FLOOD06950

• County: Statewide
• Basin: Statewide
• Title: Techniques of Water-Resources Investigations of the US Geological Survey General Procedure for Gaging Streams
• Date: 1/1/1968
• Prepared By: USGS
• Floodplain - Doc Type: Educational/Technical/Reference Information

10

TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS

sectinn dnwnstream frnm the injectinn pnint
permits the cnmputatinn .of stream discharge.
The accuracy .of the method critically depends
upon cnmplete mixing .of the injected snlutinn
through the stream cross sectinn befnre the
sampling statinn is reached and upon nn adsorp-
tinn .of the tracer .on stream-botrom materials.
The methnd is rec.ommended .only fnr those sites
where cnnventinnal methnds cannnt be em-
plnyed .owing tn shallnw depths, extremely high
velocities, .or excessive turbulence. A detailed
descriptinn .of the procedures and equipment
used in measuring discharge by a dye-dilutinn
methnd is given bJ! Cnbb and Bailey.' Figure
9 shnws the pressurized constant-rate tanks
used tn inject fluorescent dye snlutinns intn the
streams, and figure 10 shnws cnllected sample
bnttles ready fnr field testing with a f1unrnmeter
.on the tailgate of a vehicle.

Discharge Ratings

The computatinn .of cnntinunus recnrds .of
discharge at gaging statinns depends .on defini-
tinn of the discharge rating fnr the channel.
Discharge ratings may be simple .or cnmplex.
The rating may cnnsist .of a simple relatinn be-
tween stage and discharge .or .of several rela-
tinn curves which define discharge as a functinn
of stage, slnpe, rate .of change .of stage, or other
variables. The expressinn "discharge rating" is
an all-inclusive term tn describe the .one or
m.ore relations used to determine the discharge
frnm measured parameters .of f1nw.

Stage-discharge relations

Discharge ratings at a large majnrity .of
gaging statinns consist .of relatinns between
stage and discharge. These stage-discharge re-
latinns are rarely permanent, particularly at
Inw f1nw, because of changes in the stream chan-
nel such as scnur and fill, aquatic grnwth, ice,
.or debris .or because of changes in bed rough-
ness. Frequent discharge measurements are
necessary tn define the stage-discharge relatinn
at any time.

~ Cobb. E. D., and BailE"}', .J. F.. Meal'lurement of discharge
b}' d}'e-dilutlon methods: U,S. Geol. Surve}' Teelmiqoes Water-
R,,~ollret'S Inv., nnpub. data.

Figure 9.-Pressuriud constcnt.rate injection tanks for injec-
tion of dye into streams.

The relatinn of stage tn discharge is gen-
erally contrnlled by a sectinn .or reach .of chan-
nel below the gage, known as the station con-
trol. Sectinu controls may he either natural
.or constructed, and may consist .of a ledge .of
r.ock across the channel, a boulder-cnvered
riffle, an .overflow dam or any other physical
feature capable .of maintaining a fairly stable
relatinn between stage and discharge. Sectinn
contrnls are commonly effective only at low dis-
charges, and are cnmpletely submerged by
channel c.ontrol at medium and high discharges.
Channel control consists .of all the physical
features of the chanuel which determine the
stage .of the river at a given pnint fnr a certain
rate .of f1nw. These featlll'es include the size,
slnpe, rnughness, aliuement, cnnstrictinns and
expansinns, and shape .of the channel. The
reach .of channel which acts as the c.ontrnl may
lengthen as the discharge increases; such
changes intrnduce new features which affect
the stage-discharge relatinn.
Knnwledge .of the channel features which

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