1、BSI Standards PublicationWB11885_BSI_StandardCovs_2013_AW.indd 1 15/05/2013 15:06Hydrometry Open channel flow measurement using thin-plate weirsBS ISO 1438:2017 ISO 2017Hydrometry Open channel flow measurement using thin-plate weirsHydromtrie Mesure de dbit dans les canaux dcouverts au moyen de dver
2、soirs paroi minceINTERNATIONAL STANDARDISO1438Third edition2017-04Reference numberISO 1438:2017(E)National forewordThis British Standard is the UK implementation of ISO 1438:2017. It supersedes BS ISO 1438:2008, which is withdrawn.The UK participation in its preparation was entrusted to Technical Co
3、mmittee CPI/113/2, Flow measurement structures.A list of organizations represented on this committee can be obtained on request to its secretary.This publication does not purport to include all the necessary provisions of a contract. Users are responsible for its correct application. The British Sta
4、ndards Institution 2017 Published by BSI Standards Limited 2017ISBN 978 0 580 86786 6ICS 17.120.20Compliance with a British Standard cannot confer immunity from legal obligations. This British Standard was published under the authority of the Standards Policy and Strategy Committee on 30 June 2017.A
5、mendments/corrigenda issued since publicationDate Text affectedBRITISH STANDARDBS ISO 1438:2017 ISO 2017Hydrometry Open channel flow measurement using thin-plate weirsHydromtrie Mesure de dbit dans les canaux dcouverts au moyen de dversoirs paroi minceINTERNATIONAL STANDARDISO1438Third edition2017-0
6、4Reference numberISO 1438:2017(E)BS ISO 1438:2017ISO 1438:2017(E)ii ISO 2017 All rights reservedCOPYRIGHT PROTECTED DOCUMENT ISO 2017, Published in SwitzerlandAll rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized otherwise in any form or by any me
7、ans, electronic or mechanical, including photocopying, or posting on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below or ISOs member body in the country of the requester.ISO copyright officeCh. de Blandonnet 8 CP 401CH-12
8、14 Vernier, Geneva, SwitzerlandTel. +41 22 749 01 11Fax +41 22 749 09 47copyrightiso.orgwww.iso.orgBS ISO 1438:2017ISO 1438:2017(E)Foreword v1 Scope . 12 Normative references 13 Terms and definitions . 14 Symbols and abbreviated terms . 15 Principle 26 Installation . 26.1 General . 26.2 Selection of
9、 site . 26.3 Installation conditions 26.3.1 General 26.3.2 Weir . 36.3.3 Approach channel . 36.3.4 Downstream channel . 47 Measurement of head 47.1 Head-measuring devices 47.2 Stilling or float well . 57.3 Head-measurement section . 57.3.1 Upstream head-measurement . 57.3.2 Downstream head measureme
10、nt 57.4 Head-gauge datum (gauge zero) . 58 Maintenance 69 Rectangular thin-plate weir 69.1 Types 69.2 Specifications for the standard weir 89.3 Specifications for installation . 89.4 Determination of gauge zero 89.5 Discharge formulae General 119.6 Formulae for the basic weir form (all values of b/B
11、) 119.6.1 Kindsvater-Carter formula . 119.6.2 Evaluation of Cd, kb and kh 119.6.3 Formulae for Cd . 139.6.4 Practical limitations on h/p, h, b and p . 149.7 Formulae for full-width weirs (b/B = 1,0) 149.7.1 Modular flow discharge formula .149.7.2 Non-modular flow discharge formula 1510 Triangular-no
12、tch thin-plate weir .1610.1 Specifications for the standard weir . 1610.2 Specifications for the installation 1910.3 Specifications for head measurement 1910.3.1 General. 1910.3.2 Determination of notch angle 1910.3.3 Determination of gauge zero 1910.4 Discharge formulae General 2010.5 Formula for a
13、ll notch angles between /9 and 5 /9 radians (20 and 100) .2010.5.1 Kindsvater-Shen formula . 2010.5.2 Evaluation of Cd and kh 2010.5.3 Practical limitations on , h/p, p/B, h and p . 2210.6 Formula for specific notch angles (fully-contracted weir) .2210.7 Accuracy of discharge coefficients Triangular
14、-notch weirs .23 ISO 2017 All rights reserved iiiContents PageBS ISO 1438:2017ISO 1438:2017(E)11 Uncertainties of flow measurement 2311.1 General 2311.2 Combining measurement uncertainties . 2411.3 Uncertainty of discharge coefficient, u*(Cd), for thin-plate weirs 2511.4 Uncertainty budget. 2612 Exa
15、mple .2612.1 General 2612.2 Characteristics Gauging structure 2612.3 Characteristics Gauged head instrumentation 2712.4 Discharge coefficient . 2712.5 Discharge estimate . 2712.6 Uncertainty statement . 27Annex A (informative) Flow measurement with small weir tanks .30Annex B (normative) Guide to th
16、e design and installation of a flow straightener 32Annex C (informative) Introduction to measurement uncertainty34Annex D (informative) Sample measurement performance for use in hydrometric worked examples .42Annex E (informative) Specimen tables .45Bibliography .60iv ISO 2017 All rights reservedBS
17、ISO 1438:2017ISO 1438:2017(E)ForewordISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work of preparing International Standards is normally carried out through ISO technical committees. Each member body intereste
18、d 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. ISO collaborates closely with the International Electrotechnical Com
19、mission (IEC) on all matters of electrotechnical standardization.The procedures used to develop this document and those intended for its further maintenance are described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the different types of ISO documents
20、should be noted. This document was drafted in accordance with the editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. ISO shall not be held responsible
21、for identifying any or all such patent rights. Details of any patent rights identified during the development of the document will be in the Introduction and/or on the ISO list of patent declarations received (see www .iso .org/ patents).Any trade name used in this document is information given for
22、the convenience of users and does not constitute an endorsement.For an explanation on the voluntary nature of standards, the meaning of ISO specific terms and expressions related to conformity assessment, as well as information about ISOs adherence to the World Trade Organization (WTO) principles in
23、 the Technical Barriers to Trade (TBT) see the following URL: www .iso .org/ iso/ foreword .html.This document was prepared by Technical Committee ISO/TC 113, Hydrometry, Subcommittee SC 2, Flow measurement structures.This third edition cancels and replaces the second edition (ISO 1438:2008), which
24、has been technically revised. It also incorporates the Technical Corrigendum ISO 1438:2008/Cor 1:2008.The major changes from ISO 1438:2008 are as follows:a) the modular flow discharge formula for weirs with weir plate height of 1 m p 2,5 m has been supplemented in 9.7.1;b) the Cdformula for rectangu
25、lar weir with b/B = 1,0, Formula (5), has been corrected to the same formula as the full-width weir, Formula (15);c) subclause numbers of 9.6 have been re-numbered. ISO 2017 All rights reserved vBS ISO 1438:2017BS ISO 1438:2017Hydrometry Open channel flow measurement using thin-plate weirs1 ScopeThi
26、s document defines the requirements for the use of rectangular and triangular (V-notch) thin-plate weirs for the measurement of flow of clear water in open channels under free flow conditions. It includes the requirements for the use of full-width rectangular thin-plate weirs in submerged (drowned)
27、flow conditions.2 Normative referencesThe following documents are referred to in the text in such a way that some or all of their content constitutes requirements of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced docu
28、ment (including any amendments) applies.ISO 772, Hydrometry Vocabulary and symbols3 Terms and definitionsFor the purposes of this document, the terms and definitions given in ISO 772 apply.ISO and IEC maintain terminological databases for use in standardization at the following addresses: IEC Electr
29、opedia: available at h t t p :/ www .electropedia .org/ ISO Online browsing platform: available at h t t p :/ www .iso .org/ obp4 Symbols and abbreviated termsSymbol Unit DescriptionA m2Area of approach channelB m Width of approach channelb m Measured width of the notchbmaxm Width of notch at maximu
30、m head (V-notch)C Discharge coefficient (gauged head)CdCoefficient of dischargef Drowned flow reduction factorCvCoefficient of velocityebm Random uncertainty in the width measurementg m/s2Acceleration due to gravityH m Total head above crest levelh m Upstream gauged head above crest level (upstream
31、head is inferred if no subscript is used)J Numerical constantl m Distance of the head measurement section upstream of the weirn Number of measurements in a setp m Height of the crest relative to the floorQ m3/s Volumetric rate of flowINTERNATIONAL STANDARD ISO 1438:2017(E) ISO 2017 All rights reserv
32、ed 1BS ISO 1438:2017ISO 1438:2017(E)Symbol Unit DescriptionS Submergence ratio, h2/h1S1Modular limitVm/s Mean velocityU % Expanded percentage uncertaintyu*(b) % Percentage uncertainty in bu*(C) % Percentage uncertainty in Cu*(E) % Percentage uncertainty in datum measurementu*(h1) % Percentage uncert
33、ainty in h1u*(Q) % Percentage uncertainty in Q Notch angleSubscripts1 upstream2 downstreame effectiver rectangulart triangular5 PrincipleThe discharge over thin-plate weirs is a function of the upstream head on the weir (for free-flow), upstream and downstream head (for drowned flow), the size and s
34、hape of the discharge area, and an experimentally determined coefficient which takes into account the head, the geometrical properties of the weir and approach channel, and the dynamic properties of the water.6 Installation6.1 GeneralGeneral requirements of weir installations are described in the fo
35、llowing clauses. Special requirements of different types of weirs are described in clauses which deal with specific weirs (see Clause 9 and Clause 10).6.2 Selection of siteThe type of weir to be used for discharge measurement is determined in part by the nature of the proposed measuring site. Under
36、some conditions of design and use, weirs shall be located in rectangular flumes or in weir boxes which simulate flow conditions in rectangular flumes. Under other conditions, weirs may be located in natural channels, as well as flumes or weir boxes, with no significant difference in measurement accu
37、racy. Specific site-related requirements of the installation are described in 6.3.6.3 Installation conditions6.3.1 GeneralWeir discharge is critically influenced by the physical characteristics of the weir and the weir channel. Thin-plate weirs are especially dependent on installation features which
38、 control the velocity 2 ISO 2017 All rights reservedBS ISO 1438:2017ISO 1438:2017(E)distribution in the approach channel and on the construction and maintenance of the weir crest in meticulous conformance with standard specifications.6.3.2 WeirThin-plate weirs shall be vertical and perpendicular to
39、the walls of the channel. The intersection of the weir plate with the walls and floor of the channel shall be watertight and firm, while the weir shall be capable of withstanding the maximum flow without distortion or damage.Stated practical limits associated with different discharge formulae such a
40、s minimum width, minimum weir height, minimum head, and maximum values of h/p and b/B (where h is the measured head, p is the height of crest relative to floor, b is the measured width of the notch and B is the width of the approach channel), are factors which influence both the selection of weir ty
41、pe and the installation.6.3.3 Approach channelFor the purposes of this document, the approach channel is the portion of the weir channel which extends upstream from the weir a distance not less than five times the width of the nappe at maximum head. If the weir is located in a weir tank, ideally, th
42、e length of the tank should equal up to 10 times the width of the nappe at maximum head. Information on the use of small weir tanks is given in Annex A.The flow in the approach channel shall be uniform and steady, with the velocity distribution approximating that in a channel of sufficient length to
43、 develop satisfactory flow in smooth, straight channels. Figure 1 shows measured velocity distributions perpendicular to the direction of flow in rectangular channels, upstream from the influence of a weir. Baffles and flow straighteners can be used to simulate satisfactory velocity distribution, bu
44、t their location with respect to the weir shall be not less than the minimum length prescribed for the approach channel.The influence of approach-channel velocity distribution on weir flow increases as h/p and b/B increase in magnitude. If a weir installation unavoidably results in a velocity distri
45、bution that is appreciably non-uniform, the possibility of error in calculated discharge should be checked by means of an alternative discharge-measuring method for a representative range of discharges.If the approach conditions are judged to be unsatisfactory, then flow straighteners shall be intro
46、duced in accordance with Annex B.If the maximum head to be measured is restricted to (2/3)p for all types of weirs, flow straighteners can be used to reduce the effective length of the approach channel to B + 3hmaxfor triangular and rectangular weirs and to B + 5hmaxfor full-width weirs.NOTE This re
47、striction on the maximum head to be measured is necessary due to distortion of the velocity near the water surface in the approach channel that results from flow coming through the openings in the baffle of the flow straightener. ISO 2017 All rights reserved 3BS ISO 1438:2017ISO 1438:2017(E)a)b)c)NO
48、TE The contours refer to values of local flow velocity relative to the mean cross-sectional velocity.Figure 1 Examples of normal velocity distribution in rectangular channels6.3.4 Downstream channelFor most applications, the level of the water in the downstream channel shall be a sufficient vertical
49、 distance below the crest to ensure free, fully ventilated discharges. Free (non-submerged) discharge occurs when the discharge is independent of the downstream water level. Fully ventilated discharge is ensured when the air pressure on the lower surface of the nappe is fully ventilated. Drowned flow operation is permitted for full-width weirs under certain conditions (see 9.7.2). Under these circumstances, downstream water levels may rise above crest level.7 Measurement of head7.1 Head-measuring devicesI
