Streamflow Measurements

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STREAMFLOWMEASUREMENTS


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INTRODUCTION4.1


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WHAT IS

STREAM?

IS A FLOW CHANNELINTO WHICH THESURFACE RUNOFF

FROM A SPECIFICBASIN DRAINS.

STREAMFLOW?

IS THE ONLY PART OFTHE HYDROLOGICALCYCLE THAT CAN BEMEASUREACCURATELY.

MEASUREd IN m3/s


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MEASUREMENT OFSTAGE4.2


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THE STAGE OF A RIER DEFINED AS ITSWATER!SURFACE ELEATION MEASUREDABOE A DATUM. THIS DATUM CAN BE

THE MEAN!SEA LEEL "MSL# OR ANYARBITRARY DATUM CONNECTEDINDEPENDENTLY TO THE MSL.


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TWO TYPES OF STAGEMEASUREMENTS

MANUAL GAUGES

STAFF GAUGE WIRE GAUGE

AUTOMATIC

STAGE

RECORDERS

FLOAT!GAUGERECORDER

BUBLE GAUGE


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STAFF GAUGE

THE SIMPLEST OF STAGEMEASUREMENTS.


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WIRE GAUGEA MEACHANICAL COUNTERMEASURES THE ROTATION OF

THE WHEEL WHICH ISPROPORTIONAL TO THELENGTH OF THE WIRE PAIDOUT.


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FLOAT GAUGERECORDER

COMMON TYPE OFAUTOMATIC STAGERECORDER.


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BUBLE GAUGE

A PRESSURE GAUGE THATMEASURES THE GAS

PRESSURE WHICH IN TURN ISE$UAL TO THE WATERCOLUMN ABOE THE OUTLET.


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STAGE DATAOFTEN PRESENTED IN THE FORM OF A

PLOT OF STAGE AGAINST CHRONO!

LOGICAL TIME %NOWN ASHYDROGRAPH.

IMPORTANT IN DESIGN OF HYDRAULICSTRUCTURES& FLOOD WARNING AND

FLOOD WARNING AND FLOOD!PROTECTION WOR%S FOR ITSDETERMINATION OF STEAM DISCHARGE.


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MEASUREMENT OFELOCITY4.3


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IMPORTANT ASPECT OF MANY DIRECTSTEAM FLOW MEASUREMENT

TECHNI$UES.

ONE OF THE MOST COMMONMECHANICAL DEICE USED TODETERMINE THE ELOCITY IS THECURRENT METER BUT CAN ALSO BEDETERMINED BY OTHER MEANS LI%E

FLOATS. FIRST CURRENT METERS WAS INENTED

BY ROBERT HOO%E "1''3# BUT IN THEPRESENT WE USE HENRY(S DESIGN IN

1)').


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TYPES OF CURRENTMETERS

VERTICAL-AXIS

HORIZONTAL-

AXIS


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VERTICAL-AXIS

HORIZONTAL-

AXIS

CONSIST OF APROPELER MOUNTEDAT THE END OF THEHORI*ONTAL SHAFT.

CAN REGISTERELOCITIES IN THERANGE OF +.1, TO 4.+m/s AND WITH ANACCURACY OF 1- AND

IMPROES TO ABOUT+.2,- AT AT ELOCITYOF .3 m/s AND ABOE.

CONSIST OF ASERIES OF A CONICALCUPS MOUNTEDAROUND A ERTICALAIS.

NORMAL RANGE OFELOCITIES IS FROM+.1, TO 4.+ m/s WITHAN ACCURACY OF

1.,+- AND IMPORESTO ABOUT +.3+- INECESS OF 1 M/S.


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CALIBRATION RELATION BETWEEN THE STREAMELOCITY AND REOLUTIONS PERSECOND OF THE METER AS IN THEE$UATION IS CALLED THE CALIBRATIONE$UATION.

CALIBRATION ARIES FROM EACHINSTRUMENT AND IS DETERMINED BY

TOWING THE INSTRUMENT IN A SPECIAL

TAN% CALLED TOWING TANK.


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FIELD USE


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SOUNDING WEIGHTS


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ELOCITY MEASUREMENT BY FLOATS

A FLOATING OBECT ON THE SURFACEOF A STREAM WHEN TIMED CAN YIELD

THE SURFACE ELOCITY BY THERELATION


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AREA!ELOCITY METHOD4.4

DIRECT METHOD


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METHOD OF DISCHARGE MEASUREMENTCONSIST ESSENTIALLYOF MEASURINGAREA OF CROSS!SECTION OF THE RIERAT A SELECTED SECTION CALLEDGAUGING SITE AND MEASURING THEELOCITY OF FLOW THROUGH THECROSS!SECTION AREA.

THERE ARE CRITERIAS WHICH ARE

NEED TO BE ADOPTED.


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THE STREAM SHOULD HAE A WELL!DEFINED CROSS!SECTION WHICH DOESNOT CHANGE IN ARIOUS SECTION.

IT SHOULD BE EASILY ACCESIBLE ALLTHROUGH THE YEAR.THE SITE SHOULD BE IN A STRAIGHT&

STABLE AREA.THE GAUGING SITE SHOULD BE FREE

FROM BAC% WATER EFFECTS IN THECHANNEL.

CRITERIA0


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THE SEGMENT WIDTH SHOULD NOT BEGREATER THAN 1/1, TO 1/2+ OF THEWIDTH OF THE RIER.

THE DISCHARGE IN THE SEGMENTSHOULD BE LESS THAN 1+- OF THE

TOTAL DISCHARGE.THE DIFFERENCE OF ELOCITIES IN

ADACENT SEGMENTS SHOULD NOT BE

2+-.

GUIDELINE TO SELECT THE

NUMBER OF SEGMENT


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IN NATURAL RIERS& THE ERTICALSFOR ELOCITY MEASUREMENT ARE NOTNECESSARILY E$UALLY SPACED.

AREA!ELOCITY METHOD IS ALSOCALLED& STANDARD CURRENT METERMETHOD.

NOTE


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CALCULATION


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CALCULATION


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CALCULATION


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MOING BOAT METHOD A SPECIAL PROPELLER!TYPE CURREN

METER WHICH IS FREE TO MOE ABOUT

A ERTICAL AIS IS TOWED IN A BOATAT A ELOCITY BAT THE RIGHT ANGLES

TO THE STEAM FLOW.


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DILUTION TECHNI$UES OF STREAMFLOWMEASUREMENT

4.,


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DILUTION METHOD OF FLOW

MEASUREMENT DEPENDS UPON THECONTINUITY PRINCIPLE APPLIED TO A

TRACER WHICH IS ALLOWED TO MICOMPLETELY WITH THE FLOW& ALSO

%NOWN AS CHEMICAL METHOD.TWO METHOD WAS SHOWN IN THE

BOO%& ONE WAS&INECTION/GULP/INTEGRATION METHOD&

AND THE OTHER& CONSTANT RATEINECTION/PLATEAU GAUGING.


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TRACERS


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DILUTION METHOD HAS THE MAOR

ADANTAGE THAT THE DISCHARGE ISESTIMATED DIRECTLY IN AN ABSOLUTEWAY. IT IS A PARTICULAR ATTRACTIEMETHOD FOR A SMALL TURBELENT

STREAMS& SUCH AS THOSE INMOUNTAINOUS AREA. WHERE SUITABLE&IT CAN BE USED AS AN OCCASIONALMETHOD FOR CHEC%ING THE

CALIBRATION& STAGE!DISCHARGECURES& ETC. OBTAINED BY OTHER !MEHTODS


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ELECTROMAGNETIC METHOD4.'

DIRECT METHOD


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BASED ON THE FARADAY(S PRINCIPLETHAT AN EMF IS INDUCED IN THECONDUCTOR WHEN IT CUTS A NORMALMAGNETIC FIELDS.

INOLES SOPHISTICATED AND

EPENSIE INSTRUMENT AND HAS BEENSUCCESSFULLY TRIED IN A NUMBER OFINSTALLATIONS.

TODAY& ELECTROMAGNETIC

FLOWMETERS CAN MEASURE THEDISCHARGE TO AN ACCURACY OF 3-.


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ULTRASONIC METHOD4.

DIRECT METHOD


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THIS IS ESSENTIALLY AN AREA!ELOCITY

METHOD WITH THE AERAGE ELOCITYBEING MEASURED BY ULTRASONICSIGNALS.

THE METHOD WAS FIRST REPORTED BY

SWENGEL "1,,#& SINCE THEN IT HASBEEN PERFECTED AND COMPLETESYSTEMS ARE AAILABLE COMMERCIALLY.


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INDIRECT METHODS4.)


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FLOW MEASURING

STRUCTURES BASIC PRINCIPLE GOERNING THE USEOF A WEIR& FLUME OR SIMILAR FLOW!MEASURING STRUCTURES IS THAT THESESTRUCUTURES PRODUCE A UNI$UE

CONTROL SECTION IN A FLOW. CAN BE BROADLY CONSIDERED UNDERTHREE CATEGORIES.


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CATEGORIES0THIN!PLATE STRUCTURESW LONG!BASE WEIRS FLUMES


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SLOPE!AREA METHOD


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SLOPE!AREA METHOD


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SLOPE!AREA METHOD


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SLOPE!AREA METHOD


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RE$UIREMENTS0 SELECTION OF A REACH IN WHICH

CROSS!SECTIONAL PROPERTIES

INCLUDING BED ELEATIONS ARE%NOWN AT ITS END.

THE ALUE OF MANNING(S NWATER SURFACE ELEATION AT THE

TWO SECTION.

Streamflow Measurements

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