.

0-Gee control section

2 Cipolletti weirs.

Trapezoidal flumes.

Trapezoidal flumes.

120° V-notch weirs.

120° V-notch weirs, 3 feet

high.

Combination 90° V-notch

weir and 3- and 10-foot

flumes.

Combination 90° V-notch

weir and 6-foot Cipolletti

weir.

120° V-notch weirs

Some in combination with Vnotch; flume has capacity

of 0.5 to 300 c.f.s.

Operated in cooperation

with U.S. Geol. Survey.

In planning stage.

In cooperation with Payette

National Forest, Idaho.

3 watersheds, 149 to 250

acres; rated by velocity

head rod.

3 watersheds, 150 to 300

acres; rated by velocity

head rod; in cooperation

with City of Portland.

2 watersheds, average 150

acres.

3 watersheds, concrete-block

weir construction, 500 to

1,000 acres.

Watersheds range from 70

to 550 acres; operated in

cooperation with U.S.

Geol. Survey.

Watersheds range from 120

to 560 acres; operated in

cooperation with U.S.

Geol. Survey.

35
PARTIAL LIST OF STREAM-GAGING STATIONS BEING USED FOR RESEARCH ON

SMALL WATERSHEDS IN THE UNITED STATES—Continued

Operating

agency

Location Type of gaging station Remarks

Pacific Southwest Forest & Castle Creek Experimental

Area, near Soda Springs,

Calif.

Sagehen Experimental

Area near Hobart Mills,

Calif.

Yuba Gap Experimental

Area, near Sierraville,

Calif.

Young Bay, Admiralty Island, Alaska.

Cohocton, N.Y.

Parshall flume 1 watershed, 4 square miles;

Range Experiment Station (Berkeley, Calif.)-

Continued. Variable-notch weir

operated in cooperation

with U.S. Geol. Survey.

1 watershed, 11 square miles;

Rated section

gaging by U.S. Geol.

Survey.

1 watershed, 7.6 square

miles; gaging by Calif.

Dept. of Water Resources.

2 watersheds, 2,500 and 3,000

acres.

Switzer Creek Watershed

Alaska Forest Research Broad-crested weirs

Center (Juneau, Alaska).

Agricultural Research 1:10 broad-crested V-notch

weir.

1:10 and 1:2 broad-crested

V-notch weirs.

H-type flumes

Service (stations operated by Soil and Water Dutchess County, N.Y

2,215 acres.

Millbrook school, 76 to 1,570

Conservation Research acres.

Division except as noted College Park, Md

in remarks). Watkinsville, Ga 1:5 broad-crested V-notch

weir.

H-type flumes; 1:2 broadcrested V-notch weir; rectangular culverts with

Virginia V-notch low-flow

controls.

1:5 broad-crested V-notch

weirs.

H-tvne flumes

1 drainage area, 19 acres.

Culvert stations at widely

dispersed watersheds;

drainage areas, 185 to 2,000

acres.

2 drainage areas, 46 and 82

acres. Operated by Agr.

Engin. Dept., Univ. of

Illinois.

Operated by Michigan Agr.

Expt, Sta.

Drainage areas of 1 to 17,500

acres.

4 drainage areas, about 10

acres each.

23- to 330-acre drainage

areas.

About 3-acre drainage areas.

Blacksburg, Va

Monticello, 111

East Lansing, Mich

Coshocton, Ohio Dual Parshall flumes, with

15-foot main throat and 1-

foot low-flow throat; Columbus deep-notch lowflow control at current

meter-rated section; 1:5

broad-crested V-notch

weirs; H-type flumes of

several sizes.

Agricultural Research 4.5-foot H-type flumes

Service (Continued).

Moorefield, W Va

Fennimore. Wis 1:3 and 1:5 broad-crested Vnotch weirs.

LaCrosse. Wis Trapezoidal flumes

Colbv, Wis 1:5 broad-crested V-notch

weir

1 drainage area, 345 acres.

Stillwater, Okla Rectangular highway culverts equipped with weir

sill for low-flow measurement.

H-type flumes

16- to 206-acre drainage

areas.

About 5-acre drainage

areas.

Drainage areas of 3 to 4,400

acres.

Drainage areas of 3 to 4,400

acres.

Drainage areas of about 700

acres.

Drainage areas, 360 to 28,100

acres; capacity of largest

flume, about 18,000 c.f.s.

Drainage areas, 40 to 170

acres.

Cherokee, Okla

Riesel, Tex 15-, 10-, and 6-foot Parshall

flumes with Columbus

deep-notch low-flow control; Columbus deep-notch

low-flow control at current meter-rated section;

H-type flumes.

1:3 broad-crested V-notch

weirs for low-flow control

at current meter-rated

sections; H-type flumes.

1:3 and 1:5 broad-crested Vnotch weirs.

Tombstone critical-depth

flumes.

1:3 broad-crested V-notch

weirs.

Hastings, Nebr

S afford, Ari z

Tombstone, Ariz

Albuquerque, N. Mex

36
PARTIAL LIST OF STREAM-GAGING STATIONS BEING USED FOR RESEARCH ON

SMALL WATERSHEDS IN THE UNITED STATES—Continued

Operating:

agency

Location

Agricultural Research

Service (Continued).

School of Forestry, Penn

State University (University Park, Pa.).

U.S. Geological Survey..

Tennessee ValleyAuthority

(Knoxville, Tenn.).

Santa Rosa, N. Mex

Oxford, Miss

Newell, S. Dak

Danville, Vt

Leading Ridge Watersheds

and Shale Hills Watersheds, near State College,

Pa.

Tar Hollow State Park,

Ohio.

Lebanon State Forest, New

Jersey.

White Hollow Watershed,

Union County, Tenn.

Pine Tree Branch, near

Lexington, Tenn.

Parker Branch Research

Watershed, near Asheville, N.C.

Western North Carolina

Research Watersheds,

near Waynesville and

Asheville, N.C.

North Citico Creek, near

TelHco Plains, Tenn.

Type of gaging station

Tombstone critical-depth

flume.

Current meter-rated stations; H-type flumes; trapezoidal flumes.

Water-level recorders on

large-capacity stock

ponds.

1:10, 1:5, and 1:3 broadcrested V-notch weirs;

current meter-rated section.

Combination 90° V-notch

and Trenton control

weirs; combination 4.5-

foot H-type flume with

sharp-crested 60° V-notch

weir; composite 30°-150°

sharp-crested V-notch

weir; sharp-crested parabolic-notch weir.

V-notch weir, wide-angle,

broad-crested, rated.

Trenton-type weirs

Modified Albany weir..

Columbus deep-notch weir.

Modified Albany weir

2-foot H-type flumes; le

foot San Dimas flumes.

Rectangular weir, 66 feet

long by 3 feet deep, with

low-water section, 10 feet

by 1 foot.

Remarks

1 drainage area, 42,900

acres; capacity of flume

about 18,000 c.f.s.

Flumes on areas of less than

5 acres; current meterrated stations, 100 acres to

117 square miles.

Drainage areas of 30 to 1,110

acres.

Drainage areas of 150 to

27,500 acres.

watersheds, 25 to 300

acres; in cooperation with

Pa. Dept. of Forests and

Waters and Northeast.

Forest Expt. Sta.

1 forested watershed, 1.5

square miles.

2 watersheds, about 1,500

acres each; in cooperation

with N.J. Dept. of Conserv.

and Econ. Devlpmt. and

Rutgers Univ.

1 watershed, 2.68 square

miles; calibrated in TVA

laboratory.

1 watershed, 88.2 acres.

1 watershed, 966 acres; in

cooperation with North

Carolina State Col.

4 watersheds, 3.7 to 5.6

acres; in cooperation with

North Carolina State Col.

1 watershed, 7.04 squaremiles; in cooperation with

U.S. Forest Service.

U.S. GOVERNMENT PRINTING OFFICE : 1964 OL—717-764

37