hydrometry in the light

Prospects

hydrometry in the light

modern technology, by K.K. Framji

Introduction

ïñree hundred years of scientific hydrology have resulted in a sound development of methods and instrumentS.The prospects of success with new techniques promise impressive results in the future.The honour done to me in being invited to speak to such a

distinguished gathering is indeed an honour done to

all

I shall therefore try to deal with the achievements and aims of all international organizations in the search for new and better techniques and instruments of measure- ment.

Activities of international organizations In the fields of hydrometry there are several international organizations which are active with different aims.The total interest of the

IS0 lies in the development of standards on established methods and equipment for measurements and observations;others (e.g.

FAO,ICID,WHO) have the interest of a'user' of the standards;others still (e.g.WM0) are active both as promoters of standardization and in using the standards for making

observations,while the IAHS works and aims at promoting progress on new measuring methods and instruments and the IAEA for the employ- ment of special nuclear techniques in the measurements.

ment in the accuracy or the performance of conventional instruments,the WMO project on the Intercomparison of Hydrometric Instruments is of special significance.Under this project the instruments most frequently used in surface water hydrometry,namely water level recorders for stage measurements and current meters for measuring velocities,are proposed to be scientifically intercompared by

independent laboratory and field tests.

For advancing the trends towards improve-

flew deveZopment8 in hydrometkc method8 or inatmmente

Measurement of water stages

The measurement of stage is the most important for flow measurements,because it is the base to which all other measurements are related.me reading of stage may be required as a single instantaneous measure- ment or as a continuous or virtually

continuous record of the stage.The conven- tional water-level gauges are either of the direct or the indirect type,with measuring instruments of the fixed or movable type, such as vertical and inclined gauges,needle gauges,float gauges and wire weight gauges classified as direct reading instruments in as much as the readings are made directly in units of length,without any intervening influences.Indirect water-level indication devices include transducer systems which convert a pressure or electrical signal to an output which is proportional to the water-level.Severa1 types of transducers are available including the gas-electric

(the bubble gauge),the gas-mechanic and the pressure-electric.

The gas-purge (bubbler) technique consists in a small discharge of non- corrosive gas (e.g. dry nitrogen) or

compressed air flowing into a tube,the free end of which is fixed at an elevation below the water column to be measured.The sensor, which is located at the opposite end,detects

the pressure of the gas required to displace the liquid in the tube.ühen the prerequisite installation and operation requirements have been observed,the river stage may be recorded to

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Both the servo-manometer and the servo-beam balance are press;re sensors that convert the pressure detected to a rotational shaft position proportional to the height of the column of water.The range and response of the instrument have to be compatible with the anticipated ranges and rate of changes in water level as indicated in ISO/TC 113/WG 5/Qoc.96.An account of the design and performance of two under-level transducers that have been developed to meet the rather unasual conditions encountered in Australian rivers are described in a paper presented to the Koblenz Symposium.

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Strip-chart recorders have been used to record stream stages for over 50 years.The time and stage scale are chosen to suit a particular station in range and sensitivity of the stage changes,but the instrument should be capable of recording the stage to the nearest 3 mm.Digita1 water level

recorders have been developed to take advantage of the availability of electronic computers for automatic computation and

processing of hydrometric data.Coded recorder outputs in the form of punched paper tape, magnetic tape or printed paper tape are available.The digital recorders have proved accurate and reliable and their use permits automatic computation of discharge records and greatly facilitates both tele-trans- mission of data and the automatic storage and retrieval of data on water levels and discharges.

The digital recording of water levels with the aid of acoustics and its application

to hydrological pumping tests have been reported.The acoustic technique makes it possible to obtain data of an immense number of measured values at low cost,to adapt the recording programme to the special conditions,and to store these data in a form which is directly accessible to a computer and an automatic graph plotter.

Measurement of discharge

The classical method of discharge measurement involves observations of velocity,depth and width at various points in the cross section.

The oldest method of velocity measurement by using floats has been improved during recent years for use in canals with aquatic weeds.The theoretical basis of the integrating float method has also been established.

Measurement of peak discharge by indirect methods such as slop-area,contracted opening, flow-over-dam,flow-through-culvert,are

described in detail in WMO Technical Note No. 90,Velocities are however currently

measured by current meters,which have not changed in basic design for decades,but improvements have been added to allow

measurements of the angle of velocity,trsns- mission of information on velocity,and reliable measurement of velocity under many different special conditions.Mechanica1 current meters are usually individually calibrated in towing tanks ,but with the

better precision of manufacture of current meters there are distinct prospects that calibration of only a sample from a group of current meters will give equal reliability and accuracy in measurements.The United States Geological Survey (USGS) has already discontinued its practice of rating each current meter used in discharge measurement.

Research is under way to develop other means of calibration such as in the flow of a submerged jet.

In the velocity-area method,the precise location of position of observations has in the past been achieved on wide streams by the "pivot point" method or by the sextant.

Electronic instruments that permit the precise location of position of observations on large streams are now available.By using water jets,it is now possible to keep the boat virtually motionless in fast waters.

The conventional velocity-area methods as well as the alternative methods of measure- ment of flow by the dilution method and by measuring structures are unsuitable for large rivers.A major effort continues to be devoted to the development of new methods of discharge measurements.

One new method, the"moving boat" method has already been established as a particularly usef u1 method in measuring the discharge of large streams and estuarieS.In the moving boat method,a number of observations are made while the observer is aboard a small boat traversing the cross-section along a pre-selected path that is normal to the flow, a sonic counter recording the geometry of the cross-section and a continuously operating current meter sensing the combined stream and boat velocities during the traverse which is made without stopping.This technique is particularly useful at remote sites where no measuring facilities exist and during floods when facilities may be inundated or

inaccessible,or at locations where unsteady flow conditions require rapid measurements.

Where information is available,these measure- ments are said to compare with concurrent measurements obtained by conventional

methods and agreement is said to be generally within 5 per cent.

another new method,is to measure the velocity of flow at a certain depth by simultaneously

transmitting sound pulses through the water from transducers located on either side of

The principle of the ultrasonic method,

K. K. Framji

the river.The difference between the time of travel o f the pulses crossing the river in an upstream direction and those travelling downstream is directly related to the average velocity of the water at the depth of the transducers which can then be related to the average velocity of flow of the whole cross-section.If desired,by incorporating an area factor in the electronic processor,the system can be made to produce an output of discharge.Such ultrasonic systems have been successfully installed on the River Thames in the United Kingdom and in the Columbia river in the U,S.A.References at the end of this paper give more detailed information on ultrasonic flow meters.

A third new method,the electromagnetic method,involves the utilisation of the earth's magnetic field for stream gauging.This

method has been developed in the United Kingdom and France and in the Netherlands several estuarial measuring stations using the earth's magnetic field were installed.

This method has not made significant impact on stream gauging due probably to its high cost and complexity and its unsatisfactory accuracy.However,it has promising prospects under conditions of weed growth and bed silt.

cally measures open water discharge and produces a discharge by means of magnetic induction is described in The Proceedings of the Koblenz Spposium.The air-bubble method developed by the National Water

Authority of Hungary which has certain merits in big drainage channels is also described in these Proceedings.

There seems little doubt,however,that during the last quarter of the twentieth century the new methods briefly described above will have a large part to play in the measurement of stream flow in many countries throughout the world.

A monitoring installation which automati-

Measurement of dhcharge under ice cover A possible new technique for estimation of river discharges under ice cover with

reasonable accuracy has been given a limited trfal in Canada and is based on the concept that a relationship exists between the discharge based on a single velocity in a cross-section and that by the conventional

method.An alternative technique,adopted in Hungarp,relates stream flows under an ice cover to those in open surface conditions, for ice covers of 0.20 to 0.50 m thickness.

F Z m measuring instrumenta

With the completion of standards on the basic instruments used with the conventional method of flow measurement,the Working &oup of ISO/RC 113 on flow measuring instruments plan to turn their attention to the more sophisticated instrumentS.The increasing complications of problems and the require- ments of greater accuracy require such

tools.Perhaps their immediate future attention will engage them over:

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manager beset with many difficulties to make crucial decisions A t h real-time data.

Digital depth measurements are described

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in the Proceedings of the Koblenz Sympoiuum as well as recording and tele-transmission of hydrological data.

optics,acoustics and nuclear energy is growing rapidly and opening new approaches to more accurate measurements of open channel f1ow.A number of new instruments for the measurement of water level and velocity

employing one or more of the above disciplines are either under development or in the

experimental stages .Among these are the acoustic velocity meter,the doppler velocity meter, the electro-magnetic velocity meter, the optical current meter,the nuclear current meter,the eddy shedding current meter and the acoustic level follower.

Knowledge in the fields of electronics,

66

Special hydrometric ships

In recent years,a number of special ships have been built for hydrometric work,in particular for the measurement of current speed,discharge,bed load and suspended transport in estuaries and inland water9.A special survey-cum-research vessel(1ength 18.3 m,breadth 4.80 m,depth 1,75 m,draught loaded 0.96 m) has been built in a dockyard in Calcutta for similar work on the Hoghly.

Reference is also invited to the FAO publi- cation on the subject.0ne aspect which needs mentioning and which is often overlooked is

that the current environment and tidal rise are more significant parameters in shallow areas partly submerged during high waters.

High-powered light-weight boats (e.g.

aluminium boats) of shallow draught fitted with echo-sounders are also used,but

experience difficulties from extensive wave effects over the sand.

M e a s k n g structures

Conventional measuring devices which are still used include the Rehbock,the Cipoletti, the Thomson,the Venturi,the Crump and the Inglis weirs and flumes.Internationa1 standards for various types of structures are now on the anvi1,namely for thin plate weirs,broad-crested weirs and flumes;

within these broad groups there are sub- divisions according to the geometry and the characteristic features of individual types.

Furthermore,several other measuring devices are under discussion,e.g. weir with

adjustable crest,trapezoidal profile weir, and hydrofoil weir,etc.Future trends in the development of these measuring devices are hard to forecast,except for the likely advances in the measurement of head,which will change from the visual observations by the human eye to electronic measurements and recording (on paper or punch tape),etc.

Already many installations are operated in these sophisticated ways

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measuring structures,such as the precise

effect of submergence and of the boundary effect which cause significant errors await re9earch.A very interesting paper from Dr.O.Starosolszky on this subject sets out the problems under investigation of head loss,operating costs of measurement,

tail water submergence and the mean error of water volumes determined on the basis of observed rates of flow.For the most

important of these,the effect of submergence, an ingenious semi-graphical method has been suggested.

02 Eution methods

The dilution method is frequently used nowa- days for the single measurement of flow of liquids,particularly for measurement of flow of mountain streams:flow under ice cover and of flashy floods.It is claimed to have been successfully used for measurements up

to 2,000 m3ls;and with an accuracy as high as 98 per cent for smaller dischargeS.Both constant rate injection and the integration method are in' current usage .The tracer used most commonly is sodium bichromate,but

rhodamine,sodium chloride and lithium chloride, among others,are also used.In the field of radio-isotopes,the most commonly used elements are bromine 82 and iodine 131,but the

appearance of "radio element generators" opens up new possibilities.It is now possible even to envisage continuous discharge measurements using an indium-tin generator,and preliminary experiments have been reported.While

international standards,both of the constant rate injection method and the integration method for chemical dilution have been

finalized,a draft proposal is under considera- tion on the radio-isotope technique.An

important hitherto unresolved subject for research is the minimum "mixing length", i. e.

the distance from the injection point to the sampling point where complete mixing has taken place,because investigations made in Australia and India have shown large probable dis- crepancies in results on this account.

New techniques for measurement of dis- charge by dye-dilution used by the USGS and

€or developing stream hydrographs by fluores- cent tracers as well as precision and bias of the results of dilution gauging have been described in papers presented to the Koblenz symposium.

K. K. Framji

Measurement of sediment transport

Measurement of suspended sediment load There are two methods of measurement of suspended sediment: (i) the indirect method of measurement in which the concentration of the sediment and the current velocity at a point are measured practically simultaneously with the aid of separate devices; and (2) the direct method of measurement in which vith the aid of one device the sediment discharge at a point is measured at once (no information being obtained about the velocity and discharge of the water at the point of sampling).There are a number of conventional sampling methods

(one point,multipoint,Straub,Luby,etc.) and there are various types of suspended load samplers (e.g. instantaneous,point integrating, depth integrating,etc.)

Concentrated research has been directed towards the design and development of a suitable suspended load sampler,and one good produce is the Delft Bottle DF 12.

For continuous measurements of suspended load in rivers,the photometric turbidity method is being developed ans has promising prospects .%o turbidimeters ("Sigris t photo- meter" and "Askania turbidimeter") have been tested in the Hydrological Service of Bayern and are reported to be promising.

Measurement of bed sediment

The rate of bed sediment movement is difficult to measure because stream-bed material usually moves in the form of ripples,sand bars or dunes .There are also considerable difficulties in designing a sampler that will not disturb the stream bad and the movement of the bed sediment.The Hydraulic Structures Bureau of the Netherlands Government have designed a pressure-different type sampler for which a very high efficiency has been claimed.This design,called the ARNHEM or Dutch Sampler, is widely used in Europe.Another pressure- difference sampler called "Sphinx" was developed at the Hydraulic Laboratory of Delft for measuring bed-lead discharge of find sand size.At the Federal Institute of Hydrology in Koblenz,a device has been recently developed and tested which makes it possible simultaneously to measure the

quantity of bed load transport and to observe it acoustically.Bed1oad in rivers draining

small basins is transported by flood waves and is not susceptible to measurement by the classical bedload samplers.For such cases, a new method ("strip method") of providing special sediment traps at different positions in the cross-section has been reported from Bulgaria.

The applications of fluorescent tracers in routine sediment discharge measurements have been investigated by the USGS and others.

According the USGS investigations,the steady- dilution method or the time-integrction method is recommended for high velocity,flat- bed conditions,while the spatial-integration method is preferred for the dune bed case.

A water quality sampler must be an optimum combination of the best adapted flow sensor, power source,intake,distribution system, container and even recording device.For

surveillance of water quality,the Proceedings of the Koblenz Symposium describes the design aspects of the coninuous,unattended,

colorimetric modules and sample conditioners and suggests techniques for obtaining overall system compatibility.The evolution of

automatic water-quality monitoring and the automated water-quality monitoring system now in use by the USGS which comprises a pump,a sample chamber,sensors,signal conditioners,servo programmer and recorder are also described in these Proceedings.

Measurement of water temperature

Temperature measurements are required in hydrometry for a number of purposes.Water thermometers,mechanical and electrica1,have been in use for point-to-point measurements.

An infrared radiation thermometer was developed in 1961 for remote recording and rapid monitoring of surface water temperatures of large bodies of water.The radiation

thermometer senses the radiant energy (heat) from the surface over which it is trans- ported and a sensitive large ingtrumgnt can be effective over aorange of -2 +35 C with an accuracy of 20.2 C.

Trends towards improvements in accuracy of measurements

This paper o n the prospects of hydrometry would be incomplete without reference to the accuracies of the existing methods and equipment and the trends towards.improvinp, these accuracies.But before improvements can be made there must be knowledge of the magnitude of error in the existing methods and equipment.ISO/TC 113 has been actively engaged over this basic investigation for the past few years,starting with evolving a standard form for the more detailed measurements which are prerequisite to the determination of the errors.Valuable reports on this subject were presented at Koblenz.

A report investigatinR the total error in measurement of flow by velocity-area methods will shortly be published.Also,a uniform methodology for determination of the magnitude of errors in the velocity-area techniques of flow measurements in both open channels (TC 113) and closed conduits

(TC 30) has been" recently finalized.

The statistical study of errors in measurements of flow has conclusively shown that the largest error arises from insufficient data for tracing the bed profile precisely.

Trends in hydrometry are therefore directed towards development of sophisticated instru- ments for precise position fixing and measuring

the bed profile with sufficient accuracy and resolution.For example,for proper position fixing , the "Ralog" , the "Hydrodis t" and the

"Autotape" and the "Hi-Fix" instruments have been developed to suit polar,circular and hyperbolic base coordinates respectively.

An instrumentation system comprising an instrument capable of measuring bed profiles with sufficient accuracy and resolution by sonic depth measurement (Sonar) a Bludworth recorder and an IBM 1801 digital computer for data storage has been evolved which will give a meaningful computation by digital techniques of the statistical properties of bed forms.

Data collection and transmission via satellite WMO Operational Hydrology Report No. 2

discusses technological progress in the automa-ic instrumentation and transmission systems for hydrological purposes and includes

guidance o n the choice of instruments and types of installation for various climatic and geographical conditionS.The development of a Geostationary Operational Environmental Satellite System (GOES) will permit the continuous real-time acquisition of obcerva- tions from a large number of stations over a wide area and will ultimately be used as a data relay for the real-time readout and use of data from automated observing platforms.

Under W O sponsorship it is planned to operate a system of GOES satellites all over the world for real-time acquisitiun and transmission of data.The potential of satel- lites as water data collection and trans- mission media has so far been only scratched and their future can only be imagined.

processing system,known by the name of World Weather Watch (WWW),is being installed for operational use ali the world over

through international cooperation coordinated by the World Meteorological Organization.

Modern systems for hydrological data collection, transmission and processing have been

indicated by Professor Nemec in his remarkable recent book, Engineering Hydrology.

A global data collection,transmission and

Recommendations and conclusions

There is a positive need for better com- munications of the important new methods and instruments and the trends towards improvement of existing methods and instru- mentS.The Unesco-WO-IAHS Koblenz Symposium, 1970,satisfied an important need in this respect.There should be such symposia organ- ized regularly at intervals of 5 to 7 years.

The Inter-Agency Panel on Standardization in Hydrology should be activated and widened to include all international agencies engaged in hydrometry.

of modern technolozy- that is ,modern sciences, engineering and modern materials

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clearly bright for developing more precise methods and instruments in hydrometry.

Sciences such as electronics and computer science,ultrasonic methods and telemetry, coupled with the use of light-weight plastics, special non-ferrous alloy materials,and

special hydrometric ships and light aluminium or fibre-glass boats,point to good prospects of achieving a very high degree of precision All in all, the prospects from the use

K. K. Frarnjì

and uniformity in measurements.In the not too distant future one may also conceive of promising prospects of hydrometry from the use of space craft and the application of earth satellites in hydrometry.The sky is the limit!

Re ferences

D.J.Sherlock et al,l973.Water-level trans- ducers .Hydrometry, Proceedings of the Koblenz Symposium, 1970. (Studies and Reports in Hydrology,No .13)Paris ,Unesco/

WMO/IAHS.Vols. I-II.pp.46-62.

W O Guide to Hydrometeoroloq-ìcal Practices.

Geneva,l970.WMO,No.16€!,T.P.82,pp.11-31.

WMO .Surface water teve ts and streamf tow.

CHy-IV/Doc.3,WMO Commission for

Hydrology,fourth session,Buenos Aires, April 1972.

Durbaum,H.J. and Kohlmeier,R. Digital recording of water levels with the aid of acoustics and its application to hydrological pumping tests .Proceedings, KobZenz Symposium, 1970. OP it .pp .11-31.

Prochazka,Joseph,Use of depth floats in drainage canals with aquatic weed., Proceedings, Kob lenz Symposhm, 19 70.

op.cit.pp.197-205.

Liu,H.Flow measurement by the integrating float method .Proceedings, Koblenz S Y ~ ~ O S ~ W ~ , 1970. OP .cit., pp .188-197.

WMO.Measurement of peak discharge by indirect methods.Technica1 Note No.90,WMO-No.225.

TP .119,1968.

measurements.ì+oceedings,Koblenz

Carter,Rolland W.Accuracy of current meter symposium, 1970. op.cit. ,p.88.

Symposium,l970.op.cit. ,pp.99-108.

Davidian,Jacob.Calibration of current meters in a submerged jet .Proceedings, Koblenz Smoot,George F.Flow measurement of some of the world's major rivers by the moving boat method .Proceedings, Kobtenz

Sympositan, 1970. OP. ci t. ,pp. 149-161.

Herschy,Reginald W.Modern Developments in River Gauging.United Kingdom Water Resources Board paper presented in Edinbyrgh.

Kinosita,T.Ultrasonic measurement of dis- charge in rivers.îroceedings,Koblenz Symposium, 1970. op.cit. ,pp. 388-400.

Gils,H.Discharge measurement in open water by means of magnetic induction.h.oceed.ings, Kobtenz Symposium, 1970. op. ci t. , pp. 374- 382.

David,L.J.The air bubble method of flow measurement and its application.

Proceedings, Kob lenz Symposium, 19 70.

op.cit.,pp.361-373.

Stri1aeff.P.W. and Wadel,J.H.Measurement of discharge under ice cover.h.oceedings, Koblenz Symposium,1970.op.cit. ,pp.214-

227.

streamflow-under ice cover.Proceedings, Koblenz Symposium, 1970. op .cit .pp .228-

235.

Glover,John R.Digita1 measurements of river bed profiles .Proceedings, Koblenz Sympo- Szilagyi,J.andMuszkalay,L.Estimation of

S i m . op .tit .pp .483-490.

Coppens à'EeckenbruRge G.,et al.Système de télélimnimetrique LGR.ProcsedZngs, Kobtenz Symposiwn,op.cit.pp.681-692.

Dubreuil P.,Hlavek,R.Nouveaux limnigraphes et automatisation de la gestion d'un

réseau hydrométrique en France.Procsedings, Kobtenz Symposium. O Q .cit .pp ,692-705,

Puskás T. ,Karasai,H.Hydre II automatic digital telemetering system.Proceedings, Koblsnz Symposium.op.cit.pp.717 and 722.

measured data in hydrology and relevant WMO activities ,Proceedings, Kob Zen8 Sympo- Jansen,H.,Sindern,J.Special hydrometric ships Walser,E.Recording and teletransmission of

siwìt.op.cit .pp.753-761.

for the inland waterways of the Federal Republic of Germany ,Proceedings, Kob Zenz Symposium. op .tit .pp ,639-647.

FAO.Research Vessel Dasign.Rome,1961.

w M 0 . ü ~ ~ of weirs and flumes in stream gauging.

Starosolszky

WMO-N0.280,1971.

O.PrOblems in the design of measuring instruments .Proceedings,Koblenz SympoSium.op.cit.pp.162-168.

André,H.,Richer,C.,Douillet,G.Les jaugeages par la mé-ihode de dilution in 1970.Proceed- ings,Koblenz Symposium.op.cit.pp.239-250.

Barnes,H.H. Jr.,Kilpatrick,F.A.Techniques for measuring discharge by dye-dilution.

Proceedings, Koblenz Symposium. op .ci t .pp.

fluorescent tracers. Proceed;ng8

,

Goodell,B.C.,Steppuhn,H.Stream hydrographs by Symposium. op .cit .pp .261-270.

70

Wilson,A.L.Precision and bias of the results of dilution gauging.Proceedings, Koblenz Symposium. op .-it .pp. 289-299.

ISO/TC 113 WG 5/30: Revised Draft Proposal for an IS0 Recommendation on Methods for Measurement of' Suspended Sediment in Open Channels.

Burz , J. Experiences with pho tometric turbidi ty measurements .Proceedings, Koblenz Symposium.

OP .tit .pp. 519-530.

Hinrich,H.Bedload measurement by means of bottom plates and bed load samplers with hydrophone attachments.Proceedings, Koblenz Symposium. op .cit .pp .544-552.

Georgiev,B.V.,Parazov,R.D,A method for measuring the quantity of bed load transported by short flood waves.

Proceedings, Kob Lenz Symposium. op. ci t.

p p .531-537.

sediment movement using fluorescent tracers .Proceedings, Koblenz Symposium.

Nordin,C.F.,Rathbun,R.E.Field studies of

op .tit .pp .552-561.

Edwards,William M.,Lloyd,Harrold L.

Instrumentation considerations for studies of quality of runoff from small agricultural watersheds.ProcsadEn8, KobZenz Symposium.op.cit.pp.575-581.

Zand,S.M.The colorimetric front-end sensors in automatic surveillance of water quality .Proceedings, Koblena Symposium.

0p.cit.pp.608-612.

Smoot ,George F.Water-quality monitoring and data transmission.Proceedings, Koblenz Symposium. op .cit .pp .522-729.

Prospects of hydrometry iii the light of the moderi1 technology bv K.K. Framii

Abstract

Botma,H.,Struyk,A.J.Errors in measurement of flow by velocity area methods.

ProceedZngs, Koblenz Symposium. op. ci t.

pp. 771-784.

at flow measurement stations.Proceed- ings, Koblenz Symposium. op .cit .pp. 109- 131.

Investigations of the total error in measurement of flow by velocity-area methods (Part I-General Reports;

Part II-Description of Method;Part III- Recommendation on the Collection of Data for Error Investigation) .August, 1971 (unpublished).

Proceedings, Kob Lenz Symposium. op. ci t Herschy,Reginald W.The magnitude of errors

ISO/TC 113/WG-l.(Netherlands 16) 177.

Lohrberg,W.Modern position fixing methods.

pp.466-476.

Glover,John.R.,Digital measurements of river bed profiles using a general- purpose data acquisition system.

Procaedings,Koblenz Symposium. op .cit.

p p .483-490.

WMO.Automatic collection and transmission of hydrological observations. W O 1973.

(Operational Hydrology Report No.2,WMO- No.337).

Allen F.Flanders,Schiesl,Joseph W,Hydrologic data collection via geostationary

satellite.XEEE transactions on geo- science electronics.Vol.GE-lO.No.1, January 1972,pp.47-51.

Nemec, Jaromir .Engineering Hy&oZo.gy. McGraw- Hil1,New York,1972.pp.281.

In the field of hydrometry a number of International organizations are currently active,of which ISO,üMO,Unesco,FAO,IAEA and IAHS have formed an Inter-Agency Panel on Standardization and for which UM0 provides the technical secretarirt.Major progress has occurred ir. the development and improvement of instruments and methods of observation of water stage,discharge,sediment

transport and water quality.The precise measurement of stage is important because it is basic to all other measurewnts.Some of the modern sensing devices,such as the bubble gauge.the servo- manometer and the beam balance deserve attention.Digiti1 water- level recorders have been developed to take advantage of electronic computers for automatic computation and processing of hydrometric data.Diglta1 water level recorders baaed on acoustics have also been developed.With respect to measurements.

of discharge,there are distinct prospects that in future, calibration of only one sample from a group of current meters will be.the normal practice for equally reliable results.The statistical study of errors in measurements of flow has shown that the largest error arises from insufficient data in precisely tracing the bed profile.Sophist1cated instruæents for accurate position fixing and measuring the bed profile

K. K. Frarnji

with sufficient resolution (e.g. the "ñalog",the "Hydrodist"

and the "Hi-Fix") have been developed.New methods have become, none the less,necessary for discharge measurements of large rivers and estuaries,as the conventional methods are time- consuming,tedious and costly.The m v i n g boat method has become well established after successful measurements of large rivers.

such as the Mekong,Mississippi or the Amazon (87,600 m3/s or over 3 million f3/s).It has been tested over a range of depths

3-63 m (10 to 200 feet).Its particular merit is the speed of completion of measurement and the low cost of the equipment.

The results are within 5 per cent of results of measurements by conventional methods.The principle of the ultrasonic method is to measure the velocity of flow at a certain depth by the different between the travel time of the sound pulses travelling upstream and of those travelling downstream through the water from transducers located in staggered positions on either side of the river.By incorporating an area factor in the electronic processor,the system can directly produce an output of

discharge.Such systems have been successfully installed on the River Thames in the United Kingdom and o n the Columbia in the U.S.A.The electromagnetic method involves the use of the earth's magnetic field for stream gauging.The accuracy obtained by this method is,however,not satisfactory,due to several complicating factorS.New methods of discharge measure- ments,such as the "air bubble method" and an automatic

monitoring installation based on magnetic indication and entirely without components are under tria1.A major effort continues to be devoted to the development of flow measuring instrumentS.and attention will soon be directed to standard- ization of echo (sonic) sounders and of telemetric instrumen- tation for observinb and transmitting observed data without relaying through observers.Following the rapid advances in the related sciences,a number of new instruments will come up for consideration,such as the acoustic level follower,the acoustic velocity meter,the doppler velocity meter.the optical current meter,the nuclear current meter,the eddy shedding current meter,etc.The future trends in the development of measuring structures are hard to forecast except for the almost certain substitutions of visual observationa of water level by

analogue and digital sensing and recording,or acoustic recording of water 1evels.and the like.0ther problems in the design of measuring structures,such as the effects of submergence and the boundary effects which cause significant differences in the results await research.Single measurements of flow by dilution methods,up to 2000 m3/s (70000 f3/s),have been success- fully accomplished.It is now possible even to envisage

continuous discharge measurements by using an indium-tin generator.An important unresolved subject for research is the minimum "mixing length" necessary from the injection point to the sampling point.With respect to the measurement of sediment transport,research is concentrated on the design and development of a suitable suspended. load sampler and one promising product has been the Delft Bottle DF12.The classical gravimetric method is time consuming and costly.while the photometric method appears to have promising prospects.Furthermore,both the method for measuring the rate of bed sediment load and the development of a sampler which will not disturb the stream bed or the sediment flow near the bed are still in the experimental stage.

The Arnhem or Dutch Sampler for measuring normal bed sediment and the Sphinx Sampler for measuring bed load fine sand size are amongst the most promising.An adaptation by adding a hydro- phone attachment to the Arnhem type has been tested for checking

the sediment load measurement acoustically.For surveillance of water qua1ity.a suggestion has been made for continuous, unattended,colorimetric modules and sample containers and the corresponding methods for obtaining overall system compatibility.

72

Another automated water quality monitoring system in use by the United States Geological Survey (USGS) is worth further study

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technology

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Sciences and technologies,such as computer-science electronics, ultra-sonic and telemetry,the use of light-weight plastics and special non-ferrous alloys,the application of specially-

designed hydrometric ships and aluminium and fibre-glass boats

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all point to future prospects of achieving high degrees of precision and uniformity in measurements.Also in the not too distant future the use of spacecraft and earth satellites for automatic transmission of automatically observed data is no longer in the realm of fantasy.The sky is the limit!

All in all,therefore,the prospects from the use of modern

Les perspectives de l'hydrométrie i la lumière de la technologie moderne.

par K.K. Framji R 1 ~ m m ~

Un certain nombre d'organisations internationales exercent normalement leurs activités dans le domaine de l'hydrométrie.

Parmi ceiles-ci,l'ISO,1'OMM,l'Unesco,la FA0,l'AIEA et 1'AISH ont constitué un Groupe interinstitutions de normalisation dont l'OMM assure le secrétariat technique.Des progrès très importants ont été réalisés pour la mise au point et l'amélioration des instruments et des méthodes d'observation du niveau de l'eau,des débits,des transports de sédiments et de la qualité de l'eau.

La mesure précise du niveau de l'eau est d'une grande importance, car elle est à la base de toutes les autres mesures.Certains des dispositifs de mesures modernes,tels que le limnigraphe 5 bulle, le servo-manonètre et le "fléau équilibré" (beam balatce),méritent d'être pris en considération.Des 1.imnimètres enregistreurs numériques ont été mis au point pour permettre d'utiliser des calculateurs électroniques pour le calcul et le traitement auto- matiques des données hydrométriques.0n a également réalisé des limnimètres enregistreurs numériques basés sur 1'accoustique.En ce qui concerne les mesures de débit,il apparalt clairement maintenant que,dans l'avenir,il suffira,dans la pratique courante, d'étalonner un seul échantillon prélevé dans un groupe de moulinets pour obtenir une fiabilité 6quivalente.L'étude statistique des erreurs dans les mesures d'écoulement a montré que la plus grande erreur résuie du manque de données suffisantes pour tracer exacte- ment le profil du lit.On a donc mis au point des instruments perfectionnés pour fixer correctement la position et mesurer le profil en travers avec un nombre de points suffisants (exemple.

le "Ralo~",1'"Hydrodist'' et le "Hi-Fix")

n'en sont pas moins devenues nécessaires pour les mesures des débits des grands fleuves et des estuaires, car les méthodes classiques demandent du temps et sont aussi fastidieuses que coÛteuses.La méthode du bateau mobile a maintenant fait ses preuves,après la réussite des mesures effectées sur de grands fleuves comme le Mékong,le Mississippi et l'Amazone (87.600m3/s, soit plus de 3 millions de DiedS cubes par seconde).Elle a été essayé sur des profondeurs allant de 3 à 6 3 m (de 10 à plus de 200 pieds).Son avantage particulier réside dans la rapidité d'exécution des mesures et le faible prix de l'équipment,et les résultats obtenus ne s'écartent pas de plus de 5% de ceux des mesures effectuées selon les méthodes classiques.Le principe de la méthode par ultra-sons consiste à mesurer la vitesse de de l'écoulement à une certaine profondeur d'après la différence entre la durée du tra)et,à travers l'eau,des impulsions sonores remontant et descendant le courant et engendrées 5 partir d'émetteurs situés en quinconce de chaque côté du cours d'eau.En incorporant un facteur de surface dans le processeur électronique,ce système peut fournir directement une indication du débit.11 a été installé avec succès en Angleterre, sur la Tamise,et aux Etats-Unis,sur la Columbia River.La méthode électro-magnétique utilise le champ

De nouvelles méthodes

K. R Framji

magnétique terrestre pour le jaugeage des cours d'eau.La précision obtenue par cette méthode n'est toutefois pas satisfaisante,en raison de complications dues

a

De grands efforts continuent 2 être consacrés à la mise au point d'instruments de mesure de l'écoulement,et l'attention sera bientôt dirigée vers la normalisation des échosondeurs et des instruments de télémesures pour l'observation et la transmission des données observées sans avoir à les relayer par des observateurs.

A la suite des progrès rapides réalisés dans les sciences correspondantes,un certain nombre de nouveaux instruments vont être à leur tour examinés,tels que le détecteur de niveau acoustique le compteur de vitesse acoustique,le compteur de vitesse par effet Doppler,le moulinet optique,le moulinet nucléaire,le moulinet dit

"eddy shedding current meter",etc.Les tendances futures en matière de réalisation d'ouvrage servant aux mesures sont difficiles à prevoir,sauf le remplacement presque certain des observations visuelles des niveaux de l'eau par des systèmes de détection et d'enregistrement analogiqueset numériques ou par l'enrigistrement acoustique de ces niveaux et autres procédés identiques.11 reste encore des recherches à faire en ce qui concerne d'autres problèmes relatifs à la conception meme des ouvrages servant aux mesures tels que les effets de leur submersion et de leur fonctionnement en conditions limltes,quientra€nent des différences notables dans les résultatS.Des mesures individuelles d'écoulement par des

méthodes de dilution,jusqu'à 2.000 m3/s (70.000 pieds cubes/seconde) ont été effectuées avec succès.11 est même désormais possible d'envisager dea mesures de débit continues en ayant recours à un générateur indium-étain.Un important sujet de recherches, non encore rBsolu,est la "longeur de mélange'' minimale nécessaire entre les points d'injection et de prélèvement.En ce qui concerne les mesurer de transport de sédiments,les recherches sont concentrées sur la conception et la mise au point d'un échantillonneur

approprié de matériaux en suspension,et la bouteille de Delft DF 1 2 a donné des résultats prometteurS.La méthode gravimétrique classique est longue et coÛteuse;par contre.la méthode photométrique semble donner des résultats très encourageants.De plus,la méthode utilisée pour mesurer le taux du charriage de fond,et la mise au point d'un échantilloneur qui ne dérange pas le lit du cours d'eau ou l'écoulement des sédiments près du fond,en sont encore au stade expérimenta1.L'échantillonneur d'Arnhem ou hollandais pour la mesure de la charge de fond normale,et l'echantillonneur Sphinx pour celle des sédiments ayant la finesse du sable,figurent parmi les types les plus prometteurs.On a essayé d'adapter un échantill- onneur du type Arnhem au contrôle acoustique des mesures de charge solide, en lui adjoignant un hydrophone.Pour la surveillance de la qualité de 1'eau.on a suggéré des modules colorimétriques continus,non surveillés,et des récipients pour échantillons,ainsi que les méthodes correspondantes permettant d'obtenir une compat- ibilité pour l'ensemble du système.Un autre système automatisé de surveillance de la qualité de l'eau et utilisé par 1'USGS

(United States Geological Survey) mériterait une étude plus poussée.

Tout bien considéré ,les perspectives futures qu'apporte l'utilisation des techniques modernes-ou,autrement dit, l'application des des sciences modernes et le recours à

des outils et à des matériaux modernes-sont nettement excellentes pour tout ce qui concerne la mise au point de méthodes et

d'instruments, hydrométriques précis .La science8 et la technique, n o t a m e n t les applications de l'informatique électronique,lea ultra-sonS.la télémétrie,l'utilisation de matériaux plastiques légers et d'alliages spéciaux non-ferreux,l'emploi de navires hydroditriques spécialement équipés et de bateaux en aluminium et en fibre de verre-apportent avec elles la promesse de 74

réalisations futures d'un haut degré de précision et d'unifor- misation des mesures.C'est aussi dans un avenir qui n'est plus maintenant très éloigné que l'utilisation de vaisseaux spatiaux et de satellites terrestres pour la transmission automatique de données observées automatiquement, ne fera plus partie du domaine de l'imagination.11 n'y aura plus d'autre limite que l'espace:

Perspectivas de la hidrometría a la luz de la teciiologin moderiia, por K.K. Frarnji

R c 5 L 1 I? 1 ?I I

Varias organizaciones internacionales realizan actualmente actividades en el campo de la hidrometria.En particular,la IS0,la OMM,la Unesco,La FAO, el OIEA y la AIHC han constituido un &up0 interinstitucional de expertos en normalizaciön del que la OMM asume la secretarie técnica.Se han realizado grandes progresos en la concepcion y el perfeccionamiento de instrumentos y métodos de observación del nivel de agua,gasto.transporte de sedimentos y calidad del agua.La medición precisa del nivel es esencial porquesirvede base a todas las demas.Algunos de los instrumentos de percepcion modernos,como el medidor de burbuja, el servomanBmetro y la balanza de flefe.son dip;nos de estudio.

Se han ideado limnigrafoc digita1es.a fin de utilizar las computadoras electrónicas para el calculo automatico y el procesamiento de

datos hidrométricos.Se han concebido iqualmente limnigrafos digitales acÚsticos.Con respecto a la medida del cauda1,hay grandes posibilidades de que en el futuro la calibración de una Única muestra de un grupo de molinetes hidrométricos sera una práctica normal que permitira obtener resultados igualmente fiableS.El estudio estadístico de los errores de las mediciones de la corriente ha puesto de manifiesto que el error mayor s e debe a los datos insuficientes en el trazado preciso del perfil del fondo.Se han inventado instrumentos perfeccionados para determinar la situación exacta y medir el perfil del fondo con suficiente precisión (por ejemp1o:el "Ralog",el "Hydrodist" y el "Hi-fix")

.

Con todo,ha sido preciso descubrir nuevos métodos para medir el caudal de los grades rios y los estuarios.dado que los métodos tradicionales son lentos.pesados y costosas.El método del buque movil ha confirmado su validez con su acertada medida de grandes rios corn,, el Mekong,el Mississippi o el Amazonas (87.600 m3/s o mas de 3 millones de pies3/s).Se ha probado en profundidades de 3 a 63 m (10 a 200 pies).Sus ventajas principales son la rápidez con que completa la medición y el bajo costo del equipo.Sus resultados no difieren en mas del 5% de las medidas obtenidas con los métodos tradicionales.El principio del método ultrasónico consiste en medir la velocidad de la corriente a cierta profundidad por la diferencia del tiempo de propagación de las ondas sonoras aguas arriba y aguas abaj0.a partir de transductorec situados en posiciones escalonadas a ambas orillas del rio.Incorporando un factor-area de seccion-al elaborador electrÓnico,el sistema puede presentar direictamente el calculo del caudal.Esos sistemas se han instalado cone éxito en el Tamesis (Reino Unido) y en el Columbia de los Estados UnidoS.El método electromagnético entrana la utilización del campo magnético terrestre para el aforo de caudaleS.La precision obtenida con este método no es, sin embargo,satisfactoria, dehido a diversas dificultadeS.Se estan probando nuevos métodos para medir la corriente,como el

"tBétodo de la burbuja de aire" y una instalaciön automatica de observación basada en induccion magnética.Se sigue trabajando intensamente en la creación de instrumentos para medir el caudal y pronto seprestartíatención a la normalización de los ecosondas y de los instrumentos telemétricos de observación y transmisi6n de los datos observados sin retransmisión por medio de observadores.

Como resultado de los r6pidos progresos de otras ciencias afines.se podrán tomar en consideración algunos instrumentos nuevos como el observador acústico del nive1,el velocimetro acústico, el velocimetro por efecto Doppler,el molinete hidrom6tric.o hptico,

K. K. Framji

el molinete hidrométrico nuclear,el molinete "eddy shedding",etc.

Es difícil prever el futuro de las estructuras que se usan para medici6n, si se exceptua que es casi seguro que las observaciones visuales del nivel del agua se sustituiran por métodos de

percepción y registro analógicos y numéricos, o de registro acustico, y otras semejanteS.Las investigaciones tropezaran con otros

problemas que plantea el diseno de tales estructuras como son

los efectos de la sumersión y de borde,los cuales ocasionan diferencias Importantes en los resultados.le han efectuado con éxito mediciones únicas de la corriente por métodos de diluciÓn,de hasta

2.000m3/s (70.000 pies3/s) .Ahora es posible prever incluso la medición continua del caudal utilizando un generador de índio y estano.Un tema de InvestigaciÖn importante no resuelto es el del "camino de mezcla" minimo necesario desde el punto de inyeccion hasta el punto de muestra.Con respecto a la medicion del transporte de sedimento,la inveatigacion se centra en el diseño y fabricación de un tomamuestras de materiales en suspensión adecuad0.y un articulo prometedor ha sido la botella Delft DP12.El método gravi- métrico clásico es lento y costoso,mientras que el método fotométrico parece tener perspectivas prometedoras.Por otra parte,tanto el método de medición de la velocidad de acarreo del sedimento del

fondo como la produccion de un tomamuestras que no perturbe el fondo del curso de agua ni el movimiento del sedimento cerca del fondo están todavia en fase experimental .El tomamuestras Arnhem o Dutch para medir el sedimento normal del fondo y el tomamuestras Sphinx para medir el arrastre de arenas finas figuran entre los más prometedoreS.Se ha puesto a prueba una adaptación del tipo Arnhem, incorporándole un hidrofono ,para comprobar acGsticamente la medición del arrastre.Para vigilar la calidad del agua, se ha sugerido la utilizacion permanente y automitica de recipientes

de muestras y módulos colormétricos, y de los métodos correspondientes para asegurar la compatibilidad general del sistema.Otro sistema automatizado de vigilancia de la calidad del agua utilizado por el USGS (United States Geological Survey)merece ser estudiado 6 s a fondo.

Por consiguiente.en general las posibilidades de emplear la tecnologia moderna,es decir, de aplicar las ciencias modernas y usar instrumentos y materiales modernos,son francamente excelentes en

10 que se refiere al establecimiento de métodos exactos y a la fabricación de instrumentos precisos de hidtometria. Exis ten buenas perspectivas de lograr un alto grado de precisión y uniformidad en las mediciones gracias a ciencias y técnicas como la electrónica

de la computadora, el ultrasonido y la telemetrfa,el empleo de plasticos de poco peso y de aleaciones especiales no ferrosas y la aplicacion de navios especialmente diseliados para fines hidrométricos y de buques de aluminio y vitrofibra.Por otro lado, no tardará mucho en que el uso de astronaves y satélites terrestres para la transmisión a u t o d t i c a de datos observados automáticamente dejara de pertenecer al reino de la fantasia. El limite es el cielo!

76

K. K. Frarnji

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