BS ISO 4377-2012 Hydrometric determinations Flow measurement in open channels using structures Flat-V weirs《比重测定 构造物的明渠液体流量测量 V形平面溢流堰》.pdf

1、raising standards worldwideNO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAWBSI Standards PublicationBS ISO 4377:2012Hydrometric determinations Flow measurement in openchannels using structures Flat-V weirsBS ISO 4377:2012 BRITISH STANDARDNational forewordThis British Standard i

2、s the UK implementation of ISO 4377:2012. Itsupersedes BS ISO 4377:2002 which is withdrawn.The UK participation in its preparation was entrusted to TechnicalCommittee CPI/113/2, Notches weirs and flumes.A list of organizations represented on this committee can beobtained on request to its secretary.

3、This publication does not purport to include all the necessaryprovisions of a contract. Users are responsible for its correctapplication. The British Standards Institution 2012. Published by BSI StandardsLimited 2012ISBN 978 0 580 70396 6ICS 17.120.20Compliance with a British Standard cannot confer

4、immunity fromlegal obligations.This British Standard was published under the authority of theStandards Policy and Strategy Committee on 31 August 2012.Amendments issued since publicationDate Text affectedBS ISO 4377:2012Reference numberISO 4377:2012(E)ISO 2012INTERNATIONAL STANDARD ISO4377Fourth edi

5、tion2012-08-01Hydrometric determinations Flow measurement in open channels using structures Flat-V weirs Dterminations hydromtriques Mesure de dbit dans les canaux dcouverts au moyen de structures Dversoirs en V ouvert BS ISO 4377:2012ISO 4377:2012(E) COPYRIGHT PROTECTED DOCUMENT ISO 2012 All rights

6、 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 either ISO at the address below or ISOs member body in the country of the r

7、equester. ISO copyright office Case postale 56 CH-1211 Geneva 20 Tel. + 41 22 749 01 11 Fax + 41 22 749 09 47 E-mail copyrightiso.org Web www.iso.org Published in Switzerland ii ISO 2012 All rights reservedBS ISO 4377:2012ISO 4377:2012(E) ISO 2012 All rights reserved iiiContents Page Foreword . v 1

8、Scope 1 2 Normative references 1 3 Terms and definitions . 2 4 Symbols 3 5 Characteristics of flat-V weirs 4 6 Installation 4 6.1 Selection of site . 4 6.2 Installation conditions 7 6.3 Weir structure 8 6.4 Downstream conditions 8 7 Maintenance . 8 8 Measurement of head(s) . 9 8.1 General . 9 8.2 St

9、illing (gauge) wells . 9 8.3 Zero setting 11 8.4 Location of head measurement sections 13 9 Discharge relationships 14 9.1 Equations of discharge . 14 9.2 Effective heads 15 9.3 Shape factors . 16 9.4 Coefficient of velocity . 16 9.5 Conditions for modular/drowned flow 18 9.6 Drowned flow reduction

10、factor 21 9.7 Limits of application 28 10 Computation of discharge 29 10.1 General . 29 10.2 Successive approximation method . 29 10.3 Coefficient of velocity method . 31 10.4 Accuracy 32 11 Uncertainties in flow determination 32 11.1 General . 32 11.2 Combining uncertainties 33 11.3 Uncertainty in

11、the discharge coefficient u*(CDe)68for the flat-V weir 34 11.4 Uncertainty in the drowned flow reduction factor u*(Cdr) . 34 11.5 Uncertainty in the effective head . 35 11.6 Uncertainty budget 35 11.7 Variation of uncertainty with flow and uncertainty in mean daily flow and the daily flow volume 36

12、12 Examples 37 12.1 Example 1 Computation of modular flow at low discharge 37 12.2 Example 1 Uncertainty in computed discharge . 39 12.3 Example 2 Computation of drowned flow at high discharge . 41 12.4 Example 2 Uncertainty in computed discharge . 43 Annex A (normative) Velocity distribution . 46 B

13、S ISO 4377:2012ISO 4377:2012(E) iv ISO 2012 All rights reservedAnnex B (informative) Introduction to measurement uncertainty 47 Annex C (informative) Performance guide for hydrometric equipment for use in technical standards 56 Bibliography 59 BS ISO 4377:2012ISO 4377:2012(E) ISO 2012 All rights res

14、erved vForeword ISO (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 interested in a subject for wh

15、ich 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 Commission (IEC) on all

16、matters of electrotechnical standardization. International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2. The main task of technical committees is to prepare International Standards. Draft International Standards adopted by the technical committees are ci

17、rculated to the member bodies for voting. Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote. 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 respo

18、nsible for identifying any or all such patent rights. ISO 4377 was prepared by Technical Committee ISO/TC 113, Hydrometry, Subcommittee SC 2, Flow measurement structures. This fourth edition cancels and replaces the third edition (ISO 4377:2002), which has been technically revised to update the trea

19、tment of uncertainty to be consistent with the other standards relating to flow measurement structures. BS ISO 4377:2012BS ISO 4377:2012INTERNATIONAL STANDARD ISO 4377:2012(E) ISO 2012 All rights reserved 1Hydrometric determinations Flow measurement in open channels using structures Flat-V weirs 1 S

20、cope This International Standard describes the methods of measurement of flow in rivers and artificial channels under steady or slowly varying conditions using flat-V weirs (see Figure 1). Annex A gives guidance on acceptable velocity distribution. 2 Normative references The following documents, in

21、whole or in part, are normatively referenced in this document and are indispensable for its application. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies ISO 772, Hydrometry Vocabulary and s

22、ymbols ISO/TS 25377, Hydrometric uncertainty guidance (HUG) BS ISO 4377:2012ISO 4377:2012(E) 2 ISO 2012 All rights reserved3 Terms and definitions For the purposes of this document, the terms and definitions given in ISO 772 apply. Dimensions in millimetres hbm1:5R 2H1max. H1max.- H1max.- 2H1max.10

23、H but not 3H1max.25 H but not 3H1max.p2p10,4 b0,1 b11:212345678100Key 1 head gauging section b crest width 2 upstream tapping H difference between the invert (apex) of the V and the top of the V 3 stilling wells H1maxmaximum upstream total head above crest elevation 4 crest tapping h gauged head abo

24、ve lowest crest elevation 5 flow p difference between mean bed level and lowest crest elevation6 downstream head measuring point 7 minimum 100 mm above stilling basin level 8 limits of permissible upstream and downstream truncations Figure 1 Triangular profile flat-V weir BS ISO 4377:2012ISO 4377:20

25、12(E) ISO 2012 All rights reserved 34 Symbols The following is a list of symbols used, with the corresponding units of measurement. SymbolaMeaning Units A Area of cross-section of flow m2 B Width of approach channel m b Crest width m CDCoefficient of discharge Non-dimensionalCDe Effective coefficien

26、t of discharge Non-dimensionalCdrDrowned flow reduction factor Non-dimensionalCCoefficient of approach velocity Non-dimensionalg Gravitational acceleration (standard value) ms2H Total head above lowest crest elevation m H1eTotal effective upstream head m H2eTotal effective downstream head m H1max Ma

27、ximum upstream total head above crest elevation m h Gauged head above lowest crest elevation m h1Upstream gauged head m h1eEffective upstream gauged head m h2Downstream gauged head m h2eEffective downstream gauged head m hpSeparation pocket head m hpeEffective separation pocket head relative to lowe

28、st crest elevation m h, H Difference between lowest and highest crest elevations m K1,K2Constants Non-dimensionalkhHead correction factor m L1Distance of upstream head measurement position from crest line m m Crest cross-slope (1 vertical: m horizontal) Non-dimensionaln Number of measurements in a s

29、et Non-dimensionalp Difference between mean bed level and lowest crest elevation m Q Qdfv t Discharge Total daily flow volume Measurement observation frequency time m3s1m3d1minutes v Mean velocity at cross-section m/s a Mean velocity in approach channel m/s uhAbsolute uncertainty in head measurement

30、 m u(E) Absolute uncertainty in gauge zero m u*(CD) Percentage uncertainty in discharge coefficient Non-dimensional u*(C)Percentage uncertainty in coefficient of velocity Non-dimensional u*(Cdr) Percentage uncertainty in drowned flow reduction factor Non-dimensional u*(h)Percentage uncertainty in he

31、ad measurement Non-dimensional u*(He)Percentage uncertainty in total effective head Non-dimensional U*(Q) U*(Qdmf) U*(Qdfv) Percentage uncertainty in discharge determination Percentage uncertainty in the daily mean flow Percentage uncertainty in the total daily flow volume Non-dimensional Non-dimens

32、ional Non-dimensional Zh, ZHShape factors Non-dimensional Coriolis energy coefficient Non-dimensional BS ISO 4377:2012ISO 4377:2012(E) 4 ISO 2012 All rights reservedSubscript 1 denotes upstream value 2 denotes downstream value e denotes “effective” and implies that corrections for fluid effects have

33、 been made to the quantity a denotes approach channel 5 Characteristics of flat-V weirs The standard flat-V weir is a control structure, the crest of which takes the form of a shallow V when viewed in the direction of flow. The standard weir has a triangular profile with an upstream slope of 1 (vert

34、ical): 2 (horizontal) and a downstream slope of 1:5. The cross-slope of the crest line shall not be steeper than 1:10. The cross-slope shall lie in the range of 0 to 1:10 and, at the limit when the cross-slope is zero, the weir becomes a two- dimensional triangular profile weir. The weir can be used

35、 in both the modular and drowned ranges of flow. In the modular flow range, discharges depend solely on upstream water levels and a single measurement of upstream head is sufficient. In the drowned flow range, discharges depend on both upstream and downstream water levels, and two independent head m

36、easurements are required. For the standard flat-V weir, these are the upstream head, and the head developed within the separation pocket which forms just downstream of the crest or, as a less accurate alternative, the head measured just downstream of the structure. The flat-V weir will measure a wid

37、e range of flows and has the advantage of high sensitivity at low flows. Operation in the drowned flow range minimizes afflux at very high flows. Flat-V weirs shall not be used in steep rivers (see 6.2.2.6), particularly where there is a high sediment load. There is no specified upper limit for the

38、size of this structure. Table 1 gives the ranges of discharges for three typical weirs. Table 1 Ranges of discharge Elevation of crest above bed Crest/cross-slope ratio Width Range of discharge m m m3s10,2 1:10 4 0,015 to 5 0,5 1:20 20 0,030 to 180 (within maximum head of 3 m) 1,0 1:40 80 0,055 to 6

39、30 (within maximum head of 3 m) 6 Installation 6.1 Selection of site 6.1.1 The weir shall be located in a straight section of the channel, avoiding local obstructions, roughness or unevenness of the bed. BS ISO 4377:2012ISO 4377:2012(E) ISO 2012 All rights reserved 56.1.2 A preliminary study of the

40、physical and hydraulic features of the proposed site shall be made, to check that it conforms (or can be constructed or modified to conform) to the requirements necessary for measurement of discharge by the weir. Particular attention shall be paid to the following: a) the adequacy of the length of c

41、hannel of regular cross-section available (see 6.2.2.2); b) the uniformity of the existing velocity distribution (see Annex A); c) the avoidance of a steep channel (see 6.2.2.6); d) the effects of increased upstream water levels due to the measuring structure; e) the conditions downstream (including

42、 such influences as tides, confluences with other streams, sluice gates, mill dams and other controlling features, such as seasonal weed growth, which might cause drowning); f) the impermeability of the ground on which the structure is to be founded and the necessity for piling, grouting or other me

43、ans of controlling seepage; g) the necessity for flood banks, to confine the maximum discharge to the channel; h) the stability of the banks, and the necessity for trimming and/or revetment; i) the uniformity of the approach channel section; j) the effect of wind on the flow over the weir, especiall

44、y when it is wide and the head is small and when the prevailing wind is in a transverse direction. k) If silt removal could be an operation and maintenance requirement, consideration should be given to the accessibility of the site for heavy plant following construction and reinstatement of the site

45、. l) A suitable location is required for the instrument building/housing to allow the effective operation and maintenance of the intake pipe and stilling well. 6.1.3 If the site does not possess the characteristics necessary for satisfactory measurements, or if an inspection of the stream shows that

46、 the velocity distribution in the approach channel deviates appreciably from the examples shown in Figure 2, the site shall not be used unless suitable improvements are practicable. 6.1.4 Weirs act as obstacles to the movement of most fish and other aquatic species. Care should therefore be taken to

47、 ensure that the installation of gauging structures such as flat-V weirs does not have a detrimental effect on the aquatic ecology where this might be an issue. In addition, care should be taken to ensure that any gauging structure complies with the relevant national and international legislation an

48、d regulations, for example the European Parliament EU Water Framework Directive (Directive 2000/60/EC). Where the movement of aquatic life could be compromised by the installation of a flow measurement structure, this may have to be reflected in the design, e.g. limit the crest height and provide an

49、 adequate depth of stilling basin. Alternatively, a fishpass could be installed (ISO 26906). BS ISO 4377:2012ISO 4377:2012(E) 6 ISO 2012 All rights reserved1,20,90,81,11,01,31,21,10,70,80,91,0a) leftright1 100 6,9 % b) leftright110 9,0% 1,31,00,81,20,81,01,21,10,90,81,0c) leftright1 100 12,3 % d) leftright11001,2% 1,21,11,00,90,80,71,21,10,90,8 1,0e) leftright1 100 0,6 % f) leftright1 100 0,9 % Figure 2 Examples of velo