ISO-4373-1995.pdf

4B5Lî03 0b2093b T38 D I N T E R NAT I O NA L STANDARD IS0 4373 Second edition 1995-1 0-1 5 Measurement of liquid flow in open channels - Water-level measuring devices Mesure de débit des liquides dans les chenaux - Appareils de mesure du niveau deau Reference number IS0 4373: 1995(E) COPYRIGHT International Organization for Standardization Licensed by Information Handling Services COPYRIGHT International Organization for Standardization Licensed by Information Handling Services 4851903 Ob20937 974 W IS0 4373:1995lEl Contents Page Scope 1 Normative references ._ . , . 1 Definitions . 1 Accuracy of stage measurements 1 Gauge datum . 1 Environment 2 Direct water-level indicating devices . . 2 Indirect water-level indication devices 8 Recording devices . 15 10 Errors, 18 Annex A Stilling wells and intakes . 21 O IS0 1995 All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from the publisher. International Organization for Standardization Case Postale 56 CH-1 21 1 Genève 20 Switzerland Printed in Switzerland II COPYRIGHT International Organization for Standardization Licensed by Information Handling Services COPYRIGHT International Organization for Standardization Licensed by Information Handling Services 4851903 Ob20938 800 8 IS0 IS0 4373:1995(El Foreword IS0 (the International Organization for Standardization) is a worldwide federation of national standards bodies (IS0 member bodies). The work of preparing International Standards is normally carried out through IS0 technical committees. Each member body interested in a subject for which a technical committee has been established has the right to be represented on that committee. International organizations, governmental and non-governmental, in liaison with ISO, also take part in the work. IS0 collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization. Draft International Standards adopted by the technical committees are circulated to the member bodies for voting. Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote. International Standard IS0 4373 was prepared by Technical Committee ISO/TC 1 13, Hydrometric determinations, Subcommittee SC 5, Instru- ments, equipment and data management. This second edition cancels and replaces the first edition (IS0 4373:1979), which has been technically revised. Annex A forms an integral part of this International Standard. . 111 COPYRIGHT International Organization for Standardization Licensed by Information Handling Services COPYRIGHT International Organization for Standardization Licensed by Information Handling Services IS0 4373:1995(E) 4853903 Ob20939 7Y7 W 0 IS0 Introduction The collection of water-level records with respect to time generally forms the basis for obtaining a systematic record of stream flow at a gauging station. This water-level record, together with periodic discharge measurements, can be converted by one or more methods (see IS0 1 100) into a continuous record of discharge. The accuracy of the record of dis- charge is governed in large part by the accuracy of the record of water level. It is essential that this be detected and recorded efficiently and with an accuracy sufficient for the purposes for which the stream flow data are required. Water-level records, besides being used to produce stream flow data, also have an intrinsic value in monitoring the level of any body of water. It must also be recognized that, however accurate the inherent performance of a water-level recording installation, the application of routine operational and maintenance procedures is essential to achieving design performance. Although the design and operation of water-level measuring devices is described in terms of the devices in current use, this International Stan- dard is not intended to inhibit further development. Rather it is intended to encourage the introduction of improved instrumentation exhibiting bet- ter performance. iv COPYRIGHT International Organization for Standardization Licensed by Information Handling Services COPYRIGHT International Organization for Standardization Licensed by Information Handling Services Y851903 Ob20940 469 M INTERNATIONAL STANDARD Q IS0 IS0 4373:1995(E) Measurement of liquid flow in open channels - Water-level measuring devices 1 Scope This International Standard specifies the functional requirements and operational procedures for stage detecting, encoding and recording devices for measuring water levels in open channels. Because of the widespread use of stilling wells in the measure- ment of water levels, information on stilling wells is given in annex A to this International Standard. 2 Normative references The following standards contain provisions which, through reference in this text, constitute provisions of this International Standard. At the time of publi- cation, the editions indicated were valid. All standards are subject to revision, and parties to agreements based on this International Standard are encouraged to investigate the possibility of applying the most re- cent editions of the standards indicated below. Members of IEC and IS0 maintain registers of cur- rent ly va l id l nternationa l Standards. IS0 772:-), Measurement of liquid flow in open channels - Vocabulary and symbols. IS0 1 100-1 :I 981, Liquid flow measurement in open channels - Pari 1: Establishment and operation of a gauging station. is0 1 100-2:1982, Liquid flow measurement in open channels - Part 2: Determination of the stage- discharge relation. 3 Definitions For the purposes of this International Standard, the definitions given in IS0 772 and the following defi- nitions apply. 3.1 encoding: Method by which a data signal is changed into a suitable set of bits for data recording. 3.2 parity check: Addition of an extra bit to a data signal so that the total number of bits in a sample are either always even or always odd. 4 Accuracy of stage measurements For the measurement of stage with respect to a gauge datum, an uncertainty of f 10 mm may be satisfactory in some installations: in others, uncer- tainty of b) durable and easy to maintain; c) simple to install and use. The material of which a gauge is constructed shall be durable, particularly in alternating wet and dry con- ditions, and also in respect of the resistance to wear or fading of the markings. The material should have a low coefficient of expansion with respect to tem- perature or wetting effects, commensurate with ac- curacy requirements. 7 . 1 . 3 Graduation 7 . 1 . 3 . 1 The graduations shall be clearly and perma- nently marked directly on a smooth surface or on a gauge board. The numerals shall be legible and placed so that there is no possibility of ambiguity. A typical example is shown in figure 1. 7.1.3.2 The graduations of an inclined gauge may be directly marked on a smooth surface or on a gauge board, as described in 7.1.3.1, or marked on manu- factured gauge plates designed to be set to a speci- fied slope. An inclined gauge should be calibrated in situ by precise levelling from the station benchmark. 7.1.3.3 Gauge plates shall be manufactured in suit- able lengths, often 1 m, with the width of the scale not less than 50 mm. 7.1.3.4 The marking on the gauge should be made to read in multiples of millimetres. The smallest graduation shall depend on the accuracy required, but may correspond to 10 mm. 7.1.3.5 The markings of the subdivisions shall be accurate to f 0,5 mm, and the cumulative error shall not exceed 0,l % or 0,5 mm, whichever is smaller. 7.1.4 Installation and use 7.1.4.1 General The gauge should preferably be placed near the side of the stream, so that a direct reading of water level may be made. If this is impractical because of ex- cessive turbulence, wind effect or inaccessibility, the measurement may be made in a suitable permanent stilling bay or stilling well in which the wave actions are damped and the level of the water surface follows the fluctuations of the water level in the stream. To ensure this, intakes to stilling wells should be properly designed and located (see annex A). The gauge should be located as closely as possible to the measuring section without affecting the flow conditions at this point. If possible, the gauge should not be placed where the water is disturbed by turbu- 2 COPYRIGHT International Organization for Standardization Licensed by Information Handling Services COPYRIGHT International Organization for Standardization Licensed by Information Handling Services - 4853703 Ob20742 231 W IS0 4373:1995(E) 150 L- Detachable plate for metre numeral Figure 1 - Typical details of vertical staff gauge lence, or where there is danger of damage by drift. Bridge abutments or piers are generally unsuitable lo- cations. Wherever the gauge is situated, it shall be readily and conveniently accessible so that the ob- server may make readings as nearly as possible at eye level. The gauge board or plate shall be securely fixed to the backing but provision must be made for re- moving the gauge board or plate for maintenance or adjustment. The edges of the gauge board should be protected. 7.1.4.2 Vertical gauges A suitable backing for a vertical gauge is provided by the surface of a wall having a vertical or nearly vertical face parallel to the direction of flow. The gauge board or backing plate shall be attached to the surface so as to present a vertical face to receive the gradu- ations. The gauge board and backing plate shall be securely fastened to the wall. Gauges may be fixed to piles, either driven firmly into the river bed or banks, or set in concrete so as to be free from sink- ing, tilting or washing away. In either case the anchorage shall extend below the ground surface to a level free of disturbance by frost. In order to avoid velocity effects which may hinder accurate reading, a pile may be shaped to present a streamlined profile upstream and downstream or the gauge may be situ- ated in a bay where it will not be exposed to the force of the current. Where the range of water levels ex- ceeds the range of a single vertical gauge, additional sections may be installed on the line of the cross- section normal to the direction of flow. 7.1.4.3 Inclined gauges An inclined gauge shall be installed in such a manner to follow the contour of the river bank. The profile of the bank may be such that a gauge of a single slope may be installed; frequently however, it may be necessary to construct the gauge in several sections, each with a different slope. The general installation requirements given in 7.1.4.1 apply. 3 COPYRIGHT International Organization for Standardization Licensed by Information Handling Services COPYRIGHT International Organization for Standardization Licensed by Information Handling Services = 4851903 Ob20943 178 IS0 4373:1995(E) 8 IS0 7.2 Needle gauges 7.2.3 Material 7.2.1 General A needle water-level gauge consists of a device with an end point and some means of determining the point's exact vertical position relative to datum. The two types of needle gauges are a) the point gauge, whose tip approaches the free surface from above, and b) the hook gauge, which is hook-shaped, and whose tip is immersed and approaches the free surface from below (see figure 2). The vertical position may be determined by a gradu- ated scale, a tape with some vernier arrangements, or an arrangement to detect linear movement elec- tronically with a digital indicator similar to a digital micrometer. The scale is movable and graduated to read downward from top to bottom in metres. Application of needle gauges consists of positioning the needle of the gauge near the water surface and detecting the moment the tip touches the free sur- face, as if trying to pierce its “skin“. Setting a point exactly at the water surface may be facilitated by electrical, visual light-emitting diode (LED) display and/or acoustic (electronic buzzer) indicators. The advantage of water-level needle gauges is their high measuring accuracy, whereas their disavantage is their small measuring range, usually about 1 m. However, this disadvantage can be overcome by in- stalling a series of datum plates at different levels. 7.2.2 Functional requirements A hook or point gauge and auxiliary parts shall be made throughout with durable corrosion-resistant materials. 7.2.4 Graduation The graduation of a hook or point gauge shall be in millimetres and shall be clearly and accurately marked. A vernier or micrometer head may be provided which allows reading to 0,l mm. However, such a reading accuracy is normally only required for laboratory measurements. 7.2.5 Installation and use 7.2.5.1 A hook or point gauge may be mounted over an open water surface at the edge of a stream if conditions permit. If this is not practical because of turbulence, wind effect or inaccessibility, a suitable permanent stilling bay or stilling well should be in- stalled. 7.2.5.2 The location of the hook or point gauge should be as close as possible to the stage-measuring section and should be conveniently accessible to the observer. 7.2.5.3 The gauge shall not be installed in a location where the water surface is disturbed by turbulence, wind effect or afflux. The vicinity of bridge abutments or piers is generally unsuitable. 7.2.5.4 Where more than one datum plate or bracket is provided at different levels, it is preferable that all should lie on the line of a single cross-section normal to the direction of flow in the stream. If this is not practicable and it is necessary to stagger the points, all should lie within a distance of 1 m on either side 7.2.2.1 A hook- or point-gauge installation shall per- mit measurement of stage to be made at all levels, from below the lowest to above the highest levels anticipated. of the cross-section line. 7.2.2.2 There shall be good illumination of the place where the tip meets the free liquid surface; if this is not the case, gauges with electronic meters for indi- cation shall be used. 7.2.2.3 The hook or point shall be made of metal sufficiently strong to resist deformation in transport and under field conditions of use. The tip shall be tapered to a point having an included angle of ap- proximately 60“ and the point shall be rounded to a radius of approximately 0,25 mm (see figure 3). 7.2.5.5 Datum plates and brackets shall be mounted on a secure foundation which extends below the frost line. 7.2.5.6 The elevation of the datum plates, with ref- erence to which the level of the free water surface is determined, shall be established with great care. This elevation shall be checked from the station benchmark at least annually. The tolerance on the transfer of level from the station benchmark to each datum plate shall not exceed 1,0