Hydrometry:
IProceedings
of
the Koblenz S y m p o s i u m SeptemberI970
Hydrométrie
Actes
du
colloque de Coblence, , I SeptembreI9 70
Volume
I
A contribution to the International Hydrological Decade Une contribution, à la Décennie hydrologique internationale Con resúmenes en español
Pesm~e no p y c c m
Unesco - W M O - IAHS
Studies and reports in hydrology I Études et rapports d'hydrologie 13
Recent titles in this series /Titres récents dans cette collection
10. Status and trends of research in hydrology / Bilan et tendances de la recherche en hydro- logie. Published by Unesco / Edité par l'Unesco.
11. World water balance: Proceedings of the Reading Symposium, July 1970 / Bilan hydrique mondial : Actes du colloque de Reading, juillet 1970. Vol. 1-3. Co-edition IASH- Unesco Coédition AIHS- Unesco.
12. Research on representative and experimental basins: Proceedings of the Wellington (N. 2.) Symposium, December 1970 / Recherches sur les bassins représentatifs et expérimentaux:
Actes du colloque de Wellington (N.-Z,), décembre 1970, Co-edition IASH-Unesco / Coédi- tion AIHS- Unesco.
13. Hydrometry: Proceedings of the Koblenz Symposium, September 1970 / Hydrométrie:
Actes du colloque de Coblence, septembre 1970. Vols 1, 2. Cosedition Unesco-WMU.
IAHS / Coédition Unesco-OMM-AIHS.
For details of the complete series please see the list printed at the end of this work La liste complète des titres de cette collection figure la fin de cet ouvrage
Published jointly by Unesco, Place de Fontenoy, 75700 Paris, World Meteorological Organization, 41 av. Giuseppe Motta, Geneva, and the International Association of Hydrological Sciences (Secretariat:
Dr. G. Kovács, Research Institute for Water Resources Development, liikóczi Út 41, Budapest VIII)
Printed by Imprimerie Louis-Jean, Gap Publié conjointement par
l’Unesco, p.lace de Fontenoy, 75700 Paris,
l’Organisation mét6orologique mondiale, 41, av. Giuseppe-Motta, Genève, et l’Association internationale d’hydrologie scientifique (Secrétariat:
Dr. G. Kovács, Institut de recherches des ressources hydrauliques, Rákóczi Út 41, Budapest VIII)
Imprimerie Louis-Jean, Gap ISBN 92-3-001051-0
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0
Unesco 1973 Printed in FrancePreface
The International Hydrological Decade (IHD) 1965-74 was launched by the General Conference of Unesco at its thirteenth session to promote international co-operation in research and studies and the training of specialists and technicians in scientific hydrology. Its purpose is to enable all countries to make a fuller assessment of their water resources and a more rational use of them as man’s demands for water constantly increase in face of developments in population, industry and agriculture.
In 1972 National Committees for the Decade had been formed in 107 of Unesco’s 130 Member States to carry out national activities within the programme of the Decade. The implementation of the programme is supervised by a Co-ordinating Council, composed of twenty-one Member States selected by the General Conference of Unesco, which studies proposals for developments of the programme, recommends projects of interest to all or a large number of countries, assists in the development of national and regional projects and co-ordinates international co-operation.
Promotion of collaboration in developing hydrological research techniques, diffus- ing hydrological data and planning hydrological installations is a major feature of the programme of the IHD which encompasses all aspects of hydrological studies and research. Hydrological investigations are encouraged at the national, regional and international level to strengthen and to improve the use of natural resources from a local and a global perspective. The programme provides a means for countries well advanced in hydrological research to exchange scientific views and for developing countries to benefit from this exchange of information in elaborating research projects and in implementing recent developments in the planning of hydrological installations.
As part of Unesco’s contribution to the achievement of the objectives of the IHD the General Conference authorized the Director-General to collect, exchange and disseminate information concerning research on scientific hydrology and to facilitate contacts between research workers in this field. To this end Unesco has initiated two series of publications: Studies and Reports in Hydrology and Technical Papers in Hydrology.
The Studies and Reports in Hydrology series, in which the present volume is published, is aimed at recording data collected and the main results of hydrological studies undertaken within the framework of the Decade, as well as providing information on research techniques. Also included in the series willbe proceedings of symposia. Thus, the series comprises the compilation of data, discussions of hydro- logical research techniques and findings, and guidance material for future scientific investigations. It is hoped that the volumes will furnish material of both practical and theoretical interest to hydrologists and governments participating in the IHD and respond to the needs of technicians and scientists concerned with problems of water in all countries.
A number of these volumes have been published jointly with the International Association bf Hydrological Sciences and the World Meteorological Organization which have co-operated with Unesco in the implementation of several important projects of the IHD.
Préface
La Conférence générale de l’Unesco, à sa treizième session, a décidé de lancer, pour la période s’étendant de 1965 à 1974, la Décennie hydrologique internationale (DHI), entreprise mondiale visant à faire progresser la connaissance en matière d’hydrologie scientifique par un développement de la coopération internationale et par la forma- tion de spécialistes et de techniciens. Au moment oÙ l’expansion démographique et le développement industriel et agricole provoquent un accroissement constant des besoins en eau, la DHI permet à tous les pays de mieux évaluer leurs ressources hydrauliques et de les exploiter plus rationnellement.
I1 existe actuellement dans 107 des 130 Etats membres de l’Unesco un comité national qui, pour tout ce qui a trait au programme de la Décennie, impulse les activités nationales et assure la participation de son pays aux entreprises régionales et internationales. L’exécution du programme de la DHI se fait sous la direction d‘un Conseil de coordination composé de 21 Etats membres désignés par la Conférence générale de l’Unesco ; ce conseil étudie les propositions concernant le programme, recommande l’adoption de projets intéressant l’ensemble des pays ou un grand nombre d’entre eux, aide à la mise sur pied de projets nationaux et régionaux, et coordonne la coopération à l’échelon international.
Le programme de la DHI, qui porte sur tous les aspects des études et des recherches hydrologiques, vise essentiellement à développer la collaboration dans la mise au point des techniques de recherches, dans la diffusion des données hydrolo- giques, dans l’organisation des installations hydrologiques. I1 encourage les enquêtes nationales, régionales et internationales tendant à accroître et à améliorer l’utilisation des ressources naturelles, dans une perspective locale et général:. I1 permet aux pays avancés en matière de recherches hydrologiques d’échanger des informations ; aux pays en voie de développement, il offre la possibilité de profiter de ces échanges pour élaborer leurs projets de recherches et pour planifier leurs installations hydrologiques en tirant parti des acquisitions les plus récentes de l’hydrologie scientifique.
Pour permettre à l’Unesco de contribuer au succès de la DHI, la Conférence générale a autorisé le Directeur général à rassembler, à échanger et à diffuser des informations sur les recherches d’hydrologie scientifique et à faciliter les contacts entre les chercheurs dans ce domaine. A cette fin, l’Unesco fait paraître deux nouvelles collections de publications : “Etudes et rapports d’hydrologie” et “Notes techniques d’hydrologie”.
La collection “Etudes et rapports d’hydrologie”, dans laquelle est publié le présent ouvrage, a pour objet de présenter les données recueillies et les principaux résultats des études effectuées dans le cadre de la Décennie et de fournir des informations sur les techniques de recherche. On y trouve aussi les Actes de colloques réunis sur ce sujet. Cette collection publie donc des données, des techniques et des résultats de recherches ainsi qu’une documentation pour les travaux scientifiques futurs.
On espère que ces volumes apporteront aux hydrologues et aux gouvernements qui participent à la DHI des matériaux d‘un intérêt tant pratique que théorique, et
Puéface
qu’elle répondra aux besoins des techniciens et des hommes de science de tous pays qui s’occupent des problèmes de l’eau.
Certains de ces ouvrages sont publiés en coopération avec l’Association inter- nationale des sciences hydrologiques ou l’organisation météorologique mondiale dans le cadre de projets réalisés conjointement par ces organisations et l’Unesco.
Contents
Table des matières
Volume I
Foreword / Avant-propos pages xiü, xv
I. M E A S U R E M E N T OF WATER STAGES / MESURE D E S NIVEAUX D'EAU
The analysis of float and hydrostatic level gauges and the choice of optimal values of their basic elements
Digital recording of water levels with the aid of acoustics and its application to'hydrological pumping tests
Hydrometric stations in arid zones
A portable water-stage recorder for experimental hydrological measurements J. Martinec
A. M. Dimaksian
H. J. DÜrbaum and R. Kohlmeier D. Kornitz
Water-level transducers
Stream gauging network of the lower Mekong basin
D. J. Sherlock, R. L. Hitchcock and H. L. Stark V. Taweesup Water-level gauging by pressure measuring R. Zayc
II. M E A S U R E M E N T OF DISCHARGE / JAUGEAGE DU DEBIT
11.1 Measurement of discharge by measuring velocity in a cross-section Jaugeage du débit par la mesure de la vitesse dans une section transversale The analysis of the possibilities of current meter operation in turbulent streams
Accuracy of current meter measurements Calibration of current meters in a submerged jet The magnitude of errors at flow measurement stations
Relation entre la pulsation et la précision du jaugeage par moulinets L. Muszkalay
Instruments for measurement of currents and levels in natural reservoirs and rivers G. K. Popandopulo
P. N. Burtsev and M. M. Baryshnikova
R. W. Carter J. Davidian
R. W. Herschy
3 11 31 41 46 63 69
79 86 99 1 o9 132 142
ContentslTable des matières
Flow measurement of some of the world’s major rivers by the moving-boat
method G. F. Smoot 149
Problems in the design of measuring structures O. Starosolszky 162 T h e evaluation of discharge measurements in streams with changing flow
conditions K. Bellin 169
L a perche de jaugeage à intégration “AGAR” A. Duboë 181 Flow measurement by the integrating float method H. Liu 188 Use of depth floats in drainage canals with aquatic weed 197 Les jaugeages au moulinet et au flotteur ?i l’heure du calcul automatique
J.A. Rodier 206
Measurement of discharge under ice cover P. W. Strilaeff and J. H. Wedel 214 Estimation of streamflow under the ice cover J. Szildgyi and L. Muszkalay 228
J. Procha‘zka
11.2 Tracer methods /Jaugeage par traceurs Les jaugeages par la méthode de dilution en 1970
G. Douillet 239
Techniques for measurement of discharge by dye dilution
H. André, C. Richer et
H, H. Barnes,
Jr., and F. A. Kilpatrick 25 1
260 Stream hydrographs by fluorescent tracers B. C. Goodell and H. Steppuhn Chemical method of water flow measurement in open channels
T. Czarnocki 271
Stream gauging with portable equipment 279
Precision and bias of the results of dilution gaugings 289 R. Kellerhals and M. Church
A, L. Wilson
11.3 Measuring structures Ouvrages servant aux mesures
Adverse-bottom-slope weir and orifice M. I. Rbaza 303 Laboratory calibration of the Walnut Gulch supercriticd flow-measuring
flume W, R. Gwinn 310
Free surface subcritical flow measurement G. V, Skogerboe and
L. H. Austin 319
Flow over side-weirs K. Subramanya and S. C. Awasthy 328 Gauging stations on sediment-loaded mountain rivers E. Walser 336 Flow measurement of low-gradient streams in sandy soils
J. M. Sheridan 345
P. Yates and
ContentslTable des matières
11.4. Other methods / Autres méthodes
Measurement and estimation of flood discharges
The air-bubble method of flow measurement and its application L. J. Dávid
M. A. Benson
Discharge measurement in open water by means of magnetic induction H. Gils
Accuracy and rationalization of river discharge measurements I. F. Karasev and A, N. Chizhov
Ultrasonic measurement of discharge in rivers
Measurement of discharge as inflow into leaky reservoirs A recording meter for measuring the ,overland flow
W. Krause
T. Kinosita
W. G. Knisel, Jr.
C. Peschke and Hydraulic model study to determine a stage-discharge relationship S. K. Stephens and-H. L. Stark
Problems of flow measurement in large reservoirs
LE (Leading Edge) Flowmeter-a unique device for open channel discharge measurement H. Holmes, D. K. Whirlow and L. G. Wright
J. Urban
A constant discharge siphon for flow measurement and control Ben Chie Yen and Ven Te C h o w
355 361 374 382 388 400 408 412 423 432 444
Foreword
Hydrometry has developed from a mere description of magnitudes of hydrological events to a modern science with sophisticated techniques for measuring phenomena in the water and on the surface of water, including nowadays the use of space technology .
The Co-ordinating Council for the International Hydrological Decade, recognizing the importance of hydrometry and the application of modern methods for evaluating and processing hydrological data, has developed various international programmes related to hydrometry. To give further impetus to the development of measuring techniques and to enable a broader application of the findings, Unesco convened an International Symposium on Hydrometry in Koblenz (Federal Republic of Germany) from 13 to 19 September 1970. This symposium was organized in co-operation with the World Meteorological Organization, the International Association of Hydrolo- gical Sciences and the National Committee for the IHD of the Federal Republic of Germany.
The technical preparation of the symposium was undertaken by an Organizing Committee and Secretariat under the leadership of Dr. J. Wallner, president of the Federal Institute for Hydrology, Koblenz. The symposium was attended by about 520 participants from fifty countries and four international organizations.
The scientific programme of the symposium covered the following main subjects:
Measurement of water stages and discharge;
Measurement of depth, temperature and water quality;
Measurement of solid matter transport;
Special techniques, including recording and teletransmission of data;
Evaluation of measured data.
All the work of the symposium was conducted in plenary session. The following scientists took the chair: Mr. S. Dumitrescu (Unesco), Mr. H. André (France), Mr. W. Friedrich (Federal Republic of Germany), Mr. R. MarcoviC (Yugoslavia), Mr. K. Subramanya (India), Mr. E. Walser (Switzerland), Mr. R. Zayc (Federal Republic of Germany), Mr. R. Carter (United States), Mr. R. Herschey (United Kingdom) and Professor L. J. Tison (International Association of Hydrological Sciences).
Eighty-seven papers submitted by specialists from twenty-one countries were discussed within the framework of the programme outlined above; they are repro- duced in these proceedings with minor abbreviations and editorial changes. They are preceded by abstracts in English, French, Russian and Spanish. Reports of discus- sions on individual papers are given after the relevant paper.
It is hoped that these proceedings, published jointly by Unesco, W O and IAHS, willbe of value in transmitting information on the most up to date theories and techniques concerning hydrometry.
Avant-propos
L'hydrométrie, qui à ses débuts se bornait à décrire l'ampleur des phénomènes hydrologiques, est devenue une science moderne utilisant des techniques perfection- nées pour mesurer les phénomènes qui se produisent dans l'eau et à la surface, y compris, aujourd'hoi, la technologie spatiale.
Le Conseil de coordination de la Décennie hydrologique internationale, conscient de l'importance que présentent l'hydrométrie et l'applicatiqn de méthodes modernes à l'évaluation et au traitement des données hydrologiques, a élaboré divers program- mes internationaux relatifs à l'hydrométrie. Pour stimuler encore davantage le déve- loppement des techniques de mesure et pour permettre une application plus large des découvertes, l'Unesco a réuni un Colloque international sur l'hydrométrie, à Coblence (République fédérale d'Allemagne), du 13 au 19 septembre 1970. Ce colloque a été organisé avec le concours de l'organisation météorologique mondiale, de l'Association internationale d'hydrologie scientifique et du Comité national pour la DHI de la République fédérale d'Allemagne.
La préparation technique du colloque a été assurée par un comité d'organisation et un secrétariat sous la direction du D'. J. Wallner, président de l'Institut fédéral d'hydrologie de Coblence. Environ 520 participants de 50 pays et de 4 organisations internationales ont pris part au colloque.
LÆ programme scientifique du colloque portait sur les principales questions suivantes :
Mesure des niveaux d'eau et jaugeage du débit.
Mesure de la profondeur, de la température et de la qualité de l'eau.
Mesure des transports solides.
Techniques spéciales, y compris l'enregistrement et la télétransmission des Evaluation des mesures obtenues.
mesures.
Tous les travaux du colloque se sont déroulés en séance plénière. Les spécialistes ci-après ont pris la parole : M. S. Dumitrescu (Unesco), M. H. André (France), M. W. Friedrich (République fédérale d'Allemagne), M. R. MarcoviC (Yougoslavie), M. K. Subramanya (Inde), M. E. Walser (Suisse), M. R. Zayc (République fédérale d'Allemagne), M. R. Carter (Etats-Unis d'Amérique), M. R. Herschey (Royaume-Uni) et le professeur L. J. Tison (Association internationale d'hydrologie scientifique).
Quatre-vingt- sept communications présentées par des spécialistes de vingt et un pays ont été examinées dans le cadre du programme esquissé ci-dessus. Elles sont reproduites dans les présents Actes, parfois légèrement abrégées ou avec quelques modifications de forme ; elles sont en outre précédées d'un résumé en anglais, en français, en espagnol et en russe. Les comptes rendus des débats sur une communi- cation particulière suivent immédiatement le texte de celle-ci.
On espère que ces Actes, publiés conjointement par l'Unesco, l'OMM et l'AIHS, contribueront à la diffusion de l'information sur les théories et les techniques les plus modernes concernant l'hydrométrie.
I Measurement of water stages Mesure
des niveaux d’eau
The analysis of float
and hydrostatic level gauges and the choice of optimal values of their basic elements
A. M. Dimaksian
State Hydrological Institute, Leningrad, U.S.S.R.
Abstract. Optimum conditions for the operation of float water-level recorders are attained when the equilibrium of the system is disturbed only within strict limits during the rise or fall in the water level.
The method used in the design of the system makes it possible to select a given accuracy and a specified range of measurements at the basic design stage.
Analysis of the operation of hydrostatic level gauges shows that their net error lies within 1 c m of water level. Estimation of the allowable error permits a choice of the value of the quantization and the assessment of the principal elements in the design of the instrument for telemetry.
ANALYSE DES LIMNIMETRES A FLOTTEUR ET LIMNIMETRES HYDROSTATIQUES.
CHOIX DES VALEURS OPTIMALES D E LEURS ELEMENTS PRINCIPAUX
Résumé. Les conditions optimales pour l’utilisation des limnimetres 2 flotteur sont atteintes lorsque le système est en déséquilibre dans les limites strictes pendant la montée et la baisse de niveau de l’eau. Les méthodes de calcul du système assurent le choix des éléments principaux constructifs du système avec une précision et une amplitude de mesure données.
L’analyse des limnimètres hydrostatiques témoigne que leur erreur totale ne dépasse pas 1 c m en hauteur d’eau. La détermination de cette erreur permet de choisir un pas optimal de la quantification du convertisseur et de calculer les éléments principaux de la construction d’appa- reils 2 transmission d’informations i distance.
ANÁLISLS DE
MEDIDORES.DE
NIVEL HIDROSTÁTICOS Y DE FLOTADOR, Y ELECCION D E VALORES OFTIMOS P A R A SUS ELEMENTOS BASICOSResumen. Se alcanzan condiciones Óptimas para el funcionamiento de los medidores de nivel de flotador en el caso de que el equilibrio del sistema se perturbe dentro de límites estrictos, en la elevaciÓn o descenso del nivel de agua.
El método para el cálculo del sistema permite la elección de sus elementos básicos de diseño para la precisión necesaria y para el tipo de mediciones a realizar.
El análisis del funcionamiento de medidores de nivel hidrostático muestra que su error neto es del orden de 1 cm.
La estimación del error permite elegir el paso de cuantificación del convertidor, y calcular los elementos principales del instrumento para la transmisión telemétrica de la información.
AHAAM3 IIOIIRABKOBbIX kI rMAPOCTATHVECKMX YPOBHEMEPOB M BM6OP OJITEIMAAbHbIX 3HAYEHM.IW M X OCHOBHbIX 3AEMEMTOB Pe3IOMe. T e o p m IIOIMaBICOBbIX YJOBHeMepOB IIpB PaCCMOTPeHkIkI CHCTeMbI
-
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-
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A. M. Dimaksian
The static régime of a float gauge is characterized by the equilibrium for the system (Fig. 1):
F2
=
F, - F3 (1)where F, is the force of gravity acting on the float, F 2 is the force of gravity acting on the counterweight, F, is the carrying capacity of the float immersed to a depth X.
When the water surface is not enclosed then, according to Archimedes’ prin- ciple :
x
F3
=
Y, . S(X) * dxwhere S(x) is the cross-sectional area of the float and y,,, is the specific weight of the surface water layer. For a float of constant cross-section
F3
=
yw * S * X,7r
where x is the depth to which the float is immersed. Since S
= -
. d2 at the depth x, the carrying capacity is4
where cl is the diameter of the cylindrical part of the float.
(1) is disturbed. For a fall in water level
In a dynamic régime [ref. 13 the float follows the water level when equilibrium
F2
<
(FI - F,) + AF, and for a rise in water levelFz
>
(FI - F,) - AF, (3) where AF, is the increment of the carrying capacity of the float. It is impor- tant that these inequalities should occur at the extremes of the measurement range, If Ah is the total increment of the depth of float immersion, thenC
Analysis of float and hydrostatic level gauges and choice of values
1
F
- +
5 6
-
-\T-
---7
I
t
--- -
d - I
Figure 1. Diagram of float levelgauge 1 - float wheel
2 - float 3
-
fittings4 - counterweight 7 - additional weight.
5. 6 -- cable
A. M. Diindksian
I l I
Figure 2. Electrical scheme of hydrostatic level gauge.
Analysis of float and hydrostatic level gauges and choice of values
where Ah
=
Ah' + Ah"; and Ah' and Ah" are increments of the depth of float immersion during the fall and rise of water level respectively.From inequalities (2) and (3) it follows that the float starts moving downwards when the water level is Ah' lower than the horizon b - b. During the rise in level, F, becomes less by U,. The equilibrium is disturbed when the water level is Ah" highar than the horizon b - b.
Inequalities (2) and (3) show that the force of gravity on the float (within the limits F2
=
(FI - F3) ?Z AF,) is automatically regulated by the carrying ca- pacity of the float. It is evident that the change in the depth of float immersion shows the total error of the system. The increment of depth of float immersion is not constant and depends on many factors. From (4) it appears thati.e. in order to diminish Ah, it is necessary either to diminish AF, or to increase the float diameter, which is more effective since the denominator includes the square of the diameter.
In general form:
Ah
= f
>FI,
,u,,
Ffr 2 Y, , AZ) (5)where F:, F; are the forces of gravity acting on the left and right sides of the cable;
AF, is the carrying capacity of the immersed part of the cable and the counter- weight; F,, is the frictional force acting on the instrument; AZ is the linear thermal expansion of the left part of the cable (II). Among the factors affecting the accuracy of measurement, Fi , Fi, AF, and to a certain extent F,, are related to water level fluctuations, while y,and AZ depend on water and air temperature.
Where there is a fall in the water level (fl) when F; + O and
pl
-+ plmax,the F,$= 5
- €fl -k Ffr-
AF,.total acting force is
+ '22max)
For a rise in water level, when
pl
+ O whileF,
AF,,?
=
F),-
Ffr-
AF,-
AF3H?'
= F!,
- FI - AF, f Ffr.or Finally,
71 Y,
AF,,
=-
4-
[d2 (Ah',-
Ah: 2 Ahfr)-
(d: a, 4- di-
]),Z (6)where Ah;, Ah: and Ah,, are the increments of float immersion due to the forces Fi, FI and F,; d, and a2 are the diameter and the height of the counterweight; d, and I, are the diameter and the length of the submerged part of the cable.
The total error is
Ah,= Ah; - Ah; - Ah,c - Ah,, k Ah,,
where Ah,, and Ah,, are the errors due to the lifting forces of the counterweight and of the cable, respectively.
A. M. Dimaksiuri
As is evident from equation 6 the float system has an error asymmetry.
Errors due to the changes of water density (Ac) and air temperature (AZ) always have opposite signs. Therefore the total error is Ah,= k A C A 1. The changes of A C and AZ occur due to daily and seasonal water and air temperature fluctuations.
The resultant error value for the significant factors is
Here it is supposed that AhH and Ah, appear independently of each other.
The value A C might be neglected in most cases, since under actual conditions it is less than 0.01 cm.
The design of the water level recorder mechansism depends mainly on the deter- mination of A h from equation 7.
Some basic conclusions may be reached on the design of a float-operated re- corder:
1. The optimum height of the float’s cylindrical part (u) should be a little greater or, ideally, equal to the maximum error amplitude, i.e.
a =
Ah,,, ;2. The accuracy of measurement of the float gauge depends mainly on the increment of the float’s carrying capacity AF3 at given values of d,, and
qnax
;3. The force of gravity on the counterweight F2 is at an optimum when it is numerically equal to the maximum increment of the float’s carrying capacity, i.e.
F2 =AF,,, , provided that conditions (2) and (3) are observed;
4. The asymmetric error is characteristic of the float gauge, the range of the error depending on the choice (design) of the basic elements of the instrument.
Hydrostatic level gauges may be divided into three main groups: (a) combined or autonomic instruments; (b) instruments with a pneumatic or hydraulic connexion to the channel; (c) monitoring instruments with an electrical connexion. Hydrostatic level gauges with electrically operated communication lines seem to possess the greatest advantages for water stage observations, namely that they can be automated simply.
If the pipe (1) of the mercury manometer is affected by the hydrostatic water pressure P,, while the pipe of the measuring unit (2) is affected by the atmospheric pressure Pa (Fig. 2), the equilibrium is
where h, is the difference in the height of the liquid (mercury) columns in the manometer pipe, y 1 is the specific weight of the liquid in the manometer. y 1 = pig, where p 1 is the density of the liquid in the manometer and g is gravitational acceleration. Thus, in order to measure water level (FI) relative to the reference datum, it is sufficient to measure the difference in pressure in the manometer.
While calibrating the level gauge it is sufficient to establish the relation h, =f(H), Since equation 8 is linear, h, = f(H) is linear also.
The static characteristic of the level gauge is easy to determine. If the water level equals H and the specific weight of the liquid y,, the hydrostatic water pressure is P,
=
H. y, and the height of the mercury column in the manometer isAnalysis of float and hydrostatic level gauges and choice of values
pw YW
Y1 71
h,
=-
or 61, = H . - .From equation 9 it is clear that the change in the specific weight of water and mercury due to temperature variations should be taken into consideration.
If a U-shaped manometer (Fig. 2) is placed in a bell of a cylindrical or conic shape and the pipe (1) is connected to the pressure receiver of the instrument, while the pipe of the measuring unit (2) is connected to the atmosphere, then the changes in the mercury column in the manometer due to the hydrostatic pressure of the water might be transformed into a digital impulse code. The cylindrical pipe in which the measuring unit of the instrument is placed is insulated from the pressure receiver.
The pressure receiver is connected to the manometer by means of a brass pipe of small diameter, approximately 10 cm long.
The systematic errors in the instrument depend mainly on the temperature variations of its surroundings. These errors occur because of the thermal expansion in the junctions of the instrument [ , the change of water density h and the rise of water level in the pressure receiver (2). The analysis of these errors shows that, irrespective of temperature fluctuations, the resultant error
2
=
([+ h) - E (1 01is almost completely compensated.
Thus, for instance, in the case of a range of measurement of water level from O to 10 m and temperature fluctuations from O" to 25°C for fresh water, the average value 2
<
1 cm, provided the diameters of manometer pipes 1 and 2 are equal.Experimental investigations corroborated these theoretical conclusions [ 21.
In the case of the electrically operated instrument, the principle used in the transformation of the linear movement of mercury into a digital impulse code is clearly shown. It consists of a pointer (3), a micrometer (4) with a sliding nut (51, reversible micromotor (6), two relays (7) and switching-over and blocking con- tacts (8).
In the case of the remote control of the instrument (manual or automatic) the pointer is lowered from its bench-mark position until it touches the mercury, then the motor is put into reverse by the relay and this raises the pointer to its initial position and thus the electric current to the motor is interrupted. When the pointer is lowered, a triple-edged interrupter sends a series of impulses to the communication line proportional to the water level. The unit of sampling (quantization) is close to 1 cm of water level. The discrepancy between the sampling unit and the actual value of the level is taken into account by the calibration of the instrument.
As experience of gauge operation in natural conditions shows, the total error P of the system (including the errors of conversion and recording) does not exceed 1 cm of water level, irrespective of the measurement range. The error is estimated from the formula
P
=
J[([ 4- A) - €12 + b; (111 where b, is the height of water level variation, corresponding to the number of unrecorded impulses.The estimation of the error 2 makes it possible to choose the value of the impulse and to determine the principal elements of instrument design. The distance of
A. M. Dimaksian
telemetric transmission of the information depends on the voltage drop in the communication line and is practically unlimited. The instrument is fed by a source of constant current with voltage from 22 to 30 V, irrespective of the voltage drop in the line.
BIBLIOGRAPHY / BIBLIOGRAPHIE
1. Dymaksian, A. M. 1967. Tochnost ismereniya i metodika rascheta poplavkovoy sistemy urovnemera [Measurement accuracy and computation technique for float system of a level gauge]. Trudy Cos. Gidrologicheskogo Instituta, vyp. 249.
2. Dymaksian, A. M. 195 7. Novye teleismeritelnye gidrometeorologicheskiya pribory [ N e w telemetric hydrometeorological instruments], Leningrad, Gidrometeoisdat.
Digital recording of water levels with the aid of acoustics and its application to hydrological pumping tests
H. J. Dürhaum and R. Kohlmeier
Federal Geological Survey (Bundessanstalt für Bodenforschung), Hanover, Federal Republic of Germany
Abstract. In pumping tests, the desired data can frequently be obtained only at considerable expense and effort.
In most cases, manual recording involves high labour costs and yields few and insufficiently accurate measurements. Conventional automatic devices are often subject to mechanical disturb- ances and are often unable to follow quick changes in stage, due to the mechanical follower arrangement of floats and probes. As a result, the cost of instrumentation rises almost linearly with the number of measuring points. The immense number of measured values resulting from a pumping test is presented in the form of lists or analoguerecords; detailed evaluation requires an extremely long time.
To overcome these difficulties by modern techniques, the following measuring method was chosen: ultrasonic vibrators acting as transmitters and receivers are suspended motionless in the water at the ground-water observation points. The transit time of an ultrasonic pulse travelling from the vibrator to the water surface and back is measured with the aid of an extremely accurate microchronometer. Multiplication of this transit time by the sound velocity gives the distance between vibrator and water surface. The resolving power is about 1 mm. The distances between vibrator and water surface are measured in sequence and recorded (as transit time), together with date and hour of the measurement and the number of the measuring point, on punched tape. From the punched tape, the data are transferred to a magnetic disc where they are available for direct use by the computer. The drawdown curves are graphically and numerically evaluated with the aid of various programmes. The resulting possibilities are indicated by means of several examples.
ENREGISTREMENT DIGITAL DES NIVEAUX DE L’EAU PAR DES METHODES ACOUSTIQUES ET APPLICATION A DES TESTS HYDROLOGIQUES DE POMPAGE Résum6 Ce n’est qu’à grands frais qu’on peut obtenir les données de mesure dksirables à l’aide d’essais de pompage.
L‘enregistrement manuel fournit, dans la majorité des cas, des données trop peu nombreuses et trop inexactes et nécessite des frais de personnel trop 61ev6.s. Les appareils automatiques qui étaient en usage jusqu’ici se sont fréquemment trouvés en réparation et, souvent, ils ne sont pas capables de suivre les variations rapides des niveaux d‘eau souterraine à cause du système mécanique de poursuite des flotteurs d’enregistrement ou des sondes. Dans le cas de ce mode opératoire technique, les dépenses pour les appareils augmentent à peu près de façon linéaire par rapport aux postes d’observation des niveaux d’eau souterraine qu’il faut saisir. Le nombre immense des valeurs enregistrées lors d’un essai de pompage se présente sous forme de listes ou enregistrements analogues ; une évaluation détaillée requiert un temps extraordinairement élevé.
Afin de surmonter ces difficultés et afin d’effectuer la mise en service rationnelle de moyens modernes, la méthode de mesure suivante a ét6 choisie : des vibrateurs ultrasoniques utilisés c o m m e postes émetteurs et récepteurs sont suspendus immobiles dans les postes d’observation des niveaux d’eau souterraine tout en étant plongés dans l’eau. La durée du parcours d‘une impulsion ultrasonique allant depuis le vibrateur ultrasonique la surface de l’eau et retour est mesurée 2 l’aide d’un appareil d’une précision extrême pour mesurer les petits intervalles de temps. Cette durée du parcours donne, après multiplication par la vitesse du son, la distance entre le vibrateur ultrasonique et la surface de l’eau. Le pouvoir résolvant s’élèveà 1 m m . Ces distances entre vibrateur et surface de l’eau sont interrogées 2 l’aide d’une programmation appropriée et sont poinçonnées SUI une bande perforée (sous forme de la durée du parcours) conjointement
H. J. Dürbaum and R. Kohlmeier
avec la date et l'heure précises de la mesure ainsi qu'avec le numéro du poste d'observation. Les données sont reportées depuis la bande perforée sur une plaque de mise en mémoire magnétique ; puis elles sont disponibles 2 la lecture directe de l'ordinateur. Les courbes d'abaissement de l'eau souterraine sont évahées du point de vue graphique et numérique 2 l'aide de programmations diverses. Les possibilités déduites de cette évaluation graphique et numérique sont montrées l'aide de quelques exemples.
MEDIDOR,AUTOMÁTICO DE NIVELES CON LA AYUDA DE APARATOS AC~STICOS Y su
APLICACION A LOS ENSAYOS D E BOMBEO
Resumen. Las medidas necesarias en las pruebas de bombeo, se obtienen normalmente con dificultad y coste elevado.
En la mayoría de los casos, el registro manual da lugar a un número insuficiente de datos de escasa precisión y origina elevados costos de mano de obra. Los dispositivos automáticos convencionales han mostrado frecuentemente su propensión a la interferencia, y muchas veces son incapaces de seguir cambios de nivel que se produzcan con rapidez, debido al dispositivo de seguimiento mecánico de flotadores e indicadores. E n consecuencia, los costos de equipo se elevan casi linealmente con el número de puntos de medida a cubrir. El gran número de medidas que resultan de una prueba de bombeo se presenta en forma de listas o resúmenes, exigiendo su evaluación detallada tiempos extremadamente largos.
Para superar estas dificultades y permitir la utilización de medios modernos, se eligió el siguiente método de medición: se introducen en el agua vibradores ultrasónicos, que actúan como transmisores y receptores sin movimiento en el agua, en los puntos básicos de observación.
El tiempo de tránsito de un esfuerzo ultrasónico que se desplaza desde el vibrador a la superficie del agua y vuelve, se mide con ayuda de un microcronómetro extremadamente preciso. AI multiplicar este tiempo de tránsito por la velocidad del sonido, se obtiene la distancia entre el vibrador y la superficie del agua. El poder de apreciación viene a ser de 1 m m . Las distancias entre el vibrador y la superficie del agua se mide a intervalos, y se registran (como tiempo de tránsito) con la fecha y hora de su medición, y el número de puntos de medida, sobre cinta perforada. A partir de la cinta perforada, los datos se pasan a un disco magnético que puede introducirse directamente en un ordenador Mediante diversos programas, se pueden evaluar gráfica y numéri- camente las curvas de descenso de superficie. En varios ejemplos se indican las posibilidades de utilización del método.
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Digital recording of water levels with the aid of acoustics
1 INTRODUCTION
It is frequently found that detailed measurements during hydrological pumping tests can be carried out only at very great expense. Manual recording may yield data which are too sporadic and inaccurate. On the other hand, much of the usual equipment for automatic recording which is on the market is relatively susceptible to mechanical disturbances and is not sufficiently adaptable in the event of abrupt change of water level. The cost of such equipment increases approximately linearly with the number of recording stations. Finally, a detailed interpretation of the great number of measured values which are accumulated in lists or on analogue recording charts necessitates a great expenditure of time.
To avoid these difficulties in the recording and evaluation of pumping tests, a method has been developed which makes use of modern electronic equipment and techniques. The travel time of ultrasonic pulses can be measured with an accuracy of 0.1 ps. This corresponds to an accuracy of about 1 mm in determining the distance of a vibrator from the water level in an observation well. The data may be transferred to a magnetic disc store where they are directly accessible to the digital computer. It is then possible to digest and interpret many more data than are usually available in order to characterize the drawdown around a pumping well as a function of time and position more accurately.
2 THE MEASURING DEVICE 2.1 Fundamentals
The method employed is based on the measurement of transit-time to and from the water surface of an ultrasonic pulse emitted by a vibrator suspended at a fixed depth below the water level.
The ultrasonic vibrator is used simultaneously as a pulse generator and as a pulse receiver. Measurement is effected by means of an echo-sounding device for ultrasonic pulses. A sonic velocity in the water of approximately 1,450 m.s-' gives a transit- time of approximately I .4 ps per mm of distance. In order to achieve a resolution of 1 mm, an accuracy of 0.1 ps for the transit-time is required.
2.2
To reduce costs, it was decided not to use a special design for the vibrators. Instead, ultrasonic vibrators which are already in series production were relied upon. Several factors should be considered in choosing the frequency of the ultrasonic vibrator. It must be high enough for the rise-time of pulses to be less than 1.4 ps, equivalent to a transit-time of 1 mm at the desired resolution. The higher the frequency, the smaller
Selection of the ultrasonic vibrators
H. J. Diirbaum and R. KohImeier
are the dimensions of the ultrasonic vibrators that can be supplied in series for equal ultrasonic power, and the smaller is the radiation angle of the vibrator. O n the other hand, as the absorption of ultrasonic energy in water increases as the second power of the frequency, the lowest possible frequency ought to be chosen. Hence, after testing various ultrasonic vibrators, a frequency of 1 MHz was chosen, for which the rise-time of pulses is about 0.25 p. At this frequency only piezoelectric transformers can be considered.
2.3
A commercial ultrasonic vibrator with a resonance frequency of 1 M& was chosen.
The diameter of the ultrasonic vibrator is 22 mm, so that a probe of 45 mm diameter is possible for use in 2 inch (51 mm) tubes. The probes are approximately 450 mm long to prevent tilting in the tube and are freely suspended in the observation wells at some distance below the water level. The weight of the probe chosen is such that the cable is kept taut.
2.4 Measuring apparatus
A block diagram is shown in Fig. 1. The device is subdivided into analogue and digital parts. The analogue part is made up of the pulse generator, the amplifier for the reflected pulses and a scanner. The digital part contains a digital clock, the program- ming unit and the output unit for data, with a tape perforator as a recording device.
The electronic counter for short-time measurement combines the two parts of the device. It transforms the analogue transit-time into a digital value.
Construction of the measuring probe
2.4.1 The pulse generator
The pulse generator is a tube generator which, after being triggered, generates a 1 MHz highly damped sine wave; the damping is of approximately 20 db/period. The amplitude is approximately 500 V with the ultrasonic vibrator connected to a cable 15 m long.
2.4.2
The amplifier for the reflected pulses must have a high mput sensitivity and, at the same time, an extreme input overdrive capacity, as it first receives the full voltage of the radiated pulse at the input and, only a few microseconds later, the reflected pulses of but a few microvolts or millivolts. It is constructed as a fully transistorized amplifier. The amplifier has a limiting stage in the input followed by impedance- transforming stages which increase the input resistance. The next stage is selected by means of a resonance circuit tuned to 1 MHz. The output of the amplifier is of extremely low resistance so as to choke-off damped oscillations; this is effected by means of a wide-band transformer, so that the output is free of d.c. voltage. After that the signal is rectified and passes through a filter network whose time constants have been chosen so that the output signal represents in practice the envelope curve of the amplified and rectified echo pulses. This output signal cannot be utilized immediately as an input to stop the counter, since it also includes energy derived from the directly radiated pulse as well as statistically distributed external and internal noise. 'Therefore a threshold circuit has been incorporated into the subse- quent output amplifier to transmit only signals that exceed a preset amplitude. The direct signal is cut off by a grating circuit which opens an amplifying path only after a certain adjustable time interval after departure of the transmitted pulse and blocks
The amplifer for the reflected pulses
