1、BRITISH STANDARD BS 3680-10B: 1980 ISO 4363:1977 Methods of measurement of Liquid flow in open channels Part 10: Sediment transport Part 10B: Measurement of suspended sediment ISO title: Liquid flow measurement in open channels Methodsfor measurement of suspended sediment UDC 532.543:532.574:532.584
2、:556.535.6BS3680-10B:1980 This British Standard, having been prepared under the directionof the Industrial-process Measurement and Control Standards Committee, was published under the authority ofthe Executive Board and comesinto effect on 31March1980 BSI 08-1999 The following BSI references relate
3、to the work on this standard: Committee reference PCL/3 Draft for comment 79/25374 DC ISBN 0 580 11241 1 Cooperating organizations The Industrial-process Measurement and Control Standards Committee, under whose direction this British Standard was prepared, consists of representatives from the follow
4、ing Government departments and scientific and industrial organizations: British Gas Corporation British Industrial Measuring and Control Apparatus Manufacturers Association British Steel Corporation Control and Automation Manufacturers Association (BEAMA) Council of British Manufacturers of Petroleu
5、m Equipment Department of Industry (Computers Systems and Electronics) Electrical, Electronic, Telecommunications and Plumbing Union Electricity Supply Industry in England and Wales Electronic Engineering Association Engineering Equipment Users Association Institute of Measurement and Control Instit
6、ution of Electrical Engineers Institution of Gas Engineers Oil Companies Materials Association Post Office Engineering Union Scientific Instrument Manufacturers Association Sira Institute The organizations marked with an asterisk in the above list, together with the following, were directly represen
7、ted on the committee entrusted with the preparation of this British Standard: Association of River Authorities Department of the Environment (Hydraulic Research Station) Department of the Environment (Water Engineering Division including Water Data Unit) Institute of Water Hydrology Institution of W
8、ater Engineers and Scientists Amendments issued since publication Amd. No. Date of issue CommentsBS3680-10B:1980 BSI 08-1999 i Contents Page Cooperating organizations Inside front cover National foreword ii 0 Introduction 1 1 Scope and field of application 1 2 References 1 3 Terminology 1 4 Units of
9、 measurement 2 5 Measurement of suspended sediment load 2 6 Errors 5 Figure 1 Definition sketch 2 Figure 2 Sediment discharge computation curves 4 Table Methods of selecting sampling points in a vertical 6 Publications referred to Inside back coverBS3680-10B:1980 ii BSI 08-1999 National foreword Thi
10、s British Standard is identical with ISO4363:1977 “Liquid flow measurement in open channels Method of measurement of suspended sediment”, published by the International Organization for Standardization (ISO). Terminology and conventions. The text of the International Standard has been approved as su
11、itable for publication, without deviation, as a British Standard. Some terminology and certain conventions are not identical with those used in British Standards; attention is especially drawn to the following. Wherever the words “International Standard” appear, referring to this standard, they shou
12、ld be read as “British Standard”. At present there is no corresponding British Standard for ISO3716. The technical committee has reviewed the provisions of ISO3716 and has decided that they are acceptable for use in conjunction with this standard. A British Standard does not purport to include all t
13、he 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 immunity from legal obligations. Cross-references International Standard Corresponding British Standard ISO 748:1979 BS 3680 M
14、ethods of measurement of liquid flow in open channels Part 3A:1980 Velocity area methods (Identical) ISO 772:1978 Part 1:1979 Vocabulary and symbols (Technically equivalent) Summary of pages This document comprises a front cover, an inside front cover, pagesi andii, pages1 to8, an inside back cover
15、and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover.BS3680-10B:1980 BSI 08-1999 1 0 Introduction Sediment has been defined generally as solid particles which are moved
16、or might have been moved by flow in a channel. It creates numerous problems for the engineer, the agriculturist and the forester all along the channel. It raises the stream bed which increases the flood heights and inundation; it piles up in large quantities behind dams, thereby reducing their capac
17、ities and hindering their functions; it causes rivers to meander and often to leave their original courses and flow along a new course, devastating vast areas of land; it silts up irrigation and navigation channels making them less efficient. The forester is confronted with the soil erosion and has
18、to devise measures for effective soil conservation. Erosion is caused by water, wind, ice and human activities such as cultivation, etc. Clods and aggregates of soil in the catchment area are broken down into small particles which are thrown into suspension and carried away as sediment. Not all the
19、eroded materials get into the stream channel. The total amount of eroded material which travels from source to a downstream measuring point is termed the sediment transport. Therefore, for a thorough understanding of the individual problems, a comprehensive knowledge of sediment movement and the met
20、hods of determination of sediment load is absolutely essential. 1 Scope and field of application This International Standard gives methods for detailed measurement of sediment concentration and also methods for routine sampling. Because sediment load is highly variable with stage and is also highly
21、variable at the same stage in different floods, and because the bulk of sediment is carried in floods, accurate computation of total sediment flow in a period entails routine sampling at normal flows combined with frequent routine sampling on rise, fall and peak in floods. Details regarding the inst
22、ruments used in the determination of suspended sediment load are covered in ISO3716. 2 References ISO 748, Liquid flow measurement in open channels Velocity-area methods. ISO 772, Liquid flow measurement in open channels Vocabulary and symbols. ISO 3716, Liquid flow measurement in open channels Func
23、tional requirements and characteristics of suspended sediment load samplers. 3 Terminology 3.1 For a proper comprehension of sediment movement and related terms, the flow of water over an artificially flattened bed of sediment may be considered. From no movement of bed material at very low velocitie
24、s, some particles begin to move with the increase of velocity by sliding, rolling or hopping along the bed (“bed load”); at still higher velocities particles of bed are thrown into suspension by turbulence (“suspended load”). The suspended load also includes finer particles in near permanent suspens
25、ion brought in from the catchment (“wash load”). “Bed load” and “suspended load” may occur simultaneously, but the borderline between them is not well defined. From the point of transport of sediment the “total load” comprises bed load and suspended load, the latter including “wash load”. From the p
26、oint of origin of the sediment, the “total load” comprise the “bed material load” (including the suspended portion) and the “wash loads”. 3.2 For the purpose of this International Standard, the following definitions shall apply, in addition to those given in ISO772. 3.2.1 sediment transport: The mov
27、ement of solids transported in any way by a flowing liquid. From the point of transport, the sum of the suspended load transported and bed load transported. From the point of origin the sum of the bed material load and the wash load. 3.2.2 total load: From the point of transport of sediment, the “to
28、tal load” comprises “bed load” and “suspended load”, the latter including “wash load”. From the point of origin of the sediment, the “total load” comprises the “bed material load” (including the suspended portion) and the “wash load” (seeFigure 1). 3.2.3 bed material: The material, the particle size
29、s of which are found in appreciable quantities in that part of the bed affected by transport. 3.2.4 bed material load: The part of the total sediment transport which consists of the bed material and whose rate of movement is governed by the transporting capacity of the channel. 3.2.5 suspended load:
30、 That part of the total sediment transported which is maintained in suspension by turbulence in the flowing water for considerable periods of time without contact with the stream bed. It moves with practically the same velocity as that of the flowing water. It is generally expressed in mass or volum
31、e per unit of time. 3.2.6 bed load: The sediment in almost continuous contact with the bed, carried forward by rolling, sliding or hopping.BS3680-10B:1980 2 BSI 08-1999 3.2.7 wash load: That part of the suspended load which is composed of particle sizes smaller than those found in appreciable quanti
32、ties in the bed material. It is in near permanent suspension and, therefore, is transported through the stream without deposition. The discharge of the wash load through a reach depends only on the rate with which these particles become available in the catchment and not on the transport capacity of
33、 flow. It is generally expressed in mass or volume per unit of time. 3.2.8 sediment concentration: The ratio of the mass or volume of the dry sediment in a water-sediment mixture to the total mass or volume of the suspension. 4 Units of measurement The units of measurement used in this International
34、 Standard are metres, kilograms and seconds. The concentration of suspended sediment is preferably expressed in parts per million (by mass or volume). For convenience, it is sometimes expressed in grams or milligrams per litre. 5 Measurement of suspended sediment load 5.1 Principles of measurement T
35、here are two methods, namely: a) INDIRECT METHOD, in which the time-averaged concentration of the sediment and the time-averaged current velocity at a point are measured practically simultaneously with the aid of separate devices and multiplied to obtain the sediment load. b) DIRECT METHOD, in which
36、 with the aid of one device the time-averaged suspended sediment load at a point is measured directly. 5.1.1 Indirect method of measurement The time-averaged concentration of suspended sediment () and the time-averaged current velocity () are measured practically simultaneously at a large number of
37、points (m) in the sampling area of a cross-section. Each concentration and velocity is representative over a small area (% a i ) of a sampling cross-section. The sum of all the areas (% a i ) is the sampling area (A). The suspended sediment load (Q s ) is determined by using the formula The right-ha
38、nd side of the above equation should be multiplied by C when Q sis expressed as mass per unit of time, where C is a coefficient having the dimension of mass of sediment per unit volume of flow. NOTEAs a suspended sediment sampler cannot take samples near the bed of the channel where the concentratio
39、n is quite high, the suspended sediment load is determined for, and applicable only to, the “sampled zone” of the channel. 5.1.2 Direct method of measurement The water-sediment mixture flows through a sampler in such a way that the mixture enters the nozzle of the sampler with almost the same veloci
40、ty as the undisturbed flow. Due to decrease of velocity, the sediment material settles in settling chambers of the instrument. Figure 1 Definition sketch . . . (1) c i v iBS3680-10B:1980 BSI 08-1999 3 At the measuring point, the time-averaged suspended sediment load per unit area () is determined di
41、rectly from the relationship: where v is a dimensionless coefficient, which may vary with grain size, current velocity and the type of nozzle see note under5.5.3.1; t is the measuring time. The value () is representative of an area (% a i ). Therefore, the suspended load transport through the sampli
42、ng area (A) can be determined by using the formula: NOTESince a suspended sediment sampler cannot take samples near the bed of the channel where concentration is quite high, the suspended sediment load is determined for, and applicable only to, the sampled zone of the channel. 5.2 Selection of site
43、Since the requirements for the selection of site for measurement of suspended load are usually similar to the ones for measurement of discharges, the site should normally be selected in accordance with ISO748. 5.3 Requirements for measurement of concentration of suspended sediment The concentration
44、of suspended sediment not only changes from point to point in a cross-section but also fluctuates from moment to moment at a fixed point. The kind of sampler and the technique of sampling used will depend on a large number of factors. The average suspended sediment concentration at a vertical in a c
45、ross-section can be determined either by averaging over the depth, at each of a number of points in the vertical, or by using an integrating depth sampler which automatically takes a sample in which the concentration of suspended sediment is the average concentration in the vertical (see5.4.3). The
46、suspended sediment concentration, as well as the particle size of sediment, in a flowing stream generally increases from top to bottom and it also varies transversely across the section. The variation depends upon the size and shape of the cross-section, the stage of flow and other channel character
47、istics. Hence, a preliminary investigation must be made to select the sampling points on a vertical and also the number and location of the sampling verticals, taking into consideration the accuracy desired and the resources available. A comparative summary of the sampling methods and their reliabil
48、ity is given in the Table and the methods are described in5.4.3. For the determination of both the magnitude and the location of the point of mean concentration of sediment, sediment concentration shall be determined at several points in a vertical. 5.4 Procedure for computation of sediment load fro
49、m measurements obtained by the indirect method 5.4.1 General The procedure for obtaining the mean sediment discharge per unit width is as follows: 5.4.1.1 Draw the velocity distribution and sediment concentration curves as inFigure 2a) and Figure 2b). The curves shall be drawn up to the sampled zone. 5.4.1.2 Determine the product of concentration () and velocity at corresponding points () and plot the rate of sediment discharge curve as in Figure 2c). 5.4.1.3 The suspended sediment load per unit width can be obtained numerically by a rule such as the tra
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