1、BRITISH STANDARDBS ISO 4360:2008Hydrometry Open channel flow measurement using triangular profile weirsICS 17.120.20g49g50g3g38g50g51g60g44g49g42g3g58g44g55g43g50g56g55g3g37g54g44g3g51g40g53g48g44g54g54g44g50g49g3g40g59g38g40g51g55g3g36g54g3g51g40g53g48g44g55g55g40g39g3g37g60g3g38g50g51g60g53g44g42g
2、43g55g3g47g36g58BS ISO 4360:2008This British Standard was published under the authority of the Standards Policy and Strategy Committee on 31 March 2008 BSI 2008ISBN 978 0 580 55141 3National forewordThis British Standard is the UK implementation of ISO 4360:2008. It supersedes BS 3680-4B:1986 which
3、is withdrawn. The UK participation in its preparation was entrusted by Technical Committee CPI/113, Hydrometry, to Subcommittee CPI/113/2, Notches, weirs and flumes.A list of organizations represented on this committee can be obtained on request to its secretary.This publication does not purport to
4、include all the necessary provisions of a contract. Users are responsible for its correct application.Compliance with a British Standard cannot confer immunity from legal obligations.Amendments/corrigenda issued since publicationDate CommentsReference numberISO 4360:2008(E)INTERNATIONAL STANDARD ISO
5、4360Third edition2008-03-01Hydrometry Open channel flow measurement using triangular profile weirs Hydromtrie Mesure de dbit des liquides dans les canaux dcouverts au moyen de dversoirs profil triangulaire BS ISO 4360:2008ii iiiContents Page Foreword iv 1 Scope . 1 2 Normative references . 1 3 Terms
6、 and definitions. 1 4 Symbols . 1 5 Principle. 2 6 Installation . 2 6.1 General. 2 6.2 Selection of site 2 6.3 Installation conditions 3 7 Maintenance 6 8 Measurement of head(s) 6 8.1 General. 6 8.2 Location of head measurement(s) 6 8.3 Gauge wells . 6 8.4 Zero setting . 9 9 Discharge characteristic
7、s 9 9.1 Equations of discharge 9 9.2 Coefficients . 10 9.3 Limitations. 10 10 Uncertainties of flow measurement 12 10.1 General. 12 10.2 Combining measurement uncertainties . 13 10.3 Uncertainty of discharge coefficient u(Cd) for the triangular profile weir. 14 10.4 Uncertainty budget . 14 11 Exampl
8、e . 15 11.1 General. 15 11.2 Characteristics Gauging structure. 15 11.3 Characteristics Gauged head instrumentation . 15 11.4 Discharge coefficient 16 11.5 Discharge calculation. 16 11.6 Uncertainty statement 16 Annex A (informative) Introduction to measurement uncertainty. 18 Annex B (informative)
9、Sample measurement performance for use in hydrometric worked examples 26 Bibliography . 28 BS ISO 4360:2008iv Foreword ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work of preparing International Standards is
10、 normally carried out through ISO 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
11、 in the work. ISO collaborates closely with the International Electrotechnical Commission (IEC) on all 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 pr
12、epare International Standards. 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. Attention is drawn to the possibility that
13、 some of the elements of this document may be the subject of patent rights. ISO shall not be held responsible for identifying any or all such patent rights. ISO 4360 was prepared by Technical Committee ISO/TC 113, Hydrometry, Subcommittee SC 2, Flow measurement structures. This third edition cancels
14、 and replaces the second edition (ISO 4360:1984), of which it constitutes a technical revision. BS ISO 4360:20081Hydrometry Open channel flow measurement using triangular profile weirs 1 Scope This International Standard specifies methods for the measurement of the flow of water in open channels und
15、er steady flow conditions using triangular profile weirs. The flow conditions considered are steady flows which are uniquely dependent on the upstream head and drowned flows which depend on downstream as well as upstream levels. 2 Normative references The following referenced documents are indispens
16、able for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. ISO 772, Hydrometric determinations Vocabulary and symbols 3 Terms and definitions For the purpos
17、es of this document, the terms and definitions given in ISO 772 apply. 4 Symbols A m2area of approach channel B m width of approach channel b m breadth of weir crest perpendicular to flow direction C discharge coefficient Cdcoefficient of discharge Cvcoefficient of velocity Cv f combined coefficient
18、 of velocity Em elevation of ultrasonic air range sensor above hydraulic datum f drowned flow reduction factor g m2/s acceleration due to gravity Hm total head relative to crest level hm gauged head relative to crest level (upstream head is inferred if no subscript is used) N number of measurements
19、in a set p m height of weir (difference between mean bed level and crest level) Q m3/s volumetric rate of flow ()*u percentage uncertainty in parameter v m/s mean velocity U % expanded percentage uncertainty BS ISO 4360:20082 Subscripts: 1 upstream 2 downstream c combined p measured crest tapping he
20、ad above crest level 5 Principle The discharge over a triangular profile weir is a function of the upstream head on the weir (for free flow), upstream and downstream head (for drowned flow), experimentally determined coefficients, the geometrical properties of the weir and approach channel and the d
21、ynamic properties of the water. 6 Installation 6.1 General The required conditions regarding selection of site, installation conditions, the measuring structure, the approach channel, the downstream channel, maintenance, measurement of head, and stilling or float wells which are generally necessary
22、for flow measurement are given in the following sub-clauses. 6.2 Selection of site A preliminary survey shall be made of the physical and hydraulic features of the proposed site, to check that it conforms (or can be made to conform) to the requirements necessary for accurate measurement by a weir. P
23、articular attention should be paid to the following features in selecting the site: a) availability of an adequate length of channel of regular cross-section; b) the existing velocity distribution; c) the avoidance of a steep channel, if possible; d) the effects of any increased upstream water level
24、 due to the measuring structure; e) conditions downstream including such influences as tides, confluences with other streams, sluice gates, mill dams and other controlling features which might cause submerged flow; f) the impermeability of the ground on which the structure is to be founded, and the
25、necessity for piling, grouting or other means 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 in natural channels; i) the clearance of rocks or boulders from the b
26、ed of the approach channel; j) the effect of wind; wind can have a considerable effect on the flow in a river or over a weir, especially when these are wide and the head is small and when the prevailing wind is in a transverse direction. If the site does not possess the characteristics necessary for
27、 satisfactory measurement, the site shall be rejected unless suitable improvements are practicable. If an inspection of the stream shows that the existing velocity distribution is regular, then it may be assumed that the velocity distribution will remain satisfactory after the construction of a weir
28、. If the existing velocity distribution is irregular and no other site for a gauge is feasible, due consideration shall be given to checking the distribution after the installation of the weir and to improving it if necessary. BS ISO 4360:20083Several methods are available for obtaining a more preci
29、se indication of irregular velocity distribution: velocity rods, floats or concentrations of dye can be used in small channels, the latter being useful in checking conditions at the bottom of the channel. A complete and quantitative assessment of velocity distribution may be made by means of a curre
30、nt-meter or other point velocity measurements. Information about the use of current-meters is given in ISO 748 1. Further information on measuring river velocities using acoustic Doppler profilers can be found in ISO/TS 24154 5. Figure 1 gives examples of satisfactory velocity distributions. NOTE Th
31、e contours refer to values of local flow velocity relative to the mean cross-sectional velocity. Figure 1 Examples of satisfactory velocity distributions 6.3 Installation conditions 6.3.1 General The complete measuring installation consists of an approach channel, a measuring structure and a downstr
32、eam channel. The conditions of each of these three components affect the overall accuracy of the measurements. Installation requirements include features such as the surface finish of the weir, the cross-sectional shape of the channel, the channel roughness and the influence of control devices upstr
33、eam or downstream of the gauging structure. The distribution and direction of velocity have an important influence on the performance of the weir, these factors being determined by the features mentioned above. Once an installation has been installed, the user shall prevent any change which could af
34、fect the discharge characteristics. 6.3.2 Measuring structure The structure shall be rigid and watertight and capable of withstanding flood flow conditions without distortion or fracture. It shall be at right angles to the direction of flow and shall conform to the dimensions given in the relevant c
35、lauses. The weir comprises an upstream slope of 1 (vertical) to 2 (horizontal) and a downstream slope of 1 (vertical) to 5 (horizontal). The intersection of these two surfaces forms a straight line crest, horizontal and at right angles to the direction of flow in the approach channel. Particular att
36、ention shall be given to the crest itself, which shall possess a well-defined corner of durable construction. The crest may be made of pre-formed sections, carefully aligned and jointed, or may have a non-corrodible metal insert, as an alternative to in situ construction throughout. BS ISO 4360:2008
37、4 The dimensions of the weir and its abutments shall conform to the requirements indicated in Figure 2. Weir blocks may be truncated but not so as to reduce their dimensions in plan to less than hmaxfor the 1:2 slope and 2 hmaxfor the 1:5 slope. Figure 2 shows the general arrangement of the triangul
38、ar profile weir. 6.3.3 Approach channel On all installations, the flow in the approach channel shall be smooth, free from disturbance and shall have a velocity distribution as satisfactory as possible over the cross-sectional area. This can usually be verified by inspection or measurement. In the ca
39、se of natural streams or rivers, this can only be attained by having a long straight approach channel free from projections into the flow. Figure 1 gives examples of satisfactory velocity distributions. The following general requirements shall be complied with. a) As the altered flow conditions due
40、to the construction of the weir might cause a build-up of shoals of debris upstream of the structure, which in time might affect the flow conditions, the likely consequential changes in the water level shall be taken into account in the design of gauging stations. b) In an artificial channel, the cr
41、oss-section shall be uniform and the channel shall be straight for a length equal to at least 5 times its water-surface width. c) In a natural stream or river, the cross-section shall be reasonably uniform and the channel shall be straight for a sufficient length to ensure a regular velocity distrib
42、ution. d) If the entry to the approach channel is through a bend, or if the flow is discharged into the channel through a conduit or a channel of smaller cross-section, or at an angle, then a longer length of straight approach channel may be required to achieve a regular velocity distribution. e) Ba
43、ffles shall not be installed closer to the points of measurement than a distance 10 times the maximum head to be measured. f) Under certain conditions, a standing wave may occur upstream of the gauging device, e.g. if the approach channel is steep. Provided that this wave is at a distance of not les
44、s than 30 times the maximum head upstream, flow measurement is feasible, subject to confirmation that a regular velocity distribution exists at the gauging station and that the Froude number in this section is no more than 0,6. Ideally, high Froude numbers should be avoided for accurate flow measure
45、ment. If a standing wave occurs within this distance, the approach conditions and/or the gauging device shall be modified. BS ISO 4360:20085Key 1 upstream head measurement 2 crest tapping head measurement 3 gauge wells 4 crest tappings 5 limit of truncated sections Figure 2 General arrangements of t
46、he triangular profile weir 6.3.4 Downstream channel The channel downstream from the structure is usually of no importance as such if the weir has been designed so that the flow is modular (i.e. unaffected by tailwater level) under all operating conditions. A downstream gauge shall be provided to mea
47、sure tailwater levels to determine if and when drowned flow occurs. In the event of the possibility of scouring downstream, which phenomenon may also lead to the instability of the structure, particular measures to prevent this happening may be necessary. A crest tapping and separate stilling well s
48、hall be fitted if the weir is designed to operate in a drowned condition or if there is a possibility that the weir may drown in the future. The latter circumstance may arise if the altered flow conditions due to the construction of the weir have the effect of building up shoals of debris immediatel
49、y downstream of the structure or if river works are carried out downstream at a later date. BS ISO 4360:20086 7 Maintenance Maintenance of the measuring structure and the approach channel is important to secure accurate continuous measurements. The approach channel shall be kept free of silt, vegetation and obstructions which might have deleterious effects on flow conditions specified for the standard installation. The float well and the entry from the approach channel shall also be kept clean and free from deposits. The downstream channel shall be kept free of ob
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