1、raising standards worldwideNO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAWBSI Standards PublicationBS ISO 2425:2010Hydrometry Measurementof liquid flow in open channelsunder tidal conditionsBS ISO 2425:2010 BRITISH STANDARDNational forewordThis British Standard is the UK imple
2、mentation of ISO 2425:2010. Itsupersedes BS ISO 2425:1999 +A1:2003 which is withdrawn.The UK participation in its preparation was entrusted to TechnicalCommittee CPI/113/1, Velocity area methods.A list of organizations represented on this committee can beobtained on request to its secretary.This pub
3、lication does not purport to include all the necessaryprovisions of a contract. Users are responsible for its correctapplication. BSI 2010ISBN 978 0 580 59633 9ICS 17.120.20Compliance with a British Standard cannot confer immunity fromlegal obligations.This British Standard was published under the a
4、uthority of theStandards Policy and Strategy Committee on 31 December 2010.Amendments issued since publicationDate Text affectedBS ISO 2425:2010Reference numberISO 2425:2010(E)ISO 2010INTERNATIONAL STANDARD ISO2425Third edition2010-12-01Hydrometry Measurement of liquid flow in open channels under ti
5、dal conditions Hydromtrie Mesurage du dbit des liquides dans les canaux dcouverts dans des conditions de mare BS ISO 2425:2010ISO 2425:2010(E) PDF disclaimer This PDF file may contain embedded typefaces. In accordance with Adobes licensing policy, this file may be printed or viewed but shall not be
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10、l copyrightiso.org Web www.iso.org Published in Switzerland ii ISO 2010 All rights reservedBS ISO 2425:2010ISO 2425:2010(E) ISO 2010 All rights reserved iiiContents Page Foreword iv 1 Scope1 2 Normative references1 3 Terms and definitions .1 4 Abbreviated terms.2 5 Principles of methods of measureme
11、nt2 5.1 General .2 5.2 Single measurement methods .2 5.3 Continuous measurement methods2 6 Special considerations and choice of method.3 6.1 Special considerations .3 6.2 Choice of method 4 7 Measurement of tidal flow 6 7.1 Techniques for single measurements of tidal flow6 7.2 Techniques appropriate
12、 for continuous measurement of tidal flow10 8 Uncertainties in tidal flow measurement 12 8.1 General .12 8.2 Uncertainties in measurement by velocity area method.12 Annex A (informative) Measurement of tidal flow by cubature method16 Annex B (informative) Measurement methods suitable for tidal flow
13、conditions20 Annex C (informative) Record of velocity measurement of a tidal river (see 7.1)22 Annex D (informative) Measurement of tidal flow using an acoustic Doppler velocity meter (see 7.1) 24 Bibliography27 BS ISO 2425:2010ISO 2425:2010(E) iv ISO 2010 All rights reservedForeword ISO (the Intern
14、ational 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 which a technical committee has b
15、een 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 matters of electrotechnical sta
16、ndardization. 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 circulated to the member bodies f
17、or 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 responsible for identifying any or a
18、ll such patent rights. ISO 2425 was prepared by Technical Committee ISO/TC 113, Hydrometry, Subcommittee SC 1, Velocity area methods. This third edition cancels and replaces the second edition (ISO 2425:1999), which has been technically revised. It also incorporates the Amendment ISO 2425:1999/Amd.1
19、:2003. Annex D on measurement of tidal flow using an acoustic Doppler velocity meter has been added. BS ISO 2425:2010INTERNATIONAL STANDARD ISO 2425:2010(E) ISO 2010 All rights reserved 1Hydrometry Measurement of liquid flow in open channels under tidal conditions 1 Scope This International Standard
20、 provides a summary of recommended methods for the determination of liquid flow in tidal channels, special consideration being given to those techniques that are either unique to or particularly appropriate for application under tidal conditions, including treatment of uncertainties. Reference is al
21、so made, where appropriate, to methods for the determination of flow in non-tidal channels, but attention is drawn to their limitations with respect to practicality and/or uncertainty. This International Standard does not describe alternative methods, such as the use of weirs, flumes, dilution gaugi
22、ng, salt velocity and floats, although they might be suitable under certain conditions, especially where the effect of tides only impedes and does not stop or reverse the passage of stream flow. These methods are described in detail in other International Standards. This International Standard speci
23、fies two types of technique: a) techniques for single measurements of tidal flow; b) techniques for continuous measurement of tidal flow. Annex A specifies the cubature method of measurement. Annex B specifies methods for the determination of flow under tidal conditions, and Annex C gives an example
24、 of the computation for a single vertical. Similar computations are possible for other verticals. Annex D describes the determination of tidal flow using an acoustic Doppler velocity meter. 2 Normative references The following referenced documents are indispensable for the application of this docume
25、nt. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. ISO 748:2007, Hydrometry Measurement of liquid flow in open channels using current-meters or floats ISO 772, Hydrometry Vocabulary and s
26、ymbols ISO 1100-1, Measurement of liquid flow in open channels Part 1: Establishment and operation of a gauging station ISO 6416, Hydrometry Measurement of discharge by the ultrasonic (acoustic) method 3 Terms and definitions For the purposes of this document, the terms and definitions given in ISO
27、772 apply. BS ISO 2425:2010ISO 2425:2010(E) 2 ISO 2010 All rights reserved4 Abbreviated terms ADCP acoustic Doppler current profiler ADP acoustic Doppler profiler ADV acoustic Doppler velocimeter ADVM acoustic Doppler velocity meter 5 Principles of methods of measurement 5.1 General Tidal flow measu
28、rement can be an instantaneous rate of flow or a total volume of flow during a flood or ebb tide. The unsteady nature and change in direction of flow under tidal conditions create problems of measurement additional to those associated with the measurement of the discharge of unidirectional streams.
29、The methods specified in ISO 748, ISO 1100-1, ISO 4369, ISO 9123, ISO/TR 9823 and ISO 9825 cannot therefore always be applied to tidal channels. Any change in water quality brought about by tidal conditions can affect the methods specified in ISO 6416 and ISO 9213. For various reasons, direct measur
30、ements of velocity in tidal channels are more liable to greater uncertainty than those made under conditions of unidirectional flow. The methods of measurement in this International Standard can be grouped into either single or continuous measurements. 5.2 Single measurement methods 5.2.1 Velocity a
31、rea method At a chosen gauging site, the velocity of flow and the area of cross-section of the channel are measured. The product of these measurements at any instant is the rate of flow or discharge past the gauging site at that instant. It is referred to as the velocity area method and includes the
32、 following techniques. a) current meter from a fixed station; b) acoustic Doppler profiler or acoustic Doppler velocity meter from a fixed station; c) current meter from a moving station (moving boat); d) acoustic Doppler current profiler from a moving station (moving boat). 5.2.2 Cubature method In
33、 an area that includes a stretch of river channel and its flood plain, surface areas and rise in water level of stored water are measured at known time intervals. Volumes of stored water are computed, and the flow into the upstream stretch of river is estimated, from which the average rate of flow i
34、s determined (see Annex A). 5.3 Continuous measurement methods 5.3.1 Ultrasonic method (ISO 6416) Transducers are positioned on each bank of the river channel, such that the acoustic path is at an oblique angle to the direction of flow. The time taken for a pulse of sound to travel in both direction
35、s is measured and BS ISO 2425:2010ISO 2425:2010(E) ISO 2010 All rights reserved 3compared. From these two times, the velocity of the water can be computed. Knowledge of the cross-sectional area allows computation of discharge. 5.3.2 Electromagnetic method (ISO 9213) A horizontal coil is constructed
36、above or below a river channel. A magnetic field is generated by an alternating current and voltages are induced in the flowing water, which acts as an electrical conductor. After calibration, measurements of electrical parameters and water depth provide a means of determining the discharge. 5.3.3 A
37、coustic Doppler velocity method from a fixed station Acoustic Doppler velocity meters (ADVMs) may be horizontally or vertically oriented and shall be fixed to a bridge pier or abutment, or other stable mountable structure for horizontal mountings, or to the channel bed for vertical mountings. The AD
38、VMs measure an index velocity that is related to the measured average velocity of the channel (mean velocity) determined from current meter measurements and channel cross-sectional area. A separate water level-to-area relation is developed from regularly measured cross-sectional geometry at or near
39、the location of the ADVM. Discharge is computed as a product of the mean velocity and cross-sectional area. The acoustic Doppler velocity method can be implemented using the following techniques: a) horizontal measurement from a fixed station or stations; b) vertical measurement from a fixed station
40、 or stations; c) a combination of the horizontal and vertical methods at a fixed station. 5.3.4 Unsteady flow models Unsteady flow models may be used for computing continuous records of discharge in open channels in both tidal and non-tidal conditions. These models, however, are not applicable where
41、 a longitudinal density gradient, such as a salt-water wedge, is present. Unsteady flow models are based on the numerical solution of non-linear partial differential equations that describe gradually varied unsteady flow in open channels. The available models employ one or more of several numerical
42、computation techniques. Data requirements, which can be substantial, depend on the numerical techniques employed by the model selected. It is necessary that techniques for the application of unsteady flow models and the data requirements be clearly defined and understood for successfully computing d
43、ischarges. 6 Special considerations and choice of method 6.1 Special considerations Changes in water level at the mouth of a river due to tidal action cause backwater effects in the channel. These changes can alter water level and flow magnitude only, or water level, flow magnitude, and direction of
44、 flow. The entire flow might be reversed in direction, or only some of the flow might be reversed due to variations in the density gradient. Most flow-gauging techniques are generally best suited to conditions closely approximating to steady flow, but unsteady flow causes additional difficulties, as
45、 follows. a) At any section, water levels continuously change. b) At any point in a vertical, velocities continuously change either with or without change in direction. c) In any vertical, the continuously changing velocities could create greater velocity gradients than in channels with steady unifo
46、rm flow. BS ISO 2425:2010ISO 2425:2010(E) 4 ISO 2010 All rights reservedd) During the period of transition in flow direction (flood to ebb or ebb to flood), zero velocity can occur at a succession of points over the changing velocity profile. e) High water and low water might not take place at the s
47、ame time as the reversal in flow direction. f) The change in direction of flow might not take place at the same time throughout the wetted cross-section and the flood and ebb channels might be positioned differently in a wide cross-section. g) When the direction of flow changes, the characteristics
48、of the approach conditions from the upstream and the downstream can be different and can result in divergence (when the angle between the flood and the ebb flow is other than 180) between the flood and ebb flow. h) Flow can be stratified, with liquids of different densities in each layer. While the
49、liquid in the upper stratum may flow in one direction, the denser liquid in the lower stratum may flow at a different speed in the same or opposite direction. When a density difference due to a salt-water wedge occurs, the maximum velocity in each layer can occur at different times. i) At any section in a channel, variations in water level can cause changes in width and cross-section of flow. j) An increase in the number of measurements is required to make an estimate of discharge. k) During a tidal cycle there can be variations in sa
