1、BRITISH STANDARD BS3680-5: 1992 ISO1070:1992 Incorporating Amendment No.1 Measurement of liquid flow in open channels Part5: Slope area method of estimationBS3680-5:1992 This BritishStandard, having been prepared under the directionof the Industrial-process Measurement and Control Standards Policy C
2、ommittee, was published underthe authority of the Standards Board and comes intoeffect on 15October1992 BSI04-2000 First published October1970 Second edition October1992 The following BSI references relate to the work on this standard: Committee reference PCL/3 Draft for comment91/23585 DC ISBN 0 58
3、0 21235 1 Committees responsible for this BritishStandard The preparation of this BritishStandard was entrusted by the Industrial-process Measurement and Control Standards Policy Committee (PCL/-) to Technical Committee PCL/3, upon which the following bodies were represented: Clyde River Purificatio
4、n Board Department of the Environment Department of the Environment for Northern Ireland Institute of Measurement and Control Institution of Water and Environmental Management National Rivers Authority Water Services Association of England and Wales Welsh Office The following body was also represent
5、ed in the drafting of the standard, through subcommittees and panels: Water Research Centre Amendments issued since publication Amd. No. Date Comments 10291 July1999 Indicated by a sideline in the marginBS3680-5:1992 BSI 04-2000 i Contents Page Committees responsible Inside front cover National fore
6、word ii 1 Scope 1 2 Normative references 1 3 Definitions 1 4 Principle of the method of measurement 1 5 Selection and demarcation of site 1 6 Devices for measurement of slope 2 7 Procedure for installing gauges and making observations 2 8 Computation of surface slope 3 9 Cross-sections of the stream
7、 3 10 Computation of discharge for non-uniform and composite cross-sections 3 11 Computation of discharge for uniform cross-sections 7 12 Uncertainties in flow measurement 8 Annex A (informative) Approximate values of coefficients n and c for open channels 10 Annex B (informative) Bibliography 11 Fi
8、gure 1 Composite cross-section of a channel 4 Figure 2 Cross-section of a channel 4 Figure 3 Longitudinal section of a reach 6 Table A.1 Coefficients for channels with relatively coarse bed material andnotcharacterized by bed formation 10 Table A.2 Coefficients for channels other than those with coa
9、rse bed material 11 List of references Inside back coverBS3680-5:1992 ii BSI 04-2000 National foreword This BritishStandard has been prepared under the direction of the Industrial-process Measurement and Control Standards Policy Committee. It supersedes BS3680-5:1970 which is withdrawn. It is identi
10、cal with ISO1070:1992 Liquid flow measurement in open channels Slope-area method and its amendment1:1997, published by the International Organization for Standardization (ISO). This standard is one of a series of Parts of BS3680 on the measurement of liquid flow in open channels. The Technical Commi
11、ttee has reviewed the provisions of ISO772:1988 and of ISO4373:1979, to which normative reference is made in the text, and has decided that they are acceptable for use in conjunction with this standard. A related BritishStandard to ISO772 is BS3680-1:1983. BS3680-1 has since been revised, and is now
12、 published as BS3680-1:1991. A revision of ISO772 is in preparation. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a British Standard does not of itself confer immun
13、ity from legal obligations. Cross-references International Standard Corresponding BritishStandard ISO1100-2:1982 BS3680 Measurement of liquid flow in open channels Part3C:1983 Methods for determination of the stage-discharge relation (Identical) ISO5168:1978 BS5844:1980 Methods of measurement of flu
14、id flow: estimation of uncertainty of a flow-rate measurement (Identical) Summary of pages This document comprises a front cover, an inside front cover, pagesi andii, pages1 to12, an inside back cover and a back cover. This standard has been updated (see copyright date) and may have had amendments i
15、ncorporated. This will be indicated in the amendment table on the inside front cover.BS3680-5:1992 BSI 04-2000 1 1 Scope This International Standard specifies a method of determining liquid flow in open channels from observations of the surface slope and cross-sectional area of the channel. It is su
16、itable for use under somewhat special conditions when direct measurement of discharge by more accurate methods, such as the velocity-area method, is not possible. The slope-area method can be used with reasonable accuracy in open channels having stable boundaries, bed and sides (e.g.rock or very coh
17、esive clay), in lined channels and in channels with relatively coarse material. It may also be used in alluvial channels, including channels with overbank flow or non-uniform channel cross-sections, but in these cases the method is subject to large uncertainties owing to the selection of the rugosit
18、y coefficient (such as Mannings coefficient n or Chezys coefficient C). Generally the method may be used to determine discharge a) at the time of determining gauge heights from a series of gauges; b) for a peak flow that left marks on a series of gauges or where peak stages were recorded by a series
19、 of gauges; c) for a peak flow that left high-water marks along the stream banks. This method is not suitable for use in very large channels, channels with very flat surface slopes and high sediment load or channels having significant curvature. Although the accuracy of the results given by the slop
20、e-area method is less than that of the results given by the velocity-area method, the slope-area method is sometimes the only method that can be used for determining the extreme high-stage end of rating curves in cases where the magnitude of floods is such that other methods of measuring discharge c
21、annot be used. 2 Normative references The following standards contain provisions which, through reference in this text, constitute provisions of this International Standard. At the time of publication, the editions indicated were valid. All standards are subject to revision, and parties to agreement
22、s based on this International Standard are encouraged to investigate the possibility of applying the most recent editions of the standards indicated below. Members of IEC and ISO maintain registers of currently valid International Standards. ISO772:1988, Liquid flow measurement in open channels Voca
23、bulary and symbols. ISO1100-2:1982, Liquid flow measurement in openchannels Part2: Determination of the stage-discharge relation. ISO4373:1979, Measurement of liquid flow in open channels Water level measuring devices. ISO5168:1978, Measurement of fluid flow Estimation of uncertainty of a flow-rate
24、measurement. 3 Definitions For the purposes of this International Standard, the definitions given in ISO772 apply. 4 Principle of the method of measurement A measuring reach is chosen for which the mean area of the stream or river cross-section is determined and the surface slope of the flowing wate
25、r in that reach is measured. The mean velocity is then established by using known empirical formulae which relate the velocity to the hydraulic mean depth, and the surface slope is corrected for the kinetic energy of the flowing water and the characteristics of the bed and bed material. The discharg
26、e is computed as the product of the mean velocity and the mean area of the stream cross-section. 5 Selection and demarcation of site 5.1 Initial survey of site It is recommended that approximate measurements of widths, depths and surface slopes should be made in a preliminary survey to decide whethe
27、r the site is suitable and conforms, as far as possible, with the conditions specified in5.2 and5.3. These measurements should serve as a guide only. 5.2 Selection of site 5.2.1 There should be no progressive tendency for the river to scour or to deposit sediment. 5.2.2 Ideally, the river reach shou
28、ld be straight, and should contain no large curvatures or meanders. There should not be any abrupt change in the bed slope in the measuring reach, as can occur in rocky channels. The cross-section should be uniform throughout the reach and free from obstructions. Preferably, vegetation should be min
29、imal and as uniform as possible throughout the reach. 5.2.3 The bed material should be similar in nature throughout the reach.BS3680-5:1992 2 BSI 04-2000 5.2.4 Wherever possible, the length of the reach should be such that the difference between the water levels at the upstream and downstream gauges
30、 should be not less than ten times the uncertainty in the difference. When the uncertainty in the measurement of the water level at each gauge is similar, then the distance between the gauges should be sufficient for the fall to be not less than twenty times the uncertainty in measurement at one gau
31、ge. 5.2.5 The flow in the reach should be free from significant disturbances due to the effect of tributaries. 5.2.6 The flow in the channel should be contained within defined boundaries. If possible, reaches in which overbank flow conditions exist should not be selected. Where this is unavoidable,
32、however, a reach in which there are no very shallow flows over the flood plain should be sought, but additional computations will be necessary in the determination of discharge. 5.2.7 The site should not be subject to change in the flow regime from subcritical to supercritical or from supercritical
33、to subcritical (but see10.6). 5.2.8 A converging reach should be selected in preference to an expanding reach. Rapidly expanding reaches should not be selected (see10.4). 5.2.9 The physical characteristics of the reach should be such that the time lag of flow in the reach may be negligible. 5.3 Dema
34、rcation of site Once the measuring reach has been selected, cross-sections normal to the direction of flow shall be chosen and markers which are clearly visible andidentifiable shall be placed on both banks (seealso9.1). A reference gauge, levelled to a standard datum, shall be installed (see6.1). T
35、he site should be monitored to ensure that no physical changes occur which render it unsuitable. If changes do take place and the site cannot be successfully restored, a new site should be selected. 6 Devices for measurement of slope 6.1 Reference gauge The reference gauge shall comprise a well gaug
36、e, where feasible, preferably incorporating a vertical gauge rather than an inclined gauge. The vertical gauge (or inclined gauge) shall comply with ISO4373. The markings shall be clear and accurate and shall cover the range of stage to be measured. The reference gauge shall be securely fixed to an
37、immovable and rigid support in the stream and shall be correlated to a fixed benchmark by precise levelling to the national or another datum. 6.2 Water-level recorder Water-level recorders (if used) shall comply withISO4373. 6.3 Crest stage gauge A crest stage gauge is suitable for use where only th
38、e peak stage attained during a flood has to be determined. Peak discharges can be calculated from two or more gauges installed in a reach of the river, at locations suitable for defining cross-sectional profiles. 6.4 High-water marks The stage and slope of peak flows can be determined by surveying h
39、igh-water marks in the measuring reach. Several types of high-water mark may be found, such as drift on banks, wash lines, seed lines on trees, mud lines, and drift in bushes or trees. Each high-water mark should be rated as excellent, good, fair or poor. This information will be helpful when interp
40、reting the high-water profile and slope. 7 Procedure for installing gauges and making observations 7.1 Installation Gauges shall be installed, on both banks of the river, at no fewer than three cross-sections, making a total of at least six gauges. The gauges shall be referenced to a common datum. 7
41、.2 Procedure for observation of gauges The gauges shall be read from such a position as to avoid all parallax errors. For each measurement, the gauge shall be observed continuously for a minimum period of2min or for the period of a complete oscillation, whichever is the longer, and the maximum and m
42、inimum readings taken and averaged. When using water-level recorders, an observer should check the time displayed on each recorder against an accurate clock before and after the measurement period and also during the measurement period. All gauges should be observed as frequently as is necessary to
43、record significant changes in stage which occur during the measurement period. 7.3 Other observations The date, time, weather conditions (especially wind speed and direction), direction of the flow, and conditions of vegetation at the time of measurement should be recorded.BS3680-5:1992 BSI 04-2000
44、3 8 Computation of surface slope 8.1 Computation of surface slope from gauges The surface slope is computed from the gauge observations at the upstream and downstream gauges delimiting the measuring reach, the intermediate gauge(s) being used to confirm that the slope is uniform throughout the reach
45、. The gauges shall be read to the smallest marking on thegauge. 8.2 Computation of surface slope from high-water marks When accurate gauge levels do not exist or have been destroyed, the slope during the peak stage can be estimated from flood marks on the channel banks. Several reliable high-water m
46、arks for each bank shall be used to define the flow profile. Each high-water mark shall be defined by its position along a baseline and a graphical plot shall be made so as to provide a visual profile of the high-water marks. Irregularities in the profile can be easily seen from such a plot, which w
47、ill aid in the interpretation of the high-water profile and the water surface slope. 9 Cross-sections of the stream 9.1 Number of cross-sections A minimum of three cross-sections of the selected measuring reach are generally desirable. These shall be clearly marked on the banks by means of masonry p
48、illars or easily identifiable markers. The cross-sections shall be numbered so that the cross-section furthest upstream is identified as section1, the adjacent cross-section downstream is identified as section2, and so on. 9.2 Measurement of cross-sectional profiles The profile of each of the cross-
49、sections selected shall be measured at the same time at which the gauge observations are made, or as close as possible to this time. It is often impossible to measure the cross-section during flood and therefore an error may be introduced in the flow determination owing to an unobserved and temporary change in cross-section. If the section is stable, however, it will be sufficient to observe the cross-sections before and after a flood. Three cross-sectional profiles should be observed before and after floods where there is a difference in the velocities at the two
